Enhanced adsorption of copper ions by phosphoric acid-modified Paeonia ostii seed coats

Novel adsorbent, phosphoric acid-modified Paeonia ostii seed coats (PA-PSC) were successfully prepared by low-temperature pyrolysis to effectively remove Cu(II) from aqueous solution. The results revealed that equilibrium adsorption capacity (q_e) of PA-PSC for Cu(II) was notably enhanced up to 4-folds compared with the raw PSC. FT-IR and XPS analyses suggested that the adsorption of Cu(II) by PA-PSC was primarily ascribed to electrostatic forces and complexing effects. Besides, equilibrium and kinetic studies demonstrated that Freundlich and pseudo-second-order models were the actually fairly good approximations of Cu(II) adsorption. Thermodynamic analysis revealed that the adsorption of Cu(II) onto PA-PSC was a chemical, endothermic, and spontaneous process. Lastly, reusability study further confirmed the applicability of PA-PSC as a promising adsorbent for removing Cu(II) from aqueous solution.