Biochar production from date palm waste: Charring temperature induced changes in composition and surface chemistry

The biochars (BC) were prepared from date palm waste to investigate the influence of pyrolysis temperature (300-800 °C) on composition and surface chemistry of BC. The results showed that fixed C, ash and basic cations of BC increased while its moisture, volatiles and elemental composition (O, H, N and S) decreased with increasing pyrolysis temperature. As the surface basicity of biochar increased by increasing pyrolysis temperature, the values of pH and pHpzc were increased. The biochars produced at low pyrolysis temperature do possess some functional properties of their feedstock, whereas the aromatic functional units in biochar samples were condensed with increasing pyrolysis temperature. In this context, readily and potentially labile C oxidized using KMNO4 and K2Cr2O7 decreased with pyrolysis temperature, whereas recalcitrant C followed the opposite trend. Stronger correlations were found between volatile matter and O/C (r2 = 0.9971) than those conducted between volatile matter and H/C (r2 = 0.9325). Date palm-derived BC at 500 °C with a volatile matter less than 10% and O/C of 0.02-0.05, could be more appropriate for C sequestration. The BC may thus represent potential alternative materials for environmental management, depending upon pyrolysis temperature.