TiO2/g-C3N4复合光催化剂的制备及可见光降解罗丹明B研究

Preparation of TiO2/g-C3N4 composites and its photocatalytic mechanism for degradation of RhB under visible light

通过溶胶-凝胶法在TiO2的制备过程中掺杂入石墨相氮化碳(g-C3N4),一步反应得到TiO2/g-C3N4复合光催化剂。分别采用TEM、XRD、FTIR和UV-Vis表征手段进行催化剂的微观形貌、晶型、活性官能团和光利用率分析。以光催化降解罗丹明B(RhB)为探针反应,对复合光催化剂在不同制备条件及不同催化条件的催化活性进行了研究。结果表明,g-C3N4成功掺入TiO2中,形成TiO2/g-C3N4异质结构,并扩大了光吸收范围。其中,TiO2与g-C3N4的质量比为0.9、500℃煅烧2h所得材料的光催化性能最佳。当TiO2/g-C3N4-0.9的投加量为100mg/L,废水中RhB浓度为1×10-5mol/L,pH值为6.5,可见光下反应180min后,对罗丹明B的降解率可达到58.9%,其在弱酸弱碱环境也同样适用,且稳定性好,重复利用5次以后催化效果仍能达到58.1%。同时对其反应机理进行探究,罗丹明B的光催化反应符合准一级动力学模型,在反应体系中起主要作用的活性物质为·O-2,计算得其贡献率为75%。

On the basis of successful preparation of graphite phase carbonitride(g-C3N4) by way of the thermal polymerization doped in preparing TiO2 in the sol-gel process,the paper has succeeded in working out the TiO2/g-C3N4 composite photocatalyst through the single step reaction.And,then,it has done the characteristic analysis of the reaction morphology,the crystal type,the reactive functional groups and the light utilization efficiency of TiO2/g-C3N4-0.9 through the TEM,XRD,FTIR and UV-Vis techniques.The results of all the afforementioned analysis and identifications indicate that,g-C3N4 can be made successfully incorporated into TiO2 to form a heterogeneous structure.At the same time,the range of the light absorption can be extended,and the photogenerated electrons can be stimulated,the separation of photogenerated blanks can be promoted with the activity of the material being able to get enhanced.Assessing the catalytic activity of the composite photocatalyst under different preparation conditions,the catalytic conditions can help to make clear the material of the greatest catalytic activity with its mass ratio of TiO2 to g-C3N4 being 0.9 and with the calcination at 500 ℃ for 2 h.What is more,the aggregation of TiO2 can be effectively inhibited by the material doped at a ratio of TiO2 to g-C3N4 up to 0.9.As the result of calcination at the temperature of 500 ° C for 2 h,it proves that the crystal form being 0.9 proves both complete as well as realistic.And,then,the crystal phase ratio can be found to reach the optimal degree,whereas TiO2 and g-C3N4 can formulate the heterogeneous structure.In addition,when the dose of TiO2/g-C3N4-0.9 is 100 mg/L whereas the concentration of rhodamine B is 1×10-5 mol/L,the degradation rate of rhodamine B may likely get to 58.9% through the reaction under the visible light for 180 min.Besides,the catalyst can also function under the weak acid and weak alkaline conditions,so as to make the degradation rate relatively stable to reach 58.1% after 5 times of repeated use.Furthermore,we have also investigated the reaction mechanism by using 1 mmol/L BQ,EDTA-2 Na and methanol as scavengers of ·O-2,h+,· OH,respectively.All the above mentioned experimental results have finally proven that the photocatalytic reaction of rhodamine B tends to follow the quasi first-order kinetic model,whereas the main active species in the reaction system should be ·O-2 with a contribution rate of about 75%.