Shusheng Pan

Synthesis of mesoporous carbon capsules encapsulated with magnetite nanoparticles and their application in wastewater treatment

Mesoporous carbon capsules encapsulated with Fe3O4 nanoparticles were prepared by the successive coating of a silica layer and a subsequent mesoporous silica/carbon layer on the surface of Fe3O4 nanoparticles followed by chemical etching with NaOH solution. TEM observations show that the as-obtained samples had a rattle-like structure: Fe3O4 nanoparticles were encapsulated in the interior of the mesoporous carbon capsules. The typical nitrogen adsorption/desorption results demonstrate that the specific surface area for the as-prepared samples is up to 1570 m2 g−1, and the total pore volume is about 3.02 cm3 g−1. The porous wall structure of the lateral carbon capsules provides the sufficient spaces that contribute to high adsorption capacities and faster adsorption rates of pollutants molecules in aqueous media. The nanocomposites are superparamagnetic at room temperature with a saturation magnetization of 5.5 emu g−1, which provides the prerequisite for the fast magnetic separation in wastewater treatment application. Water treatment experiments indicated that the as-prepared samples exhibited higher adsorption rates and more effective removal capacity of organic pollutants compared with commercial activated carbon (AC), and their maximum adsorption capabilities for methylene blue (MB), congo red (CR), and phenol reached 608.04, 1656.9 and 108.38 mg g−1, respectively. The multifunctional nanocomposites can be potentially used as absorbents for fast, convenient, and highly efficient removal of pollutants from the wastewater, which will play important roles in the purification or desalination of natural water and industrial effluents.

Atomic nitrogen doping and p-type conduction in SnO2

We report the atomic N-doped SnO2 films with p-type conduction grown via reactive sputtering at high nitrogen partial pressure. From the high-resolution x-ray photoelectron spectroscopy (XPS) and x-ray diffraction patterns, it is deduced that the N 1s with binding energy of 397 eV could be attributed to the atomic N in the SnO2 films. In addition, the results of Hall effect measurement indicate that the atomic N incorporated substitutionally at O sites act as acceptors, which is responsible for the p-type conduction of the N-doped SnO2 films. It is believed that these findings should stimulate further research on p-type SnO2 films and SnO2-based ultraviolet optoelectronic devices.

Optical properties of nitrogen-doped SnO2 films: Effect of the electronegativity on refractive index and band gap

The optical properties of nitrogen-doped SnO2 films with different N2∕(N2+O2) gas ratios grown by reactive sputtering were studied by spectroscopy ellipsometry. The optical dielectric functions of the films were simulated by the Tauc-Lorentz model. It was found that the refractive index and extinction coefficient of nitrogen-doped SnO2 films increase and the band gap has a redshift with the increase of the N2 ratios. The general influences of the electronegativity and bond ionicity on the band gap, the refractive index in the spectral region below the fundamental absorption edge of nitrogen-doped SnO2, and other doped semiconductors are demonstrated.

Facile one-step synthesis of plasmonic/magnetic core/shell nanostructures and their multifunctionality

A very simple protocol, which involves the chemical reduction of AgNO3 and Fe(NO3)3 with ethylene glycol as reducing agent, has been developed for synthesizing Ag@Fe3O4 core/shell nanostructures in which the silver nanoparticle core was covered by a thicker layer of the Fe3O4 nanoparticle shell. The obtained Ag@Fe3O4 core/shell nanostructures simultaneously possess both strong magnetic responsiveness and tunable plasmonic properties. The plasmonic properties of the composite nanospheres are profoundly influenced by the high dielectric constant of the outer Fe3O4 shell layer and could be conveniently modulated over a broad spectral range spanning from the ultraviolet to near-infrared (NIR) regions (789 nm) by simply altering the thickness of the Fe3O4 shell. The localized surface plasmon resonances of the core/shell nanocomposites red-shifted with increasing thickness of the Fe3O4 shell. The morphology transformation of the Ag/Fe3O4 nanocomposites from core/shell structures with a continuous dense coating to flower-like nanostructures also allows the tuning of their plasmonic properties to be blue-shifted (to 510 nm). Catalytic degradation of rhodamine 6G (R6G) experiments show that the Ag/Fe3O4 composite nanostructures exhibit high catalytic activity by sodium borohydride. Due to the efficient optical response through localized surface plasmon resonances, the catalytic performance from the silver core and external magnetic manipulation from the Fe3O4 shell, such multifunctional nanoparticles will provide an opportunity for simultaneous optical detection and catalytic reduction with the additional benefit of relatively facile recovery and regeneration.

Recent Progress in p-Type Doping and Optical Properties of SnO2 Nanostructures for Optoelectronic Device Applications

SnO(2) semiconductor is a host material for ultraviolet optoelectronic devices applications because of its wide band gap (3.6 eV), large exciton binding energy (130 meV) and exotic electrical properties and has attracted great interests. The renewed interest is fueled by the availability of exciton emission in nanostructures, high quality epitaxial films, p-type conductivity, and heterojunction light emitting devices. This review begins with a survey of the patents and reports on the recent developments on SnO2 films. We focus on the epitaxial growth, p-type doping and photoluminescence properties of SnO(2) films and nanostructures, including the achievements in our group. Finally, the applications of SnO(2) nanostructures to optoelectronic devices including heterojunction light emitting devices, photodetectors and photovoltaic cells will be discussed.

Surface localized exciton emission from undoped SnO2 nanocrystal films

We report the UV photoluminescence properties of SnO2 nanocrystalline films. A free exciton decay centered at 3.7 eV and a strong surface localized exciton emission peak at 3.3 eV have been observed at room temperature. The peak energy of the surface localized exciton emission exhibits a redshift with increasing temperature and a blueshift with increasing excitation intensity. The surface localized exciton emission is considered to originate from the radiative recombination of exciton within the surface region of SnO2 nanocrystals. The surface defects and local disorder are believed to be responsible for the formation of band tail states at the conduction band and potential well within the band tails.

Facile synthesis of nitrogen self-doped rutile TiO2 nanorods

Nitrogen doping is a promising method to enhance the visible light absorption and photo-catalytic activity of TiO2. A new method is reported for the synthesis of nitrogen self-doped rutile TiO2 nanorods, along with the formation study of V-shaped N-doped TiO2 nanorods, using TiN as a precursor and using a hydrothermal method. Our synthesis method gives a facile and easy way to control nitrogen doping in a TiO2 lattice. Two types of the V-shaped nanorods, with a (101) coherent boundary of either 114.4° or 134.9° inner angle, were observed. The N-doped TiO2 nanorods exhibit an enhanced visible light absorption and red-shift in band gap in comparison with pure rutile TiO2 nanopowders. The mechanisms of N doping and the formation of the V-shaped nanorods are analyzed and discussed. The oriented attachment and Ostwald ripening are considered responsible for the formation and growth of the straight and V-shaped N-doped TiO2 nanorods.

Photoluminescence properties of hollow ZnS microspheres

The photoluminescence properties of hollow ZnS microspheres with different sizes and shell thickness were studied. There exist two emission bands situated in blue and green regions in the photoluminescence spectra of the microspheres: the green band has a red shift with increasing the excitation power at different temperatures, while the blue band has a blue shift at room temperature and without any changes excited at 83 K. The green emission has a normal red shift while the blue emission shows an abnormal red-blue shift with increasing temperature. The origins of anomalous photoluminescence properties were analysed and discussed in terms of the carrier localisation at the defect levels.