Femtosecond laser-induced production of ZnO@Ag nanocomposites for an improvement in photocatalytic efficiency in the degradation of organic pollutants

Abstract

Green synthesis based nanoparticle production methods and water purification techniques were carried out using pulsed laser ablation and photocatalysis degradation techniques. The femtosecond laser ablation based ZnO and Ag nanoparticles were produced with different concentration ratios such as 2.0 wt%, 4.0 wt%, 6.0 wt%, 8.0 wt% and 10.0 wt% in ultra pure water to photocatalytic degradation of methylene blue dye contaminant. Following the production of nanoparticle and photocatalysis applications, FTIR, XRD and linear absorption spectra were recorded. HRTEM and FE-SEM microscopy was carried out to determine size and shape performance of nanoparticles. The crystal peak density of ZnO and its crystal size were decreased by doping Ag into ZnO nanoparticles. LSPR peak was formed due to plasmonic properties of Ag nanoparticles in ZnO. As Ag content is increased in ZnO, it has been observed that band gap of ZnO@Ag structure is decreased. The morphological structure of ZnO is partially composed of homogeneous particle mergers while ZnO@Ag can be formed from the growth of small particles on AgO clusters. The photocatalytic activity of composite photocatalysts was systematically investigated as a function of amount of Ag nanoparticles in samples. Experimental results showed that the optimal composite was Ag-ZnO composite containing 6.0 wt% Ag. This composite photocatalyst exhibited a 68.62% higher rate constant value in the degradation of methylene blue (MB) dye molecules under visible light compared to pure ZnO nanoparticles. The improved photocatalytic performance compared to pure ZnO nanoparticles was attributed to some increase in light absorption performance, more efficient charge separation due to the gradual band structure between plasmonic Ag nanoparticles and semiconductor ZnO nanoparticles. In addition, active radicals taking role in the degradation mechanism of MB were revealed by scavenger chemical experiments.