Synthesis and characterization of novel Ag/ZnO nanoparticles for photocatalytic degradation of methylene blue under UV and solar irradiation

ZnO containing various proportions of metallic silver nanoparticles (0-5 wt% Ag) were synthesized by a combined sol-gel and chemical reduction method in which chitosan acts as a steric stabilizer and environmentally benign reducing agent for silver ions. Structural, morphological, textural, and optical properties of the prepared nanoparticles were investigated by X-ray diffraction, high-resolution transmission electron microscopy, nitrogen physisorption, diffuse reflectance spectroscopy, and photoluminescence spectroscopy. X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed the successful transformation of silver ions into metallic silver nanoparticles (Ag) and suggest a strong interaction between ZnO and silver metal. Photoluminescence analysis indicated the positive influence of metallic silver in limiting electron-hole recombination. The photocatalytic performance of Ag/ZnO nanoparticles was studied by our following the photodegradation of the dye methylene blue under UV and solar irradiation. The incorporation of an appropriate amount of Ag (3 wt%) enhanced the photocatalytic activity under UV and solar irradiation. The enhancement of photocatalytic reactivity under UV irradiation was attributed to the possible transfer of photogenerated electrons from the ZnO conduction band to the Ag Fermi level, which limits electron-hole recombination and increases the degradation efficiency. However, under solar irradiation, the higher photocatalytic reactivity was attributed to surface plasmon resonance of metallic Ag nanoparticles. Photoluminescence analysis with use of terephthalic acid revealed that incorporation of silver nanoparticles on the ZnO surface was accompanied by an increase in the concentration of hydroxyl radicals, which are considered a main reactive species in dye degradation.