Asu Ziylan Yavas

Elimination/mineralization of paracetamol (PCT) was investigated by catalytic oxidation under ultrasound, UV and both. The catalyst was synthesized by immobilization of nPt on TiO2 to benefit from the ability of Pt to facilitate charge transfer processes and to separate e(-)/h(+) pairs. It was found that increasing the Pt-loading enhanced the rate of sonochemical reactions, but retarded that of photolytic reactions, due to reduced UV absorption on the surface. Simultaneous application of sonolysis and photolysis was synergistic due to disaggregation of the particles and homogenization of the active species over the catalyst surface. The decay of PCT was highly dependent on the availability of center dot OH, as the reactions were nearly terminated in the presence of a strong center dot OH scavenger-2-propanol. However, a remarkable rate enhancement was observed in the presence of a suitable dose of I-, which scavenges both center dot OH and h(vb)(+). The result was explained by the production of excess radicals upon sonolysis of iodide solutions, and the reactivity of PCT with them. Finally, carbon mineralization was significantly hindered in the presence of both scavengers due to increased competition for center dot OH and inefficient formation of hydroquinone arising from reduced availability of h(vb)(+)

Advanced oxidation processes (AOPs) are based on the in situ production of hydroxyl radicals (center dot OH) and reactive oxygen species (ROS) in water upon irradiation of the sample by UV light, ultrasound, electromagnetic radiation, and/or the addition of ozone or a semiconductor. Diclofenac (DCF), one of the emerging organic contaminants (EOC), is of environmental concern due to its abundancy in water and is known to be subjected to AOPs. The current study uses density functional theory (DFT) to elucidate the mechanisms of the reactions between center dot OH and DCF leading to degradation by-products, P1-P9. The initial encounter of DCF with center dot OH is proposed to lead to either the abstraction of a hydrogen or the addition of the hydroxyl radical to the molecule. The results showed that OH addition radicals (R-add) are both kinetically and thermodynamically favored over H abstraction radicals (R-abs). The intermediate radicals give degradation by-products by subsequent reactions. The by-products P7 and P8 are easily formed in agreement with experimental findings. Finally, acute toxicities at three trophic levels are estimated with the Ecological Structure Activity Relationships program. DCF and most of the by-products were found to be harmful to aquatic organisms, P9 being the only by-product that is not harmful at all three trophic levels.

The study is the assessment of commercial gamma-Al2O3 and its sonolytically modified nanocomposite in catalytic ozonation of paracetamol (PCT), which is an emerging water contaminant and a highly reactive compound with ozone. The results showed that commercial alumina was ineffective regardless of the solution pH, due to the low affinity of the catalyst surface for PCT and the high reactivity of the solute with molecular ozone. The modified catalyst, which was synthesized by decoration of the original surface with nanoparticles of platinum provided considerable improvement in the performance of the catalyst, particularly in mineralization of the target compound. The presence of (OH)-O-center dot scavenging agents in solution markedly retarded the rate of PCT oxidation and organic carbon decay, to signal the importance of radical-mediated reaction mechanisms on the degradation of the compound. Finally, the attempt to accelerate the reactions by running them in the presence of ultrasound was found inadequate for the early oxidation, but highly adequate for the longer mineralization process. The failure was attributed to the diffusion of a large fraction of ozone into the gaseous cavity bubbles (reduced probability of direct reactions) and the extreme conditions of cavitation collapse that partially damaged the catalyst surface. The success (in mineralization) was explained by the shift of the reaction site from the bulk solution (poor adsorption on catalyst surfaces) to the solid surface and the gaseous cavity bubbles (via enhanced hydrophobicity), both being considerably more active reaction media

The study is about the assessment of single and multi-frequency operations for the overall degradation of a widely consumed analgesic pharmaceutical-ibuprofen (IBP). The selected frequencies were in the range of 20-1130 kHz emissions coming from probes, baths and piezo-electric transducers attached to plate type devices. Multi-frequency operations were applied either simultaneously as "duals", or sequentially at fixed time intervals; and the total reaction time in all operations was 30-min. The work also covers evaluation of the effect of zero-valent iron (ZVI) on the efficiency of the degradation process and the performance of the reaction systems. It was found that low-frequency probe type devices especially at 20 kHz were ineffective when applied singly and without ZVI, and relatively more effective in combined-frequency operations in the presence of ZVI. The power efficiencies of the reactors and/or reaction systems showed that 20-kHz probe was considerably more energy intensive than all others, and was therefore not used in multi-frequency operations. The most efficient reactor in terms of power consumption was the bath (200 kHz), which however provided insufficient mineralization of the test chemical. The highest percentage of TOC decay (37%) was obtained in a dual-frequency operation (40/572 kHz) with ZVI, in which the energy consumption was neither low nor exceptionally too high. A sequential operation (40 + 200 kHz) in that respect was more efficient, because it required much less energy for a similar TOC decay performance (30%). In general, the degradation of IBP increased with increased power consumption, which in turn reduced the sonochemical yield. The study also showed that advanced Fenton reactions with ZVI were faster in the presence of ultrasound, and the metal was very effective in improving the performance of low-frequency operations.

The increased use of engineered nanoparticles in various applications such as electronics and biomedical engineering has raised concerns about their impact on human health and the environment. In this study we investigate the fate and transport in porous media of super paramagnetic iron oxide (SPIO) nanoparticles surface coated with poly acrylic acid for size stabilization. The nanoparticle size distribution was first analyzed to assess the effect of dilution on the particle size. It was found that the poly acrylic acid is generally effective in stabilizing the size of the nanoparticles, except for highly diluted solutions. Sorption batch experiments performed at different pH values showed that the SPIO nanoparticles did not adsorb significantly on sand. Transport experiments were conducted in a sand-packed column for different SPIO injection concentrations and for upwards and downwards flow conditions. Comparison of the nanoparticle breakthrough curves to that of a conservative tra...

The study is about a novel method of decomposing and mineralizing the emerging contaminant ibuprofen (IBP) by catalytic ozonation using catalysts such as high-frequency ultrasound (US) and soluble/insoluble Fe-bearing species. Preliminary experiments with single processes were run to select the optimum values of IBP concentration, O3 flow rate and specific US power as 50 uM, 12mgmin−1,and 0.23 WmL−1, respectively. It was found that the most critical operation parameter was pH, as it controlled the mass transfer and decomposition of O3, as well as the diffusion of solutes from the bulk solution to the gas–liquid
and solid–liquid interfaces. As such, ozonation and sonication alone were most effective at pH 9.0 and 3.0, respectively owing to the higher rate of •OH production and gas–liquid interfacial reactions at these conditions. Catalytic ozonation with Fe-bearing species but no ultrasound was most effective at pH 6.5, with
a maximum degree of IBP decay in the presence of FeSO4. Catalytic ozonation with ultrasound and solid particles was effective at pH 6.5, but maximum degree of oxidation/mineralization was obtained with nanoparticles of zero-valent iron (ZVI) at pH 3.0 (100%,58%). The synergy of US+ZVI at acidic pH was attributed to: (i) the massive surface areas enriched with extensive reaction and nucleation sites, (ii) the role
of reactive Fe (furnishing out from the metal core onto the catalyst surface) and reactive oxygen species as promoters of Fenton-like reactions, and (iii) the contribution of hydrodynamic shear forces to continuous enhancement and cleaning of the catalytic surfaces.

The study is about pre-treatment of water by O3-based AOPs as O3/UV, O3/ultrasound (O3/US), O3/H2O2, O3/UV/US and O3/US/FeSO4 to remove residuals of anti-inflammatory pharmaceuticals and to propose a simple modification to an existing drinking water treatment plant (WTP) containing a pre-ozonation unit. Experiments were run in ultrapure and raw water (collected from the aeration tank of the WTP) spiked with 30 μM Diclofenac-Na (DCF)-the model compound to represent anti-inflammatory medication. The results showed that the most effective test processes were O3/US/UV and O3/US/Fe2+ (at 2-8 mgL-1 O3, 861 kHz US, 254 nm UV irradiation) that were significantly more effective than ozonation alone or other combinations. The outcome was attributed to the synergy of excess mass transfer and OH radical formation rates, and the presence of additional reaction routes and species. As such, 10-min pre-treatment of pure water by O3/UV/US and O3/US/Fe2+ provided nearly 90% DCF conversion; 26% and 46% mineralization, respectively; whereas the efficiency of conversion was slightly lower in raw water, but that of mineralization was considerably higher (55% and 58%, respectively). The outstanding performance of the processes for mineralization in raw water was attributed to the synergy of the combinations leading the interaction of excited NOM fragments with the intermediate products of DCF, followed by oxidative degradation of all to yield CO2. Coagulation/flocculation of the pretreated streams (of raw water) with alum and without chemicals respectively provided DCF-free water and about 65% DOC mineralization. Hence, integration of the existing water treatment facility with either of the above processes is an excellent option to destroy anti-inflammatory pharmaceutical residues such as DCF and to provide appreciable DOC elimination, thus lowering the probability of THM formation in the distribution system. An additional benefit offered by the second process using a ferrous salt was that it allowed for a chemical-free coagulation basin.