Functional Hydrogels for Selective Phosphate Removal from Water and Release on Demand

Commercial overuse and soaring prices of phosphate fertilizers have resulted in an adverse economic and environmental impact, threatening human health, clean water, and food security. In response to the phosphorus (P) cycling challenge, we developed a novel polyethylenimine (PEI)/poly(methyl vinyl ether-co-maleic anhydride) (PMVEMA) hydrogel system capable of efficient capture and release of inorganic phosphates with high selectivity in the presence of nitrate. This study investigated the synergistic effect of PEI and PMVEMA within the hydrogel for a broad range of eluent pH conditions and P loadings to establish the capturing capacity and selectivity of the system toward nitrate. The PEI-enriched hydrogel system was characterized by a high P capturing capacity between pH 2.0 and 7.0 with a maximum P capture of 65 mg of P/g of sorbent at an equilibrium pH of 4.5. Desorption studies indicated that the system could efficiently release captured inorganic phosphate with an efficiency of 96% under mild conditions (<0.001 M NaOH), independent of the preloaded phosphate amount and system history. This is the lowest base concentration for P desorption reported. The separation factor (α) was dependent on the pH of the eluent and was equal to approximately 50 when in the presence of nitrates.