以不同磷源制备的磷掺杂g-C_(3)N_(4)光催化剂的表征及在降解含铬电镀废水中应用的初步研究

Preparation of P-doped g-C3N4 photocatalysts with different phosphorus sources for degradation of chromium-containing electroplating wastewater

[目的]对环境有严重污染的电镀含铬废水需处理后才能排放。[方法]以尿素为原料,采用不同磷源(焦磷酸、正磷酸、亚磷酸和次磷酸),通过热缩聚法和液相蒸发法合成含氮空位的磷掺杂多孔石墨相氮化碳(g-C_(3)N_(4)),通过X射线衍射仪(XRD)、傅里叶变换红外光谱仪(FT-IR)、比表面(积)分析仪(BET)、X射线光电子能谱仪(XPS)、透射电镜(TEM)、扫描电镜(SEM)、紫外−可见分光光度计(UV-Vis)和电化学测试方法对该材料进行表征,评价其对六价铬的光催化降解性能。[结果]使用正磷酸作为磷源得到的磷掺杂g-C_(3)N_(4)降解还原六价铬的效率约为本征态g-C_(3)N_(4)的12.65倍。[结论]在氮空位、氰基和磷元素存在的情况下,磷掺杂g-C_(3)N_(4)的能带结构发生改变,电荷转移加快,展现出良好的光催化反应活性。

[Introduction]The chromium-containing electroplating wastewater which is hazardous to the environment needs to be treated prior to discharge.[Method]Phosphorus-doped porous graphitic carbon nitride(g-C_(3)N_(4))materials with nitrogen vacancies were synthesized by thermal polycondensation and liquid phase evaporation from urea with different phosphorus sources i.e.pyrophosphoric acid,orthophosphoric acid,phosphorous acid,and hypophosphorous acid,and then characterized by X-ray diffraction(XRD),Fourier-transform infrared spectroscopy(FT-IR),surface area analysis(BET),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),scanning electron microscopy(SEM),ultraviolet-visible spectroscopy(UV-Vis),and electrochemical methods,and their photocatalytic degradation performance for hexavalent chromium was evaluated.[Result]The degradation efficiency of hexavalent chromium by the phosphorus-doped g-C_(3)N_(4) prepared with orthophosphoric acid was about 12.65 times higher than that by the unmodified g-C_(3)N_(4).[Conclusion]The existence of nitrogen vacancies,cyano groups,and phosphorus changes the band structure of g-C_(3)N_(4) and prompts the charge transfer,hence the phosphorus-doped g-C_(3)N_(4) has good photocatalytic activity.