Enhanced adsorptive removal of chromium (VI) ions from wastewater with phosphorus-doped magnetite-carbon composite: advanced statistical physics modeling and kinetic studies

The primary aim of this research was to design a sustainable phosphorus-doped magnetite nanoparticle-embedded activated carbon, synthesized from Acacia falcata leaves, for the efficient adsorption of hexavalent chromium (Cr(VI)) from wastewater. The methods involved chemical modification and magnetization to synthesize the adsorbent, followed by characterization using XPS and EDS to confirm elemental composition and the reduction of Cr(VI) to Cr(III). Batch studies were carried out spanning the temperatures from 293 to 323 K, and advanced statistical physics models were utilized to examine the adsorption isotherms. The findings showed that the Two Layer One Energy model exhibited the best correlation with the experimental results (χ²: 0.003–1.262, R²: 0.997–0.999), with an orientation factor (n < 0.5) indicating parallel alignment of Cr(VI) ions on the Af-MAC, enhancing adsorption efficiency. The optimum saturation adsorption capacity was 114.09 mg/g at 303 K, exceeding values reported for comparable materials. Regeneration studies revealed only a slight decline in efficiency over five cycles due to pore blockage and chromium complexation, while cations had minimal effect, and competing anions reduced removal efficiency. The outcomes observed in this research work suggest that the synthesized Af-MAC exhibits exceptional Cr(VI) adsorption, strong reusability, and high adsorption capacity, resulting in a promising material for Cr(VI) removal.