Synthesis of (PDAN/n-TiO2) composites by in-situ 1,8-diaminophthalene polymerization for the adsorptive removal of molybdate anions

In this study, nano-titanium dioxide(n-TiO 2 ) modified with poly(1,8-diaminophthalene)(PDAN) were employed for the removal of Mo(VI) ions from aqueous solutions. The synthesized adsorbent was characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and Thermal gravimetric analysis (TGA). Key parameters influencing the adsorption performance in the batch process, including pH, adsorbent dosage, temperature, and initial metal ion concentration, were investigated at different temperatures (26, 36, and 45 °C). According to the results, the optimal conditions were determined as follows: pH = 3.5, adsorbent dosage = 0.04 g, initial concentration = 4 mg/L, temperature = 26 °C, agitation speed = 180 rpm, and contact time = 5 h. Under these conditions, the maximum adsorption capacity was found to be 4.5369 mg/g. Various isotherms and error models were employed to identify the best-fitting isotherm model and to estimate the corresponding parameters. Among them, the Radke–Prausnitz isotherm model showed the highest agreement with the experimental data. The adsorption kinetics followed a pseudo-second-order (PSO) model. Thermodynamic analysis confirmed that the adsorption of Mo(VI) ions was spontaneous and endothermic. Furthermore, the effect of interfering ions under optimal conditions was studied. Desorption experiments at different concentrations were also conducted to evaluate the reusability of the adsorbent. Among the tested desorbing agents, ammonium acetate (CH₃COONH₄) demonstrated the highest desorption efficiency of approximately 36 % at an optimal concentration of 0.5 M.