Investigating The Heterointerface Regulation And Photocatalytic Properties Of 2D G-C₃N₄-based Semiconductors

The rapid development of industrialization accelerates the consumption of fossil energy and the emission of greenhouse gases and pollutants,which leads to serious energy and environmental crisis.The development of clean energy and effective environmental control technology has become a hot topic in multi-disciplinary fields such as chemistry,environment and material science.Graphite phase carbon nitride（g-C₃N₄ or CN）has the advantages of visible absorption band gap（about 2.7 eV）,good chemical stability,environmental compatibility,simple preparation and low cost,so it has been widely studied as a promising photocatalyst for photolysis water to hydrogen,organic degradation and carbon dioxide reduction.However,due to its fast photogenerated e^--h⁺recombination rate and narrow response range of visible light,its catalytic activity and catalytic efficiency still need to be improved.Based on the understanding of the current research situation and the analysis of the existing problems,the defect regulation or element doping was combined with the construction of homojunction or heterojunction,and the doped CN and a series of CN matrix composites were prepared by in-situ thermal polymerization of ZIF-8derivatives.The synthesized materials were characterized and analyzed by XRD,SEM,TEM,XPS,UV-vis,FT-IR,ESR,EIS,Mott-Schottky,photocurrent response and transient-steady-state fluorescence spectra.The ability of photocatalytic hydrogen evolution or degradation of antibiotics was tested.Finally,the photocatalytic mechanism was proposed.The specific studies are as follows:（1）Firstly,using Cd-ZIF-8 as dopant,the locality and kinetics of Cd²⁺and-C≡N co-doping were controlled by in-situ co-doping thermal polymerization,the homojunction of CN was prepared,and the photocatalytic hydrogen evolution performance（PHE）and its improvement mechanism were studied.The catalytic activity of CN co-modified with Cd²⁺and-C≡N was significantly enhanced,which was attributed to the structural change of CN caused by the synergistic action of-C≡N and Cd²⁺.The visible light absorption of the prepared composites was significantly enhanced,and the unique double co-modification enabled the optimized CN-80 to have the highest PHE rate of 5586μmol·g^-1·h^-1,which was 4.1 times higher than that of pure CN.The analysis of energy level structure shows that the position of energy level in the doping region shifts up as a whole,and the CN homojunction is formed in the doped and undoped regions,which accelerates the separation of electron-hole pairs.The strategy of simultaneous regulation of active center and band gap structure can be achieved by co-modification of-C≡N and Cd²⁺and controlling the amount of Cd²⁺,which is expected to be extended to the design of a wider range of photocatalyst microstructure to improve PHE activity.（2）Secondly,carbon-doped ZnO/amorphous CN（C-ZnO/A-CN）Z-scheme photocatalyst with close contact was synthesized by in-situ thermal polymerization using porous ZIF-8/urea as raw material.The prepared C-ZnO/A-CN photocatalyst showed excellent removal efficiency for TC degradation under visible light（up to 80%in 30 min）.SEM and TEM studies confirmed that the synthesized heterojunction has a 2D/2D layered structure,and A-CN binds closely to C-ZnO.The energy band analysis shows that the two band arrangements are beneficial to the Z-scheme charge transfer.In particular,the donor defects of the designed C-ZnO and the acceptor defects of A-CN cooperatively quench the low-energy carriers,promote the charge separation of C-ZnO and A-CN,and enable more high-energy carriers with redox ability to participate in the photocatalytic degradation of TC.This work has important reference significance for the design of new Z-scheme photocatalyst and the treatment of antibiotic wastewater related to TC and TC.（3）Finally,glutathione（GSH）modified indium silver sulfide quantum dots（AIS QDs）,were prepared by the aqueous method.The regulation of interface defects and the photocatalytic properties of AIS/CN composite materials were studied.GSH-modified AIS QDs with different charged or protonated surface ligands can be obtained by H⁺or OH^-treatment.The PHE rate of acidic interfacial defect AIS QDs（3.0-AIS）(5.2 mol·g^-1·h^-1)is113 times higher than that of alkaline AIS quantum dot assembly（13.0-AIS）(0.045mol·g^-1·h^-1).With the extension of PL life,the variation of PHE rate with p H value of dispersion is similar.Due to the incomplete connection between the quantum dots and the sulfur vacancy（V_S）surface,a subband related to various defects（usually twins,defects and V_S）is introduced into the acidic aggregates,which traps the excited electrons and transfers them to the hydrogen-bonded GSH,thus generating H₂ more effectively than the dispersed or alkaline assembled quantum dots.In addition,the heterostructure formed by the combination of AIS and CN shows that the heterostructure formed by non-in-situ composite is not conducive to the improvement of photocatalytic hydrogen production activity.The related research results confirm the advantages of in-situ technology in the design of homostructure and heterostructure,as well as the importance of interface defect structure for the photocatalytic performance of materials,which provides a valuable reference for the development of multi-technology-regulated photocatalysis system.In general,a series of highly efficient and stable CN matrix composites were prepared by combining defect regulation or element doping with the construction of homojunction or heterojunction,which enhanced the absorption of visible light,effectively promoted the separation of photogenerated carriers,and improved the photocatalytic activity.The related research provides a systematic understanding for the interface structure design to regulate the photocatalytic performance of the materials.