Chlorine-Mediated Regeneration of Semiconducting AgCl(s) Following Light-Induced Ag0 Formation: Implications to Contaminant Degradation
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- 作者：Shikha Garg ; Hongyan Rong ; Christopher J. Miller ; T. David Waite
- 刊名：Journal of Physical Chemistry C
- 出版年：2016
- 出版时间：March 24, 2016
- 年：2016
- 卷：120
- 期：11
- 页码：5988-5996
- 全文大小：446K
- ISSN：1932-7455
文摘
AgCl(s) is a semiconductor that has been reported to photocatalytically degrade organic contaminants under visible light irradiation. On AgCl(s) irradiation, electrons are excited from the valence to the conduction band leaving holes in the valence band. While the photogenerated holes may degrade organic contaminants, photogenerated electrons in the conduction band reduce Ag(I) to form Ag(0) atoms which coalesce to form silver nanoparticles (AgNPs) that may aggregate further to form nonreactive Ag(0) assemblages. This continuous reduction of AgCl(s) to Ag(0) on irradiation results in a decrease in the concentration of AgCl(s), thereby reducing the rate of generation of holes and thus decreasing the efficacy of photoirradiated AgCl(s) as an oxidant. If this decrease in oxidizing ability is to be prevented, a pathway for continuous oxidation of Ag(0) to Ag(I) during the irradiation process is required in order to restore the activity of the AgCl(s) photocatalyst. The results of investigations described here show that chlorine, which is formed as a byproduct during AgCl(s) irradiation, oxidizes Ag(0) to Ag(I) thereby, potentially, leading to the regeneration of AgCl(s). Furthermore, these freshly regenerated AgCl(s) particles have higher reactivity than the original aged AgCl(s) particles, thereby resulting in faster degradation of organic contaminants. Our results further show that although in situ generated chlorine is able to achieve some degree of redox cycling of Ag between the +0 and +1 redox states, externally added chlorine further enhances the turnover frequency of silver, thereby resulting in more effective degradation of organic contaminants.