A study on the influence of pH changes during catalytic ozonation process on alumina, zeolites and activated carbons for the decolorization of Reactive Red-241.

Samra Sajjad,Fei Qi,Farhan Javed,Amir Ikhlaq,Syed Waqas Ahmad

doi:10.2166/wst.2020.609

Abstract

The current study focuses on a prime effect of pH changes in the catalytic ozonation process (COP) by using three main classes of catalysts such as zeolites (alumina-silicates), alumina (metal oxides), and activated carbons for decolorization of Reactive Red 241 (RR-241). The role of pH changes, point of zero charges and the effect of catalyst dose on pH change was studied. The results reveal that the overall removal efficiency of RR-241 in the case of COPs was the highest compared with single ozonation process (at pH = 7 the efficiency was 80, 65 65.5 and 60% for AC/O3, Al2O3/O3, Zeolite/O3 and O3 respectively). At initial acidic pH 4, the highest pH variations in COPs and ozonation processes were observed. Moreover, the pH changes were not found to be significant near the point of zero charges of materials (pHpzc = 6.8, 8.4 and 8.8 for zeolite, activated carbons and Al2O3, respectively. The COP in the presence of activated carbon shows the highest removal efficiency (82%) at pH 7. The material dose effect indicates that increasing the amount of catalyst (from 1 gm to 2 gm) significantly leads to a change in the pH of the solution. Results reveal the prominent effect and significance of pH changes on the efficiency of COP to determine true catalytic efficiency.

Highlights

In the recent few years, catalytic ozonation processes (COPs) have gained much attention in water and wastewater treatment applications, due to the production of highly reactive oxygen species or hydroxyl radicals in such processes
Many research articles were published without considering the pH changes in such processes, which may lead to the wrong interpretation of mechanisms while comparing various materials as a catalyst with the single ozonation process, since both the ozonation and catalytic ozonation processes are pH dependent and their reaction rates depend on the pH of water (Nawrocki )
The current study focuses on the effect of pH changes in COP by using three catalyst types for the decolorization of Reactive Red 241 (RR241)

Summary

Introduction

In the recent few years, catalytic ozonation processes (COPs) have gained much attention in water and wastewater treatment applications, due to the production of highly reactive oxygen species or hydroxyl radicals in such processes. High efficiency, lack of sludge formation, and production of hydroxyl radicals (*OH) over a wide range of pH, the heterogeneous catalytic ozonation process may be a good option among the advanced oxidation processes (AOPs) for the removal of toxic and refractory organic compounds present in wastewater (Asaithambi et al ). Jacek Nawrocki et al highlighted the controversies in the catalytic ozonation process and discussed them with possible reasons. Among those were that the pH changes during the catalytic ozonation process may alter the mechanism and overall effectiveness of the process (Nawrocki ). In the majority of studies, no attention was given to pH control, which is very important at high catalyst concentrations (Kolosov & Yargeau )

Methods

Results

Conclusion