Crystallographic characterization of Ag-doping in nanocrystallite hydroxyapatite and evaluation of photocatalytic activity of organic pollutants

Pure and different percentages (0.25, 0.5, 1.0, and 2.5%) of silver (Ag) doped hydroxyapatites (Hap) were synthesized employing the wet chemical precipitation method. The samples were characterized with the aid of X-ray diffraction (phase analysis, crystallographic characterization, and crystal size calculation using Scherrer equation and different models), scanning electron microscopy, and optical bandgap energy. The Hap containing 0.25% Ag showed better photocatalytic activity in various dye concentrations, catalyst doses, and pH. At a very low catalyst dose (0.375 g/L) and 20 ppm pollutant concentration, reaction rate, and rate constant were evaluated for the Congo Red dye, ciprofloxacin, amoxicillin, and levofloxacin. The maximum rate constant (0.0028 min⁻¹) and reaction rate (9.657 × 10⁻⁸ mole L⁻¹·min⁻¹) were found for Congo Red dye and ciprofloxacin, respectively, using 0.25_Ag-Hap (0.25% Ag-doped Hap). The energies of the valance band (3.14 eV) and conduction band (−0.36 eV) were lower in the case of 0.25_Ag-Hap than the other samples. Simplified reaction mechanisms were proposed for the photocatalytic degradation of Congo Red dye, ciprofloxacin, amoxicillin, and levofloxacin.