Controlling The Interface Between Carbon Nitride Crystals And Highly Active Crystal Facets For Enhancement The Photocatalytic Performance

The photocatalyst with high activity,high selectivity and high stability was the basis of promoting the wide application of photocatalytic technology.The interface design and regulation of crystalline photocatalytic materials was an effective method to improve the photocatalytic performance.In the photocatalytic process,the charge generation and carrier transfer efficiency played a key role in the conversion of solar energy into chemical energy.Three basic steps were involved in the complex process of charge kinetics:charge generation,charge transfer and charge consumption.In recent years,photocatalytic crystalline materials had developed from one-component semiconductor materials to multi-component hybrid coupling materials.And the crystals interface structure and regulation had become more complex and important.In this work,carbon nitride（CN）was as the carrier of carbon-based materials,and BiOI,α-Fe₂O₃,Bi₄Ti₃O₁₂with nano-structure were as the crystal interface control unit.The composite photocatalysts were prepared by hydrothermal,impregnation and solvothermal methods to improve the photoresponsive,photocharge separation efficiency and photocatalytic degradation of organic pollutants.The mechanism of photocatalytic degradation was discussed.The main research contents and results were as follows:BiOI nanocrystals/CN composites crystalline photocatalyst（BiOI-110/DCN）with oxygen-rich vacancies and highly exposed（110）crystal facets were prepared by impregnation-solvothermal method using CN as carrier,BiOI as crystal coupling unit,PVP and mannitol as additives.Firstly,the introduction of 2-amino-3,5-dibromopyrazine with electron-deficient structure significantly distorted the symmetrical structure of the crystal facet in the CN framework and the copolymerized carbon nitride（DCN）was prepared,which facilitated the separation of charge carriers.Then,the novel heterostructure BiOI-110/DCN composite photocatalyst was obtained under the control of additives.The catalytic performance of the prepared BiOI-110/DCN composite crystalline photocatalyst was significantly improved than that of BiOI-110 and DCN alone.The maximum degradation rates of oxytetracycline（OTC）and methyl blue（MB）dyes by the composite photocatalyst reached 85.6%and 96.5%,respectively.The composite photocatalyst also showed excellent stability.In addition,the photocatalytic reaction mechanism with Z-Scheme heterojunction charge transfer and highly active crystal facets synergistic effect was proposed based on active species capture experiment and band structure.The heterojunctionα-Fe₂O₃/CN crystalline photocatalysts with different crystal facet couplings were prepared by impregnation-hydrothermal method usingα-Fe₂O₃as the interface control unit and CN as the carrier.Firstly,the acetylacetone was introduced into the crystal structure of CN to cyclize its crystal frame and the cyclized carbon nitride（ACN）was prepared,so as to achieve the purpose of energy band regulation.Then,the ACN was protanted（ACN+）with more positive charge on the（002）facets to couple ACN andα-Fe₂O₃with different crystal facets,so thatα-Fe₂O₃nanosheets could be assembled parallel（Fe001/ACN）or vertically（Fe001/ACN）on ACN and ACN+surfaces.The Z-scheme heterojunction formed by different interface coupling betweenα-Fe₂O₃and ACN could improve the separation efficiency of photocarriers.The Fe110/ACN+had much higher photoactivity than ACN,ACN+and Fe001/ACN.The Fe110/ACN+composites had a removal rate for OTC with 88.6%and had excellent adsorption and catalytic effect for Congo red（CR）.In addition,the photocatalytic reaction mechanism was proposed based on the charge transfer mechanism of Z-Scheme heterojunction and the synergistic effect of crystal facets assembly by using active species capture experiment and band structure.The Bi₄Fe_xTi_3-xO₁₂/CNOH heterojunction composite crystalline photocatalyst with high activity（001）facets was prepared by sol-gel method using CN as the carrier and Bi₄Ti₃O₁₂as the interface coupling unit.The Fe element was introduced into the crystal structure of Bi₄Ti₃O₁₂(Bi₄Fe_xTi_3-xO₁₂).With the increase of Fe content,the average side length and thickness of Bi₄Fe_xTi_3-xO₁₂gradually decreased.The（001）facets with the best catalytic performance was the nanosheet with side and thickness of about 200 nm and 10 nm.Then,the hydrophilicity of CN was improved by grafting hydroxyl groups.The grafted carbon nitride（CNOH）was prepared and combined with Bi₄Fe_xTi_3-xO₁₂,which could not only solve the disadvantage of poor hydrophilicity of Bi₄Fe_xTi_3-xO₁₂,but also obtain a large area of Bi₄Fe_xTi_3-xO₁₂/CNOH heterojunction interface.The efficient interfacial charge transfer between Bi₄Fe_xTi_3-xO₁₂and CNOH was achieved.The prepared Bi₄Fe_xTi_3-xO₁₂/CNOH heterojunction photocatalyst showed a great degradation rate of 87.8%for TC.The heterojunction photocatalyst had a good inhibitory effect on the proliferation of Escherichia coli.In addition,the active species were identified by active species capture experiment,and the photocatalytic reaction mechanism was proposed based on the type-II heterojunction charge transfer and the synergistic effect of crystal facets optimization.