Bi_(5)O_(7)I/g-C_(3)N_(4)Z型异质结的常温沉淀制备及其光催化性能研究

Room-temperature precipitation synthesis and photocatalysis of Bi_(5)O_(7)/g-C_(3)N_(4) Z-scheme heterojunction

以Bi(NO3)3·5H2O､KI和g-C_(3)N_(4)为前驱体,采用常温沉淀法制备Bi_(5)O_(7)I/g-C_(3)N_(4)Z型异质结复合光催化剂,表征其光吸收性能､微观形貌､光生电子-空穴的分离效率等特性,研究新型光催化剂对RhB的可见光催化降解性能,探讨其可见光催化过程活性基团种类以及作用机理.结果表明:利用沉淀法合成Bi_(5)O_(7)I/g-C_(3)N_(4)的条件为:Bi(NO_(3))_(3)·5H_(2)O､KI和g-C_(3)N_(4)的投加量分别为4.85g､1.66g和1.61g,乙二醇的用量为50mL,反应液的pH值为12,反应搅拌速度为200r/min,反应温度为25℃.Bi_(5)O_(7)I/g-C_(3)N_(4)异质结无杂相生成且纯度高,异质结复合发生在g-C_(3)N_(4)的(002)晶面和Bi_(5)O_(7)I的(203)晶面,但g-C_(3)N_(4)和Bi_(5)O_(7)I的化学结构未受影响.Bi_(5)O_(7)I/g-C_(3)N_(4)呈三维纳米花瓣形貌结构,为光生电子-空穴的迁移提供了大量的接触位点.Bi_(5)O_(7)I的g-C_(3)N_(4)掺杂改性使其光催化活性显著增强,其光吸收边缘由425nm红移至462nm,Bi_(5)O_(7)I/g-C_(3)N_(4)的能带排列结构与Z型异质结匹配,促进了光生电子-空穴的分离.其光电流密度(11.5mA/cm)约为g-C_(3)N_(4)和Bi_(5)O_(7)I对应值的2.66倍和1.47倍.Bi_(5)O_(7)I/g-C_(3)N_(4)对罗丹明B的可见光催化降解率为93.9%,显著高于g-C_(3)N_(4)(58%)和Bi_(5)O_(7)I(49.7%)的降解效果,其光催化氧化活性主要来自羟基基团､超氧基团和光生空穴等中间态自由基.

In this work,by using Bi_(5)O_(7)I、KI and g-C_(3)N_(4) as precursors,a novel Bi_(5)O_(7)I/g-C_(3)N_(4) Z-scheme heterojunction has been synthesized successfully by precipitation method at room temperature,its property of light absorption、morphologic structure、efficiency of photogenerated electron-hole were characterized.The visible-light degradation performance on Rhodamine B(RhB)by new type composite photocatalyst､the kinds of radicals and the mechanism in photocatalytic reaction system were studied.The results revealed that:The synthesis conditions of Bi_(5)O_(7)I/g-C_(3)N_(4) by precipitation were shown as follow:4.85g Bi(NO_(3))_(3)·5H_(2)O,1.66g KI,1.61g g-C_(3)N_(4),50mL glycol,12 of reaction pH,200r/min of reaction stirring rate and ambient reaction temperature(25℃).There’s no impurity and influence on chemical structure of g-C_(3)N_(4) and Bi_(5)O_(7)I during the synthesis process,the recombination of Bi_(5)O_(7)I/g-C_(3)N_(4) crystallographic plane occured on the {002} crystal plane of g-C_(3)N_(4) and the{312}crystal plane of Bi_(5)O_(7) I.The morphologic structure of Bi_(5)O_(7)I/g-C_(3)N_(4) was 3D nano petal-like,which furnished a large number of contacting site for the transfer of photogenerated electron-hole.The doping of g-C_(3)N_(4) on Bi_(5)O_(7)I can significantly enhance photocatalytic activity,its wavelength edge of light absorption shifted to 462nm from 425nm.The band arrangement structure of Bi_(5)O_(7)I/g-C_(3)N_(4) was matched with the Z-scheme heterojunction,which promoted the separation of photogenerated electron-hole,its photocurrent density(11.5mA/cm)is 2.66 and 1.47times than that of g-C_(3)N_(4)(4.32mA/cm)and Bi_(5)O_(7)I(7.8mA/cm)respectively.The photocatalytic degradation rate for RhB by Bi_(5)O_(7)I/g-C_(3)N_(4) under visble light irradiation is 93.9%,which is 1.89 and 1.62times than that of Bi_(5)O_(7)I and g-C_(3)N_(4) respectively,the activity of photocatalytic oxidation was attributed to the intermediate radicals including·OH､·O_(2)^(-) and h^(+).