Ganeshraja Ayyakannu Sundaram
Department of Chemistry, National College (Autonomous)
Tiruchirapalli 620 001, Tamil Nadu, India
e-mail: drganeshraja13@gmail.com
In modern society, the applications on degradation of contaminants and conversion of solar energy by plasmonic system combined with metal oxide semiconductor photocatalysts have been received much attention. TiO2, ZnO and SnO2 are as some of the most extensively investigated metal oxide photocatalysts, these catalysts shows relatively high efficiency, more stable and low cost [1-2]. In the previous reports, silver halides (AgX, X = Cl, Br, I) nanoparticles (NPs) are generally working as photosensitive materials and source materials in photographic films [3]. As a result of their photosensitive characteristics, AgX are unstable under light irradiation and rarely used as photocatalysts. In recent years, to avoid the photodecomposition of AgX, supported-AgX composite photocatalysts have been reported for the degradation of dyes, decomposition of acetaldehyde, hydrogen generation and killing of bacteria, in which they display high efficiency and good stability in the use process [3-6].
Figure 1 Proposed visible light photocatalytic reaction mechanism of AgCl loaded Sn-TiO2 catalyst [7].
In one of our recent publications relates with the plasmonic system supported metal oxide semiconductor and act as efficient visible light photocatalyst. In that report, AgCl NPs loaded on tin doped titania (AST) microsphere in tune with visible-light activity [7]. To fully understand the photocatalytic property of the AgCl loaded Sn-TiO2 NPs microspheres, the possible mechanism of photocatalytic degradation of organic pollutant on the hybrid was proposed in Figure 1. Electron–hole pairs are generated by the band gap excitation of Sn-TiO2 [8]. Excited electron flow through conduction band of Sn-TiO2 to AgCl to form Ag0. For the AST samples, Sn-TiO2, having a smaller band energy gap than that of AgCl, can absorb more visible light (λ ≥ 420 nm), which generates more electrons to improve the photoreduction reaction. At the same time, under visible-light irradiation, photo-generated electron-hole pairs are formed in Ag0 due to surface plasmon resonance. The photo-excited electrons at the silver nanoparticles are back injected into the conduction band of TiO2 because the Fermi level of TiO2 and Ag0 is the same. Then, the injected electrons can be transferred to the adsorbed O2 that may form peroxide radical (O2•) and finally form hydroxide radicals (•OH). These •OH active species can cause the degradation of organic pollutants.
Figure 2 Rate constant vs various catalysts of pristine P25, AgCl, Ag/AgCl and AST samples under visible light irradiation in an aqueous medium [7].
In Figure 2 shown those photocatalytic rate constant vs different photocatalyst such as commercial and as-prepared photocatalyts with different concentration of AgCl NPs loaded and various calcinations temperatures. These experimental results clearly demonstrate that the synthesized hierarchical AST microspheres could serve as a type of photocatalyst for the efficient degradation of dye pollutants. It concludes that hierarchical silver chloride nanoparticles-Sn doped titania microspheres would be useful for inexpensive visible-light active plasmonic supported metal oxide semiconductor photocatalyst materials.
References
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