Pengfei Zhang

Solid-state synthesis of ordered mesoporous carbon catalysts via a mechanochemical assembly through coordination cross-linking

Ordered mesoporous carbons (OMCs) have demonstrated great potential in catalysis, and as supercapacitors and adsorbents. Since the introduction of the organic–organic self-assembly approach in 2004/2005 until now, the direct synthesis of OMCs is still limited to the wet processing of phenol-formaldehyde polycondensation, which involves soluble toxic precursors, and acid or alkali catalysts, and requires multiple synthesis steps, thus restricting the widespread application of OMCs. Herein, we report a simple, general, scalable and sustainable solid-state synthesis of OMCs and nickel OMCs with uniform and tunable mesopores (∼4–10u2009nm), large pore volumes (up to 0.96u2009cm3u2009g−1) and high-surface areas exceeding 1,000u2009m2u2009g−1, based on a mechanochemical assembly between polyphenol-metal complexes and triblock co-polymers. Nickel nanoparticles (∼5.40u2009nm) confined in the cylindrical nanochannels show great thermal stability at 600u2009°C. Moreover, the nickel OMCs offer exceptional activity in the hydrogenation of bulky molecules (∼2u2009nm).

Mechanochemical synthesis of porous organic materials

Porous organic materials (POMs) are of growing interest due to their potential uses in gas adsorption, separation, and catalysis. In comparison to porous inorganic materials (e.g., zeolites and metal oxides) or inorganic–organic hybrids (e.g., metal–organic frameworks), POMs possess a number of advantages, such as being composed of only light elements, possessing accessible functionality for organic reactions, having high stability in air and at atmospheric moisture levels, and possessing chemical robustness to acids and bases. Borrowed from the rich library of organic chemistry, various reaction routes like Sonogashira–Hagihara coupling, Yamamoto polymerization, Suzuki couplings, oxidative polymerization, the trimerization reaction of carbonitriles, solvothermal radical polymerization, and the imine condensation reaction, to name just a few, have been used to construct POMs. Not surprisingly, nearly all chemical transformations for POM construction proceed via solution-based synthesis methods. Just recently, much interesting progress on the mechanochemical synthesis (MS) of POMs has been made, highlighting the unique features of this method, such as solvent-free processing and fast reaction rates. In this mini-review, we wish to summarise the recent advances on the design of polymers of intrinsic microporosity, covalent–organic frameworks, covalent triazine-based frameworks, ordered mesoporous polymers, and ordered mesoporous carbons via MS. A brief comment about the MS of POMs in the future will also be discussed.

Mesoporous Mo2C/Carbon Hybrid Nanotubes Synthesized by a Dual-Template Self-Assembly Approach for an Efficient Hydrogen Production Electrocatalyst

Molybdenum carbide-containing nanomaterials have drawn considerable attention in the application of hydrogen production electrocatalysts in light of the high abundance, low cost, and Pt-like electronic structure of molybdenum carbide. In this article, we report the synthesis of one-dimensional (1D) Mo2C/carbon mesoporous nanotubes (Mo2C/C PNTs) through a dual-template self-assembly approach, which employs 1D MoO3 nanobelts as the structure-directing template as well as one of the Mo2C precursors, along with block copolymer (BCP) micelles as the pore-forming template. In aqueous solution, the interface self-assembly of the micelles with pyrrole (Py) molecules absorbed in the PEO domains leads to the tight arrangement of the micelles on the surfaces of the MoO3 nanobelts. The polymerization of Py and the subsequent pyrolysis at 800 °C under a nitrogen atmosphere yield Mo2C/C PNTs with well-defined mesopores. Among the resultant Mo2C/C PNT samples, Mo2C/C PNTs with a specific surface area of 69 m2/g, a N atom percentage of 5.5 atom %, and an optimum Mo2C content of 40 wt % exhibit the highest HER catalytic performance in 0.5 M H2SO4 electrolyte, with a low onset potential of 34 mV, a satisfied overpotential of 140 mV at 10 mA/cm2, and excellent cycling stability. This study not only opens an avenue toward new Mo2C-containing nanomaterials but also provides a new system for the fundamental study on 1D porous nanohybrids with potential applications as hydrogen production electrocatalysts.

Nitrogen-doped carbon nanosheets and nanoflowers with holey mesopores for efficient oxygen reduction catalysis

Efficient structure optimization is one of the key factors for improving the oxygen reduction reaction (ORR) catalytic performance of carbon materials. This paper describes a dual-template method for fabrication of new carbon materials as ORR catalysts, including N-doped carbon nanosheets and nanoflowers with holey mesopores, by employing a polystyrene-b-poly(ethylene oxide) block copolymer as the pore-forming agent, layered double hydroxide (LDH) nanosheets or nanoflowers as the sacrificial morphology-directing template, and m-phenylenediamine as the carbon precursor. The resultant carbon materials possess a honeycomb-like mesoporous structure with similar nitrogen contents of ∼4 wt%, an average pore size of ∼14 nm and a specific surface area of ∼260 m2 g−1. Due to the presence of the holey mesopores that facilitate mass transfer and may shorten the diffusion distance of O2 molecules to the active sites, the nanosheets and the nanoflowers exhibit excellent electrocatalytic performance when serving as metal-free ORR catalysts in basic media with high half-wave-potentials (+0.80 V) and limiting current densities (5.5 mA cm−2) which surpass those of many reported carbon-based materials with much higher surface areas but without holey pores. Moreover, the porous nanoflowers show better electrocatalytic activity than that of the nanosheets, profiting from their 3D structure that can prevent the blockage of partial holey pores caused by the preferential layer-by-layer stacking of the nanosheets.

Direct reduction of oxygen gas over dendritic carbons with hierarchical porosity: beyond the diffusion limitation

The direct activation of oxygen molecules in the gas phase at the interface of solid (catalyst), liquid (electrolyte) and gas (oxygen gas) is highly alluring for the oxygen reduction reaction (ORR) catalyst in a liquid-phase reactor. Such a multiphase pathway without the limitation of the diffusion rate of the dissolved oxygen molecules promises a much higher catalytic efficiency. However, a stable gas–liquid–solid interface can hardly be maintained due to the high surface tension of the aqueous solution to repel the gas phase on the surface of conventional ORR electrodes. Taking advantage of graphene layers with super-absorbing nature, we designed a dendritic carbon structure catalyst to stabilize oxygen bubbles in the nano-intervoids of the dendrites without loss of conductivity and structural integrity, achieving the direct reduction of oxygen gas in an aqueous electrolyte and an ultra-high ORR current density without a diffusion controlled plateau.

Ultra-Stable and High-Cobalt-Loaded Cobalt@Ordered Mesoporous Carbon Catalysts: All-in-One Deoxygenation of Ketone into Alkylbenzene

Catalytic deoxygenation represents a straightforward and core methodology for fine‐chemical production and biomass upgrading. Generally, the application of homogeneous metal complexes or heterogeneous noble‐metal catalysts prevails in academia and the chemical industry. Herein, we introduce cobalt@ordered mesoporous carbon (Co@OMC) catalysts, which are constructed conveniently by a mechanochemical coordination self‐assembly based on a renewable tannin precursor. Importantly, the Co@OMC catalysts with a high loading of inu2005situ confined Co species promote the selective deoxygenation of various ketones, aldehydes, and alcohols efficiently into the corresponding alkanes under mild conditions. Therefore, a simple, inexpensive, and heterogeneous catalyst for selective deoxygenation can be expected, meanwhile the solid‐state synthesis affords a green, rapid, and scalable pathway to Co@OMC catalysts.

Sustainable synthesis of alkaline metal oxide-mesoporous carbons via mechanochemical coordination self-assembly

A simple, solvent-free, solid-state self-assembly strategy for the synthesis of alkaline-metal-oxide-doped mesoporous carbons (MCs) with tunable mesopores (∼5–9 nm), high surface areas (up to 571 m2 g−1) and large pore volumes (up to 0.65 cm3 g−1) is developed via mechanochemical assembly between polyphenol–Ca2+/Mg2+ composites and F127 copolymers. Interestingly, the as-made MgO-MCs not only offer good CO2 capacities (up to 1.6 mmol g−1 at 0.15 bar and 273 K) and competitive CO2/N2 selectivities (up to 41) but also exhibit high dye adsorption capacities (541 mg g−1 for methylene blue and 435 mg g−1 for methyl orange).