green nickel oxide is a naturally occurring, biodegradable and environmentally friendly material that has found use in making alloys, batteries, salts, catalysts, fuel cells and other chemicals. It is also used in forming ceramic glazes and colorants.
Synthesis of NiO nanoparticles with phytochemicals from three different sources
In this study, aloe vera leaves extract, papaya peel extract and dragon fruit peel extract were reacted with nickel acetate tetrahydrate to synthesize nickel oxide nanoparticles (NiOx NPs). The physicochemical properties of the biosynthesized NPs were evaluated using UV-Vis absorption spectroscopy, EDX and scanning electron microscopy.
The synthesised NiOx NPs were found to possess a highly crystalline and rhombohedral nature with an interplanar spacing of ‘d’. This morphology, combined with the low crystallite size of the NPs, suggests that plant extracts may act as reducing or capping agents to promote efficient nickel adsorption and desorption on the nanoparticles.
Electrocatalytic water splitting with phosphate ions
The electrocatalytic performance of the green-synthesized NPs was evaluated via cyclic voltammetry. The highest electrocatalytic surface area (ESCA) was possessed by papaya-extract-mediated NiOx NPs, followed by aloe vera-mediated NiOx NPs and dragon fruit-mediated NiOx NPs.
Solution resistance, charge-transfer resistance and double-layer capacitance based on equivalent circuit fitting were calculated for each NP. The lowest solution resistance, charge-transfer resistance and double-layer capacitance was recorded for aloe-vera-mediated NiOx NPs, which is attributed to the superior conductivity of these NPs.
The NPs were also evaluated for their antibacterial activity against gram-positive and gram-negative bacteria. The Mo-doped NPs showed higher activity against both gram-positive and gram-negative strains of E. coli compared to their pure counterparts.