Xian-Fa Zhang

Facile synthesis of yolk–shell MoO2 microspheres with excellent electrochemical performance as a Li-ion battery anode

In this paper, a facile and template-free solvothermal method has been developed to synthesize yolk–shell MoO2 microspheres. The as-synthesized MoO2 microspheres are composed of both a uniform porous shell of 80 nm in thickness and a porous core constructed from primary MoO2 nanocrystal clusters of 20 nm in size. Importantly, the unique yolk–shell MoO2 microspheres exhibit excellent electrochemical performance. At a current density of 50 mA g−1, they can deliver a high specific capacity of 955 mA h g−1 in the first discharge and retain a reversible capacity of 847.5 mA h g−1 after 50 cycles. Meanwhile, even at a high current density of 2000 mA g−1, they also exhibit a specific capacity of 450 mA h g−1. This superior electrochemical performance of the as-synthesized MoO2 microspheres could be ascribed to their special yolk–shell structure, which could not only provide short Li-ion and electron pathways, but also accommodate large volume variation.

Highly sensitive H2S detection sensors at low temperature based on hierarchically structured NiO porous nanowall arrays

3D network-like, hierarchically structured, porous nanowall NiO arrays were grown in situ on ceramic tubes by a facile but environmentally friendly hydrothermal reaction with a subsequent calcination process. The arrays were constructed of the interconnected porous nanosheets, which were further assembled with abundant nanoparticles. The gas-sensing properties of such porous nanowall NiO array film sensors were investigated with eight inorganic and organic gases. The H2S-sensing performance was observed to be in a large dynamic range (1 ppb to 100 ppm) and the lowest detection limit was 1 ppb at 92 °C compared with other reported oxide-based sensors. The sensor exhibited not only high sensitivity, good selectivity and reproducibility to H2S with resistance to humidity at a low temperature of 92 °C and room temperature, but also good linear relationship under concentration ranges of ppm level (1–100 ppm) and ppb level (1 ppb to 1 ppm). The excellent sensing performance of this array film sensor to H2S could be ascribed to the porous structures in the unique nanowall arrays with a large specific surface area, which benefit H2S molecules to adsorb/desorb onto/from the array surface as well as the electron transfer. The formation of NiO arrays and their possible H2S-sensing mechanism are discussed in detail.

Highly selective NO2 sensor at room temperature based on nanocomposites of hierarchical nanosphere-like α-Fe2O3 and reduced graphene oxide

Nanosphere-like α-Fe2O3 modified reduced graphene oxide nanosheets were prepared by a simple hydrothermal method without any surfactant or template. The nanocomposites were characterized by X-ray diffraction (XRD), Raman spectra (RS), Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The α-Fe2O3 nanospheres have a hierarchical structure, with diameter of about 40–50 nm, and grow uniformly on the surface of single graphene nanosheets. α-Fe2O3/rGO nanocomposites exhibit high response of 150.63% to 90 ppm NO2 at room temperature, 65.5 times higher than the response of pure graphene, and the detection limit for NO2 can be decreased down to 0.18 ppm. A mechanism is proposed for sensing of the nanocomposites: the high response of the nanocomposites to NO2 at room temperature is the synergistic effect of the two sensing materials and large specific surface area of the nanocomposites.

Construction of monodisperse vanadium pentoxide hollow spheres via a facile route and triethylamine sensing property

Monodisperse vanadium pentoxide hollow spheres (VOHSs) were synthesized via a simple template-free solvothermal route followed by calcination in air. The as-prepared precursor and VOHSs were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron microscopy (XPS). Diameters of these VOHSs are in the range of 500–550 nm with a shell thickness of 55 nm. Building blocks of the hollow spheres are nanoplates with widths of 50–80 nm and lengths of 70–120 nm. The precursor hollow spheres gradually formed from solid spheres, to yolk–shell structures and to hollow spheres. Vanadium pentoxide based hollow sphere film sensors were fabricated via in situ solvothermal deposition and exhibited excellent sensing performances for triethylamine with an extra low detection limit of 10 ppb and good selectivity. The selectivity of the sensor might be due to the reduction of V5+ ions to V4+ ions when the VOHSs are exposed to triethylamine. The VOHSs are a potential candidate for trace triethylamine detection.

Self-assembly of [Cu3I2]- or [CuI]n-based (n = 2, 4, and ∞) coordination polymers from unsymmetrical bis(pyridyl) and in situ ligands: syntheses, structures, and properties

Five new copper coordination polymers, [CuI(L1a)]n (1), [Cu1.5I(dmtrz)0.5(PPh3)]n·0.5n(CH3CN) (2), [Cu2I2(L1b)]n (3), [Cu4I4(L2)]n·nH2O (4), and [CuI(L3)]n (5) (L1a = N-(pyridin-2-ylmethyl)-N-(pyridin-3-yl)formamide, Hdmtrz = 3,5-dimethyl-4H-1,2,4-triazole, L1b = N-(pyridin-2-ylmethylene)pyridin-3-amine, L2 = N-(pyridin-4-ylmethyl)pyridin-3-amine, L3 = N-(pyridin-3-ylmethyl)pyridin-2-amine), have been synthesized by the solvothermal reactions of CuI and three unsymmetrical bis(pyridyl) ligands in mixed methanol–acetonitrile solution and characterized using elemental analysis, IR, TG, PL, XPS, powder and single-crystal X-ray diffraction. In 1, the ligand L1a is in situ generated from N-(pyridin-2-ylmethyl)pyridin-3-amine (L1) and bridges adjacent Cu2I2 rhomboid units, forming a double chain structure. The rare Cu3I2 clusters in 2 are linked by the dmtrz− monoanion to generate a linear chain structure, in which the dmtrz− monoanion is in situ synthesized by a non-ammonia pathway. The L1b in 3 is also in situ generated from L1 and connects adjacent chair like Cu4I4 clusters into a (4,4) layer structure. By contrast, the Cu4I4 cubanes in 4 are linked by the L2 ligands to form a 2-fold interpenetration (44·62) net. The Cu(I) cations in 5 are linked by the μ3-I− ions into infinite double-stranded [Cu2I2]n ladder chains, which are further extended into a layer structure by the L3 molecules. Moreover, the binding energies of the Cu 2p3/2 level in the XPS spectra are typical for a Cu(I) oxidation state. For the N1s, the different binding energies in the XPS spectra can be attributed to the N atoms with different chemical environments. Luminescent property investigation shows that only 5 exhibits a blue emission maximum at 475 nm.

An ultraselective and ultrasensitive TEA sensor based on α-MoO3 hierarchical nanostructures and the sensing mechanism

Flower-like, hierarchically nanostructured α-MoO3 was successfully synthesized via a one-step, template-free solvothermal route. Morphological characterization demonstrated that the nanostructures were hierarchically assembled by overlapping single-crystalline nanobelts with exposed (010) facets. These nanobelts, with a width of 40–60 nm and a thickness of 20–30 nm, grew radially from the core of the α-MoO3 flower. The growth mechanism of the α-MoO3 flower was speculated to be through oriented self-attachment of the nanobelts. The gas sensor based on α-MoO3 flowers showed an excellent sensing performance towards triethylamine (TEA) in terms of a high response (931.2) and excellent selectivity towards 10 ppm TEA. Especially, the detection limit was down to 0.001 ppm at a working temperature of 170 °C. The surface status of the α-MoO3 flowers before and after exposure to TEA at 170 °C was investigated by XPS. The probable oxidization product of TEA was analyzed by GC-MS. The MoO3 sensing mechanism could be interpreted as the transformation of triethylamine to vinylamine through two catalytic oxidation processes: the reactions with chemisorbed oxygen, and with lattice oxygen. The possibility relating to an enhanced gas sensing response of the three-dimensional (3D) flower-like α-MoO3 was discussed.

A three-dimensional lead(II) coordination polymer: poly[aqua-μ-imidazole-4,5-dicarboxyl­ato-lead(II)]

In the title coordination polymer, [Pb(C5H2N2O4)(H2O)](n), the Pb(II) atom is seven-coordinated by one N atom and five O atoms from four individual imidazole-4,5-dicarboxylate (HIDC2-) groups and one water molecule. It is interesting to note that the HIDC2- group serves as a bridging ligand to link the Pb(II) atoms into a three-dimensional microporous open-framework.

The first in situ organosulfonate-templated 3-fold interpenetrating framework built from rare tetrahedral [Cu4(μ4-SO4)] SBUs

An interpenetrating framework, [Cu4(SO4)(4,4-bipy)4]n·2n(C6H5SO4) [4,4′-bipyridine = 4,4′-bipy], has been successfully synthesized viahydrothermal reaction, in which the in situ generated p-hydroxybenzenesulfonate as guests are encapsulated within the channels. The tetrahedral [Cu4(μ4-SO4)] SBUs, reported for the first time in 3D architectures, are linked by parallel double 4,4′-bipys to generate a diamondoid network formed of large adamantanoid cages which causes the 3-fold interpenetration of the networks by self-clathration. Furthermore, the existence of strong π⋯π interactions between adjacent 4,4′-bipys stabilizes the interpenetrating framework. The binding energies of the Cu 2p3/2 level in the XPS spectrum are typical for a Cu(I) oxidation state. For the O1s, the XPS spectrum could be deconvoluted into three peaks corresponding to the three kinds of O atoms with different chemical environments. This work provides a method for constructing in situ organosulfonate-templated interpenetrating metal–organic frameworks.

Highly selective and efficient adsorption dyes self-assembled by 3D hierarchical architecture of molybdenum oxide

A novel hierarchical architecture of molybdenum trioxide (α-MoO3) was synthesized via a facile template-free hydrothermal route directly by using molybdenyl acetylacetonate and acetic acid as the starting materials. SEM and TEM observations indicate that this microstructure is a flower-like microsphere with a diameter of 15 to 20 μm. It consists of numerous nanobelts with (001) preferential crystallographic plane which seemingly grow from the sphere-like core and the nanobelts were 100 nm in width, 4 μm in length and 15–20 nm in thickness. The molybdenum oxide-based hierarchical microstructure exhibits a fast and selective adsorption to the adsorbate organic pollutants with benzoic acidic group for the first time. The removal rate of α-MoO3 to RhB reaches 97.9% in 10 min at a RhB concentration of 20 mg L−1 at room temperature, which is significantly fast as well as the commercial active carbon and the maximum adsorption capacity is 9 times that of the commercial activated carbon at a RhB concentration of 200 mg L−1. The mechanism for selective adsorption was discussed according to the results of IR, XPS and theoretical calculation. XPS and IR spectra confirm the RhB molecules adsorbed on the surface of MoO3 and interacted with Mo ions. DFT calculations indicate that the larger delocalization of the organic groups, the larger amount of charges transfer, the higher binding energy of organic molecules to the (001) lattice plane of α-MoO3 surface.

Poly[[bis(pyridin-3-ol)manganese(II)]-di-μ-pyridin-3-olato]

In the title complex, [Mn(C5H4NO)2(C5H5NO)2]n or [Mn(mu-3-PyO)2(3-PyOH)2]n (3-PyO- is the pyridin-3-olate anion and 3-PyOH is pyridin-3-ol), the Mn(II) atom lies on an inversion centre and has octahedral geometry, defined by two N atoms and two deprotonated exocyclic O atoms of symmetry-related pyridin-3-olate ligands [Mn-N = 2.3559 (14) A and Mn-O = 2.1703 (11) A], as well as two N atoms of terminal 3-PyOH ligands [Mn-N = 2.3482 (13) A]. The Mn(II) atoms are bridged by the deprotonated pyridin-3-olate anion into a layer structure, generating sheets in the (-101) plane. These sheets are linked by O-H...O hydrogen bonds. There are also pi-pi and C-H...pi interactions in the crystal structure.