Synthesis of iron-doped resorcinol formaldehyde-based aerogels for the removal of Cr(VI) from water

Iron-doped resorcinol formaldehyde-based aerogels (Fe-RF-AGs) were synthesized and used for the removal of hexavalent chromium [Cr(VI)] from water using adsorption. The synthesis steps of Fe-RF-AGs comprised the gelation by the polycondensation of resorcinol and formaldehyde, followed by drying using supercritical carbon dioxide. The produced mesoporous material was in situ doped with iron (Fe) before the incipience of gel formation, using ferrocene as the metal precursor. Various analytical techniques were used to characterize the prepared materials. The batch adsorption study was performed containing different amounts of Fe in the gel, different initial Cr(VI) concentrations of the solution, and at different solution pH and temperatures. The adsorption rate was found to be first order. The equilibrium data were explained using the Freundlich isotherm. The thermodynamic calculations revealed that the adsorption of Cr(VI) was spontaneous, endothermic and irreversible over the temperature range of 20–40°C. The maximum adsorption capacity of Fe-RF-AGs for Cr(VI) was found to be approximately 55 mg/g at 30°C at the aqueous phase concentration of 275 mg/l, which is larger than most of the data discussed in the literature. The results indicated that Fe-RF-AGs can be used as an effective adsorbent for the removal of Cr(VI) ions from waste water