Controllable Preparation And Properties Of Carbon Nitride-based Nanometer Photocatalyst

In the 21st century with rapid industrialization,energy and environmental issues have become a topic of continuous concern.How to develop renewable and abundant new energy to solve fossil fuel depletion and environmental pollution has become a test.Photocatalysis is favored by researchers because of its mild conditions,high stability,high efficiency and basically no secondary pollution.The key to photocatalysis is to develop an effective semiconductor to drive the conversion of solar energy into chemical energy.However,the mainstream catalysts（metal oxides）have the disadvantages of relatively wide band gap,limited visible light absorption range and rapid carrier compounding,which limit the conversion efficiency of photocatalysts.Graphitic carbon nitride（g-C₃N₄）is a low-cost,visible-light responsive and electron-rich material widely used for energy conversion and environmental remediation.However,the defects such as low carrier utilization and few reaction sites reduce the g-C₃N₄ photocatalytic activity.In this paper,strategies such as morphology modulation,doping with different elements,vacancies and heterojunctions are used to enhance the g-C₃N₄photocatalytic performance.（1）In this study,supramolecular complexes（MA-CA）were formed from melamine and melanic acid under water bath conditions.Ammonium dihydrogen phosphate and thiourea were used as dopants to react with supramolecular aggregates under hydrothermal conditions,and finally calcined to form carbon nitride（CN）with different doping amounts.Compared with the bulk g-C₃N₄,the doped CN showed a significant enhancement in photocatalytic activity.After a series of characterization of the structure,morphology,chemical state,optical and electrochemical properties of the different CN,we found that P_（0.3）S_（0.25）-CN has good photocatalytic performance and cycling stability.This was mainly evidenced by the accumulated concentration of H₂O₂ of 1.683 m M after 120 min and another 100 min by photocatalytic oxidation in synergy with Fenton to degrade tetracycline（TC）with an efficiency of 87.3%.The photoelectric tests,XPS and ESR showed that the co-doping led to the appearance of nitrogen vacancies,which resulted in faster mass transfer efficiency and eventually exhibited excellent carrier kinetics and photocatalytic activity.HPLC-MS detailed analysis of the degradation pathway of TC,as well as free radical trapping experiments and EPR tests were performed to propose the P_（0.3）S_（0.25）-CN by photocatalytic-Fenton synergistic degradation of TC degradation mechanism.This may inspire the design of more effective carbon-based catalysts for extension.（2）To further enhance the photocatalytic performance of P-CN,MA-CA and ammonium dihydrogen phosphate were dissolved in deionized water（containing a small amount of mixed alcohol）for hydrothermal reaction to obtain thinner P-CNTH nanotubes by thermal polycondensation.The 0D/1D Ce O₂ QD/P-CNTH composites were successfully prepared by in situ growth of Ce O₂ QD under P-CNTH in a water bath.The morphology,structure and optoelectronic properties of the synthesized materials were investigated by different characterization means.The photocatalytic degradation of tetracycline（TC）and methylene blue（MB）wastewater was simulated under visible light irradiation,and their photocatalytic activity and stability were evaluated.The experimental results showed that the Ce O₂ QD/P-CNTH composites exhibited good degradation and cyclic stability for both TC and MB.In Ce O₂ QD/P-CNTH,the improved photocatalytic performance is mainly due to the shorter radial length and theπ-conjugation system along the nanotube wall that can induce the axial alignment of carriers,thus promoting the electronic conductivity and charge transfer between the interface of P-CNTH and Ce O₂ QD.Meanwhile,the high surface area of one-dimensional hollow Ce O₂ QD/P-CNTH provides a large number of reactive sites.The radical trapping and EPR experiments demonstrate that·O₂ˉ,holes play a major role in the degradation process and suggest the possibility of forming S-type heterojunctions.