Enhanced removal of Cr(VI) from aqueous solutions by polymer-mediated nitrogen-rich reduced graphene oxide

The efficient removal of heavy metal by rationally designed carbon-based adsorbents is a key challenge in the field of water purification. Herein, we report a nitrogen-enriched lignosulfonate exfoliated graphene oxide (NLEGO) for hexavalent chromium (Cr(VI)) removal from aqueous solution. The nitrogen content of N-LEGO reached 13.28%, and the ratio of N-bonding configurations (pyri-N:amine-N:pyrro-N:grap-N) was 2.3:1.6:1:2.3. For Cr(VI) with initial concentration of 70 mg L-1 under pH= 2, the residuary concentration after treated by NLEGO was close to 0.004 mg L-1, which meets the industrial wastewater discharge standard. The Cr(VI) adsorption behavior on N-LEGO can be fitted with the pseudo-second-order kinetics and Freundlich isotherm model well. The adsorption mechanism of Cr(VI) on N-LEGO includes anions electrostatic attraction, reduction and surface chelation. Density functional theory (DFT) simulations showed that N atoms doping was feasible and thermodynamically stable, meanwhile the N-doped system was easier to adsorb Cr2O72-than HCrO4-. The findings of this work can provide a new idea for the development of N-doped carbon-based adsorbents for the removal of highly toxic Cr(VI) from aqueous solutions.

Automated summary

This study reports the use of nitrogen-enriched lignosulfonate exfoliated graphene oxide (NLEGO) as an efficient adsorbent for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. The experimental results show that NLEGO has a strong adsorption capacity for Cr(VI) and can meet the industrial wastewater discharge standards. Density functional theory (DFT) simulations suggest that the adsorption mechanism of Cr(VI) on NLEGO involves electrostatic attraction, reduction, and surface chelation.