| Polymeric semiconductor graphitic carbon nitride(g-C3N4)has attracted great attentions because of its unique structure,visible-light response,high stability,energy saving and so on.However,the photocatalytic efficiency of pristine g-C3N4 directly derived from thermal polymerization of precursor is still low due to its relatively small specific surface area,low photocarrier separation and transfer rate,and high recombination rate.In this paper,aiming at overcoming the deficiency of g-C3N4,we propose the precursor-reforming strategy to adjust the morphology of g-C3N4.It can increase the specific surface area,broaden the light absorption and reduce the recombination rate of photogenerated charge carriers.Also,we constructed heterojuntions between g-C3N4 and other semiconductors to increase visible-light absorption and facilitate the separation of the photoinduced carriers,so as to improve the photocatalytic activity.The specific research content is as follows:(1)The precursor-reforming strategy was proposed.Hydrothermal pretreatment allowed monoclinic-phase melamine transforming into orthorhombic-phase melamine.After thermal polymerization process,we obtained three dimensional structured g-C3N4 composed of ultrathin porous N-doped naosheets.Under visible light illumination,the photocatalytic hydrogen production rate of the advanced g-C3N4 is about 23 times higher than that of the pure g-C3N4.And its hydrogen production apparent quantum efficiency reached at 27.8%(?=420 nm).In the pre-treatment process,the melamine undergoes a phase-transformation process as well a morphology-change procedure due to the higher pressure.After calcination,we obtained a porous sleeve-yolk-shell shaped g-C3N4.The ultrathin outer-tube and the innner-rod exhibit lots of mesopores.And the inner-rod was composed of numerous nanosheets.So the specific surface area is increased,which is beneficial for the visible light absorption.This novel structured g-C3N4 can effectively separate photo-generated electron-hole pairs,thus the photocatalytic hydrogen production and CO2 reduction ability were improved.(2)The facets-coupled photocatalytic materials BiOI(001)/g-C3N4(002)and BiOI(110)/g-C3N4+(002)have been synthesized based on different facets of semiconductor have positive or negative charge.The dichlorophenol,bisphenol A,tetracycline hydrochloride and rhodamine B photo-degradation rate of BiOI(001)/g-C3N4(002)were all higher than that of BiOI(110)/g-C3N4+(002),due to the preferred charge transfer direction in the interface of BiOI(001)/g-C3N4(002).(3)The BiVO4/g-C3N4 composite photocatalytic materials were synthesized,and the performance of visible-light-induced photocatalytic degradation on water pollutants was greatly improved.The active species trapping experiments,NBT conversion,TA-PL technology proved that the mechanism is direct Z-mechanism,which effectively promoted the charge separation rate of BiVO4/g-C3N4 composite.(4)The n-n type CeO2/g-C3N4 composite photocatalyst was prepared by in-situ co-pyrolysis method.Under visible light irradiation,the phenol photo-degradation activity of CeO2/g-C3N4 was about 68 and 17 times higher than that of pure CeO2 and g-C3N4,respectively.The performance of gas pollutants NO degradation and photocatalytic water-splitting for H2 evolution also have been improved.The g-C3N4/Ag2CO3 composite material was synthesized by in-situ deposition method.The photocatalytic degradation efficiency on liquid contaminant MO was improved compared with that of pure single component. |
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