Electron acceptors effect on photocatalytic degradation of metformin under sunlight irradiation

Abstract

The water purification is a serious issue especially with the unprecedented growth of pollutants from pharmaceutical industries. The metformin, an antidiabetic drug, is one of pharmaceutical pollutants that can be found in domestic and hospital wastewater which are suspected to affect the balance of ecosystems and the human health even at low concentrations. In this paper, we study the metformin elimination from wastewater using heterogeneous photocatalysis. We investigate the metformin degradation in aqueous medium under sunlight irradiation in the presence of titanium dioxide (TiO2) Degussa P25 (80% anatase, 20% rutile) as catalyst and in a semi-pilot solar reactor. Contrary to existing works, we use electron acceptors such as hydrogen peroxide (H2O2), potassium persulphate K2S2O8 and sodium persulphate Na2S2O8 to improve the TiO2 photocatalytic activity. Different TiO2 photocatalysts were used (P25, EL10, DT51, PC105, PC500 and T42) for preliminary study before selecting P25. The solar reactor was (i) set facing south and (ii) a peristaltic pump is used to re-circulate the treated mixture between the reactor and the reservoir in a closed circuit. During sunlight irradiation, the solution of metformin was homogenized by magnetic stirrer. The degradation was monitored by measuring the metformin concentration using a UV-visible spectrophotometer at wavelength of 236 nm. The used photocatalysts were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The average crystallite size was estimated using X-ray diffraction. The experimental results showed that metformin degradation rate in presence of electron acceptors was increased significantly during photocatalysis compared to photolysis and adsorption. The apparent rate constant of every reaction involved was evaluated and the kinetics of degradation was described by the Langmuir-Hinshelwood (L-H) model.