Degradation of Reactive Yellow 86 with photo-Fenton process driven by solar light

Harnessing bromide ions to boost peroxymonosulfate for reactive yellow 145 dye degradation

Bromide (Br-) was found in the fresh waters at concentrations from 0.1 to 1 mg/L and can be used to activate peroxymonosulfate (PMS) as a widely used chemical oxidation agent. In the present study, the reaction between PMS and Br- ions (PMS/Br- process) for the effective degradation of reactive yellow 145 (RY-145) dye was investigated by changing operational parameters vis solution pH, dosage of Br- ions and PMS, RY-145 concentration, and reaction time. Based on the results, the simultaneous presence of PMS and Br- ions in the solution led to efficient degradation of RY-145 with a synergistic index of 11.89. The degradation efficiency of RY-145 was decreased in severe basic pH and the presence of CO32- ions as a coexisting anion. Likewise, 4 mg/L of humic acid (HA), used as a classic scavenger, led to a 26.53% decrease in the RY-145 degradation efficiency. The free bromine (HOBr/OBr-), superoxide radical (●O2-), and singlet oxygen (1O2) was the dominant oxidation agents in RY-145 degradation, which confirmed the nonradical degradation pathway. In addition, PMS/Br- process showed excellent ability in mineralizing RY-145 in different aqueous solutions (total organic carbon (TOC) decreased 86.39% in deionized water and 78.23% in tap water). Although pollutants such as azo dyes can be effectively removed in the PMS/Br- process, the formation of byproducts should be strategically controlled and special attention should be paid when the PMS-based advance oxidation process is applied to treat Br- containing solutions.

Decomposition performance of hypochlorite on bead-type NiOx(OH)y catalyst: improving applicability of catalysts

An easy-to-use, pollution-free and reusable beaded NiO_x(OH)_y catalyst for improving hypochlorite oxidation was prepared by impregnating the mixture of persulfate and alkali over alumina and then reduced it with Ni²⁺. The effects of catalyst preparation conditions and reaction parameters on NaClO conversion rate and Ni²⁺ dissolution rate were studied. Impregnating the γ-Al₂O₃ beads in PS/OH^- mixed solution with 0.59 M PS and PS/OH^- molar ratio of 1.1, and then reducing with 0.8 M Ni²⁺ solution is the best condition for preparing catalyst. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The best catalytic layer is characterized by high content of chemisorbed oxygen which can be converted into atomic oxygen. The hypochlorite conversion rate increased with the catalyst dosage and reuse times, and decreased with available chlorine, while pH of hypochlorite solution had little effect on the conversion rate. After running stably for 120 h in continuous flow test, the chemisorbed oxygen content in the optimal catalytic layer decreased slightly. Atomic oxygen plays an important role in the decolorization of dye solution by NaClO/NiO_x(OH)_y system. The oxidant consumption cost of this process is much cheaper than Fenton reagent. The prepared catalyst has great potential in hypochlorite decomposition and wastewater treatment.

Quantitative structure-activity relationship in the photodegradation of azo dyes

The photolysis characteristics of azo dyes are critically important in environmental pollution control, dye-sensitized solar cells, and dyeing-related industries. However, there is still lack of quantitative relationship between the structures of azo dyes and their photolysis characteristics. To address this issue, the photolysis of 22 azo dyes were conducted side by side at three pH (4.0, 6.0, 9.0). The obtained pseudo-first order photodegradation rate constants (k₁) were processed with meta-analysis. Statistically, the hydrazone tautomer had a smaller excitation energy and was easier to undergo photolysis than the azo tautomer. The ortho-substituted sulfonate groups had an obvious protective effect on the photostability of azo dyes. The softness (s), the most positive and negative partial charge on a carbon atom (qC⁺, qC^-) were found to be crucial descriptors in the establishment of QSAR models for the photostability of azo dyes. The QSAR model at pH 9.0 was robust for predicting the photostability of azo dyes under UV irradiation. N₂-purging experiments and quantum chemical computation verified that the cleavage of azo bond was not a result of direct photolysis but was caused by the attack of photoinduced reactive oxygen species. The results here are helpful for the design of more stable azo dyes or the selection of suitable approaches for the treatment of dye-contaminated water bodies.