BACKGROUND: Nitrogen doped titanium dioxide (N-TiO2), iron doped titanium dioxide (Fe-TiO2), and undoped titanium dioxide (TiO2) nanocatalysts were synthesized using sol-gel method aided with ultrasound (US). The effects of duty cycle, US-power, and US irradiation time on catalyst characteristics were investigated so as to establish the best synthesis conditions. RESULTS: The optimum parameters for minimum mean size of catalyst particles were 60% duty cycle, 100 W power, and 20 min as irradiation time. X-Ray diffraction (XRD) analysis revealed that the primary phase of all nanocatalysts was anatase with crystallite size as 46.29 nm, 54.32 nm, and 56.17 nm for N-TiO2, Fe-TiO2, and undoped TiO2, respectively. Field electron scanning electron microscopy (FE-SEM) images confirmed that N-TiO(2 )is a mixture of TiO(2)microspheres and rice-like structures whereas Fe-TiO(2 )and undoped TiO(2 )were spherical. X-ray photoelectron spectroscopy (XPS) study showed that both N-TiO(2 )and Fe-TiO(2 )exhibited minor shifts to lower binding energies when compared to the spectra of undoped TiO2. The application studies for obtained catalysts using simple ultrasonic horn and disc horn coupled with oxidants revealed best results (51.67% reduction in COD) using disc horn for N-TiO(2 )catalyst obtained using ultrasound at pH of 12 and addition of a 20 mL per L-1 dose of H2O2. CONCLUSION: Doping TiO(2 )with metal and non-metal ions coupled with using ultrasound in synthesis improved the catalytic activity with maximum COD reduction of commercial effluent obtained for disk horn + N-TiO2+ H(2)O(2 )based approach. (c) 2025 Society of Chemical Industry (SCI).

Synthesis of Fe-TiO2 and Ce-TiO2 catalysts using conventional, and ultrasound assisted (US) homogeneous coprecipitation method has been investigated. Effects of ultrasonic irradiation time and ultrasonic power on catalyst synthesis were studied and it was elucidated that best conditions were 140 W and 60 min, respectively. Characterization using FE-SEM revealed spherical particles with the size range from 36.4 to 49.4 nm whereas XRD analysis affirmed a mixture of anatase, rutile, and brookite TiO2 phase with crystallite size ranging from 4.18 to 12.99 nm. BET analysis revealed highest specific surface area (211.59 m(2)/g) for the sonochemically synthesized Ce-TiO2. The process intensification benefits demonstrated in catalyst synthesis were better crystallinity, lower particle size, and higher surface area. The application of catalyst efficacy was tested for photocatalytic, sonocatalytic, and sonophotocatalytic oxidation where maximum decolorization as 71.97% was obtained for sonochemically synthesized Ce-TiO2 applied in the sonophotocatalytic approach. Studies related to regeneration, stability, and leaching of Ce and Ti ion from the sonochemically synthesized Ce-TiO2 catalyst were also performed. It was observed that the catalyst can be regenerated easily and there were no structural changes in the catalyst after regeneration with negligible leaching of the ions from the catalyst into the solution. Overall, an improved process for catalyst synthesis with intensified decolorization application was demonstrated based on the use of ultrasound.

The present study investigates the treatment of real coke plant effluent utilising several ultrasound -based hybrid oxidation approaches including Ultrasound (US) alone, US + catalyst, US + H2O2, US + Fenton, US + Ozone, and US + Peroxone, with main objective as maximizing the reduction of chemical oxygen demand (COD). Ultrasonic horn at power of 130 W, frequency as 20 kHz and duty cycle as 70% was applied. Study with varying catalyst (TiO2) dose from 0.5 g/L - 2 g/L revealed 1 g/L as the optimum dose resulting in 65.15% reduction in COD. A 40 ml/L dose of H2O2 was shown to be optimal, giving an 81.96% reduction in COD, based on the study of varied doses of H2O2 from 20 ml/L to 60 ml/L. US + Fenton reagent combination at optimum Fe2+/H2O2 (w/v) ratio of 1:1 resulted in a COD reduction of 85.29% whereas reduction of COD as 81.75% was obtained at the optimum flow rate of ozone as 1 LPM for US + Ozone approach. US + Peroxone demonstrated the best efficiency (90.48%) for COD reduction. To find the toxicity effects, the treated (US + peroxone) and non -treated samples were tested for the growth of bacterial cultures. It was observed that the toxicity of the treated sample increased only marginally after treatment. High -resolution liquid chromatography mass spectrometry (HR-LCMS) analysis was also performed to establish intermediate compounds. Overall, the coupling of ultrasound with oxidation processes produced better results with US + Peroxone established as best treatment approach for coke plant effluent.

In recent years, research on improving the synthesis of catalysts has been at the forefront because of advancements in nanotechnology and greener conventions. Using ultrasound (US) during nanocatalysts synthesis is one of the green approaches that can yield improved catalyst characteristics under conditions of shorter reaction time and requirement of low temperature and pressure. The current paper aims at giving an insight into US-assisted synthesis (emphasized on sol-gel and hydrothermal) of different metal oxide nanocatalysts. It has been elucidated that US-assisted synthesis gives nanocatalyst with narrower particle size distribution with lower mean size, higher surface area, better morphology with less agglomeration, and higher catalytic activity. Ultrasound has thus been demonstrated to yield improvements in morphological, optical, and electronic properties of the nanocatalysts, however, scalability and industrial application of sonochemical synthesis have not been seen very popular. Some guidelines for future research into the development of novel nanocatalysts and industrial scale-up studies are also provided. The review also summarizes the application of these metal oxides as photocatalysts for dye degradation or effluent treatment containing dyes, highlighting the fundamentals of photocatalysis as well. A comparative study has been reported for catalysts obtained using the US-assisted synthesis and conventional synthesis of the photocatalysts in terms of catalytic activity. The benefits of using ultrasound-assisted synthesis in terms of higher photocatalytic degradation have been clearly demonstrated.

Treatment of real textile industry effluent using photocatalysis, sonocatalysis, sonophotocatalysis and H2O2 assisted sonophotocatalysis have been studied based on the use of Ce-TiO2 nanocatalyst synthesized using sonochemical co-precipitation method. Characterization studies of the obtained catalyst revealed crystallite size as 1.44 nm with particles having spherical morphology. A shift of the absorption edge to the visible light range was also observed in UV-Vis diffuse reflectance spectra (UV-DRS) analysis. The effects of different operational parameters viz catalyst dose (0.5 g/L-2 g/L), temperature (30 degrees C-55 degrees C) and pH (3-12) on the COD reduction were studied. The reduction in the COD was higher at lower pH and the optimum temperature established was 45 degrees C. It was also elucidated that the required catalyst dose was lesser in combined sonophotocatalysis when compared with individual photocatalysis and sonocatalysis. Combination of processes and addition of oxidants increased the COD reduction with the sonophotocatalytic oxidation combined with H2O2 treatment showing the best results for COD reduction (84.75%). The highest reduction in COD for photocatalysis was only 45.09% and for sonocatalysis, it was marginally higher at 58.62%. The highest reduction in COD achieved by sonophotocatalysis was 64.41%. Toxicity tests coupled with Liquid Chromatography Mass Spectrometry (LC-MS) analysis revealed that there were no additional toxic intermediates added to the system during the treatment. Kinetic study allowed establishing that generalized kinetic model fits the experimental results well. Overall, the combined advanced oxidation processes showed better results than the individual processes with higher COD reduction and lower requirement of the catalyst.

Ultrasound (US)-assisted synthesis of a N-doped TiO2 catalyst supported on magnetically separable Fe3O4@ZnO particles and its subsequent application for catalytic desulfurization were performed in the present work. The catalyst was also synthesized conventionally to compare the role of acoustic cavitation (US horn working at 20 kHz frequency) in improving the catalyst characteristics. The effects of different ultrasonic (US) power (80 W to 120 W) and duration (15 min to 75 min) were studied to elucidate the best operating conditions for obtaining the minimum particle size of the catalyst. Under optimal conditions of 80 W power and 30 min of time, a minimum particle size of 31.22 μm was obtained. The particle size for the conventionally synthesized catalyst was 806.4 µm, confirming that the particles were agglomerated in the absence of ultrasound. The synthesized catalyst was used for the desulfurization of thiophene to assess the performance of the catalyst, along with a comparative study between the conventionally synthesized catalyst and that obtained using the US-assisted approach. It was evident that the performance of the catalyst synthesized sonochemically was superior, as US enhanced the activity of the catalyst by reducing the particle size and achieving homogeneity. The desulfurization achieved using the sonochemically synthesized catalyst was 47% in 100 min at a 2 g/L catalyst dose and a 3 mL/L H2O2 dose. The desulfurization was only 25% using the conventionally synthesized catalysts under the same operating conditions. Overall, the present work demonstrates the advantages of US in improving the catalyst characteristics, as well as the successful application of catalyst in desulfurization.

Photocatalysis is an environment friendly method that can be applied to degrade various organic hazardous pollutants in wastewater. Owing to the limitations of conventional semiconductor oxide-based catalysts, especially in terms of limited applicability in the visible ultraviolet (UV) or the solar regions, interest into development of improved photocatalysts has increased over the recent years. Modified photocatalysts such as different nanocomposites reduce the bandgap of single materials and also reduces the process of electron-hole recombination, giving higher efficacy for the application. This chapter deals with the basic mechanism of photocatalysis initially and highlights the different types of nanocomposite photocatalysts that have been applied for wastewater treatment. The effects of important operating parameters such as catalyst loading, pH of solution, irradiation time, light intensity, reaction temperature, pollutant concentrations, and size and structure of photocatalysts on the extent of removal of pollutants have also been discussed. Photodegradation typically increases with an increase in catalyst loading, irradiation time, and reaction temperature, whereas a lower pollutant concentration is considered beneficial for photocatalysis. In addition to effect of operating conditions on the efficacy of degradation, an overview on recent trends in photocatalytic reactors has been presented. Different illustrations of nanocomposites highlighting their potential use in wastewater treatment have also been presented. It is generally observed that nanocomposites are better photocatalysts than pure nanoparticles giving higher efficacies for pollutant removal.

•Sensitivity, Selectivity and stability of Semiconductor Metal Oxide (SMO) gas sensors are studied.•Properties and gas sensing mechanisms of SMOs are discussed in detail.•Mechanisms of dopant induced variations in SMOs to improve the gas sensing properties are reviewed.