Adsorption properties and mechanism of Cr(VI) by Fe2(SO4)3 modified biochar derived from Egeria najas

The aquatic plant Egeria najas based biochar was innovatively constructed by modifying it with Fe 2 (SO 4 ) 3 (Fe 2 (SO 4 ) 3 @EN-BC) for Cr(VI) removal. The characterizations of Fe 2 (SO 4 ) 3 @EN-BC confirmed that Fe 2 (SO 4 ) 3 was attached to biochar in form of Fe 2 O 3 after hydrolysis and calcination under high temperature. The results showed that Fe 2 (SO 4 ) 3 @EN-BC had a high removal efficiency of Cr(VI) with approaching 99.88%, which was about 7 times higher compared to unmodified biochar (EN-BC). Batch experiments of Cr(VI) removal included initial concentration, reaction temperature, solution pH and kinetics were conducted. The adsorption kinetics could be more accurately explained using pseudo-second order kinetics model , indicating the chemical adsorption controlled the reaction process. According to the Langmuir model, the maximum adsorption capacities for Cr(VI) were 138.79, 159.36 and 190.91 mg/g at 298, 313 and 333 K, respectively. Moreover, based on FTIR and XPS results, the Fe 2 (SO 4 ) 3 @EN-BC surface was loaded with many functional groups conducive to Cr(VI) adsorption. The main removal mechanisms of Cr(VI) by Fe 2 (SO 4 ) 3 @EN-BC included adsorption and reduction, and the percentage of Cr(VI) removed by adsorption and reduction were 19.1% and 80.9%, respectively.