Oxidized cellulose-based material and method for producing the same

Abstract

This disclosure provides a method for treating biological waste and similar waste sources with nitric acid. When the waste source includes plant-based fibrous materials, animal and food waste, the method of the present invention provides the extraction and use of nanostructured cellulose (nanocellulose) having an anionic surface charge for adsorbing cationic contaminants such as ammonium, and a selective and environmentally friendly method for functionalizing cellulosic biomass.

Description

Technical Field

[0001] Government Rights This invention was made with government support under grant number 2140820 awarded by the National Science Foundation. The government has certain rights in this invention.

Background Art

[0002] Separation processes are important in many industries. Membrane separation technology can be used in many separation processes. These processes include water purification, desalination, air filtration / separation, gas separation, membrane bioreactors, and the like.

[0003] However, in some cases, water purification using an adsorbent material may be more desirable. The use of an adsorbent material is relatively easy to utilize, has a low cost, and in some cases can exhibit better performance than filtration techniques by removing dissolved particles that are too small to be mechanically removed by other means.

[0004] The production of nanocellulose as a scaffold is important for industries with problems such as agriculture, as a biodegradable and sustainable natural-derived material. The processes for producing nanocellulose require energy-intensive technologies, harmful or toxic chemicals, and unsustainable feedstocks or reagents.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Improved materials and methods for use in separation processes, including water purification, are still desired.

Means for Solving the Problems

[0006] The present disclosure provides a method for treating biological waste and similar waste sources with nitric acid. In an aspect, the present disclosure includes a step of contacting a biological waste source with nitric acid, an optional step of contacting the biological waste source and nitric acid with sodium nitrite, a step of heating the biological waste source, nitric acid, and optionally sodium nitrite to a temperature of about 25°C to about 100°C to form a gellable nanocellulose suspension, and a step of recovering the nanocellulose suspension.

[0007] In embodiments, the nitric acid is present in solution at a concentration of about 30% to about 50%.

[0008] In some embodiments, the ratio of nitric acid in solution to the biological waste source is about 10:1 to 1:1.

[0009] In other embodiments, the sodium nitrite is present in solution at a concentration of about 15% to about 70% by mass.

[0010] In embodiments, the ratio of sodium nitrite in solution to the biological waste source is about 1:0.25 to 1:5.

[0011] In some embodiments, the step of heating the biological waste source, nitric acid, and optionally sodium nitrite is carried out over a period of about 1 hour to about 24 hours.

[0012] In embodiments, the biological waste source contains cellulose.

[0013] In some embodiments, the gellable suspension contains carboxylated cellulose nanofibers.

[0014] In embodiments, the method of the present disclosure further includes a step of contacting the biological waste source and nitric acid with sodium nitrite.

[0015] In some embodiments, the method of the present disclosure further includes a step of pretreating the biological waste source with an alkaline solution before contacting the biological waste source with nitric acid.

[0016] When used, the alkaline solution may contain KOH, NaOH, potassium phosphate, or a combination thereof.

[0017] In this embodiment, the alkaline solution has a pH of about 8 to about 14.

[0018] In some embodiments, the method of the present disclosure further includes the step of crushing the biomass in the biowaste source before contacting the biowaste source with an alkaline pretreatment agent or nitric acid.

[0019] In some embodiments, the nanocellulose in the gellable suspension has a carboxylic acid content of about 0.1 mmol / g to about 3 mmol / g.

[0020] Fertilizer produced by the method disclosed herein is also provided.

[0021] Various embodiments of the films and methods of this disclosure are described herein with reference to the drawings. [Brief explanation of the drawing]

[0022] [Figure 1] This is a flowchart showing the general process steps of this disclosure. [Figure 2] This is a schematic diagram of a system that can be used to carry out the process of this disclosure. [Figure 3] This graph shows the carboxylic acid concentration and total content plotted against the ratio of nitrite (millimoles) / jute (grams) used during nitro oxidation processes (NOP) 10, 1, and 4. All other reaction conditions were identical. [Figure 4] This graph shows the carboxylic acid concentration and total content plotted against the temperature used during the pulping phase of nitro oxidation processes (NOP) 9, 1, and 13. All other reaction conditions were identical. [Figure 5]This graph shows the carboxylic acid concentration and total content plotted against the temperature used during the oxidation steps of nitro oxidation processes (NOP) 2, 1, and 15. All other reaction conditions were identical. [Figure 6] This graph shows the carboxylic acid concentration and total content plotted for reactions using either jute or bleached jute, and involving both pulping and oxidation, or oxidation alone. All other reaction conditions were identical. [Figure 7] This graph shows the carboxylic acid concentration and total content plotted against the amount of nitrite used, either as a solid or liquid. All other reaction conditions were identical. [Figure 8] This graph shows the carboxylic acid content of cellulose nanofibers (NOCNF) nitro-oxidized from different nitro-oxidation processes (NOP), plotted against their respective crystallinity indices, as determined by wide-angle X-ray diffraction (WAXD). [Figure 9] This graph shows the Fourier transform infrared (FTIR) spectra of nitro-oxidized cellulose nanofibers (NOCNF) from jute and from different nitro-oxidation processes (NOP). The degree of crystallinity derived from the FTIR is calculated using the peak heights at 1427 cm⁻¹ and 895 cm⁻¹. [Figure 10] This graph shows the T(%)1427 / 895 values ​​plotted against the respective crystallinity index of jute and nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). T(%)1427 / 895 is calculated from the quotient of the transmittance (%) at 1427 cm⁻¹ and 895 cm⁻¹ for each sample. [Figure 11A-1] This graph shows the deconvoluted wide-angle X-ray diffraction (WAXD) patterns of jute and nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). [Figure 11A-2]This graph shows the deconvoluted wide-angle X-ray diffraction (WAXD) patterns of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). [Figure 11B-1] This graph shows the deconvoluted wide-angle X-ray diffraction (WAXD) patterns of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). [Figure 11B-2] This graph shows the deconvoluted wide-angle X-ray diffraction (WAXD) patterns of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). [Figure 12A-1] This graph shows the electrical conductivity titration curves of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). The points used to determine the acid and base curves are indicated by squares and triangles, respectively. Linear line fitting was performed, and the fitted data is shown. [Figure 12A-2] This graph shows the electrical conductivity titration curves of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). The points used to determine the acid and base curves are indicated by squares and triangles, respectively. Linear fitting was performed, and the fitted data is shown. [Figure 12A-3] This graph shows the electrical conductivity titration curves of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). The points used to determine the acid and base curves are indicated by squares and triangles, respectively. Linear fitting was performed, and the fitted data is shown. [Figure 12A-4] This graph shows the electrical conductivity titration curves of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). The points used to determine the acid and base curves are indicated by squares and triangles, respectively. Linear fitting was performed, and the fitted data is shown. [Figure 12B-1]This graph shows the electrical conductivity titration curves of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). The points used to determine the acid and base curves are indicated by squares and triangles, respectively. Linear fitting was performed, and the fitted data is shown. [Figure 12B-2] This graph shows the electrical conductivity titration curves of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). The points used to determine the acid and base curves are indicated by squares and triangles, respectively. Linear fitting was performed, and the fitted data is shown. [Figure 12B-3] This graph shows the electrical conductivity titration curves of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). The points used to determine the acid and base curves are indicated by squares and triangles, respectively. Linear fitting was performed, and the fitted data is shown. [Figure 12B-4] This graph shows the electrical conductivity titration curves of nitro-oxidized cellulose nanofibers (NOCNF) from different nitro-oxidation processes (NOP). The points used to determine the acid and base curves are indicated by squares and triangles, respectively. Linear fitting was performed, and the fitted data is shown. [Figure 13] The graphs illustrate the characterization of nitrated cellulose nanofibers (NOCNF) and ammonium-supported NOCNF, shown as NH4+@NOCNF, using (i) Fourier transform infrared spectroscopy (FTIR) highlighting the presence of C=O and OH stretching vibrations, (ii) thermogravimetric analysis (TGA) plots showing the mass of the NOCNF sample with respect to temperature, (iii) TGA showing the differential mass of the NOCNF sample to more clearly indicate the starting temperature, and (iv) wide-angle X-ray diffraction (WAXD) figures representing the crystallinity of the initial state and the adsorbed sample. [Figure 14]This figure shows images illustrating the morphological characteristics of nitro-oxidized cellulose nanofibers (NOCNF) and their respective ammonium-supported NOCNFs. (i) Atomic force microscope (AFM) images of NOCNF and (ii) ammonium-supported NOCNF. (iii) Transmission electron microscope (TEM) images of NOCNF and (iv) ammonium-supported NOCNF. [Figure 15] This graph shows adsorption data using nitro-oxidized cellulose nanofibers (NOCNF). (i) Ammonium removal rates plotted against equilibrium concentrations using NOCNF with various degrees of oxidation (DO). The Langmuir isotherms drawn for each sample faithfully represent the experimental data and general trends. (ii) Effect of pH on ammonium removal rates and zeta potential on NOCNF. Optimal adsorption capacity is observed near neutral pH conditions. (iii) Ammonium adsorption using NOCNF and the zeta potential of NOCNF as the amount of ammonium (expressed as the molar ratio of ammonium to carboxylate content) increases. The dashed lines are drawn to facilitate comparison of different measurements. (iv) Ammonium adsorption capacity using TEMPO-mediated cellulose nanofibers (TEMPO-CNF). [Figure 16] This graph shows the Langmuir fitting for (i) nitro-oxidized cellulose nanofibers (NOCNF) and (ii) TEMPO-oxidized cellulose nanofibers (TEMPO-CNF). [Figure 17] This graph shows the Freundlich fitting for (i) nitro-oxidized cellulose nanofibers (NOCNF) and (ii) TEMPO-oxidized cellulose nanofibers (TEMPO-CNF). [Figure 18] This graph shows the nitrogen composition of the tested soil over a three-week period. [Figure 19] This graph shows the mass of roots, stems, and leaves over a three-week period for each soil treatment. [Figure 20] This graph shows the nitrogen composition of roots, stems, and leaves over a three-week period for each soil treatment. [Modes for carrying out the invention]

[0023] Embodiments of the subject matter of this disclosure will be described in detail below with reference to the accompanying drawings. In this description of the disclosure, descriptions of functions or structures known in the art will be omitted in order to clarify the understanding of the concepts of this disclosure and to avoid obscuring the subject matter with unnecessary details.

[0024] The ever-growing population and the resulting human food demands are creating a crisis in the search for fresh drinking water and sustainable food production. Nutrient pollution, an inevitable consequence of agricultural and residential wastewater leaching into groundwater reservoirs, rivers, and the sea, has disrupted the nitrogen cycle and means of obtaining fresh water. One aspect of nutrient pollution is the heavy application of ammonium fertilizers in industrial agriculture in both developing and developed countries, although their consumption in crop growth is limited, and the resulting inevitable leaching is causing various environmental problems stemming from nutrient pollution.

[0025] Currently, these nutrient contaminants are not properly managed in both the agricultural and wastewater treatment sectors. For example, many wastewater treatment plants in the United States are not designed to remove nutrients, and refurbishment of treatment plants may not be feasible. Current methods for ammonium removal include electrochemical, biological nitrification and denitrification, adsorption (activated carbon and zeolite), and reverse osmosis, but these are typically costly to operate. The consequences of ammonium contamination in water bodies include eutrophication, which is the result of the unsustainable growth of water splendor, leading to the depletion of dissolved oxygen in the water and the potential death of marine life.

[0026] This disclosure provides a method for treating various biological wastes with nitric acid, and the resulting product, namely oxidized cellulose, can be used in wastewater treatment. Specifically, the waste source includes plant-derived fibrous materials, and the method provides a selective and environmentally friendly method for extracting and using nanostructured cellulose having an anionic surface charge for adsorbing cationic pollutants such as ammonium, and for functionalizing cellulosic biomass.

[0027] In the embodiment, any biological waste to be treated, such as agricultural waste, food waste, or animal waste, can be brought into contact with nitric acid. Sodium nitrite or potassium nitrite can be optionally added to the system. Adding a metal oxide catalyst may be effective in accelerating the process. The resulting oxidized cellulose and effluent formed by this process can be applied as an anionic scaffold or repair material, or as fertilizer for plants.

[0028] Whether the process produces nanocellulose fertilizer or functionalized cellulose nanofibers having an anionic surface charge (sometimes referred to herein as nitro-oxidized cellulose nanofibers (NOCNF)) will depend on the biomass being processed. For example, when forming nanocellulose fertilizer, the biomass to be processed may include animal waste, such as chicken manure, horse manure, and cow manure, as well as food waste, such as kitchen waste, used coffee grounds, and pulp.

[0029] When forming NOCNF, the starting biomass should be fibrous plant biomass. Examples of such starting biomass include, but are not limited to, cotton, jute, bagasse, spent grain, palm, and coconut. In embodiments, NOCNF may also be suitable for application to plants as a fertilizer or in the form of a supporting suspension as a water quality restoration material.

[0030] In other embodiments, the disclosure relates to the treatment of wastewater containing fibrous materials such as cellulose. If the fluid to be treated contains fibrous materials including cellulose, the fibers may be functionalized. Cellulose can be functionalized by surface modification, including carboxymethylation, carboxylation, sulfonation, and phosphorylation, or by grafting with other molecules / compounds or external agents, such as nanoparticles and their ions. In embodiments of the disclosure, carboxylation of jute fibers was carried out by a nitro-oxidation process (NOP) to extract high-charge-density nitro-oxidized cellulose nanofibers (NOCNF). Nitro-oxidation is a one- or two-step method for producing carboxylated cellulose nanofibers (CNF) from raw biomass ranging from wood to agricultural residues. NOCNF has a carboxylate ion functional group on the C6 carbon and may have up to one carboxyl group per anhydrous glucose unit (AGU).

[0031] The subsequent oxidation process, induced by the addition of sodium nitrite, yields a carboxylic acid group at the C6 position on the cellulose surface. The effectiveness of NOP is evaluated by quantifying the carboxylic acid content, product yield, and crystallinity index.

[0032] In some embodiments, the nitrooxidation process (NOP) produces nitrooxidized cellulose nanofibers (NOCNF) as an adsorbent and / or coagulant / flocculant. One advantage of carboxylated cellulose nanofibers (CNF) is their biocompatibility and biodegradability. CNF can be applied to soil while being potentially renewable.

[0033] The conventional method of using NOP to extract and oxidize cellulose involves the use of 65% nitric acid, which can be a challenge in small-scale production due to the handling of toxic acids.

[0034] According to this disclosure, low concentrations of nitric acid are used in the NOP process while using the same volume. To use the reagent more effectively, the reaction is separated into a pulping step and an oxidation step. In this process, pulping is carried out using nitric acid to remove some lignin and hemicellulose, and oxidation is carried out when sodium nitrite is added. The effects of various parameters, such as starting biomass, acid concentration, temperature, reaction time, and the amount of sodium nitrite, were investigated.

[0035] The general process of this disclosure is shown in Figure 1. The biomass / wastewater to be treated may optionally be pretreated with an alkaline solution. Suitable solutions for this pretreatment include, for example, NaOH, KOH, potassium phosphate, or combinations thereof. The pH of the solution used for this alkaline pretreatment may be about 8.0 to about 14.0, and in embodiments, it may be about 10.0 to about 12.0. The pretreated biomass may then be dried, which is referred to as “Dehumidification Process 1” in Figure 1.

[0036] Any biomass that has not been subjected to alkaline pretreatment may be separately prepared for the processes of this disclosure by first subjecting the biomass to a process to reduce the size of the particles / fibers constituting the biomass, for example by putting it into a pulverizer. The pulverized biomass and optionally alkaline pretreated biomass may then be placed in a reactor and combined with nitric acid, an oxidizing agent, and water.

[0037] The biomass treated with nitric acid may then be dried, which is referred to as “Dehumidification Process 2” in Figure 1. The fibrous material may then be separated from the liquid effluent. The liquid effluent may be contacted with a neutralizing agent, such as KOH, NaOH, NH4OH, (NH4)3PO4, K3PO4, or a combination thereof, to form a liquid fertilizer composition suitable for treating plants. In addition, if the biomass has been pretreated with an alkaline solution as described above, the effluent obtained after “Dehumidification Process 1” may be combined with the liquid effluent and neutralizing agent obtained after “Dehumidification Process 2” to form a liquid fertilizer. The fibrous material may be placed in a high-pressure homogenizer or blender to result in the formation of macroscale, microscale, or nanoscale CNF (i.e., NOCNF).

[0038] A system 10 suitable for carrying out the process of this disclosure is shown in Figure 2. As schematically shown in Figure 2, system 10 may include various reactors, grinders, storage tanks, pumps, heating elements, storage tanks, etc., for carrying out the general process shown in Figure 1. System 10 includes a reactor 12 for alkali pretreatment of any biomass. A grinder 14 may be used to finely grind a portion of the biomass. Any ground biomass and alkali pretreated biomass may then be added to reactor 20. A tank 16 containing nitric acid and a tank 18 containing water may be connected to reactor 20 to add these materials to reactor 20. Wash liquid from reactor 20 may be collected in tank 24. A mixture of solid and liquid effluent from reactor 12 may be passed through an extruder 30 and then sent to reactor 20. A mixture of solid and liquid effluent from reactor 20 may be passed through an extruder 32. From the extruder 32, the solid material is sent into a decantation vessel 40 (optional), where the NOCNF is sent into a reactor 50 for washing and homogenization or blending. The liquid effluent from the decantation vessel is sent into a reactor 60 for neutralization and the formation of liquid fertilizer, which is collected in a fertilizer storage tank 70.

[0039] The nitric acid used in the process of this disclosure may be present in the solution at a concentration of about 15% to about 70%, and in embodiments, about 25% to about 50%. The volume of nitric acid solution used to treat the biological waste will, of course, depend on the volume of biological waste to be treated. Generally, the ratio of nitric acid solution to the biological waste to be treated may be about 1:0.5 to about 1:20, and in embodiments, about 1:14.

[0040] Optionally, sodium nitrite may be further added to the wastewater to be treated. If used, sodium nitrite may be present in the solution at a concentration of about 1% to about 10%, and in embodiments, about 3% to about 7%. The volume of sodium nitrite solution used to treat biological waste will, of course, depend on the volume of biological waste to be treated. Generally, the ratio of sodium nitrite solution to biological waste to be treated may be about 1:0.25 to about 1:5, and in embodiments, about 1:2.

[0041] Nitric acid and optionally selected sodium nitrite may be brought into contact with the biological waste at temperatures of approximately 25°C to 100°C, approximately 30°C to 80°C in embodiments, and approximately 40°C to 60°C in other embodiments. Nitric acid and optionally selected sodium nitrite may be brought into contact with the biological waste for approximately 1 hour to 24 hours, approximately 2 hours to 12 hours in embodiments, and approximately 3 hours to 9 hours in other embodiments.

[0042] If the biological waste source does not contain fibrous materials, the result of processing / treatment of the above-mentioned biological waste with nitric acid and optionally sodium nitrite is a liquid biological waste effluent. Efuciates containing nutrients such as nitrates may be used as fertilizer.

[0043] When the biological waste source includes fibrous cellulose-based materials, the processes of the present disclosure produce charged nanocellulose from a biodegradable and sustainable source extracted from the fibers in the biological waste source. The charged nanocellulose may be a functionalized nanofiber or, in some embodiments, a gellable suspension. A hydrogel is produced by ionically gelling the nanocellulose suspension. This hydrogel may have a viscosity that can be characterized by a rheometer. The coefficient of complex viscosity (|η*|) can be measured at different frequencies. The storage modulus (G') and the loss modulus (G") can be further calculated from η* and can be used to indicate the ability to store energy elastically and the ability of the gel to dissipate energy as heat. By comparing the two parameters G' and G", it can be determined whether the sample is "gel-like" (solid state) (when G'>G") or in a liquid state (when G'<G").

[0044] According to the present disclosure, the NOCNF produced by the disclosed processes may be used for the remediation of ammonium contamination and subsequently recycled as a fertilizer as ammonium-supported NOCNF. The NOCNF is positioned in the middle of the cycle by adsorbing ammonium immediately after the contaminant is created. The ammonium is captured by the NOCNF before it is converted to a more difficult-to-remove form of nitrogen, such as negatively charged nitrite and nitrate. For example, a very common derivative of ammonium is urea, which is a major component of human urine. This urea is decomposed into cationic ammonium, which can then be removed using the anionic NOCNF produced by the processes of the present disclosure.

[0045] The resulting nanocellulose extract is part of a zero-waste nitrooxidation (NOP) process using relatively low concentrations of nitric acid (30-50%). This process partially deligninizes fibrous cellulosic materials by dissolving some amorphous components (hemicellulose and lignin), resulting in nanostructured microfibers. Adsorption for capturing ammonium is simple, efficient, economical, and scalable, and the ammonium impurities captured in the bioscaffold can be used, for example, as a plant fertilizer for direct ammonium adsorption.

[0046] A gellable suspension containing NOCNF produced by the process of this disclosure from the treatment of a fibrous biological waste source may have a carboxylic acid content of about 0.1 mmol / g to about 3 mmol / g, in embodiments about 0.2 to about 1.5 mmol / g, and in other embodiments about 0.5 to about 1.3 mmol / g.

[0047] As described above, the gellable suspension produced as a result of the disclosed process may be used as a fertilizer. Nanocellulose derived from the nitrooxidation process provides a relatively accessible, low-cost, and environmentally friendly methodology for upcycling biological waste into a material of value for use in countless applications, including water purification or agricultural fertilizers. The process of this disclosure provides a cost-effective, simple, and environmentally friendly process for treating wastewater and similar waste sources for future use as fertilizer. [Examples]

[0048] The materials used in these examples included jute fibers obtained from Bangladesh. Nitric acid (65%), sodium nitrite (97%), ammonium chloride (98%), and hydrochloric acid (1.0N) were purchased from Sigma Aldrich. Sodium bicarbonate was purchased from Fischer Scientific. Sodium hydroxide (99%) was purchased from Macron Fine Chemicals. The chemicals were used without any further purification. General-purpose soil was purchased from ProMix. Soybean seeds were purchased from Seed Ranch.

[0049] (Example 1) Jute fibers were cut into 5 cm lengths and then passed through a grinder with a 2 mm grid. Ten grams of the ground jute were placed in a 3-liter round-bottom flask along with 140 ml of nitric acid of various concentrations, as listed in Table 1 below.

[0050] After immersing the fibers, magnetic stirring was started at approximately 200 revolutions per minute (rpm). After a few minutes, once the stirring stabilized, various amounts of sodium nitrite were added, and the oil bath temperature was set according to Table 1 below.

[0051] After adding sodium nitrite, the round-bottom flask was sealed with a glass stopper and Parafilm. Even when sodium nitrite was not added, the round-bottom flask was stoppered after adding nitric acid. The reaction was carried out for the specified duration according to Table 1 below. After the specified duration, the oil bath was turned off, the round-bottom flask was carefully opened, and while maintaining stirring, excess gas was allowed to escape naturally from the flask. The reaction was then stopped by pouring 1 liter of deionized water into the round-bottom flask to significantly reduce the reactivity of the reagent. The suspension was poured into a beaker, and the suspended solid was allowed to settle. The supernatant was decanted and replaced with fresh deionized water. This decantation process was repeated until the pH of the supernatant reached 2.

[0052] Next, the fibers were washed using 40 μm filter paper and deionized water until the filtrate achieved a stable electrical conductivity.

[0053] (Example 2) Bleached jute fibers were used for comparison with pre-treated fibers. The jute fibers were cut into 5 cm lengths and then passed through a grinder with a 2 mm grid. Approximately 30 grams of the ground jute were suspended in a 1% (w / v) sodium chlorite solution in 0.1 M acetate buffer at pH 5. The suspension was stirred at 65°C for 3 hours. The fibers were vacuum filtered and rinsed with deionized water. This procedure was repeated three times. A final wash was performed to ensure that the effluent had the same electrical conductivity as deionized water. The fibers were then placed in a large glass dish and dried in a 50°C oven for 24 hours. The dried bleached fibers were passed through a grinder to pulverize the combined fibers.

[0054] Table 1 below summarizes the reaction conditions for the nitro oxidation reactions carried out according to the procedures of Examples 1 and 2. The nitro oxidation reactions are numbered 1 to 15. Typically, the reaction was carried out in two stages: a pulping stage and an oxidation stage. Bold cells indicate how they differ from NOP 1. Cells with (l) indicate that sodium nitrite was added as a solution over 1 hour using the minimum amount of water required to dissolve the sodium nitrite. NOP 14 has (l)*, which means that the sodium nitrite solution was added over 3 hours.

[0055] [Table 1]

[0056] Characterization of NOCNF produced in Examples 1 and 2 Typically, 270 grams of a 0.1 wt.% NOCNF suspension was prepared from a stock NOCNF suspension. The pH of the suspension was adjusted to pH 2.5 using dilute hydrochloric acid. The suspension was then titrated 1 ml at a time with 0.05 M sodium hydroxide until the pH reached 10. Using a more dilute sodium hydroxide solution would likely yield better resolution. In any case, measuring the pH of the titrant is more important than using the mass of sodium hydroxide to calculate the concentration. This is because sodium hydroxide is hydroscopic, while a pH meter can be accurately calibrated using a fresh reagent. The electrical conductivity of the sample was measured and plotted against the volume of titrant. The resulting graph should have three linear curves. As the titrant is added from volume 0 to V1, the electrical conductivity should decrease up to a certain volume. This specific volume is designated as V1. This is a result of the neutralization of free acid present in the suspension due to the addition of an excess amount of acid relative to the carboxylic acid content. After V1, adding further titrant does not significantly change the electrical conductivity of the suspension because it neutralizes the protons bonded to the carboxylic acid group. This holds true up to a certain volume, which is designated as V2. After this volume, further titrants introduce free hydroxides, thereby increasing the electrical conductivity. Since hydronium has a higher electrical conductivity than hydroxides, a steep decrease in the electrical conductivity gradient is generally followed by a gradual increase. The carboxylic acid concentration can be calculated using Equation 1.

[0057]

number

[0058] In the formula, C trepresents the concentration of the titrant. The molecule is typically converted to mmol. m represents the mass of solid NOCNF, which can be calculated by first converting the mass percentage (wt.%) of the suspension (typically the mass percentage of solid NOCNF as the mass of the suspension) to a fraction by dividing wt.% by 100. This mass is then quantified by multiplying it by the mass of the original suspension used before dilution. The final value is expressed in mmol as the carboxylic acid content per gram of solid NOCNF.

[0059] Due to the low carboxylic acid content of these samples, titrator concentrations of less than 0.03 M were used in the neutral range to generate more data points. Furthermore, all samples were titrated using an autoburette capable of dispensing 0.05 ml at a time. Combining lower titrator concentrations with smaller titration volumes helped increase the number of data points generated in the neutral range.

[0060] Generally, linear fitting on acid and base curves was used to determine at what volume the transition occurred. These linear fits should have a good R-squared value, typically 0.9–0.99. One problem with this method is considering how many points to include in the linear fit. Acid curves can be relatively long, sometimes consisting of more than 50 points. Considering that neutral curves may only have 4 points, such an excess of data on the acid curve can lead to an R-squared value of 0.99. 2 It is possible to incorporate the entire neutral curve while maintaining the values. In this study, both the acid and base curves were limited to 10 points each, and the R-squared value was set to 0.99 to induce good sensitivity to the transition point.

[0061] Fourier transform infrared spectroscopy Fourier transform infrared spectroscopy (FTIR) was recorded using a Thermo Scientific Nicolet iS10 FT-IR Spectrometer in attenuated total internal reflection (ATR) mode. Sixteen scans at a resolution of 4 were averaged. The instrument was equipped with a DTGS KBr detector, KBr beam splitter, IR light source, Smart iTR accessory, and diamond window. Samples were typically 400 to 4000 cm⁻¹. -1 It was measured up to that point.

[0062] Wide-angle X-ray diffraction Wide-angle X-ray diffraction (WAXD) patterns were measured and recorded using a Rigaku MiniFlex scanner. The sample was measured from 5 to 45 degrees, in 0.02-degree increments, at a rate of 5 degrees / minute. The scanning axis was set to theta / 2-theta in continuous mode, and the intensity was measured in counts per second (CPS). Voltage and current were set to 40kV and 15mA, respectively, using Cu Kα rays. 5.0-degree incident and receiving solar slits were used in conjunction with a 1.250-degree incident beam divergence limiting slit.

[0063] Effect of reaction conditions on carboxylic acid content Table 1 above shows all the reaction conditions tested, where each experiment is indexed as NOP (No. 1). The reaction conditions are divided into two parts, where nitric acid, biomass, temperature 1, and time 1 indicate the reaction conditions for pulping a specified biomass. Typically, the sample is pulped with 30% nitric acid at 50°C for 3 hours using 10 grams of raw jute. Part 2, indicated as sodium nitrite, temperature 2, and time 2, represents the oxidation step. Typically, the reaction uses 9.6 grams of sodium nitrite at 50°C for 6 hours. Several special modifications include using no sodium nitrite at all, or using sodium nitrite dissolved in water.

[0064] Table 2 below summarizes the conductivity titration data used to calculate the carboxylic acid content of all samples, and Table 3 below summarizes the collected data.

[0065] [Table 2]

[0066] [Table 3]

[0067] NOP 1 served as a baseline, and the other reactions were compared to it. NOP 1 involved pulping using 30% nitric acid and 10 grams of jute, stirred at 50°C for 3 hours. For oxidation, NOP 1 used 9.6 grams of sodium nitrite at 50°C for 6 hours. All other reactions varied only one of these experimental parameters, generally to either a positive or negative degree. Bold text in Table 1 indicates how it differs from NOP 1. NOP 1 contains 0.108 mmol of carboxylic acid per gram of solid.

[0068] NOP 2 was oxidized at a lower oxidation temperature of 25°C compared to NOP 1. The resulting carboxylic acid content of 0.047 mmol / g was slightly less than half the carboxylic acid content of NOP 1, thereby demonstrating the relationship between reaction kinetics and temperature.

[0069] NOP 3 used 15% nitric acid in the pulping stage, which is half the concentration used in NOP 1 or NOP 2. Similarly, the carboxylic acid content was 0.047 mmol / g. These experiments helped confirm the synergistic effects of both nitric acid and sodium nitrite, including the reaction of nitric acid with nitrite that produces nitrosonium ions, which are presumed to be the oxidizing agent in NOP.

[0070] NOP 4 used 14.4 grams of sodium nitrite, which is 50% more than the sodium nitrite used in NOPs 1-3. The carboxylic acid content did not increase; instead, it was measured at 0.088 mmol / g. While an increase in carboxylic acid content should have been expected, it did not; instead, it decreased by approximately 19% compared to NOP 1. This clearly demonstrates the importance of the relative concentrations of nitric acid and sodium nitrite, considering that even if excess nitrite is converted to nitrite, there is not enough nitric acid to produce nitrosonium ions.

[0071] NOP 5 was the first of two reactions testing the effect of using bleached jute instead of raw jute. Bleached jute is light white and is expected to have low hemicellulose and lignin content. Bleached jute was used as a cellulosic biomass instead to reduce the change in variables caused by using cellulose from a different plant biomass. The reaction conditions for NOP 5 were exactly the same as NOP 1, except that bleached jute was used. The carboxylic acid content was 0.091 mmol / g, which was lower than in NOP 1. Considering that bleached jute contains less hemicellulose and lignin and therefore more cellulose to be oxidized, this is likely because the amount of carboxylic acid diffused into a larger mass of cellulose. In contrast, in NOP 1, some of the jute dissolved and the remaining jute was oxidized. Or, some amorphous cellulose, hemicellulose, and lignin were oxidized, but these also dissolved and were lost during washing.

[0072] NOP 6 was prepared by minimizing the time spent in the pulping stage, instead adding sodium nitrite immediately after the addition of nitric acid. This resulted in the second highest carboxylic acid content in this study, at 0.117 mmol / g.

[0073] NOP 7 used bleached jute and, like NOP 6, neither had a substantial pulping stage; instead, sodium nitrite was added immediately after the addition of nitric acid. Similarly, NOP 7 had a higher carboxylic acid content (0.106 mmol / g) than NOP 5 (0.091 mmol / g), indicating that the carboxylic acid content increased with longer oxidation times. The longer oxidation time was due to the omission of the pulping stage, which means that the jute was fully exposed to sodium nitrite for 9 hours.

[0074] NOP 8 was investigated for the effects of a pulping step using only nitric acid over a 9-hour period, without the use of sodium nitrite. As expected, the carboxylic acid content was low at 0.020 mmol / g. The crystallinity index of NOP 8 was 58.9%, which was higher than that of jute, which was 53.78%.

[0075] NOP 9 used a reduced pulping temperature of 25°C. The carboxylic acid content was only slightly reduced to 0.096 mmol / g compared to 0.108 mmol / g for NOP 1. It was expected that the reduced temperature during the pulping stage would leave more effective acid for oxidation.

[0076] NOP 10 used 3.8 grams of sodium nitrite, which was 60% less than the amount used in NOP 1. The carboxylic acid content of 0.061 mmol / g was lower than that of NOP 1 (0.108 mmol / g), but 50% higher than the samples from reactions using a pulping temperature of 25°C or 15% nitric acid.

[0077] NOP 11 was oxidized as usual with 9.6 grams of sodium nitrite, but dissolved in 12 grams of water and added to a round-bottom flask over 1 hour using a syringe pump. The carboxylic acid content was 0.075 mmol / g, lower than NOP 1 (0.108 mmol / g) which used solid sodium nitrite. NOP 12 was prepared by doubling the amount of sodium nitrite to 19.2 grams, similarly dissolved in water, and dispersed over 1 hour via a syringe pump. The carboxylic acid content was measured at 0.088 mmol / g, a slight increase relative to the additional amount of sodium nitrite added.

[0078] One observation is the clear NO between the two types of reactions. x The issue was the amount of gas. In the reaction using dissolved sodium nitrite, the concentration of the brown gas appeared low from a qualitative standpoint at all points throughout the reaction run. When solid sodium nitrite was added, gas was released immediately upon contact of the salt with the acid, leaving a thick haze in the round-bottom flask. This was in contrast to the addition of dissolved sodium nitrite, in which case no such gas generation was observed, and the observed haze was relatively thin.

[0079] NOP 14 was similar to NOP 12, except that 19.2 grams of sodium nitrite dissolved in water was pumped into a round-bottom flask over a period of 3 hours instead of 1 hour.

[0080] NOP 13 was pulped at 60°C and showed the highest carboxylic acid content at 0.136 mmol / g.

[0081] NOP 15 had an oxidation temperature of 60°C, and its carboxylic acid content was only slightly increased compared to NOP 1.

[0082] Effect of reaction conditions on total carboxylic acid content The carboxylic acid content multiplied by the product yield reflects both the effectiveness of the oxidation and the effectiveness of the product yield. The trends in carboxylic acid content per gram and total carboxylic acid content follow the same pattern, except for both reactions using NOP 9, NOP 11, and bleached jute.

[0083] NOP 9 used a pulping temperature of 25°C, while NOP 1 used 50°C; both used the same oxidation temperature of 50°C. The total carboxylic acid content of NOP 9 was 0.5285 mmol, compared to 0.3702 mmol for NOP 1. The carboxylic acid content of NOP 9 (0.096 mmol / g) was lower than that of NOP 1 (0.108 mmol / g). Although the carboxylic acid content was similar, the total carboxylic acid content of NOP 9 was significantly higher. Using a pulping temperature of 25°C for NOP 9 may reduce the amount of jute dissolved. When sodium nitrite is added, it may react with nitric acid, reducing the strength of the acid effective in dissolving the jute.

[0084] This can be further explained by comparing it to NOP 6, which is an oxidation-only reaction. In NOP 6, sodium nitrite was added immediately after nitric acid, and then the mixture was heated to 50°C. The oxidation time for NOP 6 was 3 hours longer, but the product yields were similar for NOP 6 (49.39%) and NOP 9 (55.34%), suggesting that the slightly lower yield in NOP 9 may be due to the longer reaction time.

[0085] NOP 11 was oxidized with a sodium nitrite solution. Its carboxylic acid content was lower at 0.075 mmol / g compared to 0.108 mmol / g for NOP 1, but its total carboxylic acid content (0.3912 mmol) was higher than that measured for NOP 1 (0.3702 mmol).

[0086] The total carboxylic acid contents of NOP 5 and NOP 7, both reactions using bleached jute, were the highest at 0.6543 mmol and 0.7372 mmol respectively, except for NOP 13, and the content of NOP 13 was higher than that of NOP 5. Since the reaction was carried out with bleached jute, there should be less hemicellulose and lignin to be pulped. Probably, as a result, less of the oxidized jute was dissolved and subsequently lost during washing.

[0087] The carboxylic acid content of NOP 13 was the highest at 0.136 mmol / g, and the total carboxylic acid content was the second highest at 0.6687 mmol. By using a higher pulping temperature of 60 °C, not only did the carboxylic acid content increase, but the total yield also increased. The explanation for the case of NOP 13 may be related to the glass transition point (T g ) of lignin. The literature on pulping mentions the T g of lignin as a sharp change in the apparent softness of the material. Amorphous polymers such as lignin can have a T g , which is the temperature range in which the material transitions from a glassy state to a more rubbery state. In the case of lignin, the effective T g can decrease while water is present. The water absorbed by lignin can act as a low molecular weight diluent and thus function as a plasticizer, decreasing the T g . From the literature, it was reported that the T g is 40 °C for hemicellulose and 50 - 100 °C for lignin. In NOP 13, the higher pulping temperature of 60 °C may have been sufficient to reach the T g of lignin, and it may have been possible to dissolve more easily treatable lignin rather than cellulose. This could increase the overall product yield observed.

[0088] Other samples with comparable product yields of 49.4% were NOP 2, NOP 3, NOP 6, and NOP 9, but all of them had lower carboxylic acid content. All of the above reactions reduce the effective strength of nitric acid in some way, either by reducing the oxidation temperature, reducing the nitric acid concentration, reacting sodium nitrite with nitric acid earlier in the process, or reducing the pulping temperature. NOP 13 was differentiated from these reactions by more effectively utilizing nitric acid by reacting it with lignin, which is easier to process, and then using the remaining acid to oxidize cellulose.

[0089] Effect of sodium nitrite composition Figure 3 shows the carboxylic acid concentration and total content plotted against the ratio of nitrite (millimoles) to jute (grams) used in NOPs 10, 1, and 14. All other reaction conditions were identical. The trends in both carboxylic acid content and total content were similar when the ratio of nitrite (millimoles) to cellulose (grams) was increased from 5.5 to 13.9. Further increases in the relative amount of nitrite resulted in a greater relative decrease in carboxylic acid content compared to the total content.

[0090] Effect of pulping temperature Figure 4 shows the trends in carboxylic acid concentration and total content plotted against the pulping temperature used in NOPs 9, 1, and 13. All other conditions were identical. Both carboxylic acid concentration and total content increased with temperature, increasing by 40% from 25°C to 50°C and by 80% from 50°C to 60°C. Since pulping was performed before oxidation, changing pulping parameters such as temperature essentially altered the starting material. Using a temperature of 25°C resulted in a jute composition relatively close to the original jute composition compared to using 60°C. The study revealed the T content of lignin. gGiven that the temperature range is shown to be between 50 and 100°C, and considering that a pulping temperature of 60°C may increase interaction with nitric acid, the “starting material” for oxidation at 60°C is likely to be considerably deligninized jute biomass. When oxidation is initiated, a larger portion of the cellulose surface may be exposed to oxidation.

[0091] Effect of oxidation temperature Figure 5 shows the trends in carboxylic acid concentration and total content plotted against the oxidation temperature used in NOPs 2, 1, and 15. All other conditions were identical. Unlike pulping, all starting samples were essentially identical at the start of the oxidation step. As expected, carboxylic acid content increased with increasing oxidation temperature, while total content decreased only slightly, reflecting the trade-off of a lower product yield. Increasing oxidation to 60°C after pulping at 50°C for 3 hours did not yield the same benefits as pulping at 60°C.

[0092] Relative performance of pulping and oxidation methods for jute and bleached jute Figure 6 compares the carboxylic acid concentrations and total content plotted for reactions using jute or bleached jute, with both pulping and oxidation or oxidation alone. All other reaction conditions were identical. When oxidation alone was performed, both measured parameters increased, as indicated by the two points. Increased exposure time to sodium nitrite increases oxidation, and longer exposure to nitric acid at 50°C may lead to greater decomposition of the starting material.

[0093] This study was also conducted using bleached jute fibers to investigate the effect on starting materials with a higher cellulose content. The same conclusion was reached when using bleached jute: oxidation is more effective than pulping and oxidation. Interestingly, the higher total carboxylic acid content when using bleached jute indicated greater tolerance of the starting material to nitric acid, resulting in a higher product yield.

[0094] Relative performance of sodium nitrite in solution addition Figure 7 shows the carboxylic acid concentration and total content plotted against the amount of nitrite used, either as a solid or concentrated aqueous solution. All other reaction conditions were identical. Overall, the total content increased when sodium nitrite was added as a solution. A further increase was observed when the amount of sodium nitrite was doubled. This is a clear difference compared to when solid sodium nitrite was used, because, as seen in Figure 3, simply increasing the amount of sodium nitrite by 50% resulted in a decrease in both the content and the total content.

[0095] Observation of the molar amounts of nitric acid relative to sodium nitrite when added as a solution yielded 0.77 mol of nitric acid and 0.14 or 0.28 mol of sodium nitrite in Figure 7. While the nitric acid was still in excess, the reduced generation of reddish-brown gas from the addition of sodium nitrite solution indicated less nitric acid decomposed into nitrous oxide. This could lead to the generation of more nitrosonium ions.

[0096] When sodium nitrite solution was added over 3 hours instead of 1 hour, both the carboxylic acid content and total content, as well as the product yield, decreased. In this case, the product yield decreased by a particularly large 33.7%. This can be attributed to the jute being exposed to nitric acid for an extended period, which slowed down the oxidation process.

[0097] Effect of reaction conditions on the degree of crystallinity index Figure 8 shows the carboxylic acid content of each sample according to its crystallinity index (CI). CI is a measure of crystalline cellulose compared to amorphous cellulose. Cellulose can form crystalline fibers, and the two main packing forms are classified into cellulose I and cellulose II. Cellulose I can also be called natural cellulose, while cellulose II may be described as either mercerized or regenerated cellulose. α and Cellulose Iβ It is a class that contains cellulose I α It is found in non-vascular plants such as mosses and algae, while cellulose I β It is found in vascular plants. Cellulose I β The crystal structure of cellulose is perhaps the most studied cellulose crystallinity using X-ray diffraction and nuclear magnetic resonance techniques. β The unit cell is a monoclinic system containing two different cellulose chains, with unit cell parameters a=0.778nm, b=0.820nm, c=1.038nm, and y=96.5°. The reported lattice planes may differ depending on how the chain axis is defined. In this study, the lattice planes 101, 101, 021, 002, and 040 are used to analyze the cellulose I in the wide-angle X-ray diffraction pattern. β The crystal peaks will be assigned using the peak deconvolution method.

[0098] A summary of the peak deconvolution parameters is shown in Table 4 below.

[0099] [Table 4A]

[0100] [Table 4B]

[0101] [Table 4C]

[0102] The figures were baselined using a constant value line equal to the lowest value within the range of 5–45°2θ. Six Gaussian curves were placed on each diffraction figure, one for each lattice plane and one for amorphous cellulose. The peak centers of 101, 101, amorphous, 021, 002, and 040 were constrained to 14–16, 16–18, 19.5–22.5, 19.5–21.5, 22.5–23.5, and 34.5–35.5°2θ, respectively. After several fitting iterations to ensure that the constraints did not significantly affect the peak positions, the constraints on the peak centers were removed. After several fitting iterations, the full width at half maximum (FWHM) of the strongest crystalline peak, 002, appeared.

[0103] The FWHM of 002 is shown as peak index 5 in Table 4 and is slightly below 2.2 for most samples. Using the unique FWHM of each fitting, constraints were set on all other crystal peaks in the diffraction pattern, specifically ±0.4. In this regard, the peak of 002, which is the strongest crystal peak in each sample, was used as a reference to derive the FWHM of the crystal peaks. The FWHM of amorphous cellulose, shown as peak index 3 in Table 4, was not constrained. A typical FWHM of amorphous cellulose is greater than 9, and in some cases, the FWHM may have to be initially set to a high value such as 9 before the fitting automatically converges to this high range. In general, the peak area was not constrained except that the area was constrained to positive values ​​only. The fitting was 1.0 × 10⁻⁶ -6 The process was repeated until convergence occurred within the tolerance limit.

[0104] Figure 8 shows the carboxylic acid content according to the crystallinity index. Since crystallinity reflects the supramolecular structure rather than the surface structure of cellulose, there is no clear trend between the two parameters. This is demonstrated by NOP 8, which may have resulted in a relatively high crystallinity index without a significant increase in carboxylic acid content, as sodium nitrite was not used. Also, as seen in Figure 8, NOP 13 had the highest carboxylic acid content of all the samples tested, but its crystallinity index was below average. NOP 13 was pulped at a temperature of 60°C, so it can be assumed that at this temperature the lignin is rubbery and therefore more easily processed by nitric acid. If the lignin is more easily processed, nitric acid may not decompose the amorphous cellulose, and may only reflect a slight increase in crystallinity.

[0105] NOP 15 had a crystallinity index of 65.31%, the highest crystallinity index observed in this study. This is surprising, considering it is higher than the reaction using bleached jute. The sodium chlorite pulping process can remove lignin, in contrast to nitrate pulping, which can dissolve both lignin and cellulose. This is further explained by observing the product yields of NOP 1 (jute) and NOP 5 (bleached jute), which were 30.12% and 72.1%, respectively.

[0106] Comparison of crystallinity indices using WAXD and FTIR The Fourier transform infrared spectrum is shown in Figure 9. The main peak is at 3330 cm⁻¹ from the hydroxyl group. -1 OH stretch vibration, 2900cm -1 CH stretching vibration at 1730 cm from the carboxylic acid group. -1 C=O stretching vibrations and 1035 cm from glycosidic bonds -1 This includes CO stretching vibrations.

[0107] There are several variations of FTIR to determine the crystallinity index of cellulose. These variations compare the relative intensity or area of ​​two peaks. In this study, the lateral order index (LOI) variation was used. This method uses 1427 cm². -1 Strength at 895cm -1 It is calculated by dividing by the intensity. 1427cm -1 ~1429cm -1 The peak at 895 cm² is attributed to CH2 pinch vibrations, which occur only at the C6 carbon of cellulose. -1 The peak at 1427 cm² is related to the vibrational mode of C1 and is closely associated with β-bonded glucose polymers. This method is more amorphous in ball-milled cellulose. -1 The relative band strength was 895 cm. -1 It was developed when studies showed a decrease compared to cellulose I. In cellulose I, it is assumed that the primary alcohol O6 oxygen is hydrogen-bonded to O2 oxygen via intramolecular hydrogen bonding and to O3 oxygen via intermolecular hydrogen bonding. This regular hydrogen bonding is not expected in amorphous cellulose. Amorphous cellulose is not regularly aligned with other cellulose chains and has a greater degree of rotational freedom around its glycosidic bonds. Although the chemical compositions of crystalline and amorphous cellulose are very similar, FTIR spectroscopy has been observed to typically show bonds of the same intensity and orientation as sharper peaks. In amorphous cellulose, the hydrogen bonding is more disordered, resulting in broader peaks.

[0108] Figure 10 shows 895 cm -1 1427 cm² divided by the transmittance (%) measured by [the method used] -1 The transmittance (%) measured was plotted according to the crystallinity index (%). A straight line passing through the data points was fitted, and the coefficient of determination (COD), or R-squared value, was calculated to be 0.76.

[0109] Overall, the above examples demonstrate that a method for producing carboxylated cellulose fibers using a lower concentration of nitric acid (30%) is more scalable and safer than the original NOP using a higher concentration of nitric acid (>60%). Although the resulting carboxylic acid content was significantly lower than that achieved in the conventional NOP process, the above examples demonstrate the effectiveness of using lower concentrations of nitric acid, achieving shorter reaction times and improved pulp yield. Furthermore, these examples demonstrate how nitric acid can be used more effectively by increasing the pulping temperature to 60°C (which likely increases exposure to lignin). This oxidation process was shown to be better performed than the pulping and oxidation method, given the advantages of increased reaction time and reduced jute decomposition. Better results were also achieved by using a room temperature pulping temperature and then increasing the oxidation temperature to the default value of 50°C. Overall, significant jute decomposition was demonstrated when pulping with nitric acid at a temperature of 50°C. Alternatively, the best results were obtained by omitting the pulping step and oxidizing the cellulose with a sodium nitrite solution, or by pulping at a higher temperature.

[0110] (Example 3) Jute fibers were cut into 5 cm lengths and oxidized. Briefly, 1.0 gram of jute fiber was immersed in 14 ml of 65% nitric acid, followed by the addition of sodium nitrite. The amount of sodium nitrite was varied according to the target carboxylate content in the NOCNF. Specifically, 0.96, 0.48, and 0 grams of sodium nitrite were used to produce NOCNF (labeled NOCNF 1.1, NOCNF 0.8, and NOCNF 0.2) with carboxylate content of 1.1, 0.8, and 0.2 mmol per gram of NOCNF, respectively.

[0111] After adding sodium nitrite, the round-bottom flask was immediately sealed to prevent the loss of fumes produced from the reaction. The round-bottom flask was held at 50°C for 12 hours, then quenched with 250 ml of deionized water. The supernatant was then decanted 2-3 times and washed by centrifugation at 5000 RPM for 10 minutes to bring the pH to 2.5 or higher. The fibers were then dialyzed with deionized water until no further changes in electrical conductivity occurred within 24 hours.

[0112] The fibers obtained at this stage possess carboxylic acid functional groups. The fiber slurry was treated with sodium bicarbonate until the pH of the suspension reached 7.5. This sodium bicarbonate treatment yielded carboxylate functional groups with sodium counterions. The fibers were then dialyzed using deionized water until their electrical conductivity no longer changed within 24 hours. This slurry was passed once through a 250 bar homogenizer to fibrillate the fibers into NOCNF. The sample was kept dialyzed until use.

[0113] (Example 4) Preparation of TEMPO-oxidized CNF. TEMPO-mediated oxidized cellulose nanofibers (TEMPO-CNF) were tested for ammonium adsorption in comparison with other oxidized cellulose nanofibers. Briefly, 10 grams of pulverized bleached jute were suspended in water containing 0.16 grams of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 1.0 gram of sodium bromide. The reaction was initiated with sodium hypochlorite, stirred, and maintained at pH 10 using a dilute sodium hydroxide solution. Once no more sodium hydroxide was consumed, the sample was thoroughly washed using a dialyzing tube and defibrated using a high-pressure homogenizer. The sample was kept in a dialyzing state until use. The carboxylate content of 1.20, 1.14, and 0.86 mmol per gram of TEMPO-CNF (labeled as TEMPO-CNF 1.2, TEMPO-CNF 1.14, and TEMPO-CNF 0.86) was achieved using sodium hypochlorite concentrations of 14, 11, and 8 mmol per gram of cellulose, respectively.

[0114] (Example 5) Restoration study. The concentration of active ammonium in solution was determined using an ammonium ion selective electrode (ISE) from Vernier. When testing adsorption capacity, 3 ml of CNF and 3 ml of ammonium solutions prepared from ammonium chloride of various concentrations were added to test tubes. In this study, ppm of ammonium represents the ppm of ammonium itself, not the ppm of ammonium chloride. Since other studies may use other ammonium-based salts, it is easier to compare results by considering only ammonium. However, it is important to disclose which salt was used in case of any influencing factors from counterions. After stirring the sample for 10 seconds, it was incubated at room temperature for 24 hours. The sample was then centrifuged at 10,000 rcf for 10 minutes. The supernatant was separated and the ammonium was measured using the ammonium ISE. When testing adsorption capacity according to pH, the sample was prepared with an aqueous solution of dilute sodium hydroxide or dilute hydrochloric acid, incubated for 24 hours, and then centrifuged. In the pH test, all supernatants were adjusted to a pH of 5 and diluted to the same volume. All samples were tested against a control of the same pH, volume, and / or concentration.

[0115] The reusability of NOCNF was tested using the sodium hydroxide regeneration method. In the first cycle, a fixed volume of 25 ppm ammonium solution prepared from ammonium chloride was added to the NOCNF suspension with stirring, and excess water was removed by centrifugation. After a 5-minute waiting period, the supernatant was collected using centrifugation and the ammonium uptake was measured. The remaining solid sample was then washed with an equal volume of 0.1 M sodium hydroxide. After removing the sodium hydroxide by centrifugation, the solid was rinsed with an equal volume of deionized water. After removing the rinse water by centrifugation, another equal volume of 25 ppm ammonium solution was added to the solid and another cycle was started.

[0116] Column filtration experiments were performed using a fritless column with an adjustable stopcock. Cotton was placed at the bottom of the column to prevent sample loss. One gram of dried, frozen NOCNF 1.1 was placed in the column. A 20 ppm ammonium solution was injected into the column and collected at an average rate of 0.1 mL / min. The effluent was collected at specified time intervals. The concentration of ammonium in the effluent samples was determined.

[0117] (Example 6) Plant growth and nitrogen composition study. The nitrogen composition of nitrogen-containing treatment agents was quantified to determine how much treatment agent should be added to the soil. Approximately 20 grams of treatment agent were added to soil and then thoroughly blended in a blender. The blended soil was then placed in a large, resealable plastic bag containing 430 grams of untreated soil. The amount of treatment agent added was calculated so that the elemental nitrogen composition was 100 mg of nitrogen per kilogram of soil. The total of 450 grams of soil was shaken for several minutes and then left to stand for 24 hours.

[0118] The next day, the soil bags were shaken again for a few minutes to ensure the soil was homogeneous. 50 grams of soil were placed in each of the nine pots, according to the soil type. Soybean (glycine max) seeds were soaked in water for 24 hours, with the seeds half submerged. Two seeds were placed in each pot. After two days, the smaller of the two germinated seeds was removed, leaving only one plant in each pot. This marked the end of the germination process.

[0119] The plants were watered manually to avoid excessive leaching. A control sample was used to determine the minimum amount of water that would begin to drain from the bottom of the pot. This amount of water would be applied to all other plants. The plants were watered every other day. The plant trays were moved every other day to equalize other control variables such as relative heating and sunlight. The plants were kept in a greenhouse with sunlight exposure.

[0120] After the germination process, three plants are collected from each soil treatment once a week for three weeks. The collection process involves separating the roots, stems, and leaves of each plant. These are dried at 60°C for three days. The samples are then weighed to determine their mass, and then ground into a powder for elemental nitrogen composition analysis.

[0121] The control sample consisted of untreated soil. The urea treatment agent consisted of urea at a certain concentration. The ammonium-supported NOCNF treatment agent was prepared by mixing equal amounts of 0.1 wt.% NOCNF 0.8 with a 100 ppm ammonium solution prepared from ammonium chloride. This suspension was equilibrated over 24 hours. To remove as much of the salt solution as possible from the suspension, it was centrifuged at 20,000 rcf for 10 minutes. It should be noted that not all of the salt solution could be removed. Furthermore, the NOCNF was not homogenized. Therefore, the suspension was a mixture of microfibers with a small amount of nanofibers added. This was done to reduce material swelling. The NOCNF absorbed a considerable amount of the salt solution, but this does not reflect ammonium adsorption.

[0122] Washing of the ammonium-supported NOCNF was avoided because it significantly reduced the adsorbed ammonium. Nevertheless, the nitrogen content of all nitrogen-containing treatment agents was measured. The potassium bicarbonate treatment agent consists of potassium bicarbonate at a certain concentration. The NOP effluent treatment agent neutralized with potassium bicarbonate was prepared as follows: 200 ml of NOP effluent from a reaction similar to the one used to produce NOCNF 0.8 was placed in a beaker under stirring. The pH of the solution was approximately 0.5. Potassium bicarbonate solution was added to the solution until the pH value reached 6-7. The neutralized solution was then dried in an oven at 60°C for 3 days. The dried solid was crushed in a mortar with a pestle to obtain a homogeneous powder.

[0123] (Example 7) Sample Characterization - Ammonium Ion Selective Electrode. Ammonium concentration was determined using an ammonium ion selective electrode (ISE). The IntelliCAL ISENH4181 probe from Hach featured a non-replenished Dritek gel reference electrode and a dual junction encapsulated in an epoxy body. The selected ISE used an Ag / AgCl reference electrode and a solid PVC membrane sensor.

[0124] (Example 8) Electrical conductivity titration method. A 40 g NOCNF suspension was diluted to 0.2 wt.% with 160 g of water and stirred at 300 rpm. Dilution facilitates stirring of the suspension and avoids excessive gelation when adding the salt solution.

[0125] The pH of the suspension was adjusted to pH 2.5 using dilute hydrochloric acid. The suspension was then titrated in 1 ml increments with 0.05 M sodium hydroxide until the pH reached 9 (note that a more dilute sodium hydroxide solution can be used). In any case, measuring the pH of the titrant is important for more accurate concentration calculation. The electrical conductivity of the sample was measured and plotted against the volume of the titrant.

[0126] The resulting graph should contain three linear curves. As the titrant is added from volume 0 to V1, the electrical conductivity should decrease up to a certain volume. Let's designate this volume as V1. This is because the addition of an excess amount of acid relative to the carboxylate content neutralizes the free acid present in the suspension; in this case, the acid is far more conductive than sodium or chloride. Adding further titrant will not change the electrical conductivity of the suspension because it neutralizes the protons bonded to the carboxylate groups. This holds true up to a certain volume, which we will designate as V2. Beyond this volume, further titrants introduce free hydroxides, thereby increasing the electrical conductivity. The carboxylate concentration can be calculated using Equation 1 above.

[0127] (Example 9) Zeta potential. Colloidal particles are typically charged particles that are in a stable suspension state in a dispersion medium. Colloids can range from aerosols to foams, emulsions, sols, gels, and solids. NOCNF behaves as a solution when diluted, in which oxidized cellulose is a solid particle dispersed in liquid water (which acts as the dispersion medium). Colloidal particles are electrically neutral because each particle is equilibrated by another particle of the opposite sign. The distribution of these ions explains how an electrical double layer is formed. The electrical double layer consists of three main parts. Dispersed particles in a colloidal suspension have a surface charge. This surface charge is equilibrated by counterions of the opposite sign, attracted via Coulomb forces, also called electrostatic forces. The second component is called the Stern layer, and the boundary of this layer is called the Stern plane. The diffusion layer is the third component and consists of the dispersion medium and more counterions loosely bound to the particles. These layers are then defined as the electrical double layer. The boundary of the diffusion layer is defined as a slip plane. The potential in the electric double layer is maximum in the Stern layer and approaches zero at the slip plane. The potential at the slip plane is defined as the zeta potential.

[0128] The mean zeta potential of the samples was obtained using a ZetaProbe Analyzer from Colloidal Dynamics. Samples were measured using a dielectric constant of 5.0 and a density ratio of 1.5 g / ml. Samples were stirred at 300 rpm and titrated in an autoburette. Water was used to suspend all samples. Niobium electroacoustic (ESA) electrodes and KSiW calibration suspensions were used with this instrument. Samples were treated with either hydrochloric acid or sodium hydroxide in an autoburette to achieve the desired pH before analysis.

[0129] (Example 10) Fourier transform infrared spectroscopy (FTIR) was recorded using a Thermo Scientific Nicolet iS10 FT-IR Spectrometer in attenuated total internal reflection (ATR) mode. Sixteen scans at a resolution of 4 were averaged. The instrumentation included a DTGS KBr detector, KBr beam splitter, IR light source, Smart iTR accessory, and diamond window. Samples were generally 400 to 4000 cm⁻¹. -1 It was measured up to that point.

[0130] (Example 11) Thermogravimetric analysis (TGA) was performed using a TA Q50. Samples were heated in a nitrogen atmosphere from 25°C to 850°C at a rate of 10°C per minute. Sample mass was monitored over temperature. Samples were measured on a platinum pan. Differential mass plotted against temperature (expressed as % / min), also known as differential thermogravimetric analysis (DTG), more clearly shows small changes in mass.

[0131] (Example 12) Wide-angle X-ray diffraction (WAXD) patterns were measured and recorded using a MiniFlex from Rigaku. The sample was measured from 5 to 100 degrees, in 0.02-degree increments, at a rate of 5 degrees / minute. In continuous mode, the scanning axis was set to theta / 2-theta, and intensity was measured in counts per second (CPS). Voltage and current were set to 40kV and 15mA, respectively, using Cu Kα rays. 5.0-degree incident and receiving solar slits were used in conjunction with a 1.250-degree incident beam divergence limiting slit.

[0132] (Example 13) Atomic force microscopy (AFM) measurements were performed using a Bruker Dimension ICON atomic force microscope from Bruker. This instrument was fitted with a Bruker OTESPA tip with a tip radius of 10 nm. 10 μL of a 0.005 wt.% suspension was placed on the surface of a silica plate and allowed to air dry. The sample was measured in tapping mode.

[0133] (Example 14) Transmission electron microscopy (TEM) was performed using a JEOL JEM 1400 with an acceleration voltage of 120 kV. Samples were prepared on a 300-mesh copper grid (Ted Pella Inc.), and 10 μL of 0.01 wt.% sample was spread thinly on the grid. After removing excess fluid, the samples were stained with 10 μL of 2 wt.% uranyl acetate aqueous solution. After removing excess solution, the grid was allowed to air dry.

[0134] (Example 15) Scanning electron microscopy (SEM) was performed using a ZEISS Crossbeam 340 with an electron high voltage of 3 kV and an acceleration voltage of 30 kV. Samples were prepared by spreading a 0.1 wt.% suspension of NOCNF thinly onto a silicon wafer and then coating it with gold sputtering.

[0135] (Example 16) Elemental nitrogen analysis. The elemental nitrogen composition of the sample was determined using a LECO 628 Series combustion-type elemental analyzer. In this study, 0.2 grams of dry, pulverized sample was packed into an aluminum pellet. The sample mass was entered into the instrument's software, and the aluminum pellet was then loaded into a gravity-fed autoloader. The sample was heated to 1050°C using oxygen gas.

[0136] Results and Discussion Structural characteristics evaluation The chemical changes in jute fibers after the nitro oxidation process and sodium bicarbonate treatment were evaluated by FTIR. The results are shown in 13(i). By FTIR, 3339 cm was obtained. -1 The OH stretching vibration of the hydroxyl group at 2894 cm² -1 CH compression vibration at 1035 cm -1 The corresponding major peaks of the cellulose skeleton were shown from the CO stretching vibrations at 1602 cm. NOCNF is 1602 cm. -1 It shows a unique peak due to C=O stretching vibration, which confirms the presence of carboxylate ion groups formed by the nitro oxidation process and sodium bicarbonate treatment.

[0137] Figures 13(ii) and 13(iii) show the TGA of NOCNF. The data represents mass as a function of temperature. This data provides information about the thermal stability of the material and the residual mass remaining after thermal decomposition. The decomposition temperature of NOCNF began at 165°C. In NOCNF, the initial decomposition temperature is related to the glucuronic acid of cellulose. At 850°C, the residual mass percentage remaining is around 10%, which corresponds to the thermally decomposed hemicellulose and lignin components present in NOCNF.

[0138] Figure 13(iv) shows the WAXD figure of NOCNF. The cellulose I structure is indicated by the 2θ peak positions at 16°, 18°, and 24°, corresponding to the (101), (101), and (002) planes, respectively. The cellulose I crystal structure of jute is maintained after modification by the nitro-oxidation process.

[0139] The AFM and TEM images in Figure 14 show the morphology of the samples. NOCNF appeared fibrous, and no significant changes were observed in the sample mixed with ammonium chloride. Microscopic analysis images show that even when concentrated nitric acid was used, a fibrous structure similar to that of TEMPO-CNF oxidized at a milder reaction condition of pH ≈ 10 was maintained.

[0140] Characterization of recovered ammonium-supported NOCNF The thermal decomposition of ammonium-supported NOCNF was studied. The results are shown in Figures 13(ii) and 13(iii). The decomposition temperature of ammonium-supported NOCNF was 115°C, which was lower than that of NOCNF (165°C). From the DTG, it was observed that this initial peak had the maximum differential mass at 204°C. Ammonium chloride has been reported to have a reversible crystallization transition temperature at 186°C, causing a small change in mass. Since NOCNF after ammonium adsorption is expected to contain some crystalline ammonium chloride, this peak was also observed. Ammonium chloride decomposes into ammonia and hydrogen chloride gas at 338°C. This corresponds to the right shoulder of the main DTG peak.

[0141] The chemical form of ammonium after adsorption onto NOCNF was indirectly confirmed by X-ray diffraction of ammonium-supported NOCNF, as shown in Figure 13(iv). The X-ray diffraction pattern of ammonium-supported NOCNF had 2θ peaks at 16°, 18°, and 24°, corresponding to the (101), (101), and (002) planes of NOCNF. Other peaks of ammonium-supported NOCNF at 23.7°, 33.7°, 41.13°, 47.7°, 53.6°, 59.1°, 69.3°, 73.7°, and 78.7°, respectively, in the (100), (110), (111), (200), (210), (211), (220), (221), and (310) planes, which matched those of ammonium chloride. The ammonium-supported NOCNF exhibited two distinct minute peaks at 32.7° and 46.5°, corresponding to the (200) and (220) planes of sodium chloride, respectively. This indicated the formation of a small amount of sodium chloride salt due to the exchange of the original counterions of NOCNF with ammonium.

[0142] Ammonium removal efficiency of NOCNF Figure 15 shows the adsorption capacity of NOCNF according to equilibrium ammonium concentration. Three NOCNF samples with different carboxylate content of 1.1, 0.8, and 0.2 mmol / g were prepared and tested for ammonium adsorption (the samples are referred to as NOCNF 1.1, NOCNF 0.8, and NOCNF 0.2). In addition, TEMPO-CNF with various carboxylate content of 1.20, 1.14, and 0.86 mmol / g were used for ammonium adsorption, as shown in Figure 15 (the samples are referred to as TEMPO-CNF 1.2, TEMPO-CNF 1.14, and TEMPO-CNF 0.86). In all cases, a common trend was observed in that the adsorption capacity of all CNF samples increased up to a certain limit with increasing ammonium equilibrium concentration. This observation is caused by saturation of the adsorption site of CNF due to the interaction of positively charged equivalent mass ammonium ions. The adsorption behavior was modeled using Langmuir and Freundlich isothermal models, and the fitting data is summarized in Tables 5 and 6. These two models represent monolayer and multilayer adsorption modes, respectively. It was interesting to note that the percentage of ammonium removed increased as the equilibrium concentration of ammonium decreased, while the absolute removal increased as the equilibrium concentration increased. NOCNF 1.1 and NOCNF 0.8 showed removal rates of 46.9–51.9% at 2.5 ppm ammonium and 11.8–13.7% at 62.5 ppm ammonium. NOCNF 0.2, which contains lower carboxylate ions, has removal rates of 39.4% at 2.5 ppm ammonium and 17.3% at 2.5 ppm ammonium.

[0143] Based on the Langmuir isotherm, the maximum adsorption capacity (Q m ) can be calculated, Q m This is a theoretical value extrapolated from the following fitting curve. The experimental results for all tested CNF samples used in the Langmuir isothermal model are shown in Table 5. The Langmuir isothermal model is expressed as follows:

[0144]

number

[0145] (In the formula, Q e C is the equilibrium adsorption capacity. e Q is the equilibrium concentration of ammonium. m Q is the maximum adsorption capacity of the monolayer, and b is the Langmuir adsorption constant. m C e / Q e to C e (Determined as the reciprocal of the slope calculated from the linear fit when plotted against ).

[0146] [Table 5]

[0147] On the other hand, the Freundlich isotherm model can be expressed as follows:

[0148]

number

[0149] Here, log Q e log C e Plot the result against K and apply a linear fit to it. F n is the intercept of the linear fit, and n is the reciprocal of the slope of the linear fit.

[0150] Using the Langmuir isotherm, in NOCNF 1.1, Q m 22.7 mg / g, R 2 The result was calculated to be 0.992. In NOCNF 0.8, Q m The value is 19.2 mg / g, R 2 It was 0.994, and with NOCNF 0.2, it was 4.97 mg / g, R 2 The value was 0.970. The R of good isothermal formulas was observed in all NOCNF samples. 2The values ​​demonstrated good compatibility with the Langmuir isothermal model. The trend of adsorption capacity using NOCNF provided evidence that the carboxylate group content is involved in ammonium adsorption, and that ammonium adsorption can be regulated through the concentration of carboxylate groups.

[0151] The ammonium removal rate was also tested on TEMPO-CNF samples, and the results are shown in Figure 15. In TEMPO-CNF 1.2, Q m The value is 16.4 mg / g, R 2 The result was calculated to be 0.981. In TEMPO-CNF 1.14, Q m The value is 18.2 mg / g, R 2 It was 0.970, and in TEMPO-CNF 0.2, it was 12.8 mg / g, R 2 The value was 0.859. When comparing samples with similar carboxylate content, the maximum adsorption in TEMPO-CNF was slightly lower than that of NOCNF. This may be related to the different processes used to extract the CNF. The morphology of NOCNF and TEMPO-CNF differed significantly, with the latter having a larger fiber aspect ratio.

[0152] All adsorption results from both CNF samples fit well with the Freundlich isotherm model, and R 2 The values ​​range from 0.904 to 0.972 (Table 6). The corresponding isotherm plots are shown in Figure 16.

[0153] [Table 6]

[0154] The Freundlich isotherm model describes a multilayer adsorption process in which adsorbents can be adsorbed onto other layers of adsorbents.

[0155] Influence of pH on the zeta potential and adsorption capacity of NOCNF Figure 15 shows how the pH of NOCNF affects the zeta potential and adsorption capacity. The negative value of the zeta potential of NOCNF decreased as the pH became increasingly acidic, with the corresponding change in zeta potential ranging from -107 mV to -60 mV. The carboxylate group in NOCNF is a weak acid and is therefore easily affected by pH changes. The maximum adsorption capacity was recorded at pH 6, which is weakly acidic to neutral. In this environment, the carboxyl ion functional group should be located near its pKa and be able to freely exchange counterions. Ammonium with a pKa value of 9.25 will exist in ammonium form at pH=6, but will transition to ammonia form as the pH increases. At pH 8, a small amount of ammonium may be in equilibrium with ammonia, a neutral molecule that is less likely to be adsorbed on NOCNF. Similarly, since the carboxylate ion is a conjugate base of a weak acid, it is more selective to protons than to ammonium.

[0156] The effect of adsorbed materials on zeta potential Figure 15 also shows the effect of adding ammonium solution on the zeta potential of NOCNF. The adsorption capacity is plotted for comparison. The zeta potential remained relatively constant even as the adsorption capacity increased. When the adsorption capacity reached its limit, the zeta potential shifted from negative to positive, and the molar ratio of ammonium ions to carboxylate ions approached 1. This indicates that the limit of adsorption capacity is the number of carboxylate groups, and that the amount of ammonium supported on these functional groups is 1:1. Furthermore, a rapid change in the zeta potential was observed when the carboxylate ion groups reached saturation.

[0157] NOCNF in column filtration 1.0 gram of lyophilized NOCNF was placed in a column, and a 20 ppm ammonium solution was injected at an average flow rate of 0.1 mL / min and collected. The effluent solution decreased from 19.7 ppm to 15.7 ppm in 15 minutes. Subsequently, by 67 minutes, the effluent solution gradually decreased to 14.1 ppm. The gradual decrease in concentration is explained by uneven solution retention by the NOCNF. When the solution was first introduced into the dry column, the contact time with the column was short. Once the solution was able to penetrate the solid, there was sufficient time for the ammonium to adsorb to the NOCNF.

[0158] The NOCNF (NOCNF 1.1) generated here demonstrated relatively good ammonium adsorption of 22.7 mg / g.

[0159] A maximum adsorption capacity of 42.7 mg / g was observed in hydrogels prepared using polyvinyl alcohol (PVA), acrylic acid, and tourmaline. While some of the listed materials are chemically unsustainable, non-biodegradable, somewhat toxic, or have lower efficiency, NOCNF is biodegradable, non-toxic, has good adsorption efficiency, and requires only simple chemical treatment.

[0160] Demonstration of ammonium-supported NOCNF as a fertilizer Figures 18–20 show the effects of treated soil types on the nitrogen composition of soybean soil, roots, stems, and leaves, as well as the mass of roots, stems, and leaves, over a three-week period. Five different soil types were tested. These soils included a control, as well as soils treated with urea, ammonium-supported NOCNF, potassium bicarbonate, and NOP effluent. NOP effluent was collected from the reaction with NOCNF 0.8. This effluent was then neutralized to pH 6–7 with potassium bicarbonate and dried in an oven at 50°C for 72 hours. The control consisted of untreated soil. Urea was used as a comparison with typical nitrogen fertilizers.

[0161] The ammonium-supported NOCNF demonstrated how spent NOCNF can be used after ammonium remediation. The elemental nitrogen composition of the centrifuged ammonium-supported NOCNF was 6.1% by mass, which reflected some of the excess ammonium chloride solution that could not be easily separated. The NOP effluent demonstrated how nitrogen-enriched effluent from NOP can be utilized. The elemental nitrogen composition of the NOP effluent was 7.4%, with a potassium content of 16.25%. Since the NOP effluent was neutralized with potassium bicarbonate, treatment with potassium bicarbonate alone was also studied.

[0162] The nitrogen composition in the soils showed a gradual decrease in elemental nitrogen content over time in all soils. As expected, the nitrogen composition in the untreated soils (i.e., control and potassium bicarbonate) had relatively low nitrogen levels in the first week. This reflects the absence of any additional nitrogen added to the soil and the presence of nitrogen already present in the soil. The decrease in nitrogen content was small over the next two weeks, which is likely due to the absence of any added nitrogen. The nitrogen present in the control and potassium bicarbonate is likely fixed, as it took a long time for these nitrogen molecules to reach a stable and fixed state.

[0163] After one week, the nitrogen composition of the urea-treated soil was the highest. Urea is a neutral molecule and is hydrolyzed to ammonium and carbamate ions by enzymes in the soil. Enzymes such as urease tend to be abundant in natural soils. The carbamate ions then decompose to ammonium and bicarbonates. This process takes several days. In contrast, the adsorption of ions such as calcium and magnesium, exchanged for the original ammonium counterions on carboxylate sites on the cellulose surface, can occur within seconds. This explains why the nitrogen content of ammonium-supported NOCNF was the lowest among the nitrogen-containing samples. The ammonium is rapidly replaced and then either leaches out or is taken up by plants. It is likely that most of the ammonium was not fixed, because if it were, this would also be reflected in the elemental nitrogen analysis. The nitrogen composition of the NOP leachate soil was higher than that of the ammonium-supported NOCNF. The nitrogen composition of soil treated with NOP runoff was slightly lower in the first week and slightly higher in the third week compared to soil treated with urea.

[0164] Figures 19 and 20 show the results of the statistically evaluated soil. One-way analysis of variance (ANOVA) was used for the statistical evaluation, followed by a pairwise t-test with Bonferroni correction, assuming different variances. The number of pairswise t-tests was calculated using Equation 4 below, where k represents the number of groups being compared.

[0165]

number

[0166] Since we were comparing five different groups, the number of pairwise t-tests was equal to 10. The alpha value was corrected using the Bonferroni correction, which was calculated by dividing the original alpha value of 0.05 by the number of t-tests performed. In this study, the alpha value used was 0.005.

[0167] In Figure 19, the mass of roots, stems, and leaves increased over a three-week period. This was expected, as plant mass should not decrease unless the plant is under some kind of stress. Due to the short three-week trial period, factors such as nutrient depletion were not significant. Furthermore, considering the steady positive growth, none of the soil treatments were clearly acutely toxic to the plants. The graphs in Figure 19 are categorized by root, stem, and leaf growth. The mass of each component was compared over time. Relative growth was compared using the calculated average values. However, comparing statistical differences between soils is more relevant. These differences are indicated by the lowercase letters above each soil type. Soils sharing the same letter have no statistically significant differences from each other.

[0168] All root masses were equivalent in the first week. In the first week, the germination process likely still had the primary influence on relative root growth. Early root growth was largely influenced by the seed itself. Nutrient access depends on the plant's root system network, although the seed had some nutrient storage at the start. Factors such as soil moisture tend to have a stronger influence on germination. By the second week, root growth from NOP leachate was greater than that from the control, ammonium-supported NOCNF, and potassium bicarbonate. Soil treated with urea was designated as ab, and it is shown to be statistically equivalent to a and b. Since NOP leachate contains nitrogen and potassium, both of which are essential nutrients for plants, an increase in plant growth, expressed as root mass, was expected. In the third week, all root masses were equivalent.

[0169] The stem mass was also similar across all soil samples for each week.

[0170] Finally, leaf mass was observed to be equivalent after one week. By the second week, leaf growth in urea-treated soil was higher than in the control sample. By the third week, leaf mass was equivalent to the control, but leaf mass from NOP-treated soil was greater than that of the control. The leaf mass from NOP-treated soil was 0.60 grams, while the leaf mass from the control was 0.47 grams.

[0171] Figure 20 plots the nitrogen composition of roots, stems, and leaves over time on a weekly basis. The nitrogen composition of roots was similar in weeks 1 and 2. By week 3, the nitrogen composition of NOP effluent was higher than that of the control, at 2.75% and 1.80%, respectively.

[0172] The nitrogen composition of the stems in the first week could not be measured because a 0.1-gram sample was required for analysis. Furthermore, nitrogen levels were comparable across all samples during their respective periods.

[0173] Nitrogen is used in plants to produce chlorophyll, which is the molecule used in photosynthesis and is more commonly found in leaves. This was observed in this study and demonstrated by the average nitrogen composition in control soils at week 3, which was 3.3%, 2.7%, and 1.2% in leaves, roots, and stems, respectively. In Figure 20, the nitrogen composition in leaves was highest at week 1 and was similar across all soils. At week 2, the nitrogen composition of soils containing urea, ammonium-supported NOCNF, and NOP leachates was higher than that of the control. At week 3, only urea and NOP leachates (with nitrogen compositions of 5.02% and 4.87%, respectively) showed a nitrogen composition higher than that of the control (3.34%).

[0174] Environmental impact In summary, the feasibility of sustainably supplied, low-cost, plant-derived, negatively charged nanocellulose capturing ammonium in the nitrogen cycle via adsorption and column filtration is demonstrated. The desire to remove ammonium before nitrification and denitrification in this study simplifies the nitrogen cycle, thereby mitigating environmental problems such as eutrophication, acid rain, and leachate. Typical wastewater treatment plants utilize a multi-step process in which nitrifying bacteria oxidize ammonium to nitrites and nitrates, and then ultimately to nitrogen gas. The above example demonstrates a one-step procedure for ammonium remediation using NOCNF. NOCNF, tested at different relative ammonium concentrations, pH, and oxidation levels, shows relatively good ammonium removal rates at neutral pH. The ammonium adsorption results fit a Langmuir isothermal model, thereby indicating a monolayer adsorption process. Furthermore, this mechanism is confirmed by ammonium adsorption results stoichiometrically associated with the carboxylate group at a 1:1 molar ratio (at this ratio, the zeta potential is no longer negative). It is clear that NOCNF can be effectively applied to the treatment of ammonium-containing wastewater from urban sewage, source-separated urea, and fishing grounds. Furthermore, this ammonium-supported NOCNF has been proven to be a nutrient-rich, biodegradable fertilizer in equivalent fertilization studies during early plant growth, including those using commercially available standards such as urea.

[0175] Table 7 below summarizes the ammonium repair data obtained for NOCNF produced according to the examples.

[0176] [Table 7A]

[0177] [Table 7B]

[0178] [Table 7C]

[0179] Experiments under stronger oxidation conditions generated highly charged fibers. These can be fibrillated into nanofibers using a high-pressure homogenizer. When the acidic groups are converted to carboxylate ion groups, the cellulose nanofibers form a stable colloidal suspension, which can adsorb cations such as ammonium or crosslink with polyvalent cations such as aluminum to form a stable gel for removing fluoride anions.

[0180] (Example 17) NOP cellulose often contains a mixture of macrofibers / microfibers or nanofibers with varying degrees of oxidation (i.e., the amount of carboxylate groups on the cellulose fibers). Macrofibers or microfibers with the smallest amount of carboxylate groups tend to settle or precipitate from the solution.

[0181] Alternatively, oxidized NOP fibers often aggregate when the carboxylate group is protonated at an acidic pH < 5.0 (the pKa of the carboxylic acid is approximately 5). When the pH was adjusted to 6.55 with ammonium hydroxide (NH4OH), a colloidally stable suspension of oxidized NOP cellulose was observed. While we do not wish to be bound by either theory, this is thought to be due to the deprotonation of the carboxylate group caused by strong repulsive forces between the fibers.

[0182] Oxidized cellulose fibers were prepared with slight modifications as described in Example 3 (NOCNF 1.1) above. 20 grams of jute were treated with 280 mL of 50% nitric acid (HNO3) in a 4 L round-bottom flask and sealed. After 1 hour, a solution containing 19.2 grams of sodium nitrite (NaNO2) dissolved in 40 mL of deionized water was added dropwise to the reaction flask via an addition funnel. After the addition of NaNO2, the addition funnel was removed, the flask was sealed, and the reaction was allowed to proceed for a total reaction time of 9 hours. The pH of the oxidized cellulose fibers (pH 2.5) was adjusted to pH 6.55 using a 50% (v / v) ammonium hydroxide (NH4OH) solution. To avoid the use of a homogenizer, a benchtop regular coffee grinder was used to prepare the suspension of high-viscosity cellulose fibers.

[0183] 80 mL of the obtained oxidized cellulose suspension (≒2.5 Wt%) was diluted with 40 mL of deionized water and then blended using a regular coffee grinder for approximately 3 to 6 minutes. After blending, a 1.63 Wt% high-viscosity suspension containing defibrated oxidized cellulose macrofibers / microfibers and / or nanofibers was obtained. Furthermore, due to the change in viscosity, numerous trapped air bubbles were observed in the suspension. These bubbles are thought to facilitate plant root growth by increasing the amount of oxygen when the obtained suspension is used as a fertilizer.

[0184] (Example 18) Hydrogels were prepared by combining 5 mL of 1.63 wt.% CNF with 250 μL of 100 mM CaNO3 solution and 500 μL of 100 mM CaNO3 solution, respectively. In both samples, successful hydrogel formation was observed, and the gel remained at the bottom of the vial. Further hydrogels were prepared by adding 250 μL of 100 mM CaNO3 solution and 500 μL of 100 mM CaNO3 solution, respectively, with a diluted CNF concentration of 0.84 wt.%. Good hydrogel formation was observed even at this reduced CNF concentration. Interestingly, as described in Example 17 above, all prepared hydrogels contained air bubbles after blending.

[0185] (Example 19) Hydrogels prepared from homogenized CNF (sample names: T1 and T2) were prepared as follows: In the case of biomass, if the particles were larger than approximately 5 mm, they were passed through a grinder with a 2 mm grid. The ground sample was then placed in a round-bottom flask with biomass and 50% HNO3 in a 1:14 ratio. The reaction flask was sealed and immersed in an oil bath maintained at 50°C for 1 hour. After 1 hour, a solution containing biomass and NaNO2 (mmol) in a 1:14 ratio was added dropwise using an addition funnel. After addition, the addition funnel was removed, the flask was sealed, and the reaction was allowed to proceed for a total of 9 hours. Once the reaction was complete, the product was separated by filtration and / or decantation, and the reaction effluent was collected separately from the oxidized fibers. The fibers were then washed with deionized water until the pH was above 2.5 and stored until further use. Blended CNF (sample names: H2 and H3) was prepared for comparison. Hydrogels H2 and H3 were prepared by adding 0.84 wt% blended CNF to 650 μL of 200 mM CaNO3 and 1300 μL of 200 mM CaNO3, respectively. Hydrogels T1 and T2 were prepared by adding 0.93 wt% blended CNF to 650 μL of 200 mM CaNO3 and 1300 μL of 200 mM CaNO3, respectively.

[0186] Aside from slight wt% differences between H2 and H3 and T1 and T2, the pH of both systems was 6.55 (H2 / H3) and 6.1 (T1 / T2). Hydrogels of both blended and homogenized CNF were obtained, and the overall stability of the H3 and T2 hydrogels was observed to be higher than that of the H2 and T1 hydrogels.

[0187] While we do not wish to be bound by any particular theory, the difference in stability is thought to be due to the fact that the higher concentrations of CaNO3 in H3 and T2 allowed for crosslinking of more fibers compared to the lower concentrations of CaNO3 (i.e., H2 and T1). The H3 and T2 hydrogels were able to support a mass of nearly 25 grams, whereas the H2 and T1 hydrogels collapsed at that mass.

[0188] (Example 20) NOP cellulose oxide was pH-adjusted to 6.55 using NH4OH as described in Example 17 above (before blending), and then centrifuged at 3000 rpm for 15 minutes. This yielded a clear supernatant containing nanofibers and a precipitate of macrofibers and / or microfibers.

[0189] The precipitated fibers obtained in this way were then combined with 5 mL of acetone or deionized water, respectively. The two samples (precipitated fibers + water and precipitated fibers + acetone) were then dried in an oven at 60°C for 2 to 4 days. It was observed that acetone accelerated the drying process of the fibers (completely dried within 2 days) compared to the fibers dried with water (which took approximately 4 to 5 days to dry).

[0190] The dried sample was then crushed and ground into a powder using a mortar and pestle. Both powders were then dispersed in an aqueous phase, sonicated for 2-3 hours, and then blended for 10 minutes.

[0191] The above process yielded stable and well-dispersed oxidized NOP cellulose fibers, which were then used to prepare the hydrogels discussed below.

[0192] (Example 21) A hydrogel was prepared using the fibers generated in Example 20 above. Approximately 5 mL of the blended (5 minutes vs. 10 minutes) acetone + water-dried oxidized fibers (1.1 Wt.%) were combined with 250 μL of 200 mM CaNO3 solution. A hydrogel was formed as a result.

[0193] Approximately 15 mL of hydrogel was also prepared by adding 1.3 mL of 200 mM CaNO3 solution to the above fibers (acetone + water-dried oxidized fibers, i.e., 1.1 Wt.%). The resulting hydrogel was observed to be able to support a mass 140 to 320 times its own mass, demonstrating excellent stability.

[0194] Overall, it was found that NOP cellulose oxide can be dried and successfully redispersed well in an aqueous medium, allowing it to be reused in a stable hydrogel formulation. Such a drying process for cellulose oxide is expected to significantly reduce material transportation costs, i.e., the costs of transporting them and preparing hydrogels at the point of use.

[0195] It will be understood that various modifications can be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but rather as merely an example of a preferred embodiment. Those skilled in the art will recall other modifications within the scope and spirit of this disclosure. Such modifications and variations are intended to fall within the following claims. [Explanation of Symbols]

[0196] 10 Systems 12 Reactors 14. Crusher 16 tanks 18 tanks 20 Reactors 24 tanks 30 Extruder 32 Extruder 40 Decantation containers 50 Reactors 60 Reactors 70 Fertilizer storage tanks

Claims

1. A process of contacting a biological waste source with nitric acid, A step of contacting a biological waste source and nitric acid with sodium nitrite, which can be selected as needed. A process of heating a biological waste source, nitric acid, and optionally selected sodium nitrite to a temperature of approximately 25°C to approximately 100°C to form a gellable nanocellulose suspension, The process of recovering the nanocellulose suspension and Methods that include...

2. The method according to claim 1, wherein nitric acid is present in the solution at a concentration of approximately 30% to approximately 50%.

3. The method according to claim 1, wherein the ratio of nitric acid in the solution to the biological waste source is about 10:1 to 1:

1.

4. The method according to claim 1, wherein sodium nitrite is present in the solution at a concentration of about 15% by mass to about 70% by mass.

5. The method according to claim 1, wherein the ratio of sodium nitrite in the solution to the biological waste source is approximately 1:0.25 to 1:

5.

6. The method according to claim 1, wherein the step of heating a biological waste source, nitric acid, and optionally sodium nitrite is carried out for about 1 hour to about 24 hours.

7. A fertilizer comprising an effluent or gelatable suspension produced by the method described in claim 1.

8. The method according to claim 1, wherein the biological waste source comprises cellulose.

9. The method according to claim 8, wherein the gellable suspension comprises carboxylated cellulose nanofibers.

10. The method according to claim 1, further comprising the step of contacting a biological waste source and nitric acid with sodium nitrite.

11. The method according to claim 1, further comprising the step of pre-treating the biological waste source with an alkaline solution before contacting the biological waste source with nitric acid.

12. The method according to claim 11, wherein the alkaline solution is selected from KOH, NaOH, potassium phosphate, or a combination thereof.

13. The method according to claim 11, wherein the alkaline solution has a pH of about 8 to about 14.

14. The method according to claim 11, further comprising the step of crushing the biomass in the biological waste source before contacting the biological waste source with an alkaline pretreatment agent or nitric acid.

15. The method according to claim 11, wherein the gellable nanocellulose suspension has a carboxylic acid content of about 0.1 mmol / g to about 3 mmol / g.

16. A fertilizer comprising a gellable nanocellulose suspension produced by the method described in claim 11.

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