Enhanced electrochemical decontamination and water permeation of titanium suboxide reactive electrochemical membrane based on sonoelectrochemistry

Reactive electrochemical membrane (REM) allows electrochemical oxidation (EO) water purification under flow-through operation, which improves mass transfer on the anode surface significantly. However, O₂ evolution reaction (OER) may cause oxygen bubbles to be trapped in small-sized confined flow channels, and thus degrade long-term filterability and treatability of REM. In this study, ultrasound (ultrasonic vibrator, 28 kHz, 180 W) was applied to EO system (i. e. sonoelectrochemistry) containing titanium suboxide-REM (TiSO-REM) anode for enhanced oxidation of 4-chlorophenol (4-CP) target pollutant. Both experimental and modeling results demonstrated that ultrasound could mitigate the retention of O₂ bubbles in the porous structures by destructing large-size bubbles, thus not only increasing permeate flux but also promoting local mass transfer. Meanwhile, oxidation rate of 4-CP for EO with ultrasound (EO-US, 0.0932 min⁻¹) was 216% higher than that for EO without ultrasound (0.0258 min⁻¹), due to enhanced mass transfer and OH production under the cavitation effect of ultrasound. Density functional theory (DFT) calculations confirmed the most efficient pathway of 4-CP removal to be direct electron transfer of 4-CP to form [4-CP]⁺, followed by subsequent oxidation mediated by OH produced from anodic water oxidation on TiSO-REM anode. Last, the stability of TiSO-REM could be improved considerably by application of ultrasound, due to alleviation of electrode deactivation and fouling, indicated by cyclic test, scan electron microscopy (SEM) observation and Fourier transform infrared spectroscopy (FT-IR) characterization. This study provides a proof-of-concept demonstration of ultrasound for enhanced EO of recalcitrant organic pollutants by REM anode, making decentralized wastewater treatment more efficient and more reliable.     

Sonocatalytic injury of cancer cells attached on the surface of a nickel–titanium dioxide alloy plate

The present study demonstrates ultrasound-induced cell injury using a nickel–titanium dioxide (Ni–TiO₂) alloy plate as a sonocatalyst and a cell culture surface. Ultrasound irradiation of cell-free Ni–TiO₂ alloy plates with 1 MHz ultrasound at 0.5 W/cm² for 30 s led to an increased generation of hydroxyl (OH) radicals compared to nickel–titanium (Ni–Ti) control alloy plates with and without ultrasound irradiation. When human breast cancer cells (MCF-7 cells) cultured on the Ni–TiO₂ alloy plates were irradiated with 1 MHz ultrasound at 0.5 W/cm² for 30 s and then incubated for 48 h, cell density on the alloy plate was reduced to approximately 50% of the controls on the Ni–Ti alloy plates with and without ultrasound irradiation. These results indicate the injury of MCF-7 cells following sonocatalytic OH radical generation by Ni–TiO₂. Further experiments demonstrated cell shrinkage and chromatin condensation after ultrasound irradiation of MCF-7 cells attached on the Ni–TiO₂ alloy plates, indicating induction of apoptosis.     

Insight into the impact of excluding mass transport,heat exchange and chemical reactions heat on the sonochemical bubble yield: Bubble size-dependency

Numerical simulations have been performed on a range of ambient bubble radii, in order to reveal the effect of mass transport, heat exchange and chemical reactions heat on the chemical bubble yield of single acoustic bubble. The results of each of these energy mechanisms were compared to the normal model in which all these processes (mass transport, thermal conduction, and reactions heat) are taken into account. This theoretical work was carried out for various frequencies (f: 200, 355, 515 and 1000 kHz) and different acoustic amplitudes (P_A: 1.5, 2 and 3 atm). The effect of thermal conduction was found to be of a great importance within the bubble internal energy balance, where the higher rates of production (for all acoustic amplitudes and wave frequencies) are observed for this model (without heat exchange). Similarly, the ignorance of the chemical reactions heat (model without reactions heat) shows the weight of this process into the bubble internal energy, where the yield of the main species (OH, H, O and H₂) for this model was accelerated notably compared to the complete model for the acoustic amplitudes greater than 1.5 atm (for f = 500 kHz). However, the lowest production rates were registered for the model without mass transport compared to the normal model, for the acoustic amplitudes greater than 1.5 atm (f = 500 kHz). This is observed even when the temperature inside bubble for this model is greater than those retrieved for the other models. On the other hand, it has been shown that, at the acoustic amplitude of 1.5 atm, the maximal production rates of the main species (OH, H, O and H₂) for all the adopted models appear at the same optimum ambient-bubble size (R₀ ~ 3, 2.5 and 2 µm for, respectively, 355, 500 and 1000 kHz). For P_A = 2 and 3 atm (f = 500 kHz), the range of the maximal yield of OH radicals is observed at the range of R₀ where the production of OH, O and H₂ is the lowest, which corresponds to the bubble temperature at around 5500 K. The maximal production rate of H, O and H₂ is shifted toward the range of ambient bubble radii corresponding to the bubble temperatures greater than 5500 K. The ambient bubble radius of the maximal response (maximal production rate) is shifted toward the smaller bubble sizes when the acoustic amplitude (wave frequency is fixed) or the ultrasound frequency (acoustic power is fixed) is increased. In addition, it is observed that the increase of wave frequency or the acoustic amplitude decrease cause the range of active bubbles to be narrowed (scenario observation for the four investigated models).     

Ultrasound-engineered synthesis of WS2@CeO2 heterostructure for sonocatalytic degradation of tylosin

The main aim of the present investigation was the intercalation of WS₂ nanosheets in the structure of ceria (CeO₂) to be used for the efficient catalytic destruction of tylosin (TYL) as a macrolide antibiotic in water. As-synthesized heterostructured catalyst was placed in a sono-reactor (40 kHz and 300 W) in order to degrade TYL through the sonocatalysis. 15 wt% WS₂/CeO₂ was chosen for performing the systematic experiments. Decreasing the concentration of TYL, along with increasing the WS₂/CeO₂ dosage led to reduced degradation efficiency. The water hardness was demonstrated to be a suppressive agent on the sonocatalysis of the target pollutant. As-generated holes, OH, and also O₂⁻ were responsible for the degradation of TYL. Increasing the ultrasound power and operating temperature enhanced the degradation efficiency. The degradation rate boosted up when the temperature was raised from 10 °C (0.0107 1/min) to 40 °C (0.0165 1/min). Moreover, the lowest activation energy (E_a) for sonocatalytic degradation was obtained as 10.81 kJ/mol. The sonocatalytic activity of WS₂/CeO₂ in the sono-reactor encountered insignificant change within five consecutive operational runs (~15% reduction). The mechanism and pathways of the sonocatalytic decomposition of TYL are also proposed.     

Targeted sonodynamic therapy using protein-modified TiO2 nanoparticles

Our previous study suggested new sonodynamic therapy for cancer cells based on the delivery of titanium dioxide (TiO₂) nanoparticles (NPs) modified with a protein specifically recognizing target cells and subsequent generation of hydroxyl radicals from TiO₂ NPs activated by external ultrasound irradiation (called TiO₂/US treatment). The present study first examined the uptake behavior of TiO₂ NPs modified with pre-S1/S2 (model protein-recognizing hepatocytes) by HepG2 cells for 24 h. It took 6 h for sufficient uptake of the TiO₂ NPs by the cells. Next, the effect of the TiO₂/US treatment on HepG2 cell growth was examined for 96 h after the 1 MHz ultrasound was irradiated (0.1 W/cm², 30 s) to the cells which incorporated the TiO₂ NPs. Apoptosis was observed at 6 h after the TiO₂/US treatment. Although no apparent cell-injury was observed until 24 h after the treatment, the viable cell concentration had deteriorated to 46% of the control at 96 h. Finally, the TiO₂/US treatment was applied to a mouse xenograft model. The pre-S1/S2-immobilized TiO₂ (0.1 mg) was directly injected into tumors, followed by 1 MHz ultrasound irradiation at 1.0 W/cm² for 60 s. As a result of the treatment repeated five times within 13 days, tumor growth could be hampered up to 28 days compared with the control conditions.     

Production and dispersion of free radicals from transient cavitation Bubbles: An integrated numerical scheme and applications

As an advanced oxidation process with a wide range of applications, sonochemistry relies on acoustic cavitation to induce free radicals for degrading chemical contaminants. The complete process includes two critical steps: the radical production inside the cavitation bubble, and the ensuing dispersion of these radicals into the bulk solution. To grasp the physicochemical details in this process, we developed an integrated numerical scheme with the ability to quantitatively describe the radical production-dispersion behavior. It employs coupled simulations of bubble dynamics, intracavity chemical reactions, and diffusion–reaction-dominated mass transport in aqueous solutions. Applying this method to the typical case of argon and oxygen bubbles, the production mechanism for the main radicals is revealed. Moreover, the temporal-spatial distribution of the radicals in the liquid phase is presented. The results demonstrate that the enhanced radical production observed in oxygen bubbles can be traced to the initiation reaction O₂ + H₂O → OH+HO₂, which requires relatively low activation energy. In the outside liquid region, the dispersion of radicals is limited by robust recombination reactions. The simulated penetration depth of OH is around 0.2 μm and agrees with reported experimental measurements. The proposed numerical approach can be employed to better capture the radical activity and is instrumental in optimizing the engineering application of sonochemistry.     

Titanium-based MAX-phase with sonocatalytic activity for degradation of oxytetracycline antibiotic

In light of growing environmental concerns over emerging contaminants in aquatic environments, antibiotics in particular, have prompted the development of a new generation of effective sonocatalytic systems. In this study, a new type of nano-laminated material, Ti₂SnC MAX phase, is prepared, characterized, and evaluated for the sonocatalytic degradation of oxytetracycline (OTC) antibiotic. A variety of identification analyses, including X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometry, Brunauer-Emmett-Teller, and diffuse reflectance spectroscopy, were conducted to determine the physicochemical properties of the synthesized catalyst. By optimizing the operating factors, total degradation of OTC occurs within 120 min with 1 g L^-1 catalyst, 10 mg L^-1 OTC, at natural pH of 7.1 and 150 W ultrasonic power. The scavenger studies conclude that the singlet oxygen and superoxide ions are the most active species during the sonocatalytic reaction. Based on the obtained data and GC–MS analysis, a possible sonocatalytic mechanism for the OTC degradation in the presence of Ti₂SnC is proposed. The catalyst reusability within eight consecutive runs reveals the proper stability of Ti₂SnC MAX phase. The results indicate the prospect for MAX phase-based materials to be developed as efficient sonocatalysts in the treatment of antibiotics, suggesting a bright future for the field.     

Ultrasound/chlorine sono-hybrid-advanced oxidation process: Impact of dissolved organic matter and mineral constituents

In this work, after exploring the first report on the synergism of combining ultrasound (US: 600 kHz) and chlorine toward the degradation of Allura Red AC (ARAC) textile dye, as a contaminant model, the impact of various mineral water constituents (Cl⁻, SO₄²⁻, NO₃⁻, HCO₃⁻ and NO₂⁻) and natural organic matter, i.e., humic acid (HA), on the performance of the US/chlorine sono-hybrid process was assessed for the first time. Additionally, the process effectiveness was evaluated in a real natural mineral water (NMW) of a known composition. Firstly, it was found that the combination of ultrasound and chlorine (0.25 mM) at pH 5.5 in cylindrical standing wave ultrasonic reactor (f = 600 kHz and P_e = 120 W, equivalent to P_A ∼ 2.3 atm) enhanced in a drastic manner the degradation rate of ARAC; the removal rate being 320% much higher than the arithmetic sum of the two separated processes. The source of the synergistic effect was attributed to the effective implication of reactive chlorine species (RCS: Cl, ClO and Cl₂⁻) in the degradation process. Radical probe technique using nitrobenzene (NB) as a specific quencher of the acoustically generated hydroxyl radical confirmed the dominant implication of RCS in the overall degradation rate of ARAC by US/chlorine system. Overall, the presence of humic acid and mineral anions decreased the efficiency of the sono-hybrid process; however, the inhibition degrees depend on the type and the concentration of the selected additives. The reaction of these additives with the generated RCS is presumably the reason for the finding results. The inhibiting effect of Cl⁻, SO₄²⁻, NO₃⁻ and NO₂⁻ was more pronounced in US/chlorine process as compared to US alone, whereas the inverse scenario was remarked for the effect of HA. These outcomes were associated to the difference in the reactivity of HA and mineral anions toward RCS and OH oxidizing species, in addition to the more selective character of RCS than hydroxyl radical. The displacement of the reaction zone with increasing the additive concentration may also be another influencing factor that favors competition reactions, which subsequently reduce the available reactive species in the reacting medium. The NMW exerted reductions of 43% and 10% in the process efficiency at pH 5.5 and 8, respectively, thereby confirming the RCS-quenching mechanism by the water matrix constituents. Hence, this work provided a precise understanding of the overall mechanism of chlorine activation by ultrasound to promote organic compounds degradation in water.     

Effects of gas sparging and mechanical mixing on sonochemical oxidation activity

The effects of air sparging (0–16 L min⁻¹) and mechanical mixing (0–400 rpm) on enhancing the sonochemical degradation of rhodamine B (RhB) was investigated using a 28 kHz sonoreactor. The degradation of RhB followed pseudo first-order kinetics, where sparging or mixing induced a large sonochemical enhancement. The kinetic constant varied in three stages (gradually increased → increased exponentially → decreased slightly) as the rate of sparging or mixing increased, where the stages were similar for both processes. The highest sonochemical activity was obtained with sparging at 8 L min⁻¹ or mixing at 200 rpm, where the standing wave field was significantly deformed by sparging and mixing, respectively. The cavitational oxidation activity was concentrated at the bottom of the sonicator when higher sparging or mixing rates were employed. Therefore, the large enhancement in the sonochemical oxidation was attributed mainly to the direct disturbance of the ultrasound transmission and the resulting change in the cavitation-active zone in this study. The effect of the position of air sparging and mixing was investigated. The indirect inhibition of the ultrasound transmission resulted in less enhancement of the sonochemical activity. Moreover, the effect of various sparging gases including air, N₂, O₂, Ar, CO₂, and an Ar/O₂ (8:2) mixture was compared, where all gases except CO₂ induced an enhancement in the sonochemical activity, irrespective of the concentration of dissolved oxygen. The highest activity was obtained with the Ar/O₂ (8:2) mixture. Therefore, it was revealed that the sonochemical oxidation activity could be further enhanced by applying gas sparging using the optimal gas.     

Preparation of zinc tungstate nanomaterial and its sonocatalytic degradation of meloxicam as a novel sonocatalyst in aqueous solution

Zinc tungstate (ZnWO₄) was previously used as a photocatalyst. In this paper, for the first time as an sonocatalyst, the performance of ZnWO₄ for sonocatalytic degradation of meloxicam (MEL) under ultrasonic irradiation were studied. Firstly, ZnWO₄ nanomaterials were synthesized at different acidity (pH = 5, 6, 7, 8, 9) via the hydrothermal method. Utilizing SEM, XRD and EDS techniques to characterize composition and morphology of each product, the same crystal forms, but different morphologies (nano-sheet, nano-microspheres or nano-rod) of ZnWO₄ could be obtained. Secondly, the sonocatalytic activities of ZnWO₄ on degradation of MEL were studied. It was found that the degradation ratio varied with the synthetic pH values, with ZnWO₄ under synthetic pH = 6 exhibiting the best sonocatalytic performance (75.7%). While being synthesized at this pH value, ZnWO₄ nano-microspheres had the largest BET surface area (27.068 m²/g), the smallest particle size (40–60 nm) so as to provide more active sites on its surface, which were able to produce more reactive oxygen species (ROS) and holes under ultrasonic irradiation. These ROS and holes had a positive effect on the degradation of MEL into CO₂, H₂O and inorganic. Thirdly, various influential factors including ultrasonic power intensity, ultrasonic time, catalyst addition dosage, initial concentration of MEL solution and reusability of catalyst were also explored. Under the condition of 10 mg/L MEL concentration, 20 mg catalyst dosage, 120 min irradiation time, 0.278 W/cm² ultrasonic power intensity, the degradation ratio on MEL reached 75.7%. Finally, the presence of hydroxyl radical (OH) and singlet molecular oxygen (¹O₂) in the reaction was confirmed by adding ROS scavenger. The experimental results suggested that ZnWO₄ nanoparticle could be used not only as an effective photocatalyst, but also, under the condition of ultrasonic irradiation, a promising sonocatalyst for degradation of organic pollutants in aqueous media.     

Sonochemical synthesis of novel C60 fullerene 1,4-oxathiane derivative through the intermediate fullerene radical anion

We have discovered a selective and efficient method for the synthesis of previously unknown 1,9-(1′,4′-oxathiano)-1,9-dihydro-(C₆₀-I_h)[5,6]fullerene, a compound with the direct attachment of the sulfur atom to the fullerene core. The method is based on the reaction of C₆₀ with 1,2-hydroxythiols in the presence of inorganic bases in air under ultrasonication. The significance of ultrasound has been exemplified with the comparative conventional methods. The title compound has been identified with mass-(MALDI TOF/TOF), one- and two-dimensional NMR ¹H and ¹³C (COSY, HSQC, HMBS), IR, UV–Vis spectroscopic techniques. Using the direct EPR method, we have detected radical anion C₆₀^– (g = 2.0046 and ΔH = 2 G) as a key reaction intermediate of the sonochemical reaction. Based on the experimental results and quantum chemical calculations, we have proposed a mechanism for the conversion of C₆₀ and 2-mercaptoethanol to the C₆₀–1,4-oxathiane adduct.     

Effect of the crystalline constitution of TiO2 substrates on the growth of ultrathin Mo layer

Metallic molybdenum was deposited by magnetron sputtering on amorphous and (110) rutile TiO₂ substrates. An interfacial reaction between the deposited Mo and the TiO₂ substrates generating Ti^3 +, Ti^2 + oxidation states is evidenced by X-ray photoelectron spectroscopy. Our XPS data suggest, as compared to the (110) rutile substrate, a higher reactivity of the amorphous TiO₂ leading to a stronger Mo oxidation. In both cases, this reaction, leads to the formation of MoO_x nanostructures at the interfaces. The growth mechanism of the Mo deposit as a function of the crystalline constitution of the TiO₂ substrate was analyzed by processing the XPS data using the Quases ® software. The data reveal a layer-by-layer growth of the Mo deposit on the (110) rutile substrate and a Stranski–Krastanov growth on the amorphous one. We explain these different growth modes based on the TiO₂ surface reactivity and electronic structure using the Cabrera–Mott theory. This explanation is supported by Time-of-Flight Secondary Ion Mass spectrometry profiling.     

Ultrasonic-assisted synthesis of Ce doped cubic–hexagonal ZnTiO3 with highly efficient sonocatalytic activity

Ce doped ZnTiO₃ as a novel catalyst with highly efficient and stable sonocatalytic activity was synthesized via an ultrasound-assisted sol–gel method using non-ionic surfactant Pluronic F127 as structure directing agent. Synthesized samples were characterized by using various techniques, such as XRD, TEM, SEM, EDX, ​XRF, BET, DRS, and PL, and their sonocatalytic activity studied toward degradation of p-Nitrophenol as a model organic compound. The synthesized mesoporous Ce/ZnTiO₃ had mixed cubic–hexagonal phase with large surface area (118.2 m² g^–1) and narrow pore size distribution (4.9 nm). The effects of cerium concentration, calcination temperature, and calcination time on the structure and the sonocatalytic activity of Ce/ZnTiO₃ were studied in detail. XRD results were suggested that the relation between the phase structure and the catalytic activity is considerable. Significant decrease in band-gap and PL intensity was observed with increasing the cerium concentration in the ZnTiO₃. It became clear that the Ce/ZnTiO₃ (0.81 mol%) shows high sonocatalytic activity compared with pure ZnTiO₃ and other Ce/ZnTiO₃ samples as well as commercial TiO₂-P25. The possible mechanism for the enhanced sonocatalytic activity of Ce/ZnTiO₃ was discussed in details. The electrical energy consumption was also considered during sonocatalytic experiments.     

Sonocatalytic degradation of organic dyes and comparison of catalytic activities of CeO2/TiO2, SnO2/TiO2 and ZrO2/TiO2 composites under ultrasonic irradiation

The CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites were prepared by dispersing various nano-sized oxides (CeO₂, SnO₂, ZrO₂ and TiO₂) with ultrasound and mixing TiO₂ with CeO₂, SnO₂ and ZrO₂, respectively, in boiling water in a molar ratio of 4:1, followed by calcining temperature 500 °C for 60 min. Then a series of sonocatalytic degradation experiments were carried out under ultrasonic irradiation in the presence of CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites and nano-sized TiO₂ powder. Also, the influences of heat-treatment temperature and heat-treatment time on the sonocatalytic activities of CeO₂/TiO₂, SnO₂/TiO₂ and ZrO₂/TiO₂ composites, and of irradiation time and solution acidity on the sonocatalytic degradation of Acid Red B were investigated by UV–vis spectra. It was found that the sonocatalytic degradation of Acid Red B shows significant variation in rate and ratio that decreases in order: CeO₂/TiO₂ > SnO₂/TiO₂ > TiO₂ > ZrO₂/TiO₂ > SnO₂ > CeO₂ > ZrO₂, and the corresponding ratios of Acid Red B in aqueous solution are 91.32%, 67.41%, 65.26%, 41.67%, 28.34%, 26.75% and 23.33%, respectively. And that the degradation ratio is only 16.67% under onefold ultrasonic irradiation. Because of the good degradation efficiency, this method may be an advisable choice for the treatment of non- or low-transparent wastewaters in the future.     

Preparation and mechanism investigation of highly sensitive humidity sensor based on Ag/TiO2

In this paper, a high-performance silver-doped titanium dioxide (Ag/TiO₂) humidity sensor was synthesized using a hydrothermal synthesis method for respiratory monitoring. The sensing mechanism was studied by the first principles of density functional theory (DFT). Calculations show that the doping of Ag⁺ ions increases the adsorption energy of TiO₂ to water molecules. Furthermore, the Ti–O bond in TiO₂ is broken due to the doping of Ag⁺ ions, which promotes the generation of Ti³⁺ defects. Experiments show that the doping of Ag⁺ ions can increase the hydroxide groups, Ti³⁺ defects and oxygen vacancies on the surface of TiO₂, thus effectively improving the responsivity, linearity and hysteresis of the TiO₂ humidity sensor. Compared to TiO₂, the resistance of the Ag/TiO₂ (0.5 mM) humidity sensor reaches 4.5 orders of magnitude with a high response of 39707.1, maximum hysteresis rate of 4.6%, response/recovery time of 31 s/15 s and the best linearity in a range of 11%–95% RH. In addition, the Ag/TiO₂ humidity sensor has been successfully used to detect different modes of respiration and determine the respiratory rate under different respiratory states. Significantly, this work demonstrates potential application value in human healthcare and activities monitoring.     

Insights into the novel application of Fe-MOFs in ultrasound-assisted heterogeneous Fenton system: Efficiency,kinetics and mechanism

In this work, as a new strategy, ultrasound/H₂O₂/MOF system was firstly applied by environmental-benign Fe-MOFs (MIL-53, MIL-88B and MIL-101) for tetracycline hydrochloride removal. The synthetic Fe-MOFs were characterized by XRD, FTIR, SEM, XPS, N₂ sorption-desorption isotherms and CO-FTIR. MIL-88B demonstrated the best catalytic performance because of its highest amount of Lewis acid sites. Influencing factors, contrast experiment, and corresponding dynamics were carried out to obtain the best experimental conditions and reaction system. Under optimal conditions ([Tetracycline hydrochloride] = 10 mg/L, [MIL-88B] = 0.3 g/L, [H₂O₂] = 44 mM, [ultrasound power] = 60 W, and pH = 5.0), the-first-order kinetic rate constant k was calculated to be 0.226 min⁻¹, higher than the simple combination of the ultrasound system (0.004) and MIL-88B/H₂O₂ system (0.163), indicating the importance of synergistic effect between ultrasound and Fenton reaction. EPR test and quenching experiment proved that ·OH is mainly responsible for tetracycline hydrochloride removal. The major reaction path is the adsorption and decomposition of H₂O₂ by coordinative unsaturated iron sites on Fe-MOF, but it is not the only path. The direct decomposition of H₂O₂ and the cavitation effect caused by ultrasound also contribute to the generation of OH.     

Dry etch chemistries for TiO2 thin films

Several different plasma chemistries were investigated for dry etching of TiO₂ thin films. Fluorine-based discharges produced the fastest etch rates (∼2000 Å min⁻¹) and selectivities >1 for Si over TiO₂. Chlorine-based discharges also showed a chemical enhancement over pure Ar sputtering and had selectivities <1 for Si over TiO₂ for a range of plasma conditions. Methane–hydrogen discharges produced very slow etch rates, below those obtained with Ar sputtering. The etched surface morphologies of TiO₂ were excellent in all three types of plasma chemistry. Small concentrations (2 at.%) of chlorine- or fluorine-containing residues were identified on the TiO₂ surface after Cl₂/Ar or SF₆/Ar etching, but these residues were water soluble.     

Ultrasound assisted oxidative deep-desulfurization of dimethyl disulphide from turpentine

A promising approach of ultrasound assisted oxidative desulfurization (UAOD) was studied for deep desulfurization of simulated sulphated turpentine containing dimethyl disulphide (DMDS) as model pollutant. The effect of ultrasound parameters such as power (80–120 W) and duty cycle (50–80%) as well as operating conditions as initial concentration (50–100 ppm), volume (100–300 ml) and temperature (28 °C as ambient condition, 50–70 °C) on the extent of desulfurization have been studied. The effect of addition of various oxidizing agents such as hydrogen peroxide over the range of 3–18 g/L, Fenton reagent by varying FeSO₄ loading from 0.75 g/L to 1.75 g/L at constant H₂O₂ loading and titanium dioxide (loading over the range 1–4 g/L) in the presence of ultrasonic horn have also been investigated at laboratory scale. The addition of oxidizing agents in presence of ultrasound enhanced the extent of DMDS removal. The extent of desulfurization was found to be remarkably low for individual approaches as compared to combination approaches of US/oxidizing agents. The kinetic analysis revealed that oxidation follows first order kinetics. A significant increase in cavitational yield was observed for combination approach of US/H₂O₂/TiO₂ (5.78 × 10⁻⁹ g/L) compared to individual ultrasound approach (2.04 × 10⁻⁹ g/L). Under best conditions of 120 W power, 70% duty cycle, 50 ppm initial concentration, 15 g/L H₂O₂ loading and 4 g/L TiO₂ loading, 100% desulfurization was obtained at 23.19 Rs/L as the treatment cost. Based on the obtained results it can be concluded that US/H₂O₂/TiO₂ approach is highly efficient desulfurization technique for deep desulfurization of simulated sulphated turpentine.     

TiO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> nanoparticles synthesized using He/Ar thermal plasma and their effectiveness on low-concentration mercury vapor removal

Oxygen-vacant titanium dioxide (TiO_2−x ) nanoparticles were synthesized using thermal plasma as a heating source at various applied plasma currents and He/Ar ratios. Samples with diverse characteristics were developed and the mercury removal effectiveness was subsequently evaluated. TiO₂ nanoparticles possessing high purity and uniform particle sizes were successfully synthesized using metal titanium and O₂ as precursors and Ar as plasma gas. TiO_2−x in anatase phase with a particle size at 5–10 nm was formed at the He/Ar volume ratio of 25/75. Further increasing the He/Ar ratio elevated the plasma temperature, causing the tungsten to melt, vaporize from the cathode, and then dope into the formed TiO₂ nanoparticles. The doped W appeared to inhibit the growth of nanoparticles and decrease the crystallinity of formed anatase. The effectiveness of oxygen-vacant sites on Hg⁰ removal under the visible light circumstance was confirmed. Hg⁰ removal by the TiO_2−x nanoparticles was enhanced by increasing the O₂ concentration. However, moisture reduced Hg⁰ capture, especially when light irradiation was applied. The reduction in Hg⁰ capture may be resulted from the competitive adsorption of H₂O on the active sites of TiO_2−x with Hg⁰ and transformed Hg²⁺.     

The effect of additional doping with Nb, Al or Cu on ferromagnetism and conductivity in V-doped TiO2 powders

Rutile Ti_0.94V_0.06O₂ and Ti_0.93V_0.06M_0.01O₂ (M=Nb, Al, and Cu) polycrystalline powders are synthesized by the standard solid-state reaction method. The room-temperature saturation magnetization and resistivity of Ti_0.94V_0.06O₂ powders are 2.5×10⁻³ emu/g (≈0.60×10⁻³μ_B/V) and above 10⁷ Ω cm, respectively. The ferromagnetism weakens remarkably, and the conductivity enhances after additional doping with Nb or Al in V-doped rutile TiO₂ powders. The room-temperature magnetization and resistivity of Ti_0.93V_0.06Cu_0.01O₂ powders are 2.1×10⁻³ emu/g and 1.26×10⁶ Ω cm, respectively. Based on analysis for chemical valence of dopants by the x-ray photoelectron spectroscopy spectra, and using the bound magnetic polaron model, the microscopic mechanisms of ferromagnetism in V-doped rutile TiO₂ powders with or without additional dopants are discussed in detail.