Synthesis Of Bi₂S₃-TiO₂-RGO Composites And Photocatalytic Degradation Of Rhodamine B Under Visible Light

In order to control the increasingly severe pollution of dyestuff wastewater,two kinds of TiO₂ based photocatalysts that can respond to visible light are prepared.Firstly,the TiO₂-RGO photocatalyst was synthesized by hydrothermal method and applied for the photocatalytic degradation of Rhodamine B under visible light.The materials were characterized by TEM,XRD,BET,Raman,FTIR,XPS,UV-Vis DRS,PL and so on.The results showed that TiO₂-RGO composites could respond to the visible light and the composites had lower recombination rate of photo generated electrons and holes.The introduction of RGO greatly increased the adsorption capacity and photocatalytic ability of the photocatalyst.Under visible light,the total removal rate of Rhodamine B over TiO₂-RGO composites is 76.9%with 80 min irradiation,and the photocatalytic degradation rate constant is about 4 times than that of pure TiO₂.The results of radical trapping experiments confirmed the?O₂^-played a major role in the degradation of Rhodamine B over TiO₂-RGO composites,as for?OH and h⁺,they played a secondary role.The production of?O₂^-is closely related to the position of the conduction band.More negative conduction band results in stronger reducing capacity of electrons,which is beneficial to produce?O₂^-.In consideration of the tiny disparity between conduction band of TiO₂（-0.30 eV vs.NHE）and redox potential of O₂/?O₂^-（-0.28 eV vs.NHE）,the photocatalytic activity of photocatalyst can be further improved through compositing semiconductors with more negative conduction band based on TiO₂-RGO.Among the semiconductors,Bi₂S₃ is an excellent choice owing to its environment-friendly feature,narrow band gap and more negative conduction band.The photocatalyst of Bi₂S₃-TiO₂-RGO composites was synthesized by a facile one-step hydrothermal method and applied for the photocatalytic degradation of Rhodamine B under the visible light.The Bi₂S₃-TiO₂-RGO composites were characterized by TEM,XRD,BET,Raman,FTIR,XPS,UV-Vis DRS,PL and so on.The results indicated that Bi₂S₃-TiO₂-RGO composites were successfully prepared and Ti-O-C and S-C bonds were existing among Bi₂S₃,TiO₂ as well as RGO.Furthermore,the photocatalytic ability of Bi₂S₃-TiO₂-RGO composites was excellent under visible light due to its responding to the whole visible light region,the low recombination rate of photo generated electron-hole pairs and relatively negative conduction band.Rhodamine B photocatalytic degradation rate was 99.5%after 50min and still could reach 98.4%after five cycles.Finally,a photocatalytic degradation mechanism of Bi₂S₃-TiO₂-RGO composites was proposed based on the results of radical trapping experiments and LC-MS.In the degradation process of Rhodamine B,Bi₂S₃,TiO₂ and RGO over Bi₂S₃-TiO₂-RGO composites give full play to their respective advantages and act synergistically with each other.The?O₂^-still played a major role in the degradation of Rhodamine B.The deethyl action of?O₂^-and h⁺can remove the ethyl,carboxyl and ethylamine groups which are outside the structure of Rhodamine B.The hydroxylation of?OH can destroy the conjugated structure of Rhodamine B molecule.In the end,the Rhodamine B can be oxidized to CO₂ and H₂O.