Showing papers in "Journal of Photochemistry and Photobiology A-chemistry in 2013"

Improved photocatalytic activity of g-C3N4/TiO2 composites prepared by a simple impregnation method

Abstract: g-C 3 N 4 and TiO 2 hybrid structures are synthesized by means of a simple impregnation method having good photoactivities for the degradation of phenol under UV irradiation. From the wide structural and surface characterization we have stated that the presence of g-C 3 N 4 notably affect the surface feature of TiO 2 (surface area and pore size distribution). Enhanced photoactivities have been obtained for composites systems. The best result was obtained for 2 wt% loading of g-C 3 N 4 leading to a 70% of improvement with respect to bare TiO 2 in the reaction rate. The effective charge carrier separation was proposed as the responsible of such improved photoactivity.

Destruction of cyanobacterial toxin cylindrospermopsin by hydroxyl radicals and sulfate radicals using UV-254 nm activation of hydrogen peroxide, persulfate and peroxymonosulfate

Abstract: With increasing worldwide incidence of toxic cyanobacterial blooms in bodies of water, cylindrospermopsin (CYN) has become a significant concern to public health and water management officials. In this study, the removal of CYN by UV-254 nm-mediated advanced oxidation processes (AOPs) was evaluated. Cylindrospermopsin, at an initial concentration of 1 μM, was significantly degraded, 75% at a UV fluence of 80 mJ cm−2, 100% at 20 mJ cm−2, and 100% at 40 mJ cm−2, by UV/H2O2, UV/S2O82−, and UV/HSO5− processes, respectively, at an initial oxidant dose of 1 mM. The calculated second-order rate constants of CYN with hydroxyl radicals, k OH/CYN, was 5.1 × 109 M−1 s−1 and with sulfate radicals, k SO 4 − / CYN , was 4.5 × 109 M−1 s−1. The observed pseudo-first-order reaction rate constant increased linearly with increasing initial oxidant concentration. The destruction of CYN by both radicals was inhibited by radical scavengers, such as natural organic matter (NOM) and alkalinity. The presence of transition metals in tap water samples appeared to enhance the treatment efficiency of CYN by UV/HSO5−. The ICP-MS analysis of the metals in the water samples, revealed copper residual of 40.6 ± 3.3 μg L−1 in tap water, and 13.6 and 8.1 μg L−1 in two natural water samples. Results of this study suggest that the presence of transition metals in natural water sources could be an important factor in AOPs. This study is a new and feasible approach to remove CYN as well as other organic contaminants from water resources.

Photocatalytic degradation of atenolol in aqueous titanium dioxide suspensions: Kinetics, intermediates and degradation pathways

Abstract: Photocatalytic degradation of atenolol (ATL) was investigated in aqueous suspensions using TiO2 as photocatalyst. Complete degradation of 37.6 μM ATL was obtained after 60 min irradiation in pH 6.8 Milli-Q water in the presence of 2.0 g L−1 Degussa P25 TiO2. Degradation of ATL followed pseudo-first-order reaction kinetics. Hydroxyl radical (HO ) was determined to be the predominant reactive species during photocatalysis by means of radical probes. Major transformation products were elucidated by high performance liquid chromatograph-mass spectrometry (HPLC–MS/MS) technique. ATL photodegradation pathways included generation of 3-(isopropylamino)propane-1,2-diol and p-hydroxyphenylacetamide through ether chain cleavage, hydroxylation and the formation of 4-[2-hydroxy-3-(isopropylamino)propoxy] benzaldehyde. Frontier electron densities calculation verified the formation of mono-hydroxylation products with HO primarily attacking on benzene ring, which is in agreement with LC–MS/MS analysis. Five carboxylic acids, i.e., oxalic, glyoxylic, malonic, oxamic and formic acids were identified by ion exchange chromatography by comparison with authentic standards. Photocatalytic degradation efficiency of ATL was highly dependent on the properties of the water matrix, such as pH, the presence of organic and inorganic species (e.g., humic substance, HCO3−). River water matrix was found to play a detrimental effect on ATL photocatalytic degradation with a longer irradiation time required for complete elimination of mother compound and intermediate products. Degussa P25 exhibited the highest photocatalytic activity for oxidizing ATL as well as intermediates compared to Aldrich rutile, Millennium PC500 and Hombikat UV100.

Green synthesis of silver nanoparticles using sunlight

Abstract: Silver nanoparticles (AgNPs) are currently among the most widely used man-made nanomaterials, present in a huge range of consumer products. Here we report a simple ‘green’ method of AgNP synthesis of using an anionic surfactant without use of any additional reducing agents. It was observed that synthesis of AgNPs at room temperature (25–35 °C) using sodium dodecyl sulphate (SDS) and sunlight. The nanoparticles have been characterised using high-resolution transmission electron spectroscopy (HRTEM), UV–vis spectrophotometry, X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) and are found to have an average diameter of 30 nm. The nanoparticles are water soluble and the nature of the process is amenable to scaling up.

Photocatalytic decolorization of Rhodamine B dye using novel mesoporous SnO2–TiO2 nano mixed oxides prepared by sol–gel method

Abstract: The photocatalytic removal of Rhodamine B dye was successfully carried under UV irradiation over mesoporous SnO2/TiO2 nanoparticles embedded various molar compositions of SnO2 (0–25%) synthesized by sol–gel process using polymethylmethacrylate as template. Structural and textural features of the samples were investigated by X-ray diffraction (XRD), nitrogen adsorption–desorption isotherm, Fourier transformer infra-red (FTIR) and transmission electron microscope (TEM). The existence of tin oxide is associated with remarkable reduction in particle size to 6 nm and increasing the surface area up to161 m2/g revealing the successful role of SnO2 in manipulating high surface area nanoparticles. The TEM results revealed that well-dispersed and uniform spherical nanoparticles with diameters of 6 nm were embedded in the sample matrix. Both adsorption and UV irradiation are contribute for decolorization of about 92% of Rhodamine dye over the sample embedded 10% SnO2 after 3 h of the reaction compared with 70% only decomposition over pure titania. The photocatalytic decolorization of the dye follows a pseudo-first-order kinetics and the apparent rate constant was increase with increasing the tin oxide content up to 10%. The existence of tin oxide is associated with remarkable reduction in particle size, increasing the oxidizing power and increasing the efficiency of charge carrier separation which considered the main reasons for a remarkable increasing in the catalytic activity of the samples. As the mode of preparation is economically feasible, we can consider this catalyst to be very effective to decolorize various organic dyes.

Optimization of photocatalytic performance of TiO2 coated glass microspheres using response surface methodology and the application for degradation of dimethyl phthalate

Abstract: Hollow glass microspheres coated with photocatalytic TiO2 (HGM-TiO2), recently became commercially available and have the distinct advantages of easy separation and recovery after treatment. With this in mind, we determined the optimum conditions for hydroxyl radical generation from HGM-TiO2 photocatalysis using response surface methodology (RSM). The hydroxyl radical yield and its average generation rate are critical parameters for practical applications of TiO2 photocatalysis. In this study, terephthalic acid was used as a hydroxyl radical trap because of the selective formation of the readily detectable hydroxyl radical adduct, 2-hydroxy terephthalic acid. Three independent variables, including loading of HGM-TiO2, concentration of terephthalic acid and irradiation time, were investigated. The 3D response surface graphs of hydroxyl radical yield and average hydroxyl radical generation rate indicated that optimum conditions of loading of HGM-TiO2, concentration of terephthalate acid and irradiation time were 8.0 g/L, 4.0 mM, and 20 min, respectively. Under these optimized conditions, we measured the photocatalysis employing HGM-TiO2 for the remediation of dimethyl phthalate (DMP), as a representative compound for problematic phthalate acid esters. HGM-TiO2 photocatalysis leads to the rapid destruction of DMP and there is a linear correlation between the DMP destruction and hydroxyl radical production. The results of our study demonstrate RSM can be used to readily determine the optimal conditions for hydroxyl radical production and the subsequent treatment of target compounds may be correlated to the hydroxyl radical production during HGM-TiO2 photocatalysis.

Photochemical behavior of nanoscale TiO2 and ZnO sunscreen ingredients

Abstract: Most commercial sunscreens that use inorganic pigments (TiO2 and ZnO) employ materials with nanoscale dimensions so that the products are both transparent and smooth upon application. However, certain types of TiO2 and ZnO nanoparticles are well known for their ability to produce reactive oxygen species (ROS) upon UV illumination. Consumers would not be protected from the adverse effects of sun exposures if photoactive nanomaterials were employed in sunscreens. To evaluate whether this is the case, eight different commercial sunscreens, as well as nanoscale pigments derived from these products, were exposed to ultraviolet light and evaluated for ROS production. Redundant and complementary assays for detecting reactive oxygen species included dichlorofluorescein fluorescence, luminol chemiluminescence, and the decolorization of dyes (Congo red and Rose Bengal). Additionally, spin trap (POBN and DMPO) electron paramagnetic resonance spectroscopy provided quantitative measures of ROS generation upon UV illumination. Nanoscale TiO2 from neat sunscreens was relatively inactive upon illumination; inert oxide coatings such as alumina and silica apparently render the titania surfaces non-reactive. In contrast, ZnO derived from sunscreens produced substantial amounts of ROS upon UVA illumination. The photocatalytic activity of nanoscale ZnO suggests that more effective sunscreens would rely on strategies, such as surface coatings, designed to limit its ROS generation under ultraviolet illumination. Finally, the simple chemical assays presented here are ideal screening tools for ensuring sunscreen pigments were inert under ultraviolet illumination.

Effects of Fe(III)-concentration, speciation, excitation-wavelength and light intensity on the quantum yield of iron(III)-oxalato complex photolysis

Abstract: Iron(III)oxalato complexes do frequently occur in the environment, specifically in surface waters, in atmospheric waters (clouds, rain, fog) or in waste waters. Due to their high photo-reactivity and their absorption overlap with the actinic spectrum, Fe(III)oxalato complex photochemistry is widespread and of broad interest. Fe(III)oxalato complex photolysis in deaerated solutions using single excimer laser flash photolysis at 308 and 351 nm and continuous Hg(Xe)-lamp irradiation at 313, 366 and 436 nm was quantified via Fe(II) quantum yield measurements with phenanthroline complexometry and UV–vis detection. Measured Fe(II) quantum yields showed a dependence on initial Fe(III)ferrioxalate concentration and irradiation energy at below millimolar concentrations. Individual molar extinctions (in l mol−1 cm−1) and individual quantum yields (Φ) were determined for initial Fe(III) concentrations of 4.85 × 10−4 M for the 1:2 (FeOx2−) and 1:3 (FeOx33−) complexes applying a regression analysis for solutions containing variable ratios of 1:2 and 1:3 complexes: ɛ1:2, 308 nm = 2300 ± 90, ɛ1:3, 308 nm = 2890 ± 40, Φ1:3, 308 nm = 0.93 ± 0.09; ɛ1:2, 351 nm = 1040 ± 30, ɛ1:3, 351 nm = 1120 ± 20, Φ1:3, 351 nm =0.88 ± 0.08; ɛ1:2, 313 nm = 2055 ± 111, ɛ1:3, 313 nm = 2663 ± 37, Φ1:3, 313 nm = 0.12 ± 0.05; ɛ1:2, 366 nm = 753 ± 357, ɛ1:3, 366 nm = 709 ± 10, Φ1:2, 366 nm = 1.17 ± 1.46, Φ1:3, 366 nm = 0.91 ± 0.09; ɛ1:2, 436 nm = 55 ± 9, ɛ1:3, 436 nm = 22 ± 2, Φ1:2, 436 nm = 1.40 ± 0.40, Φ1:3, 436 nm = 1.00 ± 0.20. Individual quantum yields for the 1:2 complex could only be determined for the excitation wavelengths 366 and 436 nm due to non-linearity of the data for 308, 351 and 313 nm. The non-linearity is ascribed to complicated interactions of secondary reactions involving Fe(III)oxalato educt-complexes, carboxyl radicals and Fe(II)-radical complexes. The 1:2 complex has generally a higher quantum yield compared to the 1:3 complex at all considered wavelengths.

Photolysis of Fe(III) carboxylato complexes: Fe(II) quantum yields and reaction mechanisms

Abstract: Fe(III) carboxylato complex photochemistry can be of interest for environmental aqueous systems, oxidative processing of wastewater or laboratory photochemical applications in general. A comprehensive dataset of Fe 2+ quantum yields from the photolysis of aqueous Fe(III) complexes with malonate, succinate, glutarate, dl -tartrate, tartronate, gluconate, dl -lactate, dl -malate, pyruvate and glyoxalate has been measured. Irradiation techniques included single laser flash photolysis at 308 and 351 nm and continuous photolysis with a Hg(Xe) lamp-monochromator system at 313, 366, 405 and 436 nm. Complexes with ligands having a higher oxygen to carbon ratio tend to exhibit better photoreduction ability. Ligands containing OH, keto or diol functional groups in the α-position exhibit higher quantum yields than unsubstituted carboxylates (R-CH 2 -COOH). Generally, dissolved O 2 lowers the Fe 2+ quantum yield but at certain wavelengths, for some ligands this is the opposite. The influence of transient decay pathways and secondary red-ox reactions including interactions with dissolved O 2 has been investigated for Fe(III) glyoxalato complexes using kinetic simulations. Some complexes show a dependence of Fe 2+ quantum yield on the irradiation energy.

Enhanced photocatalytic degradation of dyes by TiO2 nanobelts with hierarchical structures

Abstract: a b s t r a c t TiO2 nanobelt membranes with hierarchical structure were successfully synthesized by sequentially autoclaving Ti at 190 ◦ C for 3 d in the presence of 10 M NaOH and 10 M KOH solutions. Microstructural characterization revealed TiO2 nanoparticles joining together and on the surface of nanobelts. These hierarchical structures form a three dimensional porous membrane which significantly enhances both surface specific area and light absorption, resulting in improved chemical adsorption capacity and pho- tocatalytic degradation efficiency relative to nanobelts with smooth surfaces using methylene blue as a model molecule. The adsorption of methylene blue to these structures follows a pseudo-second order kinetics chemisorption mechanism with rate-limited diffusion correlated to pore structure and size. The dominant reactive oxygen species are identified as hydroxyl radicals and valence band holes through the scavenging reaction. The synergistic enhancement of filtration through surface adsorption and pho- tocatalytic degradation is also demonstrated in a prototype photocatalytic membrane reactor with UV excitation at 365 nm. The reuse of nanobelt membranes after annealing shows the excellent recovery of TiO2 catalyst. These studies may contribute to additional applications of hierarchical TiO2 nanobelt membranes, including those harnessing sunlight for water treatment. © 2013 Elsevier B.V. All rights reserved.

Beyond the Beer–Lambert law: The dependence of absorbance on time in photochemistry

Abstract: The photochemical law governing chemical conversion of a photoactive species is derived and solved analytically. In the absence of solution mixing, the law predicts a remarkable symmetry in which the dependence of light intensity on distance matches the dependence of concentration on time. An exact method is described whereby a time sequence of experimental transmittance/absorbance data obtained during a light-induced chemical process can provide a value of the quantum yield for the photoreaction. It is demonstrated that this procedure is not invalidated by solution mixing.

Performance of UV/S2O82− process in degrading polyvinyl alcohol in aqueous solutions

Abstract: This study evaluates the performance of UV/S 2 O 8 2− process in degrading polyvinyl alcohol (PVA) in aqueous solutions. The effects of pH, Na 2 S 2 O 8 dose, initial PVA concentration, and addition of inorganic anions on the degradation efficiency of PVA were determined. The degradation efficiency of PVA followed the order pH 3 > pH 7 > pH 11. Additionally, higher Na 2 S 2 O 8 dose and lower initial PVA concentration were associated with high degradation efficiency of PVA. Moreover, adding Cl − and NO 3 − reduced the degradation efficiency of PVA. Radical scavenging tests adopted to identify predominant radicals reveal that SO 4 − was the predominant radical at pH 3, but OH was the predominant radical at pH 11. At pH 3, an Na 2 S 2 O 8 dose of 1.00 mM, an initial PVA concentration of 20 mg/L, and a temperature of 25 °C, the degradation efficiency of PVA in the absence of inorganic anions was 97% with the observed degradation rate coefficient of 0.3785 min −1 , as measured after 10 min. Comparison with heat/S 2 O 8 2− process reveals that UV/S 2 O 8 2− process can enhance the degradation of PVA at ambient temperature, suggesting that UV/S 2 O 8 2− process would be alternative to degrade PVA in aqueous solutions.

Tuning photophysical properties of triphenylamine and aromatic cyano conjugate-based wavelength-shifting compounds by manipulating intramolecular charge transfer strength

Abstract: A series of triphenylamine-based aromatic cyano compounds have been synthesized as red-emitting fluorophores with large Stokes shifts in both solution (>100 nm in CHCl3) and solid state (>150 nm in film). Intramolecular charge transfer (ICT) properties of the synthesized compounds are examined using UV–Vis absorptions, photoluminescence measurements and solvatochromic studies. Our studies suggest that Stokes shifts of these compounds can be fine-tuned by manipulating the ICT strength between donor and acceptor with various electronic donating groups, and the largest Stokes shifts are typically associated with compounds that have the strong ICT characters. The observed spectroscopic properties of the compounds are consistent with theoretical calculations using density function theory (DFT) or time-dependent density function theory (TD-DFT). The calculations suggest that the ICT occurs from localized HOMO to localized LUMO with magnitudes of 60–80%. The relative quantum yields of these fluorophores in solution are various and highly solvent dependent. In solid state, the quantum yields of the compounds are significantly increased and some can reach to 0.40.

Ceramic aerogels from TEMPO-oxidized cellulose nanofibre templates: Synthesis, characterization, and photocatalytic properties

Abstract: Aerogels are highly porous materials whose interesting chemico-physical properties can be exploited in several advanced applications. Ceramic aerogels based on titanium oxides, allow coupling the physical properties with the photocatalytic role of TiO2 in promoting pollutant photodegradation, selective organic photosynthesis, and antibacterial activity. Here, we prepared hybrid organic-ceramic aerogels via one-pot approach by mixing aqueous hydrogels of cellulose nanofibres with TiO2 or TiO2/SiO2 sols and subsequent freeze-drying of the obtained mixtures. The further calcination of the hybrid materials at suitable temperatures allowed achieving ceramic aerogels able to combine a pronounced adsorption efficiency of organic molecules with photocatalytic activity. The new materials have been characterized in terms of morphology, structure, and heterogeneous photo-degradation ability of potential pollutants. A possible explanation for the different behavior in adsorption affinity and photocatalytic efficiency is reported on the basis of the experimental evidences.

CdS/CdSe quantum dots co-sensitized solar cells with Cu2S counter electrode prepared by SILAR, spray pyrolysis and Zn–Cu alloy methods

Abstract: Herein, CdS/CdSe co-sensitized TiO 2 photoanodes for QDSSCs were prepared by successive ionic layer adsorption and reaction (SILAR), spray pyrolysis and zinc–copper alloy processes. The HR-TEM, SEM, EDS, XRD, UV–vis and I – V curve analyses were performed to investigate the surface and structural properties of the prepared electrodes and the efficiencies of the fabricated QDSSs. Employing different methods for preparation of Cu 2 S counter electrode affected the performance of QDSSCs under one illumination of sun (100 mW/cm 2 ) so that various conversion efficiencies ( μ ) of 3.18, 0.341 and 0.266% were measured in alloy, SILAR and spray pyrolysis methods, respectively. Therefore, among these methods, the zinc–copper alloy process with higher efficiency is preferred that gives fill factor (ff) and short circuit density ( J SC ) values of 0.44 and 11.69 mA/cm 2 . The HR-TEM images showed that CdS and CdSe QDs are in close contact with TiO 2 nanoparticles and the sizes of CdS and CdSe QDs are about 5 and 6 nm, respectively. The energy-dispersive X-ray spectroscopy (EDS) measurement confirmed that CdS and CdSe QDs are successfully deposited on the surface of the TiO 2 film. The band gaps estimated from Tauc plots using UV–vis spectra vary from 3.1 eV (without CdS and CdSe, bare TiO 2 ) to 2.38 eV (TiO 2 /CdS (3)/CdSe). The SEM images of Cu 2 S counter electrodes prepared by zinc–copper alloy indicated nanosheets with high porosity that is much suitable for injection of electrolyte while in two other approaches (SILAR and spray pyrolysis), large (∼50–70 nm) and small (∼10–17 nm) nanoparticles were observed without high porosity.

Photo-Fenton degradation kinetics of low ciprofloxacin concentration using different iron sources and pH

Abstract: The aim of the present study was to compare the degradation kinetics of low (1 mg L−1) and high (25 mg L−1) concentrations of ciprofloxacin (CIP) aiming to decrease the concentration of additives and evaluate the pH limitation by the use of low iron concentrations and organic ligands. A parameterized kinetic model was satisfactorily fitted to the experimental data in order to study the performance of photo-Fenton process with specific iron sources (iron citrate, iron oxalate, iron nitrate) under different pH medium (2.5, 4.5, 6.5). The process modeling allowed selecting those process conditions (iron source, additives concentrations and pH medium) which maximize the two performance parameters related to the global equilibrium conversion and kinetic rate of the process. For the high CIP concentration, degradation was very influenced by the iron source, resulting in much lower efficiency with iron nitrate. At pH 4.5, highest TOC removal (0.87) was achieved in the presence of iron citrate, while similar CIP conversions were obtained with oxalate and citrate (0.98 after 10 min). For the low CIP concentration, much higher conversion was observed in the presence of citrate or oxalate in relation to iron nitrate up to pH 4.5. This behavior denotes the importance of complexation also at low dosages. Appropriate additives load (320 μM H2O2; 6 μM Fe) resulted in a CIP conversion of 0.96 after10 min reaction with citrate up to pH 4.5.

TiON and TiON-Ag sputtered surfaces leading to bacterial inactivation under indoor actinic light

Abstract: a b s t r a c t This study reports the details Escherichia coli inactivation kinetics on TiON and TiON-Ag films sputtered on polyester by direct current reactive magnetron sputtering (DC) and pulsed magnetron sputtering (DCP) in an Ar/N2/O2 atmosphere. The use of TiON leads to bacterial inactivation avoiding leaching of Ag. The surface of TiON and TiON-Ag was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), electron microscopy (EM), X-ray fluorescence (XRF) and contact angle (CA) measurements. Evidence for the photocatalyst self-cleaning after the bacterial inactivation was shown by XPS, contact angle (CA) and the Zetasizer zeta-potential of the proteins. The photo-induced charge transfer from Ag2O and TiO2 is discussed considering the relative positions of the electronic bands of the two oxides. An interfacial charge transfer mechanism (IFCT) for the photo-induced electron injection is suggested. The most suitable TiON coating sputtered on polyester was 70 nm thick and inactivated E. coli within 120 min under low intensity visible/actinic light (400-700 nm, 4 mW/cm 2 ). TiON-Ag sputtered catalysts shortened E. coli inactivation to ∼55 min, since Ag accelerated bacterial inactivation due to its disinfecting properties. Evidence is presented for the repetitive performance within short times of the TiON and TiON-Ag polyester under low intensity visible light.

Investigation of OH radicals formation on the surface of TiO2/N photocatalyst at the presence of terephthalic acid solution. Estimation of optimal conditions

Abstract: The fluorescence technique for estimation of OH radicals formation on the surface of TiO 2 photocatalyst has been reported. However in this method the linear dependence between formation of 2-hydroxyterephthalic acid (2-HTA) and irradiation time not always is obtained. In this paper the influence of TA concentration on the formation of 2-HTA at the presence of TiO 2 /N photocatalyst and UV irradiation is discussed. It was proved that for low concentration of TA, its transformation to 4-hydroxybenzoic acid (4-HBA) took place whereas at higher concentration of TA formation of both, 4-HBA and 2-HTA was noticed. However there is an optimal amount of TA at which the highest yield of 2-HTA could be obtained. For the excess amount of TA an inner filter effect was observed which resulted in the reducing the yield of 2-HTA formation. Two techniques, high performance liquid chromatography (HPLC) and fluorescence spectroscopy were applied for controlling formation of TA decomposition products.

Gas phase photocatalytic oxidation of decane at ppb levels: Removal kinetics, reaction intermediates and carbon mass balance

Abstract: This study focuses on the photocatalytic oxidation of decane at ppb levels, close to indoor air conditions. Although these concentrations are typical of indoor air volatile organic compound (VOC) levels, such conditions have been poorly investigated to date. Decane conversion rates higher than 90% were reached within 15 h for the highest initial concentration tested in the operating conditions used. Despite this high decane conversion, 18 reaction intermediates were detected in the gas phase. The main compounds, in terms of concentration level in the gas phase, were formaldehyde, acetaldehyde and propanal. The amounts of these compounds in the gas phase were linearly dependent on the initial decane concentration. A reaction pathway is proposed, based on reaction intermediate temporal profiles and the literature. It consists of six main steps describing the oxidation process from decane to CO and CO2. The influence of the relative humidity level on the diversity and amounts of reaction intermediates was also studied. It was shown that moisture tends to shift the equilibrium of intermediates adsorption toward desorption, resulting in a relative increase in intermediate quantities in the gas phase. However, the monitoring of CO and CO2 formation highlighted that, at the end of the reaction, a high mineralization rate could be obtained. Finally, an overview of the photocatalytic reaction is given through the carbon mass balance determined for various reaction advancements. This approach gives an overall evaluation of the photocatalytic process performance, from primary compound removal to reaction intermediate and mineralization.

A new porphyrin bearing a pyridinylethynyl group as sensitizer for dye sensitized solar cells

Abstract: A novel porphyrin dye extended at one meso -position via an pyridinylethynyl group acting as anchoring group and three phenyl COOMe groups was synthesized and used as sensitizer for the fabrication of dye sensitized solar cells (DSSCs). The overall power conversion efficiencies (PCE) of DSSCs based on this porphyrin dye as sensitizer with and without CDCA coadsorbant are 3.36% and 4.56%, respectively. To improve the PCE of DSSC, we have incorporated Ag nanoparticles into the nano-porous TiO 2 photoanode i.e. FTO/TiO 2 /Ag-NPs and found a enhancement up to 5.66%. The improved photovoltaic performance of the DSSCs with modified photoanode is attributed to the (i) the increased light harvesting efficiency due to the plasmon enhanced optical absorption induced by Ag nanoparticles, (ii) reduced back recombination process at TiO 2 /dye/electrolyte interface, (iii) improved electron lifetime, and (iv) formation of Schottky barrier at TiO 2 /NPs-Ag.

Effect of the spectral properties of TiO2, Cu, TiO2/Cu sputtered films on the bacterial inactivation under low intensity actinic light

Abstract: Bacterial inactivation by TiO2, Cu and TiO2/Cu DC-magnetron sputtered thin films was systematically investigated in the dark and under low intensity visible/actinic light. Low intensity actinic light led to a fast 6log10 (complete) bacterial inactivation within the minute range. The TiO2/Cu bifunctional composite films led to the fastest bacterial inactivation. The Cu sputtered on the TiO2 enabled the absorption of visible light by the supported film and triggered a photo-induced IFCT effect from TiO2 to the Cu/Cu-ions. Evidence for a direct relation between the films optical absorption obtained by diffuse reflection spectroscopy (DRS) and the bacterial inactivation kinetics (CFU) is presented. The film microstructure was characterized by X-ray fluorescence (XRF) and X-ray photoelectron spectroscopy (XPS). The Tiand Cu-ions in solution were followed by inductive coupled plasma spectroscopy (ICPS). The small amount of Cu-ions determined by ICPS provide the evidence for an oligodynamic effect during bacterial inactivation. The Cu-redox changes and the ratio of the oxidized C /reduced C species were determined by XPS within the bacterial inactivation time.

Functional singlet oxygen generators based on porphyrazines with peripheral 2,5-dimethylpyrrol-1-yl and dimethylamino groups

Abstract: Photochemical, photophysical and spectral properties of three synthesized porphyrazines, with 2,5-dimethylpyrrol-1-yl and dimethylamino substituents were studied to test their potential usefulness in photodynamic therapy. The porphyrazines are metallated at the core with Mg(II) – MgPz and Zn(II) – ZnPz ions; the third one was in demetallated form ( 2HPz ). The compounds were irradiated with a xenon lamp. The photodegradation, steady-state and time-resolved absorption and emission studies of porphyrazines were performed in different solvents. Quantitative evaluation was made on the basis of photodegradation kinetic parameters. The photodegradation process appeared to follow in two ( MgPz and ZnPz ) or one ( 2HPz ) stages first-order kinetics. The demetallated porphyrazine was found to be more stable then MgPz and ZnPz . Solvatochromic effects were evaluated by monitoring the changes in UV–vis spectra. The correlation between the Q-band shift towards longer wavelengths and the refractive index of the solvent was tested. The fluorescence spectra were evaluated and the quantum yield of emission was determined. Singlet oxygen generation and quantum yield ( Φ Δ ) were investigated, in aerobic condition and in the environment with limited access of oxygen with 1,3-diphenylbenzisofuran as a chemical quencher. The mechanism of photochemical reaction for all Pzs studied was proved to be of type II.

Aquatic photochemistry of the sulfonamide antibiotic sulfapyridine

Abstract: The photolytic behavior of the sulfonamide antibiotic sulfapyridine in water was investigated using a laboratory photoreactor approximating full-spectrum sunlight. Direct photolysis of sulfapyridine was rapid, with a half-life of 2.6 h and 31 min, and an observed quantum yield of 0.0013 ± 0.0002 and 0.013 ± 0.001, for the neutral species and fully deprotonated species, respectively. Direct photolysis rates increased dramatically with degree of deprotonation, with measured p K a 1 and p K a 2 values of 2.22 ± 0.03 and 8.58 ± 0.02, respectively. Indirect photolysis was assessed using water from constructed wetland mesocosms. A four-fold increase in the dissipation rate of sulfapyridine was observed due to the influence of high levels of dissolved organic carbon, after accounting for light screening by such materials. Nitrates had no observable effect on indirect photolysis rates. Major photoproducts identified were SO 2 extrusion and OH addition products. These results show that photolytic processes are a major removal mechanism of sulfonamide drugs in aquatic systems.

Enhanced photo-Fenton process for tetracycline degradation using efficient hydrogen peroxide dosage

Abstract: The remediation of water solutions containing tetracycline antibiotic (TC) using photo-Fenton treatments has received scarce attention in the literature. However TC deserves attention due to its condition of emerging contaminant. In this work, TC oxidation in water solutions (12 L, 40 mg L −1 ) by means of photo-Fenton reaction under variable hydrogen peroxide dosage is investigated. This shows a more efficient use of the hydroxyl radicals produced in the reaction medium and enhances treatment performance. First, a suitable range of Fenton reagent loads is determined in a preliminary study. The hydrogen peroxide dosage is parameterized through two variables: the initial release of the total load, y 0 (kick-off), and the time t ini at which the continuous dosage of the rest of the load starts. Hence, a design of experiments (2 2 ) can be used to characterize the performance of the process under different hydrogen peroxide dosage protocols. The results obtained this way show that total TC remediation is attained in all the cases studied, but alike amounts of hydrogen peroxide lead to total mineralization only when the dosage scheme is conveniently tuned. Therefore, the photo-Fenton treatment has proved to be effective in removing TC from water solutions, and the opportunity for an efficient dosage to reduce the requirements of hydrogen peroxide has also been confirmed.

Enhanced photoanode properties of CdS nanoparticle sensitized TiO2 nanotube arrays by solvothermal synthesis

Abstract: We demonstrate the synthesis of CdS-sensitized TiO2 (CdS/TiO2) nanotube arrays via the solvothermal method and describe their enhanced photoelectrochemical properties. Our new approach prevents the clogging of CdS quantum dots (QDs) at the TiO2 nanotube mouth and promotes the uniform deposition of a polycrystalline CdS on the densely aligned TiO2 nanotube arrays (TiO2 NTAs). The deposition of CdS onto the TiO2 NTA can be controlled by the deposition time and the concentration of the precursors. Photoelectrochemical measurements indicate that the electrode synthesized via the solvothermal method can achieve a stable photocurrent density of 5.7 mA/cm2 at 0-V versus Ag/AgCl under AM 1.5 G illumination, which is approximately 10% higher than that prepared using the chemical bath deposition (CBD) method. Solvothermally prepared CdS/TiO2 NTAs exhibit 125-fold enhancement in their photocurrent under visible light compared with bare TiO2 NTAs, indicating facile photogenerated electron transfer from CdS to TiO2. Solvothermally prepared CdS/TiO2 NTAs shows better photostability and longer lifetime of photoelectrons compared to those prepared by CBD method suggesting more favorable CdS–TiO2 NTA interfacial contact. In general, we propose that this methodology can be useful in designing multijunction semiconductor configuration such as coating nanostructures.

A Simple Inexpensive Method for the Rapid Testing of the Photocatalytic Activity of Self Cleaning Surfaces

Abstract: A rapid, semi-quantitative, inexpensive method, using a simple digital scanner and an indicator ink, suitable for use in the laboratory, or in the field, for assessing the photocatalytic activity of commercial photocatalytic self-cleaning materials, such as glass, is described. The repeatability of the current method is found to be high and better than many of the previously reported ISO photocatalyst tests.

Synthesis of In2O3-graphene composites and their photocatalytic performance towards perfluorooctanoic acid decomposition

Abstract: Perfluorooctanoic acid (PFOA) is an emerging persistent organic pollutant, which cannot be effectively decomposed by TiO2-base photocatalysis under mild condition. The In2O3-graphene composite was synthesized and its photocatalytic performance for PFOA decomposition was investigated. The graphene was enwrapped on the surface of In2O3 via a sonication-assisted solution route followed by heat treatment. The coverage of graphene on In2O3 was influenced by the calcination temperature. The In2O3 samples partially enwrapped by graphene showed enhanced activity for PFOA decomposition, while full coverage with graphene harm the photocatalytic activity of In2O3.

Improving UV seawater disinfection with immobilized TiO2: Study of the viability of photocatalysis (UV254/TiO2) as seawater disinfection technology

Abstract: Industries located in coastal areas and maritime transport are economic activities that use large amounts of seawater. In most cases, this water requires disinfection treatment to avoid fouling problems in industrial facilities or to prevent environmental impacts after used seawater is released. This study proposes the photocatalysis with immobilized TiO 2 as a disinfection treatment for seawater and evaluate its efficacy by comparing with UV 254 radiation treatment. The experiments were carried out employing artificial seawater and using an annular UV reactor in the laboratory scale tests. Two species of marine bacteria were used as microbial indicators of the treatment efficacy: Alteromonas sp and Corynebacterium stationis . The photocatalytic treatment had faster disinfection kinetics than that using UV 254 light for both bacteria species, being necessary between 30 and 33% less UV dose to achieve the same level of disinfection. The catalyst used for photocatalytic treatment showed a progressive decay of activity until its complete inactivation after 215 h of treatment, due to factors such as fouling or catalyst loss.

Photoluminescent PMMA polymer films doped with Eu3+-β-diketonate crown ether complex

Abstract: In this work it is reported the photoluminescence sensitization effect of the bis(dibenzo-18-crown-6)diaquatris(thenoyltrifluoroacetonate)europium(III) compound, [Eu(tta) 3 (DB18C6) 2 (H 2 O) 2 ], doped into a blend of poly(methylmethacrylate) (PMMA) and polyethylene glycol (PEG) in film form. The TGA results indicate that the Eu 3+ -complex precursor is immobilized in the polymer matrix by the interaction between the Eu 3+ complex and the oxygen atoms of the PMMA polymer. The thermal behavior of these luminescent systems is similar to that of the undoped polymer. The emission spectra of the Eu 3+ -complex in the PMMA/PEG blends recorded at room temperature exhibit the characteristic bands arising from the 5 D 0 → 7 F J ( J = 0–4) intraconfigurational transitions. The emission quantum efficiency of the Eu 3+ ion doped films increased significantly, indicating an effective interaction between the Eu 3+ -complex and the polymer matrix, and both the substitution of water molecules in the first coordination sphere and an efficient luminescence co-sensitization of the Eu 3+ luminescent centers.

Facile synthesis, sensor activity and logic behaviour of 4-aryloxy substituted 1,8-naphthalimide

Abstract: A series of 4-phenoxy- and 4-alkoxy-1,8-naphthalimide fluorophores have been synthesized in high yields at room temperature applying novel facile synthesis One of the compounds was designed as a fluorescent PET sensor according to the “ fluorophore-spacer-receptor ” model The ability of this molecule to detect protons and transition metal cations with pronounced selectivity towards Fe 3+ was demonstrated Moreover the 4-phenoxy substituted 1,8-naphthalimides were highly solvent sensitive and able to detect small quantities of water The potential of the 1,8-naphthalimide sensor to execute INHIBIT logic function at molecular level was also demonstrated