Photodegradation of methyl red by advanced and homogeneous photo-​Fenton's processes: A comparative study and kinetic approach

The degrdn. of methyl red (MR)​, an azo dye, was carried out by the homogeneous photo-​Fenton's process (HPFP) and the advanced photo-​Fenton's process (APFP) using sym. peroxides such as hydrogen peroxide and ammonium persulfate (APS) as oxidants. The APFP showed higher efficiency than their homogeneous counterparts even at high dye concns. due to the faster redn. of Fe3+ to Fe2+ ions on the iron surface. H2O2 proved to be a better oxidant for both the processes. However, APS efficiently inhibited the pptn. of iron oxy hydroxides at higher dosage of iron powder compared to H2O2 by providing excess acidity to the reaction medium. The rate const. for the kinetics of decolorisation by various oxidn. processes is of the order: Fe0/H2O2/UV > Fe0/H2O2/dark > Fe0/APS​/UV > Fe2+/H2O2/UV > Fe0/UV > Fe0/APS​/dark > Fe0/dark ≈ H2O2/UV > Fe2+/APS​/UV > APS​/UV > Fe2+/H2O2/dark > Fe2+/APS​/dark ≈ Fe2+/UV. The degrdn. reaction was followed by UV-​visible and GC-​MS spectroscopic techniques. Based on the intermediates obtained, probable degrdn. mechanisms have been proposed. It was found that the initial mechanism in the APFP involves the redn. of azo groups to amines while in the case of HPFP it leads to the formation of hydroxylated products due to the oxidn. of azo groups

Photo-degradation of Di Azo Dye Bismarck Brown by Advanced photo-Fenton Process: Influence of Inorganic Anions and Evaluation of Recycling Efficiency of Iron Powder

The present research work has demonstrated the usage of zero valent metallic iron (ZVMI) in the photo-Fenton process under UV light as a promising and novel technique for the complete degradation of di azo dye Bismarck Brown (BB) in aqueous medium. The influence of various reaction parameters like concentration of oxidants/dye/iron powder and pH of the solution was investigated and optimum conditions are reported. Ammonium persulfate (APS) proved to be better oxidant in comparison with hydrogen peroxide for enhancing the degradation rate and effectively inhibited the precipitation of iron hydroxides at higher dosages of iron powder which is attributed to the acidity provided by APS which is crucial for Fenton process. The rate constant for the kinetics of degradation using various oxidation processes follows the order: Fe0/APS/UV > Fe0/H2O2/UV > Fe0/APS/dark > Fe0/UV > Fe0/H2O2/dark > Fe0/dark > H2O2/UV > APS/UV. The effects of inorganic anions that are commonly found in the industrial effluents like NaCl, KNO3, Na2SO4, Na2CO3 and NaHCO3 at different concentrations on the degradation rate were studied in detail. The degradation was followed by UV-vis and GC-MS techniques

Influence of various aromatic derivatives on the advanced photo Fenton degradation of Amaranth dye

The photo degrdn. of Amaranth (AR) dye by advanced photo Fenton process in the presence of sym. peroxides like hydrogen peroxide (H2O2) and ammonium persulfate (APS) are investigated. The influence of various reaction parameters like the effect of iron dosage, concn. of H2O2/APS, initial dye concn., effect of pH and the influence of various arom. derivs. were studied and optimum conditions are reported. The efficiency of the oxidant was strongly influenced by the nature of arom. photoproducts formed during the course of the degrdn. reaction. To study their effect on the rate of degrdn. these arom. derivs. were added in known concn. (10 ppm)​. The influence of various arom. derivs. on the degrdn. kinetics shows the following order: hydroquinones > chlorophenol > dichlorobenzene > arom. carboxylic acids > anilidine > nitrophenol. The addn. of these derivs. did not influence the degrdn. pathway although it altered the reaction rate. The percentage COD and TOC removal were detd. in presence of arom. derivs. to evaluate the complete removal of the pollutant. Based on the intermediates obtained in the UV-​vis and GC-​MS spectroscopic techniques probable degrdn. mechanism has been proposed

Mechanism of charge transfer in the transition metal ion doped TiO 2 with bicrystalline framework of anatase and rutile: Photocatalytic and photoelectrocatalytic activity

The high photocatalytic activity of the Mn2+ doped TiO 2 with bicrystalline framework of anatase and rutile is probed for the degradation of benzene under solar light with/without applied bias. The enhanced activity is attributed to the transfer of electrons from the rutile to electron trapping/lattice trapping sites of anatase and also to the impurity level created by the dopant which favours effective charge separation. The shallow detrapping nature of Mn2+ dopant additionally contributes to the overall enhancement in the photocatalytic activity especially in the presence of applied electric field