M.K. Sahoo

TiO2 photocatalysis: progress from fundamentals to modification technology

AbstractHeterogeneous photocatalysis is a promising method among advanced oxidation processes, which can be used for degradation of various organic pollutants in water and air. In heterogeneous photocatalysis, illumination of an oxide semiconductor, usually the anatage form of titanium dioxide, by UV radiation produces photo-excited electrons () and positively charged holes (). In the aqueous phase, the illuminated surface is extensively regarded as a producer of hydroxyl radicals (). These hydroxyl radicals, holes, and conduction-band electrons can degrade organic pollutants directly or indirectly. However, the massive recombination of these photo-generated charge carriers and large band gap of limits its overall photocatalytic efficiency. These limitations can be overcome by changing surface properties of titania by adding suitable electron scavengers in the reaction medium or by modifying its electronic band structure through strategies like metal ion/nonmetal atom doping, narrow band-gap semiconductor...

Removal of Acid Blue 29 in aqueous solution by Fenton and Fenton-like processes

AbstractThe decoloration and mineralization of the azo dye, Acid Blue 29 (AB 29) in aqueous solution was investigated in the presence and absence of air by Fenton and Fenton-like processes using hydrogen peroxide (HP) and sodium persulfate (SPS), respectively, as oxidants. The effect of various operational parameters and presence of , , , and ions on the decoloration was examined. Higher decoloration was observed at pH 3 and 5 in both the cases. On the basis of mineralization efficiency (34.1 and 28.5%, respectively, with HP and SPS in 180 min), it was concluded that HP is a better oxidant than that of SPS. The decoloration in the absence of air is decreased until a certain time period, beyond which it increases and becomes same as that in the presence of air. This is explained on the basis of in situ generation of HP and peroxyl radicals. Although all ions under study inhibit decoloration significantly, the inhibition efficiency of is less than that of others.

UV light-assisted mineralisation and biodetoxification of Ponceau S with hydroxyl and sulfate radicals

The present study reports simultaneous mineralisation and biodetoxification of Ponceau S (3-hydroxy-4-(2-sulfo-4-[4-sulfophenylazo]phenylazo)-2,7-naphthalenedisulfonic acid sodium salt), an azo dye, by UV light assisted oxidation with hydroxyl and sulfate radicals. Metal ion catalysts used in the work were: Fe2+ and Ag+, and the oxidants used were: hydrogen peroxide and S2O82−. Strategies adopted to make the processes environmentally benign and economically viable by achieving maximum mineralisation in the shortest possible time are described. Mineralisation efficiency (Em) of various systems was found to follow the order: Em(Fe2+/H2O2/UV) > Em(Fe2+/S2O82−/UV) > Em(Ag+/H2O2/UV) ≈ Em(Ag+/S2O82−/UV). Thus, Fe2+ and HP are the most suitable metal ion catalyst and oxidant respectively, showing higher efficiency at pH 3 followed by that at pH 6.6. It is possible to enhance the Fe2+/H2O2/UV process electrical energy efficiency by maintaining the concentration of Fe at either 0.05 mM or 0.03 mM and that of the oxidant at 2.5 mM. The bioassay study revealed that the Fe2+/S2O82−/UV process biodetoxification efficiency is higher at pH 3 (93.7 %) followed by that at pH 6.6 (80.1 %) at the concentration of Fe 2+ and S2O82− of 0.03 mM and 2.5 mM, respectively. Thus, not only the concentration of Fe2+, but also the nature of the oxidant and pH play an important role in the biodetoxification process and S2O82− possesses higher biodetoxification efficiency than H2O2.

Comparative studies of mineralization and detoxification of mordant black 17 in aqueous solution by UV light induced M n+ /H 2 O 2 and M n+ /S 2 O 8 2− systems

The present study reports a process for simultaneous mineralization and detoxification of Mordant Black 17 with high electrical energy efficiency. Hydrogen peroxide and ammonium persulphate (APS) were used for the generation of hydroxyl and sulphate radicals using UV light (λ = 254 nm) and Fe2+ and Ag+ ions as catalysts. The detoxification and energy efficiency of various processes were measured by monitoring growth inhibition of Escherichia coli and Electrical Energy per Order (EE/O) applicable for low concentration contaminants respectively. Systems catalyzed by Fe2+ are more energy efficient and possess higher mineralization and detoxification efficiency than that of Ag+. The concentration of the catalysts and oxidants were found to strongly influence the EE/O of the systems. The most cost efficient processes for simultaneous mineralization and detoxification are Fe2+/APS/UV at pH 3.00 and Fe2+/H2O2/UV at pH 3.00 and 5.78. The upper limit concentration of Fe2+ is fixed at 0.01 mM for complete detoxification. The treated solutions start detoxifying at this concentration, above which they remain more toxic than the original dye solution irrespective of the extent of mineralization. On the contrary, no such limit could be established for Ag+ systems for complete detoxification even after 91% mineralization.

Metal ion-catalyzed mineralization and biodetoxification studies of Calconcarboxylic acid in aqueous solution: effect of –COOH group

AbstractMineralization and biodetoxification studies of Calconcarboxylic acid (CCA), an azo dye, were undertaken by metal ion-catalyzed oxidation processes, viz. Fenton and Fenton-like processes and the effect of presence of –COOH group thereon were established. The metal ions used were Fe2+ and Ag+ and the oxidants used were hydrogen peroxide (HP) and ammonium persulfate (APS). For a given oxidant, Fe2+ is found to be the most suitable catalyst and among the oxidants, APS proves to be most suitable one. As all the systems yield maximum mineralization at pH 1, Fe2+/APS at pH 1 is the most suitable system. It is observed that mineralization is favored by Fe2+/HP process due to the presence of –COOH group in CCA and by Fe2+/APS process in its absence. Removal of –COOH group causes a shift in optimum pH, for Fenton process, to 3 accompanied by a corresponding drop in mineralization from 70.6 to 35.6% and an increase from 73.2 to 91.1% in Fe2+/APS system. Bioassay experiment reveals that the treated solutions...