A critical review on metal/metal oxide-modified sugarcane biochar

Metal and metal oxide modification of sugarcane-derived biochar has emerged as an effective strategy to overcome the inherent limitations of pristine biochar, including low surface functionality, limited catalytic activity, and poor recoverability. This review provides an analysis of the synthesis, properties, and applications of metal/metal oxide-modified sugarcane-based biochar across the diverse range of sugarcane feedstocks, including bagasse, straw, leaves, and filter cake. It was observed that three principal synthetic strategies were employed for metal/metal oxide-modified sugarcane biochar: ex-situ modification, in-situ modification, and emerging techniques (microwave-assisted synthesis, ultrasonication, and phytochemical reduction). Critical process variables including temperature, metal concentration, precursor selection, impregnation time, and modification technique significantly influenced the structural, textural, chemical, and magnetic properties of the resulting composites. Optimal metal loading (typically 0.5-1.0 mmol/g) achieved uniform nanoparticle dispersion (3-50 nm), while excessive loading caused agglomeration and pore blockage. The modified composites showed improved performance in heavy metal sequestration, organic dye removal, emerging contaminant adsorption, nutrient recovery, and catalytic applications. Mechanistic analysis identified surface complexation, ion exchange, electrostatic interactions, π-π interactions, and redox reactions as the primary removal pathways. Key knowledge gaps requiring future investigation include comparison of in-situ versus ex-situ modification, study of alternative thermochemical conversion technologies, scale-up studies, and evaluation of material performance under realistic multi-contaminant conditions.