Preparation Of Tin-based Photocatalyst And Its Application In Degradation Of Environmental Pollutants

Due to the highly effective and stable photocatalytic performances,tin-based photocatalysts represented by the hydroxides,binary or ternary oxides,and their complexes have broad applications for the degradation of environmental pollutants.In this work,the effects of preparation methods and synthesis conditions on the formation,structure,morphology and photocatalytic activity of ZnSn?OH?₆?ZHS?,SnO_x/Zn₂SnO₄?SZTO?and SnO_x were investigated,respectively.The optimal preparation conditions of the samples were determined and the structure-activity relationship of each sample was clarified,and the key structural factors accounting for the high photocatalytic performance were revealed.The study mainly includes the following three aspects:1.A series of ZHS samples with different surface properties were synthesized by a hydrothermal method.The effects of the preparation conditions,such as the hydrothermal temperature and solution pH,on the formation and activity of ZHS were investigated to explore the key components and structure of the sample for the high photocatalytic activity.The results show that ZHS can be successfully synthesized under the hydrothermal conditions at a temperature of 90-120 °C and a pH 4-10,but most of the ZHS samples contain trace amount of low crystalline SnO₂.These samples exhibited high activities for the degradation of gaseous benzene and methyl orange solutions.Pure phase ZHS can only be produced in a strongly alkaline solution?pH 13?with no appreciable photocatalytic activity.For the degradation of gaseous benzene,SnO₂ and ZHS can be understood as photo-active sites and adsorption activation sites,respectively,which responsible for the generation of photo-induced charge carriers and adsorption and active sites for O₂,H₂O and benzene.A synergistic effect between them leads to the high activity of the SnO₂ decorated sample.2.A one-pot hydrothermal method was developed for the preparation of SZTO.The structure,optical properties and morphology of SZTO composite photocatalyst were characterized by XRD,DRS,SEM,and XPS.Compared with the samples synthesized by the solid phase reaction and the classical P25,SZTO prepared by the one-step hydrothermal method shows higher and more stable performance for photocatalytic degradation of benzene.The high activity was attributed to the formation of type II heterojunction between SnO_x and Zn₂SnO₄,which can promote the transfer of electrons from the SnO₂ valence band to the Zn₂SnO₄ valence band,while the hole from the Zn₂SnO₄ conduction band to the SnO₂ conduction band.Thus the recombination of photogenerated carrier can be suppressed and the separation of photogenerated electrons and holes can be promoted.3.SnO₂,Sn²⁺-doped SnO₂(Sn²⁺-SnO₂),SnO/SnO₂ and SnO were selectively prepared by controlling the composition of the hydrothermal solution with SnCl2 as the precursor.The structure,absorption,morphology and photocatalytic properties of the prepared samples were studied in detail by XRD,DRS,SEM,TEM and XPS.The result show that SnO₂,Sn²⁺-SnO₂,SnO/SnO₂ and SnO can be prepared in H2O2,H2 O,urea and N2 purged urea solution,respectively.For Sn²⁺-SnO₂,Sn²⁺ doping amount can be controlled by changing the hydrothermal temperature?120-200 oC?,while for SnO/SnO₂,the coupling amount of SnO₂ can be controlled by controlling the dosage of urea?0-3 g?.Sn²⁺-SnO₂ and SnO/SnO₂ have visible light absorption,and a large amount of ·OH is generated under visible light excitation,which leads to the degradation of methyl orange.However,as Sn²⁺ easily oxidized to Sn⁴⁺,the photocatalytic performances are quite instable.