Abstract
New, more efficient methods of wastewater treatment, which will limit the harmful effects of textile dyes on the natural environment, are still being sought. Significant research work suggests that catalysts based on transition metal complexes can be used in efficient and environmentally friendly processes. In this context, a number of compounds containing manganese have been investigated. A suitable catalyst should have the capacity to activate a selected oxidant or group of oxidants, in order to be used in industrial oxidation reactions. In the present study we investigated the ability of MnIII(TPPS), where TPPS = 5,10,15,20-tetrakis(4-sulphonatophenyl)-21H,23H-porphyrine, to activate five different oxidants, namely hydrogen peroxide, peracetic acid, sodium hypochlorite, potassium peroxomonosulfate and sodium perborate, via the formation of high valent Mn(TPPS)-oxo complexes. Kinetic and spectroscopic data showed that the oxidation process is highly pH dependent and is strongly accelerated by the presence of carbonate in the reaction mixture for three of the five oxidizing agents. The highest efficiency for the oxidation of MnIII(TPPS) to high-valent Mn(TPPS)-oxo complexes, was found for peracetic acid at pH ≈ 11 in 0.5 M carbonate solution, which is at least an order of magnitude higher than the rate constants found for the other tested oxidants under similar conditions.
Highlights
Estimations concerning the amount of textile dyes that are discharged into water are quite different.Some articles state that 2% of the produced pigments are liberated in an aqueous effluent and the 10% comes from the coloration process [1]
The results showed that the second-order rate constants for the formation of high-valent Mn(TPPS)-oxo complexes are similar for the three oxidants: hydrogen peroxide, sodium hypochlorite and sodium perborate
The results presented in this paper indicate that MnIII (TPPS) can be activated by a wide range of oxidants to form a promising catalyst for many different oxidation reactions
Summary
Estimations concerning the amount of textile dyes that are discharged into water are quite different.Some articles state that 2% of the produced pigments are liberated in an aqueous effluent and the 10% comes from the coloration process [1]. Other sources claim that 280,000 tons are released yearly [2]. This does not change the fact that the scale of the problem is huge. Since insignificant amounts of dye may disrupt the water transparency, gas solubility and entail formation of toxic side products [2,3,4,5]. Due to the non-biodegradable character of dyestuffs and the possible release of toxic and carcinogenic byproducts, new methods for the degradation of dyes are still being sought [6,7,8,9,10,11,12,13]
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