Concurrent adsorption and reduction of chromium(VI) to chromium(III) using nitrogen-doped porous carbon adsorbent derived from loofah sponge

To develop highly effective adsorbents for chromium removal, a nitrogen-doped biomass-derived carbon (NHPC) was synthesized via direct carbonation of loofah sponge followed by alkali activation and doping modification. NHPC possessed a hierarchical micro-/mesoporous lamellar structure with nitrogen-containing functional groups (1.33 at%), specific surface area (1792.47 m(2)/g), and pore volume (1.18 cm(3)/g). NHPC exhibited a higher Cr(VI) adsorption affinity than the HPC (without nitrogen doping) or the pristine loofah sponge carbon (LSC) did. The influence of process parameters, including pH, dosage, time, temperature, and Cr(VI) concentration, on Cr(VI) adsorption by NHPC were evaluated. The Cr(VI) adsorption kinetics matched with the pseudo-second-order model (R-2 > 0.9983). The Cr(VI) adsorption isotherm was fitted with the Langmuir isotherm model, which indicated the maximum Cr(VI) adsorption capacities: 227.27, 238.10, and 285.71 mg/g at 298K, 308K, and 318K, respectively. The model analysis also indicated that adsorption of Cr(VI) on NHPC was a spontaneous, endothermal, and entropy-increasing process. The Cr(VI) adsorption process potentially involved mixed reductive and adsorbed mechanism. Furthermore, computational chemistry calculations revealed that the adsorption energy between NHPC and Cr(VI) (-0.84 eV) was lower than that of HPC (-0.51 eV), suggesting that nitrogen doping could greatly enhance the interaction between NHPC and Cr(VI). (c) Higher Education Press 2021

Automated summary

A nitrogen-doped biomass-derived carbon (NHPC) was synthesized by direct carbonation of loofah sponge followed by alkali activation and doping modification. NHPC showed higher Cr(VI) adsorption affinity compared to HPC (without nitrogen doping) or pristine loofah sponge carbon (LSC). The adsorption kinetics of Cr(VI) on NHPC followed the pseudo-second-order model, and the adsorption isotherm fitted the Langmuir model. The process of Cr(VI) adsorption on NHPC was spontaneous, endothermal, and entropy-increasing. Computational chemistry calculations suggested that nitrogen doping greatly enhanced the interaction between NHPC and Cr(VI).