Facile phosphorus and oxygen heteroatom functionalization of biochar based on biomass prepared by microwave pyrolysis for adsorption process of cadmium in aqueous solution

Abstract

In this study, in the first stage, biochar is produced from green pistachio hulls (PGHMAC) by microwave heating method, which saves energy, time and cost. In the second step, with the activation of phosphoric acid (H3PO4), the surface properties of the biochar were modified by phosphorus (P) and oxygen (O) doping (O- and P-doped PGHMAC). This adsorbent obtained was applied to remove cadmium (Cd(II)) from wastewater. FTIR, SEM, EDX, and ICP-OES analyses were used for the characterization of the samples. FTIR, EDX, and ICP-OES analysis results showed the presence of oxygen and phosphorus groups on the surface of the relevant adsorbent. The contents of C and O atoms for P- and O-doped PGHMAC were found to be 62.54% and 36.12%, respectively. Also, about 1.29% of P atoms were found with H3PO4 activation. The kinetic, isotherm, and thermodynamic parameters of the adsorption studies were investigated. Maximum Cd(II) adsorption capacities of P- and O-doped PGHMAC at 298 K, 308 K, and 318 K temperatures were calculated as 78.74, 109.89, and 133.33 mg/g by Langmuir model, respectively. The mechanism of Cd(II) adsorption on O- and P-doped PGHMAC has been proposed.