Chunxu Pan

Preparation of porous micro–nano-structure NiO/ZnO heterojunction and its photocatalytic property

This paper introduced a novel physical route which combined pulse electrodeposition with thermal oxidation to obtain a porous micro–nano-structure NiO/ZnO heterostructural composite. Because ZnO nanoneedle directly grew from the porous Ni foam or NiO surface, and was accompanied with a short-range atom interdiffusion at the interface between ZnO and NiO, a heterojunction was formed and exhibited a high interfacial adhesion strength and high density. The experimental results revealed this composite had excellent photocatalytic performance, 2.5 times higher than that of pure ZnO. The reason was that the NiO/ZnO heterojunction improved the separation rate of photogenerated electrons and holes, and therefore enhanced photocatalytic efficiency.

Synthesis of nitrogen doped graphene from graphene oxide within an ammonia flame for high performance supercapacitors

This paper introduces a novel process for preparing nitrogen (N) doped graphene by using an ammonia flame treatment under ambient conditions, which is simple, effective, faster and economical. That is, when graphene oxide (GO) was treated in the ammonia flame, GO not only could be reduced to graphene, but also could be doped with nitrogen atoms simultaneously. Furthermore, due to the special atmosphere in the ammonia flame, the N-doped graphene exhibited differences from the N-doped graphene by using other processes, which indicated the special properties and potential applications. The experimental results revealed: (1) the N atom concentration was up to 3.97 at% in the N-doped graphene; (2) various nitrogen species including pyridinic-N, pyrrolic-N and quaternary-N were detected in the N-doped graphene; (3) the specific capacitance of the N-doped graphene was 246.4 F g−1 at a current density of 1 A g−1 with high cycle stability, which was about 2 times higher than that of regular graphene without N-doping. It was indicated that this N-doped graphene could be an excellent electrode material for supercapacitor applications.

Interface Enhancement of Glass Fiber Reinforced Vinyl Ester Composites with Flame-Synthesized Carbon Nanotubes and Its Enhancing Mechanism

Interface enhancement with carbon nanotubes (CNTs) provides a promising approach for improving shock strength and toughness of glass fiber reinforced plastic (GFRP) composites. The effects of incorporating flame-synthesized CNTs (F-CNTs) into GFRP were studied, including on hand lay-up preparation, microstructural characterization, mechanical properties, fracture morphologies, and theoretical calculation. The experimental results showed that: (1) the impact strength of the GFRP modified by F-CNTs increased by more than 15% over that of the GFRP modified by CNTs from chemical vapor deposition; and (2) with the F-CNT enhancement, no interfacial debonding was observed at the interface between the fiber and resin matrix on the GFRP fracture surface, which indicated strong adhesive strength between them. The theoretical calculation revealed that the intrinsic characteristics of the F-CNTs, including lower crystallinity with a large number of defects and chemical functional groups on the surface, promoted their surface activity and dispersibility at the interface, which improved the interfacial bond strength of GFRP.

Electrospun nanofibers of p-type BiFeO3/n-type TiO2 hetero-junctions with enhanced visible-light photocatalytic activity

One-dimensional BiFeO3/TiO2 heterostructure nanofibers with high visible-light photocatalytic activity have been successfully obtained via a facile hydrothermal process followed by an electrospinning technique. The results show that the BiFeO3/TiO2 nanofibers are as long as dozens of micrometers with the diameters of about 100–300 nm, where BiFeO3 nanoparticles are surrounded by anatase-type TiO2 nanocrystals. Compared with the corresponding pure BiFeO3 nanoparticles, and TiO2 nanofibers, the as-prepared BiFeO3/TiO2 nanofibers exhibit a markedly enhanced photocatalytic activity in the degradation of methyl blue under visible light irradiation. The enhanced photocatalytic activity is attributed to the formed p–n heterojunction between BiFeO3 and TiO2, which results in synergistic enhancement. Notably, the BiFeO3/TiO2 nanofibers could be easily recycled without the decrease in the photocatalytic activity because of their one-dimensional nanostructural property. With their high degradation efficiency and fine recyclability, the BiFeO3/TiO2 heterostructure nanofibers will have wide application in photodegradation of various organic pollutants.

Highly Sensitive, Durable, and Multifunctional Sensor Inspired by a Spider

Sensitivity, durability, and multifunction are the essential requirements for a high-performance wearable sensor. Here, we report a novel multifunctional sensor with high sensitivity and durability by using a buckled spider silk-like single-walled carbon nanotubes (SSL-SWNTs) film as the conducting network and a crack-shaped Au film as the sensitive transducer. Its high sensitivity is inspired by the crack-shaped structure of the spiders slit organs, while the high durability is inspired by the mechanical robustness of the spider silk. Similar to the spiders slit organs that can detect slight vibrations, our sensor also exhibits a high sensitivity especially to tiny strain. The proposed quantum tunneling model is consistent with experimental data. In addition, this sensor also responds sensitively to temperature with the sensitivity of 1.2%/°C. Because of the hierarchical structure like spider silk, this sensor possesses combined superiority of fast response (<60 ms) and high durability (>10 000 cycles). We also fabricate a wearable device for monitoring various human physiological signals. It is expect that this high-performance sensor will have wide potential applications in intelligent devices, fatigue detection, body monitoring, and human-machine interfacing.

Present Perspectives of Advanced Characterization Techniques in TiO2-Based Photocatalysts

TiO2 is the most investigated photocatalyst because of its nontoxicity, low cost, chemical stability, and strong photooxidative ability. Because of the morphology- and structure-dependent photocatalytic properties of TiO2, accurate characterization of the crystal and electronic structures of TiO2-based materials and their performance during the photocatalytic process is crucial not only for understanding the photocatalytic mechanism but also for providing experimental guidelines as well as a theoretical framework for the synthesis of high performance photocatalysts. In this review, we focused on the advanced characterization techniques that are utilized in the studies on the TiO2 structures and photocatalytic performance of TiO2 and TiO2-based materials. It is therefore anticipated that this review can provide a novel perspective to understand the fundamental aspects of photocatalysis and inspire the development of new photocatalysts with superior performances.

Diamond synthesis from carbon nanofibers at low temperature and low pressure.

In this article, we report a new route to synthesize diamond by converting “solid” carbon nanofibers with a Spark Plasma Sintering system under low temperature and pressure (even at atmospheric pressure). Well-crystallized diamond crystals are obtained at the tips of the carbon nanofibers after sintering at 1500 °C and atmospheric pressure. Combining with scanning electron microscopy, transmission electron microscopy, electron-energy loss spectroscopy and Raman spectroscopy observations, we propose the conversion mechanism as follows: the disorder “solid” carbon nanofibers → well crystallined carbon nanofibers → bent graphitic sheets → onion-liked rings → diamond single crystal → the bigger congregated diamond crystal. It is believed that the plasma generated by low-voltage, vacuum spark, via a pulsed DC in Spark Plasma Sintering process, plays a critical role in the low temperature and low pressure diamond formation. This Spark Plasma Sintering process may provide a new route for diamond synthesis in an economical way to a large scale.

Preparation of a ZnO/TiO2 vertical-nanoneedle-on-film heterojunction and its photocatalytic properties

This paper introduces a process to prepare a novel ZnO/TiO2 heterojunction composite with ZnO nanoneedles vertically grown on a TiO2 film via micro-arc oxidation (MAO), pulse plating and thermal oxidation. Firstly a TiO2 thin film was prepared on a titanium substrate using MAO; then a Zn nanocrystalline film was pulse plated on the MAO film; finally the composite film was thermally treated at 380° for several hours, which transformed the Zn film into ZnO nanoneedles. SEM observations revealed that the ZnO nanoneedles were vertically grown on the TiO2 film. The advantage of the ZnO/TiO2 heterojunction was that during heat treatment, in addition to the phase transformation from Zn into ZnO, simultaneous short-range atom diffusion occurred at the interface between the ZnO nanoneedles and the TiO2 layer, which encouraged the formation of a highly efficient, strong and stable heterojunction. Photocatalytic experiments demonstrated that, compared with pure ZnO or TiO2, the as-prepared ZnO/TiO2 composites showed greater efficiency and stability in photogenerated carriers and a significantly improved photocatalytic performance, due to this special heterojunction structure.

High-voltage electric-field-induced growth of aligned “cow-nipple-like” submicro-nano carbon isomeric structure via chemical vapor deposition

In this study, a novel vertically aligned carbon material, named “cow-nipple-like” submicro-nano carbon isomeric structure, was synthesized by the thermal decomposition of C2H2 in a chemical-vapor deposition system with a high-voltage external electric field. The microstructures were characterized by using scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy, respectively. The results revealed that (1) the total height of the carbon isomeric structure was in a rang of 90-250 nm; (2) the carbon isomeric structure consisted of a submicro- or nano-sized hemisphere carbon ball with 30-120 nm in diameter at the bottom and a vertically grown carbon nanotube with 10-40 nm in diameter upon the carbon ball; (3) there was a sudden change in diameter at the junction of the carbon ball and carbon nanotube. In addition, the carbon isomeric structure showed an excellent controllability, that is, the density, height, and diameter could be controlled effectively by adjust...

The role of F-dopants in adsorption of gases on anatase TiO2 (001) surface: a first-principles study

We performed a systematic investigation of adsorption of small gas molecules (O2, CO, NO, NO2 and SO2) on pristine and fluorine doped (F-doped) anatase TiO2 (001) surface using density functional theory (DFT). Three kinds of F-dopants, which were achieved by substituting a surface O2C atom (FI), or a surface O3C (FII), or an O3C atom below a surface Ti5C with an F atom (FIII), were studied to investigate the effects on the surface properties as well as the adsorption of molecules. The influence of F-dopants on the adsorption energy, charge transfer and magnetic moment of the most stable adsorption configurations of these molecules on the surfaces are thoroughly discussed. Three types of F-dopants were found to significantly promote the adsorption of O2, NO and NO2. However, the promotive effect of FI and FII dopants was not found upon the adsorption of CO and SO2. Only the FIII dopant was found to have a promotive effect on the two molecules. The mechanisms of interactions between molecules and surfaces are examined by analyzing their electronic structure and charge transfer. The results show that Ti3+ induced by F-dopants plays an important role in enhancing the interaction between gas molecules and TiO2 surfaces.