One-step Synthesis Of Reticulated N-doped Carbonaceous Spheres And Their Applications In Removal Of Cr(Ⅵ)

Hexavalent chromium as a typical heavy metal could be enriched in animals and plants easily and eventually enter the human body through the food chain, posing a serious threat to public health. Carbonaceous materials are usually used to deal with wastewater containing Cr(Ⅵ), but the common carbonaceous materials are difficult to meet the requirement of Cr(Ⅵ) wastewater treatment. Compared to common carbonaceous materials, nitrogen-doped carbon materials exhibit higher efficiency in removal of Cr(Ⅵ) as a result of the introduction of chemical activity sites. However, there are many issues in the fabrication of nitrogen-doped carbon materials currently, such as involving complicated steps, costly carbon sources, and potential environmental problems in the process. The objective of this study is to obtain submicron nitrogen-doped carbon spheres using a common nitrogen-rich carbon source and through a simple green technology. Meanwhile, its performance on removal of Cr(Ⅵ) was evaluated.In this paper, we choose glucosamine sulfate as a starting material for preparing nitrogen-doped carbonaceous submicron spheres through an aerosol-assisted method, and SEM, TEM, FT-IR, elemental analysis, BET, Zeta potential and XPS were used to characterize the obtained materials. Results show that the materials prepared through aerosol-assisted method are submicron, and presents regular spheres. Meanwhile reticular structure were prepared during atomization precess because of glucosamine sulfate self-assembled.In the process of heavy metals Cr(Ⅵ) removal, the doping of nitrogen atoms on the surface of nitrogen-doped carbonaceous submicron spheres increased positive charge under the acidic condition, so it dramatically enhanced the Cr(Ⅵ) removal because of electrostatic attraction between protonated nitrogen and Cr(Ⅵ) anions. The removal of Cr(Ⅵ) increased from 15.5% to 100% compared with non-nitrogen carbonaceous submicron spheres. As XPS results show that Cr(VI) adsorbed on the nitrogen-doped carbonaceous submicron spheres can ultimately be reduced to Cr(Ⅲ) by the surface reducing groups of C-H and C-OH, and the reducing groups were oxidized into C-OH and C=O. The effects of N-doping amount, pH, dosage and regenaration proportion are also examined by this paper. The results show that it benefits Cr(Ⅵ) removal with the increasing of N-doping amount and the decreasing of pH.Using nitrogen-doped carbonaceous submicron spheres for the dosage of 5 g/L can reach 100% removal of 60 mg/L Cr(Ⅵ) solution. The removal was reduced gradually with the increasing of cycle, but no less than 60% was obtained in the fifth cycle.The nitrogen-doped carbonaceous submicron spheres can be prepared through a very convenient aerosol-assisted process, and the doping of nitrogen atoms dramatically enhanced the removal of Cr(Ⅵ), so they have potentials to serve as effective adsorbents for the removal of Cr(Ⅵ) ions from aqueous systems.