催化学报

催化学报 ›› 2017, Vol. 38 ›› Issue (12): 1990-1998.DOI: 10.1016/S1872-2067(17)62971-1

• 论文 • 上一篇    下一篇

硫氰根选择性吸附在g-C3N4/Ag表面增强其光催化制氢性能

陈峰a, 杨慧a, 罗玮a, 王苹a, 余火根a,b   

  1. a 武汉理工大学化学化工与生命科学学院, 湖北武汉 430070;
    b 武汉理工大学硅酸盐建筑材料国家重点实验室, 湖北武汉 430070
  • 收稿日期:2017-10-07 修回日期:2017-10-30 出版日期:2017-12-18 发布日期:2017-12-29
  • 通讯作者: 余火根
  • 基金资助:

    国家自然科学基金（51472192，21477094和21771142）；中央高校基础研究基金（WUT 2017IB002）.

Selective adsorption of thiocyanate anions on Ag-modified g-C3N4 for enhanced photocatalytic hydrogen evolution

Feng Chena, Hui Yanga, Wei Luoa, Ping Wanga, Huogen Yua,b   

  1. a School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, Hubei, China;
    b State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, Hubei, China
  • Received:2017-10-07 Revised:2017-10-30 Online:2017-12-18 Published:2017-12-29
  • Supported by:

    This work was supported by the National Natural Science Foundation of China (51472192, 21477094, 21771142) and the Fundamental Research Funds for the Central Universities (WUT 2017IB002).

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摘要：

作为一种无金属的新型半导体材料，g-C3N4因具有稳定的物理化学性质及合适的能带结构而引起人们的关注.理论上g-C3N4完全满足水分解的电势条件.然而研究发现，g-C3N4材料本身的光催化性能并不好，这主要是由于半导体材料被光激发后生成的自由电子和空穴还没来得及到达材料表面参与反应，就在材料体相内发生复合，导致电子参与有效光催化制氢反应的几率大大降低.同时还发现，将少量的贵金属，如Pt，Au，Pd作助催化剂修饰在该半导体表面，其光催化性能明显提高.但由于这些贵金属储量非常稀少，价格昂贵，导致它们的使用受到一定限制.而Ag作为一种价格远低于Pt，Au，Pd的贵金属，也得到了广泛的研究.研究表明，金属Ag储存电子的能力很好，因此可以有效地将半导体上生成的光生电子快速转移到Ag上面去，从而达到电子空穴快速分离的目的.但是在光催化制氢过程中，Ag吸附H+的能力较弱，致使电子与H+反应的诱导力较弱，使得Ag释放电子的能力较差.因此可以通过提高Ag表面对H+的吸附强度，以加速Ag的电子释放，通过表面修饰来提高Ag助剂的光催化活性.研究发现，Ag纳米粒子表面与含硫化合物之间存在很强的亲和力.硫氰根离子（SCN-）具有很强的电负性，容易吸附溶液中H+离子，并且也易吸附在Ag纳米粒子的表面.因此可以利用Ag与SCN-的作用来增强Ag释放电子的能力.
本文采用光还原法将Ag沉积在g-C3N4半导体材料表面，然后通过在制氢牺牲剂中加入KSCN溶液，利用SCN-与Ag的亲和力来提高光生电子参与光催化反应的效率.结果表明，在SCN-存在的情况下，g-C3N4/Ag的光催化制氢性能显著提高.当制氢溶液中SCN-浓度为0.3 mmol L-1时，材料的光催化制氢性能达最大，为3.89 μmol h-1，比g-C3N4/Ag性能提高5.5倍.基于少量的SCN-就能明显提高g-C3N4/Ag材料的光催化性能，我们提出了一个可能性的作用机理：金属银和SCN-协同作用，即银纳米粒子作为光生电子的捕获和传输的一种有效的电子传递介质，而选择性吸附在银表面的SCN-作为界面活性位点有效地吸附溶液中的质子以促进产氢反应，二者协同作用，加速了g-C3N4-Ag-SCN-三物种界面之间电荷的传输、分离及界面催化反应速率，有效抑制了g-C3N4主体材料光生电子和空穴的复合，因而g-C3N4/Ag-SCN复合材料的光催化制氢性能提高.考虑到其成本低、效率高，SCN-助催化剂有很大的潜力广泛应用于制备高性能的银修饰光催化材料.

关键词: 光催化, g-C3N4/Ag, 选择性吸附, 界面活性位, 光催化制氢

Abstract:

Silver-modified semiconductor photocatalysts typically exhibit enhanced photocatalytic activity toward the degradation of organic substances. In comparison, their hydrogen-evolution rates are relatively low owing to poor interfacial catalytic reactions to producing hydrogen. In the present study, thiocyanate anions (SCN-) as interfacial catalytic active sites were selectively adsorbed onto the Ag surface of g-C3N4/Ag photocatalyst to promote interfacial H2-evolution reactions. The thiocyanate-modified g-C3N4/Ag (g-C3N4/Ag-SCN) photocatalysts were synthesized via photodeposition of metallic Ag on g-C3N4 and subsequent selective adsorption of SCN- ions on the Ag surface by an impregnation method. The resulting g-C3N4/Ag-SCN photocatalysts exhibited considerably higher photocatalytic H2-evolution activity than the g-C3N4, g-C3N4/Ag, and g-C3N4/SCN photocatalysts. Furthermore, the g-C3N4/Ag-SCN photocatalyst displayed the highest H2-evolution rate (3.9 μmol h-1) when the concentration of the SCN- ions was adjusted to 0.3 mmol L-1. The H2-evolution rate obtained was higher than those of g-C3N4 (0.15 μmol h-1) and g-C3N4/Ag (0.71 μmol h-1). Considering the enhanced performance of g-C3N4/Ag upon minimal addition of SCN- ions, a synergistic effect of metallic Ag and SCN- ions is proposed-the Ag nanoparticles act as an effective electron-transfer mediator for the steady capture and rapid transportation of photogenerated electrons, while the adsorbed SCN- ions serve as an interfacial active site to effectively absorb protons from solution and promote rapid interfacial H2-evolution reactions. Considering the present facile synthesis and its high efficacy, the present work may provide new insights into preparing high-performance photocatalytic materials.

Key words: Photocatalysis, g-C3N4/Ag, Selective adsorption, Interfacial active site, Photocatalytic hydrogen evolution