Enhanced Fenton Catalytic Efficiency of γ‑Cu–Al₂O₃ by σ‑Cu²⁺–Ligand Complexes from Aromatic Pollutant Degradation

Mesoporous Cu-doped γ-Al₂O₃ (γ-Cu–Al₂O₃) was prepared via an evaporation-induced self-assembly process, in which Cu^+/2+ was co-incorporated into mesoporous γ-Al₂O₃ by chemical bonding of Al–O–Cu. The catalyst was found to be highly effective and stable for the degradation and mineralization of aromatic pollutants, as demonstrated with bisphenol A, 2,4-dichlorophenoxyacetic acid, ibuprofen, diphenhydramine, and phenytoin in the presence of H₂O₂ under neutral pH conditions. In addition, the high utilization efficiency of H₂O₂ was maintained at approximately 90% prior to the disappearance of the initial aromatic pollutants. On the basis of all of the characterization results, the pollutant degradation processes predominantly occurred on the surface of the catalyst due to the formation of σ-Cu–ligand complexes between the phenolic OH group and the surface Cu. In the reaction system, in addition to the unselective oxidation by ^•OH, H₂O₂ directly attacked the σ-Cu²⁺-complexes aromatic ring with the phenolic OH group, which resulted in the formation of ^•OH and HO-adduct radicals that were oxidized to hydroxylation products by reduction of Cu²⁺ in the σ-Cu²⁺-complexes to Cu⁺. The process prevented Cu²⁺ from oxidizing H₂O₂ to form HO₂^•/O₂^•– or O₂, and enhanced the Cu⁺/Cu²⁺ cycle, the formation of ^•OH, and the utilization efficiency of H₂O₂. Therefore, an extraordinarily high degradation and mineralization of the aromatic pollutants was observed

Mechanism of Catalytic Ozonation in Fe₂O₃/Al₂O₃@SBA-15 Aqueous Suspension for Destruction of Ibuprofen

Fe₂O₃ and/or Al₂O₃ were supported on mesoporous SBA-15 by wet impregnation and calcinations with AlCl₃ and FeCl₃ as the metal precursor and were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectra (FTIR) of adsorbed pyridine. Fe₂O₃/Al₂O₃@SBA-15 was found to be highly effective for the mineralization of ibuprofen aqueous solution with ozone. The characterization studies showed that Al–O–Si was formed by the substitution of Al³⁺ for the hydrogen of surface Si–OH groups, not only resulting in high dispersion of Al₂O₃ and Fe₂O₃ on SBA-15, but also inducing the greatest amount of surface Lewis acid sites. By studies of in situ attenuated total reflection FTIR (ATR-FTIR), in situ Raman, and electron spin resonance (ESR) spectra, the chemisorbed ozone was decomposed into surface atomic oxygen species at the Lewis acid sites of Al³⁺ while it was converted into surface adsorbed ^•OH_ads and O₂^•– radicals at the Lewis acid sites of Fe³⁺. The combination of both Lewis acid sites of iron and aluminum onto Fe₂O₃/Al₂O₃@SBA-15 enhanced the formation of ^•OH_ads and O₂^•– radicals, leading to highest reactivity. Mechanisms of catalytic ozonation were proposed for the tested catalysts on the basis of all the experimental information

Oxygen Vacancy Promoted Heterogeneous Fenton-like Degradation of Ofloxacin at pH 3.2–9.0 by Cu Substituted Magnetic Fe₃O₄@FeOOH Nanocomposite

To develop an ultraefficient and reusable heterogeneous Fenton-like catalyst at a wide working pH range is a great challenge for its application in practical water treatment. We report an oxygen vacancy promoted heterogeneous Fenton-like reaction mechanism and an unprecedented ofloxacin (OFX) degradation efficiency of Cu doped Fe₃O₄@FeOOH magnetic nanocomposite. Without the aid of external energy, OFX was always completely removed within 30 min at pH 3.2–9.0. Compared with Fe₃O₄@FeOOH, the pseudo-first-order reaction constant was enhanced by 10 times due to Cu substitution (9.04/h vs 0.94/h). Based on the X-ray photoelectron spectroscopy (XPS), Raman analysis, and the investigation of H₂O₂ decomposition, ^•OH generation, pH effect on OFX removal and H₂O₂ utilization efficiency, the new formed oxygen vacancy from in situ Fe substitution by Cu rather than promoted Fe³⁺/Fe²⁺ cycle was responsible for the ultraefficiency of Cu doped Fe₃O₄@FeOOH at neutral and even alkaline pHs. Moreover, the catalyst had an excellent long-term stability and could be easily recovered by magnetic separation, which would not cause secondary pollution to treated water

Surface Facet of CuFeO₂ Nanocatalyst: A Key Parameter for H₂O₂ Activation in Fenton-Like Reaction and Organic Pollutant Degradation

The development of efficient heterogeneous Fenton catalysts is mainly by “trial-and-error” concept and the factor determining H₂O₂ activation remains elusive. In this work, we demonstrate that suitable facet exposure to elongate O–O bond in H₂O₂ is the key parameter determining the Fenton catalyst’s activity. CuFeO₂ nanocubes and nanoplates with different surface facets of {110} and {012} are used to compare the effect of exposed facets on Fenton activity. The results indicate that ofloxacin (OFX) degradation rate by CuFeO₂ {012} is four times faster than that of CuFeO₂ {110} (0.0408 vs 0.0101 min^–1). In CuFeO₂ {012}-H₂O₂ system, OFX is completely removed at a pH range 3.2–10.1. The experimental results and theoretical simulations show that ^•OH is preferentially formed from the reduction of absorbed H₂O₂ by electron from CuFeO₂ {012} due to suitable elongation of O–O (1.472 Å) bond length in H₂O₂. By contrast, the O–O bond length is elongated from 1.468 to 3.290 Å by CuFeO₂ {110} facet, H₂O₂ tends to be dissociated into −OH group and passivates {110} facet. Besides, the new formed ≡Fe²⁺* on CuFeO₂ {012} facet can accelerate the redox cycle of Cu and Fe species, leading to excellent long-term stability of CuFeO₂ nanoplates