Yolk‐shell Co₃O₄@Fe₃O₄/C Nanocomposites as a Heterogeneous Fenton‐like Catalyst for Organic Dye Removal

Abstract

The yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites with Co 3 O 4 as the core, Fe 3 O 4 /C as the shell, and a cavity structure were synthesized by the hard template method. The physical and chemical properties of the composites were characterized by SEM, TEM, XRD, TGA, XPS, BET, and VSM. The specific surface area of yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites is 175.9 m 2 g À 1 , showing superparamagnetic properties. The yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites were used as heterogeneous Fenton catalysts to activate peroxymonosulfate (PMS) to degrade MB, which showed high catalytic degradation performance. The degradation rate of MB reached 100 % within 30 min under the circumstances of the yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites dosage of 0.1 g L À 1 , the PMS dosage of 1.0 g L À 1 , the initial MB concentration of 100 mg L À 1 , an initial pH of 5.5, and a temperature of 30 � 2 °C. The enhanced catalytic performance of the yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites can be attributed to the synergistic effect of the two catalytically active materials and the middle cavity. The effects of different operating parameters and co-existing anion species on MB degradation were also investigated. Electron paramagnetic resonance (EPR) analysis and quenching experiments confirmed that the formation of SO 4 *À in the yolk-shell Co 3 O 4 @Fe 3 O 4 /C/PMS system contributes to MB degradation. In addition, yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites can be easily separated from the pollutant solution under the action of an external magnetic field, and the degradation rate of MB can still reach 98 % after five cycles, indicating that it has good stability and reusability and has broad application prospects in the field of water purification.

Constructing Active Cu2+–O–Fe3+ Sites at the CuO–Fe3O4 Interface to Promote Activation of Surface Lattice Oxygen

“…For CFO-C and CFO-N catalysts, two broad reduction peaks are detected in the range of 275–500 °C, which may correlate with the reduction of CuO (Cu 2+ → Cu + → Cu 0 ) and the surface Fe 3+ → Fe 2+ in Fe 3 O 4 , , whereas the relatively weak peaks ranging from 600 to 800 °C may correspond to the bulk Fe 3+ → Fe 2+ and the reduction of Fe 2+ to Fe 0 . , For the CFO–C-I and CFO–N-I catalysts, an evident shift toward lower and higher temperatures occurs in the first two and the subsequent peaks, respectively, which reflects the improvement in the redox capability of Cu 2+ /Cu + and Fe 3+ /Fe 2+ , and the suppression of Fe 2+ → Fe 0 , revealing the enhancement in the complete redox cycle. In addition, the H 2 consumption increases at the initial stage (below 250 °C) for these two catalysts, accompanied by the appearance of a weak peak at approximately 180 °C (Figure e), which may be caused by the reduction of Cu 2+ at the interface in the Cu 2+ –O–Fe 3+ structure. , This further implied that the enhanced low-temperature reducibility of CFO–C-I and CFO–N-I originated from the Cu 2+ –O–Fe 3+ entity. Ultimately, the comprehensive results of Raman, XAFS, DFT calculations, O 2 -TPD, and H 2 -TPR elucidated the origin of the highly active surface O latt .…”

“…Moreover, the relatively weak diffraction peaks that correspond to the tetragonal spinel Fe 3 O 4 (JCFDS No. 19–0629) are observed at 18.2, 30.1, 57.1, and 62.7° even though the main peak at 2θ of 35.5° may overlap with that of CuO . The near-identical XRD patterns and no peak shift indicated that CuO and Fe 3 O 4 coexist in all catalysts, and the distinction in crystal structure could be neglected.…”

“…19−0629) are observed at 18.2, 30.1, 57.1, and 62.7°even though the main peak at 2θ of 35.5°may overlap with that of CuO. 33 The near-identical XRD patterns and no peak shift indicated that CuO and Fe 3 O 4 coexist in all catalysts, and the distinction in crystal structure could be neglected. Combined with the similar yields of the as-derived catalysts (Figure S3b), we concluded that the precursors as sacrificial templates could decompose completely and in situ transform into bimetal oxides, which is favorable for the formation of intimate contact interfaces between CuO and Fe 3 O 4 .…”

GQD@NiFe‐LDH Nanosheets for Photocatalytic Activity towards Textile Dye Degradation via Lattice Contraction

“…Its excellent stability properties do not allow it to auto‐degrade naturally. So, photocatalytic degradation is one of the highly acceptable green strategies for the mineralization of these industrial dye wastewater, using a stable, non‐toxic, economic, and visible light active heterogeneous photocatalyst through advanced oxidation and reduction processes [3–5] . The reactive species such as superoxide radical (O 2 − ), hydroxyl radical (⋅OH), and hole (h + ) produced in this process have a major role in the degradation of dyes, with CO 2 and H 2 O as the end product [6–11] …”

“…So, photocatalytic degradation is one of the highly acceptable green strategies for the mineralization of these industrial dye wastewater, using a stable, non-toxic, economic, and visible light active heterogeneous photocatalyst through advanced oxidation and reduction processes. [3][4][5] The reactive species such as superoxide radical (O 2 À ), hydroxyl radical ( * OH), and hole (h + ) produced in this process have a major role in the degradation of dyes, with CO 2 and H 2 O as the end product. [6][7][8][9][10][11] Among transition metal-based photocatalysts, 2D Layered photocatalysts emerged as a new class of materials originating from their distinct structures, giving rise to the anisotropy required for charge separation in photocatalytic applications.…”