Phosphate removal by anion binding on functionalized nanoporous sorbents

Phosphate was captured from aqueous solutions by cationic metal?EDA complexes anchored inside mesoporous silica MCM-41 supports (Cu(II)?EDA-SAMMS and Fe(III)?EDA-SAMMS). Fe?EDA-SAMMS was more effective at capturing phosphate than the Cu?EDA-SAMMS and was further studied for matrix effects (e.g., pH, ionic strength, and competing anions) and sorption performance (e.g., capacity and rate). The adsorption of phosphate was highly pH dependent; it increased with increasing pH from 1.0 to 6.5, and decreased above pH 6.5. The adsorption was affected by high ionic strength (0.1 M of NaCl). In the presence of 1000-fold molar excess of chloride and nitrate anions, phosphate removal by Fe?EDA-SAMMS was not affected. Slight, moderate and large impacts were seen with bicarbonate, sulfate, and citrate anions, respectively. The phosphate adsorption data on Fe?EDA-SAMMS agreed well with the Langmuir model with the estimated maximum capacity of 43.3 mg/g. The material displayed rapid sorption rate (99% of phosphate removal within 1 min) and lowering the phosphate content to ?10 μg/L of phosphorus, which is lower than the EPA's established freshwater contaminant level for phosphorus (20 μg/L).