Marble dust and Ocimum tenuiflorum mediated green synthesis of CaO nanocatalysts supported on bentonite clay and its application in biodiesel production using mustard oil

In this research work, we report the green synthesis of CaO nanoparticles supported on bentonite clay using marble dust as a precursor of calcium and Ocimum tenuiflorum leaves extract as reducing and stabilizing agent. The synthesized CaO nanoparticles were characterized using UV-Visible Spectrophotometry, Fourier Transform Infrared Spectroscopy (FT-IR), High Resolution Transmission Electron Spectroscopy (HRTEM), Field Emission Scanning Electron Microscopy / Energy Dispersive X-ray (FESEM/EDX), and Powder X-ray Diffraction (PXRD). The UV-Vis spectrophotometry and FT-IR techniques showed that the phytochemicals gallic acid and quercetin present in the leaf extract were responsible for reducing and stabilizing the clay supported CaO nanoparticles. The FESEM images revealed the layered structure of the bentonite clay which was used as a support and the TEM images showed that the particle size of the clay supported nanoparticles was 51.2 nm. These nanoparticles were effectively employed as catalysts in biodiesel production. The products of the catalytic trans-esterification reaction were identified using Gas Chromatography Mass Spectroscopy (GC-MS). The effects of different reaction parameters, such as methanol-to-oil molar ratio, reaction time, catalyst loading and temperature, were systematically investigated to optimize biodiesel production. A one-way analysis of variance (ANOVA) results confirm the significance of the optimized reaction parameters influencing biodiesel yield. GC–MS analysis confirmed more than 99% conversion of mustard oil into biodiesel under optimized transesterification conditions. This work is significant for several reasons, firstly, a green-synthetic route was employed for CaO nanoparticles which ensures an environmentally benign approach, secondly marble dust was used as a precursor for calcium which offers a way of waste management and thirdly bentonite clay was used as a support for CaO nanoparticles, which was expected to improve the benefits of supported nanoparticles in catalytic reactions over the unsupported ones.