Anatase TiO 2 nanoparticles as a reusable adsorbent for dexamethasone sodium phosphate removal from pharmaceutical wastewater

This study investigates the adsorption behavior of the pharmaceutical contaminant dexamethasone sodium phosphate (DSP) on titanium dioxide nanoparticles (TNPs) with different crystal phases. Anatase-phase TNPs exhibited a significantly higher adsorption capacity (87.61%) than rutile-phase TNPs, attributable to stronger surface interactions, including electrostatic attraction and possible inner-sphere complexation, as supported by FT-IR analysis. DSP adsorption onto anatase TNPs was highly pH-dependent, with maximum uptake observed at pH 2 and progressively reduced efficiency under alkaline conditions due to electrostatic repulsion. The presence of coexisting anions, such as HCO3− and HPO42−, interfered with DSP uptake, likely through competitive surface coordination, while adsorption equilibrium was reached within 2 min. Adsorption isotherm analysis showed that DSP adsorption followed the Langmuir model (R2 = 0.9986), indicating monolayer coverage with a maximum adsorption capacity of 24.2 mg g−1. Based on X-ray diffraction-derived surface area estimates, the calculated adsorption density was 8.19 × 1016 molecules m−2. Furthermore, DSP desorption was enhanced under basic conditions (pH ≥ 10), and anatase TNPs retained more than 90% of their adsorption capacity after 10 regeneration cycles. These findings highlight the potential of anatase TNPs as an efficient and reusable adsorbent for pharmaceutical wastewater treatment.