Microscopic mechanism about the selective adsorption of Cr(VI) from salt solution on nitrogen-doped carbon aerogel microsphere pyrolysis products.

A series of nitrogen-doped carbon aerogels (NCAs) were obtained through phase reaction polymerization and different carbonization temperatures to enhance adsorption efficacy of hexavalent chromium (Cr[VI]) from wastewater significantly. Factors that influence adsorption properties of carbon aerogel microspheres toward Cr(VI), such as pH, adsorbent content, initial Cr(VI) concentrations, and coexisting anion, were investigated. Three isotherm (Langmuir, Freundlich, and Sips) and three kinetic (pseudofirst-order, pseudosecond-order, and Elovich) models were used to interpret the adsorption process. The adsorption capacity of Cr(VI) reached 180.62 mg·g, which was superior to that of most aerogel adsorbents. In addition to the adsorption effect, the XPS results also showed that N-containing groups on the NCA surface reduce the adsorbed Cr(VI) to the less toxic Cr(III). The prepared sorbent demonstrates a negligible loss in adsorption capacity after 6 cycles. NCAs show acceptable application prospects in selective removal of Cr(VI) ions.