Surface XPS characterization of NiTi shape memory alloy after advanced oxidation processes in UV/H2O2 photocatalytic system

Surface structure of NiTi shape memory alloy (SMA) was modified by advanced oxidation processes (AOP) in an ultraviolet (UV)/H₂O₂ photocatalytic system, and then systematically characterized with x-ray photoelectron spectroscopy (XPS). It is found that the AOP in UV/H₂O₂ photocatalytic system leads to formation of titanium oxides film on NiTi substrate. Depth profiles of O, Ni and Ti show such a film possesses a graded interface structure to NiTi substrate and there is no intermediate Ni-rich layer like that produced in conventional high temperature oxidation. Except TiO₂ phase, some titanium suboxides (TiO, Ti₂O₃) may also exist in the titanium oxides film. Oxygen mainly presents in metal oxides and some chemisorbed water and OH⁻ are found in titanium oxides film. Ni nearly reaches zero on the upper surface and relatively depleted in the whole titanium oxides film. The work indicates the AOP in UV/H₂O₂ photocatalytic system is a promising way to favor the widespread application of biomedical NiTi SMA by improving its biocompatibility.     

Critical factors in sonochemical degradation of fumaric acid

The effects of critical factors such as Henry’s Law constant, atmospheric OH rate constant, initial concentration, H₂O₂, FeSO₄ and tert-butanol on the sonochemical degradation of fumaric acid have been investigated. The pseudo first-order rate constant for the sonochemical degradation of 1 mM fumaric acid is much lower than those for chloroform and phenol degradation, and is related to solute concentration at the bubble/water interface and reactivity towards hydroxyl radicals. Furthermore, fumaric acid is preferentially oxidized at the lower initial concentration. It is unreactive to H₂O₂ under agitation at room temperature. However, the degradation rate of fumaric acid increases with the addition of H₂O₂ under sonication. 0.1 mM of fumaric acid suppresses H₂O₂ formation thanks to water sonolysis, while degradation behavior is also dramatically affected by the addition of an oxidative catalyst (FeSO₄) or radical scavenger (tert-butanol), indicating that the degradation of fumaric acid is caused by hydroxyl radicals generated during the collapse of high-energy cavities.     

Performance and energetic analysis of hydrodynamic cavitation and potential integration with existing advanced oxidation processes: A case study for real life greywater treatment

The current work is a “first of a kind” report on the feasibility and efficacy of hydrodynamic cavitation integrated Advanced Oxidation Processes (AOP’s) towards treatment of a real life greywater stream in form of kitchen wastewater. The work has been carried out in a sequential manner starting with geometry optimization of orifice plate (cavitating device) followed by studying the effects of inlet pressure, pH, effluent dilution ratio on degradation of TOC and COD. Under optimized conditions of pH 3, 4 bar pressure, TOC and COD reduction of 18.23 and 25% were obtained using HC for a period of 120 min. To improve the performance of HC, further studies were carried out by integrating H₂O₂ and O₃ with HC. Using 5 g/h optimum dosage of H₂O₂, 87.5% reduction in COD was obtained beyond which it started decreasing. Moreover, integrating O₃ (57.5% reduction in COD) increased the treatment cost. However, a hybrid process (HC + H₂O₂ + O₃) yielded 76.26 and 98.25% reductions in TOC and COD within 60 min. The energetics of all the processes and the treatment costs were studied in detail and it was concluded that combined process of HC + H₂O₂ + O₃ surpassed by far the performances of HC + H₂O₂ and HC + O₃.     

Niobian iron oxides as heterogeneous Fenton catalysts for environmental remediation

Heterogeneous Fenton or Fenton-like reagents consist of a mixture of an iron-containing solid matrix and a liquid medium with H₂O₂. The Fenton system is based on the reaction between Fe^2?+? and H₂O₂ to produce highly reactive intermediate hydroxyl radicals (^???OH), which are able to oxidize organic contaminants, whereas the Fenton-like reaction is based on the reaction between Fe^3?+? and H₂O₂. These heterogeneous systems offer several advantages over their homogeneous counterparts, such as no sludge formation, operation at near-neutral pH and the possibility of recycling the iron promoter. Some doping transition cations in the iron oxide structure are believed to enhance the catalytic efficiency for the oxidation of organic substrates in water. In this work, goethites synthesized in presence of niobium served as precursors for the preparation of magnetites (niobian magnetites) via chemical reduction with hydrogen at 400°C. These materials were used as Fenton-like catalysts. Both groups of (Nb, Fe)-oxide samples were characterized by ⁵⁷Fe Mössbauer spectroscopy at 298 K. The results show that increasing niobium contents raise the catalytic potential for decomposition of methylene blue, which was, in this work, used as a model molecule for organic substrates in water.     

Improved ultrasonic degradation of hydrophilic and hydrophobic aldehydes in water by combined use of atomization and UV irradiation onto the mist surface

Ultrasonic irradiation of 430 kHz, which induces both the chemical effect of pyrolysis and the physical effect of atomization, was carried out to achieve highly effective decomposition of organic substances in water with UV₂₅₄ irradiation and H₂O₂ addition. To investigate the influence of physicochemical properties of the substrate on the degradation rate, three different aldehydes, namely, formaldehyde, acetaldehyde, and benzaldehyde, were selected as model substrates. Upon ultrasonic irradiation alone, the removal ratio of the hydrophobic substrate benzaldehyde reached 100% after 120 min, whereas the removal ratios of the hydrophilic substrates formaldehyde and acetaldehyde were only 21.1% and 53.0%, respectively. By combining ultrasonic atomization and UV₂₅₄ irradiation, formaldehyde and acetaldehyde underwent effective gas-phase decomposition on the surfaces of the mist particles. Photolysis by UV₂₅₄ irradiation mainly affected for the decomposition of aldehydes on the mist surface rather than the reaction of hydroxyl radicals derived from H₂O₂ made by water sonolysis. However, the addition of H₂O₂ effectively improved the decomposition and mineralization rates for both hydrophilic and hydrophobic aldehydes owing to the generation of hydroxyl radicals on the surfaces of the mist particles, which greatly contributed to the gas-phase decomposition. Consequently, the effective decomposition of organic pollutants was achieved regardless of their physicochemical properties in aqueous media.     

Degradation of diclofenac sodium using combined processes based on hydrodynamic cavitation and heterogeneous photocatalysis

Diclofenac sodium, a widely detected pharmaceutical drug in wastewater samples, has been selected as a model pollutant for degradation using novel combined approach of hydrodynamic cavitation and heterogeneous photocatalysis. A slit venturi has been used as cavitating device in the hydrodynamic cavitation reactor. The effect of various operating parameters such as inlet fluid pressure (2–4 bar) and initial pH of the solution (4–7.5) on the extent of degradation have been studied. The maximum extent of degradation of diclofenac sodium was obtained at inlet fluid pressure of 3 bar and initial pH as 4 using hydrodynamic cavitation alone. The loadings of TiO₂ and H₂O₂ have been optimised to maximise the extent of degradation of diclofenac sodium. Kinetic study revealed that the degradation of diclofenac sodium fitted first order kinetics over the selected range of operating protocols. It has been observed that combination of hydrodynamic cavitation with UV, UV/TiO₂ and UV/TiO₂/H₂O₂ results in enhanced extents of degradation as compared to the individual schemes. The maximum extent of degradation as 95% with 76% reduction in TOC has been observed using hydrodynamic cavitation in conjunction with UV/TiO₂/H₂O₂ under the optimised operating conditions. The diclofenac sodium degradation byproducts have been identified using LC/MS analysis.     

Photocatalytic oxidation of natural organic adsorbates on anatase TiO2 films observed by infrared adsorption spectroscopy with a multiple internal reflection geometry

Photocatalytic oxidation of organic adsorbates on anatase TiO₂ films has been examined in different atmospheres of humid air, dry air and vacuum. The photocatalytic oxidation was observed by IR absorption spectroscopy (IRAS) with a multiple-internal-reflection (MIR) geometry. The photocatalytic oxidation is the fastest in the air at a humidity of 70% where oxygen and water vapor are consuming to produce OH radicals and O₂⁻ anions on the TiO₂ surface with the UV exposure. In the dry air, a rate of the photocatalytic oxidation is almost 30% of that in the humid air, where only O₂⁻ anions oxidize the organic adsorbates. In vacuum, on the other hand, it is negligible, which suggests that adsorbed H₂O molecules do not play an important role in the photocatalytic reaction. It is suggested that an addition of the water vapor is necessary to achieve the higher catalytic activity.     

Microscopic insight into catalytic HCN removal over the CuO surface in chemical looping combustion

Hydrogen cyanide (HCN) is well-accepted as a main nitrogen-containing precursor from fuel nitrogen to nitrogen oxides. When using coal as fuel with a CuO-based oxygen carrier in chemical looping combustion (CLC), complex heterogeneous reactions exist among the system of HCN, O₂, NO, H₂O, and CuO particles. This work performs density functional theory (DFT) calculations to systematically probe the microscopic HCN heterogeneous reactions over the CuO particle surface. The results indicate that HCN is chemisorbed on the CuO surface, and the third dissociation step within the consecutive three-step HCN dissociations (HCN*→CN*→NCO*→N*) is the rate-determining step. Namely, the CN*/NCO* radicals can be deemed as an indicator of the performance of HCN removal due to their quite higher dissociation energies. With the existence of O₂, H₂O, and NO, the reaction mechanism of HCN conversion becomes extremely complex. Both DFT calculations and kinetic analyses determine that O₂, NO, and H₂O all significantly accelerate the consumption of CN*/NCO* radicals to produce various N-containing species (NOx or NH₃) to different extents. Finally, a skeletal reaction network in a system of O₂/NO/H₂O/HCN is concluded, which clearly elucidates that CuO exhibits excellent catalytic activity toward HCN removal.     

Synthesis of Blue‐, Green‐, Yellow‐, and Red‐Emitting Graphene‐Quantum‐Dot‐Based Nanomaterials with Excitation‐Independent Emission

A one‐pot method is described for the preparation of graphene quantum dots/graphene oxide (GQDs/GO) hybrid composites with emission in the visible region, through heteroatom doping and hydroxyl‐radical‐induced decomposition of GO. The NH₄OH‐ and thiourea‐mediated dissociation of H₂O₂ produces hydroxyl radicals. Treatment of GO with hydroxyl radicals results in the production of small‐sized GO sheets and GQDs, which self‐assemble to form GQDs/GO through strong π–π interactions. For example, the reaction of GO with a mixture of NH₄OH and H₂O₂ for 40, 120, and 270 min generates yellow‐emitting GQDs/GO (Y‐GQDs/GO), green‐emitting GQDs/GO, and blue‐emitting GQDs, while red‐emitting GQDs/GO (R‐GQDs/GO) are prepared by incubating GO with a mixture of thiourea and H₂O₂. From the analysis of these four GQD‐based nanomaterials by transmission electron microscopy, atomic force microscopy, and fluorescence lifetime spectroscopy, it is found that this tunable fluorescence wavelength results from the differences in particle size. All four GQD‐based nanomaterials exhibit moderate quantum yields (1–10%), nanosecond fluorescence lifetimes, and excitation‐independent emissions. Except for R‐GQDs/GO, the other three GQD‐based nanomaterials are stable in a high‐concentration salt solution (e.g., 1.6 m NaCl) and under high‐power irradiation, enabling the sensitive (high‐temperature resolution and large activation energy) and reversible detection of temperature change. It is further demonstrated that Y‐GQD/GO can be used to image HeLa cells.     

Ultrasonic degradation, mineralization and detoxification of diclofenac in water: Optimization of operating parameters

The 20 kHz ultrasound-induced degradation of non-steroidal, anti-inflammatory drug diclofenac (DCF) was investigated. Several operating conditions, such as power density (25–100 W/L), substrate concentration (2.5–80 mg/L), initial solution pH (3.5–11), liquid bulk temperature and the type of sparging gas (air, oxygen, argon), were tested concerning their effect on DCF degradation (as assessed measuring absorbance at 276 nm) and hydroxyl radicals generation (as assessed measuring H₂O₂ concentration). Sample mineralization (in terms of TOC and COD removal), aerobic biodegradability (as assessed by the BOD₅/COD ratio) and ecotoxicity to Daphnia magna and Artemia salina were followed too.DCF conversion is enhanced at increased applied power densities and liquid bulk temperatures, acidic conditions and in the presence of dissolved air or oxygen. The reaction rate increases with increasing DCF concentration in the range 2.5–5 mg/L but it remains constant in the range 40–80 mg/L, indicating different kinetic regimes (i.e. first and zero order, respectively). H₂O₂ production rates in pure water are higher than those in DCF solutions, implying that decomposition basically proceeds through hydroxyl radical reactions. Mineralization is a slow process as reaction by-products are more stable than DCF to total oxidation; nonetheless, they are also more readily biodegradable. Toxicity to D. magna increases during the early stages of the reaction and then decreases progressively upon degradation of reaction by-products; nevertheless, complete toxicity elimination cannot be achieved at the conditions in question. Neither the original nor the treated DCF samples are toxic to A. salina.     

The effects of hydrogen peroxide on the sonochemical degradation of phenol and bisphenol A

This report describes the effects of H₂O₂ concentration (0.01, 0.1, 1, and 10 mM) on the sonochemical degradation of phenol and bisphenol A (BPA) using an ultrasonic source of 35 kHz and 0.08 W/mL. The concentration of the target pollutants (phenol or BPA), total organic carbon (TOC), and H₂O₂ were monitored for each input concentration of H₂O₂. The effects of H₂O₂ on the sonochemical degradation of phenol was more significant than that of BPA because phenol has a high solubility and low octanol–water partition coefficient (K_ow) value and is subsequently very likely to remain in the aqueous phase, giving it a greater probability of reacting with H₂O₂. The removal of TOC was also enhanced by the addition of H₂O₂. Some intermediates of BPA have a high K_ow value and subsequently have a greater probability of pyrolyzing by the high temperatures and pressures inside of cavitation bubbles. Thus the removal efficiency of TOC in BPA was higher than that of phenol. The removal efficiencies of TOC were lower than the degradation efficiencies of phenol and BPA. This result is due to the fact that some intermediates cannot readily degrade during the sonochemical reaction. The H₂O₂ concentration decreased but was not completely consumed during the sonochemical degradation of pollutants. The initial H₂O₂ concentration and the physical/chemical characteristics of pollutants were considered to be important factors in determining the formation rate of the H₂O₂. When high concentration of H₂O₂ was added to the solution, the formation rates were relatively low compared to when low concentrations of H₂O₂ were used.     

Characterization of hydrogen species on TiO2 by electron-stimulated desorption

The hydrogen species in TiO₂ have been characterized using the site specificity of Electron-Stimulated Desorption (ESD). Hydrogen is found to be bonded to surface Ti's in hydride-type bonds, to subsurface or bridgebonded O's in a hydroxyl-like bond, or be part of a surface hydroxyl. Hydrogen is found at high levels in the near-surface region as a contaminant and is intimately involved in the reaction of O₂ and H₂O with the defective TiO₂ surface. It is suggested that this phenomenon may occur in a wide range of compounds.     

Degradation of reactive orange 4 dye using hydrodynamic cavitation based hybrid techniques

In the present work, degradation of reactive orange 4 dye (RO4) has been investigated using hydrodynamic cavitation (HC) and in combination with other AOP’s. In the hybrid techniques, combination of hydrodynamic cavitation and other oxidizing agents such as H₂O₂ and ozone have been used to get the enhanced degradation efficiency through HC device. The hydrodynamic cavitation was first optimized in terms of different operating parameters such as operating inlet pressure, cavitation number and pH of the operating medium to get the maximum degradation of RO4. Following the optimization of HC parameters, the degradation of RO4 was carried out using the combination of HC with H₂O₂ and ozone. It has been found that the efficiency of the HC can be improved significantly by combining it with H₂O₂ and ozone. The mineralization rate of RO4 increases considerably with 14.67% mineralization taking place using HC alone increases to 31.90% by combining it with H₂O₂ and further increases to 76.25% through the combination of HC and ozone. The synergetic coefficient of greater than one for the hybrid processes of HC + H₂O₂ and HC + Ozone has suggested that the combination of HC with other oxidizing agents is better than the individual processes for the degradation of dye effluent containing RO4. The combination of HC with ozone proves to be the most energy efficient method for the degradation of RO4 as compared to HC alone and the hybrid process of HC and H₂O₂.     

Investigation of TiO2 photocatalyst performance for decolorization in the presence of hydrodynamic cavitation as hybrid AOP

In this article, an acoustic cavitation engineered novel approach for the synthesis of TiO₂, cerium and Fe doped TiO₂ nanophotocatalysts is reported. The prepared TiO₂, cerium and Fe doped TiO₂ nanophotocatalysts were characterized by XRD and TEM analysis to evaluate its structure and morphology. Photo catalytic performance of undoped TiO₂ catalyst was investigated for the decolorization of crystal violet dye in aqueous solution at pH of 6.5 in the presence of hydro dynamic cavitation. Effect of catalyst doping with Fe and Ce was also studied for the decolorization of crystal violet dye. The results shows that, 0.8% of Fe-doped TiO₂ exhibits maximum photocatalytic activity in the decolorization study of crystal violet dye due to the presence of Fe in the TiO₂ and it may acts as a fenton reagent. Kinetic studies have also been reported for the hybrid AOP (HAOP) that followed the pseudo first-order reaction kinetics.     

Ultrasonic synthesis and photocatalytic characterization of H3PW12O40/TiO2 (anatase)

A novel H₃PW₁₂O₄₀/TiO₂ (anatase) composite photocatalyst was prepared by a high-intensity ultrasonic method using a lower temperature (80 °C) and was characterized by XRD and FT-IR. Its photocatalytic activity, using solar light, was evaluated through the degradation of organic dye methylene blue (MB) in aqueous. When MB solution (50 mg/l, 200 ml) containing H₃PW₁₂O₄₀/TiO₂ (anatase) (0.4 g) was degraded by solar irradiation after 90 min, the removal of concentration and TOC of MB reached 95% and 73%, respectively. The photocatalyst activity of H₃PW₁₂O₄₀/TiO₂ (anatase) was much higher than TiO₂ which was prepared in the same way. H₃PW₁₂O₄₀/TiO₂ remained efficient after five repeated experiments.     

Physicochemical process of non-thermal plasma at gas-liquid interface and synergistic effect of plasma with catalyst

An atmospheric-pressure plasma jet (APPJ) was directly irradiated at a gas-liquid interface under ambient conditions. The reactive oxygen species (ROS) like hydroxyl radicals (•OH), hydrogen peroxide (H₂O₂) and ozone (O₃) and also reactive nitrogen species (RNS) such as nitrogen oxides (NO_x) and nitric acid (HNO₃) formed during the plasma discharge were quantified under various experimental parameters. In a chemical dosimetry method, terephthalic acid (TA) was employed for the quantification of •OH and titanium sulfate was used to quantify the H₂O₂. Quantitative determination of NO₃⁻ was carried out by using Ion chromatography (IC). The changes in the solution pH were studied during the plasma treatment. Strong acidification along with the production of dominant reactive nitrogen species and ozone formation were observed with air. The effect of various gases, gas flow rate, various applied voltage and catalyst were studied to optimize the experimental conditions for the best performance. The influence of catalyst Fe²⁺ salt, TiO₂ on the formation of reactive species were studied. The efficiency of the plasma device for the degradation of crystal violet (CV) was also investigated with TiO₂ and Fe²⁺ salt.     

Synthesis,characteristics and sonocatalytic activities of calcined γ-Fe2O3 and TiO2 nanotubes/γ-Fe2O3 magnetic catalysts in the degradation of Orange G

In this work, γ-Fe₂O₃ and TiO₂ NTs/γ-Fe₂O₃ composites with good magnetism and sonocatalytic activity were prepared by a facile polyol method and utilize the principle of isoelectric point method, respectively. The structural and magnetic features of the prepared calcined γ-Fe₂O₃ and composite catalysts were investigated by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), surface analysis, UV–Vis diffuse reflectance spectra (UV–Vis DRS), vibrating sample magnetometry (VSM) and zeta potential analysis. The effects of calcination temperature on γ-Fe₂O₃ phase variation, physical properties and sonocatalytic properties were investigated. The porosity, specific surface area, band gap energy and sonocatalytic activity of γ-Fe₂O₃ were gradually decreased with calcination temperature increased. TiO₂ NTs/γ-Fe₂O₃ with appropriate composition and specific structural features possess synergetic effects such as efficient separation of charge carriers and hydroxyl radicals produced by heterogeneous fenton and fenton-like reactions. This enhanced the sonocatalytic activity for the degradation of Orange G under ultrasonic irradiation. The sonocatalytic reactions obeyed pseudo first-order kinetics. All these information provide insight into the design and development of high-efficiency catalyst for wastewater treatment.     

臭氧修饰(001)晶面TiO2纳米片及其光催化降解甲苯研究

本文系统研究了臭氧修饰对(001)主导晶面锐钛矿型TiO₂光催化剂降解甲苯性能的影响. 利用自行搭建的光催化VOCs降解装置对催化剂光降解甲苯的性能进行了测试. 通过多种表征手段,结合原位DRIFTS和DFT计算研究了臭氧表面修饰及甲苯吸附和降解机理. 结果表明,用臭氧进行表面修饰可以显著提高(001)主导晶面TiO₂光催化降解甲苯的性能. (001)晶面上丰富的5c-Ti不饱和配位是臭氧分子的吸附位点,其解离后形成的Ti-O键与H₂O分子结合,在表面生成大量孤立的Ti_5c-OH. Ti_5c-OH 是甲苯分子的吸附位,它的形成显著提高了对甲苯分子的吸附能力. 在光照下Ti_5c-OH与光生空穴结合能形成·OH自由基. 通过臭氧解离产生的O₂也可以与光生电子结合形成超氧自由基. 这些具有强氧化性活性自由基的形成促进了对气相甲苯的光催化降解速率.     

Quenching of Long Lifetime Emitting Fluorophores with Paramagnetic Molecules

In this work, we have studied quenching of the fluorescence of two well-known oxygen probes, 1-pyrene butyric acid (PBA) and tris(2,2’-bipyridine)ruthenium ([Ru(bpy)₃]²⁺) by reactive oxygen species (superoxide anion, nitric oxide derivative, hydrogen peroxide) and by the O₂ molecule. Both, time-resolved and steady state fluorescence measurements were performed in solution (ethanol, dimethyl sufoxide, water) and in micelles of Sodium Dodecyl Sulfate that serve as a model for membrane-containing biological structures. We have found that only the free radicals and O₂ can actively quench for the two probes, but not the diamagnetic H₂O₂. Our data correspond to the classical Stern–Volmer equation. H₂O₂ has an effect only at high molar concentrations (>0.1 M). In contrast, effective concentrations of free radicals and O₂ that lead to quenching are in millimolar range. In conclusion, our methods allows for detecting global ROS that are small free radicals without interference from the reactive hydroxyl radical. Our data suggest that the method can be used for the quantification of ROS in individual living cells based on the measurement of fluorescence lifetime of those probes.     

水相中金纳米颗粒催化的醛基选择性氧化

本文开发了一种新型的用生物质淀粉保护的金纳米颗粒作为催化剂,选择性氧化醛基得到羧酸的方法. 在4-羟甲基苯甲醛的催化氧化中,金纳米颗粒对醛基表现出了压倒性的选择性,而醇羟基则保持不变. 该非均相催化体系由可溶解的催化剂和不溶解的底物构成. 金催化剂的制备、储存、和使用都在水相中. 反应条件优化之后,双氧水被证明是最佳的氧化剂,可以得到100%转化率. 此外,在不同官能团取代的醛衍生物中,金纳米颗粒也表现出了很好的普适性. 反应结束之后,有机组分被有机溶剂萃取,而金颗粒被保留在水中通过分液分离以回收使用.