Synergistic approach of biochar valorisation for silica nanoparticles in photocatalysis and residual ash as efficient heterogeneous catalysis

Biochar, a valuable byproduct from food processing containing up to 37% silica, serves as an excellent source for extracting this versatile material with exceptional thermal insulation, absorption capacity, and mechanical strength. The alkali fusion method has emerged as the most efficient extraction technique, achieving 88% purity, which was significantly higher than conventional alkali methods. Through Response Surface Methodology optimization, maximum silica yield (65.27%) was obtained under ideal conditions: 1:1 Biochar:NaOH ratio, 15:1 liquid-to-solid ratio, 100 °C reaction temperature, and 6-hour duration. The extracted silica can be processed into high-quality nanoparticles featuring a pore volume of 0.18 cm³/g and average pore size of 18.4 nm, as confirmed by comprehensive characterization using thermogravimetry, XRD, and SEM analysis. Beyond silica production, this sustainable approach enables complete utilization of biochar, as the residual ash demonstrates effective catalytic properties for biodiesel production from Ceiba pentandra (Kapok) oil, with successful conversion verified by FTIR and GC-MS techniques. Furthermore, the silica nanoparticles exhibit remarkable environmental applications when doped with cerium oxide (1 g/L), achieving 94.81% degradation of toxic Methylene Blue dye (100 mg/L) within 90 min under UV light through photocatalytic processes. The dual utility of biochar for both high-purity silica extraction and subsequent catalytic applications presents an economically viable and environmentally sustainable solution that addresses waste management challenges while meeting industrial material demands.

Graphical Abstract