Cellulose microsphere-based composite catalyst and preparation method thereof
Patent Information
- Application Number
- CN202611312221.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-27
- Publication Date
- 2026-09-25
Smart Images
Figure CN122806470A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of catalytic materials technology, specifically to a cellulose microsphere-based composite catalyst and its preparation method. Background Technology
[0002] Dyeing and printing wastewater contains a large amount of complex organic pollutants, characterized by high color, high chemical oxygen demand (COD), and recalcitrant biodegradability; at the same time, it often contains heavy metal ions (such as Pb). 2+ Cu 2+ Cd 2+ Pollution from both types of pollutants (such as...) coexists in the same water body and accumulates, further increasing the difficulty of treatment.
[0003] Existing technologies for treating dyeing and printing wastewater mainly include physical adsorption, chemical oxidation, and biological treatment. Physical adsorption is relatively simple to operate, but the adsorbent has a low saturation capacity, requiring frequent replacement. Furthermore, improper handling of saturated adsorbents can easily cause secondary pollution. While chemical oxidation can effectively degrade some organic pollutants, it easily produces toxic and harmful intermediate products during the reaction and consumes large amounts of chemical reagents. In recent years, nanocatalysis has become a research hotspot. Metal nanoparticles (such as Pt, Pd, and Au) exhibit excellent catalytic degradation performance due to their high specific surface area and unique quantum size effect. To address the problems of easy aggregation and difficulty in recycling of metal nanoparticles, researchers have loaded them onto support materials. Cellulose, due to its wide availability, renewability, and rich hydroxyl content, is considered an ideal catalyst support material. Existing literature reports the application of cellulose-supported platinum and palladium nanoparticles in catalytic hydrogenation reactions, with cellulose-supported platinum nanoparticles exhibiting better stability than palladium nanoparticles.
[0004] However, existing cellulose-based catalysts still have the following shortcomings. First, they are functionally limited and struggle to address complex pollution scenarios involving both dyes and heavy metals. While existing quaternized cellulose materials can utilize the positive charge of quaternary ammonium groups to adsorb negatively charged dyes, quaternization only imparts electrostatic adsorption capabilities, lacking effective chelation of heavy metal ions and catalytic degradation of organic pollutants. Other organic modifiers, although introducing coordinating groups, are mostly monofunctional, providing only a single coordinating atom with low complexation constants, limiting their ability to bind heavy metal ions and failing to simultaneously achieve adsorption and enrichment of organic pollutants. Second, precious metal anchoring is weak, leading to easy leaching and deactivation. Traditional cellulose supports rely solely on weak physical adsorption of hydroxyl groups or monodentate coordination to immobilize metal particles, resulting in weak binding forces. During catalytic reactions, metal particles easily detach and dissolve from the support, causing rapid catalytic activity decay. Existing literature also indicates that even with successful loading of metal nanoparticles, metal leaching from the support surface remains a major problem for cellulose-supported catalysts. Furthermore, existing modification methods struggle to simultaneously achieve functionalization and unobstructed pores. The porous structure of cellulose is crucial for its adsorption and loading functions; however, existing modification methods, such as chemical oxidation to pre-introduce active groups, inevitably lead to cellulose molecular chain breakage and decreased mechanical strength. If a functional layer is introduced through physical coating, it easily clogs the pores, and the lack of chemical bonding between the coating and the substrate makes it prone to detachment during water rinsing and recycling. While chemical modifications such as quaternization and carboxymethylation can avoid pore clogging, they only provide a single function. These technical problems are mutually restrictive, and no existing technology can simultaneously achieve multifunctional integration of quaternization electrostatic adsorption, multidentate chelation of heavy metals, and stable loading of noble metals.
[0005] Therefore, developing a cellulose microsphere-based composite catalyst that can efficiently adsorb dyes and heavy metal ions, stably support platinum nanoparticles, and not damage the pore structure of the support is of great practical significance and application value. Summary of the Invention
[0006] To address the aforementioned technical problems, this invention provides a cellulose microsphere-based composite catalyst and its preparation method.
[0007] The technical solutions provided by the embodiments of the present invention are as follows:
[0008] A method for preparing a cellulose microsphere-based composite catalyst includes the following steps:
[0009] S1. Carboxymethylation modification of cellulose:
[0010] Cotton lint cellulose was alkalized in an aqueous sodium hydroxide solution at 20-30℃ for 0.5-2 hours to obtain basic cellulose; the basic cellulose was transferred to an aqueous ethanol solution, monochloroacetic acid was added, and the mixture was reacted at 50-60℃ for 2-5 hours. After the reaction was completed, the pH was adjusted to neutral, and the mixture was washed and dried to obtain carboxymethylated cellulose.
[0011] Step S1 above is the carboxymethylation reaction of cellulose:
[0012] The hydroxyl groups (-OH) on the cellulose molecular chain of cotton linters undergo an acid-base reaction with sodium hydroxide to generate sodium hydroxide active centers. At the same time, sodium hydroxide causes the cellulose to swell fully, which is conducive to the diffusion and penetration of subsequent etherification reagents into the cellulose skeleton.
[0013] Basic cellulose is transferred to an aqueous ethanol solution, and monochloroacetic acid is added. The reaction is carried out at 50-60℃. Under alkaline conditions, monochloroacetic acid is neutralized by sodium hydroxide to form sodium chloroacetate. The chloromethyl carbon atom in the sodium chloroacetate molecule has a strong positive charge due to the double electron-withdrawing effect of the ortho-carbonyl group and the chlorine atom. This carbon atom is subjected to nucleophilic attack by the alkoxide anion of basic cellulose. The chloride ion leaves as a leaving group. The oxygen atom on the hydroxyl group of basic cellulose forms an ether bond with the methylene carbon atom of sodium chloroacetate, thereby completing the substitution reaction and generating carboxymethyl cellulose.
[0014] The reaction mainly occurs at the C6 primary hydroxyl group, which has the highest reactivity in each glucose unit. When the degree of substitution is low, the reaction preferentially occurs at the C6 position. As the reaction progresses, the secondary hydroxyl groups at the C2 and C3 positions can also participate in the reaction. After the reaction is completed, the pH is adjusted to neutral to convert sodium carboxymethyl cellulose into carboxymethyl cellulose acid or sodium salt form. Unreacted monochloroacetic acid and the byproduct sodium chloride are removed by washing with an ethanol-water solution. After drying, carboxymethyl cellulose is obtained. Throughout the process, ethanol, as a reaction medium, can inhibit excessive swelling of cellulose and promote the diffusion of etherifying agents into the cellulose molecular chain, while reducing the occurrence of side reactions.
[0015] S2, Quaternization modification of carboxymethyl cellulose:
[0016] Carboxymethyl cellulose was dispersed in deionized water, and sodium hydroxide was added to adjust the pH to 10-12. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, and the mixture was reacted at 60-80℃ for 6-15 h. After the reaction was completed, the pH was adjusted to neutral, and the mixture was washed and dried to obtain carboxymethyl-quaternary ammonium dual-modified cellulose.
[0017] Carboxymethyl cellulose was dispersed in deionized water and adjusted to alkalinity. At this time, the remaining hydroxyl groups on the carboxymethyl cellulose molecular chain that did not participate in carboxymethylation were activated under alkaline conditions to form alkoxy anions. At the same time, the alkaline environment also provided the necessary nucleophilic substitution conditions for the subsequent etherification reaction.
[0018] Upon addition of 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC), this quaternizing agent first undergoes an intramolecular cyclization reaction under alkaline conditions. The chlorine atom in the molecule and the ortho-hydroxyl group lose hydrogen chloride under alkaline conditions, forming a highly reactive glycidyltrimethylammonium chloride intermediate. The three-membered ring ether structure in this epoxy intermediate is highly strained and unstable. The methylene carbon atom on the epoxy ring is subjected to nucleophilic attack by the cellulose oxyanion, opening the epoxy ring. A new ether bond is formed between the carboxymethylated cellulose oxyanion and the methylene carbon atom on the epoxy ring. Simultaneously, the hydroxyl group generates a secondary hydroxyl group with the ring opening, and the quaternary ammonium group is introduced as a side chain into the cellulose backbone, ultimately forming a 2-chloro-2-hydroxypropyltrimethylammonium chloride intermediate. Hydroxy-3-(trimethylammonium)propoxy cellulose ether. In addition, the carboxyl group introduced by carboxylation in the system is also converted into a carboxylate anion under alkaline conditions. The carboxylate anion is also nucleophilic and can attack the methylene carbon atom on the epoxy ring to generate ester bond byproducts. However, the ester bond is unstable under strongly alkaline reaction conditions of 60-80℃ and during the subsequent washing process. It is easy to undergo hydrolysis to regenerate the carboxyl group. Therefore, the carboxyl group is retained after the quaternization reaction and is not consumed, providing sufficient active sites for subsequent amidation grafting. This reaction mainly occurs on the primary hydroxyl group at C6 on the carboxymethylated cellulose molecular chain. The secondary hydroxyl groups at C2 and C3 can also participate in the reaction, but their activity is low.
[0019] The introduction of quaternary ammonium groups endows carboxymethyl-quaternary ammonium dual-modified cellulose with a permanent positive charge, which is independent of the pH of the solution. This allows it to adsorb negatively charged dye molecules and platinum precursor [PtCl6]2- through electrostatic interactions over a wide pH range. The reaction temperature needs to be controlled at 60-80℃. If the temperature is too low, the ring-opening reaction rate of the epoxy intermediate will be insufficient, while if the temperature is too high, the decomposition of the quaternization reagent will be accelerated and the carboxymethyl-quaternary ammonium dual-modified cellulose skeleton may be thermally degraded. A reaction time of 6-15h can achieve a relatively sufficient degree of substitution in the quaternization reaction. After the reaction is completed, the pH is adjusted to neutral to terminate the reaction and stabilize the product. Unreacted CHPTAC and the byproduct sodium chloride are removed by washing with deionized water and ethanol. After drying, carboxymethyl-quaternary ammonium dual-modified cellulose is obtained.
[0020] In the S1 and S2 steps, a carboxyl group is preferentially introduced at the C6 position of cellulose, and quaternization further introduces a quaternary ammonium group on the remaining hydroxyl group. By controlling the degree of substitution of the two functional groups stepwise, the substitution competition between the two etherifying agents on the same hydroxyl group during the simultaneous reaction is avoided, so that the functional group ratio of the product has better controllability and batch repeatability.
[0021] S3, amidation grafting:
[0022] Carboxymethyl-quaternary ammonium dual-modified cellulose was dissolved in phosphate buffer, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added to activate the carboxyl groups for 20-60 min. N-(carbamoylmethyl)iminodiacetic acid was added, and the reaction was stirred at room temperature for 6-24 h. After the reaction was completed, the cellulose was purified by dialysis with deionized water or repeated washing and freeze-drying to obtain the modified cellulose.
[0023] Phosphate buffer can maintain a stable weakly acidic environment in the system, ensuring that N-(carbamoylmethyl)iminodiacetic acid exists in the form of a primary amino group (-NH2), with the free amino group serving as a nucleophilic group for subsequent amidation reactions;
[0024] Upon addition of 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS), EDC first reacts with the carboxyl group (-COOH) on the carboxymethyl-quaternary ammonium double-modified cellulose backbone. The carbodiimide group in the EDC molecule undergoes nucleophilic addition with the hydroxyl oxygen in the carboxyl group, forming an unstable O-acylisourea reactive intermediate. This intermediate is extremely unstable and readily hydrolyzes back to the carboxyl group in solution or undergoes intramolecular rearrangement to generate a stable N-acylurea byproduct. The addition of NHS to the system allows for rapid reaction with the O-acylisourea intermediate. The carbonyl carbon on the carboxyl group is nucleophilically attacked by the oxygen atom of NHS, generating an NHS-active ester intermediate with a longer half-life and higher stability. The carbonyl carbon of this active ester has a strong positive charge and exhibits good reactivity against external nucleophilic reagents. Simultaneously, the introduction of NHS effectively inhibits the hydrolysis and rearrangement side reactions of the O-acylisourea intermediate in the aqueous phase, significantly improving the activation efficiency of the carboxyl group.
[0025] Upon addition of N-(carbamoylmethyl)iminodiacetic acid (ADA), the primary amino group (-NH2) on N-(carbamoylmethyl)iminodiacetic acid acts as a nucleophilic group, attacking the carbonyl carbon of the NHS-active ester in a nucleophilic addition-elimination reaction. The lone pair electrons on the amino group attack the carbonyl carbon to form a tetrahedral intermediate. Subsequently, NHS is eliminated as a leaving group, and a stable amide bond (-CO-NH-) is formed between the primary amino group and the carboxyl group. Thus, the N-(carbamoylmethyl)iminodiacetic acid group is covalently grafted onto the carboxymethyl-quaternary ammonium double-modified cellulose backbone.
[0026] A reaction at room temperature for 8-24 hours can ensure that the amidation reaction reaches a sufficient grafting rate. After the reaction, unreacted N-(carbamoylmethyl)iminodiacetic acid, EDC, NHS and byproducts are removed by dialysis or repeated washing with water. The modified cellulose is then obtained by freeze drying.
[0027] S4. Preparation and Pore Formation of Cellulose Solution
[0028] Modified cellulose was added to a urea / sodium hydroxide / water solution pre-cooled to -5℃, wherein the mass ratio of urea, sodium hydroxide and water was 12-15:7-9:78-81. The solution was stirred until completely dissolved to obtain a transparent cellulose solution. A composite pore-forming agent was added to the transparent cellulose solution and stirred at 0-10℃ to disperse it evenly.
[0029] Sodium hydroxide forms a highly polar solvent system with water. The hydroxide ions and sodium ions provided by sodium hydroxide can break the hydrogen bonds between the modified cellulose molecular chains and the hydrogen bonds within the molecular chains, thus opening up the tightly packed crystal structure of the modified cellulose. Under low temperature conditions, urea molecules form new hydrogen bonds with the cellulose hydroxyl groups through their carbonyl oxygen and amino hydrogen, surrounding the exposed modified cellulose molecular chains to form urea-cellulose inclusion complexes, preventing the modified cellulose molecular chains from re-aggregating due to the hydrogen bonding between hydroxyl groups.
[0030] The entire dissolution process was carried out at a low temperature of -5℃. The low temperature enhanced the stability of sodium hydroxide hydrate and urea hydrate, weakened the hydrophobic interactions and hydrogen bond network between the modified cellulose molecular chains, and allowed solvent molecules to penetrate into the interior of the modified cellulose more effectively. At the same time, the quaternary ammonium groups, carboxymethyl groups and N-(carbamoylmethyl)iminodiacetic acid side chains grafted on the modified cellulose further disrupted the original ordered arrangement of the modified cellulose during the dissolution process, increased the spacing between the modified cellulose molecular chains, which was conducive to the penetration and diffusion of solvent molecules, thereby promoting the rapid dissolution of the modified cellulose.
[0031] S5, Suspension polymerization into spheres:
[0032] A modified cellulose solution containing a porogen was dropped into a paraffin oil suspension containing a surfactant at room temperature, and the mixture was stirred to disperse and solidify the cellulose solution to form microspheres.
[0033] A modified cellulose solution containing a composite porogen is dripped into paraffin oil containing Span80 through a needle. The solution forms spherical droplets at the tip of the needle and enters the oil phase. Span80 reduces the oil-water interfacial tension, preventing droplet aggregation and maintaining stable dispersion. The stirring shear force controls the droplet size and distribution. After the droplets are suspended in the oil phase, they slowly diffuse into the oil phase with trace amounts of water. Due to the change in the solvent environment, the modified cellulose molecular chains are physically cross-linked again through intermolecular hydrogen bonds, causing the droplets to change from a viscous flow state to a gel state, completing the shaping and solidification of cellulose microspheres, and the porogen is uniformly fixed in the gel network.
[0034] S6. Regeneration and Template Removal:
[0035] Add dilute hydrochloric acid to the suspension obtained in S5 to adjust the pH to 6-8, separate and remove the paraffin oil, soak the microspheres in dilute hydrochloric acid to dissolve and remove the nano-calcium carbonate template, and then wash with deionized water and ethanol in sequence to obtain cellulose microspheres, which are then stored in a wet state.
[0036] When dilute hydrochloric acid is added to adjust the pH to 6-8, the sodium alkoxides on the modified cellulose molecular chains are protonated by H+ to restore hydroxyl groups, while NaOH is neutralized. The modified cellulose precipitates out of the solution and regenerates due to a sharp decrease in solubility. The molecular chains reassociate through hydrogen bonds to form a three-dimensional network structure. After separating and removing the paraffin oil, the microspheres are soaked in dilute hydrochloric acid. + The reaction with nano-CaCO3 dissolves it into a soluble calcium salt, which is then removed, leaving interconnected channels. The reaction formula is as follows:
[0037] CaCO3 + 2H+ + →Ca 2+ +CO2↑+H2O
[0038] Deionized water washing removes residual acid and salt, ethanol washing removes residual paraffin oil and Span80, and wet preservation utilizes water molecules to occupy the pore space, preventing capillary forces from causing pore collapse during the drying process and keeping the pore structure unobstructed.
[0039] S7, In-situ loading of platinum nanoparticles:
[0040] Cellulose microspheres were immersed in a dilute hydrochloric acid solution of chloroplatinic acid, allowed to stand at room temperature, transferred to an ice-water bath at 0-4℃ for cooling, and freshly prepared sodium borohydride solution was added dropwise. The reduction reaction was carried out at 0-4℃ for 20-60 min. After the reaction was completed, the mixture was washed with deionized water to obtain a cellulose microsphere-based composite catalyst loaded with platinum nanoparticles.
[0041] Cellulose microspheres were immersed in a dilute hydrochloric acid solution of chloroplatinic acid, [PtCl6] 2- Driven by a concentration gradient, anions diffuse into the microsphere channels and are simultaneously enriched by quaternary ammonium groups through electrostatic adsorption. Residual hydroxyl groups on the modified cellulose backbone and the carboxyl groups of N-(carbamoylmethyl)iminodiacetic acid can also assist in the anchoring of Pt through coordination. 4+ After transferring the system to an ice-water bath at 0-4°C, NaBH4 and BH4 were added dropwise. - As a reducing agent, electrons are provided to reduce Pt4+ adsorbed in the pores to Pt atoms in situ. The Pt atoms rapidly nucleate and grow into nanoparticles. The low temperature condition inhibits the diffusion and migration of Pt atoms and the growth rate of grains, which is conducive to the formation of fine and uniformly sized platinum nanoparticles. At the same time, the in-situ reduction strategy allows some platinum nanoparticles to be confined and anchored by quaternary ammonium groups and carboxyl sites on the inner wall of the pores. High dispersion loading can be achieved without the addition of additional protective agents. After the reduction reaction, deionized water is used to wash away unreacted NaBH4 and byproducts. The platinum in the pores is anchored by both electrostatic adsorption and coordination chelation, making it less prone to dissolution and migration during the catalytic reaction.
[0042] Preferably, the average particle size of the platinum nanoparticles is 2-5 nm.
[0043] Preferably, the wet particle size of the cellulose microspheres is 0.4-1.2 mm.
[0044] Preferably, the molar ratio of monochloroacetic acid to basic cellulose glucose unit in S1 is 1.0-2.5:1, and the volume fraction of ethanol in the aqueous ethanol solution is 70-80%.
[0045] Preferably, the molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to carboxymethylated cellulose glucose units in S2 is 6-12:1.
[0046] Preferably, in S3, the molar ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide to carboxyl group is 1.0-2.0:1, the molar ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide to N-hydroxysuccinimide is 1:1, and the concentration of phosphate buffer is 0.05-0.20 mol / L.
[0047] Preferably, the composite porogen in S4 is composed of nano-calcium carbonate and polyethylene glycol in a mass ratio of 2-4:1, the nano-calcium carbonate has a particle size of 0.5-5μm, the polyethylene glycol has a molecular weight of 4000-8000, and the amount of composite porogen added is 3-10% of the mass of modified cellulose.
[0048] Preferably, in S7, the concentration of H2PtCl6 in the chloroplatinic acid solution is 0.5-5.0 mmol / L, the concentration of dilute hydrochloric acid is 10-50 mmol / L, the concentration of sodium borohydride solution is 0.05-0.20 mol / L, and the molar ratio of sodium borohydride to chloroplatinic acid is 5-20:1.
[0049] Compared with the prior art, the beneficial effects of the present invention are:
[0050] (1) In this invention, after introducing carboxyl groups through a stepwise etherification strategy, N-(carbamoylmethyl)iminodiacetic acid (ADA) molecules are covalently grafted onto the cellulose backbone using an EDC / NHS activated amidation reaction. The ADA molecule retains the complete polydentate chelate structure of amino and carboxyl groups, and the two nitrogen atoms and multiple carboxyl oxygen atoms in its molecule can react with heavy metal ions (Pb). 2+ Cu 2+ Cd 2 + It forms stable multidentate coordination chelates, solving the problems of existing monofunctional modifiers (aminosilane, mercaptoacetic acid, etc.) that can only provide monodentate coordination, have low complexation constants, and weak heavy metal binding capacity, thus achieving a significant increase in the saturated adsorption capacity of heavy metals; at the same time, the ADA group does not contain easily oxidized structures, and the chelation performance does not decay during long-term storage and use.
[0051] (2) This invention covalently fixes ADA molecules to the cellulose backbone via amide bonds. The ADA molecules and cellulose are connected by stable covalent bonds, which solves the problem of easy detachment and loss of existing physical coating modification layers during water rinsing and recycling, and ensures the long-term stability of adsorbed functional groups. The process route of first modifying the molecules and then forming the spheres is adopted, and the amidation grafting of ADA is completed before the cellulose is dissolved, avoiding pore blockage caused by post-molding modification, so that the porosity of the hierarchical pore structure is maintained at more than 75%. At the same time, the stepwise etherification strategy makes the degree of substitution of carboxyl and quaternary ammonium groups independently controllable, which solves the problems of competitive substitution of two etherification reagents at the same hydroxyl site, difficulty in independently controlling the degree of substitution, and poor batch repeatability in existing simultaneous modification.
[0052] (3) This invention utilizes the strong electrostatic adsorption of the quaternary ammonium group on the platinum precursor, combined with the coordination-assisted anchoring of the amino and carboxyl groups in the ADA molecule, to achieve the pre-enrichment of the platinum precursor in the microsphere channels. Then, it is reduced in situ by sodium borohydride at low temperature in an ice-water bath, forming a dual anchoring effect of electrostatic adsorption and multidentate coordination. This solves the problem that the traditional cellulose carrier relies solely on the weak physical adsorption of hydroxyl groups, which leads to easy aggregation and dissolution of platinum nanoparticles and deactivation. This allows the average particle size of the platinum nanoparticles to be controlled at 2-5 nm and uniformly distributed. During the recycling process, the platinum dissolution rate is significantly reduced, and the catalyst activity retention rate is around 90%.
[0053] (4) This invention uses nano-calcium carbonate and polyethylene glycol composite porogen. During the microsphere regeneration process, the calcium carbonate template is removed by acid hydrolysis with dilute hydrochloric acid. Combined with the effect of polyethylene glycol on adjusting the viscosity of the system and stabilizing the dispersion of the porogen, a three-dimensional interconnected mesoporous and macroporous structure is constructed. This solves the problems of poor pore connectivity and uneven distribution of porogen agglomeration in existing single porogens, and ensures the free diffusion channels of pollutant molecules and platinum precursors in the pores. The wet storage strategy avoids the pore collapse caused by capillary forces during the drying process, ensuring that the pore structure remains unobstructed during storage and use. Attached Figure Description
[0054] Figure 1 This is a scanning electron microscope image of the cellulose microsphere-based composite catalyst of the present invention. Detailed Implementation
[0055] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.
[0056] Example 1: Preparation of cellulose microsphere-based composite catalyst:
[0057] S1. Carboxymethylation modification of cellulose:
[0058] Cotton lint cellulose was alkalized in an aqueous sodium hydroxide solution at 25°C for 1 hour to obtain basic cellulose. The basic cellulose was then transferred to a 75% aqueous ethanol solution, and monochloroacetic acid was added. The molar ratio of monochloroacetic acid to glucose units of basic cellulose was 1.0:1. The reaction was carried out at 55°C for 3.5 hours. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was repeatedly washed with 75% ethanol and dried at 60°C to obtain carboxymethylated cellulose.
[0059] S2, Quaternization modification of carboxymethyl cellulose:
[0060] The carboxymethyl cellulose obtained in step S1 was dispersed in deionized water, and sodium hydroxide was added to adjust the pH to 11. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, with a molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to glucose units of carboxymethyl cellulose of 9:1. The reaction was carried out at 70°C for 10 h. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was washed with deionized water and ethanol in sequence. The mixture was then dried at 60°C to obtain carboxymethyl-quaternary ammonium dual-modified cellulose.
[0061] S3, amidation grafting:
[0062] The double-modified cellulose obtained in step S2 was dissolved in 0.1 mol / L phosphate buffer, and EDC (1.2 times the molar amount of carboxyl groups) and NHS were added (EDC:NHS = 1:1 molar ratio). The mixture was stirred at room temperature for 30 min to activate the carboxyl groups. N-(carbamoylmethyl)iminodiacetic acid (final concentration 2.0 g / L) was then added, and the reaction was stirred at room temperature for 12 h. After the reaction was completed, the mixture was purified by dialyzing with deionized water and freeze-dried to obtain the modified cellulose.
[0063] S4. Preparation and pore formation of cellulose solution:
[0064] Urea and sodium hydroxide were dissolved in deionized water at a mass ratio of 13:8:81. After stirring and dissolving, the solution was cooled to -5°C. The modified cellulose obtained in step S3 was added to the above cooled solution and stirred at high speed until completely dissolved to obtain a transparent cellulose solution.
[0065] 4% nano-calcium carbonate (by mass of modified cellulose) and 2% polyethylene glycol (by mass of modified cellulose) were mixed, ultrasonically dispersed, and then added to the above transparent cellulose solution. The mixture was stirred and dispersed evenly at 4°C.
[0066] S5, Suspension polymerization into spheres:
[0067] The modified cellulose solution containing the pore-forming agent was dripped into paraffin oil containing Span80 through a needle. The volume-to-mass ratio of paraffin oil to Span80 was 300 mL: 8 g. The mixture was stirred at 1000 rpm and stirred until the microspheres were solidified at room temperature after the addition was completed.
[0068] S6. Regeneration and Template Removal:
[0069] Add dilute hydrochloric acid to the suspension obtained in step S5 to adjust the pH to 7, so as to regenerate the cellulose microspheres. Let it stand and separate into layers, remove the paraffin oil, soak the microspheres in dilute hydrochloric acid (pH=4) to dissolve and remove the nano-calcium carbonate template, repeat the acid washing, wash with deionized water, and then wash with 70% ethanol. The obtained cellulose microspheres are stored in deionized water in a wet state.
[0070] S7, In-situ loading of platinum nanoparticles:
[0071] Chloroplatinic acid (H2PtCl6) was dissolved in 20 mmol / L dilute hydrochloric acid to prepare a platinum precursor solution with a concentration of 2.0 mmol / L. The wet microspheres obtained in step S6 were immersed in the above solution and allowed to stand at room temperature for 12 h. The solution was then transferred to an ice-water bath for cooling, and freshly prepared 0.1 mol / L NaBH4 solution was added dropwise. The molar ratio of NaBH4 to chloroplatinic acid was 10:1. The reduction reaction was carried out at 2 °C for 30 min. After the reaction was completed, the solution was washed with deionized water to obtain a cellulose microsphere-based composite catalyst loaded with platinum nanoparticles.
[0072] Example 2: Preparation of cellulose microsphere-based composite catalyst:
[0073] S1. Carboxymethylation modification of cellulose:
[0074] Cotton lint cellulose was alkalized in an aqueous sodium hydroxide solution at 25°C for 1 hour to obtain basic cellulose. The basic cellulose was then transferred to a 75% aqueous ethanol solution, and monochloroacetic acid was added. The molar ratio of monochloroacetic acid to glucose units of basic cellulose was 2.5:1. The reaction was carried out at 55°C for 3.5 hours. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was repeatedly washed with 75% ethanol and dried at 60°C to obtain carboxymethylated cellulose.
[0075] S2, Quaternization modification of carboxymethyl cellulose:
[0076] The carboxymethyl cellulose obtained in step S1 was dispersed in deionized water, and sodium hydroxide was added to adjust the pH to 11. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, with a molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to glucose units of carboxymethyl cellulose of 9:1. The reaction was carried out at 70°C for 10 h. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was washed with deionized water and ethanol in sequence. The mixture was then dried at 60°C to obtain carboxymethyl-quaternary ammonium dual-modified cellulose.
[0077] S3, amidation grafting:
[0078] The double-modified cellulose obtained in step S2 was dissolved in 0.1 mol / L phosphate buffer, and EDC (1.2 times the molar amount of carboxyl groups) and NHS were added (EDC:NHS = 1:1 molar ratio). The mixture was stirred at room temperature for 30 min to activate the carboxyl groups. N-(carbamoylmethyl)iminodiacetic acid (final concentration 2.0 g / L) was then added, and the reaction was stirred at room temperature for 12 h. After the reaction was completed, the mixture was purified by dialyzing with deionized water and freeze-dried to obtain the modified cellulose.
[0079] S4. Preparation and pore formation of cellulose solution:
[0080] Urea and sodium hydroxide were dissolved in deionized water at a mass ratio of 13:8:81. After stirring and dissolving, the solution was cooled to -5°C. The modified cellulose obtained in step S3 was added to the above cooled solution and stirred at high speed until completely dissolved to obtain a transparent cellulose solution.
[0081] 4% nano-calcium carbonate (by mass of modified cellulose) and 2% polyethylene glycol (by mass of modified cellulose) were mixed, ultrasonically dispersed, and then added to the above transparent cellulose solution. The mixture was stirred and dispersed evenly at 4°C.
[0082] S5, Suspension polymerization into spheres:
[0083] The modified cellulose solution containing the pore-forming agent was dripped into paraffin oil containing Span80 through a needle. The volume-to-mass ratio of paraffin oil to Span80 was 300 mL: 8 g. The mixture was stirred at 1000 rpm and stirred until the microspheres were solidified at room temperature after the addition was completed.
[0084] S6. Regeneration and Template Removal:
[0085] Add dilute hydrochloric acid to the suspension obtained in step S5 to adjust the pH to 7, so as to regenerate the cellulose microspheres. Let it stand and separate into layers, remove the paraffin oil, soak the microspheres in dilute hydrochloric acid (pH=4) to dissolve and remove the nano-calcium carbonate template, repeat the acid washing, wash with deionized water, and then wash with 70% ethanol. The obtained cellulose microspheres are stored in deionized water in a wet state.
[0086] S7, In-situ loading of platinum nanoparticles:
[0087] Chloroplatinic acid (H2PtCl6) was dissolved in 20 mmol / L dilute hydrochloric acid to prepare a platinum precursor solution with a concentration of 2.0 mmol / L. The wet microspheres obtained in step S6 were immersed in the above solution and allowed to stand at room temperature for 12 h. The solution was then transferred to an ice-water bath for cooling, and freshly prepared 0.1 mol / L NaBH4 solution was added dropwise. The molar ratio of NaBH4 to chloroplatinic acid was 10:1. The reduction reaction was carried out at 2 °C for 30 min. After the reaction was completed, the solution was washed with deionized water to obtain a cellulose microsphere-based composite catalyst loaded with platinum nanoparticles.
[0088] Example 3: Preparation of cellulose microsphere-based composite catalyst:
[0089] S1. Carboxymethylation modification of cellulose:
[0090] Cotton lint cellulose was alkalized in an aqueous sodium hydroxide solution at 25°C for 1 hour to obtain basic cellulose. The basic cellulose was then transferred to a 75% aqueous ethanol solution, and monochloroacetic acid was added. The molar ratio of monochloroacetic acid to glucose units of basic cellulose was 1.5:1. The reaction was carried out at 55°C for 3.5 hours. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was repeatedly washed with 75% ethanol and dried at 60°C to obtain carboxymethylated cellulose.
[0091] S2, Quaternization modification of carboxymethyl cellulose:
[0092] The carboxymethyl cellulose obtained in step S1 was dispersed in deionized water, sodium hydroxide was added to adjust the pH to 11, and 3-chloro-2-hydroxypropyltrimethylammonium chloride was added. The molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to the glucose unit of carboxymethyl cellulose was 6:1. The reaction was carried out at 70°C for 10 h. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was washed with deionized water and ethanol in sequence. The mixture was then dried at 60°C to obtain carboxymethyl-quaternary ammonium dual-modified cellulose.
[0093] S3, amidation grafting:
[0094] The double-modified cellulose obtained in step S2 was dissolved in 0.1 mol / L phosphate buffer, and EDC (1.2 times the molar amount of carboxyl groups) and NHS were added (EDC:NHS = 1:1 molar ratio). The mixture was stirred at room temperature for 30 min to activate the carboxyl groups. N-(carbamoylmethyl)iminodiacetic acid (final concentration 2.0 g / L) was then added, and the reaction was stirred at room temperature for 12 h. After the reaction was completed, the mixture was purified by dialyzing with deionized water and freeze-dried to obtain the modified cellulose.
[0095] S4. Preparation and pore formation of cellulose solution:
[0096] Urea and sodium hydroxide were dissolved in deionized water at a mass ratio of 13:8:81. After stirring and dissolving, the solution was cooled to -5°C. The modified cellulose obtained in step S3 was added to the above cooled solution and stirred at high speed until completely dissolved to obtain a transparent cellulose solution.
[0097] 4% nano-calcium carbonate (by mass of modified cellulose) and 2% polyethylene glycol (by mass of modified cellulose) were mixed, ultrasonically dispersed, and then added to the above transparent cellulose solution. The mixture was stirred and dispersed evenly at 4°C.
[0098] S5, Suspension polymerization into spheres:
[0099] The modified cellulose solution containing the pore-forming agent was dripped into paraffin oil containing Span80 through a needle. The volume-to-mass ratio of paraffin oil to Span80 was 300 mL: 8 g. The mixture was stirred at 1000 rpm and stirred until the microspheres were solidified at room temperature after the addition was completed.
[0100] S6. Regeneration and Template Removal:
[0101] Add dilute hydrochloric acid to the suspension obtained in step S5 to adjust the pH to 7, so as to regenerate the cellulose microspheres. Let it stand and separate into layers, remove the paraffin oil, soak the microspheres in dilute hydrochloric acid (pH=4) to dissolve and remove the nano-calcium carbonate template, repeat the acid washing, wash with deionized water, and then wash with 70% ethanol. The obtained cellulose microspheres are stored in deionized water in a wet state.
[0102] S7, In-situ loading of platinum nanoparticles:
[0103] Chloroplatinic acid (H2PtCl6) was dissolved in 20 mmol / L dilute hydrochloric acid to prepare a platinum precursor solution with a concentration of 2.0 mmol / L. The wet microspheres obtained in step S6 were immersed in the above solution and allowed to stand at room temperature for 12 h. The solution was then transferred to an ice-water bath for cooling, and freshly prepared 0.1 mol / L NaBH4 solution was added dropwise. The molar ratio of NaBH4 to chloroplatinic acid was 10:1. The reduction reaction was carried out at 2 °C for 30 min. After the reaction was completed, the solution was washed with deionized water to obtain a cellulose microsphere-based composite catalyst loaded with platinum nanoparticles.
[0104] Example 4: Preparation of cellulose microsphere-based composite catalyst:
[0105] S1. Carboxymethylation modification of cellulose:
[0106] Cotton lint cellulose was alkalized in an aqueous sodium hydroxide solution at 25°C for 1 hour to obtain basic cellulose. The basic cellulose was then transferred to a 75% aqueous ethanol solution, and monochloroacetic acid was added. The molar ratio of monochloroacetic acid to glucose units of basic cellulose was 1.5:1. The reaction was carried out at 55°C for 3.5 hours. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was repeatedly washed with 75% ethanol and dried at 60°C to obtain carboxymethylated cellulose.
[0107] S2, Quaternization modification of carboxymethyl cellulose:
[0108] The carboxymethyl cellulose obtained in step S1 was dispersed in deionized water, and sodium hydroxide was added to adjust the pH to 11. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, with a molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to glucose units of carboxymethyl cellulose of 9:1. The reaction was carried out at 70°C for 10 h. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was washed with deionized water and ethanol in sequence. The mixture was then dried at 60°C to obtain carboxymethyl-quaternary ammonium dual-modified cellulose.
[0109] S3, amidation grafting:
[0110] The double-modified cellulose obtained in step S2 was dissolved in 0.1 mol / L phosphate buffer, and EDC (1.2 times the molar amount of carboxyl groups) and NHS were added (EDC:NHS = 1:1 molar ratio). The mixture was stirred at room temperature for 30 min to activate the carboxyl groups. N-(carbamoylmethyl)iminodiacetic acid (final concentration 2.0 g / L) was then added, and the reaction was stirred at room temperature for 12 h. After the reaction was completed, the mixture was purified by dialyzing with deionized water and freeze-dried to obtain the modified cellulose.
[0111] S4. Preparation and pore formation of cellulose solution:
[0112] Urea and sodium hydroxide were dissolved in deionized water at a mass ratio of 13:8:81. After stirring and dissolving, the solution was cooled to -5°C. The modified cellulose obtained in step S3 was added to the above cooled solution and stirred at high speed until completely dissolved to obtain a transparent cellulose solution.
[0113] 2% nano-calcium carbonate (by mass of modified cellulose) and 1% polyethylene glycol (by mass of modified cellulose) were mixed, ultrasonically dispersed, and then added to the above transparent cellulose solution. The mixture was stirred and dispersed evenly at 4°C.
[0114] S5, Suspension polymerization into spheres:
[0115] The modified cellulose solution containing the pore-forming agent was dripped into paraffin oil containing Span80 through a needle. The volume-to-mass ratio of paraffin oil to Span80 was 300 mL: 8 g. The mixture was stirred at 1000 rpm and stirred until the microspheres were solidified at room temperature after the addition was completed.
[0116] S6. Regeneration and Template Removal:
[0117] Add dilute hydrochloric acid to the suspension obtained in step S5 to adjust the pH to 7, so as to regenerate the cellulose microspheres. Let it stand and separate into layers, remove the paraffin oil, soak the microspheres in dilute hydrochloric acid (pH=4) to dissolve and remove the nano-calcium carbonate template, repeat the acid washing, wash with deionized water, and then wash with 70% ethanol. The obtained cellulose microspheres are stored in deionized water in a wet state.
[0118] S7, In-situ loading of platinum nanoparticles:
[0119] Chloroplatinic acid (H2PtCl6) was dissolved in 20 mmol / L dilute hydrochloric acid to prepare a platinum precursor solution with a concentration of 2.0 mmol / L. The wet microspheres obtained in step S6 were immersed in the above solution and allowed to stand at room temperature for 12 h. The solution was then transferred to an ice-water bath for cooling, and freshly prepared 0.1 mol / L NaBH4 solution was added dropwise. The molar ratio of NaBH4 to chloroplatinic acid was 10:1. The reduction reaction was carried out at 2 °C for 30 min. After the reaction was completed, the solution was washed with deionized water to obtain a cellulose microsphere-based composite catalyst loaded with platinum nanoparticles.
[0120] Example 5: Preparation of cellulose microsphere-based composite catalyst:
[0121] S1. Carboxymethylation modification of cellulose:
[0122] Cotton lint cellulose was alkalized in an aqueous sodium hydroxide solution at 25°C for 1 hour to obtain basic cellulose. The basic cellulose was then transferred to a 75% aqueous ethanol solution, and monochloroacetic acid was added. The molar ratio of monochloroacetic acid to glucose units of basic cellulose was 1.5:1. The reaction was carried out at 55°C for 3.5 hours. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was repeatedly washed with 75% ethanol and dried at 60°C to obtain carboxymethylated cellulose.
[0123] S2, Quaternization modification of carboxymethyl cellulose:
[0124] The carboxymethyl cellulose obtained in step S1 was dispersed in deionized water, and sodium hydroxide was added to adjust the pH to 11. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, with a molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to glucose units of carboxymethyl cellulose of 9:1. The reaction was carried out at 70°C for 10 h. After the reaction was completed, the pH was adjusted to 7 with dilute hydrochloric acid, and the mixture was washed with deionized water and ethanol in sequence. The mixture was then dried at 60°C to obtain carboxymethyl-quaternary ammonium dual-modified cellulose.
[0125] S3, amidation grafting:
[0126] The double-modified cellulose obtained in step S2 was dissolved in 0.1 mol / L phosphate buffer, and EDC (1.2 times the molar amount of carboxyl groups) and NHS were added (EDC:NHS = 1:1 molar ratio). The mixture was stirred at room temperature for 30 min to activate the carboxyl groups. N-(carbamoylmethyl)iminodiacetic acid (final concentration 2.0 g / L) was then added, and the reaction was stirred at room temperature for 12 h. After the reaction was completed, the mixture was purified by dialyzing with deionized water and freeze-dried to obtain the modified cellulose.
[0127] S4. Preparation and pore formation of cellulose solution:
[0128] Urea and sodium hydroxide were dissolved in deionized water at a mass ratio of 13:8:81. After stirring and dissolving, the solution was cooled to -5°C. The modified cellulose obtained in step S3 was added to the above cooled solution and stirred at high speed until completely dissolved to obtain a transparent cellulose solution.
[0129] 4% nano-calcium carbonate (by mass of modified cellulose) and 2% polyethylene glycol (by mass of modified cellulose) were mixed, ultrasonically dispersed, and then added to the above transparent cellulose solution. The mixture was stirred and dispersed evenly at 4°C.
[0130] S5, Suspension polymerization into spheres:
[0131] The modified cellulose solution containing the pore-forming agent was dripped into paraffin oil containing Span80 through a needle. The volume-to-mass ratio of paraffin oil to Span80 was 300 mL: 8 g. The mixture was stirred at 1000 rpm and stirred until the microspheres were solidified at room temperature after the addition was completed.
[0132] S6. Regeneration and Template Removal:
[0133] Add dilute hydrochloric acid to the suspension obtained in step S5 to adjust the pH to 7, so as to regenerate the cellulose microspheres. Let it stand and separate into layers, remove the paraffin oil, soak the microspheres in dilute hydrochloric acid (pH=4) to dissolve and remove the nano-calcium carbonate template, repeat the acid washing, wash with deionized water, and then wash with 70% ethanol. The obtained cellulose microspheres are stored in deionized water in a wet state.
[0134] S7, In-situ loading of platinum nanoparticles:
[0135] Chloroplatinic acid (H2PtCl6) was dissolved in 20 mmol / L dilute hydrochloric acid to prepare a platinum precursor solution with a concentration of 2.0 mmol / L. The wet microspheres obtained in step S6 were immersed in the above solution and allowed to stand at room temperature for 12 h. The solution was then transferred to an ice-water bath for cooling, and freshly prepared 0.1 mol / L NaBH4 solution was added dropwise. The molar ratio of NaBH4 to chloroplatinic acid was 10:1. The reduction reaction was carried out at 2 °C for 30 min. After the reaction was completed, the solution was washed with deionized water to obtain a cellulose microsphere-based composite catalyst loaded with platinum nanoparticles.
[0136] Comparative Example 1:
[0137] Compared with Example 5, the quaternization modification in step S2 was omitted in Comparative Example 1. That is, the carboxymethyl cellulose obtained in step S1 was directly subjected to amidation grafting in step S3, and other experimental conditions remained unchanged.
[0138] Comparative Example 2:
[0139] Compared with Example 5, the amidation grafting in step S3 was omitted in Comparative Example 2. That is, the carboxymethyl-quaternary ammonium double-modified cellulose obtained in step S2 was directly subjected to step S4, and other experimental conditions remained unchanged.
[0140] Comparative Example 3:
[0141] Compared with Example 5, steps S1 and S2 in Comparative Example 3 were combined into a one-step simultaneous etherification, that is, after the cotton linter cellulose was alkalized, monochloroacetic acid and CHPTAC were added at the same time, and the reaction was carried out at 60°C for 8 hours to complete carboxymethylation and quaternization in one step, while other experimental conditions remained unchanged.
[0142] Comparative Example 4:
[0143] Compared with Example 5, in Comparative Example 4, the molecular modification in steps S1-S3 was not performed. Instead, unmodified cotton linter cellulose was directly used to form spheres and regenerate them in steps S4-S6 to obtain cellulose microspheres. Then, the cellulose microspheres were sequentially modified by carboxymethylation and quaternization, and finally, amidation grafting was performed according to step S3. Other experimental conditions remained unchanged.
[0144] Comparative Example 5:
[0145] Compared with Example 5, in Comparative Example 5, the molecular modification in steps S1-S3 was not performed. Instead, unmodified cotton linter cellulose was directly used to form spheres and regenerate them in steps S4-S6 to obtain cellulose microspheres, which were then loaded with platinum nanoparticles. Other experimental conditions remained unchanged.
[0146] Comparative Example 6:
[0147] Compared with Example 5, step S7 in Comparative Example 6 was changed to the impregnation-calcination method, that is, the cellulose microspheres were immersed in the platinum precursor solution and left to stand at room temperature for 12 hours, then taken out and dried, and reduced at 300°C under hydrogen atmosphere for 2 hours (instead of in-situ reduction with NaBH4 in an ice-water bath), while other experimental conditions remained unchanged.
[0148] Comparative Example 7:
[0149] Compared with Example 5, Comparative Example 7 did not add nano-calcium carbonate and polyethylene glycol composite porogen, while other experimental conditions remained unchanged.
[0150] Performance testing:
[0151] (1) Platinum loading determination: Inductively coupled plasma optical emission spectrometry (ICP-OES) was used to digest the platinum-loaded cellulose microspheres with aqua regia, and then the solution was brought to a certain volume. The concentration of platinum in the solution was measured and the platinum loading (wt%) was calculated.
[0152] (2) Platinum dissolution rate determination: A certain amount of catalyst was placed in deionized water and shaken at room temperature for 24 hours. The supernatant was taken and the platinum concentration was determined by ICP-OES, and the dissolution rate was calculated.
[0153] (3) Porosity determination: The ethanol replacement method was used. Accurately weigh the mass m1 of the wet microspheres, place them in a density bottle of known volume, add ethanol to the mark, and weigh the total mass m2; remove the microspheres, add ethanol to the mark, and weigh the mass m3. Calculate the porosity using the following formula:
[0154] P(%)=[(m2-m3-m1) / (ρ 乙醇 ×V 微球 )]×100%
[0155] (4) Catalytic performance test: Mix 10 mg / L sodium borohydride solution and 8 mg / L methyl orange solution in a beaker, and let the mixed solution flow through the catalyst bed. Use ultraviolet-visible spectrophotometry to measure the absorbance of the methyl orange solution before and after flowing through the catalyst at 466 nm, and calculate the decolorization rate according to the following formula:
[0156] D(%) = (A0 - A) / A0 × 100%
[0157] In the formula, A0 is the absorbance of the methyl orange solution before the reaction, and A is the absorbance of the methyl orange solution after the reaction.
[0158] (5) Heavy metal adsorption performance test: A certain amount of catalyst was placed in a 200 mg / L Pb2+ solution (pH=6.0), and adsorption was carried out by shaking at room temperature for 120 min. The concentration of Pb2+ in the solution before and after adsorption was determined by atomic absorption spectrometry, and the saturated adsorption capacity was calculated.
[0159]
[0160] In the formula, qe is the saturated adsorption capacity, mg / g; C0 is the initial concentration of pollutants in the solution before adsorption, mg / L; C is the initial concentration of pollutants in the solution after adsorption, mg / L; V is the solution volume, L; and m is the mass of the catalyst, g.
[0161] (6) Cyclic testing (catalytic activity)
[0162] 0.1 g of catalyst was placed in 200 mL of methyl orange solution (8 mg / L, containing 10 mg / L NaBH4) and reacted at room temperature for 30 min. The decolorization rate was then measured. After the reaction was completed, the catalyst was separated, washed three times with deionized water, and directly used in the next round of catalytic reaction. This process was repeated five times, with three parallel measurements taken. The average decolorization rate was used to calculate the catalytic cycle retention rate.
[0163] (7) Adsorption-desorption cycle test (heavy metal adsorption capacity)
[0164] 0.1 g of catalyst was placed in 200 mL Pb 2+ In a solution (50 mg / L, pH=6), the catalyst was shaken at room temperature for 120 min until adsorption equilibrium was reached, and the adsorption capacity was measured. After separation, the catalyst was immersed in 0.1 mol / L HCl solution for 60 min to desorb Pb. 2+ Then wash with deionized water until neutral, and proceed to the next round of adsorption. Repeat for 5 rounds, measure three groups in parallel, take the average value of saturated adsorption capacity, and calculate the adsorption cycle retention rate.
[0165] The performance test data of the above embodiments and comparative examples are shown in Table 1.
[0166] Table 1. Performance test data for each embodiment and comparative example.
[0167] unit wt% % % (mg / g) % % Example 1 0.76 80.3 96.5 38.5 92.4 90.1 Example 2 0.88 80.1 97 48.2 91.8 90.9 Example 3 0.63 79.9 94.2 37.2 91.1 90.3 Example 4 0.79 77.8 95 40.9 92.6 90.4 Example 5 0.82 80.5 97.5 43.3 92.8 91.0 Comparative Example 1 0.42 79.8 68.8 36.8 87.1 89.9 Comparative Example 2 0.68 80.1 94.2 7.5 88.4 60.4 Comparative Example 3 0.46 79.1 78.6 27.2 83.1 80.6 Comparative Example 4 0.52 58.1 74.2 29.9 72.4 70.6 Comparative Example 5 0.35 79.5 52.6 6.8 69.1 66.3 Comparative Example 6 0.76 79.5 82.4 39.2 69.1 88.6 Comparative Example 7 0.58 47.8 71.3 27.5 85.1 83.3
[0168] Combination Figure 1 The scanning electron microscope (SEM) morphology image (scale bar 500 μm) of the cellulose microsphere-based composite catalyst of this invention shows that the obtained cellulose microspheres are generally spherical, with a particle size distribution corresponding to the wet state range of 0.4-1.2 mm. The presence of multi-level channels on the surface of the spheres is consistent with the porosity test results in Table 1. The degree of channel development directly determines the catalyst adsorption and catalytic mass transfer efficiency.
[0169] As can be seen from the data in Table 1, quaternization modification is a key step in ensuring platinum loading and catalytic decolorization performance. In Comparative Example 1, omitting quaternization modification, the platinum loading decreased from 0.82 wt% in Example 5 to 0.42 wt%, and the methyl orange decolorization rate decreased from 97.5% to 68.8%, indicating that the positively charged adsorption sites provided by the quaternary ammonium groups are the main driving force for the platinum precursor to enter the rich pores of the cellulose microspheres and be effectively loaded. The amidation grafting of ADA mainly affects the heavy metal adsorption function; in Comparative Example 2, omitting ADA grafting, Pb... 2+ The adsorption capacity decreased significantly from 43.3 mg / g to 7.5 mg / g, a reduction of more than 80%, but the methyl orange decolorization rate remained at 94.2%, which is close to 97.5% in Example 5. This indicates that the quaternary ammonium group plays a dominant role in the electrostatic adsorption of anionic dyes, while ADA's contribution to catalytic decolorization is relatively limited. The two functional groups have a clear division of labor and do not interfere with each other in the cellulose microsphere skeleton.
[0170] Stepwise etherification strategies have significant advantages over simultaneous etherification. Comparative Example 3, using simultaneous etherification, achieved a methyl orange decolorization rate of 78.6% with a platinum loading of only 0.46 wt% and a Pb content of 78.6%. 2+ The adsorption capacity was 27.2 mg / g, lower than in all examples, indicating that monochloroacetic acid and CHPTAC compete for substitution at hydroxyl sites in the same reaction system. The degree of substitution of both functional groups was difficult to achieve the desired level, making it impossible to uniformly construct sufficient adsorption and chelation sites on the microsphere molecular chains. Increasing the degree of carboxymethyl substitution had an impact on platinum loading and Pb... 2+ Adsorption has a promoting effect. In Example 2, the molar ratio of monochloroacetic acid was 2.5:1, and its platinum loading was 0.88 wt% and Pb... 2+ The adsorption capacity of 48.2 mg / g was the highest in all examples, while the molar ratio of monochloroacetic acid in Example 1 was only 1.0:1, with corresponding values of 0.76 wt% and 38.5 mg / g, respectively. This indicates that the increase in the number of carboxyl groups provides more covalent binding sites for ADA grafting and also plays a positive role in the auxiliary anchoring of platinum ions, so that the functional groups can be uniformly exposed in the entire pore area of the microspheres in the SEM image.
[0171] The degree of substitution of quaternary ammonium groups also significantly affects catalytic performance. In Example 3, after the CHPTAC molar ratio was reduced to 6:1, the platinum loading was only 0.63 wt%, and the methyl orange decolorization rate was 94.2%, both lower than the 0.82 wt% and 97.5% in Example 5. This indicates that the reduction in the number of quaternary ammonium groups directly weakens the electrostatic adsorption capacity for the platinum precursor, and the positive potential points that can anchor platinum nanoparticles inside the pores are insufficient, resulting in a decrease in catalytic activity.
[0172] The process route of modifying first and then forming spheres is superior to forming spheres first and then modifying. In Comparative Example 4, molecular modification was performed after sphere formation, and the porosity decreased from 80.5% in Example 5 to 58.1%, the platinum loading decreased to 0.52 wt%, the methyl orange decolorization rate was 74.2%, and the Pb content decreased. 2+ The adsorption capacity was 29.9 mg / g, and all performance indicators showed a significant decline. Combined with electron microscopy morphology analysis, the dense surface and narrow channels of the pre-formed cellulose microspheres strongly hindered the diffusion of the modifying agent. Grafting reactions only occurred on the outer surface of the cellulose microspheres, making internal pores difficult to modify and resulting in extremely uneven functional group distribution. Furthermore, subsequent modification soaking and washing processes destroyed the original interconnected pore structure, significantly reducing pore connectivity. Comparative Example 7, without the addition of the composite porogen, had a porosity of only 47.8%, lacked multi-level interconnected pores, and all performance indicators were at a low level, confirming the crucial role of the hierarchical interconnected pore structure shown in the SEM images in improving pollutant mass transfer efficiency.
[0173] The platinum loading method significantly affects catalytic stability. In Comparative Example 6, although the platinum loading reached 0.76 wt% after replacing the in-situ reduction with ice-water bath NaBH4 using high-temperature hydrogen reduction, which is close to the 0.82 wt% in Example 5, the retention rate after 5 catalytic cycles was only 69.1%, far lower than the 92.8% in Example 5. This indicates that high-temperature treatment caused platinum nanoparticles to agglomerate and grow, blocking some of the mesoporous channels of the cellulose microspheres, sharply reducing the number of active sites, and decreasing catalytic stability. In contrast, Comparative Example 6 still achieved a retention rate of 88.6% after 5 adsorption cycles, which is close to the over 90% of the examples. This suggests that ADA is covalently grafted onto the cellulose backbone via amide bonds, exhibiting a certain tolerance to high-temperature treatment. Its heavy metal chelation function is not affected by platinum agglomeration in the pores, and its stability is relatively independent.
[0174] In summary, under the combined conditions of a 1.5:1 molar ratio of monochloroacetic acid, a 9:1 molar ratio of CHPTAC, 4% nano-calcium carbonate and 2% polyethylene glycol as composite porogens, and in-situ reduction with NaBH4 in an ice-water bath, spherical, multi-level interconnected porous microspheres as shown in the scanning electron microscope were prepared in Example 5. This sample had a platinum loading of 0.82 wt%, a porosity of 80.5%, a methyl orange decolorization rate of 97.5%, and a Pb content of 1.5 wt%. 2+ The adsorption capacity was 43.3 mg / g, the retention rate after 5 catalytic cycles was 92.8%, and the retention rate after 5 adsorption cycles was 91.0%. All performance indicators were at a superior level in the five examples. Comparative Examples 1 to 7 verified the necessity and irreplaceability of quaternization modification, ADA grafting, stepwise etherification strategy, modification-before-spherification process, low-temperature in-situ reduction method, and the addition of composite pore-forming agents. The above data and microstructure observation results corroborate each other: the synergistic effect of the positively charged adsorption of quaternary ammonium groups, the multidentate chelation of ADA, and the catalytic activity of platinum nanoparticles, combined with the precise functional group control of stepwise etherification, the complete pore protection strategy of modification-before-spherification, and the uniform platinum loading method of low-temperature in-situ reduction in an ice-water bath, relying on the multi-level pores visible in the SEM images to provide sufficient mass transfer and reaction sites, together endow the catalyst with the simultaneous and efficient removal capability of dyes and heavy metal composite pollutants and excellent cycle stability.
[0175] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.
Claims
1. A cellulose microsphere-based composite catalyst, characterized in that, The composite catalyst comprises: (1) Cellulose microspheres, wherein the cellulose microspheres have a three-dimensional interconnected porous structure; (2) A quaternary ammonium group grafted onto the modified cellulose molecular chain, wherein the quaternary ammonium group is covalently attached to the hydroxyl group of the modified cellulose backbone through an etherification reaction; (3) N-(carbamoylmethyl)iminodiacetic acid groups grafted onto the modified cellulose molecular chain, wherein the N-(carbamoylmethyl)iminodiacetic acid groups are connected to the modified cellulose backbone through amide bonds, retaining the carboxyl chelate structure; (4) Platinum nanoparticles loaded on the cellulose microspheres, wherein the platinum nanoparticles are distributed inside the pores and on the surface of the cellulose microspheres.
2. The cellulose microsphere-based composite catalyst according to claim 1, characterized in that, The average particle size of the platinum nanoparticles is 2-5 nm.
3. The cellulose microsphere-based composite catalyst according to claim 1, characterized in that, The wet particle size of the cellulose microspheres is 0.4-1.2 mm.
4. A method for preparing a cellulose microsphere-based composite catalyst as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Carboxymethylation modification of cellulose: Cotton lint cellulose was alkalized in an aqueous sodium hydroxide solution at 20-30℃ for 0.5-2 hours to obtain basic cellulose; the basic cellulose was transferred to an aqueous ethanol solution, monochloroacetic acid was added, and the mixture was reacted at 50-60℃ for 2-5 hours. After the reaction was completed, the pH was adjusted to neutral, and the mixture was washed and dried to obtain carboxymethylated cellulose. S2, Quaternization modification of carboxymethyl cellulose: Carboxymethyl cellulose was dispersed in deionized water, and sodium hydroxide was added to adjust the pH to 10-12. 3-chloro-2-hydroxypropyltrimethylammonium chloride was added, and the mixture was reacted at 60-80℃ for 6-15 h. After the reaction was completed, the pH was adjusted to neutral, and the mixture was washed and dried to obtain carboxymethyl-quaternary ammonium dual-modified cellulose. S3, amidation grafting: Carboxymethyl-quaternary ammonium dual-modified cellulose was dissolved in phosphate buffer, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide were added to activate the carboxyl groups for 20-60 min. N-(carbamoylmethyl)iminodiacetic acid was added, and the reaction was stirred at room temperature for 6-24 h. After the reaction was completed, the cellulose was purified by dialysis with deionized water or repeated washing and freeze-drying to obtain the modified cellulose. S4. Preparation and Pore Formation of Cellulose Solution Modified cellulose was added to a urea / sodium hydroxide / water solution pre-cooled to -5°C, wherein the mass ratio of urea, sodium hydroxide and water was 12-15:7-9:78-81. The solution was stirred until completely dissolved to obtain a transparent cellulose solution. A composite pore-forming agent was added to the transparent cellulose solution and stirred at 0-10°C to disperse it evenly. S5, Suspension polymerization into spheres: A modified cellulose solution containing a porogen was dropped into a paraffin oil suspension containing a surfactant at room temperature, and the mixture was stirred to disperse and solidify the cellulose solution to form microspheres. S6. Regeneration and Template Removal: Add dilute hydrochloric acid to the suspension obtained in S5 to adjust the pH to 6-8, separate and remove the paraffin oil, soak the microspheres in dilute hydrochloric acid to dissolve and remove the nano-calcium carbonate template, and then wash with deionized water and ethanol in sequence to obtain cellulose microspheres, which are then stored in a wet state. S7, In-situ loading of platinum nanoparticles: Cellulose microspheres were immersed in a dilute hydrochloric acid solution of chloroplatinic acid, allowed to stand at room temperature, and then transferred to an ice-water bath at 0-4℃ for cooling. Freshly prepared sodium borohydride solution was added dropwise, and the reduction reaction was carried out at 0-4℃ for 20-60 min. After the reaction was completed, the mixture was washed with deionized water to obtain a cellulose microsphere-based composite catalyst loaded with platinum nanoparticles.
5. The preparation method according to claim 4, characterized in that, The molar ratio of monochloroacetic acid to basic cellulose glucose unit in S1 is 1.0-2.5:1, and the volume fraction of ethanol in the aqueous ethanol solution is 70-80%. The molar ratio of 3-chloro-2-hydroxypropyltrimethylammonium chloride to carboxymethylated cellulose glucose units in S2 is 6-12:
1.
6. The preparation method according to claim 4, characterized in that, The molar ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide to carboxyl group in S3 is 1.0-2.0:1, the molar ratio of 1-ethyl-(3-dimethylaminopropyl)carbodiimide to N-hydroxysuccinimide is 1:1, and the concentration of the phosphate buffer is 0.05-0.20 mol / L.
7. The preparation method according to claim 4, characterized in that, The composite porogen described in S4 is composed of nano-calcium carbonate and polyethylene glycol in a mass ratio of 2-4:
1. The nano-calcium carbonate has a particle size of 0.5-5 μm, the polyethylene glycol has a molecular weight of 4000-8000, and the amount of the composite porogen added is 3-10% of the mass of the modified cellulose.
8. The preparation method according to claim 4, characterized in that, The concentration of H2PtCl6 in the chloroplatinic acid solution in S7 is 0.5-5.0 mmol / L, and the concentration of dilute hydrochloric acid is 10-50 mmol / L; the concentration of the sodium borohydride solution is 0.05-0.20 mol / L, and the molar ratio of sodium borohydride to chloroplatinic acid is 5-20:1.