Concurrent Synthesis and Immobilization of Ag Nanoparticles over TiO2 via Plasma Reduction for Photocatalytic Treatment of Methyl Blue in Water

Abstract

Pure TiO₂ nanoparticles (TiO₂NPs) were produced via the sol-gel method and then coated with silver nanoparticles (AgNPs) to reduce their optical band gap. The concurrent synthesis and immobilization of AgNPs over TiO₂NPs was achieved through the interaction of an open-air argon plasma jet with a solution of silver nitrate/stabilizer/TiO₂NPs. The one-pot plasma synthesis and coating of AgNPs over TiO₂NPs is a more straightforward and environmentally friendly method than others. The plasma-produced Ag/TiO₂ nanocomposites were characterized and tested for their photocatalytic potential by degrading different concentrations of methyl blue (MB) in water. The dye concentration, oxidant dose, catalyst dose, and reaction time were also optimized for MB degradation. XRD results revealed the formation of pure AgNPs, pure TiO₂NPs, and Ag/TiO₂ nanocomposites with an average grain size of 12.36 nm, 18.09 nm, and 15.66 nm, respectively. The immobilization of AgNPs over TiO₂NPs was also checked by producing SEM and TEM images. The band gap of AgNPs, TiO₂NPs, and Ag/TiO₂ nanoparticles was measured about 2.58 eV, 3.36 eV, and 2.86 eV, respectively. The ultraviolet (UV) results of the nanocomposites were supportive of the degradation of synthetic dyes in the visible light spectrum. The AgNPs in the composite not only lowered the band gap but also obstructed the electron-hole recombinations. The Ag/TiO₂ composite catalyst showed 90.9% degradation efficiency with a 5 ppm dye concentration after 120 min of light exposure.

Keywords: Ag-coated TiO2; photodegradation; plasma reduction method; semiconductor photocatalyst; synthetic dyes.