Degradation of Reactive Azo Dyes by UV/H₂O₂: Impact of Radical Scavengers

Abstract

Hydroxyl radical (*OH) scavenging effects of carbonate (CO3(2-)), bicarbonate (HCO3-) and chloride (Cl-) ions on the performance of an ultraviolet light-hydrogen peroxide (UV/H2O2) advanced oxidation process were investigated using a reactive azo dye, C.I. Reactive Red 141 as the model compound. It was found that in the absence of scavengers, complete color removal was possible in 15 min under the experimental conditions employed. The rate of color decay was inhibited remarkably with increasing concentrations of bicarbonate and carbonate species, especially when the distribution of alkalinity favored the dominance of carbonate ions. It was further observed that chloride inhibited the rate only when it was between 100-1250 mM as Cl, and was ineffective at higher concentrations.

Novel active heterogeneous Fenton system based on Fe3−xMxO4 (Fe, Co, Mn, Ni): The role of M2+ species on the reactivity towards H2O2 reactions

“…The organic compounds added were phenol, hydroquinone, methylene blue and also the salt Na 2 CO 3 , which are good radical scavengers [23][24][25]. The obtained results are displayed in Fig.…”

“…The dye methylene blue show several advantages, such as: (i) it allows the use of simple spectrophotometric measurements at 633 nm to monitor the reaction and its kinetics and (ii) the cationic dye does not adsorb on the iron oxides surface since at the reaction pH (5.5-6.0) the oxides surfaces are positively charged according to their PZC (6.6 up to 8.0 for magnetite and maghemite and 6.7-10.0 for ␣-Fe 2 O 3 ) [24,25]. In fact, preliminary experiments with methylene blue solutions and different iron oxides, i.e.…”

Feasibility analysis of color removal from textile dyeing wastewater in a fixed-bed column system by surfactant-modified zeolite (SMZ)

“…In the biological treatment systems, the recalcitrant nature of azo dyes, together with their toxicity to microorganisms, makes aerobic treatment difficult whereas, a wide range of azo dyes is decolorized anaerobically [6,7]. On the other hand, adsorption [8][9][10], oxidation [11,12] and membrane [13] processes are major technologies that are used for wastewater treatment in the textile industry.…”

Photolysis, oxidation and subsequent toxicity of a mixture of polycyclic aromatic hydrocarbons in natural waters

“…Further experiments showed no effect of phosphate ions (0-1900 mg L −1 ) on the decay of the PAHs. Gultekin and Ince [34] reported only a slight inhibition of color removal using LP lamp and 4.1 mM hydrogen peroxide at chloride concentration below 100 mM (3.5 g L −1 ). At higher concentrations >100 mM of chloride a significant decreases in degradation of the color was observed.…”

“…8. (8) The formed carbonate radicals are highly selective and react relatively slowly with organic compounds [34]. They may also react with hydrogen peroxide to originate peroxy radical (HO 2 ·) [35] which is a much less reactive species than the hydroxyl radical.…”