An Efficient and Regenerable Quaternary Starch for Removal of Nitrate from Aqueous Solutions

This paper presents a study of NO3- ions sorption from an aqueous solution using quaternary starch derivatives. For this; the derivatization was carried out by an improvised method for the synthesis of a gemini-like structure, which is unique and has two quaternary ammonium functionality per anhydroglucose units of starch. Mohr's method was used, to characterize the synthesized bis-quaternary starch as chloride ion content, and the results supported a chloride content of 13.5-14.4% with the total ion exchange capacity of 3.8-4.2 mequiv/g. A series of batch experiments were conducted to examine the effects of structure, contact time, concentration, pH, and effect of co-ions on the sorption of NO3-. The results showed an increase in sorption capacity with an increase in the concentration of NO3-, while the presence of competing anions such as PO43-, HCO3-, and SO42- showed marginal effect on the NO3- sorption capacity. The increase in pH from 4.0 to 6.5 also effected the NO3- sorption process marginally. Moreover, the quaternary starch exhibited 78.5% efficiency even after the eighth sorption - desorption cycle. The kinetic and thermodynamic adsorptions of NO3- ions from the aqueous solutions were also investigated for the synthesized quaternary starch derivative. The adsorption kinetics data were best described by the pseudo-second-order rate equation. The equilibrium data agreed well with the Langmuir model. The maximum capacity for quaternary starch can be deduced from the obtained correlation coefficients and was calculated at approximate to 205mg/g in the isotherm model, which is preferential to the earlier reported commercialized Purolite technology. In conclusion; the bis-quaternary starch structure is successfully synthesized in uniform and high modification and shows significant potential for removal of NO3- ions from aqueous solution.