KMnO4-activated spinach waste biochar: An efficient adsorbent for adsorption of heavy metal ions in aqueous solution

Developing advanced carbon materials by utilizing biomass waste has attracted much attention. Herein, a novel carbon adsorbent derived from Spinach waste was prepared by using pyrolysis procedure with KMnO4 as the activator. The preparation condition such as activator mass ratio (0–0.16) and activation temperature (200–800 °C) were comprehensively studied. The optimal sample (SBC-0.08–500) showed a 7.38-fold increase in specific surface area compared to the original biochar (SBC-500). Adsorption experiments revealed that SBC-0.08–500 had efficient removal capabilities for Cd(II), Pb(II), Cu(II), and Zn(II) ions. The maximum adsorption capacities for Cd(II), Pb(II), Cu(II), and Zn(II) ions at 298.15 K were 1.66, 2.88, 1.31, and 2.09 mmol∙g−1, respectively. Thermodynamic results indicated that the adsorption of Cd(II), Pb(II), and Zn(II) ions on SBC-0.08–500 was a spontaneous endothermic process. Additionally, SBC-0.08–500 had a high affinity for Pb(II) ions, making it a potential selective adsorbent for the removal of mixed heavy metal ions. The mechanism underlying the adsorption process was attributed to multiple interactions, including ion exchange, electrostatic interaction, and surface complexation. The as-prepared biochar by oxidative activation pyrolysis effectively solves the issues of subsequent chemical recycling and secondary pollution, thus providing greater potential for large-scale use.