Facile modification strategies on hydrochar-based carbon particles with hydrothermal carbonization from green pistachio hulls for the removal of cadmium ions from aqueous solutions

The aim of this study is based on the efficient removal of cadmium ions (Cd2+) from aqueous solutions with the adsorbent obtained by various modification strategies on hydrochar-based carbon particles obtained by hydrothermal carbonization from green pistachio hulls as a precursor. Hydrochloric acid (HCl), sodium hydroxide (NaOH), or phosphoric acid (H3PO4) were used to functionalize the surface to increase the adsorption capacity of hydrochar. Maximum Cd2+ adsorption capacity from environmental waters by PHHC-NaOH hydrochar at 298 K was found to be 526.31 mg/g. Surface morphology and chemical compositions of hydrochar were investigated by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), energy-dispersive spectroscopy (EDS), and thermogravimetric/differential (TG-DTA) and nitrogen adsorption/desorption analyses. Isotherm, kinetic, and thermodynamic properties were evaluated in detail. Also, possible mechanisms for Cd2+ binding on modified hydrochar were evaluated.