In situ IR and pulse reaction studies on the active oxygen species over SrF2/Nd2O3 catalyst for oxidative coupling of methane

Pulse reaction method and in situ IR spectroscopy were used to characterize the active oxygen species for oxidative coupling of methane (OCM) over SrF₂/Nd₂O₃ catalyst. It was found that OCM activity of the catalyst was very low in the absence of gas phase oxygen, which indicated that lattice oxygen species contributed little to the yield of C₂ hydrocarbons. IR band of superoxide species (O₂⁻) was detected on the O₂-preadsorbed SrF₂/Nd₂O₃. The substitution of ¹⁸O₂ isotope for ¹⁶O₂ caused the IR band of O₂⁻ at 1128 cm⁻¹ to shift to lower wavenumbers (1094 and 1062 cm⁻¹), consistent with the assignment of the spectra to the O₂⁻ species. A good correlation between the rate of disappearance of surface O₂⁻ and the rate of formation of gas phase C₂H₄ was observed upon interaction of CH₄ with O₂-preadsorbed catalyst at 700 °C. The O₂⁻ species was also observed on the catalyst under working condition. These results suggest that O₂⁻ species is the active oxygen species for OCM reaction on SrF₂/Nd₂O₃ catalyst.     

Mass spectra of negative ions in air-like gas mixtures at atmospheric pressure

We have obtained mass spectra of negative ions produced by rays in artificial air at atmospheric pressure (N₂: 80%, O₂: 20%, H₂O: 20–1500 ppm, CO₂: 0.2–300 ppm, NO, NO₂ 0.02 ppm). We observed two main categories: hydrates built on simple ions (O₂⁻, O₃⁻, OH⁻, CO₃⁻, CO₄⁻, HCO₃⁻, NO₂⁻, NO₃⁻), hydrates built on complex ions (NO_x⁻, HNO_γ, HCO₃⁻HNO_x, x = 2,3; Y = 2, 3). For high values of hygrometry, CO₂ content and ageing time (5 msec) we observe the disappearance of O₂⁻, O₃⁻, OH⁻ hydrates whereas the major part of the spectrum consists of complex ions.     

Electronic and ionic conductivity of TiO2 single crystal within the n–p transition range

The electrical conductivity of TiO₂ single crystal (rutile) was determined within the n–p transition regime in the temperature range 985–1387 K and p(O₂) 1–10⁵ Pa. The determined values of the p(O₂) exponent differ from those predicted by defect disorder models (in both n- and p-type regimes), which were derived assuming validity of ionic charge compensation. This difference allows the evaluation of the ionic conductivity. The ionic component thus determined within the n–p transition regime exhibits an activation energy of E_a=158 kJ mol⁻¹. It was found that the ionic transfer number for undoped TiO₂ at the n–p transition is approximately 0.5. The electronic conductivity component was used to determine the width of the forbidden gap of TiO₂ (E_g=2.86 eV).     

ESR study of the initial stages of the photocatalytic oxidation of toluene over TiO2 powders

In the present work, the initial stages of the photocatalytic oxidation of toluene over two commercial TiO₂ powders were investigated at the molecular level by ESR spectroscopy. UV-irradiation of the TiO₂ samples, which present different phase composition and surface area, gave rise to several oxygenated radicals like O⁻, O₂⁻ and O₃⁻, as well as Ti³⁺ centers. The proportion of these species generated depends on the gaseous environment (vacuum or oxygen), and the structural and morphological characteristic of the TiO₂ samples. In contrast, co-adsorption of toluene and oxygen on any of the TiO₂ samples studied yields upon UV illumination slightly different ESR signals, which have been assigned to the formation of benzylperoxy radicals, Ph-CH₂OO, adsorbed on the semiconductor. Such species are only detected when TiO₂ is exposed to toluene–oxygen mixtures enriched in the organic, and under these conditions neither of the other oxygenated radicals is formed. The reasons for this behavior are discussed on the basis of the mechanism for the photocatalytic oxidation of toluene.     

Effect of pH, inorganic ions, organic matter and H2O2 on E. coli K12 photocatalytic inactivation by TiO2: Implications in solar water disinfection

The effect of different chemical parameters on photocatalytic inactivation of E. coli K12 is discussed. Illumination was produced by a solar lamp and suspended TiO₂ P-25 Degussa was used as catalyst. Modifications of initial pH between 4.0 and 9.0 do not affect the inactivation rate in the absence or presence of the catalyst. Addition of H₂O₂ affects positively the E. coli inactivation rate of both photolytic (only light) and photocatalytic (light plus TiO₂) disinfection processes. Addition of some inorganic ions (0.2 mmol/l) like HCO₃⁻, HPO₄²⁻, Cl⁻, NO₃⁻ and SO₄²⁻ to the suspension affects the sensitivity of bacteria to sunlight in the presence and in absence of TiO₂. Addition of HCO₃⁻ and HPO₄²⁻ resulted in a meaningful decrease in photocatalytic bactericidal effect while it was noted a weak influence of Cl⁻, SO₄²⁻ and NO₃⁻. The effect of counter ion (Na⁺ and K⁺) is not negligible and can modify the photocatalytic process as the anions. Bacteria inactivation was affected even at low concentrations (0.2 mmol/l) of SO₄²⁻ and HCO₃⁻, but the same concentration does not affect the resorcinol photodegradation, suggesting that disinfection is more sensitive to the presence of natural anions than photocatalytic degradation of organic compounds. The presence of organic substances naturally present in water like dihydroxybenzenes isomers shows a negative effect on photocatalytic disinfection. The effect of a mixture of chemical substances on photocatalytic disinfection was also studied by adding to the bacterial suspension nutrient broth, phosphate buffer and tap water.     

Hydroxyapatite photocatalytic degradation of calmagite (an azo dye) in aqueous suspension

The hydroxyapatite (HAP) is prepared by precipitation method and examined for the photocatalytic degradation of calmagite, a toxic and non-biodegradable azo-dye compound. The physicochemical properties of hydroxyapatite material were characterized using BET surface area, XRD, FT-IR, and SEM analysis. The FT-IR analysis of the hydroxyapatite revealed that the peak intensity due to absorbance of surface PO₄³⁻ group centered at wave number 1030 cm⁻¹ is drastically decreased upon exposure to UV for 1 h. The study includes dark adsorption experiments at different pH conditions, influence of the amount of catalyst, and effect of pH on photocatalytic degradation of dye, chemical oxygen demand (COD) removal, biological oxygen demand (BOD₅) increase and SO₄²⁻ and NO₃⁻ ions evolution during the degradation. At optimum photocatalytic experimental conditions the same is compared with commercial degussa P-25 TiO₂. The photocatalytic treatment significantly reduced the COD (92% removal) and increased the BOD₅/COD ratio to 0.78. Considerable evolution of SO₄²⁻ (8.5 mg L⁻¹) and NO₃⁻ (12.2 mg L⁻¹) ions are achieved during the degradation process, thus reflecting the usefulness of the hydroxyapatite photocatalytic treatment in calmagite removal in wastewater.     

The effect of oxygen concentration on the reduction of NO with propylene over CuO/γ-Al2O3

The effect of oxygen concentration on the pulse and steady-state selective catalytic reduction (SCR) of NO with C₃H₆ over CuO/γ-Al₂O₃ has been studied by infrared spectroscopy (IR) coupled with mass spectroscopy studies. IR studies revealed that the pulse SCR occurred via (i) the oxidation of Cu⁰/Cu⁺ to Cu²⁺ by NO and O₂, (ii) the co-adsorption of NO/NO₂/O₂ to produce Cu²⁺(NO₃⁻)₂, and (iii) the reaction of Cu²⁺(NO₃⁻)₂ with C₃H₆ to produce N₂, CO₂, and H₂O. Increasing the O₂/NO ratio from 25.0 to 83.4 promotes the formation of NO₂ from gas phase oxidation of NO, resulting in a reactant mixture of NO/NO₂/O₂. This reactant mixture allows the formation of Cu²⁺(NO₃⁻)₂ and its reaction with the C₃H₆ to occur at a higher rate with a higher selectivity toward N₂ than the low O₂/NO flow. Both the high and low O₂/NO steady-state SCR reactions follow the same pathway, proceeding via adsorbed C₃H₇---NO₂, C₃H₇---ONO, CH₃COO⁻, Cu⁰---CN, and Cu⁺---NCO intermediates toward N₂, CO₂, and H₂O products. High O₂ concentration in the high O₂/NO SCR accelerates both the formation and destruction of adsorbates, resulting in their intensities similar to the low O₂/NO SCR at 523–698 K. High O₂ concentration in the reactant mixture resulted in a higher rate of destruction of the intermediates than low O₂ concentration at temperatures above 723 K.     

Effect of ammonium polyacrylate on rheology of anatase TiO2 nanoparticles dispersed in silicon alkoxide sols

Ammonium polyacrylate (NH₄PA) was introduced into powdered mixtures consisting of anatase-structured TiO₂ nanoparticles and silicon alkoxide precursors at the sol level, and the rheological behavior of the mixtures was examined under various solid loadings (φ=0.05–0.13 in volumetric ratios), shear rates (  s⁻¹) and NH₄PA concentrations. The alkoxide precursors were mixtures of tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄), ethyl alcohol (C₂H₅OH), H₂O and HCl in a constant [H₂O]/[TEOS] ratio of 11. The nanoparticle–sol mixtures generally exhibited a pseudoplastic flow behavior over the shear-rate regime examined. The NH₄PA appeared to serve as an effective surfactant which facilitates the suspension flow by reducing the flow resistance at low NH₄PA concentrations. At φ=0.10, a viscosity reduction ca. 85% was found at  s⁻¹ when the NH₄PA concentration was held at 2.5 wt.% of the solids. As the NH₄PA exceeded a critical level, e.g., [NH₄PA]≥3.0 wt.%, the NH₄PA acted as a catalyst which quickly turned the TiO₂–silica sol mixtures (φ=0.10) into a gelled structure, resulted in a pronounced increase of mixture viscosity. The maximum solids concentration (φ_m) of the mixtures was experimentally determined from a derivative of relative viscosity, i.e., (1−η_r^−1/2)–φ dependence. The estimated φ_m increased from 0.127 to 0.165 when NH₄PA of 0.5 wt.% was introduced into the TiO₂–silica sol mixtures.     

Reductive decomposition of nitrate ion to nitrogen in water on a unique hollandite photocatalyst

Photocatalysis of a hollandite compound K_xGa_xSn_8−xO₁₆ (x = ca. 1.8) was examined for the reduction of nitrate ion with a reducing agent of methanol in water under UV irradiation. Hollandites have a characteristic one-dimensional tunnel structure. The hollandite powder, which was prepared by the sol–gel method and unloaded with any additives like metals, was used as the photocatalyst and its photocatalytic reaction was analyzed quantitatively by using ion chromatography and on-line mass spectrometry, and its reaction mechanism was analyzed by in-situ FT-IR. The hollandite photocatalyst showed a significant activity for the formation of N₂ from NO₃⁻. The nitrate was reduced to N₂ and NO₂⁻, while the reducing agent methanol was partly oxidized to change to formic acid. The conversion of NO₃⁻was proportional to the yields of N₂, NO₂⁻, and HCOO⁻. The present photocatalyzed decomposition of NO₃⁻ to N₂ would be a useful photocatalysis for the environmental protection of water.     

Purification/deodorization of indoor air and gaseous effluents by TiO2 photocatalysis

Our objective was to further assess the capabilities of TiO₂ to purify/deodorize indoor air and industrial gaseous effluents. Using a laboratory photoreactor including a lamp emitting around 365 nm and a TiO₂-coated fiber glass mesh, we first determined that the removal rate of three very different pollutants (CO, n-octane, pyridine) was 5–10 μmol per Wh consumed by the lamp for 50–2000 ppmv concentrations and 25–50 l h⁻¹ flow rates (dry air or O₂). We inferred that this order of magnitude allows, by use of a reasonable-size apparatus, the abatement of pollutants in constantly renewed indoor air, except CO and CH₄ that are too concentrated. Using a TiO₂ photocatalysis-based individual air purifier prototype, we showed, through distinctive analytical measurements, that the average concentrations of benzene, toluene and xylenes were indeed reduced by a factor of 2–3 in an ordinary non-airtight room. We also showed that O₃ addition in O₂ very markedly increases the mineralization percentage of n-octane, under otherwise identical conditions, in the laboratory photoreactor without photoexcitation of O₃; this property of O₃ can expand the application field of photocatalytic air purification in industry, at least in some cases.     

Nanosized perovskite-type oxides La1−xSrxMO3−δ (M = Co, Mn; x = 0, 0.4) for the catalytic removal of ethylacetate

Nanometer perovskite-type oxides La_1−xSr_xMO_3−δ (M = Co, Mn; x = 0, 0.4) have been prepared using the citric acid complexing-hydrothermal-coupled method and characterized by means of techniques, such as X-ray diffraction (XRD), BET, high-resolution scanning electron microscopy (HRSEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and temperature-programmed reduction (TPR). The catalytic performance of these nanoperovskites in the combustion of ethylacetate (EA) has also been evaluated. The XRD results indicate that all the samples possessed single-phase rhombohedral crystal structures. The surface areas of these nanomaterials ranged from 20 to 33 m² g⁻¹, the achievement of such high surface areas are due to the uniform morphology with the typical particle size of 40–80 nm (as can be clearly seen in their HRSEM images) that were derived with the citric acid complexing-hydrothermally coupled strategy. The XPS results demonstrate the presence of Mn⁴⁺ and Mn³⁺ in La_1−xSr_xMnO_3−δ and Co³⁺ and Co²⁺ in La_1−xSr_xCoO_3−δ, Sr substitution induced the rises in Mn⁴⁺ and Co³⁺ concentrations; adsorbed oxygen species (O⁻, O₂⁻, or O₂²⁻) were detected on the catalyst surfaces. The O₂-TPD profiles indicate that Sr doping increased desorption of the adsorbed oxygen and lattice oxygen species at low temperatures. The H₂-TPR results reveal that the nanoperovskite catalysts could be reduced at much lower temperatures (<240 °C) after Sr doping. It is observed that under the conditions of EA concentration = 1000 ppm, EA/oxygen molar ratio = 1/400, and space velocity = 20,000 h⁻¹, the catalytic activity (as reflected by the temperature (T_100%) for EA complete conversion) increased in the order of LaCoO_2.91 (T_100% = 230 °C) ≈ LaMnO_3.12 (T_100% = 235 °C) < La_0.6Sr_0.4MnO_3.02 (T_100% = 190 °C) < La_0.6Sr_0.4CoO_2.78 (T_100% = 175 °C); furthermore, there were no formation of partially oxidized by-products over these catalysts. Based on the above results, we conclude that the excellent catalytic performance is associated with the high surface areas, good redox properties (derived from higher Mn⁴⁺/Mn³⁺ and Co³⁺/Co²⁺ ratios), and rich lattice defects of the nanostructured La_1−xSr_xMO_3−δ materials.     

Photocatalytic oxidation of CO with various oxidants by Mo oxide species highly dispersed on SiO2 at 293 K

The photocatalytic oxidation of CO into CO₂ with oxidants such as NO, N₂O and O₂ proceeded efficiently on a Mo/SiO₂ with high Mo dispersion under UV light irradiation. It was found that the reaction rate greatly depended on the kind and concentration of the oxidant. Photoluminescence investigations reveal the close relationship between the reaction rate and the relative concentration of the photo-excited Mo⁶⁺-oxide species, i.e. charge transfer–excited–triplet state (Mo⁵⁺–O⁻)^*, under steady-state reaction conditions. Moreover, the photocatalytic oxidation of CO with O₂ in excess H₂ was carried out to test suitability for applications to supplying pure H₂. This reaction was seen to proceed efficiently on Mo/SiO₂ with a high CO conversion of 100% and CO selectivity of 99% after 180 min under UV light irradiation, showing higher photocatalytic performance than TiO₂ (P-25) photocatalyst. UV–vis, XAFS, photoluminescence and FT-IR investigations revealed that the high reactivity of the charge transfer–excited–triplet state (Mo⁵⁺–O⁻)^*, with CO as well as the high reactivity of the photoreduced Mo-oxide species (Mo⁴⁺-species) with O₂ to produce the original Mo-oxide species (Mo⁶⁺O²⁻), played a crucial role in the reactions.     

Kinetics of Fischer–Tropsch synthesis on titania-supported cobalt

Rate data have been obtained for CO hydrogenation on a well-characterized 11.7% Co/TiO₂ catalyst in a differential fixed bed reactor at 20 atm, 180–240°C, and 5% conversion over a range of reactant partial pressures. The resulting kinetic parameters can be used to model precisely and accurately the kinetics of this reaction within this range of conditions. Turnover frequencies and rate constants determined from this study are in very good to excellent agreement with those obtained in previous studies of other cobalt catalysts, when the data are normalized to the same conditions of temperature and partial pressures of the reactants. Based on this comparison CO conversion and the partial pressure of product water apparently have little effect on specific rate per catalytic site. The data of this study are fitted fairly well by a simple power law expression of the form −r_CO=kP_H2^0.74P_CO^−0.24, where k=5.1×10⁻³ s⁻¹ at 200°C, P=10 atm, and H₂/CO=2/1; however, they are best fitted by a simple Langmuir–Hinshelwood (LH) rate form −r_CO=aP_H2^0.74P_CO/(1+bP_CO)² similar to that proposed by Yates and Satterfield.     

Oxidative gas phase carbonylation of methanol to dimethyl carbonate over chloride-free Cu-impregnated zeolite Y catalysts at elevated pressure

Incipient wetness impregnation of zeolite Y with copper(II) nitrate solution and inert activation at 650 °C led to active catalysts for the oxidative carbonylation of methanol to dimethyl carbonate in the gas phase. Activities were measured under elevated pressure (0.4–1.6 MPa) with feed compositions of CO/MeOH/O₂ = 40/20/6–1.5 vol.% (balanced by N₂) over zeolite Y loaded with 10–17 wt.% copper. It could be shown that inert activation at 650 °C enhanced the activity, and that Cu loading of 14–17 wt.% gave the best performance. By combined XRD, TEM, TPR and DRIFT characterization it was found that the inert activation initiated dispersion of crystalline CuO, auto-reduction of Cu²⁺ to Cu⁺ and redistribution of copper ions with enrichment inside the supercages of the zeolite. The O₂ content of the feed was found to control the selectivity to dimethyl carbonate. Dimethyl carbonate selectivities of 70–75% were achieved within the temperature range of 140–170 °C at an O₂ content of 1.5 vol.%. This allowed space-time yields of dimethyl carbonate up to 632 g l_cat⁻¹ h⁻¹ at methanol conversions of 5–12%. Formation of the main side product, dimethoxymethane, was surprisingly affected by CO, which is not in line with suggested reaction pathways. A mechanism is proposed including formation of surface carbonate structures as common intermediate.     

Untersuchung über die anionenadsorption mit hilfe markierter ionen

From previous work, the adsorption of anions is regarded as an essential factor for the different corrosion behaviour of metals in solutions containing different anions. Adsorption is measured by means of ³⁶Cl⁻, ⁸²Br⁻, ¹⁸ F⁻, ³⁶ClO₄⁻, ³⁵O₄²⁻, H³⁵S⁻ and ¹⁴CN⁻ on Pt, Ni and Fe in the form of sheets and evaporated films. Besides the determination of the adsorption after dipping into the solution, a method has been developed for the measurement of adsorption in contact with the solution and for the determination of its kinetics. The method can also be applied to O₂-free metal surfaces produced under vacuum. In this case, however, very rapid adsorption is observed, whereas normally saturation is reached only after many hours. It is concluded that, in general, exchange between oxygen on the metal and the anion takes place rather than simple adsorption.

The distribution of the anions adsorbed on the metal surface has been studied by autoradiography; adsorption takes place preferentially at the grain boundaries and increases when the crystal size decreases.

These results confirm the interpretation of passivation as a competition between various processes: metal dissolution, coverage by a passivating oxide film, and displacement of oxygen by anions.     

Rhodium deposits on pyrolytic graphite substrate: Physico-chemical properties and electrocatalytic activity towards nitrate reduction in neutral medium

The electrodeposition of metallic rhodium on pyrolytic graphite from 10 mM Na₃RhCl₆ + 0.5 M NaCl aqueous solution was studied by potentiostatic method with the use of a double-pulse technique involving nucleation and growth pulses. Physico-chemical properties of Rh deposits were investigated by electrochemical methods and scanning electron microscopy. The activity of Rh-modified graphite electrodes towards nitrate reduction in neutral medium was demonstrated, the activation energy of nitrate reduction and NO₃⁻ Langmuir adsorption constant on Rh deposits were determined.

The use of double-pulse technique resulted in enhanced surface coverage in comparison with usual potentiostatic deposition and in decreasing the mean particle size down to 30 nm, while the specific catalyst surface area attains 32 m² g⁻¹. The increase in the nucleation pulse duration from 20 to 100 ms enhances the mass catalytic activity towards NO₃⁻ reduction, which reaches 175 A g⁻¹ for the best samples. Irrespectively of electrodeposition parameters, only NH₃ and NO₂⁻ were detected as nitrate reduction products. The rate of NO₃⁻ destruction was equal to which is much higher than that of most of Pd/Cu-based nitrate hydrogenation systems and Ag/TiO₂ photocatalysts.     

NOx adsorption on MnO2/NaY composite: an in situ FTIR and EPR study

The NO, NO/O₂, and NO/O₂/H₂O adsorption on MnO₂/NaY (5 and 15 wt.% MnO₂) composite catalyst and NaY has been studied by means of in situ FTIR and EPR spectroscopy at elevated temperatures and during heating under reaction-like conditions. NO adsorption and co-adsorption of NO and O₂ on NaY and MnO₂/NaY proceeds via oxidation of NO forming NO₂⁻ and NO₃⁻ species. Whereas the manganese dioxide preferably acts as oxidising agent, the zeolite stores the NO_x species as nitrite and nitrate ions in the solid. In the presence of oxygen, the nitrate formation is enhanced due to additional oxidation of NO through gaseous oxygen leading to NO₂. Dimerisation of NO₂ to N₂O₄ and following disproportionation of the latter causes the formation of NO⁺ and NO₃⁻ species which are associated with nucleophilic zeolitic oxygen and especially alkali cations of the zeolite, respectively. The presence of oxygen facilitates reoxidation of Mn²⁺ which keeps more Mn ions in the active state. Pre-adsorbed water and higher amounts of water vapour in the feed hinder the NO adsorption by blocking the adsorption sites and shift the nitrate formation to higher temperatures. The quantities and thermal stability of the nitrates formed during NO and NO/O₂ adsorption differs which points to a different mechanism of nitrate formation. In the absence of gaseous oxygen, nitrates are formed by participation of only lattice oxygen. In the presence of oxygen, nitrate formation by dimerisation and disproportionation reactions of NO₂ dominates. The manganese component of the composite catalyst supports the oxidation of NO to nitrite and subsequently to nitrate. During this process Mn⁴⁺ is reduced to Mn²⁺ as evidenced by in situ EPR measurements.     

The influence of pH on reaction pathways for O2 reduction on the Au(100) face

Oxygen reduction on the Au(100) face was studied by the rotating disk-ring electrode technique in solutions of anions which adsorb strongly on gold (HSO₄⁻/SO₄²⁻ and/or OH⁻) over the entire pH range. The specific adsorption of OH⁻ anions, which is a pH dependent process, is found to play the key role in determining the reaction pathways. In the absence of OH⁻ adsorption, for pHs below 6, the reduction of O₂ begins as a 2e-process. Due to the increase in local pH during O₂ reduction, the reaction pathway turns into a 4e-reduction at a certain potential depending on the pH of the solution. For pHs higher than 6, O₂ reduction begins as a 4e-process in the potential region where specifically adsorbed OH⁻ anions are present.     

Optimisation of degradation conditions of 1,8-diazabicyclo[5.4.0]undec-7-ene in water and reaction kinetics analysis using a cocurrent downflow contactor photocatalytic reactor

The photocatalytic degradation of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, a non-biodegradable nitrogenous organic compound) in water was optimised under UV radiation using titanium dioxide photocatalyst. The reactor used was a pilot scale cocurrent downflow contactor photocatalytic reactor (CDCPR), a system offering very high mass transfer efficiency. The effect of photocatalyst loading, initial substrate concentration, temperature, pH, and different combinations of UV, O₂, H₂O₂ and TiO₂ on the photocatalytic oxidation of DBU was investigated. The TiO₂ photocatalyst used was Degussa VP Aeroperl P25/20, a granulated form of Degussa P-25, recently developed to ameliorate downstream catalyst separation problems. The CDCPR was fitted with an internally and vertically mounted 1.0 kW UV lamp. The reactions were carried out at 40–60 °C and 1 barg, with the reactor being operated in closed loop recycle mode and suspended photocatalyst being re-circulated. Optimisation of reaction conditions using a combination of TiO₂, UV radiation and O₂ gave the most rapid degradation and mineralisation of the DBU in comparison with other processes. Under optimised conditions, 100% degradation of DBU was achieved in 45 min, with a quantum yield of 7.39, using a 1 kW lamp, 0.5 g/dm³ TiO₂, 100 mg/dm³ DBU, 1 barg, 50 °C and pH of 3.17. Investigating the reaction pathway and its modelling showed a first order dependency, incorporating the effect of first intermediates of degradation. The activation energy was found to be 54.68 kJ mol⁻¹ showing a significant influence of temperature on the photocatalytic degradation of DBU.     

Efficient destruction of bacteria with Ti(IV) and antibacterial ions in co-substituted hydroxyapatite films

Hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂: HAP) was co-substituted with Ti(IV) and antibacterial ions (Ag⁺, Cu²⁺ or Zn²⁺) (HAPTiM), by coprecipitation and ion-exchange methods. Both HAPTiAg and HAPTiCu coated on porous spumous nickel film showed high efficiency for killing Escherichia coli and Staphylococcus aureus in the dark and under weak UVA irradiation, respectively. Moreover, their bactericidal activities were much higher than that of P25-TiO₂ film. The studies of ESR revealed that not only O₂⁻ was formed on HAPTiM, HAPTi, HAP and P25-TiO₂ films under weak UVA irradiation, but also at ambient temperature without light O₂⁻ was generated on HAPTiCu, HAPTiAg, and HAPTi. The redox couples of Cu⁰/Cu²⁺ and Ag⁰/Ag⁺ in the structure of HAPTiCu (Ag) caused the transfer of electron leading to the O₂⁻ generation under the above conditions. The higher bactericidal activities of HAPTiM were due to the synergy of the oxidation role of the O₂⁻ and the bacteriostatic action of antibacterial ions. The process of the damage of the cell wall and the cell membrane was directly observed by TEM, and further confirmed by the determination of potassium ion (K⁺) leakage from the killed bacteria.