Shuzo Kutsuna

Effect of Pd-photodeposition over TiO2 on product selectivity in photocatalytic degradation of vinyl chloride monomer

Abstract Effects of metal co-catalysts, Pd and Pt, on photocatalytic degradation of vinyl chloride monomer (VCM) were studied. Pd-photodeposited TiO 2 (Pd-TiO 2 ) did not produce any chlorinated organic compounds into the gas phase, while pure TiO 2 produced monochloroacetylchloride and phosgene. The amounts of CO and formic acid formed by Pd-TiO 2 were much smaller than those by TiO 2 , and the CO 2 production proceeded selectively. However, Pd-TiO 2 decomposed VCM more slowly and produced a larger amount of adsorptive chlorinated organic compound, as compared with TiO 2 . Photodeposited Pd is considered to inhibit the VCM decomposition pathway in which the gaseous byproducts are formed by the aid of Cl − ion adsorbed on the photocatalyst. The electron spin resonance (ESR) suggested that the photodeposited Pd suppress the formation of active species, such as Ti 3+ , O 2 − and OH, which are responsible for the formation of gaseous byproducts.

Photochemical decomposition of pentafluoropropionic acid to fluoride ions with a water-soluble heteropolyacid photocatalyst

Abstract Pentafluoropropionic acid (CF 3 CF 2 COOH; PFPA) was decomposed to F − and CO 2 with a water-soluble homogeneous photocatalyst, H 3 PW 12 O 40 . This is the first example of a photocatalytic system for CF bond cleavage in a perfluorinated acid compound having both CF 3  and CF 2  units. The catalytic reaction proceeds in water at room temperature under irradiation with UV-Vis light in the presence of oxygen. Gas chromatography–mass spectrometry (GC–MS) showed no trace of environmentally undesirable species such as CF 4 , which is often observed in the decomposition of perfluorinated compounds by extremely high energy techniques such as electron beam irradiation. In addition to F − ions, small amounts of trifluoroacetic acid (TFA) were detected in the reaction solution. The proposed reaction mechanism involves redox reactions of PFPA and TFA with the catalyst.

A product study of the OH radical initiated oxidation of perchloroethylene and trichloroethylene

Abstract Gas-phase reactions of perchloroethylene (PER) and trichloroethylene (TCE) initiated with hydroxyl radical (OH) were studied by using a photochemical reaction chamber, in order to clarify their degradation products, particularly carbon tetrachloride (CCl4) in connection with stratospheric ozone depletion by chlorine. As degradation products of PER, phosgene (COCl2), trichloroacetylchloride (TCAC) and CCl4 as well as CO and CO2 were identified, while dichloroacetylchloride (DCAC) and chloroform (CHCl3) were observed for TCE. Formation of CCl4 was confirmed, but its yield was estimated to be lower than 0.1% of the PER degraded. It was inferred that chlorine atom produced through the PER-OH and TCE-OH reactions was involved in the degradation of PER and TCE, leading to formation of TCAC and DCAC in that order and that CCl4 and CHCl3 was probably produced through photodecomposition of TCAC and DCAC, respectively.

Adsorption and reaction of trichlorofluoromethane on various particles

As a possible tropospheric sink of trichlorofluoromethane (CCl3F), its adsorption and reaction on solid particles were studied with or without UV light longer than 310 nm. The adsorption and photodesorption occurred for most of the particles examined. The amounts depended not only on the BET surface area but also on the chemical property of the particles. The reaction rates were less than 0.1% h-1. The surface induced degradation of CCl3F in air was confirmed under photoirradiation at room temperature by the detection of Cl- or F- on some metal oxides. When the particles were pretreated with heat and evacuation, the reaction rate became larger and disproportionation of CCl3F took place. The tropospheric lifetime of CCl3F was reevaluated based on a reported model. It is suggested that the heterogeneous reaction of CCl3F on particles may be a possible tropospheric sink.

Oxygen-induced efficient mineralization of perfluoroalkylether sulfonates in subcritical water.

The decomposition of perfluoroalkylether sulfonates C(2)F(5)OC(2)F(4)SO(3)(-) and C(3)F(7)OC(2)F(4)SO(3)(-) in subcritical water was investigated, and the results were compared with those for perfluorobutanesulfonate (C(4)F(9)SO(3)(-)), which has no ether linkage. This is the first report on the use of subcritical water to decompose perfluoroalkylether sulfonates, which are being developed as alternative surfactants to environmentally persistent and bioaccumulative perfluoroalkylsulfonates. Whereas C(4)F(9)SO(3)(-) showed little reactivity in subcritical water, C(2)F(5)OC(2)F(4)SO(3)(-) decomposed efficiently in subcritical water ( approximately 350 degrees C) in the presence of oxygen gas to form F(-) and SO(4)(2-) in the aqueous phase and CO(2) in the gas phase as major products. Trifluoroacetic acid (CF(3)COOH, TFA) and trifluoromethane (CF(3)H) were also detected as minor products in the aqueous and gas phases, respectively. Similar decomposition behavior was observed for C(3)F(7)OC(2)F(4)SO(3)(-), which decomposed at a rate that was somewhat higher than that of C(2)F(5)OC(2)F(4)SO(3)(-). When argon was used in place of oxygen gas, the time profile of the decrease in the amount of C(2)F(5)OC(2)F(4)SO(3)(-) remained almost unchanged, but the product distribution changed markedly: the amounts of F(-), SO(4)(2-), and CO(2) dramatically decreased, the amounts of TFA and CF(3)H increased, and a new product, HCF(2)SO(3)(-), was detected. These results clearly indicate that treatment with subcritical water in the presence of oxygen gas effectively mineralized perfluoroalkylether sulfonates to F(-), SO(4)(2-), and CO(2). On the basis of a product analysis, we propose a decomposition mechanism.

Fourier transform infrared measurement of the formation of nitrogen compounds on sodium chloride particles exposed to the ambient air in the Arctic

The role of heterogeneous reactions on sea salts in the formation of particle nitrogen compounds in the Arctic during polar sunrise was studied. A diffuse reflection type Fourier transform infrared spectrometer was used to measure surface products on sodium chloride (NaCl) particles exposed to the ambient air at Alert, Northwest Territories, Canada (82.5°N, 62.3°W). The accumulation of nitrogen compounds on NaCl was observed in both winter and spring, while the rate in winter was greater. The important role of ambient N2O5 as well as HNO3 in the formation of nitrogen compounds on NaCl is deduced. The nitrogen compounds observed might be mainly composed of nitrate ion whose electronic states were different from those of nitrate ion in water solution and/or crystal. Its reactivity, including its possible photolysis to NO2−, is noted as to a potential formation pathway of particle nitrite in spring.

Transformation and decomposition of 1,1,1-trichloroethane on titanium dioxide in the dark and under photoillumination

Abstract 1,1,1-Trichloroethane (CH3CCl3) in dry air was decomposed to carbon dioxide (CO2), chlorine (Cl2) and hydrogen chloride (HCl) at 313–353 K through a heterogeneous photochemical reaction on titinium dioxide (TiO2). The reaction proceeded on TiO2 mainly through the following two steps: (1) thermal catalytic elimination of HCl to produce 1,1-dichloroethene (CH2CCl2), and (2) photochemical decomposition of CH2CCl2 to CO2 and other products. Photo-oxidation of chloride took place on TiO2, which could keep the catalytic activity of TiO2, since inhibitors like HCl could be removed from the surface. A potential influence of the heterogeneous reaction on estimation of the tropospheric lifetime of CH3CCl3 and/or tropospheric OH budget, is suggested.

Photocatalytic mineralization of hydroperfluorocarboxylic acids with heteropolyacid H4SiW12O40 in water

The decomposition of hydroperfluorocarboxylic acids [H-PFCAs; HC(n)F(2)(n)COOH (n=4 and 6)] induced by heteropolyacid photocatalyst H(4)SiW(12)O(40) in water was investigated, and the results are compared with the results for the corresponding perfluorocarboxylic acids (PFCAs; C(n)F(2)(n)(+1)COOH). This is the first report on the photochemical decomposition of H-PFCAs, which are being developed as alternative surfactants to environmentally persistent and bioaccumulative PFCAs. H-PFCAs were not decomposed by irradiation with UV-Visible light (>290 nm) in the absence of H(4)SiW(12)O(40). In contrast, UV-Visible light irradiation of H-PFCAs in the presence of H(4)SiW(12)O(40) efficiently decomposed H-PFCAs to F(-) and CO(2). The decomposition reactions showed pseudo-first-order kinetics, and the decomposition rate constants were 1.8-2.5 times higher than those for the corresponding PFCAs. The reaction mechanism can be explained by elimination of H(+) from the ω-H atom of the H-PFCAs by the excited catalyst, followed by formation of perfluorodicarboxylic acids.

Laboratory study on heterogeneous degradation of methyl chloroform (CH3CCl3) on aluminosilica clay minerals as its potential tropospheric sink

Heterogeneous reactions of methyl chloroform (1,1,1-trichloroethane, CH3CCl3) with alminosilica clay particles were examined between 288 and 313 K as a potential sink. Allophane and halloysite particles exhibited the activity to transform CH3CCl3 to 1,1-dichloroethene (CH2 = CCl2). The dependence of the reaction rate on the pretreatment, temperature, and relative humidity suggested that the reaction could proceed under environmental conditions. Illumination of light with wavelength longer than 300 nm did not affect CH3CCl3 decay but caused heterogeneous degradation of CH2 = CCl2 on clay particles. The lower limit of overall sticking coefficient for fresh allophane and halloysite particles was estimated to be 6×10−9 and 1.1×10−8, respectively. Heterogeneous degradation of CH3CCl3 on mineral aerosols and/or soils is worth taking into consideration in deriving tropospheric OH concentrations from global budget concentrations of CH3CCl3.

Visible light-induced decomposition of a fluorotelomer unsaturated carboxylic acid in water with a combination of tungsten trioxide and persulfate

Photochemical decomposition of a fluorotelomer unsaturated carboxylic acid, C3F7CFCHCOOH (1), in the presence of WO3 and an electron acceptor (S2O8(2-) or H2O2) in water under visible-light irradiation was investigated. Under an O2 atmosphere, 1 was not decomposed either by TiO2 (P25) or WO3 alone. A combination of WO3 and H2O2 also resulted in almost no decomposition of 1. In contrast, irradiation in the presence of a combination of WO3 and S2O8(2-) (potassium salt) efficiently decomposed 1 to F(-), CO2, C3F7COOH, and C2F5COOH. The decomposition of 1 was affected by the counter cation of S2O8(2-): the decomposition extent was higher with K2S2O8 than with (NH4)2S2O8. The decomposition of 1 was further enhanced when the reaction in the presence of WO3 and K2S2O8 was carried out under an argon atmosphere. Under O2, the amount of H2O2 formed in the reaction solution was an order of magnitude higher than the amount formed under argon. This fact suggests that the decrease in the decomposition of 1 under O2 can be ascribed to the formation of H2O2, which consumed S2O8(2-) and SO4(-).