Design And Performance Study Of Carbon Nitride Based Photo-enzyme Coupling System

Environmental pollution and energy crisis are the major problems of the 21st century.Enzyme catalysis technology has been widely concerned because of its characteristics of environmental protection,specificity and high efficiency.Among them,oxidoreductase is an important industrial biocatalcatalyst with high selectivity and mild reaction conditions.However,most redox enzymes require redox medium to participate in the reaction and natural enzyme molecules are sensitive to the environment,difficult to recycle and high application cost natural defects limit their industrial application in the field of environmental protection and energy.Therefore,the development of functional carrier materials combined with enzyme immobilization technology to achieve simple and efficient in-situ generation（regeneration）of redox medium is very important for industrial biocatalysis.Inspired by natural photosynthesis,this paper takes graphitic carbon nitride（g-C₃N₄）as photocatalyst and combines it with biocatalyst（cytochrome C,horseradish peroxidase,ethanol dehydrogenase）to construct a g-C₃N₄-based photo-enzyme coupling system by means of adsorption method and biomimetical mineralization method,combining the high efficiency of photocatalysis technology with the specificity of enzyme catalysis.The structural morphology,physical and chemical properties,enzymatic properties,photocatalytic properties of the photo-enzyme coupling system,as well as the mechanism and law of the excitation,migration and conversion of photogenerated electron-hole pairs in the composite system were systematically studied.The details are as follows:1.A g-C₃N₄-based nonmetallic composite photocatalyst（PEDOT/CN）with 1D/2D complex heterojunctions was prepared by in-situ thermal polymerization,which improves the performance of pure g-C₃N₄ and is used for the immobilization of Cyt c.By optimizing the immobilization process,it was found that the maximum loading amount of Cyt c on PEDOT₃/CN reached 528.29 mg/g.By regulating the proportion of Cyt c,the best photo-enzyme coupling system Cytc_0.5/PEDOT₃/CN was prepared and applied to the degradation of BPA in water.The degradation rate of Cytc_0.5/PEDOT₃/CN was 68.22%within 60 min,which was 1.61 times than that of PEDOT₃/CN.The calculated rate constant k of Cytc_0.5/PEDOT₃/CN is 0.0195 min^-1,which is 2.03 times that of PEDOT₃/CN(0.0096 min^-1).The main active species were·OH,h⁺and H₂O₂during the degradation of BPA by Cytc_0.5/PEDOT₃/CN through free radical capture and ESR characterization.2.The highly adsorbent Ppy was prepared by chemical polymerization and used for immobilization of HRP.The prepared HRP/Ppy has high loading amount of HRP（831.00 mg/g）and excellent storage stability.88.26%of the initial enzyme activity is still retained after 18 days of storage.Moreover,HRP/Ppy/CN photo-enzyme coupling catalytic system was further constructed by combining with g-C₃N₄.Because Ppy acted as an electronic transmission channel in the light-enzyme coupling system,the synergies of HRP/Ppy/CN light-enzyme coupling system were improved,and the degradation rate of BPA reached 86.03%in 60 min,which was 1.91 times that of pure g-C₃N₄.The main active substances in the degradation of BPA by HRP/Ppy/CN were·O₂^-and h⁺through free radical capture experiments and ESR.3.HRP-CN/Cu₃（PO₄）₂ hybrid nanoflowers were constructed by introducing g-C₃N₄ into the system of enzyme-inorganic hybrid nanoflowers by biommineralization.Because of the unique three-dimensional nanoflower structure of the HRP-CN/Cu₃（PO₄）₂ photo-enzyme coupling system,it not only shows excellent immobilized enzyme properties,but also has better tolerance to extreme acid,alkali and high temperature.Compared with the traditional enzyme-inorganic hybrid nanoflowers,the introduction of semiconductor（g-C₃N₄）not only increased the fixing rate of HRP（36.2%）,but also enhanced the enzyme activity of immobilized HRP.The residual activity was 83.6%after 5 cycles.In addition,HRP-CN/Cu₃（PO₄）₂ showed higher catalytic activity against BPA.The degradation rate of BPA by HRP-CN/Cu₃（PO₄）₂within 60 min was 72.98%,which was about 15.49 times that of HRP/Cu₃（PO₄）₂（4.71%）.The improvement of activity was attributed to the introduction of g-C₃N₄,which produced H₂O₂ and activated HRP under visible light.In addition,the photo-fenton system is constructed by the formation of Cu²⁺(Fe³⁺),photo-generated electrons and H₂O₂,which produces a large amount of·OH and completely degrades BPA into CO₂and H₂O.Finally,the degradation pathway and mechanism of BPA were studied by MS technology.4.Combined with biomimetic mineralization method and one-step calcination method,UIO-66 with mesoporous pore channels was prepared and used for the immobilization of ADH to obtain the immobilized alcohol dehydrogenase（ADH/UIO-66）.After the immobilization process optimization（the content of UIO-66 was 1 mg;ADH concentration was 0.3 mg/m L;the immobilization time was 8 h）,the optimal fixation capacity of ADH/UIO-66 was 264.84 mg/g.The optimum photo-enzyme coupled catalyst（ADH/UIO-66/CN-2）was obtained by adjusting the content of immobilized ADH,and was used for the photo-decomposition of water to produce hydrogen and the conversion of acetaldehyde,realizing the simultaneous use of photogenerated electrons and holes.The hydrogen production rate is 1618.45μmol h^-1g^-1,3.84 times that of pure g-C₃N₄.The acetaldehyde conversion rate can reach 1.82mmol h^-1 g^-1,and the quantum efficiency at 400 nm is 9.36%.Finally,combined with a series of photoelectric performance tests and band structure calculations,the internal mechanism of the transfer rate and separation efficiency of photogenerated electron-hole pairs was analyzed,and the possible photocatalytic mechanism was proposed.5.Coenzyme factor（NADH）was grafted onto the surface of g-C₃N₄ by covalent binding and further used for immobilization of ADH to achieve co-immobilization of enzyme and coenzyme（ADH/CN-NADH）.The optimal immobilization process showed that the optimal fixation capacity of ADH/CN-NADH was 216.69 mg/g.Compared with free ADH,ADH/CN-NADH has excellent p H stability and cycling stability.ADH/CN-NADH still retained 82.03%activity at p H 5.0,and 87.10%enzyme activity after 8 cycles.By adjusting the ratio of ADH in the photo-enzyme coupling system,the composite with the best performance（ACN-10%）was obtained,and the photocatalytic performance of hydrogen production and acetaldehyde conversion was performed.The hydrogen production rate and acetaldehyde conversion rate were2717.01μmol h^-1 g^-1 and 11.44μmol h^-1 g^-1,respectively,which were 4.27 and 6.05times of that of pure g-C₃N₄.The AQE value at 400 nm was as high as 12.85%,suggesting that the construction of the photo-enzyme catalytic system is beneficial to improve the performance and carrier separation efficiency of the photocatalyst.