Amine functionalization of nanocellulose and its use as an adsorbent

Abstract

The present disclosure provides cellulose based adsorbents and their use in removing impurities from liquids, including water. The celluloses are alkylamine functionalized celluloses which may be contacted with a liquid, including water, to remove impurities therefrom.

Description

AMINE FUNCTIONALIZATION OF NANOCELLULOSE AND ITS USE AS AN ADSORBENTCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of, and priority to, U.S. Provisional Patent Application Serial No. 63 / 649,987 filed on May 21, 2024. The entire contents of the foregoing application are incorporated by reference herein.GOVERNMENT SUPPORT

[0002] This invention was made with government support under CBET-2052772 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present disclosure relates to amine functionalized nanocelluloses and their use in removing anionic impurities from liquids, including water.BACKGROUND

[0004] Cellulose, the major constituent of plant cell walls, is the most abundant biopolymer on earth, and thus it is a sustainable and renewable resource for energy and production of various materials. The presence of hydroxyl groups in the cellulose molecule provides a unique platform for molecular modifications to form different useful derivatives. Among these derivatives, oxidized celluloses have been used in biomedical applications due to their unique properties related to biodegradability, biocompatibility and / or bioadsorbability.

[0005] Water shortage is a global concern of the growing population. Worldwide, over 7% of the total population lacks access to clean drinking water due to contamination, including high fluoride contamination. Improved methods for treating water are needed.SUMMARY

[0006] The present disclosure provides functionalized cellulose materials and their use in removing impurities from liquids, including water. In embodiments, the present disclosure includes an alkylamine functionalized cellulose includingwhere R is an alkyl group selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, or combinations thereof and n is from about 1,000 to about 15,000.

[0007] In embodiments, the cellulose of the alkylamine functionalized cellulose is obtained from a plant biomass. Suitable plant biomasses include lignocellulose wood, non-lignocellulose wood, lignocellulose, pure cellulose, grasses, phytoplanktons, algal celluloses, tunicate celluloses, and combinations thereof.

[0008] In some embodiments, the plant biomass is obtained from non-wood sources selected from jute, bamboo, cotton, banana rachis, wheat straw, barley, hemp, flax straw, coconut fiber, soy hull, pea hull fiber, rice husk, sugarcane bagasse, pineapple leaf rachis, sisal fiber, tunicates, black spruce, eucalyptus, valonia, bacterial celluloses, spinifex, and combinations thereof.

[0009] In embodiments, the alkylamine functionalized cellulose has a charge density from about 0.2 mmol / g to about 2.0 mmol / g.

[0010] Methods of the present disclosure include a method for removing negatively charged impurities from a liquid, by contacting the liquid with the alkylamine functionalized cellulose of the present disclosure. In embodiments, the liquid to be treated may be water.

[0011] In some embodiments, the negatively charged impurities include polyfluoroalkyl substances, perfluoroalkyl substances, and combinations thereof.

[0012] Methods of the present disclosure also include methods for making an alkylamine functionalized cellulose including dispersing wood fibers in a suitable solvent to form a first suspension; contacting the first suspension with an oxidizing agent to produce dialdehyde functionalized cellulose; and contacting the dialdehyde functionalized cellulose with a second solvent to form a second suspension. The method further includes contacting the second suspension with an alkylamine having a chain length from about 1 to about 12 carbon atoms wherein the ratio of alkylamine to aldehyde groups of about 10:1; followed by contacting the second suspension with 2-picoline-borane at a ratio of 2-picoline-borane to aldehyde groups of about 5:1 to form a mixture; stirring the mixture at room temperature for a period of time from about 5 hours to about 80 hours; and recovering the alkylamine functionalized cellulose.

[0013] In embodiments, the oxidizing agent is added to the first suspension at an amount from about 1 mmol / g of cellulose to about 20 mmol / g of cellulose.

[0014] In some embodiments, the oxidizing agent may be sodium periodate, potassium periodate, rubidium periodate, combinations thereof, and the like.

[0015] In embodiments, the method for making an alkylamine functionalized cellulose further includes stirring the first suspension at a temperature from about 30 °C to about 80 °C, for a period of time from about 1 hour to about 48 hours prior to contacting the first suspension with the oxidizing agent.

[0016] In some embodiments, the dialdehyde functionalized cellulose is at a concentration from about 0.1 wt% to about 20 wt% of the second suspension.

[0017] In some embodiments, the alkylamine is selected from methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, combinations thereof, and the like.

[0018] In embodiments, the ratio of alkylamine to aldehyde group in the second suspension is from about 10 to about 1.

[0019] In some embodiments, the method for making an alkylamine functionalized cellulose further includes adjusting the pH value of the second suspension to from about 2 to about 5.

[0020] In other embodiments, recovering the alkylamine functionalized cellulose occurs by subjecting the second suspension to defibrillation.

[0021] In some embodiments, the resulting alkylamine functionalized cellulose has a charge density from about +17.70 mV to about +30.81 mV.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are included to provide further understanding of the subject technology and are incorporated in and constitute a part of this specification, illustrate aspects of the disclosure and together with the description serve to explain the principles of the subject technology.

[0023] Figure 1 is a reaction scheme showing the two-step synthetic route for producing alkylamine functionalized cellulose, also referred to herein as cationic dialdehyde cellulose (C- DAC) adsorbents of the present disclosure;

[0024] Figure 2 is a graph showing the Fourier Transform Infrared (FT-IR) spectra for alkylamine celluloses produced in accordance with the present disclosure;

[0025] Figure 3 shows transmission electron microscopy (TEM) images of (a) C4-DAC (butylamine (C4)), (b) C8-DAC (octylamine (C8)), and (c) C12-DAC (dodecylamine (C12) of the present disclosure;

[0026] Figure 4 are images showing contact angle measurements for (a) C4-DAC, (b) C8- DAC and (c) C12-DAC of the present disclosure;

[0027] Figure 5 are graphs depicting the adsorption capacity of the C-DAC adsorbents of the present disclosure, C4-DAC, C8-DAC and C12-DAC, for (a) perfluorobutanoic acid (PFBA) (300 mg / L cellulose with 100 ppm PFBA), (b) perfluorooctanoic acid (PFOA) (30 mg / L cellulose with 20 ppm PFOA) and (c) perfluorooctane sulfonic acid (PFOS) (30 mg / L cellulose with 50 ppm PFOS);

[0028] Figure 6 are graphs depicting the kinetics of (a) PFOS, (b) PFOA, (c) PFBA adsorbed by C8-DAC (C8-DAC dosage = 36 mg / L; PFAS concentration = 10 ppb), and (d) the removal percentage comparison at 1 minute;

[0029] Figure 7 is a graph depicting the results of competition of different ions with C8-DAC and PFBA system; and

[0030] Figure 8 is a graph depicting the results of a desorption study, showing the desorption percentage for PFBA and PFOA by using different regenerant solvents.DETAILED DESCRIPTION

[0031] The following detailed description of embodiments of the disclosure will be made in reference to the accompanying drawings. Explanation about related functions or constructions known in the art are omitted for the sake of clearness in understanding the concept of the disclosure to avoid obscuring the disclosure with unnecessary detail.

[0032] The present technology discloses the efficient removal of polyfluoroalkyl and perfluoroalkyl substances (collectively PFAS) by functionalized cationic cellulose nanofibers as adsorbent-based coagulants. PFAS are a group of synthetic chemicals which are widely used in industry. The chemical structure of PFAS contains hydrophobic carbon-fluorine chains and hydrophilic functional heads (carboxylic, sulfonic acid, etc.), making it hard to be removed from water and destroyed after removal.

[0033] According to the present disclosure, lignocellulose biomass feedstocks are used as sustainable resources to produce nanocellulose scaffolds functionalized by oxidation methods, where alkylamine grafting is applied to the scaffolds to create cationic adsorbents that can be used as coagulants or flocculants to be removed anionic PFAS substance. Specifically, cationic nanocellulose scaffolds containing grafted chains with amine end groups -NH2+- and alkyl linkages (-CH2-)x were synthesized. These grafted chains can attract anionic PFAS compounds, such as perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), and / or perfluorobutanoic acid (PFBA), through combined electrostatic and hydrophobic interactions. The experimental results indicate that the produced bioadsorbents have excellent ability for PFAS removal, with rapid adsorption rate and high adsorption capacity.

[0034] Alkylamine functionalized celluloses of the present disclosure, also referred to herein as cationic dialdehyde cellulose (C-DAC) materials have many potential applications for water purification, such as removal of anionic contaminants including inorganic nutrients (e.g., nitrides, phosphates) and PFAS chemicals.

[0035] According to the present disclosure, the structure of C-DAC may be modified for PFAS removal. In embodiments, the C-DAC materials may be in the form of a suspension, which can be used as coagulants / flocculants to remove PFAS.

[0036] In some embodiments, a removal procedure using the C-DAC of the present disclosure may include the following. Upon the addition of an appropriate amount of cationic nanocellulose suspension to the PF AS-contaminated water, anionic PFAS molecules can be adsorbed onto the nanocellulose scaffold and form a PFAS-loaded nanocellulose gel. The gel can be removed from water by microfiltration using low pressure and / or gravity.

[0037] As noted above, embodiments of the disclosure described herein provide compositions and methods for removal of anionic impurities, such as poly- and perfluoroalkyl substances, from liquids, including water, by contacting the liquid with a suspension including functionalized cationic cellulose nanofibers of the present disclosure as adsorbent-based coagulants. Cellulose macrofibers and nanofibers used in in the compositions and methods are functionalized so that they are cationic, i.e., positively charged and prepared by methods within the purview of a person of ordinary skill in the art, including 2,2,6,6-tetramethylpiperidine-l-oxyl (TEMPO) oxidation, nitro-oxidation, combinations thereof, and the like.

[0038] Cellulose nanofibers for use in accordance with the present disclosure may be obtained from any and all raw biomasses, such as lignocellulosic wood or non-wood sources including, but not limited to, jute, bamboo, cotton, banana rachis, wheat straw, barley, hemp, flax straw, coconut fiber, soy hull, pea hull fiber, rice husk, sugarcane bagasse, pineapple leaf rachis, sisal fiber, tunicates, black spruce, eucalyptus, valonia, bacterial celluloses, phytoplanktons, algal celluloses, tunicate celluloses, grasses including spinifex grasses, and combinations thereof.

[0039] The direct use of biomass from lignocellulose wood or non-wood sources, without the need for conventional extraction / pretreatment steps, can immediately reduce the consumption of many potentially toxic chemicals, in some cases by as much as 50-60%.

[0040] Preparation of C-DAC in accordance with the present disclosure includes two steps: oxidation and reductive amination. First, an aldehyde group is reacted with an amine to form an imide bond. A reducing agent then converts the imide bond to a secondary amine.

[0041] A summary of the preparation of C-DAC in accordance with the present disclosure is set forth in Figure 1 and includes the following general procedure. As set forth in Figure 1, wet wood pulp fibers may be dispersed in a suitable solvent, such as water, deionized water, aqueous acid, aqueous alkali, combinations thereof, and the like, to obtain a first suspension. The amount of wood pulp fibers in the resulting first suspension may be from about 0.1 wt% to about 20 wt% of the first suspension, in embodiments from about 1 wt% to about 5 wt% of the first suspension, in embodiments about 1.25 wt% of the first suspension.

[0042] In embodiments, an oxidizing agent may be dissolved in water or a similar solvent and added to the above first suspension at a suitable amount, in embodiments from about 1 mmol / g of cellulose to about 20 mmol / g of cellulose, in embodiments from about 4 mmol / g of cellulose to about 10 mmol / g of cellulose, in embodiments about 5 mmol / g of cellulose. Suitable oxidizing agents include sodium periodate, potassium periodate, rubidium periodate combinations thereof, and the like.

[0043] The first suspension may then be stirred at a suitable temperature, in embodiments from about 30 °C to about 80 °C, in embodiments from about 45 °C to about 60 °C, in embodiments about 55 °C, for a period of time from about 1 hour to about 48 hours, in embodiments from about 5 hours to about 30 hours, in embodiments about 24 hours. In some embodiments, the stirring occurs in the absence of light. After the reaction is complete, the solid product may be washed and subjected to vacuum filtration until the conductivity of the filtrate is < 10 ps / cm.

[0044] The resulting dialdehyde functionalized cellulose (DAC) may then undergo the second step of the reaction depicted in Figure 1 to graft alkylamine groups on the cellulose scaffold.Different alkyl length lengths may be used, which may be from about 4 carbon atoms to about 12 carbon atoms. For example, suitable alkylamines which may be used include methylamine (Cl), ethylamine (C2), propylamine (C3), butylamine (C4), pentylamine (C5), hexylamine (C6), heptylamine (C7), octylamine (C8), nonylamine (C9), decylamine (CIO), undecylamine (Cl l), dodecylamine (Cl 2), combinations thereof, and the like. The resulting alkylamine functionalized cellulose, also referred to herein as a “C-DAC” may be referred to in accordance with the alkylamine used to generate the C-DAC, e.g., C4-DAC (butylamine (C4)), C8-DAC (octylamine (C8)), C12-DAC (dodecylamine (C12)), etc.

[0045] The second step of the reaction may be briefly summarized as follows. The DAC dried sample may first be mixed with a suitable amount of solvent, such as deionized water to form a second suspension. In embodiments, the amount of DAC may be present at a concentration from about 0.1 wt% to about 20 wt% of the second suspension, in embodiments from about 1 wt% to about 5 wt% of the second suspension, in embodiments about 1 wt% of the first suspension.

[0046] The alkylamine with the desired alkyl length is then added to the second suspension at a ratio of alkylamine to aldehyde group of about 10: 1, in embodiments about 5: 1, in embodiments about 1:1, and a suitable acid, such as HC1, may be used to adjust the pH value to 2-5, in embodiments 3-4.

[0047] Next, 2-picoline-borane is added to the second suspension at a ratio of 2-picoline- borane to aldehyde group of about 5:1, in embodiments about 2:1. The 2-picoline-borane may be in a solution, using a solvent such as deionized water.

[0048] The second suspension is then stirred at room temperature for a suitable period of time, in embodiments from about 1 hour to about 100 hours, in embodiments from about 5 hours to about 80 hours, in embodiments about 72 hours.

[0049] After the reaction, the product, which is an alkylamine functionalized cellulose, also referred to herein as a C-DAC, may be washed to reach a low conductivity in the fdtrate of from about 1 pS to about 20 pS, in embodiments from about 5 pS to about 10 pS.

[0050] The alkylamine functionalized cellulose (C-DAC), still in suspension form, may then be defibrillated with a homogenizer. The homogenizer may operate at a pressure from about 250 bar to about 350 bar, in embodiments about 300 bar, for a suitable number of cycles, in embodiments from about 3 cycles to about 10 cycles, in embodiments about 5 cycles, to obtain a suspension having the resulting C-DAC nanocellulose in an amount from about 0.1 wt% to about 0.5 wt%, in embodiments about 0.3 wt%.

[0051] The resulting alkylamine functionalized cellulose (C-DAC) includes both cationic amine groups and hydrophobic alkyl chains (C1-C12). The major adsorption mechanism of PFAS by the C-DAC of the present disclosure thus involves both electrostatic and hydrophobic interactions.

[0052] While Figure 1 depicts the use of butylamine, octylamine and dodecylamine as the alkylamine in producing the C-DAC, any of the alylamines noted above may be utilized in the reaction scheme depicted in Figure 1. Accordingly in embodiments, the resulting C-DAC produced following the methods of the present disclosure may be of the following formula:where R is an alkyl group selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, or combinations thereof, and n is from about 1,000 to about 15,000, in embodiments from about 3,000 to about 12,000.

[0053] The C-DAC carries a charge density from about 0.2 mmol / g to about 2.0 mmol / g, in embodiments from about 0.5 mmol / g to about 1.5 mmol / g, in embodiments from about 0.83 mmol / g to 1.29 mmol / g. Other units for measuring charge density include mV. In embodiments, the C-DAC may have a charge density from about +17.70 mV to about +30.81 mV.

[0054] The resulting C-DAC may then be utilized to effectively remove negatively charged impurities (e.g., X’ (halogenated ions, such as F'), NO2', NOa', PO42', SO42', CN', AsOa, phenoxide, PFAS, combinations thereof, etc.) from liquids, including water.

[0055] The resulting C-DAC includes both the alkyl hydrophobic chain from the alkylamine while maintaining positive charged amine groups. Different lengths of alkylamine, such as butylamine, octylamine and dodecylamine can be attached to cellulose to tune the hydrophobicity and solubility of the resulting C-DAC. The resulting C-DAC may then be used to remove anionic impurities from liquids, including in some embodiments long-chain and shortchain PFAS.

[0056] In embodiments, the C-DAC may be in a gel or suspension form. For example, upon the addition of an appropriate amount of a suspension including the C-DAC to PFAS- contaminated water, the anionic PFAS molecules can be adsorbed onto the nanocellulosescaffold of the C-DAC and form a PFAS-loaded nanocellulose gel. The gel can then be removed from water by microfiltration method using low pressure and / or gravity.

[0057] For post treatment, since the PFAS are concentrated on the cellulose scaffold surface, a destruction technique could be applied to further break down PFAS into small nontoxic molecules. For example, flash heating at high temperatures (above 2,000 K) may be used to degrade PFAS into carbon dioxide and fluorine gas. Meanwhile, the heating process can convert the cellulose scaffold into graphene materials as a valuable byproduct, which can offset the overall treatment cost.

[0058] The cellulose scaffold used to form the adsorbent of the present disclosure is nontoxic and biodegradable, including basic a glucose unit with plenty of hydroxyl sites. The present disclosure provides a chemical modification of cellulose material, resulting in cationic amine functional groups as well as C-H alkyl chains on the scaffold surface. The modification route of the cellulose scaffold can be carried out by a two-step reaction using water as solvent. The resulting nanocellulose adsorbents based on cationic dialdehyde celluloses (C-DAC) are efficient adsorbents and coagulants for removal of PFAS from water, driven by both electrostatic and hydrophobic interactions. The adsorption efficiency of C-DAC against both long and shortchain PFAS outperformed the common adsorbents such as activated carbons, especially for short-chain PFAS removal.

[0059] The adsorbents of the present disclosure are cost-effective PFAS remediation materials, offering a complementary alternative to traditional adsorbents such as activated carbons and ion exchange resins. By leveraging the abundance and unique properties of cellulose, the adsorbents of the present disclosure provide a sustainable and efficient solution to the pressing issue of PFAS contamination in water sources.

[0060] The adsorbents of the present disclosure have the following advantages over the existing adsorbents:1. Nanocellulose is more sustainable and cost-effective than synthetic polymer for PFAS removal :■ Nanocellulose can be produced from any lignocellulose biomass, including underutilized wood and non-wood waste.■ Only a two-step reaction is necessary to convert cellulose into the disclosed cationic nanocellulose adsorbent. The resulting products contain abundant positively charged amine groups with tunable hydrophobic alkyl tails that offer both electrostatic and hydrophobic interaction sites to adsorb anionic PFAS.■ The cationic adsorbents of the present disclosure are effective for removing both long- chain and short-chain PFAS.2. Fast Adsorption Process:■ The kinetic results showed that the removal of PFAS with adsorbents of the present disclosure takes a relatively short time (80% removal in 1 minute), while commercial granular activated carbons usually take several days to reach the sorption equilibrium.3. High Removal Efficiency:■ The adsorbents of the present disclosure are capable of removing a wide range of anionic PFAS at concentrations from part per million (ppm) to part per billion (ppb) levels.■ As described in greater detail below in the Examples, the adsorbent of the present disclosure exhibited especially good adsorption capacity for PFAS removal (72-132mg / g for PFBA, 235-346 mg / g for PFOA and 576-697 mg / g for PFOS) at ppm level (1- 100 ppm) in water system.4. Environmental-friendly:■ The nanocellulose scaffold is biodegradable and nontoxic, and there is no safety issue and will not cause secondary contamination when it is applied in drinking water treatment.5. PFAS-loaded nanocellulose can be readily coupled to a destruction method:■ For example, after adsorption, the PFAS / nanocellulose aggregate can be flash burnt at high temperature to destroy PFAS into nontoxic small molecule, and simultaneously convert nanocellulose scaffold into graphene as a valuable by-product.

[0061] The following Examples are being submitted to illustrate embodiments of the present disclosure. The Examples are intended to be illustrative only and are not intended to limit the scope of the present disclosure. Also, parts and percentages are by weight unless otherwise indicated. As used herein, "room temperature" refers to a temperature of from about 20°C to about 30°C.EXAMPLES

[0062] Sodium periodate, butylamine, octylamine (99%) and dodecylamine (98%) were purchased from Sigma Aldrich. Borane-2-methylpyridine complex (95%) was purchased from Thermo Scientific. All of the used PFAS chemicals are the same from Chapter 3.2. Centrifugal filters (Amicon Ultra-15-3OK) were purchased from Merck Millipore Ltd.EXAMPLE 1

[0063] DAC containing 5.8 mmol / g of aldehyde group was first prepared by mixing 400 ml 1.25 wt% of bleached wood pulp suspension with 6.42 grams sodium periodate under dark conditions at 55 °C for 24 hours, as shown in steps 1-3 in Figure 1. For the second step, 2 grams of DAC in dried mass was weighted at first then mixed with 200 ml of deionized (DI) water. Then 8.3 grams of the butylamine (C4) was added into the suspension, using the HC1 solution to adjust the pH level to 3-4. Next, 2.4 grams of 2-picoline-borane was dissolved into 200 ml of DI water (slightly heated to 50 °C), then the solution was transferred into the cellulose suspension. The mixture was stirred for 72 hours at room temperature. After the reaction, the product was filtered and washed with 500 ml ethanol and 1000 ml DI water. The resulting butylamine functionalized DAC (C4-DAC) in the gel suspension form was further purified with dialysis process until the conductivity was close to DI water.

[0064] The nitrogen and carbon weight percentages were determined as 1.16% and 44.6%, respectively. The degree of substitution was about 14.7% with amine group amount about 0.83 mmol / g. The Zeta potential was measured as +23.14 mV. From the FTIR spectra (Figure 2), the peak at 1650 cm'1could be attributed from amine and aldehyde groups, while the C-H bond peak intensity is lowest locating at 2840 cm'1.

[0065] As described in greater detail below, the C4-DAC suspension was tested against PFOS, PFOA and PFBA to evaluate the adsorption capacity. By mixing 10 ml of 30 mg / L nanocellulose with 20 mg / L of PFAS individually for 24 hours, the equilibrium adsorption capacity was determined by LC-MS / MS measurements. The results indicate that the Qe of C4- DAC was 576 mg of PFOS / g of cellulose, 235 mg of PFOA / g of cellulose, and 72 mg of PFBA / g of cellulose, respectively.EXAMPLE 2

[0066] DAC containing 5.8 mmol / g of aldehyde group was first prepared by mixing 400 ml 1.25 wt% of bleached wood pulp suspension with 6.42 grams sodium periodate under dark conditions at 55 °C for 24 hours, as shown in steps 1-3 of Figure 1. For the second step, 2 grams of DAC in dried mass was mixed with 200 ml DI water. Then 14.7 grams of the octylamine (C8) was added into the suspension, using the HC1 solution to adjust the pH level to 3-4. Next, 2.4 grams of 2-picoline-borane was dissolved into 200 ml of DI water (at 50 °C), which was subsequently transferred into the whole biomass mixture. The mixture was stirred for 72 hours under room temperature. After the reaction, the product was filtered and washed using 500 ml ethanol and 1000 ml DI water until the conductivity in the filtrate was below 5 ps / cm. The resulting octylamine DAC (C8-DAC) sample showed a white pulp appearance, where the pulp suspension was defibrillated using homogenization at 300 bar for 5 cycles to obtain a 0.3 wt% nanocellulose suspension. The nitrogen and carbon weight percentages in this sample were 1.59% and 49.4%, respectively. The degree of substitution was about 21.2% having the amine group content at about 1.13 mmol / g. The Zeta potential was measured as +30.81 mV. From the FTIR spectra (Figure 2), the peak at 1650 cm'1could be attributed from amine and aldehyde groups, while the C-H bond peak intensity was located at 2840 cm'1.

[0067] As described in greater detail below, the C8-DAC samples were tested against PFOS, PFOA and PFBA to evaluate the adsorption capacity. By mixing 10 ml of 30 mg / L cellulose with 20 mg / L PFAS individually for 24 hours, the equilibrium adsorption capacity of C8-DAC was 679 mg of PFOS / g of cellulose, 336 mg of PFOA / g of cellulose and 132 mg of PFBA / g of cellulose, respectively.EXAMPLE 3

[0068] DAC containing 5.8 mmol / g of aldehyde group was first prepared by mixing 400 ml 1.25 wt% of bleached wood pulp suspension with 6.42 grams sodium periodate under dark conditions at 55 °C for 24 hours, as shown in steps 1-3 of Figure 1. For the second step, 2 grams of DAC in dried mass was mixed with 200 ml DI water. Then 16.6 grams of the dodecylamine (C12) was added into the suspension, using the HC1 solution to adjust the pH level to 3-4. Next, 2.4 grams of 2-picoline-borane was dissolved into 200 ml of DI water (at 50 °C), which was subsequently transferred into the whole biomass mixture. The mixture was stirred for 72 hours under room temperature. After the reaction, the product was filtered and washed using 500 ml ethanol and 1000 ml DI water until the conductivity in the filtrate was below 5 ps / cm. The resulting dodecylamine DAC (C12-DAC) sample showed a white pulp appearance, where the pulp suspension was defibrillated using homogenization at 300 bar for 5 cycles to obtain a 0.3 wt% nanocellulose suspension.

[0069] The nitrogen and carbon weight percentages in this sample were 1.81% and 51.9%, respectively. The degree of substitution was about 28.0% having the amine group content at about 1.29 mmol / g. The Zeta potential was measured as +11.74 mV. From the FTIR spectra (Figure 2), the peak at 1650 cm'1could be attributed from amine and aldehyde groups, while the C-H bond peak intensity was located at 2840 cm1.

[0070] Summarizing Examples 1-3, a new kind of alkylamine modified adsorbent / coagulant based on dialdehyde cellulose was synthesized following the reaction scheme as shown in Figure 1. There are two factors controlling the degree of functionalization and product yield.

[0071] In the first step of oxidation, a higher ratio of sodium periodate can lead to a higher amount of aldehyde group, but a lower yield of the product. For example, 9 mmol / g of NaIO4generated DAC containing 10 mmol / g of -CHO with less than 10% of yield. However, adding too much sodium periodate would generate excess amount of waste and the related possible side reaction of cellulose chain breakage makes DAC product soluble in water, which also impacted the degree of amination in the following step. After several trials, the condition of 5 mmol / g (NaIO4 / cellulose) was optimized for the next step with the moderate degree of oxidation (4.7 mmol / g -CHO) and reasonable yield (60-80%).

[0072] In the second step of amination, different chain-length of alkylamine can be attached on the nanocellulose scaffold, which could adjust the hydrophobicity and solubility to achieve the different removal efficiency against various PFAS compounds. Examples 1-3 successfully grafted butylamine (C4), octylamine (C8) and dodecylamine (Cl 2) on cellulose. The C4-DAC was showed in gel suspension form, while C8-DAC and C12-DAC were obtained as white fibrous solid. The longer alkylamine such as hexadecylamine (Cl 6) was not feasible for reaction due to its low solubility in water.EXAMPLE 4

[0073] pH titration was used to quantitively analyze the amount of aldehyde groups on DAC produced in Examples 1-3. In this test, 40 ml of 0.25M NH4OH HCI was prepared, and the pH was adjusted to be around 4 by NaOH. Subsequently, 0.1 grams of dried DAC was added into the solution and was stirred overnight. During the reaction, NH4OH would react with -CHO and release equimolar of HC1, resulting in a lower pH value. Then 0. IM NaOH was used to titrate the solution until the pH value returned to the initial value around 4. The -CHO amount was calculated as follows: n (-CHO) in mmol / g = C (NaOH)*V (NaOH) / M (sample) (1)where V is the NaOH volume added, C is the NaOH concentration (mol) and M is the cellulose mass (g).

[0074] It was noted that the different ratio of sodium periodate used resulted in DAC with different amounts of aldehyde groups. For example, when 5 mmol / g of sodium periodate was used, the resulting DAC possessed 4.7 mmol / g of aldehyde groups. When 6 mmol / g of sodium periodate was used, the resulting DAC possessed 5.8 mmol / g of aldehyde groups.EXAMPLE 5

[0075] Elemental analysis was carried out by combustion gas chromatography associated with a thermal conductivity detector (GC-TCD) to determine the presence of amine groups on C- DAC. The degree of substitution (DS%) and the amine group content were estimated by using carbon and nitrogen weight percent in each of sample as follows:n (-NH-) in mmol / g = N% *1000 / 100*14.01 (3)

[0076] The above formulae were based on the assumption that each of the substituted anhydroglucose unit only contains one alkylamine group. In each substituted anhydroglucose unit, there are 1 nitrogen and (6+n) carbons (n is the carbon number on alkylamine). In each nonsubstituted anhydroglucose unit, there are 6 carbons.EXAMPLE 6

[0077] OCA 15EC optical contact angle goniometer (Dataphysics Instruments) was used for contact angle measurement. 0.5 pL of water droplet was added on the target membrane surface and photos were taken by attached high-speed camera.EXAMPLE 7

[0078] Fourier-Transform Infrared Spectroscopy (ALPHA FT-IR Spectrometer, Bruker Optics Inc.) was used to investigate the functional groups and chemical bonds on cellulose materials. The zeta potential of C-DAC suspension (0.1 wt%) was characterized via Zetaprobe analyzer (Colloidal Dynamics) to measure surface charge density. TEM images were acquired by JEOL 1400 LaB6 Soft Bio TEM (Japan) to estimate the fiber size and dimension.

[0079] The synthesized cellulose adsorbent (as shown in Figure 1) C4-DAC, C8-DAC, C12- DAC were first characterized by FT-IR to determine the presence of functional groups. In Figure 2, several characteristic peaks were detected for all three products, including N-H and -OH group at 3350 cm'1, C-H bond at 2840 cm'1and C-N and C=O bond at 1650 cm'1.

[0080] Although there was no clear identification for the amine group difference on cellulose adsorbent due to overlap of several peaks at similar position, the C-H peak intensity showed a certain trend that C12-DAC > C8-DAC > C4-DAC, which corresponds to the increase of alkyl chain length and indicates the successful synthesis of three products. Furthermore, based on the elemental analysis of carbon and nitrogen percentage, the amine group content was calculated to be from 0.83-1.29 mmol / g (shown in Table 1 below). Among them, the C12-DAC had the highest amine functionality. However, the C12-DAC showed the lowest zeta potential, while C8- DAC had more positive surface charge density.Table 1 Zeta potential measurement at pH 4 and the calculated amine group content from elemental analysis resultSample Zeta Potential Amine group content Degree of at pH 4 (mV) from elemental analysis substitutionC4-DAC +25.10 0.83 mmol / g 14.7%C8-DAC +30.81 1.13 mmol / g 21.2%C12-DAC +17.70 1.29 mmol / g 28.0%

[0081] To further investigate the fiber dimension and the physical properties of modified cellulose, TEM and contact angle measurement were conducted. As seen in Figure 3 insert (a), C4-DAC behaved as a gel suspension instead of visible white fibers, containing discrete nanocellulose fibers with roughly 100 nm length and 4-5 nm width. It indicated that the butyl chain had the minimum effect on cellulose surface properties. Insignificant changes of surface hydrophobicity were observed from contact angle measurement (Figure 4 insert (a)) where C4- DAC is still mostly hydrophilic with good hygroscopicity. Octylamine began to interfere with the fiber dispersion by triggering entanglement to offset the electrostatic repulsion effect from pronated amine groups (Figure 3 insert (b)). In this case, the system mainly consists of microfiber and bulky aggregates with several hundred nm long. The solubility of longer alkyl chain was also decreased and converts the product into fibrous solid. Dodecylamine even strengthens the intermolecular hydrophobic interaction leading to significant aggregation behavior (Figure 3 insert (c)). This clump cellulose network might affect the PFAS adsorption through steric effect with less adsorption sites and lower surface area. In terms of hydrophobicity change, both C8-DAC and C12-DAC become super hydrophobic with contact angle at 125° and 147°, respectively (Figure 4 inserts (b) and (c)). Next step we expect to compare those three adsorbents for long-chain and short-chain PFAS removal, to reveal the role of hydrophobic and electrostatic interaction in terms of PFAS adsorption mechanism.EXAMPLE 8

[0082] The previous synthesized cellulose adsorbents of Examples 1-3 (C4-DAC, C8-DAC, C12-DAC) were tested for PFAS adsorption. PFOS, PFOA, PFBA were selected as PFAS targets to compare the influence from different chain-length and hydrophobicity on PFAS. At the condition of 30 mg / L cellulose mixing with PFAS for 24 hours, the adsorption capacity (Qe) of each PFAS was plotted in Figure 5. It was noticed that C8-DAC showed the best potential to remove PFAS among the three cellulose candidates. The possible reason might be that C8-DAC has the most suitable surface charges along with the moderate hydrophobic alkyl chains. For C4- DAC, the amine group content is slightly lower from elemental analysis and titration results, while C12-DAC had significant self-aggregation between cellulose fibers (shown in Figure 3 insert (c)) which might obstruct the adsorption sites and reduce surface area.

[0083] The above factors contribute to the fact that C8-DAC possessed almost two times higher of the PFBA adsorption (132 mg / g) than that of C4-DAC (72 mg / g) and C12-DAC (75 mg / g). Meanwhile, C8-DAC still exhibited improved adsorption for long-chain PFAS with much higher Qe (697 mg / g for PFOS and 367 mg / g for PFOA), due to stronger adsorption affinity for long-chain PFAS. The equilibrium adsorption capacity of C12-DAC was 604 mg of PFOS / g of cellulose, 346 mg of PFOA / g of cellulose and 75 mg of PFBA / g of cellulose, respectively.

[0084] Furthermore, C8-DAC was analyzed for comprehensive adsorption studies. First, adsorption kinetics were investigated at environmentally relevant conditions (10 ppb) for PFAS in Figure 6. With the addition of 36 mg / L C8-DAC, over 90% of PFOS and PFOA was adsorbed within 1 minute, while PFBA showed 50% removal at the first 1 minute as well, indicating the long-chain PFAS adsorption was much faster under the same conditions.

[0085] Isotherm studies were also performed to assess the maximum adsorption capacity for different PFAS compounds. The equilibrium adsorption capacity (Qe) reached 650, 400 and 200 mg / g for PFOS, PFOA and PFBA, respectively. This may be due to existing stronger electrostatic adsorption affinity from long-chain PFAS where higher Qe was observed, thus additional hydrophobic sites only provided limited enhancement. On the other hand, C8-DAC exhibited molecular entanglement network which might induce favorable physical sorption to short-chain PFAS.

[0086] The data obtained establishes that electrostatic interaction is dominant with strong binding forces at relatively low PFAS concentration, while hydrophobic / fluorine-fluorine interaction contributes to PFAS recognition and adsorption affinity. The synergistic effect from both fluorinated and cationic groups resulted in higher removal of PFOA compared to a single functional group system.EXAMPLE 9Ion Competition Test

[0087] To learn more about the mechanism and the role of electrostatic interaction in shortchain PFAS removal, an ion test was designed to mix C8-DAC with PFBA and different salts. Relevant results are shown in Figure 7. Ion concentration and valence charge are two important factors contributing to the ionic strength. There are two possible competing interaction mechanisms: 1) the cation could neutralize the anionic PFAS leading to its lower adsorption with cationic cellulose; 2) the anion could also compete with PFAS to interact with cationic amine group on cellulose scaffold.

[0088] The major anionic influence was observed when 10 mM NaCl was compared with 10 mM NaNCh, the higher PFAS suppression from NCh' ion was attributed to higher electronegativity. Although both Cl’ and NCh’ have a -1 charge, the higher electron density on NO3’ triggered stronger electrostatic interactions. The even lower PFAS adsorption with coexisting 5 mM Na2SC>4 also supported that divalent ion (SO42') had larger competitive affinity due to higher screening effect. As for NaiPCh (a strong base), the pH in the mixture increased to above 11, leading to no adsorption of PFBA. On the other hand, the cationic effect was less severe where there was no large Qe difference between 5 mM MgCh and 10 mM MgCh.

[0089] Ion size could affect the adsorption at porous structured material and highly charged surface. In order to consider the ion size effect, hydrated ion size data was included as a reference (Na+ 3.58 A < Mg 2+ 4.28 A, SO42- 3.79 A > NO3- 3.35 ~ Cl- 3.32 A). No clear trend was observed with hydrated ion diameter and PFAS inhibition.

[0090] All of the above data indicated that the electrostatic interaction played an important role in PFBA adsorption with C-DAC adsorbent, with the major competitive mechanism between anion and negatively charged PFAS.EXAMPLE 10Desorption Study

[0091] A desorption study was conducted to support the adsorption mechanism theory and evaluate the potential regeneration method. The general procedure was that PFBA or PFOA was first mixed with C8-DAC to reach adsorption equilibrium. Then, a centrifugal filter unit was used to separate and preserve the cellulose solid with PFAS adsorbed. Finally, the desorption solution was soaked with the cellulose solid with PFAS adsorbed. The eluted PFAS in solution was measured and divided by the adsorbed amount to calculate desorption percentage. PFAScontrol group without cellulose adsorbent was also tested to confirm no apparent filter loss during centrifugation.

[0092] The desorption efficiency depended on choice of solution. For instance, organic solvents such as methanol and ethanol targeted the hydrophobic adsorptive sites, while NaOH as a basic inorganic solvent could neutralize the positively charged group and thus minimize the electrostatic interaction.

[0093] The results in Figure 8 showed that for both long-chain and short-chain PFAS, NaOH itself was able to desorb 70-80% of PFAS from C8-DAC, which is close to the efficiency of NaOH / MeOH mixture. The MeOH alone was very limited to desorbing any PFAS. It is believed that charge interaction was the dominant driving force to adsorb PFAS under C8-DAC even though there are potential hydrophobic sites.

[0094] Based on the above data, the adsorption mechanism of C-DAC is controlled by electrostatic interaction, with feasible PFAS regeneration by easily using alkaline solution to increase the pH. Unlike the commercially available granular activated carbons or ion exchange resins which usually need a combination of organic and inorganic regenerant to achieve efficient PFAS recovery, C-DAC has potential economic benefits in terms of lower material cost and the ability for regeneration of the materials.

[0095] In summary, the above Examples establish that three different alkylamine modified nanocellulose products (C4-DAC, C8-DAC and C12-DAC) were successfully prepared and examined for long-chain and short-chain PFAS removal. Synthetic routes were first optimized and material characterization results from TEM indicated that a longer alkyl chain might not further promote the PFAS adsorption due to severe fiber aggregation. The C8-DAC showed the highest adsorption capacity for both long-chain and short-chain PFAS among the threecandidates, with equilibrium adsorption capacity of 650, 400 and 200 mg / g for PFOS, PFOA and PFBA, respectively. The higher uptake of PFBA could be attributed to the additional physical sorption including Van der Waals force and size-related mechanism. In addition, the ion competition test pointed out the important role of electrostatic interaction in PFBA adsorption, with strong correlation to the valence charge of anion and pH.

[0096] Desorption tests provided additional insights into the adsorption / desorption mechanism. The adsorption of PFBA is primarily governed by electrostatic interactions, evidenced by its high desorption percentage when using NaOH. In the case of PFOA, electrostatic forces remain dominant, although desorption is facilitated by MeOH, which reduces hydrophobic forces. Long-chain PFAS compounds are influenced by both mechanisms.

[0097] Overall, the Examples show that introducing hydrophobic alkyl chains of certain lengths can enhance the adsorption of both long-chain and short-chain PFAS and illustrate the role of electrostatic interaction in long-chain and short-chain PFAS removal.

[0098] While the disclosure has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in from and details may be made therein without departing from the spirit and scope of the present disclosure and equivalents thereof.

Claims

WHAT IS CLAIMED IS:

1. An alkylamine functionalized cellulose comprising:where R is an alkyl group selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, or combinations thereof and n is from about 1,000 to about 15,000.

2. The alkylamine functionalized cellulose of claim 1, wherein R is selected from the group consisting of butyl, octyl, and dodecyl.

3. The alkylamine functionalized cellulose of claim 1, wherein the cellulose of the alkylamine functionalized cellulose is obtained from a plant biomass, wherein the plant biomass includes at least one of lignocellulose wood, non-lignocellulose wood, lignocellulose, pure cellulose, grasses, phytoplanktons, algal celluloses, or tunicate celluloses.

4. The alkylamine functionalized cellulose of claim 1, wherein the cellulose of the alkylamine functionalized cellulose is obtained from a plant biomass, wherein the plant biomass is obtained from non-wood sources including at least one of jute, bamboo, cotton, banana rachis, wheat straw, barley, hemp, flax straw, coconut fiber, soy hull, pea hull fiber, rice husk, sugarcane bagasse, pineapple leaf rachis, sisal fiber, tunicates, black spruce, eucalyptus, valonia, bacterial celluloses, or spinifex.

5. The alkylamine functionalized cellulose of claim 1, wherein the alkylamine functionalized cellulose has a charge density from about 0.2 mmol / g to about 2.0 mmol / g.

6. The alkylamine functionalized cellulose of claim 1, wherein n is from about 3,000 to about 12,000.

7. A method for removing negatively charged impurities from a liquid, comprising contacting the liquid with the alkylamine functionalized cellulose of claim 1.

8. The method of claim 7, wherein the liquid is water.

9. The method of claim 7, wherein the negatively charged impurities include at least one of polyfluoroalkyl substances or perfluoroalkyl substances.

10. A method for making an alkylamine functionalized cellulose comprising: dispersing wood fibers in a suitable solvent to form a first suspension; contacting the first suspension with an oxidizing agent to produce dialdehyde functionalized cellulose; contacting the dialdehyde functionalized cellulose with a second solvent to form a second suspension; contacting the second suspension with an alkylamine having a chain length from about 1 to about 12 carbon atoms wherein a ratio of alkylamine to aldehyde groups of about 10: 1; contacting the second suspension with 2-picoline-borane at a ratio of 2-picoline-borane to aldehyde groups of about 5: 1 to form a mixture;stirring the mixture at room temperature for a period of time from about 5 hours to about 80 hours; and, recovering the alkylamine functionalized cellulose.

11. The method of claim 10, wherein the oxidizing agent is added to the first suspension at an amount from about 1 mmol / g of cellulose to about 20 mmol / g of cellulose.

12. The method of claim 10, wherein the oxidizing agent is at least one of sodium periodate, potassium periodate, or rubidium periodate.

13. The method of claim 10, further comprising stirring the first suspension at a temperature from about 30 °C to about 80 °C, for a period of time from about 1 hour to about 48 hours prior to contacting the first suspension with the oxidizing agent.

14. The method of claim 10, wherein the dialdehyde functionalized cellulose is at a concentration from about 0.1 wt% to about 20 wt% of the second suspension.

15. The method of claim 10, wherein the alkylamine is selected from methylamine, ethylamine, propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, or combinations thereof.

16. The method of claim 10, wherein the ratio of alkylamine to aldehyde group in the second suspension is from about 10 to about 1.

17. The method of claim 10, further comprising adjusting pH value of the second suspension to from about 2 to about 5.

18. The method of claim 10, wherein recovering the alkylamine functionalized cellulose occurs by subjecting the second suspension to defibrillation.

19. The method of claim 10, wherein the alkylamine functionalized cellulose has a charge density from about +17.70 mV to about +30.81 mV.

20. The method of claim 10, wherein the alkylamine is selected from the group consisting of butylamine, octylamine and dodecylamine.

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