Abstract
This work investigates the degradation of the azo dye solochrome dark blue (SDB) by measurement of the photocatalytic, sonocatalytic and sonophotocatalytic activities, under low ultrasonic frequency (40 kHz) and UV-C (254 nm) light, using Mn-doped ZnS semiconductor quantum dots (Mn2+:ZnS Qds) as catalysts, prepared by a simple chemical precipitation procedure. In order to study the different morphological and optical crystal properties, various characterization techniques were used, such as high resolution transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, N2 adsorption-desorption at −196 °C and ultraviolet-visible spectroscopy. The average particle size of the semiconductor Qds was in the range of 3–4 nm. The optimal parameters affecting dye degradation, such as the catalyst loading, solution pH, time of irradiation, initial concentration of dye, dopant concentration, ultrasonic power and frequency effect were evaluated. The synthesized catalytic material exhibited a high activity for sonophotocatalytic degradation of SDB (89%), larger than that observed for sonocatalysis (69.7%) or photocatalysis (55.2%) alone, which was due to the improved electron-holes separation, formation of more reactive radicals and enhancement of the active surface area. Qds showed good stability and reusability after five repeated cycles. Finally, the degradation products were identified by liquid chromatography-mass spectrometry (LC-MS).
Highlights
From the viewpoint of environmental sustainability, textile processing and production release a huge quantity of polluted wastewaters, which enter the environment with unknown effects on health
The results show that the photocatalytic activity of quantum dots (Qds) remarkably improved with the use of ultrasound, compared to another study dealing with sonophotocatalysis, as well as the other conventional methods for the removal of Solochrome dark blue (SDB) molecules from an aqueous solution [52,53,54,55,56,57]
When comparing the contact time for degradation, and the initial concentration of dye and dosage of catalyst, the results indicate that the results obtained with Mn2+ :zinc sulfide (ZnS)
Summary
From the viewpoint of environmental sustainability, textile processing and production release a huge quantity of polluted wastewaters, which enter the environment with unknown effects on health. Solochrome dark blue (SDB) is mainly used as an indicator in complexometric titrations for the determination of total hardness of water due to elements such as calcium, zinc, magnesium, and to a lesser extent for other metal ions, including manganese These metal ions readily undergo oxidation in alkaline media to form products of uncertain stoichiometry. The goal was to improve the efficiency of the ultrasonic-based process for low-cost degradation of organic pollutants This combination of ultrasound with a Mn2+ :ZnS Qds photocatalyst was rarely investigated. The results show that the photocatalytic activity of Qds remarkably improved with the use of ultrasound, compared to another study dealing with sonophotocatalysis, as well as the other conventional methods for the removal of SDB molecules from an aqueous solution [52,53,54,55,56,57]
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