Tailoring the transesterification activity of MgO/oxidized g-C3N4 nanocatalyst for conversion of waste cooking oil into biodiesel

Abstract

As a prospective heterogeneous catalyst for transesterification, magnesium oxide (MgO) has long been regarded as a possible candidate. Pure MgO, on the other hand, has a narrow range of applications because of its small surface area and short catalytic lifetime. To overcome these problems, in this work, graphitic carbon nitride (g-C3N4) with higher oxygen doping levels was applied to construct a noteworthy, persistent, and carbon-modified MgO catalyst. The molar ratios of urea to melamine and the mass ratios of oxidized g-C3N4 to MgO in the preparation step are two effective parameters, which were optimized with the Response Surface Methodology (RSM). The significant increase in oil conversion was attained by incorporating O@g-C3N4 nanoparticles composed of urea to melamine at a molar ratio of 2:1 in MgO at a mass percentage of 16.7. O@g-C3N4 had an outstanding effect on the immobilization of oxygen-rich functional groups on the MgO-based catalyst and an increase in the surface area. Also, the effects of transesterification parameters and their interactions on oil conversion were explored using the RSM, and then reusability tests were carried out using the fine-tuned parameters. The prepared catalysts were characterized using a variety of methods, including Field-Emission Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (FESEM-EDS), Fourier Transform Infrared (FTIR) spectroscopy, Temperature Programmed Desorption of CO2 (CO2-TPD), Brunauer-Emmett-Teller (BET) analysis, and powder X-Ray diffraction, in order to determine their basicity, morphology, and composition. The optimum biodiesel yield of 98.80% was attained at 99.6 °C for 133 min with a catalyst quantity of 5.9 wt% and a methanol to oil molar ratio of 14.6. The stability and lifespan of the as-optimized catalyst (OCN2MgO(0.2)) were confirmed over four consecutive cycles. It can be concluded that this solid catalyst could be used to convert low-cost waste cooking oil into biodiesel in a single step.