Autosensitized Photooxidation of the Rose Hip (Wild Rose) Oil - Mechanism and Quantum Yield for Singlet Molecular Oxygen O2 (1 Δg) Generation

The autosensitized photooxidation of the fatty acid components of rose hip (Wild Rose) oil was studied. Two important facts arise from the present investigation: a) Fatty acids of rose hip oil decompose upon visible light irradiation in the absence of external sensitizers by a mechanism that involves O₂(¹Δ_g). The pigments present in rose hip oil themselves efficiently sensitize the generation of O₂(¹Δ_g) with a quantum yield of 0.038 (upper limit). b) Visible irradiation also produces the degradation of the anthocyanines, native pigments which could behave as O₂(¹Δ_g) sensitizers in the oil. In this case a mechanism involving the production of superoxide ions by the pigment and further attack of the radicals on the phenol groups of the anthocyanine could account for the observed experimental evidences. These results should be carefully considered in a practical sense when rose hip oil is stored or employed under daylight conditions. Exposure to visible radiation may cause irreversible transformations in rose hip oil.     

A Study of Ozone Generation by Negative Corona Discharge Through Different Plasma Chemistry Models

The Steady radial distribution of chemical species in a wire‐to‐cylinder ozone generator filled with pure oxygen has been computed by applying four different plasma chemistry models of increasing complexity. The most complete model considers ten species (e, O₂ ⁺, O₂ ^?, O₃ ^?, O^?, O₂, O₂(¹Δ_g), O₂(¹∑_g ⁺), O and O₃) and 79 reactions, including ionization by electron impact, electron attachment and detachment, electron-ion recombination, charge transfer, etc. The chemical model is coupled with the electrical model through Poisson's equation. The spatially averaged ozone density has been computed as a function of the current intensity and compared with the experimental values obtained by UV spectroscopy.     

The Reactions of Bromide with Ozone Towards Bromate and the Hypobromite Puzzle: A Density Functional Theory Study

Taking the solvent water into account, the energetics of the reactions of O₃ with Br^? leading to BrO₃ ^? have been calculated by Density Functional Theory at the B3LYP/6–311+G(d)/SCRF =COSMO level. Br^? reversibly forms an adduct, BrOOO^?, (ΔG?=?+6 kJ mol^?1) that decays spin allowed into BrO^? and O₂(¹Δ_g) (ΔG?=?+13 kJ mol^?1). BrO^? undergoes an oxidation to BrO₂ ^? and a reduction to Br^?. This may be accounted for if two different adducts, OBrOOO^? and BrOOOO^?, decay into BrO^? plus O₂ and Br^? plus 2 O₂. After cyclization, OBrOOO^? may also lead to Br^? plus 2 O₂.     

Triplet-state quenching by photostabilizers of polyolefins

Paramagnetic nickel(II) complexes which are used as commercial photostabilizers of polyolefins are shown in laser photolysis studies to quench the triplet state of benzophenone in dilute benzene solution. The efficiency of quenching observed is less than that of diamagnetic square-planar nickel(II) complexes which are more effective photostabilizers of polypropylene in “Xenotest” experiments. The observed rate constants for quenching of triplet benzophenone are compared with those observed by other workers for quenching of singlet oxygen, O₂^*(¹Δ_g), in dilute solution. The relevance of these studies to the understanding of photodegradation in polyolefins is discussed.     

Controllable synthesis of CaTi2O4(OH)2 nanoflakes by a facile template-free process and its properties

Serrated leaf-like CaTi₂O₄(OH)₂ nanoflake crystals were synthesized via a template-free and surfactant-free hydrothermal process. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The growth process for CaTi₂O₄(OH)₂ nanoflakes was dominated by a crystallization–dissolution–recrystallization growth mechanism. BET analysis showed that CaTi₂O₄(OH)₂ nanoflakes had mesoporous structure with an average pore size of 8.7 nm, and a large surface area of 88.4 m² g⁻¹. Cyclic voltammetry and galvanostatic charge–discharge tests revealed that the electrode synthesized from CaTi₂O₄(OH)₂ nanoflakes reached specific capacitances of 162 F g⁻¹ at the discharge current of 2 mA cm⁻², and also exhibited excellent electrochemical stability.     

Enhancement of combustion of a hydrogen-air mixture by excitation of O<Subscript>2</Subscript> molecules to the <Emphasis Type="Italic">a</Emphasis><Superscript>1</Superscript>Δ<Subscript><Emphasis Type="Italic">g</Emphasis></Subscript> state

The possibility of increasing the laminar flame velocity in a hydrogen-air mixture by excitation of O₂ molecules into the a ¹Δ _g singlet state. The presence of 10% of O₂(a ¹Δ _g ) molecules in oxygen is demonstrated to result in noticeable (up to 50%) enhancement of mixture burning. The temperature of combustion products and also the concentrations of H₂O, NO, and other constituents increase. The greatest effect of O₂(a ¹Δ _g ) molecules is manifested in combustion of lean mixtures; the least pronounced effect is observed in rich mixtures. These effects are caused by intensification of the chain mechanism in the presence of a super-equilibrium amount of excited O₂(a ¹Δ _g ) molecules in a hydrogen-air mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 4, pp. 3–12, July–August, 2008.     

Microwave-assisted synthesis and electrochemical characterization of TiNb2O7 microspheres as anode materials for lithium-ion batteries

TiNb₂O₇ microspheres are prepared via a microwave-assisted solvothermal method. The microwave irradiation lowers the compound formation temperature to 600°C, and highly crystalline TiNb₂O₇ powders are obtained upon calcination at 800°C. Morphological analysis of the sample shows uniformly distributed microspheres with a particle size of around 1 μm. The Li⁺-ion diffusion coefficient calculated from the electrochemical impedance result is around 1.21 × 10⁻¹³ cm² s⁻¹, which is 1.5 times higher than the sample obtained from the conventional solvothermal method. The TiNb₂O₇ sample derived from microwave yields a high discharge capacity of 299 mA h g⁻¹ at 0.1 C, whereas the sample synthesized via the conventional solvothermal process yields only 278 mA h g⁻¹ at 0.1 C. Excellent rate capabilities such as 220 mA h g⁻¹ at 5 C and 180 mA h g⁻¹ at 10 C are also observed for the microwave-assisted solvothermal sample. Moreover, the sample exhibits a large capacity retention of 95.5% after 100 discharge–charge cycles at 5 C. These results reveal the appropriateness of the microwave-assisted solvothermal process to prepare TiNb₂O₇ powders with superior properties for battery applications.     

Synthesis,optical, and magnetic properties of six-layered Aurivillius bismuth ferrititanate

This work reports on the preparation, structure, photochemical, and magnetic properties of six-layered Aurivillius bismuth ferrititanates, that is, Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles. The samples were prepared through the modified citrate complexation and precursor film process. The XRD Rietveld refinements were conducted to study the phase formations and crystal structure. The morphological and chemical component characteristics were investigated using SEM, TEM, and EDX analyses. Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles present an indirect allowed transitions with band energies of 2.04, 2.03, and 2.02 eV, respectively. The hybridized (O2p+Fet_2g+Bi6s) formed the valence band (VB) and electronic components of (Ti–3d+Fe–e_g) formed the conduction band (CB) of this six-layered Aurivillius bismuth ferrititanate. The three samples showed efficient photocatalytic degradation of Rhodamine B (RhB) dyes with the excitation wavelength λ > 420 nm. The optical absorption, photodegradation, and magnetic abilities were improved through microstructural modification on “B” site via partial substitution of Mg²⁺ and Nb⁵⁺ for Ti⁴⁺. The photocatalytic results were discussed based on the layer structure and multivalent Fe ions. Fe^3+/2+ in the perovskite slabs (Bi₅Fe₃Ti₃O₁₉)²⁻ could act as the catalytic mediators in the photocatalysis process. As a photocatalyst, Aurivillius Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticle is advantageous due to its photocatalytic and magnetically recoverable abilities.     

Agar-assisted sol-gel synthesis and electrochemical characterization of TiNb2O7 anode materials for lithium-ion batteries

TiNb₂O₇ powders are synthesized via a newly developed agar-assisted sol-gel process for the first time. Phase-pure TiNb₂O₇ powders are obtained upon calcination at 800 °C. On contrast, TiNb₂O₇ powders synthesized via the conventional solid-state method require high calcination temperature at 1100 °C for the complete compound formation. The samples synthesized with agar improve the morphology with submicron-sized particles. The formed porous structure is favorable for enhancing the electrochemical kinetics due to the large contact area between the electrode and the electrolyte. Based on the electrochemical active surface area analysis, the electrical double-layer capacitance of TiNb₂O₇ powders synthesized via both the agar-assisted and the solid-state method is 145 mF cm^?2 and 22 mF cm^?2, respectively. The electrochemical active surface area of the sample prepared via the agar-assisted method is higher than that of the sample prepared via the solid-state method. The TiNb₂O₇ sample synthesized via the agar-assisted process yields 284 mAh g^?1 at 0.1 C, whereas the sample synthesized via the conventional solid-state method yields only 265 mAh g^?1 at 0.1 C. The discharge capacities of the agar-assisted synthesized sample are 205 mAh g^?1 and 174 mAh g^?1 at 5 C and 10 C, respectively. Moreover, the sample exhibits high capacity retention of 91% after 100 discharge-charge cycles at 5 C. Based on the obtained results, the agar-assisted sol-gel process is inferred as one of the facile methods for preparing high performance anode materials for lithium-ion batteries.     

Reducing atmosphere improves the conductivity of NaTi2(PO4)3/C material for hybrid aqueous rechargeable lithium-ion battery anode

Hybrid aqueous rechargeable lithium-ion batteries (HARLIBs) have lower cost and better safety performance than conventional lithium-ion batteries (organic electrolytes). The challenge faced by HARLIBs are the narrow selection of anode and cathode materials, and overcoming the problems of capacity decay of anode and cathode materials in aqueous electrolytes. NaTi₂(PO₄)₃, which has a stable three-dimensional open framework structure, shows certain applicability in HARLIBs, but its inherent low electronic conductivity leads to poor utilization of active materials and inferior rate performance. In this article, we propose an experimental method that can improve the conductivity of NaTi₂(PO₄)₃/C, and study the electrochemical performance of NaTi₂(PO₄)₃/C aqueous half-cell and NaTi₂(PO₄)₃/C||LiMn₂O₄ hybrid aqueous full cell. The results show that Ti³⁺/oxygen vacancies can endow NaTi₂(PO₄)₃/C with higher conductivity and improve the specific capacity and rate capability (69 mAh·g^?1, 7C). At 1C, the second discharge specific capacity is 98.46 mAh·g^?1. After 100 cycles, the Rct was 2.92 × 10^?2 Ω. The NaTi₂(PO₄)₃/C//LiMn₂O₄ full cell can provide a discharge specific capacity of up to 101.07 mAh·g^?1. The synthesized NaTi₂(PO₄)₃/C material can be applied to the anode electrode of hybrid aqueous lithium-ion full cell.     

Crystal structure and luminescence mechanism of novel Fe3+-doped Mg0.752Al2.165O4 deep red-emitting phosphors

Nonstoichiometric alumina-rich spinel provides diverse and changeable local environments for transition-metal dopants. In this contribution, novel Mg_0.752Al_2.165−xO₄:xFe³⁺ deep red-emitting phosphors were designed and prepared by the solid-state reaction method. The red emission presents an unexpected shift from 735 to 770 nm by comparing with Fe³⁺-doped MgAl₂O₄. The excitation spectrum of Mg_0.752Al_2.165−xO₄:xFe³⁺ is broadened in the UV region with a new strong peak at 320 nm. The crystal structure refinement and NMR spectra fitting reveal that the cation vacancies and disorder increase with excess Al³⁺ entering the spinel crystal lattice. According to the results of EPR, NMR, and PL/PLE measurements, it was proposed that the Fe³⁺ ions locate at the distorted octahedral coordination. The changes of the local structure of Fe³⁺ ions promote the doublet state's involvement in the d−d transition. It was proposed that the new excitation peak at 320 nm in Mg_0.752Al_2.165−xO₄:xFe³⁺ is associated with the transitions from the ground state ⁶A_1g(⁶S) to the ⁴A_2g(⁴F)/T_1g(⁴P) and doublet states. The transition between the lower energy excited state of ²T_2g(²I) and ⁶A_1g(⁶S) mainly contributes to the deep red emission and the red-shifting effect.     

Synthesis of carbon coated Bi2O3 nanocomposite anode for sodium-ion batteries

Bi₂O₃ is a promising sodium storage material due to its high gravimetric specific capacity. However, Bi₂O₃ possesses lower electrochemical performance due to its poor electrical conductivity and structural integrity during Na⁺ insertion/extraction process. Here, we prepared a carbon coated Bi₂O₃ nanocomposite by a redox reaction and a carbon coating process. In this nanocomposite, the carbon layer can avoid the direct contact between Bi₂O₃ and electrolyte, which inhibits the repeated formation and decomposition of solid electrolyte interface film. Additionally, the carbon layer can enhance the electrical conductivity of Bi₂O₃ and suppress its aggregation due to its volume change during charge and discharge process. In addition, nano-sized Bi₂O₃ can reduce the transport distance of Na⁺ and electron. The nanocomposite shows excellent cycling performance and rate capability as anode for sodium-ion batteries. A high capacity of 421 mAh g⁻¹ can be maintained after 100 cycles at 1500 mA g⁻¹ and 392 mAh g⁻¹ can be shown at 3200 mAh g⁻¹.     

Structural evolution of hierarchical porous NiO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composites and their application for removal of dyes by adsorption

Hierarchical porous NiO/Al₂O₃ composites were successfully prepared by two-steps. First, the core-shell structured Al₂O₃ microspheres were prepared via a template-free hydrothermal route using KAl(SO₄)₂·12H₂O and Al₂(SO₄)₃·18H₂O as aluminum source. Then, the NiO/Al₂O₃ composites with micro- and nano-hierarchical structures were prepared by a hydrothermal method combining the subsequent calcination process. The obtained characterization result presented that the morphology of hierarchical Al₂O₃ microsphere tuned to irregular platelets by simply varying Ni/Al ratios. The BET analysis showed that the special surface area from 52.12m² g^?1 to 214.8m² g^?1 after two hydrothermal complex process. Effects of Ni/Al ratio, adsorbent dosage, Congo red (CR) concentration, coexisting ions, adsorption time and temperature were investigated. The obtained results indicated that NiO/Al₂O₃ composite had the high adsorption efficiency (99.6%) and great adsorption capacity (186.9mg g^?1) under the optimum conditions. The adsorption isotherm and kinetics data were found to be well fitted and in good agreement with the Langmuir isotherm model and pseudo-second order model, respectively. The hierarchical porous NiO/Al₂O₃ composites presented remarkably higher adsorption efficiency during five recycling, which showed their potential as the highly efficient adsorbent for removal of CR in wastewater.     

Photodegradation of tetracyclines in aqueous solution by using UV and UV/H2O2 oxidation processes

BACKGROUND: The objective of the present study was to analyse the kinetics of photodegradation of three antibiotics from the tetracycline group (tetracycline (TC), chlortetracycline (CTC) and oxytetracycline (OTC)), and the influence of the operational variables: (1) initial concentration; (2) initial solution pH; (3) addition of hydrogen peroxide; (4) effect of the aqueous matrix (ultrapure water (UW), surface water (SW), groundwater (GW) and waste‐water (WW) on these processes. RESULTS: The results obtained show that the photodegradation of the three tetracyclines fits first‐order kinetics. The degradation rate depends on initial concentration and pH. Low concentrations of H₂O₂ markedly increased the efficacy of TC photolysis, with a linear relationship between degradation rate and H₂O₂ concentration for concentrations of 2 × 10^?2 to 2 × 10^?1 mmol L^?1. The photodegradation rate is higher in real waters than in ultrapure water. The toxicity of oxidation by‐products formed during tetracyclines photooxidation process was determined by a bioluminescent test, showing that toxicity increases during the process. CONCLUSIONS: Oxidation of tetracyclines by UV radiation alone is slow due to the low quantum yield determined. The UV/H₂O₂ process is an interesting alternative to oxidise tetracyclines in aqueous solution, because this process decreases total organic carbon concentration and tetracyclines oxidation by‐products toxicity. Copyright © 2010 Society of Chemical Industry     

Synthesis and hydrothermal stability of U doped zirconolite–sphene composite materials

Two series of U doped zirconolite–sphene composite materials were prepared by solid state reaction method: CaZr_(1?m)U_mTi₂O₇?(1?m) Ca_(1?x)U_xAl_2xTi_(1?2x)SiO₅ (m?=?7x) and Ca_(1?n)U_6nZr_(1?5n)Al_2nTi_(2?2n)O₇?(1?5n) Ca_(1?y)U_yAl_2yTi_(1?2y)SiO₅ (n?=?5y/6). The effects of U content on the phase structure of the composite materials were mainly investigated. The results show that the optimal synthesis temperature of the composite material is ～1230°C. In comparison with the incorporation of U in the Zr site of zirconolite, U incorporation in the Ca site of zirconolite using Al as charge compensating ions was not very efficient. Hydrothermal stability of the U doped zirconolite–sphene composite material was examined by modified product consistency test method at 90°C in deionised water (pH 7). The normalised U leach rate is fairly constant in a low value below 10^?5 g m^?2 day^?1 after 28 days.     

Complexes of Hydrogen Peroxide with Dioxoactinide(VI) Species in Aqueous Carbonate and Bicarbonate Media. Formation of An(VI)–H2O2 Complexes

The spectra for 1:1 complexes formed between triscarbonatouranium(VI) + H₂O₂ and triscarbanatoneptunium(VI) + H₂O₂ are presented. The respective rates of formation (25°C, 0.05 M NA₂CO₃) are 565 ± 41 M⁻¹ s⁻¹ and (2.19 ± .01) X 10³ M⁻¹ s⁻¹. The corresponding activation parameters are ΔH* = 67.8 ± 3.2 kJ/m, 43.6 ± 2.0 kJ/m, ΔS* = 30 ± 11 J/m °K and −36 ± 7 J/m °K, respectively. The U(VI) complex appears to be stable over a period of months while the Np(VI) complex is formed as a transient species that disappears via a complex process.     

Pseudocapacitive properties of electrodeposited porous nanowall Co3O4 film

A porous nanowall Co₃O₄ film is prepared by a facile cathodic electrodeposition. The as-prepared porous nanowall Co₃O₄ film shows a net-like porous structure with huge porosity. The porous network is made up of free standing interconnected Co₃O₄ nanoflakes with a thickness of 20 nm. As cathode material for pseudocapacitors, porous nanowall Co₃O₄ film exhibits weaker polarization, higher electrochemical reactivity and better cycling performance as compared to the dense Co₃O₄ film. The specific capacitance of porous nanowall Co₃O₄ film is 325 F g⁻¹ at 2 A g⁻¹ and 247 F g⁻¹ at 40 A g⁻¹, respectively, much higher than that of the dense Co₃O₄ film (230 F g⁻¹ at 2 A g⁻¹ and 167 F g⁻¹ at 40 A g⁻¹). The better pseudocapacitive performances of the porous nanowall Co₃O₄ film are attributed to its highly porous morphology, which provides large reaction surface and short ion diffusion paths, and relaxes the volume change caused by the reaction during the cycling process.     

Simple solvothermal synthesis of magnesium cobaltite microflowers as a battery grade material with high electrochemical performances

In this paper, a simple solvothermal method accompanied with a post annealing process was used to synthesize porous and hierarchical MgCo₂O₄ microflowers (MFs), which were composed of many tightly connected nanosheets. The entire synthesis process was accomplished without any surfactant or template participation. The specific surface area of MgCo₂O₄ MFs with mean pore size of 29.6 nm was as high as 71.58 m² g⁻¹. A typical three-electrode system was used to investigate the electrochemical properties of MgCo₂O₄ MFs-based electrode in 2 M of potassium hydroxide aqueous solution as electrolyte. The results demonstrated that such working electrode delivered a specific capacity of 313.3 C g⁻¹ at 1 A g⁻¹, and still remained 189.4 C g⁻¹ even at the current density increasing to 16 A g⁻¹. In addition, the capacity retention reached 74.5% after 5000 cycles at 5 A/g, suggesting its excellent long-term stability. MgCo₂O₄ MFs with highly specific surface area as well as mesoporous microstructures are significantly beneficial to rapid Faradic reaction, in that it ensures sufficient contact of electrolyte/electrode materials and shortens diffusion paths for ions/electrons, as well as maximizes the number of active sites. The synthesis procedure of MgCo₂O₄ MFs proposed in this work is simple and cheap, and is expected to be employed for the preparation of other binary metal cobaltite as well.     

Sn substitution endows NaTi2(PO4)3/C with remarkable sodium storage performances

The further development of clean energy requires the use of more stable and reliable energy storage system. In addition to lithium ion battery power supplies, sodium ion batteries also have prospects for application and development thanks to the low cost and abundant resource. NaTi₂(PO₄)₃ has attracted much attention due to its three-dimensional channels for sodium ion transfer. In order to meliorate sodium storage properties of NaTi₂(PO₄)₃ electrode, a facile strategy of Sn substitution at Ti sites was employed, and a series of electrodes were successfully synthesized through sol-gel route. The electrochemical performances of Sn substituted composites are significantly improved compared with bare NaTi₂(PO₄)₃/C. And it was found that NaSn_0.2Ti_1.8(PO₄)₃ (NTP/C-Sn-2) delivers the largest capacity, and it also demonstrates the outstanding cycling performances. NTP/C-Sn-2 has discharge capacity of 131.1 mAh g⁻¹ at 4 A g⁻¹ in rate test and 121.4 mAh g⁻¹ at 1 A g⁻¹ after 1000 cycles in cycling test. The experimental results show that NaTi₂(PO₄)₃/C with Sn substitution with proper content exhibits the great potential in anode for sodium ion batteries, and can further provide reference for next generation electrode materials and battery systems.     

The contribution of singlet oxygen to the photofading of triphenylmethane and related dyes

The contribution of singlet oxygen (¹Δ_gO₂) to the photofading of Crystal Violet in some solvents is examined. The rates of photofading in dichloromethane or acetone are accelerated in the presence of singlet oxygen sensitizers, e.g. Methylene Blue. The rates are retarded by adding effective singlet oxygen quenchers such as β-carotene or nickel dimethyldithiocarbamate. It seem shtat Crystal Violet is mainly photooxidized to give Michler's ketone and p-dimethylaminophenol via the reaction with singlet oxygen, which can be generated by the dye itself or by an added sensitizer. The effect of various singlet oxygen quenchers on the photostability of coloured materials derived from colour formers, such as Crystal Violet Lactone and 3-diethylamino-6-methyl-7-anilinofluoran, is examined also on silica gel.