Page - 141 - in Photovoltaic Materials and Electronic Devices

with a needle tip. Then, a high voltage source was connected to the needle tip while a sheet of aluminum foil was employed as the collector. The voltage between the needletipandcollectorwassetat10kV,andthedistancewas15cm. Theas-collected nanofiberswerecalcinedatarateof25˝C/handremainedfor2hat520˝Ctoobtain TiO2 NFs. 3.2. FabricationofBiOI/TiO2 Nanofibers The p-BiOI/n-TiO2 NFs were synthesized through the SILAR process. Typically, 0.25 mM Bi(NO3)3¨5H2O solutions were prepared with deionized water as solution A, and equivalent concentration of KI solution were prepared as solution B. The TiO2 nanofibers were first immersed into solution A for 2 min, rinsed with deionized water,andthenimmersedintosolutionBfor2min, rinsing likewise. Thefour-step procedure formsonecycleandtheBiOIwouldincreasebyrepeatingthecycles. A seriesof samples,withdifferentcyclesof10,20and30werepreparedanddenoted as BiOI/TiO2-C10, BiOI/TiO2-C20 and BiOI/TiO2-C30. After that, the samples were thoroughlyrinsedwithdeionizedwaterandallowedtodryat60˝Covernight. All the samples are listed in Table 1. Pure BiOI nanosheets were prepared by mixing solutionAandB, thenrinsedanddried. 3.3. Characterizations Sanningelectronmicroscopy(SEM,Quanta 250FEG,FEI,Hillsboro,OR,USA) and high-resolution transmission electron microscopy (HRTEM; JEOL JEM-2100, JEOL, Tokyo, Japan) were used to characterize the morphologies of the products. The X-ray diffraction (XRD) measurements were carried out using a D/max 2500 XRD spectrometer (Rigaku, Tokyo, Japan) with a Cu Kα line of 0.1541 nm. The X-ray photoelectron spectroscopy (XPS) was performed on a VG-ESCALAB LKII instrument (VG, Waltham, UK) with Mg KαADES (hυ = 1253.6 eV) source at a residualgaspressureofbelow10´8 Pa. Thespecificsurfaceareaof thesampleswere measured with a Micromeritics ASAP 2010 instrument (Micromeritics, Norcross, GA,USA)andanalyzedbytheBrunauer-Emmett-Teller (BET)method. TheUV-vis diffuse reflectance spectra were measured at room temperature with a UH4150 spectrophotometer (Hitachi,Tokyo, Japan). 3.4. PhotocatalyticTests A 150 W xenon lamp with a cut off filter (ě420 nm) was used as the visible light source forphotocatalysis. UsingMOasmodelpollutants,photocatalyst (0.1g)was suspendedinMOsolution(100mL,10mg/L)withstirring. Thesolutionwaskept in the dark for 30 min to reach adsorption-desorption equilibrium between the organic molecules and the photocatalyst surface. Then, 4 mL reacted solutions in series were takenoutandanalyzedevery1h. TheconcentrationsofMOinthereactingsolutions 141