Construction of Ag_3PO_4/Ag_2MoO_4 Z-scheme heterogeneous photocatalyst for the remediation of organic pollutants

Hole/electron separation and charge transfer are the key processes for enhancing the visible-light photocatalysis performance of heterogeneous photocatalytic systems.To better utilize and understand these effects,binary Ag3PO4/Ag2MoO4 hybrid materials were fabricated by a facile solution-phase reaction and characterized systematically by X-ray diffraction（XRD）,energy-dispersive spectroscopy,Fourier transform infrared spectroscopy,Raman spectroscopy,field-emission scanning electron microscopy and ultraviolet-visible diffuse-reflectance spectroscopy.Under visible-light illumination,a heterogeneous Ag3PO4/Ag/Ag2MoO4 photocatalyst was constructed and demonstrated enhanced photocatalytic activity and photostability compared with pristine Ag3PO4toward the remediation of the organic dye rhodamine B.The Ag3PO4/Ag2MoO4 hybrid catalyst with8%mole fraction of Ag2MoO4 exhibited the highest photocatalytic activity toward the removal of typical dye molecules,including methyl orange,methylene blue and phenol aqueous solution.Moreover,the mechanism of the photocatalytic enhancement was investigated via hole- and radical-trapping experiments,photocurrent measurements,electrochemical impedance spectroscopy and XRD measurements.The XRD analysis revealed that metallic Ag nanoparticles formed initially on the surface of the Ag3PO4/Ag2MoO4 composites under visible-light illumination,leading to the generation of a Ag3PO4/Ag/Ag2MoO4 Z-scheme tandem photocatalytic system.The enhanced photocatalytic activity and stability were attributed to the formation of the Ag3PO4/Ag/Ag2MoO4Z-scheme heterojunction and surface plasmon resonance of photo-reduced Ag nanoparticles on the surface.Finally,a plasmonic Z-scheme photocatalytic mechanism was proposed.This work may provide new insights into the design and preparation of advanced visible-light photocatalytic materials and facilitate their practical application in environmental issues.

Construction of carbon nitride and MoS_2 quantum dot 2D/0D hybrid photocatalyst:Direct Z-scheme mechanism for improved photocatalytic activity

Graphite‐like carbon nitride(g‐C3N4)‐based compounds have attracted considerable attention because of their excellent photocatalytic performance.In this work,a novel direct Z‐scheme system constructed from two‐dimensional(2D)g‐C3N4nanoplates and zero‐dimensional(0D)MoS2quantum dots(QDs)was prepared through the combination of a hydrothermal process and microemulsion preparation.The morphologies,structures,and optical properties of the as‐prepared photocatalysts were characterized by X‐ray diffraction,X‐ray photoelectron spectroscopy,atomic force microscopy,transmission electron microscopy,and UV‐vis diffuse reflectance spectroscopy.In addition,the photocatalytic performances of the prepared2D/0D hybrid composites were evaluated based on the photodegradation of rhodamine B under visible‐light irradiation.The results demonstrated that the introduction of MoS2QDs to g‐C3N4greatly enhanced the photocatalytic efficiency.For the optimum7%MoS2QD/g‐C3N4photocatalyst,the degradation rate constant was8.8times greater than that of pure g‐C3N4under visible‐light irradiation.Photocurrent and electrochemical impedance spectroscopy results further demonstrated that the MoS2QD/g‐C3N4composites exhibited higher photocurrent density and lower chargetransfer resistance than those of the pure g‐C3N4or MoS2QDs.Active species trapping,terephthalic acid photoluminescence,and nitro blue tetrazolium transformation experiments were performed to investigate the evolution of reactive oxygen species,including hydroxyl radicals and superoxide radicals.The possible enhanced photocatalytic mechanism was attributed to a direct Z‐scheme system,which not only can increase the separation efficiency of photogenerated electron‐hole pairs but also possesses excellent oxidation and reduction ability for high photocatalytic performances.This work provides an effective synthesis approach and insight to help develop other C3N4‐based direct Z‐scheme photocatalytic systems for environmental purification and energy conversion.