Multifactorial Optimization of Biochar Synthesis from Pea Pods Using the RSM Method: Insights into Process Parameters and Adsorption Capabilities Towards Cr(VI) and CO2

Biochar synthesis is a complex process influenced by multiple factors and requiring an efficient optimization approach to maximize the yield and its physico-chemical properties. This study employs Response Surface Methodology (RSM) as a valuable tool that reduces the number of experiments needed to study multiple variables and their interactions based on three responses, including the yield percentage, the BET surface area, and the zeta potential. The Doehlert experimental design was applied to optimize biochar production from peas pods, using three key parameters: the impregnation ratio, pyrolysis temperature, and heating time. This design produced a highly accurate second-order quadratic model for three responses (R2 = 0.985, 0.988, and 0.991), identifying significant interactions between the different synthesis parameters (p < 0.001). The experimental results revealed that both the pyrolysis temperature and impregnation ratio positively influenced the surface area of the biochar. In contrast, the heating time had a negative effect on the surface area. Furthermore, the impregnation ratio was found to significantly reduce the carbon yield. Two samples, representing low and high surface areas from the 15 experimental trials of the RSM, were selected for a further evaluation of their adsorption efficiency for hexavalent chromium (Cr(VI)) and carbon dioxide (CO2).