Yuanjun Liu

Facile Fabrication and Enhanced Sensing Properties of Hierarchically Porous CuO Architectures

Hierarchically porous CuO architectures were successfully fabricated via copper basic carbonate precursor obtained with a facile hydrothermal route. The shape of the precursor is preserved after its conversion to porous CuO architectures by calcination. The obtained CuO are systemically characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller N(2) adsorption-desorption analysis. The results reveal that hierarchical CuO microspheres are monoclinic structure and are assembled by porous single-crystal sub-microplatelets. The Brunauer-Emmett-Teller N(2) adsorption-desorption analysis indicates that the obtained CuO has a surface area of 12.0 m(2)/g with pore size of around 30 nm. The gas sensing performance of the as-prepared hierarchical CuO microspheres were investigated towards a series of typical organic solvents and fuels. They exhibit higher sensing response than that of commercial CuO powder. Their sensing properties can be further improved by loading of Ag nanoparticles on them, suggesting their potential applications in gas sensors.

Hierarchical NiO hollow microspheres assembled from nanosheet-stacked nanoparticles and their application in a gas sensor

A facile and robust route for the mass preparation of hollow NiO microspheres assembled from nanosheet-stacked nanoparticles is developed. The Ni(HCO3)2 precursor with a hollow spherical structure was firstly prepared by a hydrothermal reaction without any surfactants or organic additives. The reaction generated gas bubble may act as a template for the formation of Ni(HCO3)2 hollow microspheres. These are converted into hierarchical NiO hollow microspheres assembled from nanoparticles (with diameter of ∼25 nm) upon calcination, which are further assembled by the stacking of ultrathin nanosheets. The hierarchical NiO hollow structures are attractive for catalyst, sensor and environmental applications, benefiting from their large surfaces. The sensing properties of the hierarchical NiO hollow microspheres were evaluated. They show high sensitivity, short response and recovery times, and good response and recovery characteristics to n-butanol. As compared with NiO nanoparticles with similar dimensions (∼20–35 nm), the nanoparticle assembled NiO hollow microspheres exhibit enhanced gas sensing properties. The effective integration of several nanostructures in one microunit would provide a novel way to design new materials for nanodevices.

Photochemical deposition of Ag nanocrystals on hierarchical ZnO microspheres and their enhanced gas-sensing properties

We present a facile photochemical route to load Ag nanoparticles on hierarchical ZnO microspheres forming Ag–ZnO nanocomposites, which were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. The results reveal that Ag nanoparticles with average diameters of 5–6 nm are uniformly deposited on the surface of ZnO, and there are not any voids or organic linkers or surfactants at the interfaces between Ag and ZnO. The distribution density of Ag nanoparticles on ZnO can be tuned by the concentration of the silver precursor. In addition, the hierarchical ZnO microspheres and Ag–ZnO nanocomposites were configured as high performance sensors to detect ethanol and formaldehyde. Importantly, in comparison with the pure ZnO microspheres, the Ag-loaded ZnO nanocomposite sensors show 8.9-fold and 2.1-fold enhancement in gas responses to 100 ppm of ethanol and formaldehyde at 350 °C, respectively. This enhancement may originate from the effective chemisorption of molecular oxygen or atomic oxygen on Ag in the Ag–ZnO nanocomposites.

Concave Co3O4 octahedral mesocrystal: polymer-mediated synthesis and sensing properties

Co3O4 mesocrystals with concave octahedral structures were successfully prepared by a facile, polymer-mediated route. The Co3O4 mesocrystals are obtained from the oriented aggregation of primary nanocrystals from their six identical [100] directions. After a thorough investigation of their structure as a function of the adopted preparation parameters such as reaction time and the amount of polymer, the gas sensing performance of the Co3O4 mesocrystals was studied with formaldehyde and ethanol as probe analytes. It was found that they show high sensitivity and good response and recovery characteristics. As compared with Co3O4 powder, the Co3O4 mesocrystals exhibit 1.8-fold and 1.4-fold enhancement in gas responses to 100 ppm of formaldehyde and ethanol, respectively.

Flexible magnetic nanoparticles-reduced graphene oxide composite membranes formed by self-assembly in solution.

A facile and robust route for the pre-synthesized Fe(3)O(4) nanoparticles (NPs) exclusively assembled on both sides of reduced graphene oxide (RGO) sheets with tunable density forming two-dimensional NPs composite membranes is developed in solution. The assembly is driven by electrostatic attraction, and the nanocomposite sheets display considerable mechanical robustness, such as it can sustain supersonic and solvothermal treatments without NPs falling off, also, can freely float in solution and curl into a tube. The obtained two-dimensional composite grain membranes exhibit superparamagnetic behavior at room temperature but responds astutely to an external magnetic field. In addition, these magnetic composite membranes show an enhanced absorption capability for microwaves. The grain sheets are attractive for biomedical, sensors, environmental applications and electric-magnetic devices benefited from large surfaces, high magnetization moment, and superparamagnetic properties. The effective integration of oxide nanocrystals on RGO sheets provides a new way to design semiconductor-carbon nanocomposites for nanodevices or catalytic applications.

Co3O4 nanostructures with a high rate performance as anode materials for lithium-ion batteries, prepared via book-like cobalt–organic frameworks

The self-assembly of cobalt coordination frameworks (Co-CPs) with a two-dimensional morphology is demonstrated by a solvothermal method. The morphology of the Co-CPs has been controlled by various solvothermal conditions. The two-dimensional nanostructures agglomerated by Co3O4 nanoparticles remained after the pyrolysis of the Co-CPs. The as-synthesized Co3O4 anode material is characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge measurements. The morphology of Co3O4 plays a crucial role in the high performance anode materials for lithium batteries. The Co3O4 nanoparticles with opened-book morphology deliver a high capacity of 597 mA h g-1 after 50 cycles at a current rate of 800 mA g-1. The opened-book morphology of Co3O4 provides efficient lithium ion diffusion tunnels and increases the electrolyte/Co3O4 contact/interfacial area. At a relatively high current rate of 1200 mA g-1, Co3O4 with opened-book morphology delivers an excellent rate capability of 574 mA h g-1.

CN foam loaded with few-layer graphene nanosheets for high-performance supercapacitor electrodes

Recently, three-dimensional porous carbon-based foams have attracted increasing interest owing to their exciting potential applications in various fields. Herein, hierarchical porous monoliths, CN foam loaded with free few-layer graphene nanosheets, have been prepared. In this method, graphene oxide sheets were first loaded on the usual melamine foam that was selected as the raw material for the CN framework. With a subsequent annealing process in N2 atmosphere, the melamine foam was converted into a CN foam; simultaneously, the graphene oxide sheets were converted into reduced graphene oxide, to form a reduced graphene oxide–CN composite. The loading density of graphene on the CN framework can be tuned by the dosage of graphene oxide. The obtained composite monoliths exhibit excellent cycling performance and good rate capacity when used as pseudocapacitive electrode materials. At current densities of 0.5 and 10 A g−1, the optimized electrode exhibits areal specific capacitance of 1067 and 463 mF cm−2, respectively, with excellent cycling stability. The excellent property can be attributed to the unique macropore structures that endow sufficient space available to interact with the electrolytes, and the pseudocapacitive contribution originated from the nitrogen and oxygen composition. This facile synthesis strategy and the good electrochemical properties suggest that the synthesized CN–graphene composites are promising materials for supercapacitor application.

Pt-doped graphene oxide/MIL-101 nanocomposites exhibiting enhanced hydrogen uptake at ambient temperature

Nanocomposites of Pt-doped graphene oxide (GO) and a chromate–organic framework (MIL-101) were prepared through the in situ solvent-thermal method. The parent materials and all composites have been characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, and gas adsorption analysis. The results indicated that the incorporation of a Pt/GO component did not prevent the formation of MIL-101 units. However, the crystallinities, morphologies, and surface areas of the composites were affected obviously by the Pt/GO content. The significant enhancement by a factor of 1.57–2.69 of hydrogen storage capacities at ambient temperature and 10 bar for the composites can be attributed reasonably to the spillover mechanism in such a system, in which Pt nanoparticles act as the spillover source of hydrogen molecules, while GO and MIL-101 act as the primary and secondary receptors, respectively.

Peroxidase-Like Catalytic Activity of Ag3PO4 Nanocrystals Prepared by a Colloidal Route

Nearly monodispersed Ag3PO4 nanocrystals with size of 10 nm were prepared through a colloidal chemical route. It was proven that the synthesized Ag3PO4 nanoparticles have intrinsic peroxidase-like catalytic activity. They can quickly catalyze oxidation of the peroxidase substrate 3, 3, 5, 5-tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue color. The catalysis reaction follows Michaelis-Menten kinetics. The calculated kinetic parameters indicate a high catalytic activity and the strong affinity of Ag3PO4 nanocrystals to the substrate (TMB). These results suggest the potential applications of Ag3PO4 nanocrystals in fields such as biotechnology, environmental chemistry, and medicine.

Sustainable processing of waste polypropylene to produce high yield valuable Fe/carbon nanotube nanocomposites

With the increasingly serious environmental contamination and energy crisis, it is highly necessary that polyolefin-based waste plastics are converted into valuable materials by innovative upcycling processes. This study presents an environmentally benign and solvent-free autogenic process to produce sponge-like Fe/carbon nanotube nanocomposites by catalytic pyrolysis of waste polypropylene (PP) at 600 °C. The composition and morphology of the products were characterized by powder X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results show that the products are Fe/carbon nanotube nanocomposites with sponge-like structures, and the diameter of the carbon nanotubes is about 30 nm while the diameter of the Fe nanoparticles in the carbon nanotubes is also about 30 nm, which illustrates that the size of the Fe nanoparticles determines the diameter of the carbon nanotubes. Nitrogen adsorption–desorption measurements indicate that the Brunauer–Emmett–Teller (BET) surface area is calculated to be 197.6 m2 g−1, and the Barrett–Joyner–Halenda (BJH) adsorption cumulative volume of pores is up to 0.2860 cm3 g−1. Magnetic measurements at room temperature indicate that the values of saturation magnetization (62.7 emu g−1) and coercivity (187.3 Oe) of the sponge-like Fe/carbon nanotube nanocomposites are different from those of bulk Fe due to the broad distribution of carbon nanotubes and the small size of the Fe nanoparticles.