Guorui Yang

Fabrication of one-dimensional heterostructured TiO2@SnO2 with enhanced photocatalytic activity

TiO2@SnO2 nanosheets@nanotubes heterostructures were successfully prepared by a facile two-step method: prefabricated SnO2@PNT coaxial nanocables based on the in situ growth of SnO2 in the sulfonated gel matrix of polymeric nanotubes, and then the assembly of TiO2 nanoclusters that consist of ultrathin nanosheets through a solvothermal process. These heterostructures were characterized for the morphological, structural and optical properties by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible (UV-vis) and diffuse reflectance spectroscopy (DRS). The photocatalytic investigations showed that the TiO2@SnO2 heterostructures possessed enhanced photocatalytic efficiency in the photodegradation of Rhodamine B (RhB) and photocatalytic H2 evolution from water splitting under ultraviolet (UV) light irradiation, compared with the pristine TiO2 nanosheets, SnO2 nanotubes, the mechanically mixed two samples and P25. The enhanced photocatalytic performance can be ascribed to the beneficial microstructure and synergistic effects of coupled TiO2@SnO2 nanosheets@nanotubes heterostructures.

A facile one-step synthesis of three-dimensionally ordered macroporous N-doped TiO2 with ethanediamine as the nitrogen source

In this paper, three-dimensionally ordered macroporous (3DOM) N-doped anatase TiO2 (N-TiO2) photocatalysts with well-defined macroporous skeletons were prepared using a simple one-step colloidal crystal-templating method. Organic ammonia ethanediamine was used as the nitrogen source during preparation to enhance nitrogen incorporation into the TiO2 lattice. The photocatalytic performance of the as-prepared 3DOM N-TiO2 was investigated by measuring the degradation of rhodamine B (RhB) and the generation of H2 from water splitting under simulated visible-light conditions. In comparison with the pure TiO2 and N-doped TiO2, the results of photodegradation and photocatalytic hydrogen generation reactions showed that the 3DOM N-TiO2 sample exhibited excellent catalytic activity under visible-light irradiation. In addition, various analytical techniques have been used to characterize the crystal phase, morphology and optical absorption of the obtained samples. The results showed that the 3DOM N-TiO2 catalyst was successfully synthesized by the one-step colloidal crystal-templating method, and the as-prepared samples possessed well-defined 3DOM skeleton structure, high crystallinity and enhanced visible-light-driven photocatalytic activities.

Synthesis of one-dimensional NiFe2O4 nanostructures: tunable morphology and high-performance anode materials for Li ion batteries

In this study, various controllable one-dimensional NiFe2O4 nanostructures including solid nanofibers, yolk/shell nanofibers and nanotubes have been successfully synthesized by a novel “electrospinning–hydraulic agitation” combined method. The morphologies, components and structures of different NiFe2O4 samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption–desorption curve, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and inductively coupled plasma-atomic emission spectrometry (ICP-AES). A possible formation mechanism for the different morphologies was proposed based on the experimental results. More importantly, this method has been verified to be universally applicable for fabricating a variety of ferrite materials with tunable shapes, such as CoFe2O4, ZnFe2O4, CdFe2O4 and α-Fe2O3. Compared with the NiFe2O4 nanoparticles, solid nanofibers and yolk/shell nanofibers, the NiFe2O4 nanotubes exhibited a superior lithium storage capacity, which stabilized at an average capacity of 1349 mA h g−1 even after 220 cycles at a current density of 100 mA g−1. The unique one-dimensional continuous tubular nanostructures and the higher surface area of NiFe2O4 nanotubes deliver a prominent contribution to the excellent electrochemical performance.

Fabrication and formation mechanism of Mn2O3 hollow nanofibers by single-spinneret electrospinning

Mn2O3 hollow nanofibers (Mn2O3 HNs) have been prepared by direct annealing of electrospun polyvinylpyrrolidone (PVP)/manganese acetate composite nanofibers. The morphology, crystal structure and compositions of the Mn2O3 HNs were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). The results indicated that composite nanofibers after calcination at high temperature still retain their fibrous morphology with a fascinating hollow structure. The resultant HNs are Mn2O3 of high purity. The temperature-dependent experiments were carried out to monitor the evolution process of Mn2O3 HNs. The well-defined Mn2O3 HNs are the products of the reversed crystallization during the annealing process.

Plasma polymerization and deposition of linear, cyclic and aromatic fluorocarbons on (100)-oriented single crystal silicon substrates

Fluoropolymer films were deposited on the Ar plasma-pretreated Si(100) surfaces by plasma polymerization of perfluorohexane (PFH, a linear fluorocarbon), perfluoro(methylcyclohexane) (MCH, a cyclic fluorocarbon), and hexafluorobenzene (HFB, an aromatic fluorocarbon) under different glow discharge conditions. The effects of the radio-frequency plasma power on the chemical composition and structure of the plasma-polymerized fluoropolymer films were studied by x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, time-of-flight secondary ion mass spectrometry, and water contact angle measurements. The changes in structure and composition of the three types of the plasma-deposited films from those of the respective fluorocarbons were compared. Under similar glow discharge conditions: (i) the extent of defluorination was highest for the PFH polymer, (ii) the deposition rate was highest for the HFB polymer, (iii) the cyclic structure of MCH was less well preserved than the aromatic structure of HFB, (iv) aliphatic structures appeared in the plasma-deposited MCH polymer, and (v) the plasma-polymerized HFB has the highest thermal stability due to the preservation of the aromatic rings. The adhesive tape peel test results revealed that the plasma-polymerized and deposited fluoropolymer layers were strongly bonded to the Ar plasma-pretreated Si(100) surfaces.

Cobalt nanoparticles encapsulated in carbon nanotube-grafted nitrogen and sulfur co-doped multichannel carbon fibers as efficient bifunctional oxygen electrocatalysts

Developing flexible, efficient, and cost-effective electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) is of paramount importance for designing fuel cells, metal–air batteries and water splitting units. Herein we present an economical approach for the synthesis of self-standing cobalt nanoparticles (NPs) anchored on carbon nanotube-grafted multichannel carbon fibers, co-doped with nitrogen and sulfur (Co@NS/CNT-MCFs), which exhibit comparable ORR (OER) activity to that of commercial Pt/C (RuO2) catalysts in terms of a half-wave potential of 0.837 V for the ORR, and a mere 362 mV overpotential at a current density of 10 mA cm−2 for the OER, as well as remarkable stability in an alkaline medium. The excellent electrocatalytic properties can be attributed to the hierarchically porous network structure and multiple heteroatom dopants introduced, which favor efficient reagent/product mass transport, in addition to providing a great number of active sites. As a proof of concept, the designed flexible catalysts are also employed as air cathodes in an assembled lithium–oxygen (Li–O2) cell with high specific capacity and outstanding operational durability. These results demonstrate the potential of this novel approach in developing suitable catalysts to enable the next generation of metal–air batteries.

Fabrication and photocatalytic activities of SrTiO 3 nanofibers by sol–gel assisted electrospinning

Abstract SrTiO3 nanofibers were successfully prepared by a facile electrospinning method with subsequent calcination in air. These one dimensional nanostructures were characterized for the morphological, structural and optical properties by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV–visible diffuse reflectance spectroscopy. The photocatalytic investigations showed that the SrTiO3 nanofibers possessed enhanced photocatalytic efficiency in photodegradation of rhodamine B and photocatalytic H2 evolution from water splitting under ultraviolet light irradiation, compared with the SrTiO3 nanoparticles and P25. The enhanced photocatalytic performance can be ascribed to the beneficial microstructure and more negative conduction band edge compared with P25.

Design and synthesis of porous channel-rich carbon nanofibers for self-standing oxygen reduction reaction and hydrogen evolution reaction bifunctional catalysts in alkaline medium

Carbon-nanofiber-based (CNF-based) nonprecious catalysts and electrodes are essential components in next generation energy conversion and storage technologies. Moreover, porous architectures are highly desirable for active material embedded CNFs. Despite recent progress, controllable synthesis of porous CNFs with favorable mechanical properties is still challenging. Herein, we present a general and novel approach to prepare porous and channel-rich CNFs on a large scale through a free-surface electrospinning technique and subsequent carbonization of polyacrylonitrile (PAN)/cellulose acetate (CA) nanofibers. The resultant free-standing and flexible PAN/CA CNFs (CACNFs) possess abundant porous and channel-rich structures, which can be easily controlled by adjusting the weight ratio of PAN and CA. Based on the porous CACNFs, binder-free Fe3C embedded Fe/N doped CACNF films are successfully prepared. Combining the porous channel-rich structures and the high electrical conductivity of the carbon fibers, abundant accessible active sites and fast mass transport pathways are generated in the carbon fibers, leading to favorable catalytic activity and superior stability for ORR (half-wave potential 12 mV more positive than that of Pt/C) and HER (overpotential 440 mV@80 mV cm−2 and more than 100 000 s catalytic stability) in alkaline medium, demonstrating their promising potential for application in fuel cells, metal–air batteries and water splitting devices.

Thermal and electroless deposition of copper on poly(tetrafluoroethylene-co-hexafluoropropylene) films modified by surface graft copolymerization

Surface modification of Ar plasma-pretreated poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) film via UV-induced graft copolymerization, under atmospheric conditions, with 4-vinylpyridine (4VP), 2-vinylpyridine (2VP) and 1-vinylimidazole (VIDz) was carried out to improve the adhesion with the thermally evaporated and the electrolessly deposited copper. The surface composition and structure of the graft-copolymerized FEP films were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM), respectively. The electroless plating of copper on the graft-copolymerized FEP film could be carried out in the absence of sensitization by SnCl/sub 2/ (the Sn-free activation process). The adhesion strength of the thermally evaporated and the electrolessly deposited copper on the FEP surfaces was affected by the type of monomers used for graft copolymerization and the surface graft concentration. The T-peel adhesion strengths of the electrolessly deposited copper on the 4VP, 2VP and VIDz graft-copolymerized FEP films with 90-s of Ar plasma pretreatment were about 9.8 N/cm, 7.3 N/cm and 4.9 N/cm, respectively.

Fabrication of a well-aligned TiO2 nanofibrous membrane by modified parallel electrode configuration with enhanced photocatalytic performance

Aligned nanofibers play a significant role in the organic or inorganic material relevant applications because of their remarkable anisotropy, high surface-to-volume ratio, enhanced mechanical properties and charge transfer efficiency. In this work, highly aligned TiO2 nanofibers were continuously prepared over large areas via an updated electrospinning configuration consisting of two parallel electrodes and one additional assistant electrode. Because of the higher quantity and mechanical strength, the aligned TiO2 nanofibers could form an independent membrane. The morphology, thermal stability, structure, optical properties and charge transfer efficiency of this membrane were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TG), X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS), UV-visible (UV-vis) diffused reflectance spectroscopy (DRS) and electrochemical impedance spectroscopy (EIS). Compared with the traditional electrospun TiO2, the well-aligned TiO2 nanofibrous membrane exhibited excellent photoelectrochemical performance and enhanced photocatalytic degradation efficiency of rhodamine B, which means it is a promising material to replace traditional TiO2 for solar light utilization and organic pollutants degradation.