Facile Green Synthesis of ZnO NPs and Plasmonic Ag-Supported ZnO Nanocomposite for Photocatalytic Degradation of Methylene Blue

Abstract

Removing organic pollutants, textile dyes, and pharmaceutical wastes from the water bodies has become an essential requirement for a safe environment. Therefore, the present study aimed to prepare semiconductor zinc oxide nanoparticles (ZnO NPs) and plasmonic Ag-supported ZnO nanocomposite (ZnO–Ag) using an environmentally friendly bio-approach as an alternative to hazardous synthesis approaches. ZnO NPs and ZnO–Ag nanocomposite were characterized by using UV–Vis diffuse reflectance spectroscopy (UV–DRS) (the Ag-supported ZnO nanocomposite exhibited an absorption band between 450–550 nm, attributed to the Ag NPs surface plasmon resonance (SPR)), Photoluminescence (PL) spectral investigation, which revealed the PL emission intensity of ZnO–Ag NPs was lower than pure ZnO NPs, describing an extended electron-hole pair (e--h+) lifespan of photogenerated charge carriers, Fourier transform infrared spectroscopy (FTIR), FT-Raman, and X-ray diffraction (XRD) analyses were deduced. In addition, energy dispersive X-ray spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) were performed and further ascertained the successful biosynthesis and thermally stable ZnO Nps and ZnO–Ag nanocomposite. The as-prepared ZnO–Ag nanocomposite displayed increased photocatalytic characteristics due to the decline in the bandgap energy from 3.02 eV (ZnO NPs) to 2.90 eV (ZnO–Ag nanocomposite). The photocatalytic activity of the developed nanocomposite for the degradation of methylene blue (MB) dye, a primary textile industry released water-pollutant, was conducted under UV light irradiation. Meanwhile, the maximum % degradation of MB dye molecules was attained by 98.0 % after 60 min exposure of UV-light irradiation. Increased photocatalytic activity of ZnO–Ag nanocomposites and a faster rate of MB degradation were achieved by the deposition of plasmonic Ag NPs and the surface plasmon resonance (SPR) effect possessed by Ag NPs. The primary oxidative route that resulted in MB degradation was the production of hydroxyl radicals (OH•). The SPR effect of the photocatalyst induced the synergistic enhancement of the optical response and separation of the photo-induced charge carriers. The combined study gives comprehensive information and directions for future research on noble metal-modified nanocatalysts for direct applications in the photocatalytic degradation of textile and organic wastes in water.