Natural Zeolite Supported Photocatalysts for the Simultaneous Degradation of Dyes in Aqueous Solutions

Abstract

The discharge of synthetic dyes into water bodies poses severe environmental risks due to their toxic and recalcitrant nature. This study presents a catalyst for pollutant removal, specifically targeting the degradation of dyes (i.e., methylene blue and congo red) as model compounds to evaluate the material’s photocatalytic performance. Comprehensive material characterization employing FESEM-EDX analyses elucidates the successful incorporation of natural zeolite. The influence of various parameters that affect photocatalyst performance (i.e., contact time, initial dye concentration, catalyst dosage, and scavenger) was also investigated. Natural zeolite exhibits significant adsorption capacity in the initial stage, particularly toward MB, which contributes greatly to total removal efficiency. Photocatalytic test demonstrated that natural zeolite achieved the highest dye degradation, retaining over ~98% for MB and ~65% for CR. Photolysis control tests show that direct degradation by UV without a catalyst is limited, so the performance improvement mainly comes from the role of zeolite in facilitating the adsorption-photodegradation process. To identify the dominant reactive species, scavenger experiments were conducted using isopropyl alcohol (IPA), benzoquinone (BQ), and EDTA. The results showed that the addition of BQ drastically reduced degradation (~15%), while IPA had a smaller effect, indicating that superoxide radicals (O2-•) and positive holes (h+) were the main species involved, while hydroxyl radicals (•OH) contributed only minimally. Natural zeolite has been proven to work as an affordable and effective material for dye waste treatment. These results emphasize the potential of natural zeolite for industrial wastewater treatment. However, further optimization is needed to improve performance in anionic dyes.