Gemini surfactant-modified montmorillonite with tetrachloroferrate (FeCl4-) as a counterion simultaneously sequesters nitrate and phosphate from aqueous solution.

Alkyl quaternary ammonium-modified clay minerals, which are common environmentally friendly materials, have been widely studied and applied for the removal of pollutants. However, there are few reports on functionalizing the counterions to expand the application. In this study, the cationic gemini surfactant butane-1,4-bis(dodecyl dimethyl ammonium bromide) (gBDDA) and tetrachloroferrate (FeCl4-) are designed to modify montmorillonite (Mt), and the obtained FeCl4-/Gemini-Mt composite (FeOMt) is used for the removal of nitrate and/or phosphate from aqueous solution. The successful intercalation of gBDDA and favorable loading of FeCl4- into FeOMt are suggested by the characterization results of X-ray diffraction and Raman spectroscopy. Nitrate and/or phosphate are rapidly sequestered, and the respective maximum uptakes of 8.77 (N) and 28.1 (P) mg/g in the binary system are obtained. The phosphate uptake is stably maintained against many coexisting ions, but the nitrate uptake decreases with the increase in ionic strength. FeOMt is reusable and shows comparable uptake for nitrate and phosphate with respect to gBDDA-modified Mt and polymerized ferric chloride. Considering the multi-functionality and facile synthesis, FeOMt shows promising potential in the purification of wastewater contaminated simultaneously by poorly hydrated anions (e.g., ClO4-, TcO4-, etc.) and iron-selective anions (e.g., H2AsO4-, etc.).