Assessment of molecularly imprinted polymers as phosphate sorbents

Phosphorus (P) is a non-renewable natural resource which is used extensively in agriculture as a fertilizer. Phosphate (PO₄^3-) rocks are mined to meet growing agricultural demands induced by rising global populations. Much of the P used in agricultural fields finds its way into surface waters where it permanently resides, leading to devastating effects on the aquatic ecosystem through eutrophication of the waterbodies. This research was aimed at developing a sorbent that can engender a P reuse cycle by utilizing eutrophic surface waters as viable P sources (mines). The goal was to develop a sorbent which can selectively recover low concentration (≤100 P μg L^-1) typical of eutrophic waters. Molecularly imprinted polymers (MIPs) were identified as a potential technology for accomplishing this goal. Three MIPs were screened for viability by assessing their sorption capacities. After the initial screening, one MIP was selected for further studies. The selected MIP was found to have partial PO₄^3- selectivity and tunable P sorption capacity. Adjusting the template:monomer ratio resulted in an increase in P sorption capacity from ∼11 to ∼28 mg PO₄^3--P g^-1, making this MIP competitive with existing technologies. The MIP was characterized to understand the polymer chemistry and mechanisms of P-removal. The possible mechanisms of aqueous P removal by the MIP were identified as selective chemical binding to the imprinted recognition sites and electrostatic attraction.