Fabrication and photocatalytic activities in visible and UV light regions ofAg@TiO2 and NiAg@TiO2 nanoparticles

Abstract

Completely discrete Ag@TiO2 and NiAg@TiO2 nanoparticles were prepared by the hydrazine reduction ofAg+/Ni2+ ions and the subsequentsol–gel coating of TiO2 in an aqueous solution of CTAB. TEM analysis revealed that their core diameters were6.55 ± 1.20 and 7.57 ± 1.33 nm, respectively, and their shell thicknesses were 2.59 and 2.80 nm, respectively.By the analyses of EDX, UV–vis absorption spectra, FTIR spectra, and zetapotential, their core–shell structure, crystal structure, optical properties, andsurface state were demonstrated. In addition to exhibiting significant absorption inthe visible light region, it was noted that they had lower zeta potentials thanTiO2 nanoparticles, which favored the adsorption of positively charged organiccompounds on the particle surface and thereby increased the photocatalyticreaction rate. By measuring the photocatalytic degradation rate of rhodamine B,Ag@TiO2 and NiAg@TiO2 nanoparticles were demonstrated to possess significantly higher photocatalytic activities thanTiO2 nanoparticles in the visible light region because of the formation of Schottky barrierbanding at the core–shell interface as well as the excitation of photogeneratedelectrons from the surface of Ag or NiAg cores to the conduction band ofTiO2 shells.Although NiAg@TiO2 nanoparticles had lower photocatalytic activity thanAg@TiO2 nanoparticles owing to weaker surface plasmon resonance, they could be recovered magneticallyfrom the treated solutions. Under UV light illumination, the photocatalytic activities ofAg@TiO2 andNiAg@TiO2 nanoparticles were lowerthan that of TiO2 nanoparticlesbecause of the lower TiO2 content and the transfer of photogenerated electrons fromTiO2 shells to Ag or NiAg cores, which also acted as the new recombination centers ofphotoinduced electrons and holes and hence led to a decrease in the photocatalytic activity.