Chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent and its preparation method and application

Abstract

The present invention provides a chitosan-nano titanium dioxide-coated bamboo shoot shell biochar adsorbent and its preparation method and application, which belong to the field of chemical adsorption. The preparation method provided by the present invention comprises the following steps: (1) preparing titanium dioxide colloid by a sol-gel method; (2) mixing the titanium dioxide colloid obtained in the step (1) with bamboo shoot shell powder, and then standing and calcining in sequence to obtain a nano-titanium dioxide-coated bamboo shoot shell biochar material; (3) mixing the nano-titanium dioxide-coated bamboo shoot shell biochar material obtained in the step (2) with a chitosan solution, and then adding the mixture dropwise to a coagulation solution to obtain microspheres; (4) mixing the microspheres obtained in the step (3) with a glutaraldehyde solution to carry out a cross-linking reaction to obtain a chitosan-nano titanium dioxide-coated bamboo shoot shell biochar adsorbent. The adsorbent provided by the present invention has high adsorption efficiency for silver ions and good adsorption capacity.

Description

Technical Field

[0001] The present invention relates to the field of chemical adsorption, in particular to a chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent and a preparation method and application thereof. Background Art

[0002] Silver is widely used in various fields of industrial manufacturing due to its excellent ductility, thermal conductivity, photosensitivity, electrical and chemical properties, and antimicrobial properties. For example, it is used in highly sensitive physical instrument components, various automated devices, rockets, submarines, computers, nuclear devices, and numerous contact points in communication systems. However, the manufacturing process of these instruments and equipment releases large amounts of industrial wastewater containing low-concentration silver, which can cause serious damage to terrestrial and aquatic ecosystems and ultimately have adverse effects on human health through various ingestion routes. Therefore, the adsorption and secondary recycling of silver ions from wastewater has important social and economic significance.

[0003] Bamboo shoot shells are waste products from bamboo shoot processing, and their main components are lignin, cellulose, and hemicellulose. Bamboo shoot shells have a high water content and are easily rotten. A large amount of bamboo shoot shells, whether discarded, randomly piled up, or burned, will cause serious pollution to the environment. Currently, the preparation of biomass and its derived biochar adsorption materials from agricultural waste and their application in water pollution treatment has become a hot topic. However, powdered biochar is difficult to separate from water bodies and easily causes secondary pollution, which limits its large-scale use. In addition, the biochar adsorbent materials in the prior art have the problems of small adsorption capacity, low adsorption efficiency, and high cost.

[0004] Therefore, how to prepare an adsorbent that can be stably stored in a solution and has high adsorption efficiency and good adsorption capacity for silver ions has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] The present invention aims to provide a chitosan-nano-titanium dioxide-coated bamboo shoot shell biochar adsorbent, its preparation method, and application. The adsorbent prepared by the chitosan-nano-titanium dioxide-coated bamboo shoot shell biochar adsorbent provided by the present invention can be stably stored in solution, has high adsorption efficiency for silver ions, and exhibits excellent adsorption capacity.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent, comprising the following steps:

[0008] (1) Preparing titanium dioxide colloid by sol-gel method;

[0009] (2) mixing the titanium dioxide colloid obtained in step (1) with bamboo shoot shell powder, and then sequentially allowing the mixture to stand and calcining the mixture to obtain a nano-titanium dioxide-coated bamboo shoot shell biochar material;

[0010] (3) mixing the nano-titanium dioxide-coated bamboo shoot shell biochar material obtained in step (2) with a chitosan solution and then adding the mixture dropwise to the coagulation solution to obtain microspheres;

[0011] (4) The microspheres obtained in step (3) are mixed with a glutaraldehyde solution to carry out a cross-linking reaction to obtain a chitosan-nano-titanium dioxide-coated bamboo shoot shell biochar adsorbent.

[0012] Preferably, the particle size of the bamboo shoot shell powder in step (2) is <0.15 mm.

[0013] Preferably, in step (2), the mass ratio of titanium dioxide colloid to bamboo shoot shell powder is (280-360): (7-8).

[0014] Preferably, the calcination temperature in step (2) is 500-600° C., and the calcination time is 2-4 hours.

[0015] Preferably, in step (3), the mass ratio of the nano-titanium dioxide-coated bamboo shoot shell biochar material to the chitosan in the chitosan solution is (1-1.2): (1.8-2).

[0016] Preferably, the chitosan content in the chitosan solution in step (3) is (0.036-0.5) g / mL.

[0017] Preferably, the coagulation solution in step (3) is a NaOH solution; the concentration of the NaOH solution is 0.45 to 0.55 mol / L.

[0018] Preferably, the volume content of glutaraldehyde in the glutaraldehyde solution in step (4) is 8-10%.

[0019] The present invention provides a chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent prepared by the preparation method described in the above technical solution.

[0020] The present invention provides the use of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent described in the above technical solution in the adsorption of precious metal silver.

[0021] The invention provides a preparation method of a chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent, comprising the following steps: (1) preparing titanium dioxide colloid by a sol-gel method; (2) mixing the titanium dioxide colloid obtained in the step (1) with bamboo shoot shell powder, and then sequentially standing and calcining the mixture to obtain a nano-titanium dioxide coated bamboo shoot shell biochar material; (3) mixing the nano-titanium dioxide coated bamboo shoot shell biochar material obtained in the step (2) with a chitosan solution, and then dropwise adding the mixture into a coagulation solution to obtain microspheres; and (4) mixing the microspheres obtained in the step (3) with a glutaraldehyde solution to carry out a cross-linking reaction to obtain a chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent. The invention uses bamboo shoot shells as raw materials, prepares biochar from the bamboo shoot shells, and utilizes the high carbon content and porosity of the biochar, as well as the large amount of oxygen-containing functional groups in the bamboo shoot shell biochar, to improve the adsorption rate of silver ions. Nano titanium dioxide has a high ion exchange capacity, which enables metal ions to enter the titanium dioxide interlayer for adsorption. Chitosan has a large number of functional groups, such as amino and hydroxyl groups, on its macromolecular linear skeleton, which enables it to form a chelate complex with silver ions in water. Through the double coating of the bamboo shoot shell biochar with nano titanium dioxide and chitosan, the groups capable of combining with metal silver ions contained in the adsorbent and the specific surface area of ​​the adsorbent are greatly increased, thereby improving the adsorption efficiency and adsorption amount of the adsorbent for metal silver ions, and enabling the adsorbent to exist stably in the solution. Experimental results show that the chitosan-nano-titanium dioxide-coated bamboo shoot shell biochar adsorbent prepared by the preparation method provided by the present invention has an adsorption rate of 80% for silver ions in wastewater within 1.5 hours; it has a rapid adsorption efficiency for silver ions, an adsorption rate of 86%, and a maximum single-layer adsorption capacity of 248 mg / g, and has the characteristics of high adsorption efficiency and good adsorption capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a process flow chart for preparing chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent in an embodiment of the present invention;

[0023] Figure 2 This is a SEM image of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 of the present invention at a magnification of 5000 times;

[0024] Figure 3 The SEM images of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 of the present invention at 30,000 and 50,000 times magnification are shown;

[0025] Figure 4 This is a SEM image of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 of the present invention after adsorbing silver. DETAILED DESCRIPTION

[0026] The present invention provides a method for preparing a chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent, comprising the following steps:

[0027] (1) Preparing titanium dioxide colloid by sol-gel method;

[0028] (2) mixing the titanium dioxide colloid obtained in step (1) with bamboo shoot shell powder, and then sequentially allowing the mixture to stand and calcining the mixture to obtain a nano-titanium dioxide-coated bamboo shoot shell biochar material;

[0029] (3) mixing the nano-titanium dioxide-coated bamboo shoot shell biochar material obtained in step (2) with a chitosan solution and then adding the mixture dropwise to the coagulation solution to obtain microspheres;

[0030] (4) The microspheres obtained in step (3) are mixed with a glutaraldehyde solution to carry out a cross-linking reaction to obtain a chitosan-nano-titanium dioxide-coated bamboo shoot shell biochar adsorbent.

[0031] The present invention adopts the sol-gel method to prepare titanium dioxide colloid.

[0032] In the present invention, the specific operation of preparing titanium dioxide colloid by the sol-gel method is preferably:

[0033] (a) mixing water, ethanol and acetic acid to obtain a mixed solution A;

[0034] (b) mixing a titanium source with ethanol to obtain a mixed solution B;

[0035] (c) adding the mixed solution A obtained in step (a) dropwise to the mixed solution B obtained in step (b) to carry out a hydrolysis reaction to obtain a titanium dioxide colloid;

[0036] There is no order in which steps (a) and (b) are performed.

[0037] In the present invention, water, ethanol and acetic acid are preferably mixed to obtain a mixed solution A.

[0038] In the present invention, the volume ratio of water, ethanol, and acetic acid is preferably (10-15):(20-25):(10-15), more preferably (12-15):(20-23):(10-12), and even more preferably 15:20:10. Limiting the volume ratio of water, ethanol, and acetic acid to this range can avoid precipitation during the gelation process and prevent excessive hydrolysis during the reaction by adding acetic acid.

[0039] In the present invention, the titanium source is preferably mixed with ethanol to obtain a mixed solution B.

[0040] In the present invention, the titanium source is preferably isopropyl titanate; the volume ratio of the titanium source to ethanol is preferably (10-12):(30-35), more preferably (10-11):(30-32), and even more preferably 10:30. Limiting the volume ratio of the titanium source to ethanol to the above range ensures stable gel formation.

[0041] After obtaining the mixed solution A and the mixed solution B, the present invention preferably adds the mixed solution A dropwise into the mixed solution B to carry out a hydrolysis reaction to obtain titanium dioxide colloid.

[0042] The present invention preferably performs the dropwise addition under stirring conditions; the stirring speed is preferably 175 to 185 r / min, more preferably 180 r / min. The present invention can fully mix the mixed solution A and the mixed solution B by stirring, and is conducive to the hydrolysis reaction to generate titanium dioxide colloid.

[0043] In the present invention, the dropping speed is preferably ≤0.05 mL / 2 s, more preferably 0.05 mL / 2 to 3 s. By setting the dropping speed within the above range, the present invention can avoid excessive hydrolysis and precipitation.

[0044] In the present invention, the volume ratio of water in the mixed solution A to the titanium source in the mixed solution B is preferably (10-15):(10-12), more preferably (12-15):(10-11), and even more preferably 15:10. Limiting the volume ratio of water to the titanium source to the above range ensures hydrolysis of the titanium source and produces titanium dioxide colloid.

[0045] In the present invention, secondary stirring is preferably performed after the dropwise addition is completed.

[0046] In the present invention, the secondary stirring speed is preferably 150 to 180 r / min, more preferably 160 to 170 r / min; the secondary stirring time is preferably 8 to 15 minutes, more preferably 10 minutes. Setting the secondary stirring speed and time within the above ranges can promote the hydrolysis reaction during the sol-gel process to obtain nano-titanium dioxide colloid.

[0047] After obtaining the titanium dioxide colloid, the present invention mixes the titanium dioxide colloid with bamboo shoot shell powder, and then sequentially allows the mixture to stand and calcines to obtain a nano-titanium dioxide-coated bamboo shoot shell biochar material.

[0048] In the present invention, the particle size of the bamboo shoot shell powder is preferably <0.15 mm. By limiting the particle size of the bamboo shoot shell powder to the above range, the surface area of ​​the biochar can be increased, thereby improving the adsorption performance of the adsorbent.

[0049] In the present invention, the preparation process of the bamboo shoot shell powder is preferably as follows: the bamboo shoot shells are sequentially cleaned, dried, crushed and sieved to obtain the bamboo shoot shell powder.

[0050] In the present invention, the solvent used for the cleaning is preferably deionized water; the cleaning is preferably performed three times. The present invention does not particularly limit the cleaning equipment and operation, and commonly used cleaning equipment and operations by those skilled in the art can be used. The present invention can remove impurities on the surface of the bamboo shoot shells through cleaning.

[0051] In the present invention, the drying temperature is preferably 80°C, and the drying time is preferably 2 days. The present invention does not particularly limit the drying equipment; any drying equipment commonly used by those skilled in the art can be used. The present invention can fully remove moisture from the bamboo shoot shells through drying, facilitating subsequent crushing.

[0052] The present invention has no particular limitation on the crushing equipment and operation, and equipment and operations well known to those skilled in the art may be used.

[0053] In the present invention, the sieving is preferably through a 100 mesh sieve. The particle size of the bamboo shoot shell powder can be controlled to be less than 0.15 mm by sieving.

[0054] In the present invention, the mass ratio of the titanium dioxide colloid to the bamboo shoot shell powder is preferably (280-360): (7-8), more preferably (280-315): (7-8), further preferably (280-300): (7-7.5), and most preferably 297: 7. By limiting the volume ratio of the titanium source in the titanium dioxide colloid to the mass ratio of the bamboo shoot shell powder to the above range, the nano-titanium dioxide can be better coated on the bamboo shoot shell biochar.

[0055] In the present invention, the mixing of the titanium dioxide colloid and the bamboo shoot shell powder is preferably carried out under stirring conditions; the stirring speed is preferably 150 to 180 r / min, more preferably 160 to 170 r / min; and the stirring time is preferably 15 to 25 minutes, more preferably 20 minutes. In the present invention, setting the mixing time of the titanium dioxide colloid and the bamboo shoot shell powder within the above range allows the bamboo shoot shell powder and the titanium dioxide colloid to be fully mixed, which is beneficial for the subsequent coating of the bamboo shoot shell biochar with nano-titanium dioxide.

[0056] In the present invention, the standing time is preferably 11 to 13 hours, more preferably 12 hours, and the standing temperature is preferably 25 to 30° C. In the present invention, gel can be formed by standing.

[0057] After the standing is completed, the present invention preferably sequentially dries and grinds the gel formed by the standing to obtain a xerogel.

[0058] In the present invention, the drying temperature is preferably 80-100° C., more preferably 90° C.; the drying time is preferably 8-12 hours, more preferably 10 hours. The present invention removes moisture from the gel by drying, facilitating grinding.

[0059] The present invention has no particular limitation on the equipment and operation of grinding, as long as the dried gel can be ground to a particle size of less than 0.15 mm.

[0060] In the present invention, the calcination is preferably performed in a muffle furnace; the calcination temperature is preferably 500-600°C, more preferably 550°C; and the calcination time is preferably 2-4 hours, more preferably 3 hours. Limiting the calcination temperature and time within these ranges ensures the formation and crystal stability of titanium dioxide, while also providing the biochar with a higher porosity and improving the biochar's adsorption properties.

[0061] After the calcination is completed, the present invention preferably cools, grinds and sieves the calcined product in sequence to obtain the nano-titanium dioxide-coated bamboo shoot shell biochar material.

[0062] The present invention has no particular limitation on the cooling operation, as long as the calcined product can be cooled to room temperature.

[0063] The present invention has no particular limitation on the equipment and operation of the grinding, and operations familiar to those skilled in the art may be used.

[0064] In the present invention, the sieving is preferably through a 100 mesh sieve. The present invention can make the particle size of the nano-titanium dioxide coated bamboo shoot shell biochar material less than 0.15 mm by sieving, which is beneficial to the subsequent chitosan coating.

[0065] After obtaining the nano-titanium dioxide coated bamboo shoot shell biochar material, the present invention mixes the nano-titanium dioxide coated bamboo shoot shell biochar material with a chitosan solution and then drips the mixture into a coagulation solution to obtain microspheres.

[0066] In the present invention, the mass ratio of the nano-titanium dioxide-coated bamboo shoot biochar material to chitosan in the chitosan solution is preferably (1-1.2): (1.8-2), more preferably (1-1.1): (1.9-2), and even more preferably 1: 2. The present invention limits the mass ratio of the nano-titanium dioxide-coated bamboo shoot biochar material to chitosan within the above range to ensure good coating of the nano-titanium dioxide-coated bamboo shoot biochar material by chitosan and successfully prepare microspheres.

[0067] In the present invention, the solvent in the chitosan solution is preferably an acetic acid solution; the volume concentration of the acetic acid solution is preferably 1.5-2.5%, more preferably 2%; the chitosan content in the chitosan solution is preferably (0.036-0.05) g / mL, more preferably (0.038-0.045) g / mL, and even more preferably 0.04 g / mL. Setting the chitosan content in the chitosan solution within the above range can ensure that the chitosan is fully dissolved.

[0068] In the present invention, the mixing of the nano-titanium dioxide-coated bamboo shoot shell biochar material and the chitosan solution is preferably carried out under stirring. The present invention does not particularly limit the stirring speed, and the nano-titanium dioxide-coated bamboo shoot shell biochar material can be completely dispersed in the chitosan solution using procedures well known to those skilled in the art.

[0069] In the present invention, the coagulation solution is preferably a NaOH solution; the concentration of the NaOH solution is preferably 0.45 to 0.55 mol / L, more preferably 0.5 mol / L. The present invention limits the type and concentration of the coagulation solution to the above ranges so that the mixed solution can form microspheres. Excessively high or low concentrations of the NaOH solution will not produce microspheres.

[0070] In the present invention, the droplet addition speed is preferably 0.05 mL / 2-3 s; the droplet addition device is preferably a syringe. The present invention can facilitate the formation of microspheres by controlling the droplet addition speed within the above range.

[0071] The present invention mixes a nano-titanium dioxide-coated bamboo shoot shell biochar material with a chitosan solution and then drips the mixture into a coagulation solution. The mixed solution of the nano-titanium dioxide-coated bamboo shoot shell biochar material and the chitosan solution forms a gel in the coagulation solution. The reason is that when chitosan contacts sodium hydroxide, the sodium hydroxide reacts with amino groups in the chitosan to generate ammonia salts; at the same time, the sodium hydroxide also reacts with hydroxyl groups in the chitosan to generate sodium oxide salts; these reactions cause the structure of chitosan molecules to change, thereby making it insoluble in sodium hydroxide, wherein the chitosan undergoes a gelation reaction with NaOH to form a gel, so that the mixed solution of the nano-titanium dioxide-coated bamboo shoot shell biochar material and the chitosan solution can form microspheres in the coagulation solution.

[0072] In the present invention, after the dropwise addition is completed, the process is preferably performed in sequence of standing, sieving and washing to obtain microspheres.

[0073] In the present invention, the standing time is preferably 24 hours; the standing temperature is preferably room temperature. The present invention can make the microspheres solidify better by standing.

[0074] The present invention has no particular limitation on the equipment and operation of the screening, as long as the particle size of the microspheres can be controlled to be 800 μm.

[0075] In the present invention, the cleaning solvent is preferably deionized water; the present invention has no particular limitation on the number of cleaning times, and the cleaning process may be performed until the pH of the cleaning solution is neutral.

[0076] After obtaining the microspheres, the present invention mixes the microspheres with a glutaraldehyde solution to carry out a cross-linking reaction, thereby obtaining a chitosan-nano titanium dioxide-coated bamboo shoot shell biochar adsorbent.

[0077] In the present invention, the solvent in the glutaraldehyde solution is preferably methanol; the volume content of glutaraldehyde in the glutaraldehyde solution is preferably 8-10%, more preferably 8.5-9.5%, and even more preferably 9%. Limiting the volume content of glutaraldehyde to the above range facilitates the crosslinking reaction between chitosan and glutaraldehyde in the microspheres, thereby enabling the microspheres to be stable in both acidic and alkaline solutions.

[0078] In the present invention, the microspheres are preferably allowed to stand after being mixed with the glutaraldehyde solution. In the present invention, the microspheres can be allowed to stand in the glutaraldehyde solution to facilitate the cross-linking reaction.

[0079] In the present invention, the cross-linking reaction time is preferably 22 to 26 hours, more preferably 24 hours; the cross-linking reaction temperature is preferably room temperature. The cross-linking reaction can better link the chitosan bonds on the microsphere surface and improve the stability of the microsphere in acidic solution.

[0080] After the cross-linking reaction is completed, the present invention preferably separates and dries the products of the cross-linking reaction in sequence to obtain a chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent.

[0081] In the present invention, the separation is preferably carried out by using a sieve spoon.

[0082] In the present invention, the drying is preferably to allow the separated solid to dry naturally in a culture dish.

[0083] The invention uses bamboo shoot shells as raw materials, prepares biochar from the bamboo shoot shells, and utilizes the high carbon content and porosity of the biochar, as well as the large amount of oxygen-containing functional groups in the bamboo shoot shell biochar, to improve the adsorption rate of silver ions. Nano titanium dioxide has a high ion exchange capacity, which enables metal ions to enter the titanium dioxide interlayer for adsorption. Chitosan has a large number of functional groups, such as amino and hydroxyl groups, on its macromolecular linear skeleton, which enables it to form a chelate complex with silver ions in water. Through the double coating of the bamboo shoot shell biochar with nano titanium dioxide and chitosan, the groups capable of combining with metal silver ions contained in the adsorbent and the specific surface area of ​​the adsorbent are greatly increased, thereby improving the adsorption efficiency and adsorption amount of the adsorbent for metal silver ions, and enabling the adsorbent to be stably present in the solution.

[0084] The present invention also provides a chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent prepared by the preparation method described in the above technical solution.

[0085] The invention adopts double coating of nano titanium dioxide and chitosan, which greatly increases the groups contained in the adsorbent that can combine with metallic silver ions and the specific surface area of ​​the adsorbent, thereby improving the adsorption efficiency and adsorption amount of the adsorbent for metallic silver ions.

[0086] The present invention also provides the use of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent described in the above technical solution in the adsorption of precious metal silver.

[0087] In an embodiment of the present invention, Figure 1 As shown, the preparation process of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent is as follows:

[0088] The discarded bamboo shoot shells were cleaned and dried in an oven at 80°C to obtain bamboo shoot shells without impurities, which were then crushed and sieved to obtain bamboo shoot shell powder (bamboo shoot skin powder biomass basic material);

[0089] Mixing water, acetic acid, and ethanol, and adding the resulting mixture dropwise to a mixture of isopropyl titanate and ethanol, adding bamboo shoot shell powder (bamboo shoot peel powder biomass basic material) thereto to obtain a xerogel, calcining (firing) the xerogel in a muffle furnace, and then cooling to room temperature and grinding to obtain a nano-titanium dioxide-coated bamboo shoot shell biochar material (nano-titanium dioxide-coated bamboo shoot shell biochar particles);

[0090] Nano-titanium dioxide coated bamboo shoot shell biochar material (nano-titanium dioxide coated bamboo shoot shell biochar particles) was mixed with chitosan solution (chitosan dissolved in ethanol), and then treated with NaOH solution and glutaraldehyde solution (methanol + glutaraldehyde) to obtain chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent (chitosan-coated nano-titanium dioxide biochar spherical gel adsorbent).

[0091] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0092] Example 1

[0093] A method for preparing a chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent comprises the following steps:

[0094] (1) Preparing titanium dioxide colloid by sol-gel method;

[0095] (2) mixing the titanium dioxide colloid obtained in step (1) with bamboo shoot shell powder, stirring at a speed of 180 r / min for 20 min, standing for 12 h, and drying at 80° C. for 12 h. After drying, grinding and passing through a 100-mesh sieve to make the particle size of the ground powder less than 0.15 mm to obtain a xerogel. After calcining the obtained xerogel at 500° C. for 3 h, cooling to room temperature, grinding, passing through a 100-mesh sieve to make the particle size of the ground powder less than 0.15 mm, and obtaining a nano-titanium dioxide-coated bamboo shoot shell biochar material; the mass ratio of the titanium dioxide colloid to the bamboo shoot shell powder is 297:7;

[0096] (3) The nano-titanium dioxide-coated bamboo shoot biochar material obtained in step (2) is mixed with the chitosan solution, and then added dropwise to a 0.5 mol / L NaOH solution at a rate of 0.05 mL / 2 s using a syringe, and allowed to stand in the NaOH solution for 24 h. After standing, the mixture is sieved with a sieve spoon, and the sieved microspheres are rinsed with deionized water until the pH of the cleaning solution is neutral, thereby obtaining microspheres; the solvent in the chitosan solution is acetic acid solution; the volume concentration of the acetic acid solution is 2%; the content of chitosan in the chitosan solution is 0.04 g / mL by mass to the volume ratio of the acetic acid solution; the mass ratio of the nano-titanium dioxide-coated bamboo shoot biochar material to the chitosan is 1:2;

[0097] (4) mixing the microspheres obtained in step (3) with a glutaraldehyde solution and allowing the mixture to stand for 24 hours for a cross-linking reaction, then separating the mixture with a sieve spoon, and allowing the cross-linked product to air-dry naturally in a culture dish to obtain a chitosan-nano-titanium dioxide-coated bamboo shoot biochar adsorbent; the solvent in the glutaraldehyde solution is methanol; and the volume content of glutaraldehyde in the glutaraldehyde solution is 9%;

[0098] The specific operation of preparing titanium dioxide colloid by the sol-gel method is preferably:

[0099] (a) Mix 15 mL of water, 20 mL of ethanol, and 10 mL of acetic acid to obtain a mixture A;

[0100] (b) mixing 10 mL of isopropyl titanate with 30 mL of ethanol to obtain a mixed solution B;

[0101] (c) adding the mixed solution A obtained in step (a) dropwise to the mixed solution B obtained in step (b) at a rate of 0.05 mL / 2 s, stirring at a speed of 180 r / min for 10 min to obtain a titanium dioxide colloid; the adding was carried out under stirring; the stirring speed was 180 r / min;

[0102] There is no order of precedence for steps (a) and (b);

[0103] The preparation process of the bamboo shoot shell powder is as follows: the bamboo shoot shells are washed with deionized water three times in sequence, dried at 80° C. for 2 days, crushed, and passed through a 100-mesh sieve to obtain the bamboo shoot shell powder.

[0104] The scanning electron microscope image of the chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 at 5000 times is as follows: Figure 2 As shown, from Figure 2 It can be seen that the prepared chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent is a microsphere.

[0105] The scanning electron microscopy images of the chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 at 30,000 and 50,000 times magnification are as follows: Figure 3 As shown, from Figure 3 It can be seen that the surface of the prepared chitosan-nano-titanium dioxide coated bamboo shoot biochar adsorbent is porous, and the spherical particles on the surface of the microspheres are closely arranged, which is the morphological feature of nano-titanium dioxide with good crystal form. These spherical particles are closely arranged around the pores formed by biochar. It can be seen from the morphology diagram that it has good crystal form and pore structure.

[0106] Comparative Example 1

[0107] A method for preparing a chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent comprises the following steps:

[0108] (1) Preparing titanium dioxide colloid by sol-gel method;

[0109] (2) mixing the titanium dioxide colloid obtained in step (1) with bamboo shoot shell powder, stirring at a speed of 180 r / min for 20 min, standing for 12 h, drying at 80° C. for 12 h, grinding after drying and passing through a 100-mesh sieve to make the particle size of the ground powder less than 0.15 mm, thereby obtaining a xerogel; calcining the obtained xerogel at 400° C. for 3 h, cooling to room temperature, grinding, passing through a 100-mesh sieve, and making the particle size of the ground powder less than 0.15 mm, thereby obtaining a nano-titanium dioxide-coated bamboo shoot shell biochar material; the mass ratio of the titanium source in the titanium dioxide colloid to the bamboo shoot shell powder is 297:7 g;

[0110] (3) The nano-titanium dioxide-coated bamboo shoot biochar material obtained in step (2) is mixed with the chitosan solution, and then added dropwise to a 0.5 mol / L NaOH solution at a rate of 0.05 mL / 2 s using a syringe, and allowed to stand in the NaOH solution for 24 h. After standing, the mixture is sieved with a sieve spoon, and the sieved microspheres are rinsed with deionized water until the pH of the cleaning solution is neutral, thereby obtaining microspheres; the solvent in the chitosan solution is acetic acid solution; the volume concentration of the acetic acid solution is 2%; the content of chitosan in the chitosan solution is 0.04 g / mL; the mass ratio of the nano-titanium dioxide-coated bamboo shoot biochar material to chitosan is 1:2;

[0111] (4) mixing the microspheres obtained in step (3) with a glutaraldehyde solution and allowing the mixture to stand for 24 hours for a cross-linking reaction, then separating the mixture with a sieve spoon, and allowing the cross-linked product to air-dry naturally in a culture dish to obtain a chitosan-nano-titanium dioxide-coated bamboo shoot biochar adsorbent; the solvent in the glutaraldehyde solution is methanol; and the volume content of glutaraldehyde in the glutaraldehyde solution is 9%;

[0112] The specific operation of preparing titanium dioxide colloid by the sol-gel method is preferably:

[0113] (a) Mix 15 mL of water, 20 mL of ethanol, and 10 mL of acetic acid to obtain a mixture A;

[0114] (b) mixing 10 mL of isopropyl titanate with 30 mL of ethanol to obtain a mixed solution B;

[0115] (c) adding the mixed solution A obtained in step (a) dropwise to the mixed solution B obtained in step (b) at a rate of 0.05 mL / 2 s, stirring at a speed of 180 r / min for 10 min to obtain a titanium dioxide colloid; the adding was carried out under stirring; the stirring speed was 180 r / min;

[0116] There is no order of precedence for steps (a) and (b);

[0117] The preparation process of the bamboo shoot shell powder is as follows: the bamboo shoot shells are washed with deionized water three times in sequence, dried at 80° C. for 2 days, crushed, and passed through a 100-mesh sieve to obtain the bamboo shoot shell powder.

[0118] Application Example 1 and Comparative Application Example 1

[0119] 30 mg of the chitosan-nano-titanium dioxide-coated bamboo shoot shell biochar adsorbent prepared in Example 1 and Comparative Example 1 was added to 100 mL of a solution with a silver ion content of 50 mg / L, and placed in a water bath constant temperature oscillator for continuous adsorption at 25°C and 180 r / min for 20 hours. After filtering with a 0.45 μm filter head, the filtrate was used to determine the concentration of the adsorbed silver ion solution by atomic absorption spectrometry.

[0120] The total pore volume, average pore diameter and specific surface area of ​​the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 and Comparative Example 1 were tested by a BET specific surface area tester.

[0121] Table 1 Total pore volume, average pore diameter and specific surface area of ​​chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 and Comparative Example 1

[0122] Example <![CDATA[Total pore volume (cm 3 / g)]]> Average pore size (μm) <![CDATA[Specific surface area (m 2 / g)]]> Example 1 0.154968 0.0052737 117.5396 Comparative Example 1 0.036797 0.0009792 56.38

[0123] It can be seen from Table 1 that the specific surface area of ​​the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Comparative Example 1 is significantly lower than that in Example 1. This is because the combustion temperature of the muffle furnace is low, and the optimal time point for firing titanium dioxide and biochar is not reached, so that the titanium dioxide crystal form is not well presented, and the biochar porosity is not optimal. Therefore, the specific surface area, pore volume and average pore size are all reduced. In addition to the change in specific surface area, the performance of the microsphere adsorbents prepared by the two processes of Example 1 and Comparative Example 1 is compared. The equilibrium adsorption rate of the adsorbent prepared by Example 1 for 50 mg / L silver ion solution reaches 86%, while the equilibrium adsorption rate of the adsorbent prepared by Comparative Example 1 for 50 mg / L silver ion solution only reaches 69%. This performance difference is due to the difference in firing temperature. The firing temperature of Comparative Example 1 is not enough to allow the titanium dioxide crystal form to be formed, and the Ti-O bond in titanium dioxide cannot play a major role in adsorption. In addition, the formation of biochar porosity has certain requirements on temperature. Too high or too low temperature will affect the adsorption effect of biochar. The firing temperature of 400°C in Example 1 did not completely burn the biochar, and the pore size and pore volume did not reach the optimal values. Therefore, the temperature was controlled to be the optimal firing temperature in Example 1. The ratio and firing time and temperature in Example 1 are all the optimal conditions for preparing chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent.

[0124] The scanning electron microscope image of the chitosan-nano titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 after adsorbing silver ions is as follows: Figure 4 As shown, from Figure 4 It can be seen that a large amount of silver ions ( Figure 4 The results show that the chitosan-nano-titanium dioxide-coated bamboo shoot shell biochar adsorbent prepared in Example 1 has a good ability to adsorb metallic silver.

[0125] The adsorption performance of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 was tested, and the silver ion solution concentrations before and after adsorption of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent were 50 mg / L and 7 mg / L, respectively. The chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent had an adsorption rate of 80% for silver ions in wastewater in 1.5 hours, which was 24 hours after other biochar-modified adsorption materials for silver adsorption. The chitosan-nano-titanium dioxide coated bamboo shoot shell biochar microsphere adsorbent had a rapid adsorption efficiency for silver ions. Compared with powder adsorbents, the microsphere adsorbent had a more convenient and green recycling method, and would not cause incomplete secondary pollution of water bodies. The chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared in Example 1 of the present invention had a final equilibrium adsorption rate of 86%, a maximum monolayer adsorption capacity of 248 mg / g, and excellent ability to adsorb precious metal silver.

[0126] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent, comprising the following steps: (1) Preparing titanium dioxide colloid by sol-gel method; (2) mixing the titanium dioxide colloid obtained in step (1) with bamboo shoot shell powder, and then sequentially allowing the mixture to stand and calcining the mixture to obtain a nano-titanium dioxide-coated bamboo shoot shell biochar material; (3) mixing the nano-titanium dioxide-coated bamboo shoot shell biochar material obtained in step (2) with a chitosan solution and then adding the mixture dropwise to the coagulation solution to obtain microspheres; (4) mixing the microspheres obtained in step (3) with a glutaraldehyde solution to carry out a cross-linking reaction to obtain a chitosan-nano-titanium dioxide-coated bamboo shoot shell biochar adsorbent; In the step (2), the mass ratio of titanium dioxide colloid to bamboo shoot shell powder is (280-360): (7-8); The calcination temperature in step (2) is 500-600° C. and the calcination time is 3-4 hours; In the step (3), the mass ratio of the nano-titanium dioxide-coated bamboo shoot shell biochar material to the chitosan in the chitosan solution is (1-1.2): (1.8-2).

2. The preparation method according to claim 1, wherein: The particle size of the bamboo shoot shell powder in step (2) is less than 0.15 mm.

3. The preparation method according to claim 1, wherein: The content of chitosan in the chitosan solution in step (3) is (0.036-0.05) g / mL.

4. The preparation method according to claim 1, wherein: The coagulation solution in step (3) is a NaOH solution; the concentration of the NaOH solution is 0.45 to 0.55 mol / L.

5. The preparation method according to claim 1, wherein: The volume content of glutaraldehyde in the glutaraldehyde solution in step (4) is 8-10%.

6. The chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the chitosan-nano-titanium dioxide coated bamboo shoot shell biochar adsorbent according to claim 6 in adsorbing precious metal silver.

Images