Preparation of lactic acid lactobacillus / mof composite photocatalyst and its application in degradation of chromium black t

Abstract

A method for preparing a *Lactococcus lactis* / MOF composite photocatalyst includes the following steps: Step 1: ZrCl4 and 1,3,5-tris(4-carboxyphenyl)benzene are mixed, N,N-dimethylformamide (DMF) is added, a mixed solution is obtained, and after sonication, formic acid and distilled water are added sequentially; then the mixture is dried in an oven to obtain Zr-BTB MOL; zirconium chloride octahydrate (ZrOCl2·8H2O) and trimesic acid are dissolved in a mixed solution of deionized water and formic acid, and sonicated; the above mixture is heated in an oven, then cooled to room temperature, and the product is collected by centrifugation to obtain hexazirconium oxyhydroxyl cluster-based metal-organic framework (MOF-808); Step 2: *Lactococcus lactis* is grown in *Lactobacillus delbrueckii* subsp. bulgaricus broth to obtain freshly inoculated *Lactococcus lactis*. L. lactis; Step 3: Put L. lactis Single colonies were mixed with Zr-BTB MOL and MOF-808, respectively, and centrifuged to obtain the *Lactococcus lactis* / MOF composite photocatalyst. This invention can be achieved at room temperature and pressure. L. lactis It can be efficiently combined with MOF materials while maintaining the integrity of the MOF structure during the composite process.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic wastewater treatment technology, and relates to visible light-induced photocatalytic degradation of chrome black T pollutants in water, specifically involving a type of lactococcus (Lactococcus lactis). Lactococcus lactis, L. lactis Preparation of composite photocatalysts (MOF) and their application in the photocatalytic degradation of chromium black T. Background Technology

[0002] Among various water pollutants, chrome black T dyes are a typical pollutant with wide commercial applications. Their molecules contain azo groups and other chemical groups that pose carcinogenic and teratogenic risks, but due to their stable structure, they are difficult to degrade. Currently, the main treatment technologies for chrome black T dye wastewater include adsorption, biological methods, and advanced oxidation methods. However, single treatment technologies often suffer from limited treatment efficiency, high operating costs, and the risk of secondary pollution, making it difficult to meet the current demand for "high-efficiency, low-cost, and pollution-free" treatment of chrome black T dye wastewater. Furthermore, they are unsuitable for the increasingly complex types of industrial dyes, their fluctuating concentrations, and their continuously increasing toxicity. Therefore, exploring the optimization and upgrading of single technologies and the synergistic use of multiple technologies has become a research hotspot and development trend in the field of chrome black T dye wastewater treatment.

[0003] Photocatalysis utilizes natural light energy to excite oxygen or water molecules in the environment into highly reactive free radicals, which then oxidize and degrade organic pollutants. It boasts advantages such as being environmentally friendly, energy-efficient, and cost-effective. However, the low efficiency of solar energy collection and utilization during photocatalytic degradation remains a critical challenge for its widespread application. Currently, light-harvesting systems used for pollutant degradation mainly include artificial photosynthetic systems based on semiconductors and natural photosynthetic systems based on microorganisms. Compared to photosynthetic microorganisms, semiconductors typically have higher light-harvesting efficiency, but the conversion of photoelectrons into chemical energy often requires higher thermal / kinetic energy, and the conversion of photoelectrons into stable chemical energy is difficult to achieve efficiently. In existing technologies, Zhou Shungui et al. (ACS Sustain. Chem. Eng., 2019, 7(18), 15427-15433) constructed a CdS-thioreducing Geobacter hybrid for the photo-driven biosynthetic reduction of methyl orange. In this system, part of the photogenerated electrons were used for photocatalytic reduction of methyl orange, and the other part was captured and utilized by microorganisms for the bioreduction of methyl orange. The degradation efficiency of this system was better than that of CdS or microorganisms alone. Wang Yuanpeng et al. (J. Hazard. Mater., 2022, 431, 128633) applied the CdS-thioreducing Geobacter hybrid to efficiently oxidize and reduce tetracycline. These works show that semi-artificial photosynthetic systems have dual advantages in capturing and utilizing solar energy. The photogenerated electron-hole pairs and active free radicals generated under specific wavelengths of light can effectively oxidize and eliminate organic pollutants, opening up a new way for wastewater purification.

[0004] However, the above technologies have the following drawbacks: CdS-based materials have poor photostability and are prone to photocorrosion, which leads to rapid decay of catalytic activity and secondary pollution; the system built on a single strain of Geobacterium thioreduction is only suitable for a limited number of pollutants and has poor universality for different types of organic wastewater; the interface binding of the hybrid is weak, the electron transfer efficiency between photogenerated carriers and microorganisms is limited, and the synergistic degradation efficiency has not been further improved.

[0005] Although semi-artificial photosynthesis systems have significant advantages in the degradation of organic pollutants, research in this field is still in its early stages, many important scientific questions remain unanswered, and related exploratory work urgently needs to be carried out.

[0006] For example, the selection of semiconductors is crucial as a key component of semi-artificial photosynthetic systems. However, to date, the types and quantities of semiconductors used in semi-artificial photosynthetic systems are very limited. This is due not only to the need for semiconductor modification to improve solar energy utilization and electron-hole recombination rates, but also to considerations of biocompatibility, biotoxicity under light, and system compatibility. For instance, inorganic semiconductor nanoparticles, such as CdS, InP, and carbon quantum dots, are generally synthesized through in-situ precipitation or high-temperature, high-pressure processes, making single-crystal structures difficult to characterize and structure-property relationships unclear. Furthermore, these materials typically suffer from low photogenerated carrier separation efficiency, low electron transfer-utilization efficiency at the semiconductor / microorganism interface, or limited interface area exposing microorganisms to the external environment, leading to poor system stability and low sustainability. In contrast, organic semiconductors, such as perylene diimide derivatives and fluorene derivatives, offer advantages such as tunable structure, good biocompatibility, low biotoxicity, and high extracellular electron transfer capabilities. However, their drawbacks include complex synthesis processes and low system stability and sustainability. Therefore, designing and developing semiconductors that balance high photocatalytic activity and cell viability, and whose non-biological / biological interfaces can be designed and regulated, has become a major challenge in the construction of high-performance semi-artificial photosynthetic systems. Summary of the Invention

[0007] To overcome the problems existing in the prior art, the present invention aims to provide the preparation of a *Lactococcus lactis* / MOF composite photocatalyst and its application in degrading chrome black T. This composite material preparation method has significant advantages such as simple operation, mild conditions, environmental friendliness, and good repeatability, and can be achieved at room temperature and pressure. L. lactis Highly efficient composite with MOF materials, while maximizing the retention of [material type] during the composite process. L. lactis The bioactivity and crystal structure integrity of MOFs materials provide a feasible technical path for large-scale preparation.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a lactococcus lactis / MOF composite photocatalyst includes the following steps; Step 1: Prepare MOF materials, wherein the MOF materials are Zr-BTB MOL or hexazirconium oxyhydroxy cluster-based metal-organic framework MOF-808; Step 2: Grow Lactococcus lactis in a culture medium to obtain freshly inoculated bacteria. L. lactis; Step 3: Put L. lactis Single colonies were mixed with the MOFs material, centrifuged, and then the supernatant was discarded. The mixture was washed with PBS solution by centrifugation and then separated by centrifugation to obtain the Lactococcus lactis / MOF composite photocatalyst.

[0009] The preparation method of the Zr-BTB MOL is as follows: ZrCl4 and 1,3,5-tris(4-carboxyphenyl)benzene were mixed, and N,N-dimethylformamide (DMF) was added to obtain a mixed solution. The solution was sonicated and then formic acid and distilled water were added sequentially. The solution was then heated in an oven, followed by washing and drying to obtain Zr-BTB MOL.

[0010] The preparation method of the Zr-BTB MOL is as follows: ZrCl4 and 1,3,5-tris(4-carboxyphenyl)benzene were mixed, and N,N-dimethylformamide (DMF) was added to obtain a mixed solution. The solution was sonicated and then formic acid and distilled water were added sequentially. The solution was then heated in an oven, followed by washing and drying to obtain Zr-BTB MOL.

[0011] The volume ratio of DMF:formic acid:distilled water is 10:(3-6):(0.5-2).

[0012] The items are placed in an oven for heating, followed by washing and drying, under the following conditions: After sealing with tin foil, place in an oven and heat at 120 ℃ for 36-72 h. After cooling to room temperature, centrifuge and wash 2-4 times with DMF and ethanol respectively, and then dry to obtain Zr-BTB MOL.

[0013] The preparation method of the hexazirconium oxyhydroxy cluster-based metal-organic framework MOF-808 is as follows: ZrOCl2·8H2O and pyromellitic acid were dissolved in a mixed solution of deionized water and formic acid, sonicated, heated in an oven, cooled to room temperature, and the product was collected by centrifugation. The product was washed successively with deionized water and ethanol by centrifugation and dried to obtain hexazirconium oxyhydroxy cluster metal-organic framework MOF-808.

[0014] The molar ratio of ZrOCl2·8H2O to trimesic acid is 4:1-2:1; the product is heated in an oven at 100 ℃ for 24-36 h; and the obtained product is dried at 80-120 ℃ for 6-12 h.

[0015] Weigh 0.585 g (1.82 mmol) of zirconium chloride octahydrate (ZrOCl2·8H2O) and 0.095-0.191 g (0.45-0.91 mmol, molar ratio 4:1-2:1), dissolve them in a mixture of deionized water (5 mL) and formic acid (5 mL), and sonicate for 5 minutes. Place the mixture in a 100 ℃ oven and heat for 24-36 h. After heating, cool to room temperature, collect the product by centrifugation, and wash three times each with deionized water (3 mL) and ethanol (3 mL). Finally, dry the obtained product at 80-120 ℃ for 6-12 h to obtain hexazirconium oxyhydroxyl cluster metal-organic framework (MOF-808).

[0016] Step 2 specifically involves: To maintain the viability of the strain, inoculation is required within 15 days; Lactococcus lactis is grown in De Man, Rogosa and Sharpe Broth (MRS broth). L. lactis The specific procedures for vaccination are as follows: MRS broth needs to be diluted. Mix 2.5-3.0 g of solid MRS broth with 50 mL of distilled water. This ratio can be scaled up or down proportionally. Add 0.7-0.9 g of agar powder to the liquid broth. Seal the necessary experimental tools and broth in a high-temperature, high-pressure autoclave to obtain the culture medium. Sterilize at 121 °C for 15-30 min. When the culture medium temperature drops to 50-60 °C, pour it into petri dishes. After the medium solidifies, streak colonies in four zones (on a solid culture medium plate, gradually dilute and inoculate bacteria in four zones; the core purpose is to gradually disperse the dense bacteria, eventually resulting in a single, independent colony in the last zone, facilitating subsequent pure colony selection for identification and culturing). Incubate the petri dishes in a 37 °C incubator for 12-20 h, then seal with tape and store at 2-5 °C. This yields freshly inoculated culture. L. lactis This is to prepare for subsequent integration with Zr-BTB MOL and MOF-808.

[0017] Step 3 specifically involves: Dip a spoon into the clean bench L. lactis Single colonies were placed in 8-15 mL of liquid culture medium and incubated at 37 °C for 14-24 h. After incubation, the optical density (OD) was measured, and phosphate-buffered saline (PBS) was continuously added until the OD value reached 0.5. Then, a new centrifuge tube was used. L. lactis The bacterial culture was mixed with MOF materials, and the concentration of the mixture was adjusted based on the growth curve results. It can be seen that... L. lactis / Zr-BTB MOL and L.lactis The composite concentration of / MOF-808 was 200 μg / mL, which resulted in better growth. The mixture was then shaken at 37 °C for 10–24 h, followed by centrifugation at 1000–2500 r / min. The supernatant was discarded, and the composite material was retained. The composite material was washed 3–5 times with PBS solution by centrifugation, and finally separated by centrifugation at 6000–7000 r / min.

[0018] Specific methods for photocatalytic degradation of chrome black T using composite photocatalytic materials: Experimental preparation: Prepare simulated wastewater of Eriochrome Black T with a concentration of 40-140 mg / L and place it in a light-proof container for later use; take the prepared... L. lactis / Zr-BTB MOL and L.lactis / MOF-808 composite photocatalyst material, accurately weigh according to experimental requirements (dosage 5-25 mg); Visible light catalytic degradation: The mixed system was irradiated under a visible light source (350-780 nm) and continuously magnetically stirred to ensure the uniformity of the system; Degradation effect detection: Samples were taken at 5-minute intervals during irradiation. After centrifugation, the absorbance of the supernatant at the characteristic absorption peak of Eriochrome Black T was measured using a UV-Vis spectrophotometer. The remaining concentration of Eriochrome Black T was calculated, and the degradation efficiency was obtained. Practical water application: For the degradation of Chromium Black T in complex river water environments, the composite photocatalytic material can be directly added to the river water sample containing Chromium Black T at the above-mentioned optimal dosage, and the steps can be repeated 3-6 times.

[0019] L. lactis Scanning electron microscopy (SEM) images of Zr-BTB MOL show that Zr-BTB MOL has a nanosheet-like structure, which is uniformly coated after compositing. L. lactis On the surface of the bacteria, a sheet-like MOF is formed that tightly encapsulates the bacteria, with no obvious MOF aggregation and sufficient interfacial contact. X-ray powder diffraction (PXRD) analysis confirmed that the composite Zr-BTB MOL skeleton structure is intact and the characteristic diffraction peaks are retained. Infrared (IR) spectroscopy showed the presence of characteristic peaks of C=O bonds and Zr-O bonds, indicating that the coordination structure is stable. L. lactis SEM images of MOF-808 show that the composite granular MOF-808 is uniformly adhered to the surface. L. lactis On and around the bacterial cell surface, a porous particle-bacterial cell dispersion complex structure is formed, and the MOF morphology is not destroyed. Figure 3 PXRD confirmed that the main diffraction peaks of MOF-808 after recombination matched, and the crystal structure was complete; the characteristic peaks of C=O bond and Zr-O bond in IR spectrum were clear, indicating that the cluster-based coordination framework was stable.

[0020] The beneficial effects of this invention are: L.lactis The composite of Zr-BTB MOL or MOF-808 significantly promotes the photocatalytic degradation of Chrome Black T, specifically as follows: L.lactis The promoting effect of the composite of Zr-BTB MOL and MOF-808 on the photocatalytic degradation of Eriochrome Black T originates from the synergistic reaction mechanism of biological, inorganic and organic materials. Through the interfacial interaction between the bacteria and MOF materials, the core photocatalytic links (light absorption, charge separation, generation of active species, etc.) are optimized, ultimately achieving a significant improvement in degradation performance. The specific mechanism is as follows: L. lactis The introduction of these technologies creates a "bio-semiconductor" interface, resulting in narrower band gaps (Zr-BTB MOL band gap decreased from 3.25 eV to 2.84 eV; MOF-808 band gap decreased from 3.74 eV to 3.63 eV), triggering electronic structure reconstruction. L. lactis / Zr-BTB MOL: The narrowed band gap (2.84 eV) allows photogenerated electrons to acquire higher migration kinetic energy. Simultaneously, the tight encapsulation structure of the bacteria and MOF (SEM characterization) increases the interfacial contact area, reducing charge migration resistance. Electrochemical impedance spectroscopy shows that the impedance of this composite material is significantly lower than that of pure Zr-BTB MOL, confirming improved charge separation efficiency, ultimately manifested as a stronger photocurrent density (confirmed by transient photocurrent spectra).

[0021] for L. lactis / MOF-808: The structure of MOF-808 provides a channel for charge migration, while L. lactis The bacteria adhere to the surface and surrounding areas of the pores, forming a charge trapping-transfer network. Although its band gap narrowing is less than that of Zr-BTBMOL, the synergistic effect of the porous structure and the bacteria significantly enhances the photocurrent response, and impedance spectroscopy shows that its charge transfer resistance is lower than that of pure MOF-808. Under conditions of 100 mg / L chrome black T concentration and 15 mg catalyst dosage, both composite materials exhibit excellent degradation performance. L. lactis The degradation rate constant of / Zr-BTB MOL is 0.041 min. -1 Complete degradation in 50 minutes; L. lactis The degradation rate constant of / MOF-808 is 0.043 min. -1 Complete degradation occurs within 45 minutes. Furthermore, both composite materials maintain high degradation performance even in complex river water environments. Attached Figure Description

[0022] Figure 1 It is Zr-BTB MOL, MOF-808, L.lactis / Zr-BTB MOL and L.lactis X-ray powder diffraction pattern of / MOF-808.

[0023] Figure 2 It is Zr-BTB MOL, MOF-808, L.lactis / Zr-BTB MOL and L.lactis IR spectrum of / MOF-808.

[0024] Figure 3 It is Zr-BTB MOL, MOF-808, L.lactis / Zr-BTB MOL and L.lactis Microstructure of MOF-808: (a) Zr-BTB MOL; (b) MOF-808; (c) L.lactis / Zr-BTB MOL;(d) L.lactis / MOF-808.

[0025] Figure 4 It is Zr-BTB MOL, MOF-808, L.lactis / Zr-BTB MOL and L.lactis The UV-Vis diffuse reflectance spectrum and band gap energy of / MOF-808.

[0026] Figure 5 It is Zr-BTB MOL, MOF-808, L.lactis / Zr-BTB MOL and L.lactis Transient photocurrent spectrum of / MOF-808.

[0027] Figure 6 It is Zr-BTB MOL, MOF-808, L.lactis / Zr-BTB MOL and L.lactis Impedance spectrum of / MOF-808.

[0028] Figure 7 yes L.lactis UV absorption curves of the degradation of different concentrations of Eriochrome Black T by / Zr-BTB over time: (a) Eriochrome Black T concentration of 40 mg / L; (b) Eriochrome Black T concentration of 60 mg / L; (c) Eriochrome Black T concentration of 80 mg / L; (d) Eriochrome Black T concentration of 100 mg / L; (e) Eriochrome Black T concentration of 120 mg / L; (f) Eriochrome Black T concentration of 140 mg / L.

[0029] Figure 8 yes L.lactis First-order kinetic curves of the degradation and elimination of different concentrations of Eriochrome Black T by / Zr-BTB: (a) Eriochrome Black T concentration of 40 mg / L; (b) Eriochrome Black T concentration of 60 mg / L; (c) Eriochrome Black T concentration of 80 mg / L; (d) Eriochrome Black T concentration of 100 mg / L; (e) Eriochrome Black T concentration of 120 mg / L; (f) Eriochrome Black T concentration of 140 mg / L.

[0030] Figure 9 Different load values L. lactis UV absorption curves of Zr-BTB on the degradation and elimination of Eriochrome Black T over time: (a) L.lactis / Zr-BTB loading dose is 5 mg; (b) L.lactis / Zr-BTB loading dose is 10 mg; (c) [[ID= / Zr-BTB loading dose: 20 mg; (d) ​ The loading dose of Zr-BTB was 25 mg.

[0031] ​ Different load values ​ First-order kinetic curve of Zr-BTB for the degradation and elimination of Chrome Black T: (a)​ / Zr-BTB loading dose is 5 mg; (b) ​ / Zr-BTB loading amount is 10 mg; (c) ​ / Zr-BTB loading dose: 20 mg; (d) ​ The loading dose of Zr-BTB was 25 mg.

[0032] ​ yes ​ UV absorption curves of the degradation of different concentrations of Eriochrome Black T by MOF-808 over time: (a) Eriochrome Black T concentration of 40 mg / L; (b) Eriochrome Black T concentration of 60 mg / L; (c) Eriochrome Black T concentration of 80 mg / L; (d) Eriochrome Black T concentration of 100 mg / L; (e) Eriochrome Black T concentration of 120 mg / L; (f) Eriochrome Black T concentration of 140 mg / L.

[0033] ​ yes ​ First-order kinetic curves of the degradation and elimination of different concentrations of Eriochrome Black T by MOF-808: (a) Eriochrome Black T concentration of 40 mg / L; (b) Eriochrome Black T concentration of 60 mg / L; (c) Eriochrome Black T concentration of 80 mg / L; (d) Eriochrome Black T concentration of 100 mg / L; (e) Eriochrome Black T concentration of 120 mg / L; (f) Eriochrome Black T concentration of 140 mg / L.

[0034] ​ Different load values ​ / MOF-808's UV absorption curve for the degradation and elimination of Chrome Black T over time: (a) ​ / MOF-808 loading dose is 5 mg; (b) ​ / MOF-808 loading dose: 10 mg; (c) ​ The MOF-808 loading dose was 20 mg; (d) ​ The MOF-808 loading dose is 25 mg.

[0035] ​ Different load values ​ First-order kinetic curve of the degradation and elimination of Chrome Black T by MOF-808: (a) ​ / MOF-808 loading dose is 5 mg; (b) ​ / MOF-808 loading dose: 10 mg; (c) ​ The MOF-808 loading dose was 20 mg; (d) ​ The MOF-808 loading dose is 25 mg.

[0036] ​ yes ​Cyclic performance of / Zr-BTB degrading Chrome Black T.

[0037] ​ yes ​ / Zr-BTB degradation of chrome black T in river water recycling performance.

[0038] ​ yes ​ / MOF-808 degradation of chrome black T cycling performance.

[0039] ​ yes ​ / MOF-808's ability to degrade Chrome Black T in river water and its recycling performance.

[0040] ​ yes ​ Growth curves of / Zr-BTB composite materials.

[0041] ​ yes ​ Growth curves of the MOF-808 composite material.

[0042] ​ ​ / Zr-BTB MOL and ​ Schematic diagram of the visible light degradation mechanism of chrome black T in MOF-808 composite material. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the accompanying drawings.

[0044] Example 1: Step 1: Preparation of Zr-BTB MOL: 10.12 mg of ZrCl4 and 12.5 mg of 1,3,5-tris(4-carboxyphenyl)benzene (C) were weighed into a transparent glass bottle in sequence. 27 H 18 Add 1.5 mL of DMF to a glass bottle containing O6. Sonicate the mixture for 20 min, then add 0.75 mL of formic acid and 0.15 mL of distilled water. Seal the bottle with aluminum foil and heat in an oven at 120 °C for 48 h. After cooling to room temperature, wash the bottle three times with DMF and ethanol, and dry to obtain Zr-BTB MOL.

[0045] Preparation of MOF-808: Tristyric acid (0.127 g) and ZrOCl2·8H2O (0.585 g) were dissolved in a mixed solution of deionized water (5 mL) and formic acid (5 mL), and sonicated for 5 min. The mixture was then heated in a 100 ℃ oven for 24 h. After heating, the mixture was cooled to room temperature, and the product was collected by centrifugation. The product was washed three times each with deionized water (3 mL) and ethanol (3 mL), and finally dried at 100 ℃ for 8 h.

[0046] Step 2: Inoculation procedure: Lactococcus lactis was cultured in MRS broth, which required dilution: 2.76 g of MRS broth solid was mixed with 50 mL of distilled water (this ratio can be scaled up or down proportionally). 1.5% agar powder was added to the broth and sterilized at 121 °C for 20 min. When the culture medium temperature dropped to 60 °C, the medium was poured into Petri dishes. After the medium solidified, colonies were streaked in four zones. The Petri dishes were then incubated at 37 °C for 15 h. Afterward, the Petri dishes were sealed with tape and stored at 4 °C.

[0047] Step 3: ​ Composition with MOFs: A single colony was placed in 10 mL of liquid culture medium in a clean bench and incubated at 37 °C for 14 h. After incubation, the OD value was measured, and PBS was continuously added until the OD value reached 0.5. Then, a new centrifuge tube was used to mix the MOF material and bacterial culture. The concentration of the mixture was adjusted according to the growth curve results. ​ and ​ ): ​ / Zr-BTB MOL (200 μg / mL) and ​ Mix MOF-808 (200 μg / mL) and shake at 37 °C for 12 h. Centrifuge at 1000 r / min, then discard the supernatant and retain the composite material. Wash three times with PBS solution by centrifugation, and finally separate the composite material by centrifugation at 6000 r / min.

[0048] Example 2: Step 1: Preparation of Zr-BTB MOL: 10.12 mg of ZrCl4 and 12.5 mg of 1,3,5-tris(4-carboxyphenyl)benzene (C) were weighed into a transparent glass bottle in sequence. 27 H 18Add 1.8 mL of DMF to a glass bottle containing O6. Sonicate the mixture for 20 min, then add 0.75 mL of formic acid and 0.15 mL of distilled water. Seal the bottle with aluminum foil and heat in an oven at 120 °C for 48 h. After cooling to room temperature, wash the bottle three times with DMF and ethanol, and dry to obtain Zr-BTB MOL.

[0049] Preparation of MOF-808: Tristyrene (0.127 g) and zirconium chloride octahydrate (ZrOCl₂·8H₂O) (0.585 g) were dissolved in a mixture of deionized water (6 mL) and formic acid (5 mL), and the mixture was sonicated for 5 min. The mixture was then heated in a 100 ℃ oven for 24 h. After heating, the mixture was cooled to room temperature, and the product was collected by centrifugation. The product was washed three times each with deionized water (3 mL) and ethanol (3 mL), and finally dried at 100 ℃ for 8 h.

[0050] Step 2: Inoculation procedure: Lactococcus lactis was cultured in MRS broth, which required dilution: 2.76 g of MRS broth solid was mixed with 50 mL of distilled water (this ratio can be scaled up or down proportionally). 1.5% agar powder was added to the broth and sterilized at 121 °C for 20 min. When the culture medium temperature dropped to 60 °C, the medium was poured into Petri dishes. After the medium solidified, colonies were streaked in four zones. The Petri dishes were then incubated at 37 °C for 15 h. Afterward, the Petri dishes were sealed with tape and stored at 4 °C.

[0051] Step 3: ​ Composition with MOFs: A single colony was placed in 11 mL of liquid culture medium in a clean bench and incubated at 37 °C for 14 h. After incubation, the OD value was measured, and PBS was continuously added until the OD value reached 0.5. Then, a new centrifuge tube was used to mix the MOF material and bacterial culture. The concentration of the mixture was adjusted according to the growth curve results. ​ and ​ ): ​ / Zr-BTB MOL (200 μg / mL) and ​ Mix MOF-808 (200 μg / mL) and shake at 37 °C for 12 h. Centrifuge at 1000 r / min, then discard the supernatant and retain the composite material. Wash three times with PBS solution by centrifugation, and finally separate the composite material by centrifugation at 6000 r / min.

[0052] Example 3: Step 1: Preparation of Zr-BTB MOL: 10.12 mg of ZrCl4 and 12.5 mg of 1,3,5-tris(4-carboxyphenyl)benzene (C) were weighed into a transparent glass bottle in sequence. 27 H 18 Add 2 mL of DMF to a glass bottle containing O6. Sonicate the mixture for 20 min, then add 0.75 mL of formic acid and 0.15 mL of distilled water. Seal the bottle with aluminum foil and heat in an oven at 120 °C for 48 h. After cooling to room temperature, wash the bottle three times with DMF and ethanol, and dry to obtain Zr-BTB MOL.

[0053] Preparation of MOF-808: Tristyric acid (0.127 g) and ZrOCl2·8H2O (0.585 g) were dissolved in a mixture of deionized water (7 mL) and formic acid (5 mL), and the mixture was sonicated for 5 min. The mixture was then heated in a 100 ℃ oven for 24 h. After heating, the mixture was cooled to room temperature, and the product was collected by centrifugation. The product was washed three times each with deionized water (3 mL) and ethanol (3 mL), and finally dried at 100 ℃ for 8 h.

[0054] Step 2: Inoculation procedure: Lactococcus lactis was cultured in MRS broth, which required dilution: 2.76 g of MRS broth solid was mixed with 50 mL of distilled water (this ratio can be scaled up or down proportionally). 1.5% agar powder was added to the broth and sterilized at 121 °C for 20 min. When the culture medium temperature dropped to 60 °C, the medium was poured into Petri dishes. After the medium solidified, colonies were streaked in four zones. The Petri dishes were then incubated at 37 °C for 15 h. Afterward, the Petri dishes were sealed with tape and stored at 4 °C.

[0055] Step 3: ​ Composition with MOFs: A single colony was placed in 12 mL of liquid culture medium in a clean bench and incubated at 37 °C for 14 h. After incubation, the OD value was measured, and PBS was continuously added until the OD value reached 0.5. Then, a new centrifuge tube was used to mix the MOF material and bacterial culture. The concentration of the mixture was adjusted according to the growth curve results. ​ and ​ ): ​ / Zr-BTB MOL (200 μg / mL) and ​Mix MOF-808 (200 μg / mL) and shake at 37 °C for 12 h. Centrifuge at 1000 r / min, then discard the supernatant and retain the composite material. Wash three times with PBS solution by centrifugation, and finally separate the composite material by centrifugation at 6000 r / min.

[0056] Zr-BTB MOL, MOF-808 ​ / Zr-BTB MOL and ​ Structural characterization of MOF-808: PXRD shows that ( ​ ), ​ The characteristic peaks of Zr-BTB MOL still exist after recombination, but the diffraction intensity is significantly reduced. ​ The intensity of the MOF-808 diffraction peaks is reduced after recombination, but the main peaks still match MOF-808. ​ / Zr-BTB MOL and ​ The IR spectrum of / MOF-808 indicates the presence of C=O and Zr-O bonds. ​ Zr-BTB MOL, MOF-808 ​ / Zr-BTB MOL and ​ SEM images of / MOF-808 show L. ​ Successful integration with MOF ( ​ ).

[0057] Zr-BTB MOL, MOF-808 ​ / Zr-BTB MOL and ​ Photoelectric Properties Study of MOF-808: Ultraviolet-Vis (UV-vis) Spectroscopic Research ​ The absorption wavelength of / Zr-BTB MOL is 265-328 nm, which is significantly increased compared to Zr-BTB (259-303 nm). This increased absorption wavelength range indicates that... ​ / Zr-BTB MOL has excellent light absorption properties ( ​ a). Similarly, MOF-808 and ​ The recombined absorption wavelength range is also significantly wider, with absorption wavelengths of 256-274 nm and 287-313 nm, compared to MOF-808 (254-274 nm, 286-307 nm). This increased absorption wavelength range indicates... ​ MOF-808 has the potential for excellent photocatalytic performance. ​ a). Based on the relationship between frequency and optical absorption coefficient of semiconductor materials, Zr was calculated using the Tauc curve method. BTB MOL, MOF 808 ​ / Zr BTB MOL and L. ​ / MOF The bandgap width of 808, such as ​ As shown in b, the Zr-BTB MOL, MOF-808, ​ / Zr-BTBMOL and ​ The band gaps of / MOF-808 are 3.25, 3.74, 2.84, and 3.63 eV, respectively. Further research is needed on Zr-BTB MOL, MOF-808, and... ​ / Zr-BTB MOL and ​ The separation efficiency of photogenerated electrons and holes in MOF-808 was investigated by transient photocurrent response and electrochemical impedance spectroscopy. The transient photocurrent response results showed that, compared to MOFs, [the efficiency was significantly improved]. ​ / Zr-BTB MOL and ​ The transient photocurrent response of / MOF-808 is significantly improved, among which, L. ​ / Zr-BTB MOL has the highest photocurrent density ( ​ Electrochemical impedance spectroscopy showed that, compared to MOFs, ​ / Zr-BTB MOL and ​ The impedance of / MOF-808 is significantly reduced. Figure 6 This indicates that MOFs and L. lactis The recombination can effectively avoid the recombination of photogenerated electrons and holes, and effectively improve the charge separation efficiency.

[0058] like Figure 21 As shown, lactis / Zr-BTB MOL and L. lactis / MOF-808 photocatalytic degradation of chrome black T: First, the above-synthesized L. lactis / Zr-BTB MOL was applied to the study of photocatalytic degradation of Eriochrome Black T. The study showed that as the concentration of Eriochrome Black T increased (40 mg / L → 140 mg / L), the degradation efficiency of Eriochrome Black T gradually decreased. Figure 7 and Figure 8 ).when L. lactis When the Zr-BTB MOL loading was 15 mg, the Eriochrome Black T concentration was 100 mg / L, and the degradation efficiency of Eriochrome Black T reached 92% after 55 min (…), Figure 7 d) The degradation rate constant is 0.041 min. -1 ( Figure 8 d). In addition, with L. lactis With increasing Zr-BTB MOL loading (5 mg → 25 mg), the degradation efficiency and degradation rate constant of Chrome Black T gradually increased. Figure 9 and Figure 10 When the concentration of Eriochrome Black T was 100 mg / L, the photocatalyst loading was 25 mg, and the degradation time was 50 min, the degradation efficiency of Eriochrome Black T reached as high as 98.9%. Figure 9 d) The degradation rate constant is 0.108 min. -1 ( Figure 10 d). In conclusion, 25 mg was selected. L. lactis Zr-BTB MOL and 100 mg / L Chrome Black T were used as the optimal reaction conditions for subsequent reactions. L. lactis / Zr-BTB MOL photocatalytic degradation of chrome black T. Furthermore, under optimal degradation conditions, after five consecutive photocatalytic degradation experiments, L. lactis The degradation efficiency of Zr-BTB in deionized water and river water remained at 57.8% and 70.2%, respectively. Figure 15 and Figure 16 ), and then continued research. L.lactis / MOF-808 photocatalytic degradation performance of Eriochrome Black T. Studies have shown that as the concentration of Eriochrome Black T increases (40 mg / L → 140 mg / L), the degradation efficiency of Eriochrome Black T gradually decreases. Figure 11 and Figure 12 ).when L.lactis When the MOF-808 loading amount was 15 mg, the Eriochrome Black T concentration was 100 mg / L, and the degradation efficiency of Eriochrome Black T was 86% after 50 min (… Figure 11 d) The degradation rate constant is 0.043 min. -1 ( Figure 12 d). Furthermore, with L. lactis With increasing MOF-808 loading (5 mg → 25 mg), the degradation efficiency and degradation rate constant of Eriochrome Black T gradually increased. Figure 13 and Figure 14 When the concentration of Chrome Black T was 100 mg / L, the photocatalyst loading was 25 mg, and the degradation time was 50 min, the degradation efficiency of Chrome Black T reached as high as 92.6%. Figure 13 d) The degradation rate constant is as high as 0.05 min. -1 ( Figure 14 d). In conclusion, 25 mg was selected. L. lactis MOF-808 and 100 mg / L Chrome Black T were used as the optimal reaction conditions for subsequent reactions. L. lactis A study on the photocatalytic degradation of chrome black T by MOF-808 composite materials. Under optimal degradation conditions, after five consecutive photocatalytic degradation experiments, L. lactis The degradation efficiency of MOF-808 in deionized water and river water was 65.1% and 62.6%, respectively. Figure 17 and Figure 18 ).

Claims

1. A method for preparing a *Lactococcus lactis* / MOF composite photocatalyst, characterized in that, Includes the following steps; Step 1: Prepare MOF materials, wherein the MOF materials are Zr-BTB MOL or hexazirconium oxyhydroxy cluster-based metal-organic framework MOF-808; Step 2: Grow Lactococcus lactis in a culture medium to obtain freshly inoculated bacteria. L. lactis; Step 3: Put L. lactis Single colonies were mixed with the MOFs material, centrifuged, and then the supernatant was discarded. The mixture was washed with PBS solution by centrifugation and centrifugation to obtain the Lactococcus lactis / MOF composite photocatalyst.

2. The preparation method of the Lactococcus lactis / MOF composite photocatalyst according to claim 1, characterized in that, The preparation method of the Zr-BTB MOL is as follows: ZrCl4 and 1,3,5-tris(4-carboxyphenyl)benzene were mixed, and N,N-dimethylformamide (DMF) was added to obtain a mixed solution. The solution was sonicated and then formic acid and distilled water were added sequentially. The solution was then heated in an oven, followed by washing and drying to obtain Zr-BTBMOL.

3. The preparation method of the Lactococcus lactis / MOF composite photocatalyst according to claim 2, characterized in that, The ratio of ZrCl4, 1,3,5-tris(4-carboxyphenyl)benzene, N,N-dimethylformamide, formic acid, and distilled water is (7.0-14.0) mg : 12.5 mg : 1.5 mL : (0.45-0.9) mL : (0.075-0.3) mL; The items are placed in an oven for heating, followed by washing and drying, under the following conditions: After sealing with tin foil, place in an oven and heat at 120 ℃ for 36-72 h. After cooling to room temperature, centrifuge and wash 2-4 times with DMF and ethanol respectively, and then dry to obtain Zr-BTB MOL.

4. The preparation method of the Lactococcus lactis / MOF composite photocatalyst according to claim 1, characterized in that, The preparation method of the hexazirconium oxyhydroxy cluster-based metal-organic framework MOF-808 is as follows: ZrOCl2·8H2O and pyromellitic acid were dissolved in a mixed solution of deionized water and formic acid, sonicated, heated in an oven, cooled to room temperature, and the product was collected by centrifugation. The product was washed successively with deionized water and ethanol by centrifugation and dried to obtain hexazirconium oxyhydroxy cluster metal-organic framework MOF-808.

5. The method for preparing the *Lactococcus lactis* / MOF composite photocatalyst according to claim 4, characterized in that, The molar ratio of ZrOCl2·8H2O to trimesic acid is 4:1-2:1; the product is heated in an oven at 100 ℃ for 24-36 h; and the obtained product is dried at 80-120 ℃ for 6-12 h.

6. The method for preparing the Lactococcus lactis / MOF composite photocatalyst according to claim 1, characterized in that, Step 2 specifically involves: Lactococcus lactis was grown in MRS broth medium; L. lactis The specific procedures for vaccination are as follows: Mix 2.5-3.0 g of MRS broth solid with 50 mL of distilled water; then add 0.7-0.9 g of agar powder to the broth liquid. Seal the necessary experimental tools and broth and place them in a high-temperature, high-pressure autoclave to obtain the culture medium. Sterilize at 121 ℃ for 15-30 min. When the culture medium temperature drops to 50-60 ℃, pour the medium into petri dishes. After the medium solidifies, streak colonies in four zones. Incubate the petri dishes in a 37 ℃ incubator for 12-20 h. Seal the petri dishes with tape and store them in a 2-5 ℃ refrigerator to obtain freshly inoculated culture. L. lactis .

7. The method for preparing the *Lactococcus lactis* / MOF composite photocatalyst according to claim 1, characterized in that, Step 3 specifically involves: Dip a spoon into the clean bench L. lactis Single colonies were placed in 8-15 mL of liquid culture medium and incubated at 37 ℃ for 14-24 h. After incubation, the optical density was measured, and phosphate-buffered saline was continuously added until the OD value was 0.

5. A new centrifuge tube was then used to... L. lactis The bacterial culture was mixed with MOF materials, and the concentration of the mixture was adjusted according to the growth curve results. The mixture was then shaken at 37 °C for 10-24 h, centrifuged at 1000-2500 r / min, and the supernatant was discarded. The mixture was then washed 3-5 times with PBS solution by centrifugation. Finally, it was centrifuged at 6000-7000 r / min to separate the composite material.

8. The composite photocatalytic material prepared by the method according to any one of claims 1-7 is used for the photocatalytic degradation of chrome black T in water.

9. The application according to claim 8, characterized in that: The concentration of the chrome black T is 40-140 mg / L.

10. The application according to claim 8, characterized in that: The composite photocatalyst material was added to water containing chrome black T and irradiated under a 350-780 nm visible light source. The conditions were: chrome black T concentration 100 mg / L and catalyst dosage 15 mg. L. lactis / Zr-BTB MOL completely degrades Chrome Black T in 50 minutes; L. lactis / MOF-808 completely degrades Chrome Black T in 45 minutes.

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