Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 2012"

Photoelectrocatalytic technologies for environmental applications

Abstract: This paper summarizes recent research works dealing with the development of photoelectrocatalytic oxidation technologies combining both electrolytic and photocatalytic processes. Photoelectrocatalytic technologies have received particular attention due to their potential and effectiveness in the photodegradation of refractory organic and microbial pollutants present in water and wastewater. Here, titanium dioxide (TiO2) plays the most important role compared to other semiconductor photocatalysts (CdS, ZnO, SnO2, etc.) due to its excellent chemical and physical properties. The recombination of the photogenerated electrons and holes is the main factor that generally limits the application of photocatalytic processes (PCPs) in the environmental field. Considerable efforts have been made to increase the photocatalytic efficiency and decrease the charge recombination by means of photoelectrocatalytic processes (PECPs), also referred to as electrochemically assisted photocatalytic processes, which consists of applying an external potential on photocatalysts. This paper deals with the mechanism of photoelectrocatalytic processes, the characteristics and methods for preparing a TiO2 electrode, the irradiation sources, and the types of reactors used. Moreover, the key factors affecting the photoelectrocatalytic oxidation efficiency are discussed, including the applied electrical potential, light intensity, pH, dissolved oxygen concentration, electrolyte concentration, and temperature. Finally, the paper emphasizes the recent applications of photoelectrocatalytic processes and suggests new research directions for the development of this promising technology.

Overview of the current ISO tests for photocatalytic materials

Abstract: The current eight published ISO standards associated with semiconductor photocatalysis are considered. These standards cover: (1) air purification (specifically, the removal of NO, acetaldehyde and toluene), (2) water purification (the photobleaching of methylene blue and oxidation of DMSO) (3) self-cleaning surfaces (the removal of oleic acid and subsequent change in water droplet contact angle), (4) photosterilisation (specifically probing the antibacterial action of semiconductor photocatalyst films) and (5) UV light sources for semiconductor photocatalytic ISO work. For each standard, the background is first considered, followed by a brief discussion of the standard particulars and concluding in a discussion of the pros and cons of the standard, with often recommendations for their improvement. Other possible standards for the future which would either compliment or enhance the current ones are discussed briefly.

Density functional theory study on the electronic structure of Monascus dyes as photosensitizer for dye-sensitized solar cells

Abstract: This work presents a theoretical study of electronic and redox properties of Monascus dyes using DFT and TDDFT with B3LYP/6-31+G(d,p) level. The dye properties in solvent environment were carried out with IEF-PCM(UAKS)/TDDFT/B3LYP/6-31+G(d,p) method. The ground and excited state oxidation potentials as well as electron injection from the dyes to semiconductor TiO 2 are reported. The calculation shows that all of the dyes can potentially be good photosensitizers in DSSC. Their LUMOs lie over the E cb of TiO 2 and their HOMOs lie under the reduction potential energy of the electrolytes ( I − / I 3 − ) corresponding to ability of electron transfer from the dye excited state to TiO 2 and charge regeneration after photooxidation process, respectively.

Development of a new homogenous photo-Fenton process using Fe(III)-EDDS complexes

Abstract: We report for the first time the use of Fe(III)-EDDS (EDDS: ethylenediamine-N,N′-disuccinic acid) complex as an iron source in a homogeneous photo-Fenton system. The performance of this system was followed through the formation of the radical dotOH and the degradation of 2,2-bis-(4-hydroxyphenyl)propane (BPA). It was observed that Fe(III)-EDDS can enhance the efficiency of both radical dotOH formation and BPA degradation especially near neutral pH. The effect of H2O2 concentration, Fe(III)-EDDS concentration, pH value and oxygen concentration on the BPA degradation during this photo-Fenton system was investigated. It was observed that O2 is an important parameter affecting the efficiency of this process not only due to its reactivity with BPA but also because of its effect on the iron species present in solution. Comparison with iron complexes of oxalate, citrate and EDTA have demonstrated that Fe(III)-EDDS is a very efficient iron source for this photo-Fenton process. This work also demonstrates that Fe(III)-EDDS plays a positive role in the photo-Fenton system, especially at higher pHs, and makes this system an encouraging method for the treatment of organic pollutants in the natural environment.

Transformation of 2,4-dichlorophenol by H2O2/UV-C, Fenton and photo-Fenton processes: Oxidation products and toxicity evolution

Abstract: In the present study, H2O2/UV-C, Fenton and photo-Fenton treatment of 2,4-dichlorophenol was compared in terms of oxidation products and acute toxicity. The oxidation products were identified by gas chromatography–mass spectroscopy, high performance liquid chromatography and ion chromatography, whereas changes in acute toxicity were evaluated by the Vibrio fischeri luminescence inhibition assay. H2O2/UV-C and photo-Fenton processes ensured complete 2,4-dichlorophenolremoval, detoxification and significant mineralization. Hydroquinone and formic acid were identified as the common oxidation products of the studied advanced oxidation processes investigated. 3,5-dichloro-2-hydroxybenzaldehyde, phenol, 4-chlorophenol and 2,5-dichlorohydroquinone were identified as the additional H2O2/UV-C oxidation products of 2,4-dichlorophenol. Acute toxicity decreased with decreasing 2,4-dichlorophenol and increasing chloride release.

Synthesis and structural features of mesoporous NiO/TiO2 nanocomposites prepared by sol–gel method for photodegradation of methylene blue dye

Abstract: A novel series of mesoporous NiO/TiO 2 nanoparticles was successfully synthesized by sol–gel method using cetyltrimethylammonium bromide as controlling template in attempts to study the photodegradation of methylene blue dye. Structural and textural features of the composite samples were investigated by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm, Fourier transformer infra-red (FTIR) and transmission electron microscope (TEM). The band energy gap of the samples was estimated using UV–vis spectrometer. A remarkable reduction in particle size to 4 nm and increasing the surface area up to 220 m 2 /g is detected upon increasing nickel oxide contents revealing the successful role of dopants in controlling the crystal growth and pore structure of the catalyst. Nearly complete mineralization of methylene blue dye occur significantly at higher rate over doped samples compared with pure titanium oxide. The degradation of the dye follows a pseudo first-order kinetics and the apparent rate constant increases with increasing the nickel oxide content up to 5 mol%. The exceptional photocatalytic activity of the samples was attributed to reduction in particle size, increasing in surface area, photoelectron/hole separation efficiency and the extension of the wavelength range of photoexcitation.

Efficiency enhancement by mixed cation effect in dye-sensitized solar cells with PAN based gel polymer electrolyte

Abstract: Dye-sensitized solar cells based on nano-porous TiO2 photo-anode and quasi-solid polymer (or gel) electrolytes are emerging as low cost alternatives to conventional inorganic photovoltaic devices. Although many attempts have been made in order to improve the relatively low power conversion efficiencies of these solar cells, to our knowledge there are very few reports aimed at using a binary system of two different iodide salts toward efficiency enhancement in these cells. In this paper we report for the first time in detail, the effect of using a binary iodide salt mixture with different size cations on the efficiency enhancement in dye sensitized solar cells with polyacrylonitrile (PAN) based gel polymer electrolyte and suggest a possible mechanism for this enhancement, based on short circuit photocurrent which is directly related to the iodide ion concentration [I-]. The gel electrolyte was made of PAN, ethelene carbonate (EC), Propylene carbonate (PC), salt mixture and I-2. The binary iodide salt mixture consists of potassium iodide (KI) and Tetra propyl ammonium iodide (Pr4NI). Although the gel electrolyte with 100% (w/w) KI exhibited the highest overall ionic conductivity at room temperature, it showed the lowest iodide ion (I-) contribution to conductivity. On the other hand, the electrolyte with 100% (w/w) Pr4NI exhibited the lowest overall ionic conductivity but had the highest iodide ion(I-) contribution. The dye-sensitized solar cells of configuration Glass/FTO/TiO2/N-719 Dye/electrolyte/Pt/FTO/glass were fabricated using the gel electrolytes of different salt ratios and with nanoporous TiO2 electrode sensitized with Ruthenium dye (N719). With identical electrolyte compositions, the solar cell with 100% (w/w) KI showed an efficiency of 4.98% and the cell with 100% (w/w) Pr4NI showed an efficiency of 4.47%. However, the cell with the mixed iodide system, 16.6% (w/w) KI + 83.4%(w/w) Pr4NI showed the highest efficiency of 5.36% with maximum short circuit current density (J(SC)) of 13.79 mA cm(-2), open circuit voltage (V-OC) of 679.10 mV and a fill factor of 57.25%. The variation of efficiency (eta) with iodide ion concentration [I-] follows the same trend as the J(SC) which appears to be governed by the iodide ion conductivity of the gel electrolyte. The dependence of the short circuit photocurrent and the open circuit photovoltage on the cation type generally agrees with reported data for related systems. However, the occurrence of a maximum in the solar cell efficiency and short circuit photocurrent at 16.6% (w/w)10 + 83.4% (w/w) Pr4NI salt composition is an important finding. The efficiency enhancement of about 8% achieved by employing the binary iodide mixture in the gel electrolyte instead of a single iodide salt, could be utilized for achieving efficiency enhancement in many dye sensitized solar cell systems based on polymeric, gel or solvent electrolytes.

Removal of polycyclic aromatic hydrocarbons (PAHs) from groundwater by heterogeneous photocatalysis under natural sunlight

Abstract: Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants of special concern because they are carcinogenic and mutagenic compounds. In this paper, photodegradation of a mixture of six PAHs in groundwater at pilot plant scale is reported. Semiconductor materials (ZnO and TiO 2 ) as photocatalysts in tandem with Na 2 S 2 O 8 as oxidant under natural sunlight were used. The PAHs were benzo[ a ]pyrene, benzo[ b ]fluoranthene, benzo[ ghi ]perylene, benzo[ k ]fluoranthene, fluoranthene, and indene[1,2,3- cd ]pyrene. As expected, the influence of both semiconductors on the degradation of PAHs was very significant in all cases. Photocatalytic experiments show that the addition of photocatalyst, especially for ZnO/Na 2 S 2 O 8 system, strongly improves the elimination of PAHs in comparison with photolytic tests; significantly increasing the reaction rates. The first-order equation (monophasic model) satisfactorily explained the disappearance process although it ignores small residues remaining late in the process. These residues are important from an environmental point of view and the Hoerl function (biphasic model) better predict the results obtained. In our conditions, the time required for 90% degradation was in the range 7–15 min and 18–76 min for ZnO and TiO 2 systems, respectively. Thus, the use of the tandem ZnO/Na 2 S 2 O 8 makes possible the economical decontamination of groundwater containing non-biodegradable pollutants like PAHs.

Parameters affecting sulfonamide photo-Fenton degradation – Iron complexation and substituent group

Abstract: The photo-Fenton degradation of the sulfonamide antibiotics sulfadiazine (SDZ) and sulfathiazole (STZ) mediated by Fe(III)-oxalate was studied in this work. The influence of iron complexation, H 2 O 2 concentration and pH on the initial SDZ and STZ degradation rate was evaluated. Degradation of both antibiotics is drastically improved in the presence of Fe(III)-oxalate in comparison to free iron, achieving complete degradation after 8 min irradiation at pH 2.5 in the presence of 5 mM H 2 O 2 (equivalent to H 2 O 2 /antibiotic = 50). It was also possible to extend pH range of the photo-Fenton reaction by the use of Fe(III)-oxalate reaching more the 70% degradation at pH 6, however without significant mineralization. Comparison of the degradation kinetics of both sulfonamides indicated higher recalcitrance of STZ due to the lower electron density of its thiazol ring in relation to pyrimidine ring in SDZ.

Tuned CAM-B3LYP functional in the time-dependent density functional theory scheme for excitation energies and properties of diarylethene derivatives

Abstract: We present the CAM (Coulomb Attenuated Method)-B3LYP functional tuned for excitation energies and properties of diarylethene derivatives in the time-dependent density functional theory (TD-DFT) scheme. The CAM-B3LYP parameters are tuned so as to well reproduce the experimental excitation energies and properties of a prototypical diarylethene derivative. The TD-DFT method with the tuned CAM-B3LYP parameters ( μ = 0.150, α = 0.0799 and β = 0.9201) is found to semi-quantitatively reproduce several excitation energies obtained from the experimental UV–vis spectra of 15 closed forms of diarylethene derivatives. In contrast, it turns out that the use of default CAM-B3LYP parameters ( μ = 0.33, α = 0.19, and β = 0.46) fails to well reproduce these experimental UV–vis spectra. We also clarified that this difference does not originate from the functional dependence of the ground state optimized geometry, but from the CAM-B3LYP parameter dependences of excitation energies and properties in the TD-DFT scheme.

Photocatalytic (UV-A/TiO2) degradation of 17α-ethynylestradiol in environmental matrices: Experimental studies and artificial neural network modeling

Abstract: The efficiency of heterogeneous photocatalysis to degrade 17α-ethynylestradiol (EE2), a synthetic estrogen hormone, in environmentally relevant samples was investigated. In most cases, UV-A radiation at a photon flux of 2.81 × 10 −4 einstein/min was provided by a 9 W lamp and experiments were conducted at various concentrations of Aeroxide P25 TiO 2 (50–1000 mg/L), EE2 concentrations (50–900 μg/L) and water matrices (from ultrapure water to secondary treated wastewater). Some runs were performed at photon fluxes between 6.4 × 10 −7 and 3.7 × 10 −4 einstein/min to study the effect of intensity on degradation. Changes in estrogen concentration were followed by high performance liquid chromatography. EE2 degradation, which follows first order kinetics, increases with (i) increasing catalyst loading up to a threshold value beyond which it remains unaffected; (ii) increasing photon flux and (iii) decreasing matrix complexity, i.e. the organic and inorganic constituents of wastewater retard degradation. This may be overcome coupling photocatalysis with ultrasound radiation at 80 kHz and 41 W/L power density; the combined sonophotocatalytic process acts synergistically toward EE2 degradation. Several transformation products were identified by means of UPLC–MS/MS and a reaction network for the photocatalytic degradation of EE2 is suggested. An artificial neural network comprising five input variables (reaction time, TiO 2 and EE2 concentration, organic content and conductivity of the water matrix), thirteen neurons and an output variable (EE2 conversion) was optimized, tested and validated for EE2 degradation. The network, based on tangent sigmoid and linear transfer functions for the hidden and input/output layers, respectively, and the Levenberg–Marquardt back propagation training algorithm, can successfully predict EE2 degradation.

Comparison of Hombikat UV100 and P25 TiO2 performance in gas-phase photocatalytic oxidation reactions

Abstract: The superior performance of TiO2 Hombikat UV100 coatings compared to those made of Aeroxide TiO2 P25 was evidenced in the gas-phase UV-A photocatalytic oxidation of two very different molecules with two different on-stream behaviors: MEK and H2S Despite its lower crystallinity, UV100 could take advantage of a higher light transmission through the TiO2 coating, of its smaller particle size that could lead to a better balance between surface and bulk recombinations, and also of its larger surface area This last-mentioned characteristic is of considerable interest in regard to a possible increase of the coating's pollutant adsorption capacity and its ability to generate more OH radicals In respect of the H2S oxidation reaction, the UV100 coating could benefit from its larger surface area as a means to improve its ability to store larger amounts of sulfates and thus to enhance the photocatalyst's resistance to deactivation by poisoning sulfates

Photophysical properties and interactions of xanthene dyes in aqueous micelles

Abstract: Photosensitizers (PS) photodynamic activities are regulated by their location in the biological target, which modulates their photophysical and photochemical features. In this work the PS partition for the Xanthene Dyes Fluorescein ( FSC ), Eosin Y ( EOS ), Erythrosin B ( ERY ) and Rose Bengal B ( RBB ) in biomimetic models (SDS, CTAB and Pluronic P-123 micelles) and the effects on their photophysical characteristics are evaluated. The hydrophobic and electrostatic forces that govern the PS–micelle interaction are analyzed. At physiological pH (7.25), the ability of the dianionic protolytic form of the dyes to be positioned into the micelle palisade and its micelle interaction depends not only on the hydrophobicity of the dye but also on the micellar surface charge. The Binding Constants obey exactly the same order of the Partition Coefficients for the dyes in P-123 and CTAB micelles. The Stern–Volmer treatment pointed out that dyes are located inside the micelle, especially ERY and RBB . The magnitude of the dye–micelle interaction increased from SDS, P-123 and finally CTAB micelles due to the charges between dye and micelle, and among the xanthenes, their hydrophobic characteristics. Within the micelle pseudo phase, ERY and RBB are still very efficient photosensitizers exhibiting high quantum yield of singlet oxygen, which turns them very attractive especially with P-123 polymeric system as drug delivery systems in photodynamic therapy.

Effects of TiO2 nanoparticle polymorphism on dye-sensitized solar cell photovoltaic properties

Abstract: We present a joined experimental and theoretical investigation of the TiO2 polymorphism effects on dye-sensitized solar cells (DSSCs) photovoltaic properties. TiO2 nanoparticles of pure anatase, pure rutile and pure brookite stabilized phases with various sizes have been prepared by solution sol–gel approaches in order to evaluate their properties in photovoltaic devices. For a valuable comparison, these various nanoparticles have been used to construct identical solar cells. Their properties have been thoroughly estimated and analysed by J–V curves and impedance spectroscopy measurements along with first-principles calculations based on the density functional theory (DFT) under the B3LYP approximation. In the light of DFT calculations, the open circuit voltage (Voc) behavior of the solar cells is mainly explained by the dependency of the bottom of the conduction band position on the TiO2 phase. Quantifications of electron lifetimes, transfer times, diffusion coefficients (Deff) in the various polymorph TiO2 photoanodes are also of particular importance for explaining the photovoltaic properties of the different DSSCs. We have notably found a conductivity and Deff order being rutile < brookite < anatase. The comparison of anatase and brookite based-cells shows that the latter phase is very interesting for the considered application.

Singlet oxygen dosimetry using uric acid as a chemical probe: Systematic evaluation

Abstract: The singlet oxygen generation of a photosensitizer compound (PS) is an important property for photodynamic treatments. The PS quantum yield of 1 O 2 ( Φ Δ ) is usually obtained by the time-resolved measurement of 1 O 2 phosphorescence emission. However, the equipment employed is quite expensive. In the present study, the methodology previously proposed by us for Φ Δ dosimetry using uric acid (UA) as a chemical-probe was systematically evaluated. The PS photo-excitation was achieved with a polychromatic light source (LED) that generates 1 O 2 which attacks the UA. The level of UA oxidation is proportional to a parameter called chemical photodynamic efficiency, which is correlated to Φ Δ by comparing it to a standard compound. The photobleaching reaction of the PS is considered in the calculation. Several parameters that influence this measurement have been investigated with different PS (phenothiazines, xanthenes, chlorins, and benzoporphyrin dyes) in water, ethanol, and aqueous P-123 polymeric surfactant. Excellent results were obtained when standard compounds belonging to the same class of the photosensitizer and the same solvent were used. The chemical method of 1 O 2 evaluation with UA is reliable, exact, precise, easy to perform and low cost, although limited by the standard compound employed as Φ Δ Std .

Rice grain-shaped TiO2–CNT composite—A functional material with a novel morphology for dye-sensitized solar cells

Abstract: Titanium dioxide-multiwalled carbon nanotube (denoted as TiO 2 –CNT) nanocomposites with a novel rice-grains nanostructure are synthesized by electrospinning and subsequent high temperature sintering. The rice grain-shaped TiO 2 is single crystalline with a large surface area and the single crystallinity is retained in the TiO 2 –CNT composite as well. At very low CNT loadings (0.1–0.3 wt% of TiO 2 ), the rice grain shape remains unchanged while at high CNT concentrations (8 wt%), the morphology distorts with CNTs sticking out of the rice-grain shape. The optimum concentration of CNTs in the TiO 2 matrix for best performance in dye-sensitized solar cells (DSCs) is found to be 0.2 wt%, which shows a 32% enhancement in the energy conversion efficiency. The electrochemical impedance spectroscopy (EIS) and the incident photon-to-electron conversion efficiency (IPCE) measurements show that the charge transfer and collection are improved by the incorporation of CNTs into the rice grain-shaped TiO 2 network. We believe that this facile one-pot method for the synthesis of the rice-grain shaped TiO 2 –CNT composites with high surface area and single crystallinity offers an attractive means for the mass-scale fabrication of the nanostructures for DSCs since electrospinning is a simple, cost-effective and scalable means for the commercial scale fabrication of one-dimensional nanostructures.

Cu2S/TiO2 heterojunction applied to visible light Orange II degradation

Abstract: We report on the study of some physical properties of Cu2S and their effects toward the photoactivity of the Cu2S/TiO2 heterojunction. Transport properties of Cu2S, i.e. thermoelectric power and electrical conductivity were studied and correlated to the photoelectrochemical characterization to establish the energetic diagram of the Cu2S/TiO2 heterosystem. Corrosion tests of Cu2S and Cu2S/TiO2 electrodes were carried out by plotting the polarization curves in Orange II solution in the dark and under illumination to simulate the photoactive environment. We evaluate the performance of Cu2S and Cu2S/TiO2 by determining the fill factor and the energy conversion efficiency. Electrical Impedance Spectroscopy (EIS) is used for investigation of charge carrier dynamics in these photocatalytic devices. The valence and the conduction bands were estimated to be respectively of −0.3 and of −1.5 V, which enable electron injection from activated Cu2S to an activated TiO2. The p-Cu2S/n-TiO2 is optimized by its application to Orange II degradation under visible light. The best configuration “Cu2S(60%)/TiO2” shows its maximum degradation rate (Rinitial = 9 × 10−2 mg l−1 min−1) at 15 mg l−1 of Orange II (pH ∼ 6.8). The ideal irradiation intensity is estimated to be 18.88 × 10−6 kW which results in an electrical energy consumption per order of magnitude (EE/O) of 20.95 kW h m−3.

A combined experimental and theoretical study of natural betalain pigments used in dye-sensitized solar cells

Abstract: We report results of combined experimental and theoretical studies of betalain natural dyes used as sensitizers for TiO 2 dye-sensitized solar cells (DSSCs). To analyze the compliance of the various forms of betalain dyes with the main criteria that should be met by a dye to be used as TiO 2 sensitizer in a DSSCs, we performed density functional theory (DFT) calculations, which provided the optimized geometry, electronic structure and electronic spectrum of the dyes in fully protonated as well as partially deprotonated forms, in solution. We discuss the adsorption onto the substrate, the matching of the absorption spectrum of the dye with the solar spectrum, the energy level alignment with the semiconductor and the electrolyte, and the charge transfer to the substrate. By comparing the theoretical results with the experimental data we identify the betacyanins as the useful constituents of the betalain extracts and emphasize the role of extract purification.

Semiconductor-sensitized photodegradation of s-triazine and chloroacetanilide herbicides in leaching water using TiO2 and ZnO as catalyst under natural sunlight

Abstract: In the present study, the photocatalytic degradation of five s -triazine (simazine, prometryn, terbutryn, atrazine and terbuthylazine) and three chloroacetanilide (propachlor, s-metolachlor, alachlor) herbicides in leaching water has been investigated. Zinc oxide (ZnO) and titanium dioxide (TiO 2 ) were used as semiconductors at pilot plant scale under natural sunlight. The addition of an oxidant (Na 2 S 2 O 8 ) to the semiconductor suspensions led to an increase in the rate of photooxidation. Comparison of catalysts showed that ZnO was the most efficient for catalyzing the removal of the studied compounds. Thus, more than 70% of the herbicide amount initially present in the leaching water was degraded after 240 min of illumination in the ZnO/Na 2 S 2 O 8 system. Finally, some hydroxy and dealkylated derivatives of s -triazine herbicides were isolated during the experiment.

Photocatalytic oxidation of trimethylamine and isovaleraldehyde in an annular reactor: Influence of the mass transfer and the relative humidity

Abstract: This study presents an experimental investigation of the photodegradation of two volatiles organic compounds (VOCs): Trimethylamine (TMA) and isovaleraldehyde (ISOV). Experiments were performed by using an annular plug-flow reactor. The influence of the inlet concentration, flowrate and relative humidity (RH) on the conversion rate has been studied for the two VOCs. The increase of inlet concentration leads to a lower conversion rate due to the availability of the active sites. The flowrate increase also induces a lower degradation rate due to the shorter residence time. A kinetic model based on the Langmuir–Hinshelwood (L–H) approach and taking into account the mass transfer step was developed. This allows us to determine the adsorption and kinetic degradation constants with no influence of mass transfer. This latter could be estimated by a semi-empirical correlation. In small amounts, the presence of water vapor has a promoting effect on the degradation due to the formation of OH radicals. When the RH increases, the competition between water molecules and VOCs toward the active sites becomes predominant and the degradation rate decreases. A bimolecular L–H model, including mass transfer step, was developed. A good agreement with the experimental results was observed. Moreover by derivating the equation model, the optimum RH values could be estimated for the two pollutants. These RH values are equal to 40% for isovaleraldehyde and 25% for trimethylamine.

Optical limiting performance of meso-tetraferrocenyl porphyrin and its metal derivatives

Abstract: meso-Tetraferrocenyl porphyrin and its metal derivatives were found to be excellent optical limiters towards second harmonic of Q-switched Nd:YAG nanosecond laser. meso-Tetraferrocenyl porphyrin 3a, its zinc 3b, and copper 3c derivatives exhibited superior optical limiting performance than the benchmark fullerene C60, and rest of the metal derivatives 3d–3e are comparable. Reverse saturable absorption phenomena is mainly responsible for the optical limiting behaviour in these compounds. The ratio σex/σ0 was estimated from the nonlinear transmission characteristics of 3a–3e. The ratio σex/σ0 more than 7 was obtained in case of 3a, which makes them attractive candidates as optical limiting material.

Chemical determination of singlet oxygen from photosensitizers illuminated with LED: New calculation methodology considering the influence of photobleaching

Abstract: The singlet oxygen ( 1 O 2 ) is one of the reactive species responsible for the destruction of target cells in Photodynamic Therapy (PDT). However, the quantification of 1 O 2 yields ( Φ Δ ) involves lifetime measurements with very expensive equipment. An alternative methodology is the use of a chemical trap, in the present case uric acid (UA), which promptly reacts with 1 O 2 providing the evaluation of Φ Δ . On the other hand, in the quantification of the photons absorbed by the PS employing LED as irradiation sources in this kind of experiments, it is important to evaluate the overlap of the light source in the PS spectrum. Additionally, while some PS are photostable, others may undergo photobleaching leading the amount of absorbed photons to vary with the illumination time due to PS degradation. The proposed methodology corrects this problem. The proposed dosimetry method employing UA and the absorbed photon calculations taking into account chlorophyll and xanthene dyes photobleaching resulted in Φ Δ values that agree with the literature.

Binding interaction between plasma protein bovine serum albumin and flexible charge transfer fluorophore: A spectroscopic study in combination with molecular docking and molecular dynamics simulation

Abstract: Binding interaction of plasma protein bovine serum albumin (BSA) with external flexible charge transfer fluorophore 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been explored at physiological pH (7.4) by steady state absorption, emission, fluorescence anisotropy, Red Edge Excitation Shift (REES), far-UV circular dichroism (CD), time resolved spectral measurements in combination with molecular docking and molecular dynamics (MD) simulation studies. Chemical denaturation of the protein bound probe by guanidine hydrochloride (GdnHCl) has also been tracked using the spectral response of DMAPPDN. Interaction of the probe with BSA is reflected by the massive blue shift of the fluorophore emission maxima (78 nm) with the enhancement of fluorescence intensity due to change of hydrophobic micro-environment of the probe compared to a little change in protein secondary structure. Benesi–Hildebrand plot reveals spontaneous formation of 1:1 BSA–DMAPPDN complex with binding constant 8.821 ± 0.01 × 10 3 M −1 and binding free energy change −5.359 kcal mol −1 . Molecular docking study supports the binding of probe in the hydrophobic cavity of sub domain IIA of BSA. The distance for energy transfer from tryptophan of BSA to DMAPPDN measured from fluorescence resonance energy transfer (FRET) results is in good agreement with results of molecular docking study. MD simulation predicts greater stability of BSA–DMAPPDN complex compared to the free protein.

Structural, morphological, optical and photocatalytic characterization of ZnO–SnO2 thin films prepared by the sol–gel technique

Abstract: Thin films of the mixed ZnO–SnO 2 system were obtained by employing the sol–gel technique, starting from the mixture of zinc oxide and tin oxide precursor solutions. The tin atomic concentration percentages ( X ) in the precursor solutions with respect to the ZnO + SnO 2 total growing solution were: 0, 10, 20, 30, 40 and 100 at.%, here, the ZnO atomic percentage is (100– X ). The films were deposited by the dip coating method on glass substrates and were sintered at 450, 500 and 550 °C, in an open atmosphere. The X-ray diffraction patterns show the presence of zinc oxide and tin oxide crystals. The optical properties of the films were studied by UV–vis spectroscopy. The photocatalytic activity was quantified by means of the bleaching of methylene blue. The films of the mixed ZnO–SnO 2 system show higher photocatalytic activity than the SnO 2 and ZnO films.

Synthesis and spectral properties of a novel family of photochromic diarylethenes-2,3-diarylcyclopent-2-en-1-ones

Abstract: A novel family of photochromic diarylethenes – 2,3-diarylcyclopent-2-en-1-ones (DCPs) – having high abilities to the modification reactions of ethene “bridge” is proposed. A wide series of photochromic 2,3-diarylcyclopent-2-en-1-ones have been synthesized and switch properties of obtained compounds have been studied. The main advantage of this class of photochromic diarylethenes consists in their ability to simple and various ethene “bridge” transformations. Comparing to the commonly used approach of the variations of aryl substituents the transformation of the ethene “bridge” brings many benefits such as the simplicity of introduction of different functional groups for various applications and the investigation of the correlations between photochromic molecules structures and its spectral characteristics that in turn allow synthesizing novel photochromic compounds with defined properties.

Photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene in the gas-phase over TiO2-based catalysts

Abstract: In the present work, the photocatalytic oxidation of benzene, toluene, ethylbenzene and m-xylene (BTEX) in the gas phase over various UV-irradiated TiO 2 -based catalysts was studied. Specifically, five catalysts were tested: four based on P25 from Degussa adding 0.25% (w/w) Pt, Fe or Ce (P25, P25/Pt, P25/Fe, P25/Ce) and one prepared according to the isopropoxide method. Inlet BTEX concentrations ranged in 0.5–21 ppmv, whereas oxygen concentration was fixed (21%, v/v) at all experiments and the residence time was adjusted to 11.5 s. Ce addition to P25 catalyst led to the highest photocatalytic oxidation rates for benzene and ethylbenzene, whereas P25 proved to be the most active catalyst on toluene photo-oxidation. Regarding m-xylene, the choice of the most effective catalyst depended on m-xylene reactor concentration. Taking all experimental results into account, P25/Ce was the most effective catalyst due to its superiority in the case of benzene and ethylbenzene and its comparable performance to the base catalyst for toluene and m-xylene photocatalytic oxidation. In general, all P25 based catalysts were more active than the isopropoxide catalyst. All conversions showed great dependence on the inlet concentration of the target compound. Water addition to the reactor during ethylbenzene photo-oxidation enhanced the rates achieved for all catalysts tested. It has to be noted that the differences in the reaction rates achieved from catalyst to catalyst decreased with water vapours addition to the reactor. Finally, a Langmuir–Hinshelwood kinetic model has been applied to the experimental data obtained. The kinetic data obtained confirmed the strong beneficial effect of Ce addition to P25 catalyst on benzene and ethylbenzene photocatalytic oxidation.

Treatment of synthetic textile wastewater by homogeneous and heterogeneous photo-Fenton oxidation

Abstract: The efficiencies of homogeneous and heterogeneous photo-Fenton oxidation were compared for treatment of azo dye containing synthetic textile wastewater. The influence of parameters such as the presence of NaCl and starch was evaluated and optimal iron and H2O2 dosage determined. Complete decolorization of Remazol Red RR was achieved at all investigated NaCl and starch concentration. Mineralization, in terms of COD reduction, was 96% in the homogeneous and 93% in the heterogeneous reaction, but decreased with increasing NaCl and starch concentrations. The homogeneous oxidation showed the highest efficiency in treating synthetic wastewater containing Remazol Blue RR or a mixture of Remazol Red RR and Remazol Blue RR. Nevertheless, the mineralization was significantly lower than for Remazol Red RR, which shows the dependence on dye structure. Similar amounts of iron-containing sludge were produced in the two processes, while the release of iron ions was reduced by 50% when using heterogeneous photo-Fenton. Promising results were obtained when reusing the iron powder as catalyst; complete decolorization was achieved during 20 batches. (C) 2012 Elsevier B.V. All rights reserved. (Less)

Low cost and large area novel chemical synthesis of Cu2ZnSnS4 (CZTS) thin films

Abstract: Large area thin films of Cu2ZnSnS4 (CZTS) have been successfully deposited by a novel low cost chemical synthesis route. These CZTS films are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical, wettability and optical absorption techniques. The XRD analyses revealed the formation of polycrystalline CZTS thin films with tetragonal crystal structure after annealing at 673 K. The scanning electron micrographs showed total substrate coverage with randomly distributed and diffused interlocked cubes. The optical band gap was estimated to be 1.5 eV. Wettability test revealed that as deposited and annealed CZTS films are hydrophilic with water contact angles 46° and 65°, respectively. The photoactivity of CZTS is tested by forming photoelectrochemical cell in polyiodide electrolyte.

Elaboration, charge-carrier lifetimes and activity of Pd-TiO2 photocatalysts obtained by gamma radiolysis

Abstract: The surface of four commercial TiO2 compounds (Cristal Global PC-series) has been modified by Pd nanoparticles induced by gamma radiolysis. Their photocatalytic properties have been followed by phenol and rhodamine B photocatalytic degradation in aqueous suspensions under UV and visible light. Their electronic properties have been studied by time resolved microwave conductivity (TRMC) method to follow the charge-carrier dynamics. The experiments evidence a complex behavior of the surface-Pd. Its influence depends on the pollutant and on the irradiation. The modification may be strongly favorable to the photocatalytic activity. The results have been interpreted in terms of modification of charge-carrier dynamics with TRMC measurements. The surface-Pd plays a role in charge-carrier separations, increasing the photocatalytic activity under UV-light, but shows no effect on the absorption properties, preventing the creation of an activity under visible light.

Influence of the sodium/proton replacement on the structural, morphological and photocatalytic properties of titanate nanotubes

Abstract: Titanate nanotubes (TNTs) with different sodium contents have been synthesised using a hydrothermal approach and a swift and highly controllable post-washing processes. The influence of the sodium/proton replacement on the structural and morphological characteristics of the prepared materials was analysed. Different optical behaviours were observed depending on the Na + /H + samples’ content. A band gap energy of 3.27 ± 0.03 eV was estimated for the material with higher sodium content while a value of 2.81 ± 0.02 eV was inferred for the most protonated material, which therefore exhibits an absorption edge in the near visible region. The point of zero charge of the materials was determined and the influence of the sodium content on the adsorption of both cationic and anionic organic dyes was studied. The photocatalytic performance of the TNTs samples was evaluated in the rhodamine 6G degradation process. Best photodegradation results were obtained when using the most protonated material as catalyst, although this material has shown the lowest R6G adsorption capability.