Silica extraction from rice husk functionalised by guanine for catalytic activity in phenol oxidation

This study synthesised an organic-inorganic hybrid catalysts from silica extracted from rice husk (RH). Amorphous silica was extracted from rice husk (RH) using a thermochemical sol-gel method, following mild acid treatment. The production of rice husk ash (RHA) supported guanine to form the catalyst. It was synthesised by directly incorporating guanine onto RHA silica at a suitable temperature. (3-chloropropyl) triethoxysilane (CPTES) was employed as an anchoring or silylating agent to combine silica and guanine. Guanine was used as an organic component to support the production of heterogeneous catalyst. The catalyst was named as RHACGua. It was characterised by scanning electron microscopic (SEM), energy dispersive x-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), power x-ray diffraction (XRD), nitrogen sorption analysis and nuclear magnetic resonance (NMR) for 29Si and 13C. Scanning electron microscopy analysis (SEM), power x-ray diffraction (XRD) and nitrogen sorption analysis revealed that the physical characteristic of RHACGua comprised a porous agglomerate structure in amorphous state with a specific surface area of 77.67m2 g -1 and a pore diameter of 15.81nm. Fourier transform infrared (FTIR) spectra showed a Si-O-Si shift from 1038cm-1 (RHACCl) to 1042cm-1 (RHACGua), which proved that RHACCl successfully incorporated with guanine and all anticipated functional groups were visible. The presence of retention times at the silicon centers Q4 (-111.54ppm), Q3 (-103.54ppm), T3 (-66.51ppm) and T2 (-58.32ppm) in RHACGua was identified by magic angle spinning of 29Si solid-state nuclear magnetic resonance (MAS NMR) spectroscopy. This study also examined the effectiveness of using RHACGua catalyst (catalytic activity) for phenol oxidation using hydrogen peroxide as the oxidising agent. Several parameters were examined vigorously, including solvent, catalyst mass, time, temperature, and phenol to hydrogen peroxide molar ratio. After analysing the results, the optimal conditions were 0.15g of catalyst in acetone as the solvent, maintained at 95°C for 3 hours with a molar ratio of 1:1. It was observed that without the RHACGua catalyst, the oxidation of phenol lasted for 4 hours without yielding any product, demonstrating the catalyst’s effectiveness.