| Περίληψη: | Over the last three decades there has been increasing global concern over the public health impacts attributed to environmental pollution. It is estimated that about a quarter of the diseases facing mankind today occur due to prolonged exposure to environmental pollution, which in many ways, water pollution is as serious - if not more so - than air contamination. Thousands of industrial and natural chemicals are daily discharged into the aquatic environment that some of them are not only toxic but also partly biodegradable; therefore they are not easily and completely removed in conventional wastewater treatment plants. Although most of them are present at low concentrations, but many of these micro-pollutants raise considerable toxicological concerns, particularly when present as components of complex mixtures in the texture of living organisms.
Advanced oxidation processes are set of the emerging treatment technologies for this purpose, in which developing photo-chemical processes, especially photo-catalysis via solar driven semiconductor photo-catalysts are more desirable because of using solar energy as a free, clean and renewable energy that will be present to last us indefinitely. Although relevant inorganic semiconductors are often non-toxic, cheap and abundant, but not all of them good enough in absorbing solar irradiation, quantum efficiency and chemical stability together. Designing hetero-structure semiconductor catalysts is one of the strategies in order to overcome mentioned problem, in which at least two semiconductors with different characteristics are joined to each other to enhance strengths and/or to improve weaknesses of them.
By the same token, in this research Degussa-P25 TiO2 that is famously known as an efficient catalyst in UV range with a high chemical stability and reusability, was added to the structure of Silver Orthophosphate (Ag3PO4) that is an efficient catalyst in visible range with a high quantum yield (90%) and high photo-catalytic activity, in order to boost both photo-catalytic activity and stability of them, as a novel synthesized solar driven composite photo-catalyst for degradation of Bisphenol A as a serious micro-pollutant in water.
BPA as one of the most famous endocrine disruptor chemical that has possible hazards to fetuses, infants, young children, and has been associated with congenital defects, reduced fertility, and several diseases such as neural circuit’s distress, obesity, diabetes mellitus, and cancer in humans, is widely known for its tendency to leach from polycarbonate plastics and epoxy resins, particularly those found in food packaging industries, drinking water bottles, foods and beverages tin/steel/aluminum cans, food and beverage containers, baby bottles, etc., which has made it a subject of public health and environmental concern.
In this project, photo-catalytic degradation of BPA under full spectrum simulated solar light irradiation has been studied in different conditions, including different types of catalyst, dark adsorption, different types of radiation, different concentration of the composite catalyst, different concentration of BPA, different pH and different water matrices. Also photo-catalytic activity and stability of the composite catalyst were checked during sequential runs.
The optimum ratio of Ag3PO4/TiO2 for the composite catalyst was defined 3:1 that showed higher photo-catalytic activities in comparison to its two components, under all three types of irradiation including simulated solar and its UV and visible parts, also it showed much higher efficiency under real solar irradiation. The optimum required time for appropriate adsorption of BPA at the surface of the composite catalyst under dark condition was defined 15 minutes. Full conversion of BPA under simulated solar irradiation was observed in 7.5 minutes that follows a pseudo-first order reaction kinetics with respect to initial concentration of BPA, whereas the kinetic constant decreases as the initial concentration of BPA increases. Also with increasing the catalyst concentration, BPA degradation was increased considerably. Photo-catalytic degradation of BPA in acidic pH was noticeably more efficient than in alkaline pH, whereas high pH had detrimental effects on the composite catalyst. In presence of Humic acid as a ubiquitous troublesome oxidant consumer in water matrices, efficiency reduction was not observed in photo-catalytic degradation of BPA, and also the same happened in presence of Sodium bicarbonate as a radical scavenger, which was beyond expectation for both. Full degradation of BPA in drinking bottled water containing different inorganic ions that act as radical scavengers and catalyst deactivators, was observed in 10 minutes, which looks acceptable; but degradation of BPA in secondary wastewater treatment effluent was not efficient at all, whereas only 66.5% conversion was observed after 8 hours. Furthermore, photo-catalytic stability/activity of the composite photo-catalyst was enhanced in comparison to pure silver phosphate, after 5 consecutive runs of BPA photo-catalytic degradation, also it was found that such composite photo-catalyst appeared to be a somewhat more desirable in repeated and/or long-term application under visible part of simulate solar irradiation.
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