Functionalization of a Natural Biopolymer with Aliphatic Polyamines and its Sorption Properties for Vanadium Removal from Aqueous Solutions

A low-cost natural adsorbent, Moringa oleifera, was investigated as a potential alternative for currently costly methods of removing vanadium from contaminated aqueous solutions. The unmodified bark was characterized using techniques such as N-2-BET, SEM, XRD and FTIR spectroscopy, CHNS elemental determination and AA spectroscopy. Results showed a relatively small surface area, motivating surface functionalization to enhance adsorption capacity. Chemical modification was performed using four aliphatic polyamines: ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA). The modified bark was characterized and then investigated to determine its efficiency in removing VO2+ from aqueous solutions. The bark had a mesoporous amorphous structure and was enriched with N and S groups. FTIR absorption frequencies also revealed that polyamines were indeed immobilized on the adsorbent surface. The polyamine density was calculated and was in the order of EDA>DETA>TETA>TEPA, whereas the adsorption efficiency with VO2+ was in the order DETA>EDA>TETA>TEPA. Adsorbent amination was enhanced by up to 26% and adsorption performance improved by up to 155 %. It was, therefore, concluded that chemical modification of M. oleifera using polyamines enhances adsorption of VO2+ from aqueous solutions. This can, thus, preconcentrate VO2+ in the bark leading to its use as a good water purifier.