Xiaoli Cheng

A novel strategy for making soluble reduced graphene oxide sheets cheaply by adopting an endogenous reducing agent

A facile and efficient strategy is described for the fabrication of soluble reduced graphene oxide (rGO) sheets. Different from the conventional strategies, the proposed method is based on the reduction of graphene oxide by an endogenous reducing agent from a most widely used and cost-effective solvent, without adding any other toxic reducing agent. Simultaneously, this solvent can serve as an effective stabilizer, avoiding complicated and time-consuming modification procedures. The as-prepared rGO sheets not only exhibit high reduction level and conductivity, but also can be well dispersed in many solvents. Of particular significance is that rGO sheets can be produced in large quantities. These advantages endow this proposed synthetic approach great potential applications in the construction of high-performance graphene-based devices at low cost, as demonstrated in our study of NO gas sensing.

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.

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.

Ionic liquid-assisted synthesis of α-Fe2O3 mesoporous nanorod arrays and their excellent trimethylamine gas-sensing properties for monitoring fish freshness

Large-scale and well-aligned α-Fe2O3 mesoporous nanorod arrays in situ deposited on ceramic tubes have been successfully synthesized by an ionic liquid (IL)-assisted hydrothermal reaction followed by calcination. The mesoporous sizes of the nanorods can be adjusted by changing the calcination temperature. Such an in situ assembled α-Fe2O3 mesoporous nanorod array sensor exhibited not only high sensitivity, short recovery time and good reproducibility to trimethylamine (TMA), but also a good linear relationship in a ppm level concentration range (0.1–100 ppm). Furthermore, the sensor was evaluated for a fast analysis of the primary volatiles of Carassius auratus (0–11 h) which have been analyzed using headspace solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS). Such α-Fe2O3 mesoporous nanorod arrays showed considerable potential in the identification of fish freshness. The superior gas-sensing properties of the obtained nanostructures should be attributed to the uniform mesoporous structure in the ordered nanorod arrays with a large specific surface area, as well as an appropriate amount of residual functionalized ILs, which help the TMA molecules to diffuse and adsorb onto the array surface and assist electron transfer. The formation mechanism of the mesoporous nanorod arrays was also discussed in detail.

High efficient and selective removal of Pb2+ through formation of lead molybdate on α-MoO3 porous nanosheets array

2D hand-like structured α-MoO3 porous nanosheets were grown in-situ onto a capillary by a simple hydrothermal route, on which titanium dioxide seed layer was sol-dip-coated in advance. The α-MoO3 porous nanosheets array exhibits an exceptional lead ion uptake capacity up to 1450.0mg·g-1, and can effectively reduce Pb2+ concentration from 20mg·L-1 to a low level of smaller than 3μg·L-1, well below the acceptable limits in drinking water standards (10μg·L-1) and can efficiently remove 99.9% lead ion within a few minutes at room temperature. Furthermore, α-MoO3 porous nanosheets array also has high selectivity toward Pb2+ better than Cu2+, Zn2+, Cr3+ and Cd2+. The mechanism for adsorption was discussed according to the results of Zeta potential, IR, XPS and XRD analyses. The excellent removal performance of the array to Pb2+ is resulted from the electrostatic adsorption interaction and the formation of new species lead molybdate.

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.

Enhanced Sub-ppm NH3 Gas Sensing Performance of PANI/TiO2 Nanocomposites at Room Temperature

PANI/TiO2 nanocomposites spheres were synthesized using a simple and efficient one-step hydrothermal process. The morphology and structure of PANI/TiO2 nanocomposites spheres were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The PANI/TiO2 nanocomposite sphere-based sensor exhibits good selectivity, sensitivity (5.4 to 100 ppm), repeatability, long-term stability and low detection limit (0.5 ppm) to ammonia at room temperature (20 ± 5°C). It also shows a good linearity relationship in the range of 0.5–5 and 5–100 ppm. The excellent NH3 sensing performance is mainly due to the formation of the p-n heterostructure in the nanocomposites.