Multicharge FeMn–PAA/Chitosan Composite for Phosphate and Fluoride Removal from Real Water Samples

Abstract

Phosphorus (P) and fluoride (F) contamination in natural and industrial waters poses a serious environmental challenge. Mixed iron (Fe) and manganese (Mn) oxide composites have emerged as highly effective adsorbents for the removal of these pollutants from water. However, studies on real water system applications and the design of multicharged polymer-supported systems remain limited. In this work, FeMn-mixed oxides functionalized with polyacrylic acid (as a negative charge donor) and chitosan (as a positive charge donor) were engineered and applied as efficient adsorbents for the selective removal of P and F ions from both laboratory-prepared and real water samples. The as-prepared material was comprehensively characterized before and after adsorption using advanced analytical techniques. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses confirmed that carbon, nitrogen, and oxygen functional groups, together with the active participation of Fe and Mn ions, played central roles in the adsorption process. Real water samples collected from the Peshawar District (Khyber Pakhtunkhwa, Pakistan) were tested, and batch adsorption experiments validated the high removal efficiency of the composites. The composite exhibited a specific surface area ranging from 27.4 m² g⁻¹ before adsorption to 20.4 m² g⁻¹ after dye adsorption. Batch adsorption experiments demonstrated maximum removal efficiencies of 95–99% for both dyes under optimal conditions (pH 2–10, 298 K). Overall, this study presents a robust composite-engineering strategy and highlights the practical potential of the developed material for real-world water purification, particularly in industrial applications.