A. Georgi et al. / Chemosphere 71 (2008) 1452–1460
1459
indicates a contribution of other catalysis mechanisms. One
simple hypothesis could be that the chemical reactivity of
protons is higher in the more hydrophobic microenviron-
ment of HA than in the water bulk phase, similar to a sol-
vent effect.
Georgi, A., Schierz, A., Trommler, U., Horwitz, C.P., Collins, T.J., Kopinke,
F.-D., 2007b. Humic acidmodifiedFentonreagentforenhancementof the
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Beside the micellar catalysis mechanism, the func-
tional principle of enzymes might be considered as an
alternative model for the catalytic activity of DHS. A
prerequisite for the catalytic activity of enzymes is the
binding of the substrate by means of intermolecular
interactions. In analogy, binding also seems to be
favourable for the acceleration of acid-catalyzed hydro-
lysis by DHS. The mechanisms of enzymatic reactions
are manifold. At least two of them, stabilization of
the transition state by intermolecular interactions and
general acid or base catalysis are also conceivable mech-
anisms for the catalysis effects of DHS on hydrolysis
reactions of their sorbates. A quantitative differentiation
between the possible contributions of micelle-like and
enzyme-like catalysis to the overall effect of DHS on
acid-catalyzed hydrolysis reactions is not possible based
on the present results. Experiments at varying ionic
strength might be useful to clarify this question, since
the proton accumulation effect of DHS will be largely
suppressed at I P 1 M.
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2. SPME and FQT as analytical methods. Environ. Sci. Technol. 36,
Hydrolysis is not only an important mechanism for the
transformation of xenobiotics in the environment but also
for the degradation and transformation of ‘biogenic waste’.
The finding that DHS is able to accelerate acid-catalyzed
hydrolysis reactions brings up the interesting question of
whether humic substances as the final products of humifi-
cation might themselves act as catalysts of the humification
process by means of this mechanism.
4
403–4409.
Mackenzie, K., Battke, J., Koehler, R., Kopinke, F.-D., 2005a. Catalytic
effects of activated carbon on hydrolysis reactions of chlorinated
organic compounds. Part 2: 1,1,2,2-tetrachloroethane. Appl. Catal. B –
Environ. 59, 171–179.
Mackenzie, K., Battke, J., Kopinke, F.-D., 2005b. Catalytic effects of
activated carbon on hydrolysis reactions of chlorinated organic
compounds. Part 1: c-hexachlorocyclohexane. Catal. Today 102–103,
1
48–153.
Martin-Neto, L., Traghetta, D.G., Vaz, C.M.P., Crestana, S., Sposito, G.,
001. On the interaction mechanisms of atrazine and hydroxyatrazine
2
Appendix A. Supplementary material
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New York.
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model parameters for proton binding by humic substances. Environ.
Sci. Technol. 35, 2049–2059.
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and c-hexachlorocyclohexanes. Environ. Sci. Technol. 27, 1930–1933.
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Perdue, E.M., Wolfe, N.L., 1982. Modification of pollutant hydrolysis
kinetics in the presence of humic substances. Environ. Sci. Technol. 16,
847–852.
Supplementary material contains a short description of
the model on general acid–base catalysis exerted by DHS
on reactions of freely dissolved substrates proposed by Per-
due (1983). Furthermore, the maximum possible contribu-
tion of this effect in OA hydrolysis under the experimental
conditions of this study is evaluated. This includes the
investigation of the acid–base properties of the applied
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