Study On The Enhancement Of Z-Scheme Sonocatalyst Activity By Ag₂S And FeVO₄ As Conductive Channels

In recent years,the photocatalytic technology as a kind of advanced oxidation technology?AOPs?with the advantages of strong mineralization and energy saving has been widely used in treatment of organic pollutants.The practical wastewater generally has low transparency and high concentration characteristics.Therefore,the photocatalytic technology can not effectively treat such wastewater.It is reported that the sonocatalytic degradation technology of the combination of semiconductor photocatalysts and ultrasonic irradiation has the characteristics of strong permeability and easy operation and so on,displaying good feasibility in treatment of this type wastewater.Being similar to photocatalytic method,the sonocatalytic technology displays the apparent synergistic effect of the pholocatalyst and ultrasonic irradiation,which can effectively mineralize the refractory organic pollutants.Nevertheless,the single sonocatalyst shows high electrons and holes recombination rate and low light utilization ratio,which limits its practical application.The appearence of the Z-scheme sonocatalystic system can solve these problems to some extent.Two different semiconductor sonocatalysts are combined to construct a direct Z-scheme photocatalyst,which can suppress recombination of respective photo-generated electrons and holes of two different semiconductors,broaden optical response range and intensify redox ability.Furthermore,in the Z-scheme sonocatalytic system,the use of some precious metals,graphene and carbon nanotubes as conductive channels can accelerate electrons transfer and inhibit the recombination of photo-generated electrons and holes to some extent.Nevertheless,the use of these conductive channels usually lacks the driving force of electron transfer and increases the electron flow distance.Therefore,in this study,Ag₂S and FeVO₄ as conductive channels can further solve these problems,improving the sonocatalytic activity of sonocatalysts.In the first part of the study,we prepared the SrTiO₃/Ag₂S/CoWO₄ composite by ultrasonic-assisted isoelectric point method combined with high temperature calcination method.And using the X-ray powder diffraction?XRD?,scanning electron microscope?SEM?,transmission electron microscope?TEM?,UV-vis diffuse reflection spectroscopy?DRS?,energy dispersive X-ray spectroscopy?EDX?,X-ray photoelectron spectroscopy?XPS?and luminescence spectroscopy?PL?for characterizing its crystal structure,surface morphology,band gap,chemical composition and analysis the electrons and holes recombination rate.Tetracycline was used to evaluate the sonocatalytic activity of SrTiO₃/Ag₂S/CoWO₄ composite as sonocatalyst under ultrasonic irradiation.The degradation extent of tetracycline was measured by UV-vis spectrophotometer.The effects of ultrasonic irradiation time,ultrasonic power,solution pH,sonocatalyst addition,tetracycline concentration,trapping agent and sonocatalyst cycle times on the degradation of tetracycline were studied.The degradation of organic pollutants broad-spectrum property of SrTiO₃/Ag₂S/CoWO₄ as sonocatalyst was investigated by degradating different kinds of tetracyclines.The sonocatalytic degradation route of tetracycline was speculated based on the generated intermediates.The experimental results reveal that,the existence of Ag₂S as trapezoid electronic channel and co-catalyst accelerates the transfer of electrons from conduction band CoWO₄ to valence band of SrTiO₃,enhancing sonocatalytic performance of Z-scheme SrTiO₃/Ag₂S/CoWO₄ composite.Therefore,it can be predicted that SrTiO₃/Ag₂S/CoWO₄ as sonocatalyst has potential application in environmental remediation.In the second part of the study,we prepared the KTaO₃/FeVO₄/Bi₂O₃ composite by ultrasonic-assisted isoelectric point method combined with high temperature calcination method.The X-ray powder diffraction?XRD?,energy dispersive X-ray spectroscopy?EDX?,X-ray photoelectron spectroscopy?XPS?,scanning electron microscope?SEM?,transmission electron microscope?TEM?and fourier transform infrared spectroscopy?FT-IR?,ultraviolet visible diffuse reflection spectroscopy?DRS?,photoluminescence spectroscopy?PL?,transient photocurrent response?TPR?and electrochemical impedance spectroscopy?EIS?were used to determine the crystal structure,chemical composition,surface morphology,band gap and the recombination rate of electrons and holes.The sonocatalytic activity of the KTaO₃/FeVO₄/Bi₂O₃ as sonocatalyst was studied under ultrasonic irradiation on degradation of ceftriaxone sodium.The influences of ultrasonic irradiation time,scavengers and sonocatalyst recycling times on sonocatalytic degradation of ceftriaxone sodium are examined.he sonocatalytic degradation route of ceftriaxone sodium was speculated based on the generated intermediates.The possible sonocatalytic reaction mechanism of KTaO₃/FeVO₄/Bi₂O₃ as sonocatalyst on degrading ceftriaxone sodium was proposed.The research results indicate that the prepared KTaO₃/FeVO₄/Bi₂O₃ as sonocatalyst displays a much high sonocatalytic activity in sonocatalytic degradation of ceftriaxone sodium.The enhanced sonocatalytic activity is attributed to the fact that FeVO₄ as conductive channel provides a driving force of electron transfer through valence state changes of iron and vanadium,which accelerates electrons transfer from conduction band of Bi₂O₃ to valence band of KTaO₃.The experimental results show that KTaO₃/FeVO₄/Bi₂O₃ as an excellent Z-scheme sonocatalyst can effectively degrade the organic contaminants under ultrasonic irradiation.