Facile in situ synthesis of visible-light plasmonic photocatalysts M@TiO2 (M = Au, Pt, Ag) and evaluation of their photocatalytic oxidation of benzene to phenol

Abstract

We developed a facile in situ method of preparing noble-metal plasmonic photocatalysts M@TiO 2 (M ¼ Au, Pt, Ag). In this method, the UV irradiation of TiO 2 powder dispersed in absolute ethanol generates some Ti 3+ ions on the surface of TiO 2 particles and these Ti 3+ ions, upon addition of a noblemetal salt in the dark, reduce the metal cations to deposit metal nanoparticles on the TiO 2 surface. This Ti 3+ -ion-assisted synthesis leads to a homogeneous loading of noble-metal nanoparticles on the surface of TiO 2 particles, which allows photocatalytic reactions to take place under visible-light on the whole TiO 2 surface. Among the three photocatalysts M@TiO 2 (M ¼ Au, Pt, Ag), Au@TiO 2 exhibits a high yield (63%) and selectivity (91%) for the oxidation of benzene to phenol in aqueous phenol. For this photocatalytic reaction, our study suggests a mechanism in which the visible-light absorption by the Au nanoparticles causes electron transfer from the Au nanoparticles to the TiO 2 particle, and the electrondepleted Au oxidizes phenoxy anions to form phenoxy radicals that oxidize benzene to phenol.

Effect of Noble Metals (Ag, Pd, Pt) Loading over the Efficiency of TiO2 during Photocatalytic Ozonation on the Toxicity of Parabens

“…For 1.5 wt % of Pt-TiO 2 , the diffractive peak of Pt on XRD analysis was not found due to the low amount doping [30]. The presence of gold, platinum and silver at 1 wt % load does not change the diffractive peaks of anatase phase from TiO 2 [11]. These studies reveal that the lack of detection in the XRD analysis of diffractive peaks of noble metals for different loads used in our study could also be explained by the low doped dose and/or small size of noble metals' nanoparticles.…”

“…The noble metal doped onto TiO 2 can reduce the energy band gap [11,35], which is the energy needed to move an electron from the valence band to the conduction band of the catalyst, producing photogenerated holes on the surface of the catalyst [8,10]. In addition, the presence of noble metals can reduce the recombination phenomenon between electron-hole pairs due to the scavenging of photogenerated electrons [35].…”

“…The band gap of TiO 2 can be reduced using metal (such as, Ag, Au, Pd and Pt) or non-metal (such as N and B) dopants, which allows the production of TiO 2 photogenerated electrons and holes using lower energy, such as solar irradiation [10][11][12].…”

A new bimetallic plasmonic photocatalyst consisting of gold(core)-copper(shell) nanoparticle and titanium(IV) oxide support

“…8,9 Lowering in the Fermi level of Au NPs induces the oxidation of reaction substrates on the Au surfaces, while O 2 is reduced on the TiO 2 surface. Au/TiO 2 plasmonic photocatalysts have been applied to several oxidative chemical transformations including thiol to disulfide, 10 alcohol to carbonyl compounds, [11][12][13][14] benzene to phenol, 15,16 and amine to imine. 17,18 The studies on the plasmonic photocatalysts for the oxidative chemical transformations have so far used Au NP as the light harvesting component.…”

Semiconductors in Organic Photosynthesis

“…The photocatalytic activity of TiO 2 can be modified by depositing noble metal nanoparticles on the particles surface. This is the case of the work of Zheng et al (Zheng et al, 2011). The authors developed a noble-metal plasmonic photocatalyst effective for the oxidation of benzene to give phenol under visible light irradiation.…”