g-C3N4-BiOBr复合材料制备及可见光催化性能

g-C_3N_4-BiOBr Composites: Synthesis and High Photocatalytic Performance under Visible-Light Irradiation

利用原位沉积法将Bi OBr纳米片生长到g-C_3N_4表面,制得g-C_3N_4-Bi OBr p-n型异质结复合光催化剂。采用X射线衍射(XRD)、红外光谱(FTIR)、场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)、紫外可见漫反射(UV-Vis-DRS)和荧光光谱(PL)等测试对光催化剂结构和性能进行表征。通过可见光辐照降解甲基橙水溶液检测评估复合光催化剂光催化活性。研究结果表明:复合光催化剂由Bi OBr和g-C_3N_4两相组成,Bi OBr纳米片在片状g-C_3N_4表面快速形核生长形成面-面复合结构。相比于纯相g-C_3N_4和Bi OBr,g-C_3N_4-Bi OBr复合材料具有更强可见光吸收能力,吸收带边红移。在可见光辐照100 min后,性能最佳的2:8 gC_3N_4-Bi OBr复合光催化剂光催化活性分别是纯相g-C_3N_4和Bi OBr的1.8和1.2倍,经过4次循环实验后,其降解率仍达84%,说明复合结构光催化剂催化性能和稳定性增强。复合光催化剂的荧光强度显著降低,说明光生载流子复合得到了有效抑制。复合光催化剂催化性能的提高归因于p-n型异质结促进电荷有效分离、抑制电子-空穴复合和吸收光波长范围的扩展,相比单一成分材料具有更好的催化活性和稳定性。自由基捕获实验证明,可见光降解甲基橙光催化过程中的主要活性成分为空穴,并据此提出了可能的光催化机理。

A novel p-n heterojunction composite photocatalyst of graphitic carbon nitride-Bi OBr（g-C-3N-4-Bi OBr）fabricated by deposition of Bi OBr nanoflakes on g-C-3N-4 surface were presented. The structures and properties of as-synthesized samples were characterized by X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FTIR）, field emission scanning electron microscopy（FE-SEM）, transmission electron microscopy（TEM）, UV-Vis diffuse reflection spectroscopy（DRS） and photoluminescence（PL）. The photocatalytic activity was evaluated by degradation of methyl orange（MO） aqueous solution under visible-light irradiation. The study results show that the composite photocatalysts were consisted of two components of g-C-3N-4 and Bi OBr, and the Bi OBr nanoflakes can be rapidly deposited on g-C-3N-4 sheet surface. In comparison with pure Bi OBr and g-C-3N-4,the g-C-3N-4-Bi OBr composite photocatalysts shows more absorption intensity within the visible light range and the sorption edge shifts to lower energy direction. The optimum photocatalytic activity of the 2：8 g-C-3N-4-Bi OBr composite sample was 1.8 and 1.2 times as high as those of individual g-C-3N-4 and Bi OBr after 100 minutes irradiation with visible light. After reusing 4 cycles, the photodecomposition rate of MO still remains 84%, which proves the enhancement of photocatalytic activity and stability of the composite photocatalyst. The PL emission intensity of the composite photocatalyst decreased remarkably due to the suppression of photogenerated charges recombination. The enhancement in both photocatalytic performance and stability was induced by a synergistic effect, including the improved charge separation efficiency of the photoinduced electron-hole pair at the interface of g-C-3N-4 and Bi OBr,the inhibition of photoinduced charge recombination and the extension of the absorption bands comparing with the sole component. A series of radical trapping experiments demonstrate that the holes should be the main active species in MO photodegradation and a possible photocatalytic mechanism is proposed.