Enhanced Photodegradation of PNP on Soil Surface under UV Irradiation with TiO2

Photodegradation of p-nitrophenol (PNP) on soil surface was investigated to explore the photochemical remediation of soil polluted by nitrophenols. Soil samples spiked with PNP were irradiated by UV light with and without the addition of TiO ₂ . The addition of 0.5–2 wt% TiO ₂ enhanced PNP photodegradation with approximately 1.36 times increase in apparent rate of PNP disappearance. Soil moisture, humic acid and soil pH were important factors influencing the rate of PNP photodegradation. Increase in soil moisture improved the degradation significantly, whereas humic acid reduced the degradation rate. Changes in soil pH resulted in different degradation rates, and higher degradation efficiencies were observed under alkaline condition.     

Photochemistry of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)strontium tetraglyme solutions for eventual liquid phase photochemical deposition

The mechanism of Sr(hfac)₂TG (hfac = 1,1,1,5,5,5,hexafluoro-2,4-pentanedionato and TG, tetraglyme = 2,5,8,11,14-pentaoxapentadecane) photodegradation was investigated in methanol and dichloromethane at 254 and 300 nm. In methanol, photodegradation led to SrF₂ through the attack of fluoride on the metal, occurring from the CF₃ group in the intraligand excited state π-π*. In dichloromethane, a mixture of SrCl₂ and SrF₂ was obtained in proportions dependent on the initial complex concentration and irradiation wavelength. SrF₂ was formed by photoexcited species of the complex with the same mechanism occurring in methanol. SrCl₂ was formed by a solvent-initiated reaction at 254 nm, involving substitution of ligand by chloride ion, coming from photochemical solvent decomposition, whereas at 300 nm it was formed by a solvent-assisted reaction, involving an electron transfer to solvent from excited ligand in triplet state.The photochemical kinetics were followed by UV spectrophotometry, the photodecomposition products were recognized by ESI-mass, XRD and XPS. The Sr(hfac)₂TG photodegradation was usefully exploited to obtain pure thin films or mixture of SrCl₂ and SrF₂ by the LPPD technique, operating in suitable experimental conditions. The films were characterized by SEM, XPS and XRD.     

Photocatalytic Activity of Ag/TiO2 Nanotube Arrays Enhanced by Surface Plasmon Resonance and Application in Hydrogen Evolution by Water Splitting

TiO₂ nanotube arrays (TiO₂ NTs) were fabricated by anodic oxidation and then Ag nanoparticles (Ag NPs) were assembled in TiO₂ NTs (Ag/TiO₂ NTs) by microwave-assisted chemical reduction. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence spectrum (PL), UV–vis absorption spectrum (UV–vis), and Raman spectrum, respectively. The results showed that Ag NPs were well dispersed on the surface of TiO₂ NTs with metallic state. The surface plasmon resonance (SPR) effect of Ag NPs could extend the visible light response and enhance the absorption capacity of TiO₂. Furthermore, Ag NPs could also restrain the recombination of photo-generated electron–hole pairs of TiO₂ NTs efficiently. The methylene blue photodegradation experiment proved that the SPR phenomenon had an effect on photoreaction enhancement. The results of photocatalytic water splitting indicated that Ag/TiO₂ NTs samples had better photocatalytic performance than pure TiO₂ NTs. The corresponding hydrogen evolution rate of Ag/TiO₂ NTs prepared with 0.002 M AgNO₃ solution was 3.3 times as that of pure TiO₂ NTs in the test condition. Additionally, the mechanism of catalyst activity enhanced by SPR effect was proposed.     

The Photocatalytic Activity of TiO<Subscript>2</Subscript> Thin Film Deposited on Al Plate Together with Cu(II) and Ag(I)

Cu (II) and Ag(I) together with TiO₂ powder were deposited on conducting support substrates to enhance the photocatalytic ability. The catalytic efficiency was tested by monitoring the photocatalytic degradation and detriment of methylene blue (MB) and bovine serum albumin (BSA). The conformational change of BSA induced by catalysts was also observed by circular dichroism spectroscopy.The antibacterial activities were studied by Escherichia coli. Both MB and BSA could be degraded more efficiently than pure TiO₂. After treatment with catalyst, the morphology of cells became twisted and rougher. Regular wrinkles were damaged and groove-like rift appeared on the surface. The fluorescence polarization has shown a significant decrease in membrane fluidity and the increase of permeability of cell membrane. Changes of the spectral profile of E. coli were observed, which suggested the damages of surface groups on the cell membrane.     

Physiochemical properties of n-n heterostructured TiO2/Mo-TiO2 composites and their photocatalytic degradation of gaseous toluene

The composite TiO₂/Mo-TiO₂ were prepared by a modified sol-gel method. The prepared catalysts were characterized by X-ray diffraction, BET analysis, SEM, X-ray photoelectron spectroscopy, and UV–vis diffused reflectance spectroscopy techniques. The structural characterization results demonstrated that Mo was successfully doped into the TiO₂ lattice and caused slight changes in the physiochemical properties. The UV–vis DRS showed a red shift of the adsorption edge to the visible region. The photocatalytic decomposition efficiencies of the catalysts were examined with toluene as a typical VOC in a continuous flow reactor. The photocatalytic activity of the n-n heterogeneous TiO₂/Mo-TiO₂ was greater than that of pure TiO₂ and Mo-TiO₂, and the catalyst containing a Mo/Ti mole ratio of 2.5% exhibited optimum photocatalytic properties. In general, a relative humidity of 35%, a higher oxygen content, a lower initial toluene concentration, and a higher UV intensity were beneficial for toluene decomposition.     

Integrated photocatalytic-biological reactor for accelerated phenol mineralization

An integrated photocatalytic-biological reactor (IPBR) was developed for accelerated phenol degradation and mineralization. In the IPBR, photodegradation and biodegradation occurred simultaneously, but in two separated zones: a piece of mat-glass plate coated with TiO₂ film and illuminated by UV light was connected by internal circulation to a honeycomb ceramic that was the biofilm carrier for biodegradation. This arrangement was designed to give intimate coupling of photocatalysis and biodegradation. Phenol degradation was investigated by following three protocols: photocatlysis with TiO₂ film under ultraviolet light, but no biofilm (photodegradation); biofilm biodegradation with no UV light (biodegradation); and simultaneous photodegradation and biodegradation (intimately coupled photobiodegradation). Photodegradation alone could partly degrade phenol, but was not able to achieve significant mineralization, even with an HRT of 10 h. Biodegradation alone could completely degrade phenol, but it did not mineralize the COD by more than 74%. Photobiodegradation allowed continuous rapid degradation of phenol, but it also led to more complete mineralization of phenol (up to 92%) than the other protocols. The results demonstrate that intimate coupling was achieved by protecting the biofilm from UV and free-radical inhibition. With phenol as the target compound, the main advantage of intimate coupling in the IPBR was increased mineralization, presumably because photocatalysis made soluble microbial products more rapidly biodegradable.     

Study of the photodegradation of 2-chlorobenzoic acid by TiO2 and the effects of eutrophicated water on the reaction

The photodegradation of 2-chlorobenzoic acid (2-CBA) in suspensions of TiO₂ was examined under different operational parameters. The optimal condition could be obtained through the experiment, i.e. that the concentration of 2-CBA was 30 mg/L and the dosing quantity of TiO₂ was 0.01 g under UV light in the case of pH 3.5. Above reaction process was in accordance with first order kinetics model. The influence on photocatalytic degradation caused by typical anions in eutrophicated water body such as NO₃⁻ and H₂PO₄⁻ was explored in this work, which revealed that both two anions had inhibitory effect on the degradation process. In addition, alcohol was introduced into the process to identify the degradation mechanism of 2-CBA with TiO₂, and the reaction route of 2-CBA could be predicted through the analysis on the intermediate.     

Photo-oxidation of water sensitised by ruthenium(II) tris(bipyrazine)

The excited state of ruthenium(II) tris(bipyrazine) (Ru(bipyz)₃^2+*) is quenched by the sacrificial electron acceptors, S₂O₈²⁻ and Co(NH₃)₅Cl²⁺. Under acidic solutions (pH 0), Ru(bipyz)₃^2+* is quenched by protons and therefore quite short-lived (τ = 50 ns). At pH 0, steady-state irradiation of the Ru(bipyz)₃²⁺ in the presence or absence of either S₂O₈²⁻ or Co(NH₃)₅Cl²⁺ did not produce any permanent products. In addition, no O₂ evolution was observed when an O₂ catalyst was added. At pH 6, Ru(bipyz)₃²⁺¹ is much longer-lived (τ = 1.04 μs) and steady-state irradiation of a Ru(bipyz)₃²⁺ solution containing S₂O₈²⁻, rather than Co(NH₃)₅Cl²⁺, did produce changes in absorbance, emission and pH, due to the oxidative degradation of the sensitiser. Microsecond flash photolysis work indicated that Ru(bipyz)₃^2+* is oxidatively quenched by the S₂O₈⁻ ions leading to the generation of Ru(bipyz)₃³⁺, a very strong and unstable oxidant. Steady-state irradiations carried out on the Ru(bipyz)₃²⁺/S₂O₈⁻ photochemical system at pH 6, in the presence of an O₂ catalyst, resulted in O₂ generation (φ(O₂) = 0.0025), however photodegradation of the Ru(bipyz)₃²⁺ sensitiser still took place, albeit at a reduced rate.     

Sequential degradation of <Emphasis Type="Italic">p</Emphasis>-cresol by photochemical and biological methods

Sequential photo-and biodegradation of p-cresol was studied using a mercury lamp, as well as KrCl and XeCl excilamps. Preirradiation of p-cresol at a concentration of 10^?4 M did not affect the rate of its subsequent biodegradation. An increase in the concentration of p-cresol to 10^?3 M and in the duration preliminary UV irradiation inhibited subsequent biodegradation. Biodegradation of p-cresol was accompanied by the formation of a product with a fluorescence maximum at 365 nm (λ_ex = 280 nm), and photodegradation yielded a compound fluorescing at 400 nm (λ_ex = 330 nm). Sequential UV and biodegradation led to the appearance of bands in the fluorescence spectra that were ascribed to p-cresol and its photolysis products. It was shown that sequential use of biological and photochemical degradation results in degradation of not only the initial toxicant but also the metabolites formed during its biodegradation.     

Luminescent CeCl3 nanoparticles by Tris(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)cerium diglyme photolysis in chlorinated solvents

Irradiation of [Ce(hfac)₃(diglyme)] (hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionato and diglyme (DG) = 2,5,8,11,14-pentaoxapentadecane) in chlorinated solvents (CH₂Cl₂, CCl₄) with UV light led to luminescent colloidal CeCl₃ that was characterized by transmission electron microscopy (TEM) analysis. When a substrate, quartz or silicon was present in the reaction cell, photoluminescent films were obtained, containing either pure CeCl₃ or mixtures of CeCl₃, CeF₃ and CeOx in function of the experimental parameters of irradiation. Nanostructured and luminescent pure CeCl₃ films were obtained by irradiation of the cerium complex in CCl₄ at high intensity light for a few minutes. The films were characterized by X-ray diffraction (XRD), Energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), TEM, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The kinetics of the [Ce(hfac)₃(diglyme)] solution photodegradation, followed by UV spectrophotometry and spectrofluorimetry, pointed to CeCl₃ formation by a solvent-initiated reaction, whereas the other inorganic compounds were the products of side reactions.     

Self‐Assembly Atomic Stacking Transport Layer of 2D Layered Titania for Perovskite Solar Cells with Extended UV Stability

A novel atomic stacking transporting layer (ASTL) based on 2D atomic sheets of titania (Ti_1?δO₂) is demonstrated in organic–inorganic lead halide perovskite solar cells. The atomically thin ASTL of 2D titania, which is fabricated using a solution‐processed self‐assembly atomic layer‐by‐layer deposition technique, exhibits the unique features of high UV transparency and negligible (or very low) oxygen vacancies, making it a promising electron transporting material in the development of stable and high‐performance perovskite solar cells. In particular, the solution‐processable atomically thin ASTL of 2D titania atomic sheets shows superior inhibition of UV degradation of perovskite solar cell devices, compared to the conventional high‐temperature sintered TiO₂ counterpart, which usually causes the notorious instability of devices under UV irradiation. The discovery opens up a new dimension to utilize the 2D layered materials with a great variety of homostructrual or heterostructural atomic stacking architectures to be integrated with the fabrication of large‐area photovoltaic or optoelectronic devices based on the solution processes.     

An accounting of C‐based trace gas release during abiotic plant litter degradation

Recent studies showed that photochemical breakdown (photodegradation) of plant material accounts for a substantial portion of litter decomposition and subsequent trace gas release in ecosystems under high radiative load and low precipitation. In the absence of solar radiation, thermal degradation may also cause trace gas release at temperatures below the ignition point. These observations suggest that the abiotic processes of photodegradation and thermal degradation of plant litter may be important in understanding global trace gas budgets. In a laboratory incubation study, we performed a simultaneous carbon (C) accounting of CO₂, CO, and CH₄ produced as a byproduct of photodegradation and thermal degradation of six different plant litter types that varied in chemical composition. The patterns of trace gas release during photodegradation and thermal degradation differed considerably across the six plant materials, suggesting that chemical composition of litter may influence the rates of abiotic degradation. There was a strong positive correlation between the rates of trace gas release during photodegradation and temperature. A significant portion of trace gases were produced during low temperature (< 100 °C) thermal degradation of litter in the absence of solar radiation, which was also positively correlated to temperature. In addition, both thermal degradation and photodegradation occurred in the absence of O₂. This indicates that the mechanism formerly accepted as photo‐oxidation may only be one of several photodegradation processes. We speculate that the direct breakdown of chemical groups such as carboxyl, carbonyl, and methoxyl groups may result in CO₂, CO, and CH₄ release. We suggest that the combined processes of thermal and photodegradation of litter may be a previously under accounted source of C‐based trace gases from terrestrial systems.     

Cobalt(II) Schiff base complex on multi-wall carbon nanotubes (MWNTs) by covalently grafted method: Synthesis,characterization and liquid phase epoxidation of cyclohexene by air

Cobalt [(OH)₂-salophen] (N,N′-bis(4-hydroxysalicylidene)phenylene-1,2-diamine) complex was covalently grafted on the chemical modification of multi-wall carbon nanotubes (MWNTs); [Co((OH)₂-salophen)]@MWNTs]. The as-products were characterized by spectroscopy (FT-IR, Raman, and UV–Vis), TGA, and TEM. The cobalt(II) Schiff-base complex covalently anchored on modified MWNTs was characterized by different techniques. The catalytic activity of the novel nanotubes based materials was tested in the epoxidation of cyclohexene in the iso-butyraldehyde/air system using acetonitrile as solvent and very high conversion was obtained. The experimental results indicated very good catalytic activity and selectivity in the epoxidation of cyclohexene. Repeated runs of the catalysts were carried out three times and the results indicated that the catalyst was stable for the epoxidation of cyclohexene.     

Partial depolymerization of pectin by a photochemical reaction

Complex heterogeneous polysaccharides that comprise pectin were partially depolymerized by a photochemical reaction using ultraviolet light in the presence of titanium dioxide catalyst. In a period of 6 h at pH 7, this UV/TiO₂ process decreased the average molecular weight of pectin from 400 kDa to 200 kDa. The characterization of the partially depolymerized pectin, which was fractionated by size-exclusion chromatography, was performed by ¹H NMR spectroscopy, and the spectra obtained showed that the resulting oligosaccharides and polysaccharides maintained the intact core structure of pectin. The monosaccharide content and depolymerization profile were determined by high-performance anion-exchange chromatography coupled with pulsed amperometric detection. This controlled photochemical depolymerization technique might be useful for preparation of pectin oligosaccharides as an ingredient in food and pharmaceutical products.     

Photocatalytic Reduction of CO2 into Methanol over Ag/TiO2 Nanocomposites Enhanced by Surface Plasmon Resonance

Ag-loaded TiO₂ (Ag/TiO₂) nanocomposites were prepared by microwave-assisted chemical reduction method using tetrabutyl titanate as the Ti source. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N₂ adsorption–desorption isotherms, UV–vis absorption spectrum, X-ray photoelectron spectrum, photoluminescence spectrum, and Raman scattering spectrum, respectively. Results revealed that Ag nanoparticles (NPs) were successfully deposited on TiO₂ by reduction of Ag⁺, and the visible light absorption and Raman scattering of TiO₂ were enhanced by Ag NPs based on its surface plasmon resonance effect. Besides, Ag NPs could also effectively restrain the recombination of photogenerated electrons and holes with a longer luminescence life time. In addition, photocatalytic reduction of CO₂ with H₂O on the composites was conducted to obtain methanol. Experimental results indicated that Ag-loaded TiO₂ had better photocatalytic activity than pure TiO₂ due to the synergistic effect between UV light excitation and surface plasmon resonance enhancement, and 2.5 % Ag/TiO₂ exhibited the best activity; the corresponding energy efficiency was about 0.5 % and methanol yield was 405.2 μmol/g-cat, which was 9.4 times higher than that of pure TiO₂. Additionally, an excitation enhancement synergistic mechanism was proposed to explain the experimental results of photocatalytic reduction of CO₂ under different reaction conditions.     

Photochemical and enzymatic synthesis of methanol from formaldehyde with alcohol dehydrogenase from Saccharomyces cerevisiae and water-soluble zinc porphyrin

We evaluated the photochemical and enzymatic synthesis of methanol from formaldehyde with alcohol dehydrogenase (ADH) from Saccharomyces cerevisiae and NAD⁺ photoreduction by the visible-light sensitization of zinc tetraphenylporphyrin tetrasulfonate (ZnTPPS) in the presence of methylviologen (MV²⁺), diaphorase, and triethanolamine (TEOA). When the sample solution containing ZnTPPS, MV²⁺, NAD⁺, diaphorase, and TEOA in potassium phosphate buffer solution was irradiated, the NADH produced increased with the irradiation time. After irradiation for 180 min, the conversion yield of NAD⁺ to NADH was about 60% under 0.1 mM NAD⁺ condition. The methanol production also depended on the conversion yield of NAD⁺ to NADH. After irradiation for 180 min, 0.38 μM of methanol was produced from formaldehyde (16 μM). The conversion ratio of formaldehyde to methanol was about 2.3%. This result indicates that a system for the photochemical synthesis of methanol from formaldehyde was developed with ADH and the NADH produced by the photosensitization of ZnTPPS in water media.     

Biotic degradation at night,abiotic degradation at day: positive feedbacks on litter decomposition in drylands

The arid and semi‐arid drylands of the world are increasingly recognized for their role in the terrestrial net carbon dioxide (CO₂) uptake, which depends largely on plant litter decomposition and the subsequent release of CO₂ back to the atmosphere. Observed decomposition rates in drylands are higher than predictions by biogeochemical models, which are traditionally based on microbial (biotic) degradation enabled by precipitation as the main mechanism of litter decomposition. Consequently, recent research in drylands has focused on abiotic mechanisms, mainly photochemical and thermal degradation, but they only partly explain litter decomposition under dry conditions, suggesting the operation of an additional mechanism. Here we show that in the absence of precipitation, absorption of dew and water vapor by litter in the field enables microbial degradation at night. By experimentally manipulating solar irradiance and nighttime air humidity, we estimated that most of the litter CO₂ efflux and decay occurring in the dry season was due to nighttime microbial degradation, with considerable additional contributions from photochemical and thermal degradation during the daytime. In a complementary study, at three sites across the Mediterranean Basin, litter CO₂ efflux was largely explained by litter moisture driving microbial degradation and ultraviolet radiation driving photodegradation. We further observed mutual enhancement of microbial activity and photodegradation at a daily scale. Identifying the interplay of decay mechanisms enhances our understanding of carbon turnover in drylands, which should improve the predictions of the long‐term trend of global carbon sequestration.     

Dioxygen evolution from inorganic systems. Reactions and catalytic properties of loaded TiO2 particles in photochemical dioxygen generation

The efficiency of differently prepared TiO₂ particles in photochemical water splitting through band gap irradiation of aqueous suspensions has been investigated. The effect of pH and loading with noble metals and RuO₂ has been examined. Particular attention has been devoted to dioxygen evolution and photoadsorption.     

Zirconia-Cu(I) stabilized copper oxide mesoporous nano-catalyst: Synthesis and DNA reactivity of 1,2,4-oxadiazole-quinolinepeptidomimetics-based metal(II) complexes

Abstract

Contemporary research reveals an undemanding protocol for the catalytic synthesis of 1,2,4-oxadiazole-quinolinepeptide in the incidence of a cost-effective and reusable mesoporous ZrO₂-supported Cu₂O (Cu₂ZrO₃) catalyst. This paper depicts a unique system for peptide bond synthesis staying away from toxic solvents and reactants. The catalyst was reused for four cycles without noteworthy loss in the activity, and the catalyst was genuinely heterogeneous. The method followed a simple workup procedure, and no column chromatography was needed. Further, the synthesized 1,2,4-oxadiazole-quinolinepeptide ligand (L), and its complexes of type, [FeLCl₂] and [CuL]Cl₂ were synthesized and characterized by spectral and analytical techniques. An octahedral geometry has been projected for Fe(II) complexes, while the Cu(II) complex exhibits a square planar geometry. The binding properties of the complexes with CT-DNA were studied by absorption spectral analysis, followed by viscosity measurement and thermal denaturation studies. The photo-induced cleavage studies revealed that the complexes possess photonuclease activity against pUC19 DNA under UV–visible irradiation.     

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO₂-Ag nanowires with a diameter of 200 nm and a length of 6-20 µm were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO₂ phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO₂-Ag nanowires, a TiO₂ gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO₂ gel resulted in the formation of crystalline TiO₂ nanotubes. A subsequent Ag electrodeposition step inside the TiO₂ nanotubes resulted in formation of coaxial TiO₂-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO₂) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H₂ gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min of illumination, approximately 0.2 vol% H₂ gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.