A novel ternary magnetic Fe3O4/g-C3N4/Carbon layer composite for efficient removal of Cr (VI): A combined approach using both batch experiments and theoretical calculation.

Abstract Heavy metal pollution has posed a potential hazard to the ecological environment and human health. Herein, a novel ternary magnetic adsorbent (Fe3O4/g-C3N4/Carbon layer, Carbon layer: hydrothermal products from sucrose) was synthesized through a simple hydrothermal carbonization (HTC) method for removal of hexavalent chromium (Cr (VI)) removal. The Carbon layer (CL) formed during the HTC of carbon precursors (sucrose) acted as a reducing agent. Also, it has abundant oxygen-containing groups on its surface. The Fe3O4/g-C3N4/CL had a high removal capacity for Cr (VI) (50.09 mg/g), and excellent regeneration and magnetic separation performance. Importantly, the Fe3O4/g-C3N4/CL could not only improve the adsorption ability for Cr (VI), but also strengthen the immobilization of Cr (III). Based on the comprehensive experiments and characterization, combined with DFT calculations, we proposed that, the first time, the removal of Cr (VI) was controlled by three consecutive processes: (1) ion exchange of Cr (VI) by hydroxyl groups, (2) reduction of Cr (VI) to Cr (III) by electron-donor (oxygen-containing) groups (EDGs), and (3) complexation of Cr (III) by amine groups. This study provides a new avenue for the removal of toxic oxygen anions and reveals an original removal mechanism of Fe3O4/g-C3N4/CLx (x = hydrothermal products from carbon precursors (glucose, ascorbic acid, cellulose)).