Electro-catazone treatment of an ozone-resistant drug: Effect of sintering temperature on TiO2 nanoflower catalyst on porous Ti gas diffuser anodes

Electrochemical heterogeneous catalytic ozonation (E-catazone) is a promising and advanced oxidation technology that uses a titanium dioxide nanoflower (TiO_2-NF)-coated porous Ti gas diffuser as an anode material. Our previous study has highlighted that the importance of the TiO_2-NF coating layer in enhancing OH production and rapidly degrading O₃-resistant drugs. It is well known that the properties of TiO_2-NF are closely related to its sintering temperature. However, to date, related research has not been conducted in E-catazone systems. Thus, this study evaluated the effect of the sintering temperature on the degradation of the O₃-resistant drug para-chlorobenzoic acid (p-CBA) using both experimental and kinetic modeling and revealed its influence mechanism. The results indicated that the TiO_2-NF sintering temperature could influence p-CBA degradation and OH production. TiO_2-NF prepared at 450 °C showcased the highest p-CBA removal efficiency (98.5% in 5 min) at a rate of 0.82 min⁻¹, and an OH exposure of 8.41 × 10⁻¹⁰ mol L⁻¹ s. Kinetic modeling results and interface characterization data revealed that the sintering temperature could alter the TiO₂ crystallized phase and the content of surface-adsorbed oxygen, thus affecting the two key limiting reactions in the E-catazone process. That is, ≡TiO₂ surface reacted with H₂O to form TiO₂-(OH)₂, which then heterogeneously catalyzed O₃ to form OH. Consequently, E-catazone with a TiO_2-NF anode prepared at 450 °C generated the highest surface reaction rate (5.00 × 10⁻¹ s⁻¹ and 4.00 × 10^-3 L mol^-1 s⁻¹, respectively), owing to its higher anatase content and adsorbed oxygen. Thus, a rapid O₃-TiO₂ reaction was achieved, resulting in an enhanced OH formation and a highly effective p-CBA degradation. Overall, this study provides novel baseline data to improve the application of E-catazone technology.     

Ozone-based electrochemical advanced oxidation processes

Novel processes have recently been developed that provide for the enhancement of ozonation through combination with electrochemical treatments. These are processes that can be included among those defined as advanced oxidation processes as they proceed via electrogeneration of highly oxidizing radical species.These processes are generally carried out by sparging ozone in both divided and undivided electrochemical cells in order to promote its decomposition through different mechanisms, depending on the electrode materials adopted, and in some cases still debated.This mini review presents the most recent advances in the field of electrochemically assisted ozonation.In particular, the first section is focused on the process known as electroperoxone (EP) where the ozone decomposition is enhanced by the adoption of carbon-based cathodes, due to the electrogeneration of hydrogen peroxide, while the second section is focused on the process that implies ozonation in a cell adopting metal-based cathodes.     

Application of hybrid oxidative processes based on cavitation for the treatment of commercial dye industry effluents

The present work demonstrates the significant role of ultrasound (US) in intensifying the efficacy of the combination with Fenton reagent and/or ozone for the treatment of real dye industry industrial effluent procured from the local industry. Initial part of the work focused on analysing the literature based on combination approaches of US with different oxidants applied for the treatment of real and simulated effluents focusing on the dyes. The work also provides guidelines for the selection of optimal operating parameters for maximizing the intensification of the degradation. The second part of the work presents an experimental study into combined approaches of ultrasound with ozone (O₃) and Fenton’s reagent for treatment of real effluent. Under optimized conditions (100 W, 20 kHz and duty cycle of 70%), maximum COD reductions of 94.79% and 51% were observed using a combined approach of US + Fenton oxidation followed by lime treatment for the treatment of effluent-I and effluent-II respectively at H₂O₂ loading of 17.5 g/L, H₂O₂/Fe²⁺ ratio of 3, pH of 4, CaO dose of 1 g/L and an overall treatment time of 70 min. US + Fenton + O₃ followed by lime was also applied for treatment under ozone loading of 1 g/h for the treatment of effluent-I and it was found that maximum COD reduction of 95.12% was obtained within 30 min of treatment time, indicating use of ozone did not result in significant value addition in terms of COD reduction but resulted in faster treatment. HC (inlet pressure: 4 bar) + Fenton + Lime scheme was successfully replicated on a pilot-scale resulting in maximum COD reduction of 57.65% within 70 min of treatment time. Overall, it has been concluded that the hybrid oxidative processes as US + Fenton followed by lime treatment is established as the best approach ensuring effective COD reduction at the same time obtaining final colourless/reusable effluent.     

New synthesis methods for fluorinated carbon nanofibres and applications

Several new synthesis methods of fluorinated carbon nanofibres, such as controlled fluorination using fluorinating agent (TbF₄ or XeF₂), or assisted fluorination under UV and gamma irradiation, are reviewed and compared with the direct fluorination using undiluted fluorine gas. The results highlight the different fluorination mechanisms for the direct fluorination and the new methods. The other advantage of those alternative fluorination routes is the possibility to provide fine tuning of the fluorination level, i.e. from F/C atomic ratio close to zero, as a functionalization, to the unity (CF₁) according to the required application, electrochemical or tribological. Two applications are described in this paper as a function of the fluorine content: protection against ozonation and use as solid lubricants.     

Kinetics and products of ozonation of C.I. Reactive Red 195 in a semi-batch reactor

Textile wastewater shows great threats to the environment if not well pretreated before discharge. A promising technique, ozonation, was applied to remove the color in dye solutions containing C.I. Reactive Red 195 (RR195) in a semi-batch reactor. The decolorization of RR195 by the ozone process followed pseudo-first-order kinetics. Several factors which influenced the efficiency of decolorization were studied and the reaction rate constant (k) obtained with different operational parameters was compared. Our results showed that RR195 was more easily degraded in acidic than in alkaline conditions. The dyeing auxiliaries (sodium carbonate and sodium chloride) that acted as radical scavengers could enhance the decolorization process, and the ozonation time for total color removal lengthened if the initial dye concentration was higher. The analysis of the ozonation products was performed by liquid chromatography-tandem mass spectrometer and a possible degradation pathway was predicted according to the ozonation products and structure of RR195. Our results indicated that ozonation was effective in the color removal of dyes, but further treatment might be necessary since the ozonation products are high toxic.     

Generation of Singlet Oxygen from Ozone Catalysed by Phosphinoferrocenes

Summary. A novel chemical source of singlet oxygen based on the conversion of ozone by 1,1-bis(triphenylphosphino)ferrocene as catalyst was developed into a feasible method for a preperative scale. This is, to our best knowledge, the first application of substituted ferrocenes as oxidation catalysts.     

Sonozonation (sonication/ozonation) for the degradation of organic contaminants – A review

Ozonation (OZ) is an important advanced oxidation process to purify water and wastewater. Because of the lower solubility and instability of ozone (O₃), selective oxidation and dependence on pH value, the industrial applications of OZ have been hindered by the following disadvantages: incomplete removal of pollutants, lower mineralization efficiency and the formation of toxic by-products. Meanwhile, OZ seems to have higher processing costs than other technologies. To improve the treatment efficiency and O₃ utilization, several combined processes, such as H₂O₂/O₃, UV/O₃, and Cavitation/O₃, have been explored, while the combined method of ultrasonication (US) with OZ is a promising treatment technology with a complex physicochemical mechanism. In US alone, the sonolysis of water molecules can produce more powerful unselective oxidant hydroxyl radicals (OH), and directly cause the sonochemical pyrolysis of volatile pollutants. In US/OZ, US can promote the mass transfer of O₃, and also drive the chemical conversion of O₃ to enhance the formation of OH. Various layouts of US/OZ devices and the interactive effects of US/OZ (synergism or antagonism) on the degradation of various organics are illustrated in this review. The main factors, including US frequency, pH value, and radical scavengers, significantly affect the mass transfer and decomposition of O₃, the formation of OH and H₂O₂, the degradation rates of organics and the removal efficiencies of COD and TOC (mineralization). As a result, US can significantly increase the yield of OH, thereby improving the degradation efficiency and mineralization of refractory organics. However, US also enhances the decomposition of ozone, thereby reducing the concentration of O₃ in water and impairing the efficiency of selective oxidation with O₃ molecules.     

Mechanism and dynamic study of reactive red X-3B dye degradation by ultrasonic-assisted ozone oxidation process

The effectiveness of ozone combined with ultrasound techniques in degrading reactive red X-3B is evaluated. A comparison among ozone (O₃), ultrasonic (US), ozone/ultrasonic (O₃/US) for degradation of reactive red X-3B has been performed. Results show that O₃/US system was the most effective and the optimally synergetic factor reaches to 1.42 in O₃/US system. The cavitation of ultrasound plays an important role during the degradation process. It is found that 99.2% of dye is degraded within 6 min of reaction at the initial concentration of 100 mg·L⁻¹, pH of 6.52, ozone flux of 40 L·h⁻¹ and ultrasonic intensity of 200 W·L⁻¹. Ozonation reactions in conjunction with sonolysis indicate that the decomposition followed pseudo-first-order reaction kinetics but the degradation efficiencies are affected by operating conditions, particularly initial pH and ultrasonic intensity. A kinetic model is established based on the reaction corresponding to operational parameters. In addition, the main reaction intermediates, such as p-benzoquinone, catechol, hydroquinone, phthalic anhydride and phthalic acid, are separated and identified using GC/MS and a possible degradation pathway is proposed during the O₃/US process.     

Effective removal of organics from Bayer liquor through combined sonolysis and ozonation: Kinetics and mechanism

The presence of organic compounds in the waste liquor is of serious environmental concern that has plagued the development of alumina industry (Bayer Process). The present work attempts to develop a green and efficient process for removal of organics utilizing combined effect of sonolysis and ozonation (US/O₃). The effects of reaction duration, ozone concentration and ultrasonic power are assessed for sonolysis (US), ozonation (O₃) and combination of sonolysis and ozonation (US/O₃). The optimal conditions for US/O₃ treatment system is identified to be a reaction duration of 7 h, ozone concentration of 7.65 g/h, and ultrasonic power of 600 W. The total organic carbon (TOC) removal and decolorization are 60.13% and 87.1%, respectively. The process can be scaled-up to industrial scale, which could potentially serve to be a convenient, safe and sustainable alternative to the exisiting treatment technologies. Additionally, the treated waste water can be reused contributing to an improvement in the overall economics.     

REMOVAL AND RECOVERY OF DYESTUFFS FROM DYEING WASTEWATERS

The toxic nature of some dyestuffs (DSs) has long been recognized. Accordingly, dyeing wastewaters represent a source of water contamination, and should be treated in some way so as to reduce the concentration of the polluting DSs to permissible limits, prior to dumping its wastewater. In addition, some DSs can be recovered for reuse, a point which should represent saving in the overall cost of the dyeing process. Extensive publications on the removal of DSs from dye house wastewaters have been cited in the literature in which many techniques have been applied, biological treatment being the method most widely used as a primary treatment. However, only few publications have been concerned with recovery of DSs from their wastewaters. In the present paper, numerous techniques, if not all, that are presently used for either removal or recovery of DSs have been reviewed, evaluated and compared.