Synthesis of high surface area porous biochar obtained from pistachio shells for the efficient adsorption of organic dyes from polluted water

High surface area, micro, and mesoporous functionalized biochar were prepared from pistachio shells and utilized for the adsorption of congo red (CR) and methylene blue (MB) from polluted water. The results indicate that increased pyrolysis temperature improved the porosity, specific surface area (S BET ), and pore size. The biochar obtained at 900 °C, named as PSB-900, possess an S BET of 467.8 m 2 /g with a pore diameter of 5.6 nm, which is higher than the S BET and pore size of the biochar obtained at 600 and 300 °C. The batch adsorption of CR and MB with PSB-900 was performed with different dye concentrations, adsorbent dosage, pH, and temperature to determine their impact on adsorption capacity. The experimental results were further validated with kinetics and isotherm statistics. The PSB-900 achieved the maximum adsorption capacity for CR, 614.7 and 384.2 mg/g for MB. By contrast, biochar obtained at 300 and 600 °C exhibited comparatively low adsorption capacity owing to the difficult pore-filling and low S BET . The characterization results indicate that pore filling, π-π interaction, hydrogen bonding , electrostatic interaction, and surface complexation were the fundamental features of the adsorption mechanisms of organic dyes on PSB-900. Furthermore, a reusability assessment was also conducted, and the results demonstrate that PSB-900 can be recycled after the adsorption process and exhibits good recyclability for multiple cycles.