In this study, the degradation of azo dye solutions (Reactive Red 180 and Reactive Orange 16) of textile industry wastewater was investigated for using innovative hybrid process of photocatalytic and membrane distillation (MD) processes. Photocatalytic oxidation was conducted with semiconductor catalysts (ZnO and TiO2) and their mixture under UVA and UVC irradiation. More effective results were obtained under UVA at the initial stages of the reactions for both dye solutions. ZnO and TiO2 catalysts have given similar efficient results, but results with ZnO were better at initial stages. For the next stage, hybrid design of MD and photocatalytic processes was performed sequentially. Initially, the photocatalytic process was conducted for at least 1 h at initial values of 100 mg/L RR-180 dye solutions and 1 g/L ZnO catalyst loading under UVA irradiation and then treated solution was run through the distillation module at different temperatures (30°C and 40°C) and flow rates (210, 425, and 665 mL/min). Three types of membranes (polypropylene, polytetrafluoroethylene, and polyvinylidene fluoride) with different pore sizes (0.45 and 0.22 μm) were used in the module. Increasing temperature on the side of treated solution and decreasing the temperature on the other side has increased the distillate efficiency.
SO x uptake and release properties of LaMnO 3 , Pd/LaMnO 3 , LaCoO 3 and Pd/LaCoO 3 perovskites were investigated via in situ Fourier transform infrared (FTIR) spectroscopy, temperature programmed desorption and X-ray photoelectron spectroscopy. Sulfation of the perovskite leads to the formation of surface sulfite/sulfate and bulk-like sulfate species. Pd addition to LaMnO 3 and LaCoO 3 significantly increases the sulfur adsorption capacity. Pd/LaMnO 3 sample accumulates significantly more sulfur than LaMnO 3 ; however it can also release a larger fraction of the accumulated SO x species in a reversible fashion at elevated temperatures in vacuum. This is not the case for Co-based materials, where thermal regeneration of bulk sulfates on poisoned LaCoO 3 and Pd/ LaCoO 3 is extremely ineffective under similar conditions. However, in the presence of an external reducing agent such as H 2 (g), Pd/LaMnO 3 requires much lower temperature (873 K) for complete sulfur regeneration as compared to that of Pd/LaCoO 3 (973 K). Sequential CO and SO x adsorption experiments performed via in situ FTIR indicate that in the presence of carbonyls and/or carbonates, Pd adsorption sites may have a stronger affinity for SO x as compared to that of the perovskite surface, particularly in the early stages of sulfur poisoning.
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