Journal of Photochemistry & Photobiology, A: Chemistry (v.194, #1)

Treatment of paper pulp and paper mill wastewater by coagulation–flocculation followed by heterogeneous photocatalysis by Angela Claudia Rodrigues; Marcela Boroski; Natalia Sueme Shimada; Juliana Carla Garcia; Jorge Nozaki; Noboru Hioka (1-10).
In this work is investigated the combined treatment of post-bleaching effluent from a cellulose and paper industry. The biodegradability index determined by the biochemical oxygen demand (BOD)/chemical oxygen demand (COD) ratio of in natura sample was 0.11, which implies little biodegradability and that it may not be discharged to the environment without previous treatment. First, the effluent was submitted to the coagulation–flocculation treatment applying FeCl3 as the coagulating agent and chitosan as an auxiliary. In sequence, the aqueous soluble phase obtained from the first treatment was submitted to a UV/TiO2/H2O2 system using mercury lamps. The optimized coagulation experimental conditions were chosen: pH 6.0, 80 mg L−1 of FeCl3·6H2O, and 50 mg L−1 of chitosan. The optimized photocatalysis conditions were: pH 3.0 in 0.50 g L−1 of TiO2 and 10 mmol L−1 of H2O2. COD values for the in natura sample was 1303 mg L−1 and after the optimized conditions of coagulation without chitosan and in chitosan presence were 545 and 516 mg L−1, respectively. Effluent turbidity decreased sharply after coagulations (from 10 FTU of in natura samples to 2.5 FTU without chitosan and 1.1 FTU with chitosan). Similarly, a decrease was observed for concentrations of N-ammoniac, N-organic, nitrate, nitrite, phosphate, and sulfate ions after coagulation. Additionally, it was observed an absorbance reduction of 90% at the wavelength of 500 nm and of 70–80% in regions corresponding to aliphatic and aromatic groups (254, 280, and 310 nm). The use of chitosan for quantitative purposes was not so efficient; however, it improves sedimentation and compaction. COD results of photolyzed samples by UV/H2O2 were 344 mg L−1, UV/TiO2 326 mg L−1, and UV/TiO2/H2O2 246 mg L−1. The reduction in absorbance intensity was approximately 98% for aliphatic and aromatic chromophores, and 100% for chromophores absorbing at 500 nm with color disappearance. During photodegradation, SO4 2− was formed (∼340 mg L−1 for the coagulated sample to ∼525 mg L−1) suggesting again the mineralization of the pollutant. The combined method (coagulation followed by photocatalysis) resulted in a biodegradability index of 0.71, transparency, and absence of color and odor in the treated water, suggesting again good water quality. This result is reinforced by the toxicity studies employing Artemia salina bioassay, which showed that an expressive decrease in toxic pollutants in effluents after treatment, mainly by combined processes. The wastewater treatment carried out in association at optimized experimental conditions provided good results.
Keywords: Wastewater; Coagulation; FeCl3; Photocatalysis; TiO2;

The shape and size of TiO2/ZnO composite nanoparticles can be manipulated by introducing surfactants and different Zn/Ti(OBu)4 molar ratios during the synthesis process. Different sizes of spherical TiO2/ZnO composite nanoparticles are obtained when sodium dodecyl benzene sulfonate (DBS) and different Zn/Ti(OBu)4 molar ratios are used. Cubic TiO2/ZnO composite nanoparticles, hexagonal nanorods, and nanobelts are obtained when sodium dodecyl sulfonate (SDS) and different Zn/Ti(OBu)4 molar ratios are used. The XRD study shows that there is no obvious difference in crystal composition of various shapes of TiO2/ZnO composite nanoparticles. The photocatalytic degradation of methyl orange shows significant variation in rate that decreases in the order: TiO2/ZnO composites >TiO2 (with surfactant but no Zn) >TiO2 (without surfactant and Zn). An optimal Zn/Ti(OBu)4 molar ratio of 0.25:1 is found to achieve the highest photocatalytic activity of TiO2/ZnO composite nanoparticles.
Keywords: TiO2/ZnO composite nanoparticles; Shape control; Photocatalytic activity;

A new ionic liquid based quasi-solid state electrolyte for dye-sensitized solar cells by Miao Wang; Xong Yin; Xu Rui Xiao; XiaoWen Zhou; Zheng Zhong Yang; Xue Ping Li; Yuan Lin (20-26).
Ionic liquid based quasi-solid state electrolytes were prepared by solidifying the ionic liquid electrolytes containing 1-hexyl-3-methylidazolium iodide (HMImI) or a binary mixture of HMImI and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) with an ionic liquid polymer poly (1-oligo (ethylene glycol) methacrylate-3-methylimidazolium chloride) (P(MOEMImCl)), respectively. The improvements of the ionic conductivity and the apparent diffusion coefficient of triiodide are observed in the binary ionic liquid mixture gel electrolyte. The thermal stability of the quasi-solid state electrolytes is determined by thermogravimetric analysis. The ionic liquid based quasi-solid state electrolytes were successfully used to fabricate the dye-sensitized solar cells achieving the conversion efficiency of 6.1% under the light intensity of 100 mW cm−2.
Keywords: Ionic liquids; Ionic liquid polymer; Quasi-solid state electrolytes; Dye-sensitized solar cells; Conversion efficiency;

Grid type dye-sensitized solar cell module with carbon counter electrode by Won Jae Lee; Easwaramoorthi Ramasamy; Dong Yoon Lee; Jae Sung Song (27-30).
To realize low cost, high-performance dye-sensitized solar cell (DSSC) technology on industrial scale, large area grid type DSSC module has been prepared on silver grid-embedded transparent conducting glass substrate. Commercial titanium dioxide (TiO2) and carbon powders were employed to make working and counter electrodes, respectively. Under simulated solar light (AM 1.5, P in: 100 mW cm−2), 5 cm × 5 cm size carbon counter electrode module with an active area of 11.2 cm2 shows V OC: 0.730 V, I SC: 118 mA, FF: 0.55 with 4.23% active area efficiency, which is comparable to 5.26% of platinum counter electrode module.
Keywords: Solar cell; Counter electrode; Metal grid; Module; Efficiency;

A quasi-solid-state dye-sensitized solar cell based on porous polymer electrolyte membrane by Xiao Zhang; Cong-Xiao Wang; Fu-You Li; Yong-Yao Xia (31-36).
Water was employed as plasticizer to produce porous polymer membrane. The gel polymer electrolyte containing 72% liquid organic electrolyte (0.5 M LiI, 0.05 M I 2, 0.5 M 4-tert-butylpyridine in PC) shows ionic conductivity of 6.4 × 10−4  S cm−1 due to its high porous structure. Moreover, the porous electrolyte membrane shows good mechanical strength and serves as a separator in the solar cells. Quasi-solid-state solar cells fabricated with this gel electrolyte displayed energy conversion efficiency of 6.0% when the cell gap was tuned to 30 μm. Moreover, these cells possessed much better long-term stability compared with those based on liquid organic electrolyte.
Keywords: Quasi-solid-state dye-sensitized solar cell; Gel polymer electrolyte; Porous membrane;

1-(2-Quinolyl)-2-naphthol: A new intra-intermolecular photoacid–photobase molecule by T.C. Chien; L.G. Dias; G.M. Arantes; L.G.C. Santos; E.R. Triboni; E.L. Bastos; M.J. Politi (37-48).
Photochemical and photophysical properties of 1-(2-quinolyl)-2-naphthol (2QN) in water and organic solvents, as well in glassy media were studied to investigate the occurrence of intramolecular excited state prototropic reactions between the naphthol and quinoline rings. Spectral data show the two chromophores apparently behaving independently. However, in acid aqueous media or in low polarity solvents a new electronic transition red shifted band with respect to that of the parent compounds assigned to an intramolecular H-bond and to a quinoid form, respectively, shows up. Model calculations and R–X data lend support to a minimum energy conformer having a dihedral angle of ∼ 39° between the two groups. Singlet excited state properties (S1) show a high suppressive effect of one ring over the other, resulting in very low emission yields at room temperature. The occurrence of excited state intramolecular proton transfer is observed in water (zwitter ion form) and in low polarity media (quinoid form) and originates from a previously CT H-bonded state. Phosphorescence data allowed a reasonable description of the electronic states of 2QN. In addition two new derivatives were prepared having the N atom blocked by methylation and both the N and O groups blocked by a CH2 bridge. The spectral data of these two compounds confirmed the attributions made for 2QN.
Keywords: Photoacid; Photobase; Charge transfer; Excited state intramolecular proton transfer;

A new ligand, ethylenediiminobi(6-hydroxychromone-3-carbaldehyde) Schiff-base (L), was prepared by condensation of 6-hydroxy-3-carbaldehyde chromone (CDC) with ethylenediamine. Its three rare earth complexes have been synthesized and characterized on the basis of elemental analyses, molar conductivities, mass spectra, 1H NMR, thermogravimetry/differential thermal analysis (TG-DTA), UV–vis spectra, fluorescence spectra and IR spectra. The general formula of the complexes is [LnL·(NO3)2]·NO3 [Ln = Sm (1), Eu (2), La (3)]. Complexes 1, 2 and 3, and ligand L were subjected to biological tests in vitro using HepG2 cancer cell lines. Ligand showed significant cytotoxic activity against HepG2cancer cell lines. Spectrometric titration, ethidium bromide displacement experiments and viscosity measurements indicate that Sm(III) and Eu(III) complexes strongly bind with calf thymus DNA, presumably via an intercalation mechanism. The intrinsic binding constants of complexes 1 and 2, and ligand with DNA were 9.28 × 106, 8.40 × 106 and 4.88 × 106  M−1 through fluorescence titration data, respectively.
Keywords: Ethylenediiminobi(6-hydroxychromone-3-carbaldehyde) Schiff-base; Rare earth complexes; DNA binding;

1-Oxoindan-2-yl and 1,3-dioxoindan-2-yl esters as photoremovable protecting groups by Jaromír Literák; Ľubica Hroudná; Petr Klán (59-66).
1-Oxoindan-2-yl and 1,3-dioxoindan-2-yl carboxylic acid esters react with an excess of hydrogen atom or electron donors to release the corresponding acids, in addition to indan-1-one and indan-1,3-dione, respectively, as by-products. The maximum degradation quantum yields of 1-oxoindan-2-yl esters in H-donating propan-2-ol were found to approach 10, indicating that a chain reaction process, involving hydrogen transfer from the ketyl radical intermediates formed from an excited ester by hydrogen abstraction from an alcohol, participates. Such a cleavage mechanism parallels that observed earlier in photolysis of phenacyl esters. The corresponding 4,7-dimethyl substituted derivatives showed no contribution of the photoenolization mechanism apparently because of electronic and geometric reasons. Both 1-oxoindan-2-yl and 1,3-dioxoindan-2-yl chromophores are proposed to be utilized as photoremovable protecting groups in applications when higher concentrations of the hydrogen/electron donors are experimentally feasible.
Keywords: Photochemistry; Hydrogen abstraction; Electron transfer; Indanone; Indandione; Carboxylic acid esters;

A comprehensive study of the spectral and photophysical properties of arylthiophenes by J. Seixas de Melo; J. Pina; L.M. Rodrigues; R.S. Becker (67-75).
A series of conjugated oligomers with rigid (fused-ring) structure, consisting in different polycyclic aromatic hydrocarbons (PAHs) possessing a single thiophene unit, here designated as arylthiophenes, were investigated in solution. For presentation clarity, the compounds were organized in two different groups. The first group includes the compounds where one, two, three and four benzene rings are added to a thiophene unit (a compound with two dibenzothiophene units was also investigated) and the second group includes those compounds where a single thiophene ring is located at different positions in a skeletal-type polyaromatic hydrocarbon (in the present case phenanthrene). The study includes a complete spectroscopic evaluation (including singlet–singlet and triplet–triplet absorption, fluorescence and phosphorescence spectra) as well as a photophysical evaluation (fluorescence, phosphorescence and triplet lifetimes together with fluorescence and triplet occupation quantum yields. With all the above, a complete set of deactivation rate constants (k F, k IC and k ISC) was determined. From the fluorescence and phosphorescence spectra the energy of the lowest lying singlet and triplet states (S1 and T1) and the energy of splitting between the two states ( Δ E S 1 – T 1 ) was obtained. Semi-empirical ZINDO/S-CI calculations were performed and corroborated the nature and state order experimentally obtained.
Keywords: Photochemistry; Photophysics; Arylthiophene; Fluorescence; Phosphorescence; Quantum yields; OLEDs; Oligomer; Laser flash photolysis; Thiophene; Phenanthrene;

Reactive rate constants for the quenching of the triplet state of 9,10-phenanthrenequinone by 2-propanol were measured using laser flash photolysis and deuterium isotope effects for the abstraction of the alpha hydrogen (deuterium) were determined. The values of k H/k D were 1.69, 1.45, and 1.36 in carbon tetrachloride (CCl4), chlorobenzene (CB), and acetonitrile (MeCN), respectively. These results are in agreement with a mechanism involving initial hydrogen abstraction and eliminate a mechanism involving initial electron transfer.This same reaction was studied for the triplet of benzophenone. Values of k H/k D were 2.56, and 2.28, in CCl4, and MeCN, respectively. The rate of hydrogen abstraction was faster in MeCN than in CCl4. These results are explained considering a polar transition state which is stabilized by polar solvents.
Keywords: Aromatic ketones; Ortho-quinone; Solvent effects; Transition state;

Indirect photometry and multinuclear 13C and 183W NMR study of tungstate complexes of sugar acids by Miloudi Hlaïbi; Mustapha Hor; Amina Riad; Fatiha Toumri; Jean-François Verchère; Stella Chapelle (81-91).
The tungstate complexes of the sugar acids, meso-tartaric and l-gulonic acids, have been studied in aqueous solutions. Indirect photometry has been used to determine the stability constants and the stoichiometry of these colourless complexes. Multinuclear 13C and 183W NMR spectroscopies have been used to specify the structures of the complexes and the sites of chelation of the ligand. For meso-tartaric acid, complexes of the lactic type with a mononuclear and with a dinuclear tungsten core have been identified. In these type lactic complexes, only the hydroxyl groups of the carboxyl function and the atom carbon in α position belong to the site of chelation of the tungstate complexes. Both α-hydroxyacid moieties of the meso-tartaric acid are involved in the chelation.For l-gulonic acid, lactic type complexes with a mononuclear and a dinuclear tungsten core have been observed at acidic pH. Upon increasing the pH, the lactic complexes disappear: first the mononuclear, then the dinuclear complexes. In pH range 4–8, for gulonic acid, dual lactic, threo (tetradentate) type complexes occur, the dual lactic, erythro and lactic, threo complexes exist. At pH 10, for gulonic acid, a single complex has been identified in which the ligand is pentadentate. In this complex, all carbon atoms of the ligand are involved in the site of chelation except the carboxyl atom.
Keywords: Tungstate complexes; Indirect photometry; Multinuclear 13C and 183W NMR; Site of chelation; Lactic type complexes; Erythro and threo type complexes;

The absorption and fluorescence spectral properties of 4-amino-6-oxopyrimidine (1), which has a simple streptopolymethine merocyanine skeleton, clearly showed that the molecule 1 formed the aggregate 1 n , and showed an exciton band, appearing at an absorption of 350 nm due to the red-shifted HOMO–LUMO transition. Upon light irradiation of the exciton band, a fluorescence band at 398 nm (Φ FL  = 0.10) was observed, and its decay lifetimes were determined. Based on these spectral features, the aggregated 1 n was found to be formed by J-type aggregation. The molecular orientation 1 in the crystal was revealed as being both parallel π–π stacking and hydrogen bonding chains.
Keywords: Exciton interaction; J-aggregate; Merocyanine; Fluorescence; Self-assembly;

Studies on photolithography and photoreaction of copolymer containing naphthyl in ultrathin nanosheets induced by deep UV irradiation by Wenjian Xu; Tiesheng Li; Gouliang Zeng; Suhua Zhang; Wei Shang; Yangjie Wu; Tokuji Miyashita (97-104).
A novel polymer containing photoactive naphthyl group, poly (N-dodecylmethacrylamine/β-naphtylmethacrylate) (pDDMA-NPMA) was synthesized and its molecular arrangement and photochemical reactions were investigated in ultrathin film. The polymer p (DDMA-NPMA) could self-aggregate into a crystal film at air/water interface and this monolayer could be transferred onto solid supports, giving Y-type uniform Langmuir-Blodgett (L-B) films. Upon deep UV irradiation, photochemical reaction occurred in L-B films, and the irradiated parts could be eliminated as the verified images of optic-microscopy, resulting in a fine positive tone photolithographic patterns with a resolution of 0.75 μm. Changes of molecular chemistry induced by the 248 nm light treatment were investigated by atomic force microscopy, fluorescence, ultraviolet, Flouried transform infrared spectroscopy and gel permeation chromatography (GPC). The results showed that the main route of the photoreaction was dimerization of the naphthylene, and then photodecomposition of not only naphthyl group but also main chains of polymer. In the present paper, several possible mechanisms of photochemical reaction induced by deep UV light were also proposed.
Keywords: Photochemistry; Langmuir-Blodgett films; Naphthyl; Polymer; Photodecomposition; Photolithography;

Excited-state proton transfer and geminate recombination in the molecular cage of β-cyclodextrin by Young-Shin Lee; Oh-Hoon Kwon; Han Jung Park; Jan Franz; Du-Jeon Jang (105-109).
Excited-state proton transfer and geminate recombination in aqueous heptakis(2,6-di-O-methyl)-β-cyclodextrin have been compared with those in water by monitoring the photoinduced prototropic tautomerization of 6-hydroxyquinoline, which occurs via forming anionic intermediate. Enol deprotonation decelerates by 18 times whereas its reverse process accelerates slightly with encapsulation. The imine protonation of the intermediate slows down by 8.2 times in the molecular cage. These unusual kinetic features have been explained with the geminate recombination of protons as well as the structural dynamics of solvent molecules and the relative energetics of involved species.
Keywords: Excited-state proton transfer; Heptakis(2,6-di-O-methyl)-β-cyclodextrin; 6-Hydroxyquinoline; Geminate recombination; Solvation energy;