Hierarchical materials have facilitated fascinating applications in heterogeneous catalysis due to that micro-sized bulk is easily separable and nano-sized sub-blocks can significantly enhance catalytic performance. In this study, corolla-like δ-MnO2 with sub-blocks of nanosheets, and urchin-shaped α-MnO2 with sub-blocks of nanorods were synthesized by a simple hydrothermal route. The hydrothermal temperature significantly influenced the crystal structure, morphology and textural structure of the obtained three-dimensional (3D) MnO2 catalysts. The catalytic activities of three samples prepared at 60, 100 and 110 °C (denoted as Mn-60, -100 and -110, respectively) were thoroughly evaluated by activation of peroxymonosulfate (PMS) for catalytic oxidation of phenol solutions. Based on first-order kinetics, the rate constants of Mn-60, -100 and -110 catalysts were determined to be 0.062, 0.132, and 0.075 min−1, respectively. The activation energy of Mn-100 in catalytic oxidation of phenol solutions was estimated to be 25.3 kJ/mol. The catalytic stability of Mn-100 was also tested and discussed by monitoring Mn leaching. Electron paramagnetic resonance (EPR), quenching tests, total organic carbon (TOC) analysis and identification of intermediates were applied to illustrate the activation processes of PMS and the mechanism of phenol degradation.

3D-hierarchically structured MnO2 for catalytic oxidation of phenol solutions by activation of peroxymonosulfate: Structure dependence and mechanism

In this study, magnetic carbon encapsulated nano iron hybrids (nano Fe0/Fe3C@CS) were synthesized via a novel one-pot hydrothermal method followed by self-reduction in N2 atmosphere. The structural, morphological, and physicochemical properties of the samples were thoroughly investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), N2 sorption isotherms and thermogravimetric analysis–differential scanning calorimetry (TGA–DSC). Catalytic performance of the as-synthesized nanoparticles was tested in activation of oxone® for phenol degradation in aqueous solutions. Superior catalytic performance was observed by complete removal of 20 ppm phenol within 10 min. The formation of Fe3C was found to contribute to a better stability and magnetic separation of Fe0/Fe3C@CS in its repeated uses. Both electron paramagnetic resonance (EPR) and classic quenching tests were carried out to investigate the mechanism of radical generation and evolution in phenol oxidation. Different from Co- and Mn-based catalysts in generation of sulfate radicals, Fe0/Fe3C@CS selectively induced hydroxyl radicals for phenol degradation.

A new magnetic nano zero-valent iron encapsulated in carbon spheres for oxidative degradation of phenol

The use of metal organic frameworks as hard templates for the preparation of heterogeneous catalysts is thoroughly reviewed. In this critical article, the main factors to consider when using a MOF as a sacrificial template are first discussed. Then, the existing literature on the topic is reviewed, classifying the different examples according to the MOF metal. Finally, the main advantages, limitations and perspectives of the so-called MOF mediated synthesis are outlined.

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Metal organic frameworks as precursors for the manufacture of advanced catalytic materials

New insights into heterogeneous generation and evolution processes of sulfate radicals for phenol degradation over one-dimensional α-MnO2 nanostructures

2D/2D nano-hybrids of γ-MnO2 on reduced graphene oxide for catalytic ozonation and coupling peroxymonosulfate activation

Various sizes and shapes of Mn3O4 nanocrystals have been prepared in a one-pot synthesis in extremely dilute solution by soft template self-assembly. To better control size and shape, the effects of varying the growth time, reaction temperature, surfactant, and manganese source were examined. The average size of octahedral Mn3O4 crystallites was found to be related to the reaction time, while higher reaction temperature (150 °C) and the use of a cetyltrimethylammonium bromide/poly(vinylpyrrolidone) (CTAB/PVP) mixture allowed construction of a better-defined octahedral morphologies. When PVP or poly(ethylene oxide)-poly(propylene oxide) (P123) was used as template, large-scale agglomeration resulting in loss of the octahedral morphology occurred and crystallites with a quasi-spherical shape were obtained. The nano-octahedral crystallites were shown to be an efficient catalyst for the oxidation of methylene blue.

/pdf/shape-controlled-synthesis-of-mn3o4-nanocrystals-and-their-2uupzqxhq2.pdf

Shape-controlled synthesis of Mn3O4 nanocrystals and their catalysis of the degradation of methylene blue

Aqueous Zn–iodine (Zn–I2) batteries have been regarded as a promising energy‐storage system owing to their high energy/power density, safety, and cost‐effectiveness. However, the polyiodide shuttling results in serious active mass loss and Zn corrosion, which limits the cycling life of Zn–I2 batteries. Inspired by the chromogenic reaction between starch and iodine, a structure confinement strategy is proposed to suppress polyiodide shuttling in Zn–I2 batteries by hiring starch, due to its unique double‐helix structure. In situ Raman spectroscopy demonstrates an I5−‐dominated I−/I2 conversion mechanism when using starch. The I5− presents a much stronger bonding with starch than I3−, inhibiting the polyiodide shuttling in Zn–I2 batteries, which is confirmed by in situ ultraviolet–visible spectra. Consequently, a highly reversible Zn–I2 battery with high Coulombic efficiency (≈100% at 0.2 A g−1) and ultralong cycling stability (>50 000 cycles) is realized. Simultaneously, the Zn corrosion triggered by polyiodide is effectively inhibited owing to the desirable shuttling‐suppression by the starch, as evidenced by X‐ray photoelectron spectroscopy analysis. This work provides a new understanding of the failure mechanism of Zn–I2 batteries and proposes a cheap but effective strategy to realize high‐cyclability Zn–I2 batteries.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/adma.202201716

Polyiodide Confinement by Starch Enables Shuttle‐Free Zn–Iodine Batteries

A simple method was developed for the synthesis of novel macroporous silica cages with tailored pore architecture and high thermal stability. The silica cages possess anamorphic spherical morphology and narrow particle size distribution (∼1.5 µm), consisting of numerous channels interconnected with one another to form a fully open three-dimensional network. The morphology and structure of macroporous silica cages are strongly affected by synthetic conditions, including the molar compositions of reactants, the evaporation time of solvent, and the aging conditions. The number of silica crystal nuclei in the synthesis system is the major factor that determines the formation of silica cages and the disorder-to-order transformation, which can be controlled by changing the reactant molar concentrations and the solvent evaporation time. Using the appropriate aging time in ethanol provides the possibility of effecting the transformation from disordered twisting silica nanofibers with random branches to silica cages. The transformation from the macroporous cages to the mesostructures and the formation mechanism of the cages are also discussed in detail.

Silica cages with controllable frameworks: synthesis, structure-tailoring, and formation mechanism

Co7Fe3 Nanoparticles Confined in N-Doped Carbon Nanocubes for Highly Efficient, Rechargeable Zinc–Air Batteries

Metallic lithium/sodium (Li/Na) is considered an attractive anode for future high‐energy‐density batteries. The root causes of preventing their applications come from uneven Li/Na nucleation and subsequent dendrite formation. Here, a cost‐efficient and scalable solid‐to‐solid transfer method for dense buffer layer construction on Li/Na anodes is proposed, and thin lithiophilic/sodiophilic buffer layers based on natural silk fibers derived carbon (SFC) and carbon nanotubes (CNTs) composites (denoted as SFC/CNTs) are adopted, which facilitate uniform Li/Na nucleation and dendrite‐free, lateral growth behavior upon recurring Li/Na plating/stripping processes. Lithiopilic/sodiophilic buffer layers enable long‐term cycling stability (>250 cycles) with high Coulombic efficiency (99.2% for Li and 98.8% for Na), low polarization, and flat voltage profiles. More importantly, the cycling performance of LiFePO4|Li pouch cells is largely enhanced with a lifespan of 390 cycles. Further, using ultra‐thin Li anodes (25 μm) also achieves stable LiNi1/3Mn1/3Co1/3O2|Li cells with 200 cycles under a low negative/positive ratio (1.67). Similar achievement is also realized in Na‐metal batteries with negligible capacity fading for over 600 cycles in Na3V2(PO4)3|Na cells, further demonstrating that SFC/CNT buffer layer is technically viable in practical batteries. This study provides a facile strategy for fabricating dense and uniform lithiophilic/sodiophilic buffer layers for low‐cost and scale‐up energy storage devices.

Pengqu Zhang

Papers

Shape-controlled synthesis of Mn3O4 nanocrystals and their catalysis of the degradation of methylene blue

Polyiodide Confinement by Starch Enables Shuttle‐Free Zn–Iodine Batteries

Silica cages with controllable frameworks: synthesis, structure-tailoring, and formation mechanism

Co7Fe3 Nanoparticles Confined in N-Doped Carbon Nanocubes for Highly Efficient, Rechargeable Zinc–Air Batteries

Scalable Lithiophilic/Sodiophilic Porous Buffer Layer Fabrication Enables Uniform Nucleation and Growth for Lithium/Sodium Metal Batteries