Volatile organic compounds decomposition using nonthermal plasma coupled with a combination of catalysts

A series of experiments were performed for toluene decomposition from a gaseous influent at normal temperature and atmospheric pressure by nonthermal plasma coupled with a combination of catalysts technology. Nonthermal plasma was generated by dielectric barrier discharge. γ-Al₂O₃ was used to be a sorbent and a catalyst carrier. Nanocatalysts were MnO₂/γ-Al₂O₃ coupled with modified ferroelectric of nano-Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃. γ-Al₂O₃ played an important role in prolonging reaction time of nonthermal plasma with volatile organic compounds molecules. MnO₂/γ-Al₂O₃ has an advantage for ozone removal, while nano-Ba_0.8Sr_0.2Zr_0.1Ti_0.9O₃ is a kind of good ferroelectric material for improving energy efficiency. Thus these packed materials were incorporated together to strengthen nonthermal plasma power for volatile organic compounds decomposition. The results showed the synergistic technology resulted in greater enhancement of toluene removal and energy efficiencies and a better inhibition for ozone formation in the gas exhaust. Based on the data analysis of the Fourier transforms infrared spectrum, the reaction process of toluene decomposition and the mechanism of synergistic effect are discussed. The results showed in a complex oxidation mechanism of toluene via several pathways, producing either ringretaining or ringopening products. The final products were carbon dioxide and water.     

Effects of alkaline earth metals on the surface,structure, and reactivity of α-alumina

A series of strontium- and barium-doped alumina samples were prepared by hydrolysis, in neutral medium, starting from commercial Al₂O₃, SrCO₃, and BaCO₃ materials. The precursors thus obtained were calcined under air at 700 °C; then, the bulk and surface properties of the resulting mixed oxides were characterized by nitrogen physisorption, X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H₂-TPR), thermogravimetry (TGA), and differential thermal analysis (DTA). Contrary to SrCO₃, an addition of BaCO₃ to α-Al₂O₃ increases slightly the specific surface area. XRD patterns essentially reveal the characteristic reflections assigned to α-Al₂O₃. In agreement with TGA and XRD analysis, strontium and barium carbonates remain after calcination at 700 °C, their decomposition starting above 800 °C. Let us note that this decomposition occurs more readily on AlSr-100 than on AlBa-100 with no apparent relationship with the evolution observed on the specific surface areas. H₂-TPR experiments underline a significant bulk reduction of barium and strontium carbonates taking place significantly above 900 °C with similar trend noticed during TGA regarding their thermal decomposition. However, the most relevant observation is related to a sharp enhancement of the reducibility of AlSr-y with the appearance two reduction ranges highlighting the existence of different types of interactions with strontium and the alumina substrate.     

Greenhouse gases abatement by catalytic dry reforming of methane to syngas over samarium oxide-supported cobalt catalyst

Anthropogenic activities often result in the emissions of methane (CH₄) and carbon dioxide (CO₂) which are the principal components of greenhouse gases. The mitigation of these gases to avert further occurrence of global warming has attracted a lot of research interest. In this study, the potential of greenhouse gases abatement via catalytic CO₂ (dry) reforming of methane to syngas over samarium oxide-supported cobalt (20 wt% Co/80 wt% Sm₂O₃) catalyst was investigated. The 20 wt% Co/80 wt% Sm₂O₃ material was synthesized via wet impregnation method and characterized using different instrument techniques. The methane dry reforming reaction, as well as its kinetics over the catalyst, was studied in a stainless steel fixed-bed continuous flow reactor at feed (CH₄:CO₂) ratios range of 0.1–1.0, temperature range of 923–1023 K and gas hourly space velocity (GHSV) of 30,000 h^?1. The 20 wt% Co/80 wt% Sm₂O₃ catalyst showed promising catalytic activity evident from the highest CH₄ and CO₂ conversion of ~71 and ~74% as well as the highest hydrogen (H₂) and carbon monoxide (CO) yield of ~62 and ~73%, respectively. Moreover, the methane dry reforming over the 20 wt% Co/80 wt% Sm₂O₃ catalyst produces H₂/CO ratio close to unity hence suitable for use as a chemical intermediate for synthesis of oxygenated fuels. The kinetic data obtained from the methane dry reforming were fitted to power law model. Apparent activation energies of 88.62, 80.12, 108.12 and 100.91 kJ mol^?1 were obtained for CH₄, CO₂, H₂ and CO, respectively. The characterization of the spent 20 wt% Co/80 wt% Sm₂O₃ catalyst after 4 h of time-on-stream has confirmed the presence of amorphous carbon which can easily be gasified.     

Experimental and theoretical investigations on high-pressure phase transition of Sr2Fe2O5

Sr₂Fe₂O₅ is a typical oxygen-deficient perovskite and adopts brownmillerite phase (Ibm2, Z = 4) at ambient conditions. Its high-pressure structural behavior has been investigated by both synchrotron radiation X-ray diffraction with diamond anvil cell technique and first principles calculations. Experimental results clearly show that the brownmillerite Sr₂Fe₂O₅ transforms into a tetragonal perovskite-type phase at 12.0 GPa and room temperature, and then into a Sr₂Mn₂O₅-type phase (Pbam, Z = 2) at 23.3 GPa after high-temperature annealing. The Sr₂Mn₂O₅-type phase is stable up to at least 60 GPa and it further undergoes a reversible transition to a lower symmetry phase at 79.1 GPa and ~2,000 K. The results from theoretical calculation not only confirm that the tetragonal phase of Sr₂Fe₂O₅ is isostructural with the high-temperature structure of Ba₂In₂O₅ (I4/mcm, Z = 4), but also predict a series of phase transitions from brownmillerite phase to Ba₂In₂O₅-type phase at 6.9 GPa, and then to Sr₂Mn₂O₅-type phase at 19.7 GPa, which coincides with present experiment results. Isothermal pressure–volume relationship of the Sr₂Mn₂O₅-type phase can be well described by the Birch–Murnaghan Equation of State with V ₀ = 111.6(10) ų, B ₀ = 122(9) GPa, B ₀ ^′  = 4(fixed) experimentally and V ₀ = 115.8(3) ų, B ₀ = 92(4) GPa, B ₀ ^′  = 4(fixed) theoretically. The transition mechanism from brownmillerite to Ba₂In₂O₅-type phase is the displacement of four-coordinated Fe³⁺ ions to higher coordinated positions upon compression. In addition, a semiconductor-to-metal crossover is predicted from brownmillerite to Ba₂In₂O₅-type or Sr₂Mn₂O₅-type phase.     

Mössbauer milliprobe studies of small mineral samples with a silicon drift detector

Analysis of ⁵⁷Fe transmission Mössbauer spectra collected on a system where the proportional counter has been replaced with a silicon drift detector (SDD) to test milliprobing of mineral samples is described. In the region of the 14.4 keV Mössbauer line the detector has about 70% efficiency and is capable of delivering spectroscopic information with a high energy resolution and high counting rate. Satisfactory results are obtained from a phase analysis of mixtures of olivine and ilmenite in the proportion 97:3, 99:1 wt%, where in the latter case 2.4 μg of Fe³⁺ in the form of hematite was found in the ilmenite. New perovskite-type minerals (Pb_1.33Ba_0.67Fe₂O₅, Pb_1.33Sr_0.67Fe₂O₅ and Pb_1.33Ba_0.33Sr_0.33Fe₂O₅), synthesised by a combustion method, were studied by X-ray diffraction and Mössbauer spectroscopy as well. The advantage of the system with SDD compared to a conventional Mössbauer spectrometer equipped with a proportional counter as a detector is demonstrated for the perovskite samples. The Mössbauer set-up with the silicon drift detector may be successfully used for a wide range of materials containing a negligible amount of iron.     

A multi-analytical study of the crystal structure of unusual Ti–Zr–Cr-rich Andradite from the Maronia skarn, Rhodope massif, western Thrace, Greece

Unusual Ti–Cr–Zr-rich garnet crystals from high-temperature melilitic skarn of the Maronia area, western Thrace, Greece, were investigated by electron-microprobe analysis, powder and single-crystal X-ray diffraction, IR, Raman and Mössbauer spectroscopy. Chemical data showed that the garnets contain up to 8 wt.% TiO₂, 8 wt.% Cr₂O₃ and 4 wt.% ZrO₂, representing a solid solution of andradite (Ca₃Fe³⁺ ₂Si₃O₁₂ ≈46 mol%), uvarovite (Ca₃Cr₂Si₃O₁₂ ≈23 mol%), grossular (Ca₃Al₂Si₃O₁₂ ≈10 mol%), schorlomite (Ca₃Ti₂[Si,(Fe³⁺,Al³⁺)₂]O₁₂ ≈15 mol%), and kimzeyite (Ca₃Zr₂[Si,Al₂]₃O₁₂ ≈6 mol%). The Mössbauer analysis showed that the total Fe is ferric, preferentially located at the octahedral site and to a smaller extent at the tetrahedral site. Single-crystal XRD analysis, Raman and IR spectroscopy verified substitution of Si mainly by Al³⁺, Fe³⁺ and Ti⁴⁺. Cr³⁺ and Zr⁴⁺ are found at the octahedral site along with Fe³⁺, Al³⁺ and Ti⁴⁺. The measured H₂O content is 0.20 wt.%. The analytical data suggest that the structural formula of the Maronia garnet can be given as: (Ca_2.99Mg_0.03)_Σ=3.02(Fe³⁺ _0.67Cr_0.54Al_0.33Ti_0.29Zr_0.15)_Σ=1.98(Si_2.42Ti_0.24Fe_0.18Al_0.14)_Σ=2.98O₁₂OH_0.11. Ti-rich garnets are not common and their crystal chemistry is still under investigation. The present work presents new evidence that will enable the elucidation of the structural chemistry of Ti- and Cr-rich garnets.     

Decomposition of benzene by non-thermal plasma processing: Photocatalyst and ozone effect

Plasma technology has some shortcomings, such as higher energy consumption and byproducts produced in the reaction process. However non-thermal plasma associated with catalyst can resolve these problems. Therefore this kind of technology was paied more and more attention to treat waste gas. A hybrid system comprising a non-thermal plasma reactor and nanometer titanium dioxide catalyst was used for benzene removal in the air. The paper described the synergistic effect of ozone and photocatalyst in the plasma reactor. Except of electric field strength, humidity and flow velocity, the synergistic behavior of ozone and photocatalyst was tested. The removal efficiency of benzene reaches nearly 99% when benzene concentration is 600 mg/m³, and the removal efficiency of benzene also reaches above 90% when benzene concentration is 1500 mg/m³. The plasma reactor packed with photocatalyst shows a better selectivity of carbon dioxide than that without photocatalyst. The final products is mostly carbon dioxide, water and a small quantity of carbon monoxide.     

Modeling and simulation of hybrid anaerobic/aerobic wastewater treatment system

Modeling and simulation using GPS-X software for a packed bed up-flow anaerobic sludge blanket followed by a biological aerated filter were studied. Both treatment units were packed with a non-woven polyester fabric as a bio-bed. The system was operated at a hydraulic and organic loading rate of 9.65 m³/m²/d and 2.64 kg BOD₅/m³/day. Verification of the experimental results and calibration of the model were carried out prior simulation and modeling. Variables under consideration were HLR, OLR, and surface area of the packing material. HLR and OLR are increased incrementally until the break through point has been achieved. The results obtained from modeling indicated that the treatment system has great potential to be used as an ideal and efficient option for high hydraulic and organic loading rates up to 19.29 m³/m²/d and 4.48 kg BOD₅/m³/day. The model indicated that increasing the input HLR and OLR loads to the treatment system up to 50 % of the original values achieved removal efficiencies 98 % for TSS, 88 % for BOD₅, and 85 % for COD. Moreover, increasing the HLR to four times the original value (38.59 m³/m²/d) reduced the efficiency of the treatment system to 50 % for COD and BOD₅. However, the removal rates of TSS, TKN, and TP were not affected. Also, the modeling results indicated that increasing the surface area of the packing material increased the overall efficiency of the treatment system.     

A novel continuous magnetic nano-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/perlite fixed bed reactor for catalytic wet peroxide oxidation of dyes: reactor structure

In the present work, a continuous catalytic wet peroxide oxidation fixed bed reactor was employed to treat a simulated wastewater sample with malachite green dye, as a contaminant. Natural perlite particle-supported nano-Fe₃O₄ catalyst was used as a fixed bed inside a reactor, and it was immobilized by a persistent magnetic field. The range of (perlite) particle sizes was from 100 to 1000 nm. The effects of various operating parameters, including temperature of the reactor, pH, initial hydrogen peroxide concentration and initial dye concentration, were investigated on the percentage removal of malachite green dye. Load of catalyst of 2 g and volumetric flow rate of 1 L/h were selected for all the tests. Maximum malachite green degradation was 99.5 ± 0.3%. This removal percentage was attained at temperature of 80 °C, pH = 6, initial dye concentration of 6 mg/L and initial hydrogen peroxide concentration of 100 mg/L. The process was isotherm, and the catalyst showed high catalytic activity in the steady-state condition. The loss of catalyst was less than 0.3%.     

Geochemistry and origin of Dehoo manganese deposit,south Zahedan,southeastern Iran

Dehoo manganese deposit is located 52 km to the south of Zahedan in Sistan and Baluchestan Province, southeastern Iran. This deposit that lies in the central part of the Iranian Flysch Zone is lenticular in shape and lies above the micritic limestone-radiolarite cherts of the upper Cretaceous ophiolite unit. It is hosted within the reddish to brown radiolarite cherts and in places interlinks with them, so that the radiolarite chert packages play a key role for Mn mineralization in the region. Investigated ore-paragenetic successions and the geochemical characteristics of the Dehoo deposit were studied by means of major oxide, trace, and rare earth element (REE) contents that provide information as to the mineral origin. Strong positive correlations were found between major oxides and trace elements (Al₂O₃-TiO₂, r = 0.95; TiO₂-MgO, r = 0.94; Fe₂O₃-Al₂O₃, r = 0.90; MgO-Al₂O₃, r = 0.84; MgO-Fe₂O₃, r = 0.88; Fe₂O₃-TiO₂, r = 0.91; Fe₂O₃-K₂O, r = 0.74; Al₂O₃-K₂O, r = 0.69; Al₂O₃-V, r = 0.72; TiO₂-V, r = 0.73, and MgO-V, r = 0.69) that testify to the contribution of mafic terrigenous detrital material to the deposit. Chondrite-normalized REE patterns of all ore samples are characterized by negative Ce (0.06–0.15, average 0.10) and slightly positive Eu (0.29–0.45, average 0.36) anomalies. Based on ratios of Mn/Fe (average 56.23), Co/Ni (average 0.33), Co/Zn (average 0.38), U/Th (average 3.40), La/Ce (average 1.45), La_n/Nd_n (average 2.16), Dy_n/Yb_n (average 0.33), and light REE/heavy REE (average 8.40; LREE > HREE), as well as Ba (average 920 ppm) and total REE contents (average 6.96 ppm) negative Ce and positive Eu anomalies, Dehoo could be considered a predominantly submarine hydrothermal Mn deposit complemented by terrigenous detrital mafic material.     

Structural investigations of (Ca,Sr)ZrO<Subscript>3</Subscript> and Ca(Sn,Zr)O<Subscript>3</Subscript> perovskite compounds

(Ca _x ,Sr_1?x )ZrO₃ and Ca(Sn _y ,Zr_1-y )O₃ solid solutions were synthesized by solid-state reaction at high temperature before to be studied by powder X-ray diffraction and Raman Spectroscopy. Diffraction data allow the distortion of the ABO₃ perovskite structure to be investigated according to cations substitution on A and B-sites. It is shown that distortion, characterized by Φ, the tilt angle of BO₆ octahedra, slightly increases with decreasing y content in Ca(Sn _y ,Zr_1?y )O₃ compounds and strongly decreases with decreasing x content in (Ca _x ,Sr_1?x )ZrO₃ compounds. Such results are discussed in view of the relative A and B cation sizes. Raman data show that vibrational spectra are strongly affected by the cation substitution on A-site; the frequencies of most vibrational modes increase with increasing x content in (Ca _x ,Sr_1?x )ZrO₃ compounds, i.e. with the decreasing mean size of the A-cation; the upper shift is observed for the 358 cm^?1 mode (?ν/?r = ?60.1 cm^?1/Å). On the other hand, the cation substitution on B-sites, slightly affect the spectra; it is shown that in most cases, the frequency of vibrational modes increases with increasing y content in Ca(Sn _y ,Zr_1?y )O₃ compounds, i.e. with the decreasing mean size of the B-cation, but that two modes (287 and 358 cm^?1) behave differently: their frequencies decrease with the decreasing mean size of the B-cation, with a shift respectively equal to +314 and +162 cm^?1/Å. Such results could be used to predict the location of different elements such as trivalent cations or radwaste elements on A- or B-site, in the perovskite structure.     

The disproportionation of andalusite (Al2SiO5) to Al2O3 and SiO2 under shock compression

Shock-recovery experiments have been carried out on andalusite single crystals of gem quality in a pressure range from 300 up to 575 kbar. Infrared spectroscopic investigations indicate a progressive shock-induced transformation of andalusite into short-range-ordered Al₂O₃ and SiO₂ phases within a pressure interval from ～360 to ～575 kbar. Exposure to dynamic pressures of about 575 kbar results in andalusite breaking down into incoherently crystallized γ-Al₂O₃, well-crystallized α-Al₂O₃ and X-ray amorphous SiO₂. The shock disproportionation of andalusite is presumed to take place in three separate stages of reaction. The comparison of shock-induced reactions with results from static experiments on kyanite indicates significant differences in the transformation pressures and in the mechanism of the high pressure decomposition.     

The crystal structure of disordered (Zr,Ti)O2 solid solution including srilankite: evolution towards tetragonal ZrO2 with increasing Zr

Crystal structure data are presented for seven synthetic samples of disordered zirconium-titanate solid solution (Zr,Ti)O₂, ranging in composition from x _Ti=0.43 to 0.67, thus covering compounds such as ZrTiO₄, Zr₅Ti₇O₂₄, and ZrTi₂O₆ (srilankite). The compounds, synthesized at high temperatures and various pressures in their respective stability fields, are well crystallized and of homogeneous composition. The resulting structure data are less scattered compared to previous studies that were based on compounds synthesized metastably at low temperatures and room pressure. The compounds have the structure of scrutinyite (α-PbO₂) with space group Pbcn, Z=4, unit cell parameters a=4.8495(3) Å, b=5.4635(3) Å, c=5.0462(3) Å at x _Ti=0.425 to a=4.7112(2) Å, b=5.4944(1) Å, c=4.9962(1) Å at x _Ti=0.666. The first structure refinement of pure, synthetic srilankite is presented, which is in good agreement with that of the natural counterpart. Structural trends observed in disordered zirconium-titanate solid solution along the binary join ZrO₂–TiO₂ are relatively smooth and continuous, except for rapid lengthening of an unshared octahedral edge which is anomalously short in scrutinyite-structure TiO₂. The shortness of this edge may explain the observed instability of this structure with the relatively small Ti as the dominant cation. With increasing Zr content, the average cation position moves off-centre inside the octahedron, away from two shared edges, which permits the 12 closest cation–cation distances in the structure to become more equal. The shortening of the b dimension with increasing amount of the larger cation Zr decreases the distance between octahedral Zr and two additional oxygens in an adjacent chain of edge-sharing octahedra, implying that the Zr environment is evolving towards eightfold coordination. If the two additional oxygens are considered as part of the Zr coordination polyhedron, the bonding topology of tetragonal zirconia is obtained. The compositional evolution of the cell parameters, Zr atomic coordinates and Zr coordination environment is consistent with the idea that the structure is evolving towards that of tetragonal ZrO₂. Group-theoretical relationships between scrutinyite, tetragonal zirconia, baddeleyite and fluorite structures show that the sequence of structures fluorite > tetragonal zirconia > scrutinyite > baddeleyite are all related by potentially diffusionless phase transitions driven by wavelike displacements of the oxygen substructure. The scrutinyite and tetragonal structures can act outside their stability fields as “transition states” between the structures on either side.     

Comparison of Mo/MgO and Mo/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts: impact of support on the structure and dibenzothiophene hydrodesulfurization reaction pathways

The MgO and P₂O₅-promoted γ-Al₂O₃ supports with alkaline and acidic natures, respectively, were prepared, impregnated with Mo atoms, and compared for dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction. Ultraviolet spectroscopy and the principal component analysis were used to identify the impact of the supports on the reaction pathways. The catalysts were characterized by BET surface analysis, X-ray diffraction, temperature-programmed reduction, Fourier transform infrared, and X-ray photoelectron spectroscopy. The γ-Al₂O₃-supported catalyst favors the hydrogenation pathway relative to the MgO-supported catalyst, which facilitates the direct desulfurization route. The different performance was attributed to the dissimilar Mo phases that emerged during the activation procedure. The activation under sulfo-reductive condition changed the Mo atoms on γ-Al₂O₃ support into the sulfide phase while extra oxidation took place for the MgO-supported catalyst. The migration and consumption of loosely bonded bulk oxygen atoms with under-coordinated Mo atoms on the MgO support were introduced as a possible reason for such extra oxidation. DFT calculations predicted an interaction between the Mo/MgO catalyst and DBT via the electron donation from the catalyst oxygen atoms to the aromatic rings, resulting in weakening and breaking of the C–S bonds. In spite of the higher resistance of the MgO-supported catalyst toward coking and its superior activity, its lower hydrogenation capability suggested using a dual-function catalyst. Accordingly, two catalysts were mixed and the synergism was observed in the HDS reaction of thiophene.     

Reduction of Manganese Oxides: Thermodynamic,Kinetic and Mechanistic Considerations for One- Versus Two-Electron Transfer Steps

Manganese oxides, typically similar to δ-MnO₂, form in the aquatic environment at near neutral pH via bacterially promoted oxidation of Mn(II) species by O₂, as the reaction of [Mn(H₂O)₆]²⁺ with O₂ alone is not thermodynamically favorable below pH of ~?9. As manganese oxide species are reduced by the triphenylmethane compound leucoberbelein blue (LBB) to form the colored oxidized form of LBB (λ_max?=?623 nm), their concentration in the aquatic environment can be determined in aqueous environmental samples (e.g., across the oxic–anoxic interface of the Chesapeake Bay, the hemipelagic St. Lawrence Estuary and the Broadkill River estuary surrounded by salt marsh wetlands), and their reaction progress can be followed in kinetic studies. The LBB reaction with oxidized Mn solids can occur via a hydrogen atom transfer (HAT) reaction, which is a one-electron transfer process, but is unfavorable with oxidized Fe solids. HAT thermodynamics are also favorable for nitrite with LBB and MnO₂ with ammonia (NH₃). Reactions are unfavorable for NH₄⁺ and sulfide with oxidized Fe and Mn solids, and NH₃ with oxidized Fe solids. In laboratory studies and aquatic environments, the reduction of manganese oxides leads to the formation of Mn(III)-ligand complexes [Mn(III)L] at significant concentrations even when two-electron reductants react with MnO₂. Key reductants are hydrogen sulfide, Fe(II) and organic ligands, including the siderophore desferioxamine-B. We present laboratory data on the reaction of colloidal MnO₂ solutions (λ_max?~?370 nm) with these reductants. In marine waters, colloidal forms of Mn oxides (<?0.2 µm) have not been detected as Mn oxides are quantitatively trapped on 0.2-µm filters. Thus, the reactivity of Mn oxides with reductants depends on surface reactions and possible surface defects. In the case of MnO₂, Mn(IV) is an inert cation in octahedral coordination; thus, an inner-sphere process is likely for electrons to go into the empty e _g ^* conduction band of its orbitals. Using frontier molecular orbital theory and band theory, we discuss aspects of these surface reactions and possible surface defects that may promote MnO₂ reduction using laboratory and field data for the reaction of MnO₂ with hydrogen sulfide and other reductants.     

Degradation of polyvinyl alcohol in aqueous solutions using UV-365 nm/S2O8 2− process

This investigation evaluates the effectiveness of UV-365 nm/S₂O₈ ^2? process in degrading polyvinyl alcohol in aqueous solutions. The effects of pH, Na₂S₂O₈ dosage, and temperature on the degradation efficiency of polyvinyl alcohol were studied. Under acidic conditions, the degradation efficiency of polyvinyl alcohol exceeded that under alkaline conditions. Additionally, a higher Na₂S₂O₈ dosage and a higher temperature were associated with a higher degradation efficiency of polyvinyl alcohol. The degradation rates of polyvinyl alcohol followed a pseudo-first-order kinetic model. Moreover, the observed degradation rate coefficient increased from 0.0078 to 0.4081 min^?1 when the temperature was increased from 10 to 55 °C. Also, the activation energy estimated using the observed degradation rate coefficients and the Arrhenius equation was 64 kJ/mol. At UV-365 nm, pH 3, an Na₂S₂O₈ dosage of 0.06 g/L, a temperature of 55 °C, and an initial polyvinyl alcohol concentration of 20 mg/L, around 100 % of polyvinyl alcohol was degraded, indicating that UV-365 nm/S₂O₈ ^2? process has great potential in degrading polyvinyl alcohol in aqueous solutions.     

Catalytic nonthermal plasma reactor for the abatement of low concentrations of benzene

Oxidative decomposition of dilute benzene in air was carried out in a dielectric barrier discharge reactor with inner metal fiber electrode that was later modified with transition metal oxides. Typical results indicated the best performance of the designed reactor for the removal of dilute benzene, where conventional techniques may not be efficient. The introduction of transition metal oxides in the discharge zone increased the conversion of benzene and shifted the product distribution to total oxidation. The performance of the reactor was further improved on humidification of air stream. The better performance of MnO_x/SMF over CoO_x and SMF may be due to in situ decomposition of ozone that may lead to the formation of strong oxidant atomic oxygen, whereas the best performance with TiO₂/MnO_x/SMF may be assigned due to the synergy between ozone decomposition on MnO_x surface and photocatalytic action on TiO₂.     

Catalytic ozonation of dimethyl phthalate by Ce-substituted goethite

Dimethyl phthalate (DMP) is ubiquitous in aquatic environments due to extensively used as plasticizer, which has received increasing attention in recent years. In this study, the catalytic ozonation of dimethyl phthalate was performed using Ce-substituted goethite as a novel catalyst, which was prepared by isomorphous substitution method. The specific surface area, pHpzc and surface hydroxyl density of the catalyst were determined. The catalyst was characterized using X-ray diffraction, scanning electron microscope and Fourier transform infrared spectroscopy. The removal efficiency of DMP was almost 100% after 30 min, and about 40% DMP was mineralized after 60 min, which was nearly four times higher than single ozonation. During catalytic ozonation process, anions (PO₄ ^3?, SO₄ ^2?, Cl^?) affected DMP degradation, indicating that surface hydroxyl groups on the surface of catalyst were main active sites. The electron transfer process by redox reaction between Ce³⁺/Ce⁴⁺, Fe²⁺/Fe³⁺ was proposed, and their interaction could also promote the formation of hydroxyl radicals. Ce-substituted goethite was an efficient catalyst for degradation of DMP by catalytic ozonation.     

Photocatalytic ozonation of 2, 4-dichlorophenoxyacetic acid in water with a new TiO2 fiber

More effective techniques are required to mineralize the increasing number of recalcitrant organic contaminants at low concentrations in the water environment using advanced oxidation process. Though relatively new, photocatalytic ozonation (O₃/UV/TiO₂) is considered superior to ozonation (O₃) and photocatalysis (UV/TiO₂), due to synergistic effects and use of immobilized TiO₂ photocatalysts is a milestone in advance oxidation process. This article aimed to elucidate 2, 4-dichlorophenoxyacetic acid (2, 4-D) mineralization characteristics in low aqueous solutions by O₃/UV/TiO₂ using the world’s first high-strength TiO₂ fiber catalyst in laboratory experiments. 2, 4-D degradation and TOC removal in O₃, UV/TiO₂ and O₃/UV/TiO₂ followed pseudo-first order reaction kinetic. The removal rates for 2, 4-D and TOC in O₃/UV/TiO₂ were respectively about 1.5 and 2.4-fold larger than the summation of the corresponding values in O₃ and UV/TiO₂. The O₃/UV/TiO₂ process was characterized by short-lived few aromatic intermediates, faster degradations of aliphatic intermediates and dechlorination as a major step in 2, 4-D mineralization. The significantly enhanced 2, 4-D mineralization in the process was attributed to increased ozone decomposition and reduced electron-hole recombination on TiO₂ surface resulting to a large number of OH generation. The O₃/UV/TiO₂ process with the TiO₂ fiber catalyst was very promising with respect to the major challenges being faced in AOP involving TiO₂, namely separation of powder catalyst in suspension and reduced efficiency of immobilized catalysts (e.g. TiO₂ film/fiber).     

Influence of hydroxybenzoic acids on the adsorption of Eu(III) onto α,γ-Al2O3 particles in mildly acidic conditions: A macroscopic and spectroscopic study

The influence of hydroxybenzoic acids (HAH_n), namely p-hydroxybenzoic acid (4-hydroxybenzoic acid, HPhbH) and protocatechuic acid (3,4-dihydroxybenzoic acid, HProtoH₂), on the adsorption of europium(III) onto α,γ-Al₂O₃ particles is studied as a function of acid concentration. After measuring the adsorption edge of the Eu(III)/α,γ-Al₂O₃ binary system, and using the previously studied binary component system Eu(III)/HAH_n—Moreau et al. (2015) Inorg. Chim. Acta 432, 81—, and HAH_n/α,γ-Al₂O₃—Moreau et al. (2013) Colloids Surf. A 435, 97—, it is evidenced that HPhbH does not enhance Eu(III) adsorption onto α,γ-Al₂O₃ in the Eu(III)/HPhbH/α,γ-Al₂O₃ ternary system. Conversely, HProtoH₂ enhances Eu(III) adsorption onto α,γ-Al₂O₃ in the Eu(III)/HProtoH₂/α,γ-Al₂O₃ ternary system. Adsorption of the acids are also found higher in the Eu(III)/acid/α,γ-Al₂O₃ ternary systems as compared with the corresponding binary systems assessing synergetic effects. For high HPhbH concentrations, a ternary surface species involving ≡AlOH surface sites, Eu(III), and PhbH^– is evidenced by time-resolved luminescence spectroscopy (TRLS). However, in the Eu(III)/HProtoH₂/α,γ-Al₂O₃ ternary system, chemical environment of Eu(III) is found to be very close to that in the Eu(III)/HProtoH₂ binary system. Ternary surface species could not be evidenced in the Eu(III)/HProtoH₂/α,γ-Al₂O₃ ternary system with TRLS because of the very short decay time of Eu(III) in the presence of protocatechuic acid.