Corn straw-derived biochar impregnated with alpha-FeOOH nanorods for highly effective copper removal

A novel biochar composite impregnated with alpha-FeOOH nanorods in hierarchical porous structures (alpha-FeOOH@PC) was synthesized by molten salt assisted carbonization of corn straws and hydrothermal treatment for crystallization of adsorbed ferric ions within carboxyl functionalized porous carbon. The structures and surface properties of biochar composites were characterized by scanning electron microscopy images (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, and Brunauer-Emmett-Teller (BET) analysis. The active alpha-FeOOH nanocrystals were encapsulated in the gradient porous biochar framework (macropores-mesopores-micropores) via C-O-Fe bonding. The alpha-FeOOH@PC composites presented excellent performance of both goethite containing a large amount of reactive surface hydroxyl sites and porous carbon consisting of large surface area and huge porous volume. The alpha-FeOOH@PC composites outperformed other sorbents for copper removal (adsorption capacity of 144.7 mg g(-1)). The synergistic effects of alpha-FeOOH and porous carbon in the biochar composite profoundly improved the removal efficiency (71.9%) compared to those of individual porous carbon foam (42.3%) and alpha-FeOOH nanorods (6.7%). A high adsorption capacity of 124.4 mg g(-1) was maintained after three adsorption-desorption cycles. This study suggests that biochar composite is a potentially promising candidate for environmental remediation.