Effect of operational parameters and kinetic study on the photocatalytic degradation of m-cresol purple using irradiated ZnO in aqueous medium

Abstract

A detailed investigation of photocatalytic degradation of m-cresol purple (mCP) dye has been carried out in aqueous heterogeneous medium containing zinc oxide (ZnO) as the photocatalyst in a batch reactor. The effects of some parameters such as amount of photocatalyst, dye concentration, initial pH of solution, ethanol concentration and temperature were examined. The most efficient pH in removal of the dye with photocatalytic degradation and dark surface adsorption processes was observed to be 8. The adsorption constant calculated from the linear transform of the Langmuir isotherm model was similar to that obtained in photocatalytic degradation at pH = 8; hence, the Langmuir–Hinshelwood model was found to be accurate for photocatalytic degradation at this pH. Dark surface adsorption and degradation efficiency were increased by enhancement in the temperature at the optimum pH of 8 and the apparent activation energy (Ea) for the photocatalytic degradation of mCP was determined as 14.09 kJ/mol at this pH. The electrical energy consumption per order of magnitude (EEO) for photocatalytic degradation of mCP was also determined.

Eco-Toxicological and Kinetic Evaluation of TiO2 and ZnO Nanophotocatalysts in Degradation of Organic Dye

“…Therefore, the decolorization of FB1 is more dependent on the catalyst concentration in the UV-TiO2 system than in the UV-ZnO system. The relationship between the initial decolorization rate and catalyst loading can be described as (r 0 α[catalyst] n ) at catalyst concentrations lower than or equal to the optimum concentration [23]. As seen in Figure 2b, this relationship could be described as r 0 α[TiO 2 ] 0.44 and r 0 α[ZnO] 0.30 for the UV-TiO 2 and UV-ZnO processes, respectively.…”

“…Meanwhile, the adsorption of dye molecules on the catalyst surface increased. An additional loading of catalyst might increase the opacity of the suspension, thereby decreasing the photocatalytic rate [10,23].…”

“…More hydroxyl radicals could be generated under an alkaline environment (pH = 8) by oxidizing the available hydroxide ions on the catalyst surface. Therefore, the efficiency of the HPO process can be upgraded on a logical basis [23,25]. The rates of decolorization and mineralization over TiO 2 at pH 8 increased by 8% and 11% relative to neutral pH (6.7), while their counterparts for ZnO exhibited enhancements of 26% and 34%, respectively.…”

“…In many studies, the L-H kinetic model has been used to describe the HPO reaction rate with various concentrations of a target substrate [10,36,37]. However, if the kinetic adsorption equilibrium constant is different from that obtained in the dark, the L-H kinetic model cannot be adopted [23]. Therefore, the influence of the different initial concentrations of FB1 on the surface adsorption has been studied at the same pH values (5, 6.7, and 8).…”

“…The HPO process cannot be sustained without a constant supply of dissolved oxygen [23]. Thus, air at constant flow-rate was supplied to the four corners of the reactor using a micro air compressor.…”