Thermally Tuned Friedel’s Salt for Efficient Dye Removal: Structural Memory, Adsorption Optimization, and Economical Feasibility in Azophloxin Removal

This study investigates the adsorption potential of thermally tuned Friedel’s salt (FS) for the removal of azophloxin (Acid Red 1, AR1) from aqueous solutions, emphasizing structural evolution, adsorption efficiency, and economic viability. FS was synthesized via coprecipitation (FSCO) and hydrothermal (FSHD) methods, followed by calcination at temperatures ranging from 300°C to 800°C. Comprehensive characterizations using scanning electron microscopy, x-ray diffraction, Fourier-transform infrared spectroscopy, Brunauer–Emmett–Teller, energy-dispersive x-ray spectroscopy, and zeta potential analyses revealed significant morphological and structural changes influencing adsorption capacity. FS calcined at 800°C exhibited the highest adsorption performance, with a maximum capacity of 227.39 mg/g at pH 9, attributable to enhanced porosity, surface area, and reactivity. The rehydration-induced memory effect allowed structural regeneration and its reuse, supporting the material’s sustainability. Adsorption followed both Langmuir and Freundlich isotherms, with the Langmuir model providing a superior fit, suggesting monolayer adsorption mechanisms. Furthermore, the economic assessment showed that FS800 offered the lowest cost per gram of AR1 removed ($0.09), indicating exceptional cost-effectiveness.