Selective oxidative degradation of azo dyes by hydrogen peroxide catalysed by manganese(ii) ions

Abstract

Manganese(II) ions catalyse the oxidative degradation of Calmagite (H3CAL) dye in aqueous solution 5 at 20±1°C in the pH range 7.5-9.0 using hydrogen peroxide (H2O2) as oxidant by a mechanism that involves strong complexation to the MnII centre. It is proposed that [MnIII(CAL)(O2H)]-i.e. a dye coordinated hydroperoxyl (O2H-) MnIII complex is formed and bleaching of the dye is initiated by an electron-transfer to MnIII, with the binding of H2O2 being the rate determining step. At pH 9.0 in (bi)carbonate, HCO3-, H3CAL is rapidly bleached via the in situ formation of coordinated 10 peroxycarbonate (HCO4-); a TOF (TOF = moles of dye bleached per mole of manganese per hour) of ~5000 hr-1 can be achieved. The bleaching of the related azo dyes Orange II and Orange G is different because, unlike Calmagite, they lack an o,o-dihydroxy motif so are unable to complex strongly to MnII and no oxidation to MnIII occurs. At pH 8.0 (phosphate buffer) Orange II and Orange G are not bleached but bleaching can be achieved at pH 9.0 (HCO3-buffer); the rate determining step is dye 15 coordination and it is proposed bleaching is achieved via an outer-sphere oxygen atom transfer. Mechanisms for dye bleaching at pH 8.0 and pH 9.0 are proposed using data from EPR, UV/VIS and ESI-MS. MnII/ H2O2/ HCO3-form a potent oxidising mixture that is capable of removing stubborn stains such as curcumin.

The Role of Carbonate in Catalytic Oxidations

“…Oxidation of calmagite (H 3 CAL) dye in aqueous solution using H 2 O 2 at pH 7.5−9.0 is accelerated considerably in the presence of HCO 3 − . 58 The proposed mechanism involves the following steps:…”

“…Oxidation of calmagite (H 3 CAL) dye in aqueous solution using H 2 O 2 at pH 7.5–9.0 is accelerated considerably in the presence of HCO 3 – . 58 The proposed mechanism involves the following steps: It should be pointed out that [Mn III (CAL)(HCO 4 )] − might also decompose to form a Mn IV complex and CO 3 •– anion radical. The degradation of various dyes using Mn/H 2 O 2 /HCO 3 – has been reported.…”

Overexpression of Cu/Zn Superoxide Dismutase (Cu/Zn SOD) in Synechococcus elongatus PCC 7942 for Enhanced Azo Dye Removal through Hydrogen Peroxide Accumulation

“…However, the application of this approach of bioremediation needs further optimization including the cyanobacterial cellular density to achieve a higher concentration of H 2 O 2 to be released and metal co-factors that determine the effectiveness of H 2 O 2 in the wastewater system. Manganese porphyrins in water act as catalysts for azo dye decolorization by H 2 O 2 under mild environmental conditions and the rate of dye decolorization was found to be associated with the structure of the manganese porphyrins [ 48 , 49 ]. Decomposition of various dyes through accumulated H 2 O 2 from cyanobacteria has a lot of positive environmental benefits and commercial values, which wait for their bioremediation applications.…”

Deri Sanayinde İhracatı Tehdit Eden Yasaklı Maddelerin Ayakkabılık Mamul Derilerde Araştırılması

“…Aksi halde firmalar dış piyasaya satamadıkları ürünler nedeniyle büyük zarara uğrayabilir, hatta iflas edebilir. Yapılan bir araştırmada hidrojen peroksit vasıtasıyla azo boyarmaddelerin parçalanması başarıyla gerçekleştirilmiştir [25].…”