Kinetics of the photocatalytic reduction of platinum (IV) in a batch and flow reactor

Abstract

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes.