Enhanced Photocatalytic Efficiency Of Subgroup Metal Oxides And Sulfides Modified By Graphite Phase Carbon Nitride

With the growing consumption of fossil fuel,both energy crisis and a series of environmental problems caused by the overuse of fossil fuel need to be well resolved for the development of human society.Therefore,two huge mountains must to be spaned to resolve energy crisis and elimate environmental pollution for achieving the sustainable development.Since water splitting into H₂ and O₂ successfully achieved on TiO₂ photoelectrode by Honda and Fujishima in 1972 for the first time,it is a feasible strategy that converting solar energy to hydrogen energy on semiconductor material provides a pivotal moment to perfectly solve the issue of energy and environment.Semiconductor based photocatalytic technology can not only directly use solar energy to split water into hydrogen,degrade organic pollutants,reduce CO ₂into hydrocarbon fuel and synthesize ammonia,but also simulate natural photosynthesis process.Nowdays,the study of semiconductor based photocatalytic materials mainly focus on metal oxide/sulfide?such as TiO₂,CdS et al?and polymeride?such as PANI,PPy et al?.Their photocatalytic efficiency were greatly affected by wider band gap,higher recombination rate of photo-generated carriers or much serious photo-corrosion,which has also restricted their practical application value.Hence,there is a very important significance that modifies these mentioned semiconductor mater ials to promote the development of photocatalytic technology and solve the energy and environmental problems,including broadening their visible-light-response range,increasing reactive sites on the surface of semiconductor material,enhancing the separation efficiency of photo-generated carriers,promoting the charge transfer process and improving the stability of photocatalyst.According to the basic principles of photocatalytic reaction technology,the visible-light-response range of semiconductor materials can be broadened by adjusting their electronic structure,such as doping,creating defects and forming solid solution materials,et al.Meanwhile,combining with narrow-band-gap semiconductor materials or loading noble metals is also an alternative way to increase the visible-light-absorption range,promote the separation and transfer efficiency of photo-generated carriers and improve their photo-stability.This paper mainly focuses on the band structure of g-C₃N₄-based photocatalysts and the inner link to their photocatalytic performance,which were synthesized by combing with subgroup metal sulfides?ZnS,C uS and CdS?and oxide?CuO_x?.The possibly photocatalytic reaction process and mechanism were proposed,which are based on the feasible active species testing experiments.The specific contents are as follows:?1?The nanorod-like g-C₃N₄/ZnS composites were prepared by altering the addition contents of g-C₃N₄ under low-temperature condensation reflux conditions.The related experiments have confirmed that 10 wt%g-C₃N₄/ZnS has the best photocatalytic activity for the degradation of MO dye and removal of refractory benzene wastewater,which can be attributed to the broaden visible-light-response range,enlarged specific surface area and improved separation and transfer efficiency of photo-generated carriers after the combination of g-C₃N₄ and ZnS.?2?Carnation-like CCN-CuS p-n heterojunction photocatalysts were successfully prepared by hydrothermal method.The photocatalytic performance tests of CCN-CuS composites for MB,MO and RhB three common dyes were conducted under visible light irradiation.According to the comparision of specific surface area and separation process of photo-induced carriers for single and their composites,the greatly improved photocatalytic performance of CCN-CuS composite is closely related to its high-active reaction site number and separation efficiency of photo-generated electron-hole pairs.Besides,the formation of CCN-CuS composite can greatly avoid CdS semiconductor materials suffering from serious photo-corrosion.?3?g-C₃N₄/CuO_x composites were synthesized by solvothermal method in the mixed ethanol amine-water system.Metal oxides?C uO and C u₂O?formed orderly in the CuO_x composites by changing the g-C₃N₄ dosage,resulting in the valence transition process of Cu elements.Combining the results analysis of XRD and FT-IR,the formation process of CuO_x and valence transition mechanism were systematically explored and researched by using various solvents and dosage.The results analysis of PL spectra and transient photocurrent response demonstrate that the abundant Cu metal can serve as the efficient electron transfer channel,leading to the prominent photocatalytic efficiency improvement of g-C₃N₄/CuO_x composite.Recycle experiments and XPS analysis all indicate that the as-prepred g-C₃N₄/CuO_x photocatalyst shows excel ent photo-stability.?4?The in situ formed CdS-CdWO₄ nanorods were firstly prepared via a hydrothermal process.And g-C₃N₄/CdS-CdWO₄ ternary composite photocatalysts were constructed with the volatilization of methanol.According to the comparsion of g-C₃N₄/CdS-CdWO₄ ternary composite for RhB dye degradation under visible light and simulated light irradiation,it is obvious that the composite can generate more carriers and show higher photocatalytic activity under simulated light irradiation.Photocatalytic stability tests,PL spectra and transient photocurrent response analysis conformably proved that the formation of g-C₃N₄/CdS-CdWO₄ ternary composite is more stable and can effectively prevent the metal sulfide suffering from serious photo-corrosion,compared to CdS and other binary composites.