Steady-state and transient photolysis of p-nitroaniline in acetonitrile
ABSTRACT Both transient photolysis and steady-state photo-degradation experiments were performed to gain insight into the kinetics and mechanisms of degradation of p-nitroaniline (p-NA) in acetonitrile (MeCN) solutions. Complete degradation of p-NA was observed at diverse irradiation conditions under 254 nm UV light. Once H2O2 was added into the experimental system, degradation of p-NA was enhanced remarkably. The removal rate increased rapidly with increment of the irradiation time and reached 90% at 30 min. p-NA could be totally removed after 90 min in UV/H2O2 process. In the presence of O2 and H2O2, removal rate increased linearly with increment of the irradiation time and reached 90% at 10 min. p-NA could be totally removed after 20 min in UV/(O2 + H2O2) process. For transient photolysis, excited states of p-NA were observed after 355 and 266 nm laser flash photolysis (LFP). The transient absorption spectra were recorded and bimolecular rate constant of 6.89 × 109 M−1 s−1 was calculated for the self-quenching of 3p-NA*. Production of 3p-NA* in MeCN and H2O mixed solution was also studied. LFP of p-NA with addition of H2O2 was investigated for the first time.
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ABSTRACT: Photocatalytic Hâ production from several aliphatic and aromatic compounds with water was investigated with powdered Pt/TiOâ catalyst suspended in solution. Various fossil fuels such as coal, tar sand, and pitch also reacted with water, producing both Hâ and COâ from an early stage of irradiation. The photocatalytic oxidations of their model compounds, especially a linear hydrocarbon and benzene, were studied in the presence of silver ion as an electron acceptor. For aliphatic hydrocarbons, they are oxidized to alcohols, aldehydes, and carboxylic acids, successively. COâ was found to be formed through the photo-Kolbe type of reaction of carboxylic acids produced, which explained well the result of the complete decomposition of n-hexadecane. For benzene, we could detect phenol, catechol, hydroquinone, and muconic acid. On the basis of these results, the possibility of the direct oxidation of benzene by photogenerated holes and its ring-opening process peculiar to the photocatalytic reaction are discussed. The main reaction path for COâ production was suggested in which the benzene ring opens not by way of phenol and catechol, but by way of the intermediates whose reactivities are much larger than that of benzene. 41 references, 5 figures, 4 tables.The Journal of Physical Chemistry. 04/2002; 88(18).
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ABSTRACT: An indirect electrochemical method, which is very efficient for the degradation of organic pollutants in water, is described. The method, named electro-Fenton, is based on electrocatalytical generation of Fenton's reagent to produce hydroxyl radicals, which are very active toward organic compounds. An industrial pollutant, p-nitrophenol (PNP), was chosen for this study and was eventually mineralized. The major intermediary degradation products such as hydroquinone, benzoquinone, 4-nitrocatechol, 1,2,4-trihydroxybenzene and 3,4,5-trihydroxy- nitrobenzene were unequivocally identified by HPLC and GC-MS methods. The rate constants of the hydroxylation reactions were determined. The mineralization of the initial pollutant and the intermediates formed during electro-Fenton treatment was followed by total organic carbon (TOC) analyses. Dependence of mineralization on the amount of electrical energy consumed is shown by the relative decrease of TOC values. A mineralization reaction mechanism is proposed.Environmental Science & Technology - ENVIRON SCI TECHNOL. 07/2000; 34(16).
- Transactions of the Faraday Society 01/1953; 49.