Silica-alumina composite as an effective adsorbent for the removal of metformin from water

The anti-diabetic agent metformin (MF) is one of the most prescribed pharmaceutical compound worldwide. It is not completely metabolized after administration where 52% is excreted in urine. Accordingly, it highly contributes in generating wastewater containing MF. This pollutant is not effectively removed by the conventional wastewater treatment methods. Therefore, an effective advanced treatment technique should be implemented for the removal of MF from wastewater. In this study, silica-alumina (SA) is used as an environmentally-safe and effective adsorbent for removing MF from aqueous solution by adsorption. Adsorption experiments were employed studying the effect of pH, contact time, and MF initial concentration to investigate both the removal efficiency of MF and the interaction mechanism. A set of characterization techniques, such as SEM, BET, FTIR, TPD-MS, and zeta potential were performed before and after adsorption experiments to confirm the role of structural morphology, surface area, porosity, surface acidity and charge in adsorption. The characterization analysis showed that SA has BET surface area of 470 m(2)/g. From the total BET surface area, the microporous surface area was around 31% (147 m(2)/g), while the rest corresponds to the mesoporous surface area (323 m(2)/g). The batch adsorption results showed that high concentrations of MF were efficiently removed from water samples with a maximum uptake of 46 mg/L at optimal pH 9.0 (optimal pH). The mechanism responsible for adsorption was observed to be carried out via an electrostatic interaction between a negatively charged SA and a positively charged MF. TGA/DT analysis was conducted to assess the reusability of the spent SA by thermal regeneration at 673 K. The adsorbent was completely regenerated and maintained a 95% removal after 3 cycles without impacting the surface characteristics.