异质型BiOI/NaBiO3光催化剂的合成及其光催化性能

根据表面化学蚀刻原理采用加热冷凝回流的方法制备了一系列组成的异质结构BiOI/NaBiO₃光催化剂.利用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)和紫外-可见漫反射光谱(UV-Vis-DRS)等技术对其晶相结构、微观形貌和光吸收性能进行了表征.光催化实验表明,BiOI/NaBiO₃在可见光下可以有效降解罗丹明B(RhB),当BiOI与NaBiO₃的物质的量分数为一定值时,异质结构的光催化剂明显优于单一组分的光催化活性.通过加入不同的牺牲剂及荧光实验结果推测了该异质结构材料的光催化机理,并且分析了其光生载流子的传输方向及光催化过程的活性物种.研究表明,BiOI/NaBiO₃的催化活性增强主要归结为两者之间形成了有效的异质结构,其内建电场能够促进光生载流子的分离,同时光生空穴h⁺在光催化降解过程中是主要的活性物种.

Synthesis of Heterojunction Type BiOI/NaBiO3 Photocatalyst and Enhanced Photocatalytic Activities

BiOI/NaBiO₃ heterostructure photocatalysts were synthesized using HI as etching agents to react with NaBiO₃ by a heating condensate reflux method according to surface chemical etching principle. Several characterization tools including X-ray powder diffraction (XRD), scanning electron microscope (SEM) and UV-Vis diffuse reflectance spectra (UV-Vis DRS) were employed to study the phase structures, morphologies and optical properties of the as-prepared samples respectively. From the degradation of Rhodamine B(RhB) under visible light irradiation experimental results, we can obtained that the absorption capacity of as-prepared samples were enhanced with increasing the BiOI amounts in the BiOI/NaBiO₃ heterostructures until the BiOI/NaBiO₃ ratio is 79.62%. With increasing BiOI content, the photocatalytic activity enhanced gradually and then decreased. As the BiOI content increase to 17.34%, the highest photocatalytic activity could be achieved, and the RhB almost faded completely with the time increasing to 100 min. The results show that the adsorption ability is only a factor not all to promote the photocatalytic ability. The E_VB of NaBiO₃ and BiOI were calculated to be 2.23 and 2.41 eV and the E_CB of NaBiO₃ and BiOI were-0.23 and 0.46 eV by the UV-Vis DRS method respectively. To evaluate the roles of reactive species during photocatalysis, different scavengers including benzoquinone, isopropyl alcohol and methanol were adopted as the traps for O₂^-, OH and h⁺ for RhB degradation. The results suggesting that h⁺ played major role for RhB degradation. Terephthalic acid photoluminescence (TA-PL) probing test demonstrated that OH could be negligible also. According to the band gap structure of BiOI/NaBiO₃, the effects of scavengers and the PL experimental results, a possible charge separation processes between BiOI and NaBiO₃, and the pathway for the photocatalytic activity enhancement mechanism was proposed. The heterojunction at the interface between p-BiOI and n-NaBiO₃ can efficiently reduce the recombination of photogenerated electron-hole pairs and which accounts for the enhancement of photocatalytic activity. Form the analysis of potential, it is theoretically reasonable that the photocatalytic degradation of RhB could be attributed to the reaction of hole directly rather than OH and O₂^-radicals.