Potential of nickel oxide catalyst from banana peel extract via green synthesis method in both photocatalytic reduction of methylene blue and generation of hydrogen from sodium borohydride hydrolysis

In the present work, nickel oxide (NiO) catalyst was prepared using banana peel extract as a stabilizing agent via the green synthesis method. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet spectroscopy (UV) analyses were carried out to investigate the structural and textural characteristics of the NiO catalyst. According to the XRD and TEM results, the particle size of the NiO catalyst was found to be in the range of 20–80 nm. From the EDX analysis, it was concluded that the NiO catalyst was synthesised in pure form. The potential of the NiO catalyst was tested for the first time in both the photocatalytic reduction of methylene blue (MB) and the generation of hydrogen (H₂) from sodium borohydride (NaBH₄) hydrolysis. A high decolorization efficiency of 98.09 % and a reuse efficiency of 90.89 % after five recycles were achieved for the photocatalytic reduction of MB using NiO catalyst. The photocatalytic reduction of MB was consistent with the pseudo-first order kinetic model, and the reaction rate constant was found to be 2.55 min⁻¹. The H₂ generation rate (R_H2) of 922.5 mL_H2 min⁻¹ g_cat⁻¹ at 70 °C was achieved for the NaBH₄ hydrolysis. The kinetics of H₂ generation from NaBH₄ hydrolysis was studied employing the n^th-order and the Langmuir-Hinshelwood models, and the activation energy (Ea) values were found to be 21.29 kJ mol⁻¹ and 22.23 kJ mol⁻¹, respectively. It was concluded that the NiO catalyst prepared by the eco-friendly green synthesis method has a promising potential in both photocatalytic reduction of MB and H₂ generation from NaBH₄ hydrolysis.