Preparation method of nanocellulose slow-release agent

Abstract

The invention relates to a preparation method of a nanocellulose slow-release agent, which comprises the following steps: (1) adding 1-5 parts of sodium alginate and 0.5-2 parts of polyvinyl alcohol into every 100 parts of water, heating and stirring to completely dissolve the sodium alginate and the polyvinyl alcohol to obtain a solution A; (2) crushing 0.1-0.5 part of cellulose to nanoscale, adding the solution A, mixing and continuously stirring until the cellulose is uniformly dispersed to obtain a solution B; (3) adding 1-10 parts of functional components into the solution B obtained in the step (2), and continuously stirring uniformly to obtain a slow-release agent solution; (4) adding a calcium sulfate solution into the slow-release agent solution obtained in the step (3) to obtain a cross-linked substance; and (5) freeze-drying the cross-linked product obtained in the step (4) to obtain the nanocellulose slow-release agent. The slow-release agent is high in mechanical property, good in swelling property and good in slow-release effect, long-term release of nutrient substances and oxygen can be achieved, growth and reproduction of oil-reducing microorganisms in oil-contaminated underground water are met, and degradation of petroleum pollutants in the underground water is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of groundwater treatment, specifically relating to the preparation and application of a nanocellulose-based slow-release agent. Background Technology

[0002] Oil spills can occur during the extraction, transportation, storage, and refining of petroleum, causing petroleum pollutants to enter the soil and groundwater environment. Because petroleum contains toxic substances such as polycyclic aromatic hydrocarbons (PAHs), it not only damages the ecological environment of groundwater but also affects human survival and health. Slow-release agents have been used in the biological treatment of petroleum-contaminated groundwater, but their application is limited by their slow-release and mechanical properties in complex petroleum-contaminated groundwater environments.

[0003] Polymers such as sodium alginate and polyvinyl alcohol have been used to prepare biocompatible, biodegradable, and non-toxic slow-release agents. However, their low mechanical properties make it easy for cations in the water sample to exchange with cations inside the slow-release agent, leading to decomposition and affecting the slow-release performance. In recent years, the addition of nanomaterials such as carbon nanotubes, graphene, and clay has solved this problem. However, these materials have limitations such as high cost or easy aggregation, which greatly hinder their large-scale use.

[0004] Nanocellulose (CNF) has better mechanical properties due to its sustainability, large surface area and potential active surface. Its rigid network structure forms a strong interfacial bond with the sustained-release agent through hydrogen bonds and van der Waals forces, which effectively improves the mechanical strength of the sustained-release agent.

[0005] CN111533613A discloses a nanocellulose gel-based water-retaining slow-release fertilizer. This slow-release fertilizer is obtained by adsorbing fertilizer aqueous solution with nanocellulose or oxidized nanocellulose as matrix. It has good slow-release performance, excellent water retention performance, readily available raw materials, is green and environmentally friendly, and can be completely degraded by the environment.

[0006] CN118047647A discloses a nanocellulose-based composite material with sustained-release function. Its preparation method includes: 1) reacting β-cyclodextrin with a silane coupling agent to obtain amino-modified cyclodextrin, then adding it to a polylactic acid solution to obtain grafted modified cyclodextrin; 2) adding compound fertilizer and freeze-drying to obtain a coated modified compound fertilizer; 3) soaking citric acid-modified nanocellulose in ethanol and heating to form a suspension, adding L-cysteine ​​and heating to obtain grafted modified nanocellulose; 4) adding the composite modification solution dropwise to a bentonite suspension to obtain a composite modified bentonite; 5) mixing chitosan, sodium alginate, and deionized water; 6) adding the coated modified compound fertilizer, grafted modified nanocellulose, and composite modified bentonite to obtain a composite sol; 7) adding it dropwise to a calcium salt solution to obtain a hydrogel microbead precursor; 8) soaking it in a sulfate solution to obtain composite hydrogel microbeads and freeze-drying. This material has a stable structure, high mechanical properties, and good sustained-release effect.

[0007] CN112409073A discloses a semi-interpenetrating micro-nano composite coated sugarcane leaf cellulose-based slow-release nitrogen fertilizer. The material uses sugarcane leaf cellulose, carboxymethyl cellulose, bentonite, diatomaceous earth, and nitrogen fertilizer as the fertilizer core. The preparation process is simple and low-cost, and it has a long fertilizer effect cycle and high fertilizer utilization rate. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing slow-release agents used in wastewater treatment by providing a slow-release agent that significantly improves mechanical properties while maintaining good slow-release performance by adding nanocellulose and improving the preparation method.

[0009] The objective of this invention is achieved through the following technical solution: A method for preparing a nanocellulose sustained-release agent includes the following steps: (1) Add 1-5 parts sodium alginate and 0.5-2 parts polyvinyl alcohol to every 100 parts of water, heat and stir until completely dissolved to obtain solution A; (2) Pulverize 0.1-0.5 parts of cellulose to nanoscale, add to solution A, mix and continue stirring until evenly dispersed to obtain solution B; (3) Add 1-10 parts of the functional component to the solution B obtained in step (2), and continue to stir until homogeneous to obtain a sustained-release solution; (4) Add the calcium sulfate solution to the sustained-release agent solution obtained in step (3) to obtain the crosslinked compound; (5) The crosslinked material obtained in step (4) is freeze-dried to obtain nanocellulose sustained-release agent.

[0010] The heating temperature in step (1) is 85-100℃, preferably 90-95℃; the heating time is 60-150 minutes, preferably 90-120 minutes.

[0011] In step (2), the cellulose crushing time is 0.5-6h, and the crushed particle size is 300-500nm; the amount of nanocellulose added is preferably 0.2-0.3 parts; preferably, the crushing is carried out under ultrasonic aqueous solution conditions, and after crushing, it is dried to obtain nanocellulose.

[0012] The functional component in step (3) is a nutrient or an oxygen-releasing agent. The nutrient is ammonium chloride and / or potassium dihydrogen phosphate, preferably ammonium chloride and potassium dihydrogen phosphate, with a mass ratio of 3-6:0.5-3. The oxygen-releasing agent is citric acid and / or calcium peroxide, preferably citric acid and calcium peroxide, with a mass ratio of 0.2-1:0.5-3. The stirring time is 5-30 minutes.

[0013] When the functional component is a nutrient, the calcium sulfate solution in step (4) is added to the slow-release agent solution by dripping; when the functional component is an oxygen release agent, the slow-release agent solution is frozen and then added to the calcium sulfate solution for cross-linking, the diameter of the freezing mold is 0.5-2 cm; the calcium sulfate concentration is 0.1%-0.25%, most preferably 0.15-0.2%; the cross-linking time is 6-24 h.

[0014] In step (5), the freeze-drying time is 1-4 hours, more preferably 2-3 hours; the freeze-drying temperature is -30°C to -50°C.

[0015] Another aspect of the present invention discloses a nanocellulose sustained-release agent prepared by the method described herein.

[0016] Another aspect of the present invention discloses the application of the prepared nanocellulose slow-release agent in the remediation of petroleum-contaminated groundwater, wherein the dosage of the nanocellulose slow-release agent is 0.5-10 g / m³. 3 More preferably 1-5g / m 3 .

[0017] Based on conventional understanding in the art, unless otherwise specified, the number of portions mentioned in this application refers to the mass fraction.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The slow-release agent material prepared by the present invention has a wide range of raw material sources, is inexpensive and readily available, and is biodegradable, and will not have a negative impact on the environment; (2) The preparation method of the present invention is simple, has a low risk factor, and does not involve strong acid and strong alkali or high temperature and high pressure steps; (3) The slow-release agent prepared by the present invention has a stable structure, high mechanical properties and good slow-release performance. Therefore, it has a long slow-release cycle, which can effectively solve the problems of repeated addition of nutrients and oxygen, unstable concentration and waste, greatly improve the utilization rate of nutrients and oxygen, and reduce the cost of remediation of petroleum-polluted groundwater. (4) The slow-release agent prepared in this invention incorporates nanocellulose, which has a stable structure and gives the material excellent mechanical properties. In actual groundwater environments, it can achieve long-term and stable release of nutrients and oxygen, thereby improving the remediation efficiency of oil-contaminated groundwater. Attached Figure Description

[0019] Figure 1 This is a 20 μm resolution scanning electron microscope (SEM) image of the sustained-release agent after the addition of nanocellulose; Figure 2 This is a 10 μm resolution scanning electron microscope (SEM) image of the sustained-release agent after the addition of nanocellulose. Figure 3 This is a 20 μm resolution scanning electron microscope (SEM) image of the sustained-release agent without the addition of nanocellulose. Figure 4 This is a 10 μm resolution scanning electron microscope (SEM) image of the sustained-release agent without the addition of nanocellulose. Figure 5 To determine the effect of the slow-release agent on NH4 before and after the addition of nanocellulose. + PO4 3- and DO release rate. Detailed Implementation

[0020] The technical solutions and applications of the present invention will be clearly and completely described below through embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The reagents used in the following examples are all commercially available and can be used directly without further purification.

[0022] In the following examples, the morphology and structure of the sustained-release agent were observed using a ZEISS Gemini scanning electron microscope; the mechanical strength of the sustained-release agent before and after the addition of nanocellulose was determined using a UTM5105 electronic universal testing machine.

[0023] In the following examples, the release concentrations and release rates of nutrients and oxygen by the slow-release agent were determined using the standard Nessler's reagent spectrophotometric method, the ammonium molybdate colorimetric method, and the dissolved oxygen meter method, respectively. Specifically, the method involved first measuring the concentration C of nutrients or oxygen in water at time t after adding a certain mass of the slow-release agent.t Record the results, and then measure the maximum concentration C of nutrients and oxygen that can be achieved after adding the same mass of slow-release agent. max And record; the swelling ratio of the sustained-release agent is determined by gravimetric method. The specific method is as follows: first measure the initial mass m0 of the sustained-release agent before swelling and record it, then soak it in deionized water until the mass no longer increases to obtain the mass m1 and record it.

[0024] The swelling ratio of the sustained-release agent is calculated using the following formula: Φ(g / g) = (m1-m0) / m0×100% The release rate of nutrients and oxygen by the sustained-release formulation is calculated using the following formula: λ(%) = (C t / C max )×100% Example 1 A method for preparing a nanocellulose sustained-release agent includes the following steps: (1) Add 2g sodium alginate and 0.5g polyvinyl alcohol to 100ml deionized water and heat and stir on a magnetic stirrer at 90℃ and 600rpm until completely dissolved. (2) Disperse commercially available micron-sized cellulose (d50 = 90-150μm) in deionized water, break it down to nanoparticle size (d50 = 300-500 nm), and then add 0.2g of dried nanocellulose to the mixed solution in (1) and continue stirring. (3) Then add 4g of ammonium chloride and 1g of potassium dihydrogen phosphate as nutrients and continue stirring; (4) The mixed solution from step (3) was then added dropwise to 0.15% calcium sulfate for cross-linking for 12 hours to obtain the cross-linked product; (5) The cross-linked material was frozen in a -20°C freezer for 2 hours and then freeze-dried in a freeze dryer for 36 hours to obtain nanocellulose sustained-release agent.

[0025] Example 2 A method for preparing a nanocellulose sustained-release agent includes the following steps: (1) Add 2g sodium alginate and 0.5g polyvinyl alcohol to 100ml deionized water and heat and stir on a magnetic stirrer at 90℃ and 600rpm until completely dissolved. (2) Disperse commercially available micron-sized cellulose (d50 = 90-150μm) in deionized water, break it down to nanoparticle size (d50 = 300-500 nm), and then add 0.2g of dried nanocellulose to the mixed solution in (1) and continue stirring. (3) Then add 0.5g of citric acid and 1g of calcium peroxide as oxygen release agents, and continue stirring; (4) Pour the mixed solution from (3) into a mold with a diameter of 1 cm and freeze for 2 hours. Then pour it into a 0.15% calcium sulfate solution for crosslinking for 12 hours to obtain the crosslinked product. (5) The cross-linked material was frozen in a -20°C freezer for 2 hours and then freeze-dried in a freeze dryer for 36 hours to obtain nanocellulose sustained-release agent.

[0026] The obtained nanocellulose sustained-release agent was subjected to performance testing, and the test results are as follows: Figure 1 and Figure 2 The images show scanning electron microscope (SEM) images of the nanocellulose sustained-release agent in Example 1 at magnifications of 200x and 500x, respectively. As can be seen from the images, the internal structure of the sustained-release agent with added nanocellulose is regular and there is no structural collapse. This is because hydrogen bonds are formed between nanocellulose, sodium alginate, and polyvinyl alcohol, making the cross-linked network more stable and thus enhancing the mechanical properties of the sustained-release agent.

[0027] Comparative Example 1 The operation is the same as in Example 1, except that step (2) is not performed, and a sustained-release agent without nanocellulose is obtained.

[0028] Comparative Example 2 The operation is the same as in Example 2, except that step (2) is not performed, and a sustained-release agent without nanocellulose is obtained.

[0029] Figure 3 and Figure 4 The images show scanning electron microscope (SEM) images of the sustained-release agent obtained in Comparative Example 1 at magnifications of 200x and 500x, respectively. As can be seen from the images, the internal structure of the sustained-release agent without the addition of nanocellulose partially collapsed and became irregular.

[0030] Biodegradation experiments on oily wastewater were conducted using the slow-release agents obtained in Example 1 and Comparative Example 1. The mechanical strength of the slow-release agents before and after the biodegradation experiments was measured, and the results are shown in Table 1. After adding nanocellulose, the mechanical strength of the slow-release agent before the biodegradation experiment increased from 49.18-55.36 kPa to 78.98-81.01 kPa. After the biodegradation experiment, the mechanical strength of the slow-release agent without nanocellulose decreased to 11.98-13.23 kPa, while the mechanical strength of the slow-release agent with nanocellulose remained at 52.33-50.16 kPa. Therefore, nanocellulose has potential application value in improving the mechanical properties of slow-release agents.

[0031] Table 1 Mechanical strength before degradation / kPa Mechanical strength after degradation / kPa Example 1 55.36 11.98 Example 2 81.01 52.33 Comparative Example 1 49.18 13.23 Comparative Example 2 78.98 50.16 The sustained-release agents obtained in Examples 1, 2, Comparative Example 1, and Comparative Example 2 were used to determine the sustained-release properties of nutrients and oxygen. The results are shown in Table 2. Table 2 Sustained release time / h Release rate / % Example 1 90 NH4+: 72.56 PO43-: 79.81 Example 2 120 92.11 Comparative Example 1 23.5 NH4+: 70.48 PO43-: 75.03 Comparative Example 2 90 82.91 Example 3 The amount of nanocellulose added in step (2) of Example 1 was adjusted to 0.1g. Other parameters remained the same as in Example 1, and a nanocellulose sustained-release agent was obtained.

[0032] Example 4 The amount of nanocellulose added in step (2) of Example 1 was adjusted to 0.3g. Other parameters remained the same as in Example 1, and a nanocellulose sustained-release agent was obtained.

[0033] Example 5 The amount of nanocellulose added in step (2) of Example 1 was adjusted to 0.4g. Other parameters remained the same as in Example 1, and a nanocellulose sustained-release agent was obtained.

[0034] Example 6 The amount of nanocellulose added in step (2) of Example 1 was adjusted to 0.5g. Other parameters remained the same as in Example 1, and a nanocellulose sustained-release agent was obtained.

[0035] Example 7 The calcium sulfate concentration in step (4) of Example 1 was adjusted to 0.1%. Other parameters remained the same as in Example 1 to obtain the nanocellulose sustained-release agent.

[0036] Example 8 The calcium sulfate concentration in step (4) of Example 1 was adjusted to 0.2%. Other parameters remained the same as in Example 1 to obtain the nanocellulose sustained-release agent.

[0037] Example 9 The calcium sulfate concentration in step (4) of Example 1 was adjusted to 0.25%. Other parameters remained the same as in Example 1 to obtain the nanocellulose sustained-release agent.

[0038] The swelling properties of the sustained-release agents obtained in the examples and comparative examples were tested, as shown in Table 3. The concentration of nanocellulose had a significant impact on the sustained-release performance of the agents. As the concentration of nanocellulose increased from 0 to 0.2%, the swelling ratio of the prepared sustained-release agents increased from 54.03 g / g to 62.44 g / g. However, when the concentration of nanocellulose was further increased to 0.5%, the swelling ratio of the sustained-release agents decreased from 62.44 g / g to 49.74 g / g. This is because the abundant hydroxyl groups on the NC surface form hydrogen bonds with water molecules, increasing the swelling ratio of the sustained-release agents. However, the structure of the sustained-release agents generated by high-concentration NC is dense, resulting in a lower swelling ratio and thus affecting the sustained-release performance. In addition, the concentration of calcium sulfate also had a certain impact on the sustained-release performance. When the calcium sulfate concentration was 0.15%, the swelling ratio was the largest, and the sustained-release performance was the best.

[0039] Table 3 swelling ratio Example 1 62.44 Example 3 55.24 Example 4 55.66 Example 5 53.98 Example 6 49.74 Example 7 44.17 Example 8 52.86 Example 9 56.22 This invention has been described in detail with general description and specific embodiments. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of this invention fall within the scope of protection claimed by this invention.

Claims

1. A method for preparing a nanocellulose sustained-release agent, comprising the following steps: (1) Add 1-5 parts sodium alginate and 0.5-2 parts polyvinyl alcohol to every 100 parts of water, heat and stir until completely dissolved to obtain solution A; (2) Pulverize 0.1-0.5 parts of cellulose to nanoscale, add to solution A, mix and continue stirring until evenly dispersed to obtain solution B; (3) Add 1-10 parts of the functional component to the solution B obtained in step (2), and continue to stir until homogeneous to obtain a sustained-release solution; (4) Add the calcium sulfate solution to the sustained-release agent solution obtained in step (3) to obtain the crosslinked compound; (5) The crosslinked material obtained in step (4) is freeze-dried to obtain nanocellulose sustained-release agent.

2. The method according to claim 1, characterized in that... The heating temperature in step (1) is 85-100℃, preferably 90-95℃; the heating time is 60-150 minutes, preferably 90-120 minutes.

3. The method according to claim 1, characterized in that... In step (2), the cellulose crushing time is 0.5-6h, and the crushed particle size is 300-500nm; the amount of nanocellulose added is preferably 0.2-0.3 parts; preferably, the crushing is carried out under ultrasonic aqueous solution conditions, and after crushing, it is dried to obtain nanocellulose.

4. The method according to claim 1, characterized in that... The functional component in step (3) is a nutrient or an oxygen-releasing agent. The nutrient is ammonium chloride and / or potassium dihydrogen phosphate, preferably ammonium chloride and potassium dihydrogen phosphate, with a mass ratio of 3-6:0.5-3. The oxygen-releasing agent is citric acid and / or calcium peroxide, preferably citric acid and calcium peroxide, with a mass ratio of 0.2-1:0.5-3. The stirring time is 5-30 minutes.

5. The method according to claim 1, characterized in that... When the functional component is a nutrient, the calcium sulfate solution in step (4) is added to the slow-release agent solution by dripping; when the functional component is an oxygen release agent, the slow-release agent solution is frozen and then added to the calcium sulfate solution for cross-linking, the diameter of the freezing mold is 0.5-2 cm; the calcium sulfate concentration is 0.1%-0.25%, most preferably 0.15-0.2%; the cross-linking time is 6-24 h.

6. The method according to claim 1, characterized in that... In step (5), the freeze-drying time is 1-4 hours, more preferably 2-3 hours; the freeze-drying temperature is -30°C to -50°C.

7. A nanocellulose sustained-release agent prepared by the method according to any one of claims 1-6.

8. An application of the nanocellulose slow-release agent prepared by the method of any one of claims 1-6 for the remediation of petroleum-contaminated groundwater.

9. In the application according to claim 8, the dosage of the nanocellulose sustained-release agent is 0.5-10 g / m³. 3 More preferably 1-5g / m 3 .

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