Page - 131 - in Photovoltaic Materials and Electronic Devices

visible light photocatalysts that can utilize more solar light energy in photocatalysis. Nowadays,manyeffortshavebeenemployedtoimprovethephotocatalyticefficiency of p-BiOI nanostructures [8,9]. Constructing p-n heterojunctions is considered an effective method to improve the separation efficiency of photogenerated carries due to their strong internal electric field [10–13]. Many kinds of p-n heterojunctions based on p-BiOI, such as BiOI/ZnTiO3 [14], BiOI/Zn2SnO4 [15], BiOI/ZnO [16], BiOI/Bi4Ti3O12 [17], etc., havebeenreportedwith increasedphotocatalyticactivity. Amongmanyntypesemiconductors,Titaniumdioxide (TiO2)nanostructures havebeenwidelystudiedasgoodphotocatalystsduetotheirhighefficiency,chemical stability, nontoxicity, low cost, etc. [18–24]. Coupling p-BiOI nanostructures with n-TiO2 nanostructures to form p-BiOI/n-TiO2 heterojunctions would hinder the recombinationofphotogeneratedcarriesmoreeffectively. Todate,p-BiOI/n-TiO2 nanoparticles have been widely reported with enhanced visible-light photocatalytic activity [25–27].However, thesuspendednanoparticles tendtoaggregateduringthe synthesis process and be lost in the separation and recycling process, resulting in a reduction of specific surface area and photocatalytic performance. Compared with nanoparticles,one-dimensionalnanofiberswithahighsurface-to-volumeratioaremore favorableforbothphotocatalyticactivityandrecyclingcharacteristics [28,29]. In fact, ourgrouphaspreviouslyconstructedheterojunctionsofp-BiOClnanosheets/n-TiO2 nanofibers [30] and p-MoO3 nanosheets/n-TiO2 nanofibers [31], both of which show enhanced ultraviolet photocatalytic activities and recycling properties. Therefore, there is interest in constructing p-BiOI/n-TiO2 heterojunctions using electrospun TiO2 nanofibers as n type semiconductor because of the following advantages: (1)besides the internalelectricfieldof thep-nheterojunction, theone-dimensional characters of TiO2 nanofibers could act as charge transfer channels facilitating higher charge separation efficiencies; (2) the three-dimensional open structure and large specific surface area of TiO2 nanofibers provide more active sites for the assembly of secondarynanostructureswithhighdensities; and(3) theirnanofibrousnonwoven webstructurecanbeeasilyseparatedfromfluidbysedimentation. Taking the above factors into account, in this work, the p-type BiOI nanosheets weresuccessfully synthesized onn-typeelectrospun TiO2 nanofibersby successive ionic layeradsorption andreaction (SILAR)at room temperature. The contents of BiOI in the heterojunctions of p-BiOI nanosheets/n-TiO2 nanofibers (p-BiOI/n-TiO2 NFs) could be well controlled by adjusting the cycles of SILAR. X-ray photoelectron spectrashowedthatbothTi2ppeaksofp-BiOI/n-TiO2 NFsshiftedtohigherbinding energies than that of TiO2 nanofibers, suggesting effective electrons transfer from TiO2 toBiOIintheformationofp-nheterojunction. Thep-BiOI/n-TiO2 NFsexhibited favorable visible-light photocatalytic activity for degradation of methyl orange (MO), which can be ascribed to the high specific surface area and the as-formed 131