Preparation Of Graphene/Semiconductor Composites And Their Photocatalytic Performances

Photocatalytic technology is a green technology,which is widely used in energy and environmental fields.It has important theoretical guiding significance and broad development prospects for environmentally sustainable development.Semiconductor photocatalysts are often accompanied by shortcomings such as low photocatalytic quantum efficiency,low solar energy utilization and poor light stability in independent application processes,resulting in low photocatalytic efficiency,thus greatly limiting their wide application.Graphene is an ideal carrier material for the preparation of high-efficiency composite photocatalysts due to its unique sp2 hybrid carbon atom monolayer structure,high specific surface area,excellent electron conduction rate and good light transmittance.In this paper,we utilized graphene to effectively reduces the bandgap of TiO2 by forming the chemical bond with titanium dioxide(TiO2),and applied the in-situ growth of visible-light catalyst tetrahedral silver phosphate(Ag3PO4)on graphene oxide(GO)to significantly improve the light stability of Ag3PO4.Furthermore,the GO aerogel microspheres in possess of the radially oriented microchannel loaded with high-performance catalyst Ag3PO4 are designed to fully utilize the synergistic effect of adsorption and photocatalysis,achieving the dual objectives of high photocatalytic efficiency and long-term stability.In addition,introducing the noble metal into the microspheres forms heterojunction to further enhance the photostability of the Ag3PO4 catalyst.At the meantime,the photocatalytic reaction mechanism of typical organic pollutants and heavy metal ions Cr(VI)was systematically studied.The main works are list as follows:(1)The C/TiO2@RGO core-shell nanofiber membrane photocatalytic materials were prepared by electrospinning combined with high-heat treatment using tetrabutyl titanate as precursor.The effects of different calcination temperatures(400,500,600,70?)on the crystal structure of composites and the effects of different RGO coating thickness(10,14,22,40 nm)on light absorption and photocatalytic degradation of organic dyes were investigated.The results show that the heat treatment at 600? realizes the transformation of TiO2 from amorphous to anatase phase,the reduction of GO to RGO,and formation of C-Ti chemical bond at the meantime,which promotes the rapid transfer of photogenerated electrons to RGO and the effective separation of carriers.Thus,the bandgap was reduced from 3.26 eV to 3.06 eV,and the absorption wavelength was red shifted from 380 nm to 405 nm.The photocatalytic efficiency of the composite nanofiber material is 4.1 times than that of pure TiO2.(2)In order to improve the utilization of visible light,Ag3PO4/GO visible light catalytic material was prepared by in-situ growth of tetrahedral Ag3P04 on GO sheets by electrostatic self-assembly in a mixed solvent,in which the morphology of tetrahedral Ag3PO4 with high surface energy and low holes mass can be controlled by adjusting the water/ethanol volume ratio of mixed solvent.The introduction of GO significantly improved the light absorption intensity of the hybrid materials in the visible region.Good interfacial interaction promotes the transfer of photogenerated electrons from Ag3PO4 to GO sheets,which improves the efficiency of electron-hole separation and effectively inhibits the photoetching of Ag3PO4.The hybrids deliver an excellent visible light photocatalytic efficiency of 1.65×10-2 mg·min-1·mg-1 and satisfactory photostability in a five-cycles.(3)Adsorption is the premise of heterogeneous catalytic reaction.In order to improve the adsorption rate and adsorption capacity of the catalyst,Ag3PO4/GO aerogel microspheres with radially oriented microchannel structure were prepared by electrostatic spraying combined with directional freeze drying.The radially oriented microchannel of GO microspheres is fully utilized to shorten the diffusion path of pollutants to achieve fast adsorption equilibrium in 5 min.In addition,the electronic conduction characteristics of GO improves the photocatalytic efficiency and cycle stability of Ag3PO4.Eventually,the synergistic effect of adsorption and catalysis significantly improved the photocatalytic degradation efficiency of organic dyes and bisphenol A(BPA),and the removal rate of BPA in continuous flow system for 50 h still remained above 95%.(4)Based on last work of GO aerogel microspheres loaded with single Ag3PO4 nanoparticles,noble metal Ag was introduced to prepare Ag/Ag3PO4/RGO composite aerogel microspheres with heterojunction Ag/Ag3PO4,which were used for photocatalytic reduction of Cr(VI).The Ag/Ag3PO4 heterojunction and the close interfacial interaction among the three components accelerate the transfer of electrons from Ag3PO4 conduction band to Ag and RGO sheets,and improve the photostability and photocatalytic efficiency of Ag3PO4.In addition,the surface plasmon resonance effect of Ag and the broadband absorbance of RGO significantly enhance the visible light absorption of the composite aerogel microspheres.The Ag/Ag3P04 heterojunction and the electron conduction of RGO increase the current density of the composite photocatalysts by 2.9 times higher than that of pure Ag3PO4.Further exploration of the mechanism indicates that Cr(VI)is reduced to Cr(III)by the ? electrons on rGO and the photoexcited electrons on Ag3PO4.Furthermore,the addition of methylene blue,a scavenger of oxygen free radicals and holes,greatly enhances the removal efficiency.