Study On The Synthesis Of Ag-SnO₂ Quantum Dots Matrix Photocatalysts And Their Photocatalytic Performance Under Visible Light Irradiation

Ag-SnO2 quantum dots?Ag-SnO2 QDs?,graphitic carbon nitride?g-C3N4?and Ag3PO4,which have different advantages and disadvantages,were new photocatalysts and have been studied and reported in recent years.In this work,a novel 0D/2D composite photocatalyst was synthesized by heating the homogeneous dispersion of Ag-SnO2 QDs and g-C3N4.And a novel Ag-SnO2 QDs/Ag3PO4 was successfully synthesized through in-situ precipitation strategy.XRD,SEM,TEM,HRTEM and XPS images confirmed the successful synthesis of Ag-SnO2 QDs/g-C3N4 and Ag-SnO2QDs/Ag3PO4,and Ag-SnO2 QDs were homogeneously distributed on the surface of g-C3N4 and Ag3PO4.Photocatalytic batch experiment showed that the photocatalytic efficiency of Ag-SnO2 QDs/g-C3N4 was much higher than that of pure Ag-SnO2 QDs and g-C3N4.The optimal mass ratio of Ag-SnO2 QDs to g-C3N4 was determined to be 30%?CN/AgSn-30?.Under the visible light irradiation,when the light intensity is 20 mW/cm²,the degradation rate constant of CN/AgSn-30 toward Rhodamine B(0.087 min^-1)was 7.25and 2.49 times that of pure Ag-SnO2 QDs(0.012 min^-1)and g-C3N4(0.035 min^-1),respectively.The average H2 evolution rate achieved by CN/AgSn-30 reached as high as 1320.25?mol·g^-1·h^-1 when the light intensity is 128 mW/cm².Cyclic photocatalytic experiments and XRD spectra of CN/AgSn-30 before and after the reaction demonstrated the impressive stability of the CN/AgSn-30 composite.UV-vis DRS spectra showed that the Ag-SnO2 QDs/g-C3N4 had a stronger absorption capacity in visible light region than the pure Ag-SnO2 QDs and g-C3N4.PL spectra suggested that the formation of Ag-SnO2 QDs/g-C3N4 heterojunction structure inhibited the recombination of photo-generated electrons and holes extremely.Transient photocurrent spectra and EIS spectra proved that the photocatalytic activity of Ag-SnO2QDs/g-C3N4 was significantly enhanced.Radical trapping experiments showed that superoxide radical and photogenerated holes played a major role in the degradation of Rhodamine B.According to the above results,a“Z-scheme”theory was recommended to illustrate the possible charge transfer process and photocatalytic mechanism of Ag-SnO2 QDs/g-C3N4 toward Rhodamine B.The photocatalytic capacity of the Ag-SnO2 QDs/Ag3PO4 was significantly higher than that of pure Ag-SnO2 QDs and pure Ag3PO4.The optimal mass ratio of Ag-SnO2QDs to AgNO3 was found to be 10%?10AgSn/AgP?.Under the visible light irradiation,when the light intensity is 10 mW/cm²,the degradation rate constant of 10AgSn/AgP for Rhodamine B(0.088 min^-1)was 17.60 and 2.59 times that of pure Ag-SnO2 QDs(0.005 min^-1)and Ag3PO4(0.034 min^-1),respectively.The degradation rate constant of10AgSn/AgP for Carbamazepine(0.0143 min^-1)was 11.00 and 6.81 times that of pure Ag-SnO₂ QDs(0.0013 min^-1)and Ag₃PO₄(0.0021 min^-1),respectively.Cyclic photocatalytic experiments and XPS spectra of 10AgSn/AgP before and after the reaction verified that the composite had the better stability than the two unitary materials.UV-vis DRS spectra,PL spectra,Transient photo-current spectra and EIS spectra showed that the Ag-SnO2 QDs/Ag3PO4 had a stronger absorption capacity in the visible light region than the two unitary materials and formation of Ag-SnO2QDs/Ag3PO4 heterojunction structure inhibited the recombination of photo-generated electrons and holes extremely and therefore the photocatalytic activity of the Ag-SnO2QDs/Ag3PO4 was improved.Radical trapping tests and electron spin resonance measurement showed that photo-generated holes and superoxide radical played a major role in the degradation of Carbamazepine.A“Z-scheme”theory,where metal Ag nanoparticles played the role as the charge separation center,was recommended to illustrate the possible charge transfer process and photocatalytic mechanism of Ag-SnO2 QDs/Ag3PO4.Eight degradation intermediates were identified by High Performance Liquid Chromatography-Mass spectrometry and possible degradation pathways was analyzed.The toxicity evaluation by the ECOSAR program showed that the acute and chronic aquatic toxicity of most degradation intermediates was lower than that of carbamazepine.Ag-SnO2 QDs/g-C3N4 have manifested a promising potential application in organic pollutants elimination and green energy production.While Ag-SnO2QDs/Ag3PO4 have an application potentiality to treat polluted and waste water containing CBZ.This study provided theoretical basis and technical support for the practical application of these two photocatalysts.