Preparation Of 3D Ordered Inverse Opal Composites And Its Application In Visible-light-driven Photocatalytic Degradation Of Organic Contaminants

Photocatalytic degradation is regarded as an environment-friendly wastewater treatment method.Photogenerated electrons and holes on the surface of photocatalysts are utilized to degrade and mineralize organic pollutants in water through redox reactions.However,the efficiency of photocatalytic reaction is not very high due to the poor light absorption ability and rapid rate of photogenerated electron-hole pairs recombination.Therefore,it is of great significance to modify photocatalysts to improve its activity.Inverse opals are characteristic of three-dimensional ordered macroporous structure,which have slow photon effect and multiple scattering effect.These unique optical properties effectively increase the optical path length and enhance the interaction between light and photocatalysts.Meanwhile,inverse opals exhibit large specific surface area,which provide sufficient active sites for photocatalytic reactions and is conducive to the mass and carrier transfer.In order to improve photocatalytic performance,inverse opals are utilized to construct the photocatalytic system.However,the efficiency of single-component photocatalyst is usually not very high,thereby element doping and coupling with quantum dots are utilized to construct inverse opal heterojunctions and improve the photocatalytic efficiency of inverse opals.(1)Titanium dioxide is widely used as semiconductor photocatalysts,however,its photocatalytic activity is low for the wide band gap of TiO2 and inefficient utilization of visible light.Herein,three-dimensional ordered inverse opal(IO)is used to improve the visible light utilization of titanium dioxide.Firstly,nitrogen doping is applied to broaden the visible light response range of TiO2 10.Then cadmium selenide nanoparticles are loaded on the skeleton of N-TiO2 IO to construct heterojunctions,and CdSe/N-TiO2 10 is obtained.Nitrogen doping creates N 2p band above the valence band of titanium dioxide,which effectively narrows the band gap to 3.0 eV.The introduction of cadmium selenide nanoparticles promotes carrier migration and improves the separation efficiency of photogenerated electron-hole pairs.The as-synthesized photocatalysts are used to photocatalytic degradation of Rhodamine B.CdSe/N-TiO2 IO shows good removal efficiency for Rhodamine B.Cyclic experiments indicate that CdSe/N-TiO2 IO performs stable photocatalytic activity.Nitrogen doping,cadmium selenide sensitization and slow photon effect of inverse opal synergistically enhance the photocatalytic activity.(2)Cadmium sulfide quantum dots have attracted wide attention as a highly responsive visible-light-driven photocatalyst.However,CdS quantum dots suffer from inherent photocorrosion effect.In order to suppress the photocorrosion effect,molybdenum phosphide is used as the cocatalyst of CdS QDs for its good electrical conductivity.When CdS/MoP IO is irradiated by visibe light,CdS QDs produce photogenerated electron-hole pairs.Photogenerated electrons inject from the conduction band of CdS to MoP Fermi level,while photogenerated holes accumulate in the valence band of CdS,thereby effectively inhibit charge carrier recombination.CdS/MoP IO shows good photocatalytic efficiency and stable photocatalytic activity towards phenol degradation.The heterojunction of CdS/MoP IO effectively alleviate the photocorrosion phenomenon of pure CdS QDs and improve the photocatalytic activity of CdS quantum dots.(3)Graphene quantum dots are uniformly decorated on the wall of bismuth tungstate/tungsten trioxide inverse opal by electrostatic attraction.However,the electrons in conduction band of WO3 and Bi2WO6 are not negative enough to reduce O2 to form·2-,and the lower valance band of GQDs cannot oxidize OH-to·OH.Therefore,dual Z-scheme heterostructure is constructed at the interface of GQDs and Bi/W IO.The photogenerated electrons from the conduction band of tungsten trioxide and bismuth tungstate combine with photoexcited holes in the valence band of graphene quantum dots.The migration of charge carriers result in electron accumulating in the conduction band of GQDs,and holes leaving in the valence band of WO3 and Bi2WO6.Therefore,GQDs/Bi/W IO ternary heterojunction effectively suppresses the recombination of photogenerated electron-hole pairs.GQDs/Bi/W IO performs high photocatalytic efficiency of phenol removal under visible light illumination.What's more,GQDs/Bi/W IO exhibits good photocatalytic stability.Therefore,highly ordered inverse opals help improve the visible light absorption ability of photocatalysts,and heterojunction construction effectively promote the separation and transfer of photogenerated charge carriers.The above methods synergistically improve the photocatalytic activity of nanostructured materials.