Hongchang Pang

A new single-phase white-light-emitting CaWO4:Dy3+ phosphor: synthesis, luminescence and energy transfer

A series of single-phase CaWO4:Dy3+ phosphors have been prepared via a conventional solid state reaction process. X-Ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and fluorescent decay curves were used to characterize the synthesized samples. Under UV light excitation, the CaWO4 sample shows a blue emission in a broad band centered at about 415 nm originating from the WO42− groups, while the Dy3+ ions doped CaWO4 samples show strong line emissions coming from the characteristic f–f transitions due to an efficient energy transfer from WO42− to Dy3+. The decreases of decay lifetimes of host emissions in CaWO4:Dy3+ demonstrated the energy transfer from the host to Dy3+. The energy transfer mechanism in CaWO4:Dy3+ phosphors has been determined to be a resonant type via a dipole–dipole mechanism. By simply controlling the doping concentration of Dy3+, the PL color of CaWO4:Dy3+ phosphors varies from blue to yellow-green, and especially the white light emission is realized in CaWO4:xDy3+ (x = 0.06). The PL properties of the as-prepared materials indicate that CaWO4:Dy3+ could potentially serve as a single-phase white-light-emitting phosphor in solid-state lighting and display fields.

Controllable fabrication of zinc borate hierarchical nanostructure on brucite surface for enhanced mechanical properties and flame retardant behaviors.

A novel and efficient halogen-free composite flame retardant (CFR) consisting of a brucite core and a fine zinc borate [Zn6O(OH)(BO3)3] hierarchical nanostructure shell was designed and synthesized via a facile nanoengineering route. It had been demonstrated that this unique hybrid structure possessed a high BET specific surface area (65 m(2)/g) and could significantly enhance the interfacial interaction when mixing with ethylene-vinyl acetate (EVA). This improved the transfer of stress between CFR particles and EVA matrix and increased the viscosity of EVA/EVA blends, which was beneficial for droplet inhibition and char forming. The mechanical properties and flammability behaviors of the EVA/CFR blends had been compared with the EVA/physical mixture (PM, with the given proportion of brucite and Zn6O(OH)(BO3)3). The mechanical properties of EVA/CFR blends, especially the tensile strength (TS), presented a remarkable increase reaching at least a 20% increment. Meanwhile, with the same 45 wt % of fillers, the EVA/CFR formulation could achieve a limiting oxygen index (LOI) value of 33 (37.5 % higher than that of EVA/PM blends) and UL-94 V-0 rating. Moreover, the heat release rate (HRR), peak heat release rate (PHRR), total heat released (THR), smoke production rate (SPR) and mass loss rate (MLR) were considerably reduced, especially PHRR and SPR for EVA/CFR blends were reduced to 32%. According to this study, the design of fine structure might pave the way for the future development of halogen-free flame retardants combining both enhanced mechanical properties and excellent flame retardant behaviors.

Facile synthesis of magnetic hierarchical MgO–MgFe2O4 composites and their adsorption performance towards Congo red

MgO–MgFe2O4 composites with magnetism and adsorption capacity for Congo red were synthesized by an ion exchange route using magnesium carbonate as templates. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and magnetic hysteresis loop were carried out to characterize the crystalline phase, microstructure, and magnetic property of as-obtained MgO–MgFe2O4 composites. Congo red adsorption experiments were conducted to evaluate the adsorption property of the as-synthesized samples. The results showed that the as-synthesized MgO–MgFe2O4 composites have a hierarchical structure, magnetic properties and good adsorption performance. The optimized sample exhibited an excellent adsorption capacity (498 mg g−1) for Congo red, which is much higher than many other hierarchical magnetic materials.

Synthesis of porous MgAl2O4 spinel and its superior performance for organic dye adsorption

A porous MgAl2O4 spinel (MAS) has been synthesized via a facile hard template process with further calcination, in which a hierarchical Mg5(OH)2(CO3)4·4H2O template with a high surface area was used as a hard template and magnesium source, and AlCl3·6H2O was used as an alumina source. The as-prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), thermogravimetry analysis (TGA) and N2 adsorption–desorption. The MAS samples showed superior adsorption performance, including rapid adsorption rate, excellent adsorption capacity and good reusability for removal of Congo red (CR) from aqueous solution. The superior performance could be ascribed to the strong interaction between the MAS samples and CR, as well as the hierarchical porous structure and the high specific surface area of the samples. The maximum adsorption capacity of the MAS samples for CR was nearly 845 mg g−1, which is higher than most of the previously reported adsorbents. The CR removal process was found to follow the pseudo-second-order rate equation and the Sips adsorption model.

Fabrication of nanostructured V2O5 via urea combustion for high-performance Li-ion battery cathode

Nanostructured vanadium pentoxide (V2O5) crusts were facilely synthesized via the combustion of a precursor by mixing commercial V2O5 with molten urea. The nanocrusts were transferred to nanorods during further annealing at 630 °C. Both the V2O5 nanocrusts and V2O5 nanorods were used preliminarily as a cathode material for Li-ion batteries. Their electrode performance was highly improved compared to commercial V2O5.

Constructing hierarchical architectures of Eu3+-doped Mg3B2O6 for tunable luminescent properties

Two novel hierarchical architectures, flower-like and urchin-like MgBO2(OH), were facilely fabricated through a hydrothermal process, in the absence of any surfactant or template. Mg3B2O6 can be obtained by thermal decomposition of the MgBO2(OH) precursor with the morphology well-retained. These unique Mg3B2O6 assemblies were composed of uniform nanosheets and nanobelts, respectively. Under UV excitation, Eu3+-doped Mg3B2O6 shows a strong red emission corresponding to 5D0 → 7FJ (J = 1,2,3) transition of Eu3+. Interestingly, variable architectures of Mg3B2O6:Eu3+ from flower-like to urchin-like displayed tunable emission from 592 nm (5D0 → 7F1) to 611 nm (5D0 → 7F2) through the altering of symmetry of the crystal field around Eu3+ ions. The present architectures are envisaged to be potential candidates for fluorescent lamps and field emission displays.

Directed tuning of nanostructure from 1D to 3D by doping diverse valent cations

We design an unconventional strategy for controlling the nanostructure evolution of magnesium hydroxide from lamellar to rose-like, then to torispherical species by introducing diverse valent cations (Zn2+, Al3+, Sn4+). Lattice distortion induced by invasive cations would be responsible for the morphology transformation of metal hydroxide.