Quantum Yields for the Photodegradation of Pollutants in Dilute Aqueous Solution: Phenol, 4-Chlorophenol and N-Nitrosodimethylamine

1996 ◽  
Vol 1 (2) ◽  
Author(s):  
Te-Fu L. Ho ◽  
James R. Bolton ◽  
Ewa Lipczynska-Kochany
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Peroxide ◽  
Quantum Yield ◽  
High Performance ◽  
Flash Photolysis ◽  
Quantum Yields ◽  
Visible Absorption ◽  
Dilute Aqueous Solution ◽  
Uv Visible ◽  
Photolysis Of Phenol

AbstractA broadband method has been applied to determine the quantum yields for the photochemical removal of three common pollutants: phenol, 4-chlorophenol and N-nitrosodimethylamine (NDMA) in dilute aqueous solution. Flash photolysis (xenon flash lamps) was used to cause a significant amount of photolysis without photolyzing intermediates. The analysis of reactant depletion following a single flash was carried out by high- performance liquid chromatography (HPLC) or UV/visible absorption spectroscopy. The method for determining quantum-yields employed p-benzoquinone as an actinometer and was validated by determining the average (200-400 nm) quantum yield for the generation of hydroxyl radicals from the photolysis of hydrogen peroxide (0.90 ± 0.10) and the quantum yields for the photolysis of phenol (0.13 ± 0.02) and 4-chlorophenol (0.24 ± 0.04). The values determined agree very well with the literature ones obtained with monochromatic radiation. The quantum yield for the direct photolysis of NDMA was found to be 0.11 ± 0.03 at neutral pH and 0.27 ± 0.02 at pH 2-4. Under conditions where hydrogen peroxide is the principal absorber, the NDMA quantum yield is 0.32 ± 0.04, independent of pH in the range 2-8.

The photoinsertion of tin(II) chloride into the metal–metal bond of hexacarbonylbis(tri-n-butylphosphine)dicobalt

1977 ◽  
Vol 55 (12) ◽  
pp. 2279-2285 ◽  
Author(s):  
Peter F. Barrett ◽  
Arnold Fox ◽  
Raymond E. March
Keyword(s):  
Quantum Yield ◽  
Quantum Yields ◽  
Insertion Reaction ◽  
Absorption Bands ◽  
Intense Band ◽  
Visible Absorption ◽  
Metal Bond ◽  
Metal Metal ◽  
Uv Visible ◽  
Limiting Value

The photochemical insertion reaction of SnCl2 into the metal–metal bond of [P(n-C4H9)3Co(CO)3]2 has been studied in THF at 23.0 °C at the irradiating wavelengths 365 nm, 436 nm, and 546 nm. At 365 nm, the quantum yield for the reaction increases with increasing concentration of SnCl2 and approaches a limiting value of 1.0. At 436 nm, however, the quantum yield increases above 1.0 and at 546 nm, quantum yields as high as 6 were measured. The uv–visible absorption spectrum of [P(n-C4H9)3Co(CO)3]2 shows an intense band at 372 nm and a broad shoulder at about 440 nm. A simple mechanism is proposed to operate on irradiation at 365 nm due to absorption by the intense band, but a more complicated chain mechanism is suggested to operate at 546 nm as a result of absorption by the lower energy shoulder band. It appears that both mechanisms operate on irradiation at 436 nm due to the overlap of the two absorption bands at this wavelength.

Remarkable kinetic stability of α-thiocarbamoyl substituted 4-methoxybenzylcations

1998 ◽  
Vol 76 (12) ◽  
pp. 1910-1915 ◽  
Author(s):  
Robert A McClelland ◽  
Victoria E Licence ◽  
John P Richard ◽  
Kathleen B Williams ◽  
Shrong-Shi Lin
Keyword(s):  
Key Words ◽  
Strong Interaction ◽  
Rate Constants ◽  
Flash Photolysis ◽  
Visible Absorption ◽  
Methyl Group ◽  
Thioamide Group ◽  
Azide Ion ◽  
Uv Visible ◽  
Leaving Groups

4-Methoxybenzyl cations bearing α-(N,N-dimethylcarbamoyl) and α-(N,N-dimethylthiocarbamoyl) substituents have been generated photochemically upon irradiation of precursors with pentafluorobenzoate or 4-methoxybenzoate leaving groups. The ions have been observed with flash photolysis in 40:60 acetonitrile:water and in 50:50 methanol:water, and rate constants were measured for their decay in solvent alone and for their capture by azide ion. The cations so studied and their lifetimes in 40% acetonitrile are 6, ArC+H-CONMe2, 0.6 μs; 2, ArC+H-CSNMe2, 7 ms; and 4, ArC+(CH3)-CSMe2, 6 ms, where Ar = 4-MeOC6H4. The cation 4 reacts with solvent by elimination of a proton from the α-methyl group, and the rate constant for solvent addition must be less than 1 s-1. The CSNMe2 substituted cations are 105-107-fold longer lived than analogs where the thioamide group has been replaced with an α-methyl. The UV-visible absorption spectra of these two cations also show significant differences from those of typical 4-methoxybenzyl cations. Thus, both the lifetimes and spectra point to a strong interaction of the benzylic centre with the thioamide group. Key words: flash photolysis, thiocarbamoyl stabilized carbocation, photosolvolysis.

Synthesis, spectroscopy, surface photovoltage, and electrochemical properties of porphyrin compound liquid crystals

2005 ◽  
Vol 09 (04) ◽  
pp. 231-239 ◽  
Author(s):  
Miao Yu ◽  
Guo F. Liu ◽  
Xiao L. Cui
Keyword(s):  
Liquid Crystalline ◽  
Molar Conductance ◽  
Quantum Yields ◽  
Surface Photovoltage ◽  
Luminescence Spectra ◽  
Redox Potentials ◽  
Visible Absorption ◽  
Surface Photovoltage Spectroscopy ◽  
Uv Visible ◽  
Hexagonal Columnar

Two series of porphyrin liquid crystalline compounds, meso-tetra-[(p-alkacyloxy-m-ethyloxy)phenyl]porphyrin ( TPAMEP ), and [5-(p-alkacyloxy) phenyl-10,15,20-tri-phenyl] porphyrin ( APTPP ) are synthesized and display a hexagonal columnar discotic columnar ( Col h ) phase. Their structure and properties were studied by elemental analysis, molar conductance, UV-visible and infrared spectra. Luminescence spectra of the compounds were discussed. Quantum yields of the Q band are in the region 0.007935-0.05847. The electrochemical studies show that the redox potentials do not change with the variation of the chain length. The surface photovoltage (SPV) response of the compounds was investigated by means of surface photovoltage spectroscopy (SPS) and field-induced surface photovoltage spectroscopy (FISPS), and the bands are analogous with the UV-visible absorption spectra.

Synthesis, photophysicochemical properties and TD-DFT calculations of tetrakis(2-benzoyl-4-chlorophenoxy) phthalocyanines

2014 ◽  
Vol 18 (04) ◽  
pp. 326-335 ◽  
Author(s):  
Yusuf Yılmaz ◽  
John Mack ◽  
M. Kasım Şener ◽  
Mehmet Sönmez ◽  
Tebello Nyokong
Keyword(s):  
Quantum Yield ◽  
Dft Calculations ◽  
Triplet State ◽  
Singlet Oxygen ◽  
Quantum Yields ◽  
Visible Absorption ◽  
H Nmr ◽  
Wide Range ◽  
Td Dft ◽  
The Impact

The synthesis of metal free, magnesium and zinc tetrakis(2-benzoyl-4-chlorophenoxy) phthalocyanine derivatives (2–4) is described along with their characterization by elemental analysis, IR, UV-visible absorption, and 1 H NMR spectroscopy and mass spectrometry. Trends observed in the fluorescence, triplet state, singlet oxygen and photodegradation quantum yields and the triplet state lifetimes are also analyzed. The compounds exhibit high solubility in a wide range of organic solvents and no evidence of aggregation was observed over a wide concentration range. The Zn ( II ) complex (4) was found to have a very high singlet oxygen quantum yield (ΦΔ = 0.78) in dimethylsulfoxide (DMSO) and a reasonably large triplet state quantum yield (ΦT = 0.82). The photophysical and photochemical properties clearly demonstrate that these compounds could prove useful in singlet oxygen applications such as photodynamic therapy (PDT). DFT and TD-DFT calculations were used to assess the impact of the positional isomerism of the 2-benzoyl-4-chlorophenoxy substituents on the electronic structures and optical spectroscopy.

Photolysis of hydrogen peroxide, photocatalytic effects of Cu(II) and reaction kinetics

1986 ◽  
Vol 51 (5) ◽  
pp. 973-981 ◽  
Author(s):  
Stanislav Luňák ◽  
Petr Sedlák ◽  
Josef Vepřek-Šiška
Keyword(s):  
Hydrogen Peroxide ◽  
Thermal Decomposition ◽  
Quantum Yield ◽  
Reaction Kinetics ◽  
Copper Ions ◽  
Oxidation States ◽  
Radiation Temperature ◽  
Quantum Yields ◽  
High Quantum ◽  
Catalytically Active

The quantum yield of hydrogen peroxide photolysis has been measured as a function of the concentration of photocatalytically active Cu2+ ions, intensity of photolytic radiation, temperature, and hydrogen peroxide concentration. The results obtained are consistent with the concept that high quantum yields of hydrogen peroxide photolysis (Φ >> 1) are due to thermal decomposition of hydrogen peroxide catalyzed by photochemically generated copper ions in oxidation states which are catalytically active.

Pyridone substituted phthalocyanines: Photophysico-chemical properties and TD-DFT calculations

2018 ◽  
Vol 22 (01n03) ◽  
pp. 25-31 ◽  
Author(s):  
Şaziye Abdurrahmanoğlu ◽  
Mevlüde Canlıca ◽  
John Mack ◽  
Tebello Nyokong
Keyword(s):  
Electronic Structure ◽  
Nmr Spectroscopy ◽  
Dft Calculations ◽  
Chemical Properties ◽  
Quantum Yields ◽  
Visible Absorption ◽  
H Nmr ◽  
Td Dft ◽  
Ft Ir ◽  
Uv Visible

4-(6-methyl-3-nitro-2-oxo-1,2-dihydropyridin-4-yloxy)phthalonitrile has been used to prepare a novel Zn(II) phthalocyanines with four peripheral pyridone substituents. The compound has been characterized by UV-visible absorption, FT-IR and [Formula: see text]H-NMR spectroscopy, elemental analysis and MALDI-TOF mass spectroscopy. The fluorescence, triplet quantum and singlet oxygen quantum yields have been determined and TD-DFT calculations have been used to identify trends in the electronic structure.

Synthesis of High-Performance Aqueous CdSe Quantum Dots Based on Combination of Se Source as Vapor-Phase and Hydrothermal Method

2010 ◽  
Vol 663-665 ◽  
pp. 96-99
Author(s):  
Heng Kang Qiu ◽  
Yue Shen ◽  
Lin Jun Wang ◽  
Jian Cheng Zhang ◽  
Kai Feng Qin
Keyword(s):  
Quantum Dots ◽  
Hydrothermal Method ◽  
Vapor Phase ◽  
High Performance ◽  
Hydrothermal Reaction ◽  
Water Soluble ◽  
Quantum Yields ◽  
Cdse Quantum Dots ◽  
Cdse Qds ◽  
Visible Absorption

High performance aqueous CdSe quantum dots (QDs) have been prepared by combination of Se source as vapor-phase and hydrothermal method. The main advantages of this approach included: one is to utilize H2Se vapor as a higher pure selenium source to make the prepared QDs have little other impurities, another is to obtain the QDs with characteristics of more rapid growth in the hydrothermal reaction. The as-prepared products have been characterized by ultraviolet-visible absorption spectra, photoluminescence spectroscopy (PL), X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive spectroscopy (EDS) analysis etc. The results show the as-synthesized water-soluble CdSe nanoparticles possess higher purity and quantum yields (QY), favorable narrow photoluminescence band with full width of half-maximum (FWHM) down to 40 nm, better photo-stability, and less synthetic time as compared with aqueous CdSe QDs obtained by other methods.

scholarly journals The UV-visible absorption cross-sections of IONO<sub>2</sub>

2002 ◽  
Vol 2 (3) ◽  
pp. 227-234 ◽  
Author(s):  
J. C. Mössinger ◽  
D. M. Rowley ◽  
R. A. Cox
Keyword(s):  
Cross Sections ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Laser Flash ◽  
Absorption Bands ◽  
Visible Absorption ◽  
Time Resolved ◽  
Model Calculations ◽  
Solar Photolysis ◽  
Uv Visible

Abstract. The UV-visible absorption spectrum of gaseous IONO2 has been measured over the wavelength range 245--415 nm using the technique of laser photolysis with time-resolved UV-visible absorption spectroscopy. IONO2 was produced in situ in the gas phase by laser flash photolysis of NO2/CF3I/N2 mixtures. Post flash spectra were deconvolved to remove contributions to the observed absorption from other reactant and product species. The resulting spectrum attributed to IONO2 consists of several overlapping broad absorption bands. Assuming a quantum yield of unity for IONO2 photolysis, model calculations show that during sunlit hours at noon, 53° N, the first order solar photolysis rate coefficient (J value) for IONO2 is 4.0 x 10-2 s-1.

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