Synthesis And Photocatalytic Performance Of Bismuth-based Composite Photocatalysts

Semiconductor photocatalysis technology using solar energy and photocatalysts has attracted much attention due to its extensive applications in H2 generation,CO2reduction,and pollution degradation at room temperature and ambient pressure.Nowadays,Bi₂WO₆ and Bi₂MoO₆ have been considered as promising visible-light-driven photocatalysts to decompose organic pollutants because of their unique layered structure,appropriate band gap,and stable chemical property.Unfortunately,the catalytic performance of single Bi2WO6 and Bi2Mo O6photocatalyst is not satisfactory because of the fast recombination of photogenerated carriers and limited optical absorption.Recently,synthesis of all-solid-state Z-scheme-system heterojunctions,especially construction of 2D/2D heterojunctions,is an efficient method to ameliorate the photocatalytic performance of catalysts.On the one hand,2D/2D heterojunctions can reduce the charge transport time and distance due to the large contact surface between 2D nanosheets,promoting the separation of photogenerated electron-hole pairs.On the other hand,2D/2D materials with large specific surface areas can provide a great number of active sites on their surface to oxidative decomposition of organic matter.A series of g-C₃N₄/Au/Bi₂WO₆and Bi₂MoO₆/g-C₃N₄/Au were fabricated via a photoreduction and hydrothermal reaction process to improve their photocatalytic activities.The main research contents are as follows:?1?A series of novel 2D/2D Z-scheme visible-light-driven g-C₃N₄/Au/Bi₂WO₆?CN/Au/BWO?photocatalysts were fabricated via a photoreduction and hydrothermal reaction process.CN/Au/BWO samples were characterized by various techniques,such as XRD,FTIR,TEM,XPS,BET,UV-vis DRS,and PL spectra,respectively.The photocatalytic performance of CN/Au/BWO photocatalysts was evaluated by the photodegradation of Rhodamine B under visible-light illumination.The results showed that CN/Au?1?/BWO displayed the optimum photocatalytic activity,which was 1.48 times and 1.62 times as that of Bi₂WO₆ nanosheets and g-C₃N₄,respectively.The improved photocatalytic activity of CN/Au/BWO could be mainly attributed to the construction of 2D/2D Z-scheme architectures,which not only provided abundant active sites but also effectively improved the separation rate of photogenerated carriers.It was noted that Au nanoparticles acted as a redox mediator in the Z-scheme heterostructure between Bi₂WO₆ and g-C₃N₄ to promote the transmission and separation of photo-generated electrons and holes in the middle of Bi₂WO₆ and g-C3N4.A possible photocatalytic reaction mechanism of photocatalytic RhB degradation over CN/Au/BWO was tentatively proposed through active species trapping experiments.In summary,the current study could provide a new insight for designing effective 2D/2D Z-scheme photocatalysts to guide the further improvement of their photocatalytic activity.?2?A novel 2D/2D Bi₂MoO₆/g-C₃N₄ step-scheme?S-scheme?composite by loading Au as cocatalyst was successfully fabricated using a photoreduction and hydrothermal route.The obtained Bi2MoO6/g-C3N4/Au photocatalysts were characterized by X-ray diffraction?XRD?,transmission electron microscope?TEM?,X-ray photo-electron spectroscopy?XPS?,UV-vis diffuse reflectance spectra?UV-vis?,Fourier transform infrared spectroscopy?FTIR?,photoluminescence?PL?,photocurrent response?I-t?,and electrochemical impedance spectroscopy?EIS?.The HRTEM pictures revealed that an intimate interface in composites was formed.I-t analysis result implied that Bi₂Mo O₆/g-C₃N₄/Au possessed a higher photocurrent intensity compared with pure g-C₃N₄ and Bi₂MoO₆.The optimum photocatalytic activity of Rhodamine B degradation over Bi2MoO6/g-C3N4/Au was about 9.7 times and 13.1 times higher than those of Bi₂MoO₆ and g-C₃N₄,respectively.The notably improved photocatalytic activity of Bi₂Mo O₆/g-C₃N₄/Au could be mainly ascribed to the abundant active sites and the enhanced separation efficiency of photogenerated carriers in Bi2MoO6/g-C3N4 S-scheme system.Notably,Au nanoparticles could act as a co-catalyst to further promote electron transfer and separation from the conduction band of g-C₃N₄.Additionally,a possible step-scheme photocatalytic reaction mechanism of RhB degradation over Bi₂MoO₆/g-C₃N₄/Au was proposed.PL and transient photocurrent analysis results implied that Bi2MoO6/g-C3N4/Au photocatalysts possessed the lower recombination rate of photogenerated carriers compared with pure g-C₃N₄ and Bi₂MoO₆.The present study is expected to be a useful technique in designing novel 2D/2D S-scheme heterojunction photocatalysts.