Aqueous O3 Research Articles

Degradation of di-n-butyl phthalate in aqueous solution by the O3/UV process

The degradation of di-n-butyl phthalate (DBP), which is a pollutant of concern in an aqueous environment, was investigated using the combination of ozonation with ultraviolet irradiation (O3/UV) in this study. Compared with either ozonation or UV irradiation, the hybrid system stimulated the O3 molecule photolysis and the hydroxyl radical (OH) generation; therefore, the DBP degradation through the pathway of OH attack was markedly reinforced. Since OH was a more vigorous oxidant than O3, both the kinetics of the DBP removal and the mineralization were increased. With the aqueous O3 fed rate of 4.03 mg/(L min), the spiked DBP molecules almost completely disappeared in 60 min, approximately 70% of which were converted into H2O and CO2. The effects of DBP concentration, aqueous O3 fed rate, and solution pH on the DBP degradation were also investigated. Pseudo-first-order kinetics model was able to depict the experimental data under different conditions. Eight intermediates were identified, and the DBP degradation by the O3/UV process was supposed to be mainly started with the OH attack to the aliphatic chains. Since the combination of O3 with UV benefits the complete decomposition of DBP and reduces the possible toxicity of the treated water, it is a promising process for DBP removal from an aqueous solution.

An environment friendly wet strip process for 193nm lithography patterning in BEOL applications

In semiconductor Back-End-of-Line (BEOL) processing, wet organic strippers have gained a renewed interest for removal of etched photoresist (PR) layers to replace plasma strip, which degrades porous low-k dielectrics. In this study we show how the characterization of 193-nm PR degradation by etch plasmas led to the development of an environment friendly wet strip using aqueous ozone solutions. Characterization of post-etch PR films have shown that degradation was similar to that of poly(methyl acrylate/methacrylate) (PMA/PMMA) by UV light, with formation of single and conjugated C?C bonds in PR chains. However little removal was obtained with O3/H2O strips without an organic solvent rinse, indicating reactions fragments were too long for a complete dissolution in water. In turn known effects of UV on PMA/PMMA were used to develop an optimized UV pre-treatment enabling a fully aqueous O3 strip. This process was shown to efficiently remove PR in a dual damascene application. Also we shortly discuss the impact of materials selection on process efficiency, improvement in low-k compatibility and transfer to a production environment.

Cr(VI) formation during ozonation of Cr-containing materials in aqueous suspension – implications for water treatment

Ozonation, or advanced oxidation processes (utilising ozone decomposition products as oxidants) are widely used in industrial wastewater and drinking water treatment plants. In these applications the use of ozone is based on ozone and its decomposition by-products being strong oxidants. In this paper, the possible oxidation of non-Cr(VI) Cr-containing materials suspended in water during ozonation, is presented. This study is of particular interest within the South African context, considering that South Africa holds the majority of global chromium ore resources and has the largest Cr-related industry in the world. Chromium also occurs commonly in other industrial waste materials and is a naturally-occurring element in the crust of the earth. Results indicated that in situ formation of Cr(VI) is possible during aqueous ozonation. pH had a significant influence, since the decomposition products of aqueous O3, i.e. hydroxyl radicals formed at higher pH levels, were found to be predominantly responsible for Cr(VI) formation. Increased ozonation contact time, water temperature and solid loading also resulted in higher Cr(VI) concentrations being formed.

Effects of Halides on Reaction of Nucleosides with Ozone

GRAPHICAL ABSTRACT Ozone (O3), a major component of photochemical oxidants, is used recently as a deodorizer in living spaces. It has been reported that O3 can directly react with DNA, causing mutagenesis in human cells and carcinogenesis in mice. However, little is known about the effects of coexistent ions in the reaction of O3. In the present study, we analyzed the effects of halides on the reaction of O3 with nucleosides using reversed-phase high-performance liquid chromatography with ultraviolet detection. When aqueous O3 solution was added to a nucleoside mixture in potassium phosphate buffer (pH 7.3), the nucleosides were consumed with the following decreasing order of importance: dGuo > Thd > dCyd > dAdo. The effects of addition of fluoride and chloride in the system were slight. Bromide suppressed the reactions of dGuo, Thd, and dAdo but enhanced the reaction of dCyd. The major products were 5-hydroxy-2′-deoxycytidine, 5-bromo-2′-deoxycytidine, and 8-bromo-2′-deoxyguanosine. The time course and pH dependence of the product yield indicated formation of hypobromous acid as the reactive agent. Iodide suppressed all the reactions effectively. The results suggest that bromide may alter the mutation spectrum by O3 in humans.

Survey of the yeast population inside wine barrels and the effects of certain techniques in preventing microbiological spoilage

Barrels play an important role in winemaking, giving wines a specific flavour and assisting the ageing process. However, the porosity and inertness of wood encourage the proliferation of spoilage yeasts which can severely affect wine quality. The yeast microbiota resident inside barriques located in a traditional Tuscan winery were identified by partial sequencing of the 26S rDNA gene. Most of them belonged to the Saccharomyces, Candida and Pichia genera, while Brettanomyces/Dekkera represented a limited part of the population. The ability of the isolated yeasts to spoil wine through the production of volatile phenols was evaluated. Brettanomyces showed significant production of ethylphenols, with a conversion rate of over 70%; many other species of yeast showed extensive production of vinylphenols, which can have a negative impact on wine quality. To improve the microbiological control of barrels, 4 treatments were tested for their efficacy in eradicating the yeast inside the barrels: aqueous steam (100 °C, 5–30-min treatment), UV irradiation (36-W lamp, 5–30-min treatment), gaseous O3 (40 mg/m3, 30-min treatment) and aqueous O3 (2 mg/L, 30-min treatment). Steam and O3 were the most effective treatments, eliminating about 70% of yeasts. UV appeared to be less effective, probably due to the porous nature of wood, which protects cells from direct irradiation.

Role of O3 and OH· Radicals in Ozonated Aqueous Solution for the Photoresist Removal of Semiconductor Fabrication

The role of direct oxidation by aqueous O3 and advanced oxidation by OH· in the removal of photoresist was studied by chemical kinetic simulation and experiments of O3 reactivity and decomposition in homogeneous aqueous solutions. O3 is the main species responsible for the removal of conventional photoresist in the ozonated water cleaning process, and the timing of initiator addition to ozonated water is important to maintain high O3 concentration. Simulation using t-butanol implies that maintenance of a high OH· concentration is required to remove highly implanted photoresists that O3 itself cannot easily remove.

On the Mechanism of the Decomposition of Acidic O3 Solutions, Thermally or H2O2-Initiated

Thermal or hydrogen peroxide initiated decomposition of acidic aqueous ozone is described as a chain process propagated by OH and O2-/HO2 radicals. In the absence of H2O2 added, the chain is initiated by surface-catalyzed formation of H2O2. Surface-dependent formation of H2O2 is experimentally verified. Since homogeneous radical−radical reactions are much too inefficient to account for the termination, a heterogeneous chain termination is strongly suggested. Without addition of H2O2 no dependence of the decay on the surface-to-volume ratio could be observed. However, on initial addition of H2O2 in amounts sufficient for homogeneous initiation to prevail, the rate of O3 decay becomes proportional to the surface of the reaction vessel. These findings strongly suggest that the decomposition of acidic aqueous O3 is governed by initiation and termination processes occurring at the reaction-vessel surface, while its apparent appearance of a homogeneous solution-phase reaction results from the counteractive natu...

Oxidation of Parachloronitrobenzene in Dilute Aqueous Solution by O3 + UV and H2O2+ UV : A Comparative Study

Abstract This laboratory study was designed to investigate the degradation of 4-chloronitrobenzene ([CNB] = 2.4 × 10−6 mol L−1; pH = 7.5) by H2O2/UV and by O3/UV oxidation processes which involve the generation of very reactive and oxidizing hydroxyl free radicals. The effects of the oxidant doses (H2O2 or aqueous O3), liquid flow rate (or the contact time), and bicarbonate ions acting as OH· radical scavengers on the CNB removal rates were studied. For a constant oxidant dose, the results show that the O3/UV system appears to be more efficient than the H2O2/UV system to remove CNB because of the greatest rate of OH· generation by ozone photodecomposition compared to H2O2 photolysis. However, for a given amount of oxidant decomposed, the H2O2/UV oxidant system was found to be more efficient than O3/UV. Moreover, high levels of bicarbonate ions in solution (4 × 10−3 mol L−1) significantly decrease the efficiency of CNB removal by H2O2/UV and by O3/UV oxidation processes.