Title : Searching for the synergistic effect in AOPs, Case study: Sonophotocatalytic degradation of methylene blue by anatase nanopowder
Abstract:
The Advanced Oxidation Processes (AOPs) are currently the second most widely used wastewater treatment technology, right after adsorption. Over the past 20 years, nearly all AOPs combinations have been explored in an effort to create effective hybrid technologies with the goal of increasing the production of reactive radicals (hydroxyl, oxygen singlet, sulfate and others). The simultaneous use of two or more AOPs may exhibit: i) a cumulative (additive) effect; ii) a synergistic effect - when the aggregate effect exceeds the sum of individual AOPs and iii) an antagonistic effect - when the AOPs overlap, and the overall effect is lower than the sum of individual AOPs. The synergy (S) or synergy index (ξ) are typically used to measure the effectiveness of various AOPs combinations.
The purpose of this study is to ascertain how the synergistic interaction of ultraviolet (UV) and ultrasound (US) exposure in the presence of anatase nanopowder acting as a sono-photo-catalyst is affected by various process parameters. The anatase amount, the colorant concentration, and the exposure time were taken into account as experimental factors. Methylene blue (MB), a well-known dye representative and standard model compound in photochemical studies, was chosen as the test pollutant.
50 mL batch experiments were carried out over a mixture of MB solution and TiO2 nano-powder under UV, in sonic field, and combined UV and sonic field. The synergistic effect of ultraviolet and ultrasound was studied by comparing their separate and combined effects. It was found that the TiO2 dosage is critical in achieving synergism and that sonocatalysis is more effective than photocatalysis at lower anatase concentrations (from 0.5 up to 0.6698 g/L) owing to better catalyst particle dispersion. After this particular concentration value, the particle density is high enough to diminish the effects of cavitation. Increasing the catalyst concentration from 0.6698 to 1 g/L significantly impacts photocatalysis, while sonocatalysis is less affected. In brief, it was found that for the considered experimental system the synergistic effect is only achieved for a specific interval from 0.5 to 0.6698 g/L TiO2. Outside this range, the effect changes from synergistic to antagonistic, most likely due to intense US stirring that makes the slurry less accessible to UV light.
Audience Take Away:
- Insights into sonophotocatalysis as a hybrid advanced oxidation method will be provided.
- Elementary explanations of the synergism and antagonism concepts will be given.
- Interesting experimental results comparing sonocatalysis to photocatalysis will be presented.
- Experimental proof of the synergism achievement will be supplied.
