Ultrafast removal of Cr(VI) by chitosan coated biochar-supported nano zero-valent iron aerogel from aqueous solution: Application performance and reaction mechanism

Chitosan coated biochar-supported nano zero-valent iron aerogel (C-nZVI@BC) was successfully synthesized for the efficient removal of Cr(VI) from aqueous solution. Results showed that the C-nZVI@BC has a 2.1-fold higher adsorption capacity of Cr(VI) than the uncoated sample. Chitosan coating on nZVI@BC and BC support could prevent the oxidation and agglomeration of nZVI. Ultrafast adsorption of Cr(VI) with 61 %, 77 %, and 87 % of the maximum adsorption capacities were achieved within 1 min with the initial concentrations of Cr(VI) at 100 mg/ L, 300 mg/L, and 600 mg/L, respectively. The C-nZVI@BC exhibited high adsorption performance under aerobic conditions, and showed high Cr(VI) removal rates (>83 %) in a wide pH range (2-8). Cr(VI) and Cr(III) could be simultaneously removed by C-nZVI@BC, and the key mechanisms were adsorption, reduction, and complexation. The acid and alkali resistance experiment of C-nZVI@BC showed that C-nZVI@BC still has better adsorption capacity of Cr(VI) (96.7 mg/g) in acid environment. The application of C-nZVI@BC in the simulated electro-plating wastewater treatment indicated a high removal rate of Cr(VI). C-nZVI@BC could effectively reduce the low concentration of Cr(VI) below the standard of the World Health Organization. The syringe filtration and column adsorption experiments implied the potential of C-nZVI@BC for Cr(VI) removal in groundwater. In addition, C-nZVI@BC could be a direct reducing agent for Cr(VI) and an activator of persulfate (PS) for the degradation of antibiotics, and C-nZVI@BC + PS showed 77 % and 82 % removal of tetracycline and chlortet-racycline within 5 min. Overall, C-nZVI@BC was a suitable adsorbent for pollutant removal.