Microstructural Tuning and Photocatalytic Activity of Tin-Based Oxygen-Group Composites

Author:Chen Da Yong

Supervisor:chen zhi wen


Degree Year:2019





The photocatalytic performances of semiconductors are affected by not only external environment factors but also their own physical and chemical properties,such as optical,electrical and magnetic properties.The physical and chemical properties of materials greatly rely on their constituents and microstructure,such as the crystal structure,interior defect,morphology and size.Therefore,The photocatalytic performances of semiconductors can be adjusted by tuning their constituents and microstructure.Due to their unique physical and chemical properties,SnS2 and SnO2 display very wide application prospects.Therefore,it is very important to tune their chemical constitutions and microstructure.Based on the above reasons,the microstructural and constituent tuning of SnS2 and SnO2 are performed as below:(1)SnS2 quantum dot(QDs)are assembled onto amino-functionalized graphene nanosheets(AGNSs)via a facile hydrothermal method.Electron-beam irradiation(EBI)technique is intentionally applied to irradiate the as-prepared SnS2 QDs/AGNSs.It is found that the EBI can promote the doping of N element in amino group into graphene nanosheets,enhance the crystallinity of SnS2 QDs and create a small number of lattice defects in SnS2 QDs.The correlation between the EBI dose and the photocatalytic activity of irradiated SnS2 QDs/NGNSs(SNGNSs)is systematically investigated.It is found that the SNGNSs irradiated under 70 kGy exhibit obviously higher photodegradation efficiency(95.6%)for methyl orange(MO)than the unirradiated one(59.5%).This enhanced photocatalytic activity can be ascribed to the EBI-created lattice defects in SnS2 QDs and doping N element into graphene nanosheets.The lattice defects result in a narrow band gap surface layer.The N-doped graphene nanosheets contact intimately with SnS2 QDs,which provide conveniently transport pathways for photogenerated charges.This work presents an innovative strategy for the adjustment in the microstructure of SnS2 QDs/AGNSs hybrids and the improvement of their photocatalytic activity(2)Ni doped SnS2(Ni-SnS2)is developed via a hydrothermal process.The heterostructures of Ni-SnS2 and SnO2 QDs(NiSnSO)are created by a facile oxidation procedure.Interestingly,the NiSnSO heterostructures fabricated under thermal oxidation for 100 min(NiSnSO-100)simultaneously exhibit the following advantages:(ⅰ)the Ni-doping enhances light-harvesting,extends the light response to the visible light region,and narrows the band gaps of SnS2;(ⅱ)the heterostructures promote the transport and separation of photogenerated charges from Ni-SnS2 to SnO2;(ⅲ)the SnO2 QDs facilitate the enrichment of reactants,provide more reactive centers,and product diffusion in reactive center by the confinement effect of nanoparticles.These advantages result in the obviously higher photocatalytic activity of NiSnSO-100,photodegrading 92.5%MO,greatly higher than the bare SnS2(29.8%).These results reveal that the combination of heteroatom doping and heterostructure creating is greatly important in designing nanomaterials for effectively photocatalytic applications(3)Ni doped SnO2 QDs is fabricated in a conveniently hydrothermal process.In the fabrication process,Vitamin C(VC)acts as stabilizer to avoid the precipitating of Sn4+(Ni2+),and Na2CO3 serves as precipitator to react with Sn4+(Ni2+)to produce Ni doped SnO2 QDs.The influences of the Ni doping amount on the photodegradation performance of SnO2 QDs is studied.The 1%(atomic percent)Ni doped SnO2 QDs display interesting advantages as below:(ⅰ)the Ni doping can boost light-harvesting and narrow the band gaps of the Sn02 QDs;(ⅱ)Ni,as capturing center of electron,improve separation efficiency of photogenerated charges;(ⅲ)the SnO2 QDs with ultra small particle size and large specific surface area can supply more reactive centers for photocatalytic reaction.The two important factors contribute to enhancing the photocatalytic performance of the 1%Ni doped SnO2 QDs.The 1%Ni doped SnO2 QDs photodegrade 91.5%Rhodamine B under experimental conditions,obviously surpassing that of their pure counterparts.