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Excited state intramolecular proton transfer emission in bent core liquid crystals
Publication date: 1 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 358
Author(s): Ashok K. Satapathy, Santosh Kumar Behera, Rajeev Kumar, K.L. Sandhya, C.V. Yelamaggad, Balaram Sahoo
We report the photophysics of two bent-core liquid crystals (BLCs), C56H67NO9 (BLC1) and C55H65NO9 (BLC2), containing a Schiff-base and two long alkyl chains at its two ends. The ground state dipole moment and the electronic structures of the BLCs were calculated using density functional theory (DFT). The dipole moments of the liquid crystals were estimated experimentally via solvatochromic shift of the absorption and fluorescence spectra. The dipole moments obtained experimentally are in quite good agreement with theoretically calculated values. In the fluorescence spectra of both the BLCs show an interesting feature, i.e., dual emission. This dual emission is explained via the presence of two tautomeric forms (keto and enol) of the BLCs in the excited state. The band at ∼390–450 nm is assigned to the emission due to the keto-form, whereas the band at ∼340–370 nm is due to the emission from the enol-form. Irrespective of the solvents used, the keto-band is more intense than the enol-emission-band. This intense emission from the keto-form of the tautomers is demonstrated via the excited state intramolecular proton transfer (ESIPT). From the time resolved fluorescence spectroscopy studies, a longer lifetime is obtained for the keto-band. The associated vibrational states observed in the emission spectrum are responsible for this longer lifetime. Our finding of the dual emissive nature of the liquid crystals in the visible range is potentially useful for high temperature liquid crystal display and sensing applications.
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Editorial
Publication date: 1 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 358
Author(s): Haruo Inoue, Akihiko Kudo, Hitoshi Tamiaki
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A new SnS2-BiFeO3/reduced graphene oxide photocatalyst with superior photocatalytic capability under visible light irradiation
Publication date: 15 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 359
Author(s): Mojtaba Bagherzadeh, Reyhaneh Kaveh
Herein, we report the preparation of SnS2 nanoflakes decorated with bismuth ferrite (BiFeO3) nanoparticles and reduced graphene oxide (rGO) nanosheets. The crystal structures and morphology results of composite indicated that spherical BiFeO3 nanoparticles were homogeneously attached onto the surface of SnS2 nanoflakes with the decoration of rGO sheets. The optimized photocatalyst, i.e. SnS2 (1.5)-BiFeO3/rGO (0.15) composite not only exhibites the highest photocatalytic performance for the degradation of methylene blue (MB) and Methyl orange (MO) as model reaction under visible light illumination among the individual SnS2 and BiFeO3 photocatalysts but also retains the stable photodegradation efficiency of >95% for at least 5 cycles. The significant enhancement in photoactivity under visible light illumination can be attributed to the separation and transfer of charge carriers and provides the increased number of photocatalytic active sites. According to the obtained results, a plausible mechanism of the photodegradation of dyes under visible-light irradiation in the aqueous system was finally discussed.
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Study of the effectiveness of the flocculation-photocatalysis in the treatment of wastewater coming from dairy industries
Publication date: 1 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 358
Author(s): J.J. Murcia, M. Hernández-Laverde, H. Rojas, E. Muñoz, J.A. Navío, M.C. Hidalgo
The aim of the present work was to evaluate the effectiveness of flocculation-photocatalysis as combined processes in the treatment of dairy industries wastewater. Different commercial and lab prepared flocculants and photocatalysts were evaluated. All the materials prepared were extensively characterized. Commercial materials presented the best physicochemical properties and performance in the treatment of the studied wastewater. On one hand, all the photocatalysts evaluated showed bactericidal activity for E. Coli, total coliforms and other enterobacteriaceae. Total elimination of E. coli was obtained by using commercial TiO2 P25 Evonik, under 120 W/m2 of UV–vis light intensity and 5 h of total illumination time. Other species of bacteria remained after treatment under these conditions. It was also found that the highest light intensity of 120 W/m2 led to increase the Chemical Oxygen Demand and Total Organic Carbon in the samples treated, it can be due to the faster formation of new organic compounds as intermediaries during the photocatalytic reactions at the highest photonic flux. Flocculation pre-treatment of the wastewater samples led to improve the effectiveness of the photocatalytic treatment; thus, the combination of flocculation-photocatalysis treatments at low light intensity of 30 W/m2 leads to achieve the total elimination of E. coli, and under this intensity the elimination of total coliforms and other enterobacteriaceae increased 5.48% compared to the photocatalytic treatment alone. These treatment conditions led to comply the Colombian regulations for dairy wastewater.
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Removal of ciprofloxacin from water by nitrogen doped TiO2 immobilized on glass spheres: Rapid screening of degradation products
Publication date: 15 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 359
Author(s): Xuebin Xing, Zhenxia Du, Jingcong Zhuang, Di Wang
Nitrogen doped TiO2 (N-TiO2) powders with different nitrogen doping dosages (urea) were prepared by sol gel method. Then, the powders were immobilized on the glass spheres by sodium silicate to improve its recyclability. The structure and morphological properties also were characterized. A common antibiotic ciprofloxacin (CIP) as water pollutant, was degraded to evaluate the photocatalytic activity of N-TiO2 immobilized on glass spheres. N-TiO2 sample with N/Ti weight ratio of 0.34% exhibits highest visible photocatalytic activity and the removal rate of CIP reached 90% in 90 min under visible light irradiation. The photocatalytic efficiency was hardly reduced after 5 cycle experiments, indicating that the recyclability of immobilized N-TiO2 was well. The kinetic model of degradation of CIP was confirmed as a first-order kinetic reaction model. The degradation products of CIP were analyzed by ultra-performance liquid chromatography tandem quadrupole time of flight mass spectrometry (UPLC-Q-TOF MS). A database containing 49 kinds of the degradation products of CIP already reported in the papers was established to screen the UPLC-Q-TOF MS results. 17 kinds of degradation products were found and the possible degradation pathways to CIP were inferred. The toxicological properties of these degradation products were assessed by computer software simulation. In this study, a new, simple and stable immobilization method was used to prepare N-TiO2 immobilized on glass spheres, and a rapid screening method for the degradation products of CIP was established.
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Photophysics, photochemistry and thermally-induced redox reactions of a (Pterin)rhenium(I) complex
Publication date: 1 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 358
Author(s): Fabricio Ragone, Pedro David Gara, Fernando S. García Einschlag, Alexander G. Lappin, Guillermo J. Ferraudi, Ezequiel Wolcan, Gustavo T. Ruiz
In this work, we present a whole and deep study on the thermal redox and the photophysical and photochemical reactions of a tricarbonyl Re(I) complex coordinating Pterin, fac-ReI(CO)3(pterin)(H2O) (pterin = 2-amino-4-oxo-3H-pteridine). In aqueous solutions, the fluorescence of the complex is attributed to the emitting 1IL state (τemi ∼ 7.6 ns). In MeCN, however, the luminescence was ascribed to an overlapping dual emission from 1IL and 3MLCT states (τemi1 = 8.0 ns and τemi2 = 1.0 μs). Oxygen quenching of the 3MLCT based luminescence occurred with k q = 1.6 × 109 M−1 s−1. In glasses at 77 K, nevertheless, the 3MLCT prevailed over 1IL states. Flash photolysis experiments in aqueous solutions showed the spectrum of 3IL while in MeCN the presence of 3MLCT was evident. Pulse radiolysis experiments under oxidizing and reducing environments were performed in aqueous solutions of the Re-Pterin complex. By performing multivariate curve resolution − alternating least-squares (MCR-ALS), two species were identified under reducing conditions: an intermediate related to the semireduced radical of pterin ligand and the dihydrogenated [Re(CO)3(7,8-PtrH2)(H2O)] product. TD-DFT calculations helped to ascertain the nature of these species. Flash photolysis experiments where the excited states were reduced with triethylamine were in good agreement with pulse radiolysis experiments under reductive conditions. The oxidized transient spectrum was also obtained by pulse radiolysis, which compares very well with those published for Re(II) species, leading us to propose oxidation in the metal core as the reaction product of the transient under oxidizing conditions. The combination of different spectroscopic techniques along with the theoretical calculation allowed elucidating the nature, dynamics and reactivity of the excited states prevail in a Re-Pterin complex. This is of the particular importance considering that equivalent studies have not been reported for any other rhenium complex of substituted pterins nor for complexes of other transition metal ions of pterin derivatives.
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Manipulating [2 + 2] photodimerization of 1,4-dihydropyridines within γ-cyclodextrin
Publication date: 15 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 359
Author(s): Wuji Sun, Qiangwen Fan, Hong Yan
Irradiation of 1,4-dihydropyridines (DHPs) in the presence of γ-cyclodextrin (γ-CD) performs an efficient formation of the cage-dimer under a medium-pressure mercury lamp. The cage-dimer yields for DHPs complexed within γ-CD may achieve approximately 80%, far higher than those in the non-complexed state. It is postulated that the available cavity volume in γ-CD is responsible for the observed selectivity. The formation of 1:2 host-guest inclusion complex plays an important role in this reaction, and manipulates DHPs to perform [2 + 2] photodimerization as expected. In order to investigate the inclusion process, the spectral characteristics were investigated and the theoretical study was performed using density functional theory (DFT).
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Green synthesis of fluorescent N,O-chelating hydrazone Schiff base for multi-analyte sensing in Cu2+, F− and CN− ions
Publication date: 1 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 358
Author(s): Neeraj Saini, Nicha Prigyai, Chidchanok Wannasiri, Vuthichai Ervithayasuporn, Suda Kiatkamjornwong
A colorimetric and fluorometric hydrazone Schiff’s base derived from dehydroacetic acid by three-steps and high-yield syntheses under green approach employing ethanol as a solvent has been prepared. Multi-analyte sensing for both metal cation (Cu2+) and anions (F− and CN−), with high sensitivity and competitive selectivity, was encountered. The sensing mechanism of anion detection found to be deprotonation of NH and OH moieties in the presence of ions. However, metal cation like copper(II) ions chelation with sensor, leads to diminish intra-molecular charge transfer (ICT) with chelation induced quenching of fluorescence (CHQF). Contrary, anionic interaction ensued in heightened ICT as well as photo-induced electron transfer (PET) processes. The Job’s plots interpretation rendered stoichiometry of 2:1 with Cu2+/F− and 1:1 with CN−. Moreover, the detection limits of 0.962 ppm (Cu2+), 0.023 ppm (F−) and 0.073 ppm (CN−) were much lower than WHO guidelines. Further, either water or methanol was employed to differentiate F−/CN− ions with sensor in THF, with prominent visible naked eye and fluorometric responses.
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Photo-induced processes on Nb2O5 synthesized by different procedures
Publication date: 15 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 359
Author(s): C. Jaramillo-Páez, F.J. Sánchez-Fernández, J.A. Navío, M.C. Hidalgo
The properties of Nb2O5 strongly depend on its synthesis procedure as well as the conditions of ulterior thermal treatment. We report the synthesis of Nb2O5 powders prepared by sol-gel precipitation method using niobium(V) ethoxide as precursor. Two chemical routes were chosen: the presence of tryethyl amine (TEA) as precipitant/template agent, or the oxidant peroxide method. In addition, microwave-assisted activation was also used. The as-prepared samples by the above procedures were amorphous. Structural changes upon heating from room temperature up to 800 °C were investigated by X-ray powder diffraction technique combined with thermogravimetric analysis. The sequential thermal treatment up to 800 °C promotes the crystallization of hexagonal phase to orthorhombic phase whereas the ulterior cooling to room temperature lead to a mixture of both phases. Samples calcined at selected temperatures of either 600 °C or 800 °C for 2 h, were characterized by XRD, SEM, N2-adsorption and diffuse reflectance spectroscopy (DRS). The synthetic approach routes as well as the combined microwave activation followed by ulterior thermal treatment lead to changes not only on particle size but also on the textural properties of the synthesized catalysts. The catalysts synthesized have been evaluated using Rhodamine B (RhB) as a substrate, under both UV and visible lighting conditions. None of the catalysts synthesized showed activity in the visible. Under UV-illumination conditions, some of the catalysts exhibited a relatively low photoactivity in the degradation of RhB, which is associated with a photo-sensitizing effect. However, the addition of Ag+ ions considerably increased the activity of all the catalysts in the degradation of RhB under UV-illumination conditions. A mechanism is proposed to explain the photo-induced processes obtained, leaving the door open to the possible implications of the observed results in relation to the interaction of RhB dye with noble metal nanoparticles such as silver.
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Photoelectrochemical investigations in lead-free Ba (Ti0.950Sc0.025Nb0.025)O3 ferroelectric ceramics. Application to amoxicillin photodegradation
Publication date: 1 May 2018
Source:Journal of Photochemistry and Photobiology A: Chemistry, Volume 358
Author(s): N. Haddadou, N. Bensemma, G. Rekhila, M. Trari, K. Taïbi
The composition Ba(Ti0.950Sc0.025Nb0.025)O3 (BTSN) belongs to the (1 − x)BaTiO3–xBaSc1/2Nb1/2O3 system (x = 0.05). The room temperature X-ray diffraction (XRD) analysis refined by the Rietveld method shows a tetragonal perovskite structure. The dielectric study, carried out on the ceramics in the ranges (77–500 K) and (102–2 × 105 Hz), exhibits a normal ferroelectric behavior. The ferroelectric-paraelectric phase transition appears at the Curie temperature (TC) of 338 K with a wide space charge region. The maximal dielectric permittivity (εr) is characterized by a broader peak than that observed in BaTiO3 at the temperature Tc. The slight deviation from the Curie-Weiss law is typical of ferroelectric materials with a diffuse phase transition. The polarization-electric field (P-E) loop of BTSN is in good agreement with the XRD analysis. The BTSN ferroelectric ceramic exhibits interesting photoelectrochemical properties with an optical gap of 2.60 eV and a flat band potential of −0.58 V SCE . We successfully tested the photocatalytic oxidation of amoxicillin, a pharmaceutical antibiotic currently released in water as pollutant on BTSN. The oxidation follows a first order kinetic with a half-life of 123 min under solar light and a conversion yield of 72%.
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