Study On The Modification And Performance Of SnO₂ Photocatalyst

Driven by the decrease of fossil fuel resources and the environmental pollution concerns,the search for new clean and renewable energy technologies is urgent on the research agendas of many research and development communities.In particular,the photocatalysts could utilization of solar energy for the hydrogen production and environmental decontamination.Tin oxide(SnO2)has been studied and recongnized as one of the most peromising photocatalysts.Nevertheless,the application of SnO2 in photocatalysis is quite limited as a result of its intrinsic wide bandgap and hence ineffective utilization of visible light,as well as the rapid combination of photogenerated electrons and holes.Therefore,it is important to use the appropriate methods to widen the range of light absorption and improve the effective separation of photogenerated electrons and holes.In this paper,the photocatalytic activity of SnO2 was improved by introducing the graphene quantum dots or graphite-nitride carbon.The as-prepared samples were systematically characterized by XRD,SEM,TEM,HRTEM,FT-IR,XPS,UV-vis DRS,photoelectrochemical tests,PL and EPR.Their photocatalytic activities were also evaluated towards removal of NOx at ppb-level under visible light irradiation and photocatalytic hydrogen production.The results are as follows:(1)The SnO2/GQDs composite was prepared by mechanical stirring and ultrasonic of SnO2 and g-C3N4 and applied for photocatalytic removal of nitric oxide(NO).In contrast to SnO2 alone,SnO2/GQDs composite has exhibited a remarkably enhanced activity under both full spectrum and visible light illumination.Especially,composite with 1%GQDs exhibits the highest photocatalytic NO degradation ratio of 57%and excellent selectivity with NO2 generated fraction as low as 5%under visible light.The crystal structure,morphology and surface state of the composite was further studied by X-ray diffraction,transmission electron microscopy,Fourier transformed infra red spectroscopy and X-ray photoelectron spectroscopy.Moreover,diffraction and reflectance spectra and photoluminescence spectra together with the photoelectrochemical tests show that the presence of GQDs in the composite could promote the visible light response as well as charge separation efficiency of the system.This makes SnO2/GQDS composite generate more active species(O2 and OH)for NO oxidation,as evidenced from the electron paramagnetic resonance measurements.(2)Novel SnO2/g-C3N4 nanocomposite was fabricated by a combination of pyrolyzation method and the in situ hydrolysis of SnI4 method.During whith SnO2 nanopartcles were formed in situ on g-C3N4 nanosheet,the two components of the composites displayes intimate intherface.In contrast to puer SnO2 and g-C3N4,the as-prepared SnO2/g-C3N4 exhibited enhanced visible photocatalytic activity.Highest photocatalytic NO degradation ratio of 32%and excellent selectivity with NO2 generated fraction as low as 8%under visible light.The photocatalytic hydrogen production rate of 6%SnO2/g-C3N4 was 2.0 times times that of 59.3?mol·g-1· h-1.In addition,SnO2/g-C3N4 composites showed good stability.Through diffraction and reflectance spectra and photoluminescence spectra together,it is shown that g-C3N4 and SnO2 are not only widen the visible light response range of the composites,but also can effectively reduce the photosynthetic carrier recombination rate and enhance the photocatalytic activity.