Synthesis of Zinc Oxide Nanoparticles and Cobalt doped Zinc Oxide Nanocomposites using Allium cepa l. Aqueous peel extract and evaluation of its Antimicrobial and Photocatalytic Activities

Abstract

Since dye effluents discharged from different industries lead to environmental contamination, their treatment and environmental remediation are highly desired. Due to the limitations of physical treatment methods like adsorption, photocatalytic degradation was used because of its capability to complete the degradation of dyes. On the other hand, most microbial species have shown resistance to antibiotic drugs. Concerning this, nanomaterials have been found to be a promising candidate to overcome such a problem. Metal oxide-based nanostructures are widely used in photochemical processes and antimicrobial agents due to their unique properties. But single-nanostructure metal oxide materials might suffer from low efficiency under visible light. This fact makes it important to have efficient and reliable nanocomposites for the photochemical processes. The combination of different nanomaterials to form a composite configuration can produce a material with new properties. The new properties, which are due to the synergetic effect, are a combination of the properties of all the counterparts of the nanocomposites. The main objective of this research was to synthesize ZnO NPs and Co/ZnO NCs by precipitation using red onion peel plant aqueous extract for photocatalytic and antimicrobial applications. Co/ZnO NCs were prepared from red onion peel plant aqueous extract , Zn(NO3)2 .6H2O) and Co(NO3)2.6H2O solution at 65 0C for 2 h and ZnO NPs were prepared in the same way, but without the addition of Co(NO3)2.6H2O solution. The synthesized ZnO NPs and Co/ZnO NCs were characterized by UV-Vis, XRD, FT-IR, and SEM techniques. From the UV-Vis absorption spectrum, the peaks of ZnO NPs and Co/ZnO NCs were detected at 369 and 375 nm, respectively. The XRD data showed the crystalline nature of the NPs and NCs, and the average crystallite size of ZnO NPs and Co-ZnO NCs is 27.47 and 33.97, respectively. The FT-IR result revealed the presence of important functional groups like tannins and phenolics, which were also observed in the phytochemical screening test experiment. The SEM result showed hexagonal wurtzite and spherical-like morphologies for ZnO Nps and Co/ZnO NCs, respectively. The in vitro antimicrobial test of NMs showed good antimicrobial activity, especially at high concentrations. The result indicates that Co/ZnO NCs showed enhanced antimicrobial activity compared to ZnO NPs. The photocatalytic performance of Co/ZnO NCs was further assessed by the degradation of MB dye as a model pollutant under irradiation of natural sunlight and compared with that of bare ZnO NPs. The effect of some parameters like pH, catalyst dosage, irradiation time, and initial dye concentration of MB dye on the activity of Co/ZnO NCs was also viii investigated. 98.5% and 89.3% of MB dye were degraded by Co/ZnO NCs and ZnO NPs at 60 min, which is a promising future application of solar light driven photocatalytic degradation of organic pollutants.