Removal of Nitrate from Water by Alginate-Derived Carbon Aerogel Modified by Protonated Cross-Linked Chitosan

Abstract

In this study, a carbonaceous aerogel with superior structural properties was synthesized from sodium alginate with a specific surface area and density of about 470\xa0m2\xa0g−1 and 0.05\xa0g\xa0cm−3, respectively. In order to adsorb nitrate from water, the surface of the aerogel was modified by protonated cross-linked chitosan. To investigate the morphology, elemental composition, crystalline phases and surface functional groups of the adsorbent, various techniques such as field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy were employed. To study the performance of this green adsorbent in nitrate removal process, the effect of nitrate initial concentration, adsorbent dosage, pH of solutions were investigated in batch mode. It was revealed that the Langmuir isotherm model could properly describe the experimental equilibrium data and the maximum adsorption capacity was evaluated to be about 18\xa0mg\xa0g−1 at neutral pH and room temperature. Besides, the kinetic data perfectly followed the pseudo-second order model. Thermodynamic analysis showed that the adsorption reaction was spontaneous, exothermic with decreased randomness at the solid–liquid interface. The macroscopic size of the adsorbent allowed its facile separation from the solution.