Yongcun Zou

Carbon-Armored Co9S8 Nanoparticles as All-pH Efficient and Durable H2-Evolving Electrocatalysts

Splitting water to produce hydrogen requires the development of non-noble-metal catalysts that are able to make this reaction feasible and energy efficient. Herein, we show that cobalt pentlandite (Co9S8) nanoparticles can serve as an electrochemically active, noble-metal-free material toward hydrogen evolution reaction, and they work stably in neutral solution (pH 7) but not in acidic (pH 0) and basic (pH 14) media. We, therefore, further present a carbon-armoring strategy to increase the durability and activity of Co9S8 over a wider pH range. In particular, carbon-armored Co9S8 nanoparticles (Co9S8@C) are prepared by direct thermal treatment of a mixture of cobalt nitrate and trithiocyanuric acid at 700 °C in N2 atmosphere. Trithiocyanuric acid functions as both sulfur and carbon sources in the reaction system. The resulting Co9S8@C material operates well with high activity over a broad pH range, from pH 0 to 14, and gives nearly 100% Faradaic yield during hydrogen evolution reaction under acidic (pH 0), neutral (pH 7), and basic (pH 14) media. To the best of our knowledge, this is the first time that a transition-metal chalcogenide material is shown to have all-pH efficient and durable electrocatalytic activity. Identifying Co9S8 as the catalytically active phase and developing carbon-armoring as the improvement strategy are anticipated to give a fresh impetus to rational design of high-performance noble-metal-free water splitting catalysts.

Gas uptake, molecular sensing and organocatalytic performances of a multifunctional carbazole-based conjugated microporous polymer

A multifunctional carbazole-based conjugated microporous polymer MFCMP-1 is successfully prepared by oxidative coupling polymerization using a single monomer and structurally characterized. A new three-dimensional π-conjugated polymer framework can be combined with permanent microporous, highly luminescent properties and abundant nitrogen activated sites in the skeleton. It possesses a large BET surface area of over 840 m2 g−1 with a pore volume of 0.52 cm3 g−1, and displays a high carbon dioxide uptake capacity (up to 3.69 mmol g−1) at 273 K and 1 bar, with good selectivity towards CO2 over N2 and CH4. MFCMP-1 exhibits also strong fluorescent emission at 529 nm after excitation at 380 nm in THF solution and works as a luminescent chemosensor towards hazardous and explosive molecules, such as nitrobenzene, 2-nitrotoluene, and 2,4-dinitrotoluene. In addition, MFCMP-1 features a high concentration of Lewis base nitrogen sites on its internal surfaces; it thus acts as a highly efficient recyclable heterogeneous organocatalyst towards Knoevenagel reaction of malononitrile with aromatics, heterocyclic aldehydes, and cyclic ketones. Furthermore, we further highlight that the ease of synthesis and low cost, coupled with multifunctional properties, make MFCMP-1 an attractive functional material in practical applications.

Preparation, characterization and photochemical properties of ordered macroporous hybrid silica materials based on monovacant Keggin-type polyoxometalates

High loading, three-dimensionally ordered macroporous (3DOM) hybrid silica materials based on monovacant Keggin-type polyoxometalates (POMs) [Xn+W11O39](12 − n)− (XW11; Xn+ = P5+, Si4+, Ge4+, B3+) were prepared via sol–gel as well as templating techniques. XW11 clusters were incorporated into the wall structures of macroporous silica, resulting in hybrid XW11–SiO2 composites. Formation of the hybrid materials was due to the chemical grafting of organosilanol groups from the silica network onto the surface oxygen atoms at vacant sites on the XW11 clusters. The products were characterized by UV diffuse reflectance spectra (UV/DRS), infrared (IR) spectra, 29Si and 31P MAS NMR, inductively coupled plasma atomic emission spectrometry (ICP-AES), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption isotherms. The study indicates that the primary Keggin structures remain intact in the hybrid materials, and that the products demonstrate three-dimensionally ordered macropores with pore diameters in the range of 285 to 385 nm. The composites exhibited photocatalytic activity to degrade aqueous malic acid (MA) under irradiation in the near-UV region; leakage of XW11 from the hybrid materials was hardly observed during catalytic tests.

High-temperature synthesis of ordered mesoporous silicas from solo hydrocarbon surfactants and understanding of their synthetic mechanisms

Ordered mesoporous silicas (SBA-15 or MCM-41) have been directly hydrothermally synthesized at high temperatures (160–180 °C) by using a solo hydrocarbon surfactant (P123 or CTAB). 1H NMR spectra and thermogravimetric (TG) curves showed that these hydrocarbon surfactants decomposed during the preparation process at such high temperatures. Accordingly, we proposed that the surfactant micelle plays an important role during the cooperative self-assembly of the silicates and surfactants in the initial stage for the formation of basic mesostructure, and it is no longer indispensable in the subsequent hydrothermal treatment at high temperature.

Generalized and high temperature synthesis of a series of crystalline mesoporous metal oxides based nanocomposites with enhanced catalytic activities for benzene combustion

We report here a generalized synthesis of various crystalline mesoporous metal oxides including CeO2, Cr2O3, Fe2O3, SnO2, Ce0.5Zr0.5O2, TiO2, Al2O3 and ZrO2 from the self-assembly of a basic poly 4-vinylpyridine (P4VP) template with various metal precursors based on their strong acid–base interaction under high temperature (180 °C) hydrothermal conditions. Using the typically crystalline mesoporous metal oxide of CeO2, after removing the template by calcination at 550 °C and loading with various transition metal oxides such as MnOx, various transition metal oxide functionalized crystalline mesoporous CeO2 (MnOx/P4VP–CeO2) were obtained. X-ray diffraction (XRD) patterns show that the resulting mesoporous metal oxides exhibit a high degree of crystallinity, and the transition metal oxides active sites have been successfully loaded into these samples. N2 sorption–desorption isotherms, SEM images show that the resulting crystalline mesoporous metal oxides, such as CeO2, have a large BET surface area (94 m2 g−1) and abundant mesopores, which exhibit monolithic morphology with crystal sizes ranging from 5 to 15 μm, giving a uniform pore size centered at 5 nm. XPS spectra show that the active sites such as MnOx exhibit the phases of MnO2 and Mn2O3 in P4VP–CeO2. H2-TPR curves show that MnOx/P4VP–CeO2 exhibits decreased reductive temperatures of both active sites of the MnOx and P4VP–CeO2 supporter when compared with the samples reported previously. More importantly, MnOx/P4VP–CeO2 exhibits much better catalytic activities and good recyclability for catalyzing the oxidation of benzene than that of MnOx loaded commercially crystalline CeO2, which will be very important for their wide applications for VOCs removal in industry.

Synthesis of porous In2O3 microspheres as a sensitive material for early warning of hydrocarbon explosions

Efficient detection/monitoring of low-concentration C1–C3 aliphatic hydrocarbons (e.g., methane) is a challenging task, mainly due to their intrinsically low chemical reactivity and thereby weak sensing response. Herein we report the template-free synthesis of porous nanoparticle-assembled In2O3 microspheres that can serve as a highly sensitive material for C1–C3 detection. In particular, porous In2O3 microspheres with a BET surface area of 57 m2 g−1 are prepared through simple thermal treatment of an indium glycerolate precursor. The gas-sensing properties of the porous In2O3 material are evaluated by a series of C1–C3 hydrocarbons including methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4) and acetylene (C2H2). The porous In2O3 material has the ability to detect these gases with a rapid response (<10 s) in a wide concentration range from 200 ppm to 50 000 ppm (the lower explosion limit of methane). In the testing range, the logarithm of response shows a good linear dependency on the logarithm of gas concentration, demonstrating that the porous In2O3 material may be used for quantitative detection of C1–C3 hydrocarbons. Given the rapid response and high sensitivity below the explosion limit, this porous In2O3 material is promising to provide earlier warning against the explosion risk of hydrocarbon compounds.

Facile precursor-mediated synthesis of porous core–shell-type Co3O4 octahedra with large surface area for photochemical water oxidation

A porous Co3O4 material with unique octahedron-in-octahedron core–shell-type morphology is prepared via a facile precursor-mediated synthetic route. This material possesses large surface area and good catalytic activity for water oxidation reaction.

Three-dimensional ultrathin In2O3 nanosheets with morphology-enhanced activity for amine sensing

Ultrathin materials have a wide range of applications in catalysis and sensing owing to their very large surface to volume ratio and great amount of exposed active sites. Herein, we report the synthesis of three dimensional (3D) In2O3 materials with a high surface area composed of ultrathin nanosheets, ca. 2 nm, using indium glycerolate as the precursor. The structural evolution process of the indium glycerolate precursor was monitored by thermogravimetric analysis, infrared spectroscopy and transmission electron microscopy. The resulting In2O3 nanosheets show excellent amine sensing performance at room temperature because ultrathin nanosheets offer a large amount of active sites on the surface and the 3D structure adds an additional advantage of avoiding aggregation and facilitating the diffusion of the target gas. In addition, the gas sensing mechanism is also proposed in this study.

Application of logarithmic x-axis on adsorption isotherms to improve micropore analysis

Abstract The adsorption isotherms for N 2 over zeolite samples with various structure types or various crystal sizes have been investigated systematically. It is interesting to note that the powder samples of zeolites with cavity structures show oscillation phenomena in their adsorption isotherms on logarithmic x -axis, but the samples without cavities do not show this phenomenon. With increase in the size of the zeolite crystals, the oscillation phenomenon becomes more remarkable. If crystals are large enough and have complex channel structures, even if they do not have cavities, they also exhibit a slight oscillation phenomenon. These results are very helpful to pre-determine which model should be applied for a new sample with an unknown structure, and to get more reliable data on its pore size distribution when Horvath–Kawazoe equation is used to calculate its pore size distribution.

Fast synthesis of submicron aluminosilicate (low silica/alumina ratio) zeolites under solventless microwave radiation

A promising strategy for synthesis zeolites has been reported in this paper. The method combines the advantages of both microwave heating and solventless synthesis. This method can generate zeolites under atmospheric pressure and is safe, highly efficient and environmentally benign.