Keke Huang

A Graphene-like Oxygenated Carbon Nitride Material for Improved Cycle-Life Lithium/Sulfur Batteries.

Novel sulfur (S) anchoring materials and the corresponding mechanisms for suppressing capacity fading are urgently needed to advance the performance of Li/S batteries. Here, we designed and synthesized a graphene-like oxygenated carbon nitride (OCN) host material that contains tens of micrometer scaled two-dimensional (2D) rippled sheets, micromesopores, and oxygen heteroatoms. N content can reach as high as 20.49 wt %. A sustainable approach of one-step self-supporting solid-state pyrolysis (OSSP) was developed for the low-cost and large-scale production of OCN. The urea in solid sources not only provides self-supporting atmospheres but also produces graphitic carbon nitride (g-C3N4) working as 2D layered templates. The S/OCN cathode can deliver a high specific capacity of 1407.6 mA h g(-1) at C/20 rate with 84% S utilization and retain improved reversible capacity during long-term cycles at high current density. The increasing micropores, graphitic N, ether, and carboxylic O at the large sized OCN sheet favor S utilization and trapping for polysulfides.

Energetic multi-component molecular solids of tetrafluoroterephthalic acid with some aza compounds by strong hydrogen bonds and weak intermolecular interactions of C–H⋯F and C–H⋯O

Tetrafluoroterephthalic acid, (H2tfBDC), forms nine novel crystals with a series of N-containing heterocycles: 2,3-dimethyl pyrazine (2,3-Pyr), 2,6-dimethyl pyrazine (2,6-Pyr), 2,4-diamino-6-methyl-1,3,5-triazine (dmt), Benzoguanamine (bga), 2-methylbenzimidazole (2-MeBzlmH), 1,4-bis(imidazol) butane (bimb), 2-amino-4-hydroxy-6-methyl pyrimidine (ahmp), 1,2-bis[(2-methylimidazol-1-yl)methyl] benzene (L7), and 1,4-bis[(2-methylimidazol-1-yl)methyl] benzene (L5). These crystal structures including salts/co-crystals/hydrates were analyzed and characterized by single crystal X-ray diffraction, IR, and TGA. Single crystal X-ray diffraction studies show that the huge numbers of hydrogen bonds play a significance part in assembling individual molecules into larger architectures, especially the strong N–H⋯O, O–H⋯O hydrogen bonds, and weak but highly directional C–H⋯O and C–H⋯F interactions exist commonly in all nine novel crystals. Crystal structure analysis shows that the F atom of the H2tfBDC participates in C–H⋯F hydrogen bond formation, producing different supramolecular synthons. More importantly, the N–H⋯O, O–H⋯O, and C–H⋯O hydrogen bonds are mainly involved in the supramolecular assembly of these molecules, but C–H⋯F hydrogen bonds convert two-dimensional networks into three dimensional, hence, the C–H⋯F interactions have a crucial role in the formation of higher-order supramolecular structures.

Crystal facet tailoring arts in perovskite oxides

Crystal facet engineering is an important strategy for fine-tuning the physical and chemical properties in many fields, which will provide an effective route to fundamentally understand the relationship between the surface structure and the electron state. Many researchers have worked on the technological performance improvement of noble metal nanoparticles and simple metal oxides by tailoring their crystal facets. Perovskite structure oxides are the most prominent mixed-oxide materials in the field of heterogeneous catalysis due to the acceptable catalytic activity and thermal stability. However, the utilization of perovskite oxides is still limited in comparison with noble metal catalysts because the most stable surface is usually terminated with non-catalytically active crystal facets. High-index facet tailoring may be an effective route to improve the activity of perovskite structure catalysts. So far, only several perovskite oxides have been reported on the crystal facet tailoring with well-defined polyhedral shapes. Herein, we review the recent progress in the facet tailoring arts in perovskite structure oxides. This review begins with a general introduction to facet related physical and chemical behavior and the potential facet-dependent applications. Then, the general principles of crystal growth and facet tailoring will be discussed. The principle for possible grown facets of perovskite structure oxides will be proposed. Various shape growth and facet tailoring of perovskite structure oxides will be reviewed in four parts: (i) tungsten and molybdenum trioxide (A0B+6O3); (ii) niobate and tantalite (A+1B+5O3); (iii) titanate and zirconate (A+2B+4O3); (iv) ferrite, chromite and manganite (A+3B+3O3), including mixed-valence state perovskite compounds. The facet tailoring mechanism in perovskite oxides will be discussed in the next section. Finally, an overview of the promising future of facet dependent applications will be given as a perspective outlook. Fundamental understanding of facet tailoring is expected to open up strategies for the development of highly efficient perovskite oxide materials.

Hydrothermal synthesis and magnetic properties of REFe0.5Cr0.5O3 (RE = La, Tb, Ho, Er, Yb, Lu and Y) perovskite

A low temperature, one-pot route to iron-doped rare-earth chromite perovskite was proposed. Fe half-doped rare-earth chromites, REFe0.5Cr0.5O3 (RE = La, Tb, Ho, Er, Yb, Lu and Y) were prepared via a mild hydrothermal method and their magnetic properties were studied. All of these materials are well-crystallized and the profile refinement of powder X-ray diffraction (XRD) data showed that each of them adopts an orthorhombic distorted (Pbnm) perovskite structure. The temperature dependence of the magnetization curves indicate an improved order of arrangement of Fe3+ and Cr3+ at the B-site in some samples. Hysteresis measurements of YFe0.5Cr0.5O3 indicate that saturated and remnant magnetization were improved greatly compared to that prepared via the solid state method.

Hydrothermal syntheses and photoluminescence properties of rare-earth tungstate as near ultraviolet type red phosphors

Three families of scheelite CaWO4-based red luminescent phosphors, Ca1−1.5xWO4:xEu3+ (0.02 ≤ x ≤ 0.09), Ca0.925−ySryWO4:0.05Eu3+ (0 ≤ y ≤ 0.9) and Ca0.625Sr0.30W1−zMozO4:0.05Eu3+ (0 ≤ z ≤ 0.7) were hydrothermally prepared and characterized. The substitutions of Sr2+ for Ca2+ and Mo6+ for W6+, which improve local symmetries surrounding Eu3+, assisted the energy transfer from O2− to Eu3+ in the process of optimizing the luminescence properties. The z = 0.2 members of Ca0.625Sr0.30W0.80Mo0.20O4:0.05Eu3+ exhibited excellent bright red luminescence at 616 nm under near-UV excitation, narrowed emission spectra, room temperature luminescence lifetimes of milliseconds and maximum quantum efficiencies of 49%.

Unifying miscellaneous performance criteria for a prototype supercapacitor via Co(OH)2 active material and current collector interactions

The use of transition metal oxides and hydroxides in supercapacitors can yield high specific capacity electrodes. However, the effect of interaction between active material and current collector has remained unexplored. Here the behaviour of electrodeposited hexagonal cobalt hydroxide nanosheets on a variety of substrates was investigated, and the resulting valence bonding, morphological evolutions and phase transformations examined. It is shown that the electrochemical activity of the face centred cubic (FCC) Ni substrate dramatically decreases cyclability, the FCC Cu substrate also demonstrates decreased performance, and hexagonal carbon nanofibre (CNF) and Ti substrates exhibit far more stability. The miscellaneous roles of valence bonding, redox reactions and crystal structure mismatch between active material and current collector are examined, and their consequences discussed. Using the resulting insights into performance criteria, it was possible to select a suitable substrate for the fabrication of an asymmetric supercapacitor. The high performance and stability of the device demonstrates the usefulness of this approach, and the utility of applying these insights to energy storage devices.

Hydrothermal synthesis and photoluminescence properties of rare-earth niobate and tantalate nanophosphors

Rare-earth niobate and tantalate materials are of considerable interest for use as phosphors, photocatalysts and ionic conductors. We successfully synthesized Ln3MO7 (Ln = Y, Ce, Er, Ho, Tm, Yb and Lu, M = Ta, Nb) nanophosphors by a hydrothermal method using the water-soluble Lindqvist ion polyoxometalates [HNb6O19](7-) and [Ta6O19](8-) as Nb and Ta sources. The Pawley refinements of these nanophosphors revealed that the Lu3TaO7 and Lu3NbO7 nanophosphors could be indexed in the cubic system with the space group Fm3m, and that Y3TaO7 crystallizes in orthorhombic symmetry with the space group of C2221. These three solid compounds are nanoparticles with average particle sizes of 7.5, 5.9 and 4.0 nm for Lu3TaO7, Lu3NbO7 and Y3TaO7, respectively. The photoluminescence properties of Eu(3+) doped Lu3TaO7, Lu3NbO7 and Y3TaO7 were studied, and Eu(3+)/Sr(2+) co-doped Ln3MO7 (M = Ta, Nb) has an enhanced emission intensity compared to that of Ln3MO7:Eu(3+) (M = Ta, Nb).

Synthesis of Cu–Sb–S nanocrystals: insight into the mechanism of composition and crystal phase selection

In this work, Cu–Sb–S nanocrystals (NCs) with various compositions and crystal structures are realized by only tuning the amount of 1-dodecanethiol (DDT). When the DDT amount is 3.6, 5.5, 20.5, and 25.6 mmol, pure tetragonal Cu3SbS4, cubic Cu12Sb4S13, orthorhombic CuSbS2, and orthorhombic Cu3SbS3 NCs are respectively obtained. Systematic investigations demonstrate that different amounts of DDT are responsible for formation of the different compositions and crystal structures of the initial Cu2−xS seeds, which results into the formation of various Cu–Sb–S NCs. This reaction path is further verified by control experiments from successful preparation of Cu–Sb–S NCs comparable to that of the as-prepared ones directly from the reaction of Sb2S3 NCs with Cu2−xS seeds. The current study not only provides a facile and economical way to synthesize high-quality Cu–Sb–S NCs, but also opens a new route for preparation other I–V–VI multicomponent chalcogenides NCs, such as Cu–Bi–S systems.

Self-construction of magnetic hollow La0.7Sr0.3MnO3 microspheres with complex units.

Perovskite structure La0.7Sr0.3MnO3 magnetic hollow microspheres with complex units were prepared via the hydrothermal route without hard and soft templates. The formation of hollow microspheres follows the self-construction mechanism involving oriented attachment, dissolution, and recrystallization processes. It exhibits a ferromagnetic behavior at room temperature.

Hydrogen-bonding patterns in a series of multi-component molecular solids formed by 2,3,5,6-tetramethylpyrazine with selected carboxylic acids

The analysis of noncovalent interactions in several complexes constructed from 2,3,5,6-tetramethylpyrazine with different acid ligands, 1,4-cyclohexanedicarboxylic acid, 2,6-dihydroxybenzoic acid, 2,6-pyridinedicarboxylic acid, 6-hydroxy-2-naphthoic acid, 3-nitrophthalic acid, o-phthalic acid and 3-hydroxybenzoic acid, supported by single crystal X-ray diffraction analysis is presented. It reveals that all of these forms except 2 are organic supramolecular cocrystals without charge-transfer between the multicomponent acids and the base. The noncovalent interactions directing the assemblies of the eight structures are managed by classical O–H⋯O, O–H⋯N, weak C–H⋯O and π–π stacking interactions to generate 2D or 3D supermolecular architectures. For 5, 6, 7 and 8, carboxyl/pyrazine supramolecular heterosynthons R22(6) and R22(8) containing classical O–H⋯N and weak C–H⋯O interactions, usually observed in organic cocrystals of carboxylic acid and heterocyclic base, are again confirmed to participate in constructing these hydrogen-bonding supermolecular networks. In addition, weak C–H⋯O interactions were involved in building and consolidating their structures in all organic complexes. The thermal stability of crystals 1–8 has been investigated by thermogravimetric analysis (TGA) of mass loss.