Preparation Of Nanocrystalline SnO₂ Composite Films And Their Photocatalytic Performance

SnO₂ is a kind of very important n type semiconductor metal oxide with wide band gap energy 3.6 eV.It has a broad application prospect in the gas sensor,electrode materials,solar cells and other fields since it has good gas sensitive performance and unique optical,electrical properties.However,people find that SnO₂ is also a kind of very good light catalyst along with the further study of tin dioxide and more and more people will be applied in the field of photocatalysis.Photocatalysis is with higher energy excitation under the irradiation of UV light.But because of SnO₂ having a wide level,only smaller wavelength UV light can stimulate its photocatalysis,which makes that its utilization of sunlight is low.In addition,the electron-holes that play a key role in the process of photocatalytic is easy to compound,which limits the photocatalysis of SnO₂.In order to better play a role of tin oxide in the field of photocatalytic,we must solve the problems of two aspects: one,improving the utilization rate of sun;second,reducing the recombination rate of electrons and holes.In this study,the methods of ion doping and semiconductor composition are used to modify SnO₂ and the concrete contents are as followings:1.Preparation and properties of SnO₂ and SnO₂/ZnO composite filmsIn the experiment,SnCl2·2H2O and Zn（CH3COO）2·2H2O were chosen as precursors to respectively prepare SnO₂ colloid and ZnO colloid by means of sol-gel method.The above two types of colloid prepared were mixed according to different volume ratio.Then we can find the best volume ratio with the help of the degree of degradation to acid fuchsine.The different films can be made from SnO₂ colloid and SnO₂/ZnO composite colloid attached to the clean glass sheets using dip-coating equipment.Some ions including La 、F、B were doped separately or double on the surface of the above films.Then the ion doped films were calcinated at 550℃ for 1 hour.Finally,we could obtain the best single or double doped ions concentration based on the degradation of acid fuchsine.The photocatalytic properties of SnO₂ have been improved significantly by means of the good results of the degradation of oxytetracycline and formaldehyde which are very hard to degrade.2.Characterization of SnO₂ and SnO₂/ZnO composite filmsA series of measures were employed to characterize the optical properties and structural characteristics of SnO₂ and SnO₂/ZnO composite films,which included photoluminescence（PL）,ultraviolet-visible absorption spectroscopy（UV-vis）,X-ray diffraction（XRD）.The results of PL and UV-vis indicated that multi-modification could reduce the rate of electron-hole pairs effectively and broaden the spectral response range.3.The discuss about photocatalytic mechanismSnO₂ is n-type semiconductor with the large band gap（3.6 eV）.ZnO is also n-type semiconductor with the large band gap（3.2 eV）.But it can come into being doping energy level after SnO₂ and ZnO composite.Thus,their band gap was significantly lower than single SnO₂ or ZnO for the doping energy level.For ion doping,there are two main aspects of the role: On the one hand the ion doping could form doping energy level reducing band gap energy;On the other hand the ions with positive and negative charges can become the capture trap of the electron-hole pairs which reduces their recombination rate effectively.