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Sulfidation can greatly improve the efficiency of utilization of reducing equivalents for contaminant removal; however, whether this method benefits Fenton-like reactions or not and the possible mechanism are not well understood. In this study, we revealed that surface sulfidation can greatly promote the heterogeneous Fenton activity of β-FeOOH (Fe 3 S 4 @β-FeOOH) by 40 times, in which not only the • OH formation was enhanced but also SO 4 •- as a new oxidation species was generated. Moreover, their contribution to metronidazole (MTZ) degradation was 52.5 and 37.1%, respectively. In comparison, almost no HO 2 • /O 2 •- was detected in the Fe 3 S 4 @β-FeOOH/H 2 O 2 system. These results were different from some previously reported Fenton counterparts. Based on the characterization and probe experiments, sulfur species, including S 2- , S 0 , and S n 2- , as an electron donor and electron shuttle were responsible for efficient conversion of Fe(III) into Fe(II) other than via the Haber-Weiss mechanism, leading to excellent • OH generation via a Fenton-like mechanism. Most importantly, HSO 5 - can be generated from SO 3 2- oxidized by • OH, and its scission into SO 4 •- was not dependent on the extra electric potential or Fe-O 2 -S(IV) intermediate. These findings provided new insight for utilizing sulfidation to improve the activity of iron-based Fenton catalysts.

In Fenton or Fenton-like processes, the key step is to catalyze H 2 O 2 and produce highly reactive OH radicals. More efforts are then focus on designing efficient heterogeneous Fenton catalysts by activating H 2 O 2 to generate OH at the highest possible steady state concentration. In this study, using the antibiotic ofloxacin as target organic pollutant, we firstly demonstrate a point of view for improving OH utilization efficiency by regulating surface chemical reactions to minimizing its migration distance to the target pollutant. C doped g-C 3 N 4 incorporated CuFeO 2 (CCN/CuFeO 2 ) exhibited almost ten times higher ofloxacin degradation rate constant than our previously reported CuFeO 2 {012} catalyst (0.1634 vs 0.0179 min -1 ). Since similar amount of OH was generated, the different inhibition effect of tert-butyl alcohol and nitrobenzene on the ofloxacin degradation confirmed that the much-enhanced ofloxacin degradation was attributed to the surface Fenton reaction process. According to XPS and EXAFS characterization, the C-O-Cu bond between g-C 3 N 4 and CuFeO 2 established a closed-circuit surface Fenton reaction mechanism. H 2 O 2 was adsorbed and decomposed into OH/O 2 - over ≡Cu  +  site in CuFeO 2 . The successful construction of CCN/CuFeO 2 creates a negative surface potential and benefits the enrichment of target antibiotics from water, which greatly reduces the migration distance of OH/O 2 •- to adjacent pollutant and then increases the OH/O 2 - utilization efficiency by avoiding the unwanted quenching. Hence, CCN/CuFeO 2 possesses superior Fenton catalytic activity and long-term stability., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

In this study, the highly dispersed β-FeOOH on palygorskite (H-β-FeOOH/PAL) was prepared and investigated as Fenton catalyst for H 2 O 2 activation towards metronidazole (MTZ). Based on electron spin resonance and probe techniques, hydroxyl radicles ( • OH) as main reactive oxygen species was confirmed, and much more • OH were generated over H-β-FeOOH/PAL than T-β-FeOOH/PAL using traditional impregnation method. The enhanced Fe(III) to Fe(II) cycle due to the highly dispersed β-FeOOH leads to the fast degradation of metronidazole over H-β-FeOOH/PAL. 92.8% of MTZ degradation efficiency was achieved within 180 min by adding 17 mmol/L H 2 O 2 and 40 mg/L of H-β-FeOOH/PAL at pH 6.0. The bacterial cytotoxicity during MTZ degradation process also decreased with reaction time and achieved zero at 66 min, indicating MTZ was not only efficiently degraded but also safely transformed. Besides, the possible MTZ degradation pathway was further proposed based on the intermediates identified by HPLC-MS., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The development of efficient heterogeneous Fenton catalysts is mainly by "trial-and-error" concept and the factor determining H 2 O 2 activation remains elusive. In this work, we demonstrate that suitable facet exposure to elongate O-O bond in H 2 O 2 is the key parameter determining the Fenton catalyst's activity. CuFeO 2 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 CuFeO 2 {012} is four times faster than that of CuFeO 2 {110} (0.0408 vs 0.0101 min -1 ). In CuFeO 2 {012}-H 2 O 2 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 H 2 O 2 by electron from CuFeO 2 {012} due to suitable elongation of O-O (1.472 Å) bond length in H 2 O 2 . By contrast, the O-O bond length is elongated from 1.468 to 3.290 Å by CuFeO 2 {110} facet, H 2 O 2 tends to be dissociated into -OH group and passivates {110} facet. Besides, the new formed ≡Fe 2+ * on CuFeO 2 {012} facet can accelerate the redox cycle of Cu and Fe species, leading to excellent long-term stability of CuFeO 2 nanoplates.

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 Fe 3 O 4 @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 Fe 3 O 4 @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 H 2 O 2 decomposition, • OH generation, pH effect on OFX removal and H 2 O 2 utilization efficiency, the new formed oxygen vacancy from in situ Fe substitution by Cu rather than promoted Fe 3+ /Fe 2+ cycle was responsible for the ultraefficiency of Cu doped Fe 3 O 4 @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.

Nanoscale LaFeO(3) was prepared via sol-gel method and characterized by XRD, FTIR and N2 adsorption/desorption experiment. The results indicated that, LaFeO(3) had a typical perovskite structure with a BET area of 8.5m(2)/g. LaFeO(3) exhibited excellent Fenton activity and stability for the degradation of pharmaceuticals and herbicides in water, as demonstrated with sulfamethoxazole, phenazone, phenytoin, acyclovir and 2,4-dichlorophenoxyacetic acid, 2-chlorophenol. Among them, sulfamethoxazole (SMX) could be completely removed in LaFeO(3)-H(2)O(2) system after reaction for 120 min at neutral pH. Based on the ATR-FTIR analysis, the surface complex of LaFeO(3) and H(2)O(2). was formed, which was important and essential for the enhanced Fenton reaction by accelerating the cycle of Fe(3+)/Fe(2+). Hence, more OH and O(2)(-)/HO(2)(-) were then produced in LaFeO(3)-H(2)O(2) system, resulting in more efficient removal of refractory organic compounds. Based on the surface interaction of LaFeO(3) and H(2)O(2), a heterogeneous Fenton reaction mechanism was proposed., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Layered birnessite-type manganese oxides (Na-OL-1) were prepared via a redox reaction involving MnO(4)(-) and Mn(2+) under markedly alkaline conditions. According to the XRD analysis, the resulting material exhibited a well-crystallized octahedral layer (OL) structure with several different phases, including β-MnOOH, α-MnOOH and γ-Mn(3)O(4). The catalyst was highly effective for the decolorization and degradation of methylene blue (MB) in the presence of H(2)O(2) at neutral pH. The tested MB was completely decolorized in Na-OL-1 suspension by the fraction dosing of H(2)O(2) (556.5mM at the beginning and then 183.8mM at 40 min). Based on the studies of electron spin resonance and the effect of radical scavengers, the (1)O(2) and O(2)(-) were the main reactive oxygen species (ROS) in the reaction. It was found that both oxygen and ROS were generated from the decomposition of H(2)O(2) in Na-OL-1 suspension, wherein the decomposition pathways were proposed. The generation of H(2)O(2) in Na-OL-1 suspension at air atmosphere indicated that the existence of multivalent manganese oxides greatly enhanced the interfacial electron transfer, leading to the high activity of Na-OL-1., (Copyright © 2011. Published by Elsevier B.V.)

Iron oxides coated on Fe(0) core-shell nanospheres (nIOCI) were synthesized through the reduction of ferrous sulfate aqueous solution by sodium borohydride at ambient atmosphere. The catalyst was highly effective for the degradation of humic acid (HA) in the presence of H(2)O(2) and UVA at neutral pH. Under deoxygenated conditions in the dark, the generation of hydroxyl radicals in aqueous nIOCI dispersion verified its galvanic cell-like performance, which enhanced the interfacial electron transfer and led to its higher reactivity. By the total organic carbon, the absorbance of UV(254), FTIR, the molecular weight distribution and the chemical fractional character analysis, the degradation process of HA was shown to proceed by the disappearance of aromaticity, the increase of hydrophilic fraction and aromatic ring openings into CO(2) and small organic acid. The treated HA showed much lower reactivity toward chlorine and the disinfection byproduct (DBP) formation potential was also greatly reduced. Moreover, it was found that the DBP formation potential more depended on the structure of the intermediates of HA degradation than TOC removal.

SiO2-C2H4-ferrocene (SiCFe) was synthesized by covalent grafting of ferrocene on functionalized silica gel with a -C2H4- linkage. On the basis of characterization by diffuse reflectance UV-vis spectra (DRS) and Fourier transform infrared spectra (FT-IR), ferrocene has been successfully anchored on the silica gel. Under UVA (lambdamax=365 nm) irradiation, the catalyst exhibited high photocatalytic activity in the degradation of Acid Red B (ARB), especially in the presence of H2O2. Meanwhile, the catalytic activity of SiCFe was maintained effectively even after reused for 4 times without any significant destruction of ferrocene. The influence of initial solution pH and wavelength of UV light on the catalyst's activity was also investigated. Electron spin resonance (ESR) studies revealed that both OH and HO2/O2- radicals were involved as the active species in the ARB degradation process. Furthermore, results of total organic carbon (TOC) and FT-IR analysis indicated that ARB degradation proceeded by the cleavage of NN, followed by hydroxylation and opening of phenyl rings to form aliphatic acids and further oxidization of the aliphatic acids to produce carbon dioxide and water. A possible reaction mechanism was proposed on the basis of all the information obtained under various experimental conditions.

Fe0 was calcined in air at 200 degrees C and showed enhanced activity in three cycling runs for the degradation of acid red B (ARB) in the presence of H2O2 under UVA irradiation. Subsequently, the catalyst's activity was maintained effectively after 10 successive cycling experiments. Moreover, the catalyst was found to be highly effective for the degradation of nonbiodegradable azodyes ARB, reactive brilliant red X-3B, reactive red K-2G, cationic red X-GRL, and cationic blue X-GRL at neutral pH values. On the basis of characterization by X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectra, the surface layer of the catalyst was mainly composed of alpha-FeOOH and gamma-Fe2O3, and the core was Fe0 (FeOxH2x-3/ Fe0). Fe,OxH2x3/Fe0 was very easily recovered from the reaction system by magnetic separation. The degradation of azodyes came from the synergistic effect of the catalysis of galvanic cells and the oxidation of heterogeneous photo-Fenton reaction on the basis of all information obtained under different experimental conditions. By the total organic carbon and GC-MS analysis, the degradation process of ARB was shown to proceed with decolorization and naphthalene ring openings into CO2 and small organic acid.

Abstract: Layered birnessite-type manganese oxides (Na-OL-1) were prepared via a redox reaction involving MnO4 − and Mn2+ under markedly alkaline conditions. According to the XRD analysis, the resulting material exhibited a well-crystallized octahedral layer (OL) structure with several different phases, including β-MnOOH, α-MnOOH and γ-Mn3O4. The catalyst was highly effective for the decolorization and degradation of methylene blue (MB) in the presence of H2O2 at neutral pH. The tested MB was completely decolorized in Na-OL-1 suspension by the fraction dosing of H2O2 (556.5mM at the beginning and then 183.8mM at 40min). Based on the studies of electron spin resonance and the effect of radical scavengers, the 1O2 and O2 − were the main reactive oxygen species (ROS) in the reaction. It was found that both oxygen and ROS were generated from the decomposition of H2O2 in Na-OL-1 suspension, wherein the decomposition pathways were proposed. The generation of H2O2 in Na-OL-1 suspension at air atmosphere indicated that the existence of multivalent manganese oxides greatly enhanced the interfacial electron transfer, leading to the high activity of Na-OL-1. [Copyright &y& Elsevier]