Elsevier

Chemosphere

Volume 75, Issue 1, March 2009, Pages 8-12
Chemosphere

Hydrogen peroxide decomposition on manganese oxide (pyrolusite): Kinetics, intermediates, and mechanism

https://doi.org/10.1016/j.chemosphere.2008.11.075Get rights and content

Abstract

The objective of this study is the kinetic interpretation of hydrogen peroxide decomposition on manganese oxide (pyrolusite) and the explanation of the reaction mechanism including the hydroperoxide/superoxide anion. The decomposition of hydrogen peroxide on manganese oxide at pH 7 was represented by a pseudo first-order model. The maximum value of the observed first-order rates constants (kobs) was 0.741 min−1 at 11.8 of [H2O2]/[triple bondMnO2] when [H2O2]/[triple bondMnO2] were ranged from 58.8 to 3.92. The pseudo first-order rate constants (kMnO2) approximated as the average value of 0.025 (min mM)−1 with a standard deviation of 0.003 at [H2O2]/[triple bondMnO2] ranged from 39.2 to 11.8. When [H2O2]/[triple bondMnO2] was 3.92, the rate constants (kMnO2) was 0.061 (min mM)−1 as maximum. Oxygen production showed that the initial rates increased with decreasing [H2O2]/[triple bondMnO2] and the total amounts of oxygen was slightly less than the stoichiometric value (0.5) in most experiments. However, oxygen was produced at more than 0.5 in low [H2O2]/[triple bondMnO2] (i.e. 3.92 and 9.79). The relative production of hydroperoxide/superoxide anion implied that the production increased with low [H2O2]/[triple bondMnO2], and the existence of anions suggested that the mechanism includes propagation reactions with intermediates such as hydroperoxide/superoxide anion in solution. In addition, both [H2O2] decomposition and the production of anion were accelerated in alkaline solution. Manganese ion dissolved into solution was negligible in neutral and alkaline conditions, but it greatly increased in acidic conditions.

Introduction

There has been increasing interest in finding the physical/chemical characteristics of reaction intermediates from hydrogen peroxide decomposition, because of the high reactivity, which is highly effective for the removal of contaminants (Kwan and Voelker, 2003, Seol and Javandel, 2008). One of the most well-known intermediates, the hydroxyl radical, is generated from hydrogen peroxide decomposition on iron. Known as the Fenton reaction, it has been characterized, and the reaction has been modified (Peyton et al., 1995, Lin and Gurol, 1998, Laat and Gallard, 1999, Lipczynska-Kochany and Kochany, 2008). Moreover, it has been shown that the generation of various reaction intermediates (hydroxyl radical, hydroperoxyl radical, superoxide anion, hydroperoxide anion, oxide radical ion, etc.) is possible (Buxton et al., 1988, Gonzalez and Martire, 1997).

Besides the hydroxyl radical, hydroperoxide and superoxide anion have been investigated for their identification (Pignatello, 1992, Smith et al., 2004). It has been suggested that hydroperoxide anion and superoxide anion including a hydroxyl radical provide a treatment matrix that desorbes, oxidizes, and reduces contaminants (Watts et al., 1999). In particular, hydroperoxide anion and superoxide anion have been proposed as candidates to improve the desorption of organic compounds from soils (Watts et al., 1999). Recently, superoxide anion generated from a modified Fenton system was proven to be a responsible species for carbon tetrachloride transformation (Smith et al., 2004). However, there has been no evidence for the physical role of hydroperoxide/superoxide anion for improving the desorption of contaminants.

In addition to hydrogen peroxide decomposition on iron to generate reactive reagents, hydrogen peroxide decomposition on manganese oxides has been studied to investigate the catalytic activity of manganese oxides (Zhou et al., 1998, Baldi et al., 1998), and the decomposition of hydrogen peroxide on the metals (i.e. both iron and manganese) coated filter showed that hydrogen peroxide decomposition rates mostly depend on manganese concentrations (Miller and Valentine, 1995). Moreover, it has been suggested that hydroperoxide/superoxide anions could be generated from the decomposition of hydrogen peroxide on manganese oxide including metals embedded manganese oxide catalysts (Hasan et al., 1999). However, the detection of hydroperoxide/superoxide anion produced from the reaction of hydrogen peroxide on manganese oxide (pyrolusite) has yet to be reported.

The objective of this study was to find supporting results to evaluate the role of hydroperoxide/superoxide anion for contaminant desorption. To accomplish this objective, hydrogen peroxide decomposition on manganese oxide (pyrolusite) was chosen instead of iron, because it can minimize the effect of the hydroxyl radical (strong oxidant). Hydrogen peroxide decomposition on manganese oxide (pyrolusite) was studied kinetically, and the mechanisms of this decomposition are suggested as being comprised of both the production of oxygen and the involvement of intermediates (hydroperoxide/superoxide anion). To date, the literature has shown little evidence of their existence.

Section snippets

Materials

Double deionized water (DDW) was used with a deionization system (Milli-Q Model Gradient A 10). Manganese oxide (MnO2) from near Pullman, WA was used below the size of 0.088 mm, and was identified to be pyrolusite by XRD analysis (Cu K-alpha1 X-ray radiation, 40 kV beam voltage, and 100 mA beam current). The specific surface area of MnO2 measured by the BET method using nitrogen was 6.063 m2 g−1.

Hydrogen peroxide (35%, Junsei Chemical Co.) was used. Titanium sulfate (Junsei Co.), hydroxylamine

Decomposition of hydrogen peroxide

A study on kinetic decomposition of hydrogen peroxide on manganese oxide at the initial pH 7.0 ± 0.1 was conducted in a batch reactor. The decomposition of hydrogen peroxide can be expressed with the observed first-order rate constants (kobs). The observed first-order rate constants are calculated by non-linear regression using the least-square method. Fig. 1 shows the effect of initial hydrogen peroxide (29.4–441 mM) concentration on the decomposition of hydrogen peroxide in the presence of 7.5 mM

Conclusion

The kinetics of decomposition of hydrogen peroxide on manganese oxide (pyrolusite) at initial pH 7 can be represented by a pseudo first-order rate model. The ratio of [H2O2]/[triple bondMnO2] needs to be considered as an important parameter to describe [H2O2] a decomposition rate on manganese oxide. The observed increasing first-order rate constant (kobs) and constant pseudo first-order rate constant (kMnO2) with certain ranges of [H2O2]/[triple bondMnO2] (from 11.8 to 39.2) could imply the existence of [H2O2]

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