Kinetic studies of dexamethasone degradation in aqueous solution via a photocatalytic UV/H2O2/MgO process

Abstract

Wastewaters discharged from different industries and hospitals may contain pharmaceuticals, especially dexamethasone (DEX). Thus, we applied the UV/H2O2 photocatalytic method in the presence of the MgO nanoparticles to remove dexamethasone from synthetic wastewater. Moreover, the effects of parameters such as pH (3–11), hydrogen peroxide concentration (1–8 mM), initial DEX concentration (5–30 mg/L), and catalyst dosage (0.01–0.2 g/L) during the reaction times (0–30 min) were investigated. Furthermore, the efficiency of UV/H2O2 in the presence and absence of catalysts was investigated. The photocatalyst is characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and Fourier-transform infrared spectroscopy (FTIR) techniques. It was found that the removal rate was enhanced by decreasing pH and the initial dexamethasone concentration. The removal rate was enhanced somewhat with concentrations of hydrogen peroxide and MgO. In the case of UV/H2O2/MgO, 87% removal efficiency was achieved, under the optimal conditions: pH 3, contact time of 30 min, dexamethasone concentration of 20 mg/L, H2O2 of 0.5 mM, and UV radiation of 55 watts. The kinetic data indicated that the reaction followed the second-order kinetic model. The results showed that the UV/H2O2 photochemical process can efficiently remove dexamethasone from aqueous in the presence of a MgO catalyst, and the mineralization efficiency was reached at about 98%.

Environmentally Friendly UV-C Excimer Light Source with Advanced Oxidation Process for Rapid Mineralization of Azo Dye in Wastewater

“…A dark test was also performed to check the degradation with only H 2 O 2 , and negligible degradation occurred in the aqueous dye solution, showing that the RB5 dye is quite stable under bleaching conditions. Moreover, adding TiO 2 into this process reduces the degradation efficiency because H 2 O 2 scavenges the photogenerated oxidizing species, i.e., •OH and valence band holes (see eqs and ), which would otherwise be available for the oxidative destruction of the dye molecules. Accordingly, XeI*-excimer/H 2 O 2 is a preferable method of treating wastewater because of its ability to produce •OH (on-site) and also because it is a sludge-free operation with faster kinetics …”

“…The dye degradation efficiency, energy yield, and COD reduction were estimated using the following relationships: , Degradation .25em efficiency false( % false) = C 0 − C t C 0 × 100 Energy .25em yield , .25em Y ( mg kWh ) = C 0 × V × D P × t COD .25em reduction false( % false) = C O D 0 − C O D t C O D 0 where C 0 is the initial concentration of the dye (mg/L), C t is the dye concentration after treatment time t (mg/L), V is the volume of solution treated (L), D is the fraction of pollutant removed at a time t , P is the input power (kW), t is the treatment time (hour), COD 0 is the initial value of chemical oxygen demand (mg/L), and COD t is the value of chemical oxygen demand after treatment time t (mg/L).…”

“…The dye degradation efficiency, energy yield, and COD reduction were estimated using the following relationships: 45,46 C C C Degradation efficiency(%) 100…”