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    Wyświetlanie 1-5 z 5
    Tytuł:
    Photochemical reduction of chromium(VI) by phenol and its halogen derivatives
    Autorzy:
    Mytych, Piotr
    Stasicka, Zofia
    Opis:
    Photoreduction of chromium(VI) has been investigated in solutions containing phenol or monohalogenophenol (4-bromophenol, 4-chlorophenol and 3-chlorophenol) under conditions mimicking the environmental ones. The effects of radiation wavelength, pH and molecular oxygen are analysed. The results show that chromate(VI) in excited state is reduced by phenol in its ground state via photoinduced electron transfer (PET). Moreover, solvated electrons generated by the phenol photoreaction reduce the $CrO_{4}^{2-}$ anions in their ground state. Phenol oxidation in both processes is assumed to proceed via generation of the $C_{6}H_{5}O\cdot$ radical dot radicals, which participate in further redox processes. Acidic and anoxic conditions favour the Cr(VI) photoreduction, whereas alkaline oxygenated solutions are preferable for phenol photooxidation followed by Cr(VI) thermal reduction by means of $e_{solv}^{-}$. Bromophenol appears more readily photodegradated, whereas chlorophenols are more resistant to it than unsubstituted phenol. The system consisting of chromate(VI) and phenol demonstrates the synergetic photodegradation as the phenolic substance enables photoreduction of environmental Cr(VI) and vice versa the Cr(VI) pollutant enhances photooxidation of phenol and its derivatives.
    Dostawca treści:
    Repozytorium Uniwersytetu Jagiellońskiego
    Artykuł
    Tytuł:
    Photoredox processes in the Cr(VI)-Cr(III)-oxalate system and their environmental relevance
    Autorzy:
    Mytych, Piotr
    Cieśla, Paweł
    Stasicka, Zofia
    Opis:
    Irradiation of the $[Cr(C_{2}O_{4})_{3}]^{3-}$ complex or the chromate(VI)-oxalate mixture, or the ternary system composed of Cr(III), Cr(VI) and oxalate, leads to chromium photoreductions in consequence of the ligand to metal charge transfer (LMCT) excitations induced by artificial solar radiation. In the case of the Cr(III) complex, the photoreduction involves the innersphere electron transfer leading to the formation of the Cr(II) species and the $C_{2}O_{4}\cdot^{-}$ radicals. On reacting with molecular oxygen, Cr(II) is oxidised to Cr(III) catalysing thereby the oxalate substitution reaction. Moreover, under specific conditions, Cr(II) can be also oxidised to Cr(VI). Chromate(VI) is not photoreducible, but in the presence of oxalate, or other sacrificial electron donor, the outersphere photoinduced electron transfer (PET) produces Cr(V) species and the $C_{2}O_{4}\cdot^{-}$ radicals. This initiates a series of thermal reactions leading to the formation of Cr(III) and oxidized oxalate (CO2). In the system composed of $[Cr(C_{2}O_{4})_{3}]^{3-}$ and chromate(VI), the acidic medium and anoxic conditions favour the Cr(VI) photoreduction, whereas alkaline oxygenated solutions assist the Cr(VI) photoproduction. When an approximately neutral solution equilibrated with the ambient air is irradiated intermittently, Cr(VI) is consumed and/or produced, accordingly to the time sequence of exposure and dark periods. The oscillations of Cr(VI) concentrations are accompanied by continuous oxidation of oxalate, playing the role of the sacrificial electron donor. The effects of solution pH, molecular oxygen, concentrations of reagents and cations on the reaction rates were investigated. The results of this paper revealed that the Cr(III)/Cr(VI) system under environmental conditions behaves as the photocatalytic one catalysing the oxidation of oxalate or other organic matter by molecular oxygen, contributing thereby to the abatement of pollution.
    Dostawca treści:
    Repozytorium Uniwersytetu Jagiellońskiego
    Artykuł
    Tytuł:
    Role of iron and chromium complexes in environmental self‐cleaning processes
    Autorzy:
    Kocot, Przemysław
    Cieśla, Paweł
    Mytych, Piotr
    Stasicka, Zofia
    Opis:
    The present research includes solar‐light‐driven photocatalytic cycles based on the photoreductions of Fe(III), Cr(VI), and Cr(III) compounds with EDTA, oxalate and other ligands. Molecular oxygen is needed to close the photocatalytic cycles in which the metal species plays a role of photocatalyst; it affects the reaction mechanism and rate. The photoinduced electron transfer was also investigated in the presence of some external electron donors, such as EDTA, aliphatic alcohols, phenol, and its halogen derivatives, oxalate, nitrate(III), sulfate(IV). The results apply to the removal of such hazardous environmental pollutants as chromate(VI) or phenol derivatives and such recalcitrant pollutants as EDTA.
    Dostawca treści:
    Repozytorium Uniwersytetu Jagiellońskiego
    Artykuł
    Tytuł:
    Homogeneous photocatalysis by transition metal complexes in the environment
    Autorzy:
    Mytych, Piotr
    Cieśla, Paweł
    Stasicka, Zofia
    Kocot, Przemysław
    Opis:
    The role of transition metal complexes is overviewed for the iron, copper and chromium compounds, for which photoreactivity is of crucial environmental importance. Attention is paid to these complex systems, in which metal centres are photoreduced by organic matter under solar irradiation and re-oxidized by molecular oxygen, i.e. to the systems, that play a part in the environmental photocatalysis. The photoreduction is accompanied by simultaneous oxidation of organic matter, which plays a role of ligand and/or sacrificial electron donor. Under favourable conditions a complete photodegradation of the organic pollutants can be achieved. The general mechanisms are analysed and examples of different photocatalytic behaviours are presented in some details. The systems are more sophisticated due to concurrent generation of active oxygen species, such as the $O_{2}\cdot ^{-}$, $HO_{2}\cdot$, $OH\cdot$, $H_{2}O_{2}$, and $HO_{2}^{-}$, which are involved in the redox reactions of the photocatalytic cycling and influence the pollutant degradation.Beside the monometallic cycles, the mixed metal systems can function in nature. The cooperation between the photocatalytic cycles of two metals can abate diverse environmental pollutants, but their efficiency can be either higher or lower in comparison with that of the sum of single cycles.
    Dostawca treści:
    Repozytorium Uniwersytetu Jagiellońskiego
    Artykuł
      Wyświetlanie 1-5 z 5

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