Biogenic synthesis of Azadirachta indica-mediated zirconium oxide nanoparticles: photocatalytic degradation of methylene blue and antimicrobial activity

In this work, semiconductor oxide nanoparticles were prepared by adopting a biogenic method of synthesis followed by calcination for the photocatalytic degradation of methylene blue (MB). Leaf extract of Azadirachita indica was utilized as a reducing and stabilizing agent for the synthesis of zirconia nanoparticles (AI-ZrNPs). The surface plasmon resonance peak was found at 275 nm, and the band gap calculated was around 3.004 eV. The prepared catalyst exhibited a crystalline structure with a particle size of similar to 12 nm as confirmed by X-ray diffraction and high-resolution transmission electron microscopy. The microscopic analysis further confirms the formation of spherical-shaped grains of AI-ZrNPs. The photocatalytic activity was investigated under the UV-A lamp which exhibited nearly 99.6% degradation at optimum conditions and followed pseudo-first-order kinetics (R-2 = 0.9854). To evaluate the effectiveness of AI-ZrNPs against gram-negative bacteria Escherichia coli, a bacterial susceptibility test based on disc diffusion method was performed. Lastly, based on the identification of the formed by-products of MB degradation, a plausible degradation pathway was proposed. The findings of this study proved to be quite promising to accept AI-ZrNPs as a potential catalyst for photocatalysis.