The oxidation of acid azo dye AY 36 by a manganese oxide containing mine waste

The oxidative breakdown of acid azo dye acid yellow 36 (AY 36) by a Mn oxide containing mine tailings is demonstrated. The oxidation reaction is pH dependent with the rate of decolorization increasing with decreasing pH. The oxidation reaction mechanism is initiated at the amino moiety and proceeds via successive, one electron transfers from the dye to the Mn oxide minerals. The reaction pathway involves the formation of a number of colorless intermediate products, some of which hydrolyze in a Mn oxide-independent step. Decolorization of the dye is rapid and is observed before the cleavage of the azo-bond, which is a slower process. The terminal oxidation products were observed to be p-benzoquinone and 3-hydroxybenzenesulfonate. The reaction order of the initial decolorization was determined to be pseudo fractional order with respect to pH and pseudo first order with respect to dye concentration and Mn tailings' surface area.

A new photon kinetic-measurement based on the kinetics of electron-hole pairs in photodegradation of textile wastewater using the UV-H2O2FS-TiO2 process

Actual textile wastewater and synthesized wastewater containing various textile dyes were photocatalytic degraded by the UV-H2O2FS-TiO2 process in an annular-flow photocatalytic reactor. In this process, a photon kinetic-measure was adopted to obtain constant rates of dyes decomposition. It was theorized that, by illumination at different UV frequencies, the electrons within the semiconductor were excited from the valence band to the conduction band, yielding the formation of electron-hole pairs which are the pre-requisites for photocatalysis. CPT (critical photonic time) exposure required to cause 90% of vibrations between the double and single bonds along the molecular chain of the dyes to be oxidized, was taken to measure the photocatalytic activities. The CPTs varied with the frequencies of the UV spectral areas. The derivatization of CPT from the first-order kinetic law was presented.

Order of photocatalytic degradation as ranked by critical photonic times (CPTs) indicates the composition of organic dye mixtures: selectivity of hydroxyl radicals

A simple critical photonic time (CPT) ranking method for the simultaneous determination of known organic dyes in the industrial wastewater of different concentrations was developed. A kinetic-measure, CPT theory, was developed to discriminate between the dyes in the textile effluent solution. The CPTs were calculated and ranked 1-4 from the smallest to the largest. The ranks indicate the order in which the individual dyes in the effluents were photocatalytically degraded. The described procedure allowed us to monitor the decolorization kinetics of the dyes in mixtures of different concentrations, when subjected to immobilized TiO2 photocatalysis in the presence of H2O2 from the start (H2O2FS). The outcome of hydroxyl radical (HO*) attack was consistently specific and regioselective for the individual dyes in the textile effluent. To explain the effect of HO*, the order of degradation of Acid Orange 52 < Acid Yellow 36 < Acid Red 17 < Acid Blue 45 < polyvinyl alcohol (PVA) was inferred.