Catalytic activity and mechanism of ordered mesoporous iron oxides on hydrogen peroxide for degradation of norfloxacin in water at neutral pH

Abstract

Environmental contextNorfloxacin is widely used as a human and veterinary medicine for its broad-spectrum antibacterial activity. It is chemically stable, rendering it difficult to remove from water using the traditional water and wastewater treatment techniques. We investigate the use of iron oxide catalysts for the degradation of norfloxacin in water prior to its release into the environment. AbstractThe catalytic activity of ordered mesoporous Fe2O3 (om-Fe2O3) on H2O2 oxidation of norfloxacin (NOR) under neutral pH conditions in water was investigated. Using non-ordered-mesoporous Fe2O3 as a reference (nom-Fe2O3), om-Fe2O3 with high specific surface area of 176.4m2g−1 and a uniform pore structure exhibited high catalytic activity in the decomposition of H2O2 as well as the degradation of NOR at neutral pH. Compared with nom-Fe2O3, om-Fe2O3 promoted the decomposition of H2O2 differently. The adsorption capacity of om-Fe2O3 for NOR was much higher than that of nom-Fe2O3. The adsorption efficiency of NOR on om-Fe2O3 accounted for 60.2–64.9% of the degradation efficiency in om-Fe2O3/H2O2. tert-Butanol (TBA), which is resistant to adsorption by om-Fe2O3, had no effect on the degradation of NOR by om-Fe2O3/H2O2. However, the presence of tromethamine (TMA), which was favourable to adsorption by om-Fe2O3, inhibited the degradation of NOR significantly. Based on the different effects of TBA and TMA on the degradation of NOR, it is proposed that the catalytic degradation of NOR may occur on the surface of om-Fe2O3. Hydroxyl radicals (·OH) generated may be bound on the surface of om-Fe2O3 without diffusing into aqueous solution. It is proposed that the adsorption of target organic pollutants must be considered when assessing the suitability of the om-Fe2O3/H2O2 process. The mechanism of om-Fe2O3 in promoting H2O2 decomposition into OH was also investigated.

Catalytic Ozonation in Arrayed Zinc Oxide Nanotubes as Highly Efficient Mini-Column Catalyst Reactors (MCRs): Augmentation of Hydroxyl Radical Exposure

“…These challenges are likely due to the structural limitations of the catalyst or a state of heterogeneity that may lead to inadequate bulk-to-surface ozone transfer and renewal, becoming a rate-limiting step for subsequent surface-mediated catalysis that produces HO• radicals. Furthermore, HO• populations have extremely short lifetimes (10 –9 s) and quickly decay after being catalytically generated from a surface, which may cause extremely weak radical exposure in the aqueous bulk phase during catalytic ozonation or other catalytic processes . Conducting HCO in micro or nanostructures appears to address these problems to optimize the availability of the active surface, as indicated in recent years through various membrane/ozone catalytic systems used for targeted water or wastewater treatments. − However, the current reported materials with shapeless and/or randomly distributed pores involving complex matrices have not been characterized well enough to conclude a nanostructural effect on HCO, and the tested porous structures could not satisfy the increasing demand to for a more uniform and efficient HCO platform with flexible nanoscale control of the kinetics of HO• exposure.…”