A bacterial enzyme mixed preparation for degrading PET plastic and a preparation method thereof

Abstract

The application discloses a kind of for PET plastic degradation bacterial enzyme mixed preparation and preparation method thereof, belong to enzyme preparation technical field, by forming lanthanum metal skeleton is loaded on the surface of titanium dioxide and carbonization, obtain the porous carbon layer of lanthanum doping, again after nitric acid treatment and silane coupling agent treatment, significantly increase specific surface area and roughness, enhance and calcium-based diatomite adsorption, with calcium-based diatomite as carrier, form the sodium alginate microcapsule of enzyme preparation as inclusions, load on the surface of calcium-based diatomite, to avoid titanium dioxide in photocatalysis Hydroxyl radical directly attacks enzyme preparation, prolongs the degradation effect to PET plastic, and calcium ion in calcium-based diatomite can increase the crosslinking degree with sodium alginate, increase the loading rate of sodium alginate microcapsule, improve the strength of microcapsule, further improve the sustained-release effect of enzyme preparation in microcapsule.

Description

Technical Field

[0001] This invention belongs to the field of enzyme preparation technology, specifically a bacterial enzyme mixture for the degradation of PET plastic and its preparation method. Background Technology

[0002] PET is widely used in the production of environmentally friendly garbage bags due to its excellent properties. After a large amount of these garbage bags are used, they must be degraded. Simple chemical degradation is relatively easy, but it causes a lot of pollution. Environmentally friendly biodegradation has always been a challenge for the industry. Plastic degradation refers to the way in which the molecular weight of the polymer decreases and the physical properties of the polymer material decline. Typical manifestations include: plastic becoming brittle, cracking, softening, hardening, and losing mechanical strength. The aging and deterioration of plastics is a degradation phenomenon. However, it generally takes decades or even hundreds of years for plastics to degrade to a state that is harmless to the environment and return to the natural cycle. The degradation products must eventually be decomposed into carbon dioxide and water to be considered as degradation.

[0003] Existing biodegradation methods for bio-based plastic garbage bags mainly include bio-composting, microbial degradation, and enzymatic methods, among which bio-composting and microbial degradation are more commonly used. It has been reported that bio-based plastic garbage bags can achieve a degradation rate of 60-80% in 2-3 months using bio-composting. However, its disadvantages include a long processing cycle, difficulties in efficient waste transportation, and limitations in industrialization. Bio-enzyme preparations, due to improvements in domestic fermentation enzyme activity levels in recent years, have seen a significant reduction in production costs and have proven their potential for large-scale industrial application.

[0004] Chinese patent CN119662600A discloses an enzyme preparation for catalytic degradation of bioplastics and its preparation method. It utilizes calcium-based bentonite as a carrier to load nano-titanium dioxide to prepare a catalytic additive. Nano-titanium dioxide is a common catalytic nanomaterial in the field of photocatalysis, with low manufacturing cost and photocatalytic degradation activity. Under light irradiation, it can generate free radicals, thereby initiating the oxidative degradation reaction of bio-based plastics and accelerating their degradation rate. However, in this method, the hydroxyl radicals generated by nano-titanium dioxide during photocatalysis have strong oxidizing properties, easily causing enzyme inactivation and reducing degradation efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a bacterial-enzyme mixture for the degradation of PET plastics and its preparation method. By forming a lanthanum metal framework loaded on the surface of titanium dioxide and carbonizing it, a lanthanum-doped porous carbon layer is obtained. Using calcium-based diatomaceous earth as a carrier, sodium alginate microcapsules containing the enzyme preparation are formed and loaded on the surface of the calcium-based diatomaceous earth. This avoids the direct attack of the enzyme preparation by hydroxyl radicals generated by titanium dioxide during photocatalysis, thus prolonging the degradation effect on PET plastics.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for preparing a bacterial enzyme mixture for the degradation of PET plastics includes the following steps:

[0008] Step 1: Lanthanum metal framework is loaded onto the surface of titanium dioxide and carbonized to obtain a lanthanum-doped porous carbon layer, which is then acid-washed to obtain acidified titanium dioxide. Acidified titanium dioxide, γ-aminopropyltriethoxysilane, anhydrous ethanol and deionized water are added to a reaction vessel and stirred at 50-65℃ and 400-500 r / min for 3-4 h. After filtration, the filter cake is washed with deionized water 2-4 times and vacuum dried at 60-80℃ for 1-2 h to obtain dispersed titanium dioxide.

[0009] Step 2: Add calcium-based diatomaceous earth, sodium alginate, and deionized water to a reaction vessel and stir for 10-15 minutes at 20-25℃ and 500-600 r / min. Then add 20-22 g of enzyme preparation and continue stirring for 30-40 minutes to obtain a mixed solution. Drop the mixed solution into a 3-4% calcium chloride solution, then add dispersed titanium dioxide and continue stirring for 1-2 hours. Filter the solution and wash the filter cake 2-4 times with deionized water and anhydrous ethanol, respectively. Vacuum dry at 60-80℃ for 1-2 hours to obtain a bacterial enzyme mixture for PET plastic degradation.

[0010] Furthermore, in step one, the ratio of acidified titanium dioxide, γ-aminopropyltriethoxysilane, anhydrous ethanol and deionized water is 30-35g: 20-30mL: 300-400mL: 800-900mL.

[0011] Furthermore, in step two, the ratio of calcium-based diatomaceous earth, sodium alginate, deionized water, and enzyme preparation is 100-120g: 80-90g: 800-900mL: 20-22g.

[0012] Furthermore, in step two, the ratio of the mixed solution, calcium chloride solution, and dispersed titanium dioxide is 70-80 mL: 300-400 mL: 30-40 g.

[0013] Furthermore, in step two, the enzyme preparation is any one of keratinase, alkaline lipase, neutral lipase, protease, and laccase.

[0014] Furthermore, the acidified titanium dioxide in step one is prepared through the following steps:

[0015] Modified titanium dioxide and a 1 mol / L nitric acid solution were added to a reaction vessel and stirred and acid-washed at 50-55℃ and 400-500 r / min for 1-1.2 h. After filtration, the filter cake was washed with deionized water until the final washing solution was neutral and dried under vacuum at 60-80℃ for 1-2 h to obtain acidified titanium dioxide.

[0016] Furthermore, the ratio of modified titanium dioxide to nitric acid solution is 70-80g: 200-230mL.

[0017] Furthermore, the calcium-based diatomaceous earth in step two is prepared through the following steps:

[0018] Add 100-120g of diatomaceous earth and 300-400mL of sodium bicarbonate solution with a mass fraction of 10-15% to a reaction vessel. Vacuum impregnate for 2-3h at 20-25℃ and 500-600r / min. Then add 120-140mL of calcium chloride solution with a mass fraction of 40-50% and continue the reaction for 1-2h. Filter the mixture and wash the filter cake 2-4 times with deionized water and anhydrous ethanol, respectively. Dry the mixture under vacuum at 60-80℃ for 1-2h to obtain calcium-based diatomaceous earth.

[0019] Furthermore, the ratio of diatomaceous earth, sodium bicarbonate solution, and calcium chloride solution is 100-120g: 300-400mL: 120-140mL.

[0020] Furthermore, the modified titanium dioxide is prepared through the following steps:

[0021] A solution of 2,5-diaminoterephthalic acid and N,N-dimethylformamide was added to a polytetrafluoroethylene-lined autoclave and stirred for 30-40 minutes at 20-25°C and 500-600 rpm. Then, lanthanum nitrate hexahydrate was added, and the mixture was heated to 120-130°C and reacted for 10-12 hours. Next, titanium dioxide powder with a particle size of 80-90 nm was added, and the reaction was continued for 10-12 hours. The mixture was then allowed to cool naturally to room temperature, filtered, and the filter cake was washed 2-4 times with methanol solution and deionized water, respectively. The cake was then vacuum dried at 60-80°C for 1-2 hours. The product was transferred to a muffle furnace and calcined at 500-600°C for 2-3 hours under nitrogen protection. After cooling naturally to room temperature, modified titanium dioxide was obtained.

[0022] Furthermore, the ratio of 2,5-diaminoterephthalic acid, N,N-dimethylformamide solution, lanthanum nitrate hexahydrate and titanium dioxide powder is 80-90g:700-800mL:30-40g:80-90g.

[0023] The beneficial effects of this invention are:

[0024] 1. The present invention provides a bacterial enzyme mixture for the degradation of PET plastics, which exhibits good degradation efficiency, stability, and long-lasting degradation ability. By forming a lanthanum metal framework loaded on the surface of titanium dioxide and carbonizing it, a lanthanum-doped porous carbon layer is obtained. This porous carbon layer increases the porosity of titanium dioxide. Further treatment with nitric acid and a silane coupling agent significantly increases the specific surface area and roughness, enhancing the adsorption with calcium-based diatomaceous earth. The lanthanum doping into the titanium dioxide lattice, due to the significant difference between the lanthanum ion radius and the titanium ion radius, leads to lattice distortion and local defects, reducing the recombination probability of photogenerated electrons and holes, extending carrier lifetime, and thus improving photocatalytic efficiency.

[0025] 2. This invention uses calcium-based diatomaceous earth as a carrier to form sodium alginate microcapsules containing enzyme preparations, which are loaded onto the surface of the calcium-based diatomaceous earth. The calcium ions in the calcium-based diatomaceous earth can increase the degree of cross-linking with sodium alginate, thereby increasing the loading rate of the sodium alginate microcapsules. The increased degree of cross-linking of the sodium alginate microcapsules means increased microcapsule strength, which avoids premature rupture and burst release of the internal enzyme preparations, and further improves the sustained-release effect of the enzyme preparations in the microcapsules.

[0026] 3. The calcium-based diatomaceous earth of the present invention improves the ion exchange performance of diatomaceous earth by generating calcium carbonate precipitate deposited on the surface of diatomaceous earth. The sodium alginate microcapsules loaded on the surface rupture and release enzyme preparations under external force or water absorption. The calcium ions in the calcium-based diatomaceous earth can form complexes with the enzyme, thereby improving the catalytic activity of the enzyme. In addition, the calcium-based diatomaceous earth can adsorb the substrate after being hydrolyzed by the enzyme, making the reaction more complete and increasing the reaction rate. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1: A method for preparing a bacterial enzyme mixture for PET plastic degradation, comprising the following steps:

[0029] S1: 80g of 2,5-diaminoterephthalic acid and 700mL of N,N-dimethylformamide solution were added to a polytetrafluoroethylene-lined autoclave and stirred for 30min at 20℃ and 500r / min. Then, 30g of lanthanum nitrate hexahydrate was added, and the mixture was heated to 120℃ and reacted for 10h. Next, 80g of titanium dioxide powder with a particle size of 80nm was added, and the reaction was continued for 10h. The mixture was then allowed to cool naturally to room temperature, filtered, and the filter cake was washed twice with methanol solution and deionized water, respectively. The cake was then dried under vacuum at 60℃ for 1h. The product was transferred to a muffle furnace and calcined at 500℃ for 2h under nitrogen protection. After cooling naturally to room temperature, modified titanium dioxide was obtained.

[0030] 2,5-Diaminoterephthalic acid dispersed in N,N-dimethylformamide solution coordinates with lanthanum metal in lanthanum nitrate hexahydrate to form a lanthanum metal framework supported on the surface of titanium dioxide.

[0031] S2: Add 70g of modified titanium dioxide and 200mL of 1mol / L nitric acid solution to the reactor, stir and acid wash for 1h at 50℃ and 400r / min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and vacuum dry at 60℃ for 1h to obtain acidified titanium dioxide.

[0032] After acid washing, the modified titanium dioxide surface carries a large number of oxygen-containing groups, which can increase the adsorption of calcium-based diatomaceous earth and improve the loading rate of acidified titanium dioxide.

[0033] S3: Add 30g of acidified titanium dioxide, 20mL of γ-aminopropyltriethoxysilane, 300mL of anhydrous ethanol and 800mL of deionized water to a reaction vessel, stir for 3h at 50℃ and 400r / min, filter, wash the filter cake twice with deionized water, and dry it under vacuum at 60℃ for 1h to obtain dispersed titanium dioxide.

[0034] The silane bonds generated by the hydrolysis of γ-aminopropyltriethoxysilane combine with the hydroxyl groups on the surface of acidified titanium dioxide. This bonding method replaces the weak interactions between titanium dioxide particles through hydrogen bonds and van der Waals forces, effectively inhibiting particle aggregation.

[0035] S4: Add 100g of diatomaceous earth and 300mL of 10% sodium bicarbonate solution to the reaction vessel, and impregnate under vacuum at 20℃ and 500r / min for 2h. Then add 120mL of 40% calcium chloride solution and continue the reaction for 1h. Filter the mixture and wash the filter cake twice with deionized water and anhydrous ethanol, respectively. Dry it under vacuum at 60℃ for 1h to obtain calcium-based diatomaceous earth.

[0036] Sodium bicarbonate can neutralize the acidic groups on the surface of diatomaceous earth, and at the same time, it can adsorb sodium ions and bicarbonate ions through its porous structure, providing active sites for subsequent reactions. After adding calcium chloride, the calcium ions in the solution react with the carbonate ions adsorbed on the surface of diatomaceous earth to form calcium carbonate precipitate that is deposited on the surface of diatomaceous earth.

[0037] S5: Add 100g of calcium-based diatomaceous earth, 80g of sodium alginate and 800mL of deionized water to a reaction vessel, stir for 10min at 20℃ and 500r / min, then add 20g of keratinase and continue stirring for 30min to obtain a mixed solution; add 70mL of the mixed solution dropwise to 300mL of 3% calcium chloride solution, then add 30g of dispersed titanium dioxide, continue stirring for 1h, filter, wash the filter cake twice with deionized water and anhydrous ethanol respectively, and vacuum dry at 60℃ for 1h to obtain a bacterial enzyme mixture for the degradation of PET plastics.

[0038] The carboxyl groups on the surface of sodium alginate dissociate in solution and become negatively charged. They then cross-link with positively charged calcium ions in calcium chloride through electrostatic interactions, thereby encapsulating the enzyme preparation and forming sodium alginate microcapsules. During this process, calcium carbonate distributed on the surface of calcium-based diatomaceous earth dispersed in deionized water can provide calcium ions. The provided calcium ions can increase the degree of cross-linking with sodium alginate, thereby increasing the loading rate of sodium alginate microcapsules. The increased degree of cross-linking of sodium alginate microcapsules means increased microcapsule strength, further enhancing the sustained-release effect of the enzyme preparation in the microcapsules.

[0039] Example 2: A method for preparing a bacterial enzyme mixture for PET plastic degradation, comprising the following steps:

[0040] S1: 85g of 2,5-diaminoterephthalic acid and 750mL of N,N-dimethylformamide solution were added to a polytetrafluoroethylene-lined autoclave and stirred for 35min at 22.5℃ and 550r / min. Then, 35g of lanthanum nitrate hexahydrate was added, and the mixture was heated to 125℃ and reacted for 11h. Next, 85g of titanium dioxide powder with a particle size of 85nm was added, and the reaction was continued for 11h. The mixture was then allowed to cool naturally to room temperature, filtered, and the filter cake was washed three times with methanol solution and deionized water, respectively. The cake was then vacuum dried at 70℃ for 1.5h. The product was transferred to a muffle furnace and calcined at 550℃ for 2.5h under nitrogen protection. After cooling naturally to room temperature, modified titanium dioxide was obtained.

[0041] S2: Add 75g of modified titanium dioxide and 215mL of 1mol / L nitric acid solution to the reaction vessel, stir and acid wash for 1.1h at 52.5℃ and 450r / min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and vacuum dry at 70℃ for 1.5h to obtain acidified titanium dioxide.

[0042] S3: Add 32.5g of acidified titanium dioxide, 25mL of γ-aminopropyltriethoxysilane, 350mL of anhydrous ethanol and 850mL of deionized water to a reaction vessel, stir for 3.5h at 57.5℃ and 450r / min, filter, wash the filter cake three times with deionized water, and dry under vacuum at 70℃ for 1.5h to obtain dispersed titanium dioxide.

[0043] S4: Add 110g of diatomaceous earth and 350mL of 12.5% ​​sodium bicarbonate solution to the reaction vessel, and impregnate under vacuum at 22.5℃ and 550r / min for 2.5h. Then add 130mL of 45% calcium chloride solution and continue the reaction for 1.5h. Filter the mixture, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and dry it under vacuum at 70℃ for 1.5h to obtain calcium-based diatomaceous earth.

[0044] S5: Add 110g of calcium-based diatomaceous earth, 85g of sodium alginate and 850mL of deionized water to a reaction vessel, stir for 12.5min at 22.5℃ and 550r / min, then add 21g of alkaline lipase and continue stirring for 35min to obtain a mixed solution; add 75mL of the mixed solution dropwise to 350mL of 3.5% calcium chloride solution, then add 35g of dispersed titanium dioxide, continue stirring for 1.5h, filter, wash the filter cake three times with deionized water and anhydrous ethanol respectively, and vacuum dry at 70℃ for 1.5h to obtain a bacterial enzyme mixture for PET plastic degradation.

[0045] Example 3: A method for preparing a bacterial enzyme mixture for PET plastic degradation, comprising the following steps:

[0046] S1: 90g of 2,5-diaminoterephthalic acid and 800mL of N,N-dimethylformamide solution were added to a polytetrafluoroethylene-lined autoclave and stirred for 40min at 25℃ and 600r / min. Then, 40g of lanthanum nitrate hexahydrate was added, and the mixture was heated to 130℃ and reacted for 12h. Next, 90g of titanium dioxide powder with a particle size of 90nm was added, and the reaction was continued for 12h. The mixture was then allowed to cool naturally to room temperature, filtered, and the filter cake was washed four times with methanol solution and deionized water, respectively. The cake was then dried under vacuum at 80℃ for 2h. The product was transferred to a muffle furnace and calcined at 600℃ for 3h under nitrogen protection. After cooling naturally to room temperature, modified titanium dioxide was obtained.

[0047] S2: Add 80g of modified titanium dioxide and 230mL of 1mol / L nitric acid solution to the reaction vessel, stir and acid wash for 1.2h at 55℃ and 500r / min, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and vacuum dry at 80℃ for 2h to obtain acidified titanium dioxide.

[0048] S3: Add 35g of acidified titanium dioxide, 30mL of γ-aminopropyltriethoxysilane, 400mL of anhydrous ethanol and 900mL of deionized water to a reaction vessel, stir for 4h at 65℃ and 500r / min, filter, wash the filter cake 4 times with deionized water, and dry under vacuum at 80℃ for 2h to obtain dispersed titanium dioxide.

[0049] S4: Add 120g of diatomaceous earth and 400mL of 15% sodium bicarbonate solution to the reaction vessel, and impregnate under vacuum at 25℃ and 600r / min for 3h. Then add 140mL of 50% calcium chloride solution and continue the reaction for 2h. Filter the mixture and wash the filter cake four times with deionized water and anhydrous ethanol, respectively. Dry it under vacuum at 80℃ for 2h to obtain calcium-based diatomaceous earth.

[0050] S5: Add 120g of calcium-based diatomaceous earth, 90g of sodium alginate and 900mL of deionized water to a reaction vessel, stir for 15min at 25℃ and 600r / min, then add 22g of neutral lipase and continue stirring for 40min to obtain a mixed solution; add 80mL of the mixed solution dropwise to 400mL of 4% calcium chloride solution, then add 40g of dispersed titanium dioxide, continue stirring for 2h, filter, wash the filter cake four times with deionized water and anhydrous ethanol respectively, and vacuum dry at 80℃ for 2h to obtain a bacterial enzyme mixture for PET plastic degradation.

[0051] Comparative Example 1: Based on Example 3, the modified titanium dioxide in step S2 was replaced with titanium dioxide powder with a particle size of 80-90 nm in step S1, while the other steps remained unchanged, to prepare a bacterial enzyme mixture for the degradation of PET plastics.

[0052] Comparative Example 2: Based on Example 3, the dispersed titanium dioxide in step S5 was replaced with the acidified titanium dioxide in step S2, while the other steps remained unchanged, to prepare a bacterial enzyme mixture for the degradation of PET plastics.

[0053] Comparative Example 3: Based on Example 3, without step S3, the calcium-based diatomaceous earth in step S4 was replaced with the diatomaceous earth in step S3, and the other steps remained unchanged, to prepare a bacterial enzyme mixture for the degradation of PET plastic.

[0054] The performance of the PET plastic degradation enzyme mixtures obtained in Examples 1-3 and Comparative Examples 1-3 was tested. Water was added to the PET biodegradable plastic to be treated to obtain the reaction substrate. The mass ratio of biodegradable plastic to water was 1:10. Based on the reaction substrate, the compound enzyme preparation was added to the reaction substrate at an addition rate of 1 kg / t. After thorough mixing, the reaction was carried out at 25°C and 100 r / min for 24 h. Then, the reaction temperature was raised to 40°C, and the pH was adjusted to 3.0 with citric acid for a further 24 h. After 15 days, a new PET plastic bag was added, and the temperature was controlled at 25°C. The amount of new PET plastic bag added was the same as the initial addition. The mixture was stirred at 100 r / min and reacted for 24 h. All remaining residues were collected. Each example and comparative example was repeated 3 times. The results are shown in Tables 1 and 2.

[0055] Table 1. Degradation Performance Test of Bacterial-Enzyme Mixture

[0056] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Hydrolysis rate (%) 56.87±0.23 57.56±0.12 58.10±0.18 29.25±0.11 46.01±0.36 34.21±0.27 Toughness The toughness changes significantly, and the tensile force decreases. The toughness changed significantly, and the tensile force decreased significantly. The toughness changes significantly, and the mechanical properties are lost. There was no significant change in toughness or tensile strength. Slight changes in toughness, slight changes in tensile strength There was no significant change in toughness or tensile strength. Crack condition Minor cracks Significant cracks Numerous cracks No cracks Minor cracks No cracks

[0057] Table 2. Degradation performance test of bacterial-enzyme mixture after 15 days

[0058] project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Hydrolysis rate (%) 52.35±0.15 53.28±0.34 54.86±0.28 21.26±0.16 36.26±0.19 26.12±0.21 Toughness The toughness changes significantly, and the tensile force decreases. The toughness changed significantly, and the tensile force decreased significantly. The toughness changes significantly, and the mechanical properties are lost. Toughness and tensile strength showed no significant change. Slight changes in toughness, slight changes in tensile strength Toughness and tensile strength showed no significant change. Crack condition Minor cracks Significant cracks Numerous cracks No cracks Minor cracks No cracks

[0059] As can be seen from Tables 1 and 2, the bacterial enzyme mixture for PET plastic degradation obtained in Examples 1-3 showed a significantly higher hydrolysis rate of PET plastic bags than the comparative example. The toughness of the PET plastic bags was worse than that of the comparative example, with more cracks. However, the bacterial enzyme mixture for PET plastic degradation prepared in this invention still maintained good degradation ability after 15 days. This indicates that the bacterial enzyme mixture for PET plastic degradation prepared in this invention has good degradation efficiency, stability and long-lasting degradation ability for PET plastic.

[0060] In Comparative Example 1, modified titanium dioxide was replaced with titanium dioxide powder. Lanthanum metal from lanthanum nitrate hexahydrate was coordinated with 2,5-diaminoterephthalic acid dispersed in N,N-dimethylformamide solution to form a lanthanum metal framework loaded on the surface of titanium dioxide and then carbonized, resulting in a lanthanum-doped porous carbon layer. This porous carbon layer increases the porosity of titanium dioxide. The lanthanum doping enters the titanium dioxide lattice. Due to the significant difference between the lanthanum ion radius and the titanium ion radius, lattice distortion and local defects occur, reducing the recombination probability of photogenerated electrons and holes, extending carrier lifetime, and thus improving photocatalytic efficiency.

[0061] In Comparative Example 2, dispersed titanium dioxide was replaced with acidified titanium dioxide. The silane bonds generated by the hydrolysis of γ-aminopropyltriethoxysilane combine with the hydroxyl groups on the surface of acidified titanium dioxide, thereby increasing the dispersibility of dispersed titanium dioxide and preventing agglomeration. Furthermore, γ-aminopropyltriethoxysilane contains amino groups, which can increase the adsorption of calcium-based diatomaceous earth.

[0062] In Comparative Example 3, calcium-based diatomaceous earth was replaced with diatomaceous earth. Calcium carbonate precipitate was generated and deposited on the surface of the diatomaceous earth, improving its ion exchange performance. The sodium alginate microcapsules loaded on the surface ruptured under external force or water absorption, releasing the enzyme preparation. Calcium ions in the calcium-based diatomaceous earth could form complexes with the enzyme, thereby improving the enzyme's catalytic activity. Furthermore, the calcium-based diatomaceous earth could adsorb the substrate after enzyme hydrolysis, making the reaction more complete and increasing the reaction rate. In diatomaceous earth that lost calcium ions, the ion exchange capacity decreased, and the degree of cross-linking of the sodium alginate microcapsules could not be improved.

[0063] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a bacterial enzyme mixture for the degradation of PET plastic, characterized in that, Includes the following steps: Step 1: Add 2,5-diaminoterephthalic acid and N,N-dimethylformamide solution to a polytetrafluoroethylene-lined autoclave, stir at 20-25℃ and 500-600 r / min for 30-40 min, then add lanthanum nitrate hexahydrate, heat to 120-130℃, and continue the reaction for 10-12 h. Then add titanium dioxide powder with a particle size of 80-90 nm, and continue the reaction for 10-12 h. After natural cooling, filter, wash, and vacuum dry, transfer the product to a muffle furnace, calcine at 500-600℃ for 2-3 h under nitrogen protection, and then cool naturally to obtain modified titanium dioxide. Modified titanium dioxide and a 1 mol / L nitric acid solution were added to a reaction vessel, and the mixture was stirred and acid-washed at 50-55℃ and 400-500 r / min for 1-1.2 h. The mixture was then filtered, washed, and vacuum dried to obtain acidified titanium dioxide. The ratio of modified titanium dioxide to nitric acid solution is 70-80g: 200-230mL; Acidified titanium dioxide, γ-aminopropyltriethoxysilane, anhydrous ethanol and deionized water were added to a reaction vessel and stirred at 50-65℃ and 400-500r / min for 3-4h. The mixture was then filtered, washed and dried under vacuum to obtain dispersed titanium dioxide. Step 2: Add calcium-based diatomaceous earth, sodium alginate, and deionized water to a reaction vessel, stir at 20-25℃ and 500-600 r / min for 10-15 min, then add the enzyme preparation, and continue stirring for 30-40 min to obtain a mixed solution; add the mixed solution dropwise to a 3-4 wt% calcium chloride solution, then add dispersed titanium dioxide, continue stirring for 1-2 h, filter, wash, and vacuum dry to obtain a bacterial enzyme mixture for PET plastic degradation; The calcium-based diatomaceous earth described in step two is prepared through the following steps: Diatomaceous earth and 10-15 wt% sodium bicarbonate solution were added to a reaction vessel and impregnated under vacuum at 20-25℃ and 500-600 r / min for 2-3 h. Then, 40-50 wt% calcium chloride solution was added and the reaction was continued for 1-2 h. The mixture was filtered and the filter cake was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The mixture was then dried under vacuum to obtain calcium-based diatomaceous earth. The ratio of diatomaceous earth, sodium bicarbonate solution, and calcium chloride solution is 100-120g: 300-400mL: 120-140mL; The enzyme preparation mentioned in step two is any one of keratinase, alkaline lipase, and neutral lipase.

2. The method for preparing a bacterial enzyme mixture for PET plastic degradation according to claim 1, characterized in that, The ratio of acidified titanium dioxide, γ-aminopropyltriethoxysilane, anhydrous ethanol and deionized water is 30-35g: 20-30mL: 300-400mL: 800-900mL.

3. The method for preparing a bacterial enzyme mixture for PET plastic degradation according to claim 1, characterized in that, In step two, the ratio of calcium-based diatomaceous earth, sodium alginate, deionized water, and enzyme preparation is 100-120g: 80-90g: 800-900mL: 20-22g; the ratio of mixed solution, calcium chloride solution, and dispersed titanium dioxide is 70-80mL: 300-400mL: 30-40g.

4. The method for preparing a bacterial enzyme mixture for PET plastic degradation according to claim 1, characterized in that, The ratio of 2,5-diaminoterephthalic acid, N,N-dimethylformamide solution, lanthanum nitrate hexahydrate and titanium dioxide powder is 80-90g:700-800mL:30-40g:80-90g.

5. A bacterial enzyme mixture for the degradation of PET plastic, characterized in that, It is prepared by the preparation method described in any one of claims 1-4.