Improvement of photocatalytic activity of silver nanoparticles by radio frequency oxygen plasma irradiation

Plasmonic-mediated SC arylation and SS coupling on nanostructured silver electrodes monitored by in situ surface-enhanced Raman spectroscopy

Plasmon-mediated chemical reaction (PMCR) is a highly attractive field of research. Here we report in situ surface-enhanced Raman spectroscopic (SERS) monitoring of plasmonic-mediated SS bond-forming reaction. The reaction is thought to be a self-coupling reaction proceeding by photoinduced aromatic SC bond arylation. Surprisingly, the SC arylation and SS coupling are found to be occurred on both partially oxidized silver and silver nanoparticles. The results demonstrated that silver oxide or hydroxide and small molecule donor sacrifice agent played a crucial role in the reaction. This work facilitates the in-situ manipulation and characterization of the active silver electrode interface in conjunction with electrochemistry, and also establishes a promising new guideline for surface plasmon resonance photocatalytic reactions on metal nanostructures with high efficiency.

Ag Nanoparticle-Induced Oxidative Dimerization of Thiophenols: Efficiency and Mechanism

By oxidation of silver nanoparticles (AgNPs) in two ways: thermal oxidation (TO) in molecular oxygen and cool oxidation in oxygen plasma (i.e., oxygen plasma irradiation, OPI), the efficiency and mechanism of visible light-induced selective transformation of 4-aminothiophenol (PATP) to 4,4'-dimercaptoazobenzene (DMAB) on the surface of AgNPs was explored. On the basis of the evolution of surface-enhanced Raman scattering (SERS) spectrum of PATP (10^-5 M in ethanol) with the oxidation time, it can be concluded that OPI could improve the selective transformation efficiency (η) effectively, by 87 times for only 2 s; whereas TO could improve η conditionally, increasing at first and then decreasing gradually to zero. The results imply that silver oxide is not the root cause of the increased η. Combined with the results of SERS of oxygen species on the surface of AgNPs processed by the above-mentioned two ways, superoxide (O₂^-) and electrophilic oxygen atoms (O^-) are suggested to be responsible for this selective transformation. Our study deepens the understanding of the mechanism of plasmonic photocatalysis and the role of silver oxide in selection transformation of organic molecules.

Mechanism of photocatalytic activity improvement of AgNPs/TiO2 by oxygen plasma irradiation

Plasmonic metal Ag nanoparticles (AgNPs) on TiO₂ thin films (AgNPs/TiO₂) are a kind of excellent photocatalyst of high efficiency under visible light, and thus draw great interest nowadays. Further improvement of their photocatalytic activity (PA) is difficult but is of high importance for their applications. In this paper, oxygen plasma was taken to partially oxidize AgNPs deposited on the surface of TiO₂ to form a structure with the configuration of a p-type semiconductor/plasmonic metal/n-type semiconductor (Ag₂O/AgNPs/TiO₂). The localized surface plasmon resonance (LSPR) of the AgNPs was strongly damped after oxygen plasma irradiation (OPI) but the photocatalytic activity was improved. The mechanisms of the photocatalytic activity improvement under UV and visible light were explored based on charge kinetics.

Ultrafast piezo-photocatalytic degradation of organic pollutions by Ag2O/tetrapod-ZnO nanostructures under ultrasonic/UV exposure

Ultrafast degradation of organic pollutions has been realized by the piezo-photocatalytic activity of Ag₂O/tetrapod-ZnO nanostructures under ultrasonic/UV irradiation.