Dye-sensitized BiOX(X=F、Cl):Preparation And Visible-light Photocatalysis

Semiconductor photocatalytic oxidation technology has been proved to be apromising approach for environmental pollutant remediation, because it cancompletely decompose organic pollutant into CO2and H2O at room temperature.TiO2has been considered as an excellent photocatalyst for its nontoxicity,inexpensive and chemical stability. However, due to its wide band gap (3.2eV foranatase), TiO2is known to be active only under UV light, which largely restricts itspractical applications. As a result, much attention has been focused ondesigning new photocatalysts active under visible light.In this paper, BiOF and BiOCl samples were prepared by precipitation andultrasonic irradiation respectively. CuTsPc was used as a sensitizer to synthesizeCuTsPc/BiOF and RhB was used to prepare RhB/BiOCl by impregnation process.The photocatalytic degradation of RhB and MO under visible light irradiation wasused as model reactions to evaluate the photocatalytic activity of the as-prepareddye-sensitized BiOX（X=F、Cl）. The effects of reaction conditions on thevisible-light photocatalytic performances were studied. The as-prepared sampleswere characterized by UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS),Fourier transform infrared spectroscopy (FT-IR) and Photoluminescence (PL).Active oxygen species generated on as-prepared samples during visible lightirradiation were detected by electron paramagnetic resonance (EPR) spin trappingtechnique. The photodegradation process of RhB and MO was monitored by liquidchromatography/mass spectrometry (LC-MS) techniques to identify theintermediates, and a proposed photocatalytic degradation pathway of the pollutionswas discussed.The main results are summarized as follows:(1) The CuTsPc/BiOF andRhB/BiOCl photocatalysts were synthesized by an impregnation method. Diffusereflectance spectra reveal that the absorbance range of BiOF and BiOCl areobviously extended to visible region by dye-sensitization.(2) The as-preparedsamples exhibit visible-light photocatalysis. It is found that the amount ofdye-sensitizer loaded on BiOX has a great effect on the photocatalytic activities. Thephotocatalysts with dye-sensitizer loaded at0.3wt%exhibit the best activity. The photocatalytic degradation ratio of RhB is80%over CuTsPc/BiOF for5hirradiation. About86%MO are degraded on RhB/BiOCl for70min irradiation.(3)The results of LC-MS suggest that RhB is decomposed to N-de-ethylatedintermediates at the beginning and MO is first lost methyl group. The EPR resultsindicate that the active oxygen species （·OH and O2·-） are generated onCuTsPc/BiOF, and O2·-is generated on RhB/BiOCl under visible light irradiation.(4)A possible mechanism for the photocatalysis on the as-prepared dye-sensitizedBiOX（X=F、Cl）under visible light was also proposed as follows：The dye is excitedunder visible light irradiation, and the excited dye molecule transfers electrons to theconduction band of BiOX（X=F、Cl）, and the injected electron reacts with theoxygen molecule adsorbed on surface to give oxygen species (O2and·OH), whichcan decompose the organic pollutions.The original results of this study are as follows: dye-sensitized BiOX（X=F、Cl）photocatalysts are prepared and applied in the visible-light photocatalyticdegradation of organic pollutants for the first time. A proposed photocatalyticdegradation pathway of the pollutions is also discussed.