摘要
Bismuth selenide(Bi_(2)Se_(3))is an attractive visible-light-responsive semiconductor that can absorb a full range of visible and near-infrared light.However,its poor redox capacity and rapid carrier recombination limit its application in photocatalytic oxidation.In this study,we adopted Bi_(2)Se_(3)as the couple part of graphitic carbon nitride(g-C_(3)N_(4))to construct a Bi_(2)Se_(3)/g-C_(3)N_(4)composite photocatalyst.Through in situ fabrication,the self-developed Bi2O3/g-C_(3)N_(4)precursor was transformed into a Bi_(2)Se_(3)/g-C_(3)N_(4)heterojunction.The as-prepared Bi_(2)Se_(3)/g-C_(3)N_(4)composite exhibited much higher visible-light-driven photocatalytic activity than pristine Bi_(2)Se_(3)and g-C_(3)N_(4)in the removal of phenol.The enhanced photocatalytic activity was ascribed to the S-scheme configuration of Bi_(2)Se_(3)/g-C_(3)N_(4);this was confirmed by the energy-level shift,photoluminescence analysis,computational structure study,and reactive-radical testing.In the S-scheme heterojunction,photo-excited electrons in the conduction band of g-C_(3)N_(4)migrate to the valence band of Bi_(2)Se_(3)and combine with the excited holes therein.By consuming less reactive carriers,the S-scheme heterojunction can not only effectively promote charge separation,but also preserve more reactive photo-generated carriers.This property enhances the photocatalytic activity.
光催化氧化是一种应用前景良好的环境治理技术.与絮凝、物理吸附和化学氧化等常见的方法相比,光催化氧化具有环境友好、氧化完全、方便和廉价等优势.特别是可见光光催化氧化,可利用太阳能中占比最高的可见光,在应用中更具优势.因而,探索可见光响应性能优异的光催化剂一直是光催化氧化领域的一个重要研究内容.硒化铋(Bi_(2)Se_(3))是一种带隙(带隙宽度在0.3~1.3 e V)非常窄的半导体,能吸收全部波长范围的可见光和近红外光.此外,Bi_(2)Se_(3)还具有独特的金属表面态,其表面具有良好的导电性.这些特性使其在可见光光催化氧化领域具有很大的应用潜力.然而,由于Bi_(2)Se_(3)价带位置高,氧化能力很弱,其价带上的空穴在光催化反应中难以被消耗,导致空穴大量累积,并迅速与光生电子复合,大幅降低了Bi_(2)Se_(3)的光催化性能.因此,一直以来,Bi_(2)Se_(3)很少被用于光催化反应.如何充分利用Bi_(2)Se_(3)的光响应优势,制备出性能优异的光催化剂,仍是具有挑战性和吸引力的研究方向.本文采用预先制备的Bi2O3/g-C_(3)N_(4)复合物作为前驱体,通过原位转化的方法,将前驱体置于热的Se蒸汽中,使前驱体上的Bi2O3与Se蒸汽反应,完全转化为Bi_(2)Se_(3)纳米颗粒,从而制得Bi_(2)Se_(3)/g-C_(3)N_(4)复合光催化剂(Bi_(2)Se_(3)含量约为4 wt%).透射电镜结果表明,所形成的Bi_(2)Se_(3)纳米颗粒较均匀地分布在g-C_(3)N_(4)表面.表面功函数分析发现,Bi_(2)Se_(3)与g-C_(3)N_(4)结合后,它们的费米能级分别由原来的-0.55和-0.18 e V变为平衡时的-0.22 e V,可形成指向g-C_(3)N_(4)的内建电场,有利于形成梯型(S型)异质结.在此基础上,能级位移、荧光分析、结构计算和反应自由基测试等结果表明,Bi_(2)Se_(3)和g-C_(3)N_(4)之间形成了S型异质结.在可见光光催化降解苯酚的实验中,所制备的Bi_(2)Se_(3)/g-C_(3)N_(4)复合物的光催化活性明显优于单一的Bi_(2)Se_(3)和g-C_(3)N_(4).结合比表面、孔结构、光吸收和荧光等对比分析,认为Bi_(2)Se_(3)/g-C_(3)N_(4)的这种S型异质结构在其光催化活性增强中起到了关键作用.在光照条件下,其g-C_(3)N_(4)导带中光生电子向Bi_(2)Se_(3)的价带迁移,并与光生空穴复合,从而使Bi_(2)Se_(3)导带上可保留更多的高活性光生电子参与光催化反应,由此Bi_(2)Se_(3)/g-C_(3)N_(4)的光催化活性增强.循环性能测试和光还原实验结果表明,所制备的Bi_(2)Se_(3)/g-C_(3)N_(4)复合光催化剂具有良好的稳定性.本文工作为高可见光吸收的光催化剂制备和性能增强提供了新途径和新视野.
基金
国家自然科学基金(52073034,21871030)
湖南省教育厅重点项目(18A370)
湖南省自然科学基金(2018JJ2457).
