Effect of environmentally friendly and efficient metal-free hydrochars as catalysts on sodium borohydride hydrolysis

Environmentally friendly, metal-free catalysts are important to synthesize and use, as are catalysts made from biomass-based. This study aims to obtain hydrochars from pine cones and rheum ribes shells by the hydrothermal method and use this hydrochar as a catalyst in sodium borohydride hydrolysis. The characterization of the synthesized catalyst hydrochars was carried out by XRD, BET, SEM, EDX, ICP-OES and FTIR analyses. X-ray diffraction analysis of pinecone hydrochar and rheum ribes shells hydrochar has revealed that they are both amorphous and crystalline in structure. The BET surface areas of the two hydrochars are 1.6 m²/g and 19.01 m²/g, respectively. The activity of hydrochars on the hydrolysis of sodium borohydride was evaluated under microwave irradiation at different temperatures, catalyst amounts, and different microwave powers. The hydrolysis kinetics of NaBH₄ in the presence of pine cone and rheum ribes shells hydrochars catalysts were determined according to the nth-order and the Langmuir-Hinshelwood kinetic models. The activation energies for the rheum ribes shells and pine cone hydrochars catalysts were calculated to be 88.29 kJ/mol and 78 kJ/mol, respectively. It was concluded that hydrochar prepared from waste material extract through the eco-friendly green synthesis method is promising for the hydrolysis of NaBH₄.