Mechanistic studies on the oxidative degradation of Orange II by peracetic acid catalyzed by simple manganese(ii) salts. Tuning the lifetime of the catalyst

Abstract

A remarkably efficient, catalytic oxidative degradation of Orange II in aqueous solution was observed in the presence of simple Mn(II) salts used in combination with the green oxidant peracetic acid (PAA) under mild reaction conditions at pH 9.5 and 25 1C. In order to gain further insight into the complex reaction network responsible for the fast and efficient degradation of Orange II, detailed kinetic studies on the catalytic degradation reaction were performed. The influence of the catalyst, oxidant, and buffer concentrations on the reaction course was studied in detail by in situ UV/Vis spectroscopy. The degradation rate increased with increasing catalyst and PAA concentration, decreased with increasing carbonate buffer concentration, and the reaction showed maximum reactivity at pH E 9.4. Studies performed in the absence of substrate revealed the successive formation of various high valence manganese intermediates under the selected experimental conditions. The UV/Vis spectral changes observed upon addition of PAA to a Mn(II) ion containing solution at pH 9.5 showed biphasic behavior, and led to the formation of Mn VII O 4À and colloidalMn IV O 2 as final products. Through the combination of EPR and UV/Vis spectroscopy, the presence of a Mn(IV) species during the first phase of the reaction was observed. If the addition of a dye to the Mn(II)/PAA containing reaction mixture was carried out after different delay times during the course of the reaction, significant changes observed in the degradation performance pointed to changes in the catalyst composition with time. Thereby, the highest reactivity was reached just before the formation of the high valence intermediates and colloidal Mn IV O 2 occurred. Selected catalytic experiments with different in situ formed intermediates showed the essential role of a small amount of hydrogen peroxide (omnipresent in commercial peracetic acid, 6 wt% H 2 O 2 ) for efficient catalytic dye decomposition. H 2 O 2 was shown to play a crucial role as a reducing agent in the catalytic cycle, avoiding the over-oxidation of the catalyst, and thereby extending the lifetime of the catalytic system. The data were evaluated to gain mechanistic insight into the complex chemical reactions occurring during the Mn(II) catalyzed oxidative dye degradation with PAA. A comparison with earlier results concerning the use of H 2 O 2 /HCO 3 À as oxidant was made.

Peracids in water treatment: A critical review

“…Similar results were also obtained when Mn 2+ was used as a catalyst in dye degradation by PAA [79]. Co 2+ /Co 3+ , on the other hand, resulted PAA to decompose to acetyl (CH 3 COO•) and peracetyl (CH 3 COOO•) radicals, whereas no hydroxyl radical formation was detected [111].…”

“…These radicals are together referred to as reactive oxygen species (ROS). Also a direct reaction between peracid and the target molecule or the formation of secondary oxidants is possible [79].…”

Recycled carbon (RC) materials made functional: An efficient heterogeneous Mn-RC catalyst

“…Moreover, catalytic oxidative degradation of the mono-hydroxylated product results in the formation of the corresponding demethylated species (m/z 306.0550). A poly-hydroxylated derivative of MO has been also detected i.e., m/z 368.0707 with a chemical formula C 14 indicating that the benzenesulfonate ring moiety was not hydroxylated. The observed fragmentation path is known as common behavior for the benzene sulfonic acid group [43].…”

“…In this context, new, efficient, selective, low-cost and easy to prepare Mn-catalysts remain at high demand in the field of oxidation catalysis [8]. So far, catalytic degradation of organic dyes by non-heme Mn II -HCO 3 − catalysts has been reported under mild reaction conditions, e.g., using H 2 O 2 as oxidant [11][12][13][14][15][16]. Rothbart et al investigated the oxidative degradation of Orange II by Mn II -HCO 3 − and peracetic acid [13,14].…”

“…H 2 O 2 as oxidant can be used in cases where dismutation of H 2 O 2 does not occur, and relatively mild redox potentials i.e., around 300 mV, are sufficient [8][9][10][11][12][13][14]. In the case where higher redox potentials have to be accessed and/or H 2 O 2 dismutation is a limiting factor, oxidants other than H 2 O 2 have to be used.…”