Study On The Preparation And Performance Of Tin-bismuth-based Composite Photocatalysts

Photocatalytic water treatment technology can completely decompose pollutants into small inorganic molecules of CO₂ and H₂O under sunlight irradiation.Due to the advantages of thoroughness,high efficiency and energy saving,it has extremely broad application prospects in the field of environmental pollution restoration and energy conversion.However,at the current stage,the practical application of photocatalytic technology is still facing the challenge of poor light utilization and conversion rate of the photocatalyst.Hence,to develop visible-light response photocatalyst with excellent activity,good photostability and recycling performance is a key research topic in the field of photocatalytic water treatment.Focusing on this key research topic,modification strategies of heteroatom doping and heterostructures were used to improve light harvest and separation efficiency of photo-generated charges of the research objects SnO₂ and Bi₂WO₆,in order to enhance the photocatalytic degradation efficiency for refractory organic wastewater.The study of this thesis provides a reference and basis for the preparation of high-efficiency tin-bismuth-based composite photocatalytic materials with visible-light-response and their application in photocatalytic water treatment.The main research contents of this thesis are as follows:(1)Bi-doped SnO₂ quantum dots was synthesized by hydrothermal method.The photocatalytic degradation performance of Bi-doped SnO₂ quantum dots toward rhodamine B(Rh B)and ciprofloxacin hydrochloride(CIP)under sunlight irradiation was studied.Results showed that,compared with pure SnO₂,Bi-doped SnO₂ quantum dots(with Bi doping content from 3%to 7%)had better photocatalytic performance.The optimal Bi doping amount was 5%.The photocatalytic degradation efficiency of 5Bi-SnO₂toward Rh B and CIP were 1.75 and 1.53 times that of pure SnO₂,respectively.The excellent photodegradation ability of the composite material was attributed to the upward shift of the valence band caused by the doping of Bi,which led to the narrowed band gap and the expansion of light response range as well as the improved separation efficiency of photogenerated carriers.(2)The coral branch like Bi₂O₃/SnO₂ Z-scheme heterojunction photocatalyst was constructed by a simple hydrothermal method.Performances of the as-prepared materials were evaluated by photodegradation of bisphenol A(BPA)under simulated sunlight.The influences of representative operating conditions on the photocatalytic reaction were also investigated.Research showed that the photocatalytic degradation efficiency of 1Bi₂O₃/SnO₂ toward BPA after 60 min irradiation was 93.42%,which was 14.97 times and 2.54times that of pure SnO₂ and Bi₂O₃,respectively.According to the main active species of the reaction system and band structure of the materials,Bi₂O₃/SnO₂ was inferred to be a Z-scheme heterojunction.The enhanced photocatalytic performance benefited from the enlarged light response range and increased utilization of visible light of the system as a result of the introduction of narrow band gap Bi₂O₃ as well as the improved redox ability and the effective separation of photogenerated carriers of the system caused by the formation of Z-scheme heterojunction.(3)Bi PO₄/Bi-SnO₂ quantum dots were synthesized by one-pot hydrothermal method.The photocatalytic performance of the prepared samples was evaluated by degrading Rh B and BPA under simulated sunlight.The degradation conditions for BPA were optimized and the effects of common anions in water on the photodegradation of BPA were investigated.Results showed that Bi PO₄/Bi-SnO₂ quantum dots exhibited higher photocatalytic activity.The optimal molar percentage of Bi PO₄ was 10%.The degradation rate of10BPO/BSO toward Rh B was 95.47%,which was about twice that of Bi-SnO₂(46.66%).Whereas,the degradation rate of BPA(89.87%)was 29.17%higher than that of Bi-SnO₂(60.69%).The improved photodegradation activity was due to the enhanced light absorption and increased surface area as well as the formation of type II heterojunction between the matched energy band of Bi PO₄ and Bi-SnO₂,which promoted the separation efficiency of photogenerated charges.(4)SnS₂/Bi₂WO₆ hierarchical flower-like structure was prepared through depositing the Bi₂WO₆nanoplates on the surface of hexagonal SnS₂ nanosheets.Rh B and TC were used as model pollutants to evaluate the photocatalytic performance of the samples under visible light irradiation.Besides,the influences of various process conditions on the photodegradation of TC were investigated.Moreover,the degradation of different dyes and antibiotic wastewater by the optimal sample 4SS/BWO was examined.The experimental results showed that the performance of the sample was best when the amount of SnS₂ added was 4%.The photodegradation efficiency and apparent rate constant of 4SS/BWO for Rh B were 6 times and5.05 times that of Bi₂WO₆,respectively.Whilst,the photodegradation efficiency and apparent rate constant for TC were 2.05 times and 3.72 times that of Bi₂WO₆,respectively.The enhancement of photodegradation efficiency was attributed to the red shift and strengthened light absorption as well as the increased specific surface area of the composite materials.Moreover,the formation of type II heterojunction with the matching valence and conduction band between SnS₂ and Bi₂WO₆ accelerated the transfer and separation of photogenerated carriers.