Developing earth-abundant materials to replace platinum (Pt)/Pt-based materials is an inevitable tendency for the progress of fuel cells due to the practical application limits. Recently, heteroatoms doped (N, S et al.) carbon materials, such as carbon nanotubes and graphene, have attracted great interests because of their amazing electrochemical activity towards oxygen reduction reaction (ORR). Herein, nitrogen and sulfur dual-doped three-dimensional reduced graphene oxide (NS-3DrGO) catalysts have been synthesized by a soft template-assisted approach followed by heat-pyrolysis treatment. Results indicate that with high specific surface area, sufficient porous structures, as well as the well-dispersed and doped atoms of N and S, the NS-3DrGO catalysts possess high onset/half-wave potentials together with large diffusing-limiting current density and present a four-electron transfer process in alkaline media. Specifically, at a relatively higher annealing temperature of 950 °C, the NS-3DrGO catalyst presents the optimal ORR activity compared with the others, which may be due to its highest amount (74.8 at. %) of the two active nitrogen species (pyridinic N and graphitic N) and the highest amount (79.8 at. %) of active thiophene-S together with the desirable specific surface (391.9 m2 g-1) area and multi-porous structure. Furthermore, the NS-3DrGO catalysts also exhibit superior methanol tolerance and favorable durability.Download high-res image (422KB)Download full-size image

•The SERS substrate of the Au NPs@GO film is fabricated via a facile electrostatic self-assembly method.•The Au NPs@GO films with different layers construction and surface compositions are investigated.•The SERS activities of different substrates are investigated using Rhodamine 6G as the probing molecules.•Results of assembly cycles influence on SERS performances of the Au NPs@GO films are presented.•The Au NPs@GO films present favorable reproducibility and high stability under ambient environment.The paper reports a simple electrostatic self-assembly method to fabricate the gold nanoparticles/graphene oxide (Au NPs@GO) films which present superior SERS activity. The Au NPs@GO films with different layers construction and surface compositions (with Au NPs or GO as the outer layer) are obtained simply by changing the self-assembly cycles. Results indicate that the film with two assembly cycles (F-2 film) exhibits the best SERS activity towards R6G molecules compared with that of one assembly cycle (F-1 film) and three assembly cycles (F-3 film) due to the high loadings of the absorbed Au NPs exposed on the surface of the film. Meanwhile, the Raman enhancement effect of the F-2 film with the outer layer of Au NPs is better than that of the outer layer covering with GO sheets (F-2-GO) possibly owing to the optimal synergetic effect of Au NPs and GO. Furthermore, our fabricated Au NPs@GO films present favorable reproducibility and high stability, which are significant for the practical application of these SERS substrates.

We have demonstrated a green and facile approach to prepare the gold nanoparticles-graphene oxide (Au NPs-GO) film using the electrostatic self-assembly method. Cubic Au NPs with positive charge were firstly synthesized by a seed-growth method. By alternating deposition of the negatively charged GO sheets and Au NPs on the quartz substrate, the Au NPs-GO film can be achieved. AFM images show that GO sheets fully covered the quartz substrate after twice deposition. Meanwhile, Au NPs scattered on the surface of film can be found. The Au NPs-GO film exhibits the desirable surface-enhanced Raman scattering (SERS) properties against Rhodamine 6G molecules, including the high enhancement factor of 5.1 × 105 and high detection limit of 10−10 M. Besides the strong electromagnetic effect of Au NPs, GO sheets play a key in improvement of SERS properties through the strong adsorption of molecules, favorable fluorescence quenching, and chemical enhancement effect.

A free-standing and flexible silver nanoparticle-graphene (Ag NP-GE) film with high surface-enhanced Raman scattering (SERS) sensitivity has been synthesized. Firstly, the highly stable and dispersive Ag NP-GE nanocomposite was fabricated by an in situ reduction method using graphene oxide sheets as substrates and ethylene glycol as a reduction agent in a solvothermal environment. Secondly, the Ag NP-GE films can be fabricated through vacuum filtration of the Ag NP-GE suspension. The highly SERS-active Ag nanoparticles and Ag nanoparticle aggregates make a significant contribution to the high sensitivity of SERS to rhodamine 6G molecules with an enhancement factor of 5.6 × 107.

The aim of this study is to fabricate transparent and conductive reduced graphene oxide/silver nanoparticles (RGO/Ag NPs) multilayer film by means of an electrostatic self-assembly method. In order to adsorb Ag NPs onto the surface of graphene oxide (GO) sheet easily, the stable and monodispersed Ag NPs/polyelectrolyte-poly(diallyldimethylammonium chloride) (PDDA) colloid was prepared firstly via liquid-phase reduction method, which can be used as a polycation solution in the assembly process. Through the thermal annealing, the GO film was reduced to an RGO film and the Ag NPs grew, leading to the formation of RGO film decorated by Ag NPs with large size and hemisphere-like shape. This structure can improve both optical and electrical properties of RGO film. Results indicated that high density, uniformly sized and well-distributed Ag NPs with hemisphere shape and an average particle size of 85 nm were decorated on the surface of the RGO film and also between the RGO films. The atomic ratio of Ag in RGO/Ag NPs film was 0.6%, which was much higher than that in the GE–Ag film we reported recently, obtained using AgNO3 solution. The transmittance and the sheet resistance of 4-layer RGO/Ag NPs film reached 89.2% and 8.3 kΩ □−1, respectively.

By alternating deposition of graphene oxide (GO) sheets and silver nitrate by means of an electrostatic self-assembly method, a GO–Ag+ film was prepared. After thermal annealing, a graphene–silver nanoparticle (GE–Ag) multilayer film, with high transparency and electrically conductivity, was obtained. The transmittance of a film with four assembly cycles was 86.3%, at a wavelength of 550 nm, better than that of a pure GE film (73.8%). While the surface resistance was 97 kΩ □−1, much lower than that of a pure GE film (430 kΩ □−1). The Ag nanoparticles play a crucial role in improving the properties of the GE–Ag film, acting as conductive paths and light-trapping nanoparticles, which not only reduces the reflection of the film, but also prevents the GE sheets from aggregation and provides conductive paths between sheets, improving the electrical conductivity.

In the present study, Ag nanoparticles were deposited onto graphene sheets to form graphene/Ag nanocomposites through solvothermal method using ethylene glycol or de-ionzed water/hydrazine as solvent and reducing agent. Ag particles were attached on the graphene sheets and well separated. The size and morphology of the particles were influenced by the reducing agent and solvothermal reaction. Because of the existence of Ag particles, graphene sheets were well separated both in the solution and in the film obtained via vacuum filtration method. The electroconductibility of graphene/Ag film was investigated. It was found that the film resistance were 0.85 Ω cm and 0.60 Ω cm for different reducing agents used, which were close to that of the pure graphene film with same carbon concentration (0.25 Ω cm).Highlights► Electrically conductive Ag particles were decorated onto the surface of graphene sheets to improve the dispersity. ► Graphene sheets were well separated by the existence of Ag particles and the restack of graphene sheets to form graphite-like structure via filtration process was inhibited effectively. ► The good conductivity of Ag makes contribution to the excellent conductivity of graphene/Ag composite film.

CdSe particles with wurtzite structure have been synthesized via solvothermal method using a mixed solution of triethylenetetramine (TETA) and de-ionized water (DIW). It was found that ball-like CdSe precursor with zinc-blende phase could be transformed to wurtzite structure after heat-treating at 580 °C in Ar atmosphere and the obtained microspheres were made up of many nanometer sized CdSe particles. The experimental results were compared with CdSe obtained via hydrothermal method using N2H4·H2O as the reducing agent and it was found that CdSe nanorods with wurtzite structure were obtained. It was speculated that TETA in the mixed solution played the role of reducing agent and surfactant. Both the as-prepared products and the annealed powders were systematically characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared absorbance spectroscopy (FTIR) and thermogravimetric analysis (TGA).

Negative thermal expansion (NTE) ZrW2O8 powders were prepared by step-by-step solid-state reaction with ZrO2 and WO3 powders. The coefficient of thermal expansion (CTE) of the as-prepared ZrW2O8 was around −5.08×10−6 K−1 at 20–700°C. Different amounts of ZrW2O8 powders were added in BTDA-ODA polyamic acid to form polyimide/ZrW2O8 composites (PI/ZrW2O8). With the increment of ZrW2O8, experimental results show that ZrW2O8 powders can significantly enhance the thermal stability of the composites, and reduce the thermal expansion. A 50 wt pct ZrW2O8 addition can give rise to a 31% reduction of CTE. It is suggested that the PI/ZrW2O8 composites have potential applications in high performance microelectronic devices.

In the present study, ZnSe nanostructures with complex morphologies and different phase structures were synthesized via a solvothermal approach using a mixed solution of triethylenetetramine (TETA) and de-ionized water (DIW). It was found that the phase and morphology of the as-prepared products could be controlled by changing the volume ratio of TETA to DIW. Metastable ZnSe nanoflowers with layered structure could be obtained from pure TETA, which can be transformed to the wurtzite structure after heat-treating at 500 °C in Ar atmosphere. With the addition of DIW, the morphology changed from flowers to spheres, and when the volume ratio of TETA to DIW was 1:1, loose spheres composed of nanoparticles were obtained. Variation of the TETA content in the mixed solvent also allows controlling of the crystallographic phase of ZnSe (wurtzite or zinc blende). Both the as-prepared products and the annealed powders were systematically characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared absorbance spectroscopy (FTIR), thermogravimetric analysis (TGA), and ultraviolet–visible (UV–vis) spectroscopy methods.

To prepare TiO2 intercalated tetratitanate, TiO2 solution and ultrafine layered titanate K2Ti4O9 obtained via solid-state reaction by using nanometer-sized TiO2 as raw material were used as guest and host materials respectively. The structure and morphology of the resulting samples were characterized by XRD and TEM experiments. It was found that during the intercalation process, the interlayer distance was expanded step-by-step and the interlayer structure of titanate might be destroyed and degraded to slits by prolonging the solution intercalation time. Rutile TiO2 nanofibers with the average size of 5 × 50 nm were obtained at room temperature while the duration time was prolonged to 72 h.

Ultrafine layered tetratitanate (K2Ti4O9) was prepared by stearic acid method (SAM) and the obtained powders were further used as the host material for the preparation of alumina-pillared products for the first time. The pillaring procedure was characterized by XRD experiments and the resulting products were characterized by nitrogen adsorption analysis. It was found in our experiment that ultrafine tetratitanate facilitated the formation of alumina-pillared tetratitanate with high surface area (243.5 m2 g−1) and narrow pore-size distribution.

•The N-3DrGO sample was fabricated by a simple hydrothermal method using GO, melamine and formaldehyde as the raw materials.•With porous architecture and high specific surface area, the N-3DrGO catalyst displays favorable electrocatalytic activity towards ORR.•The N-3DrGO catalyst also exhibits much better electrochemical stability and higher durability than that of the commercial Pt/C catalyst.Nitrogen-doped graphene materials provide the attractive potentials to replace the high-priced Pt and Pt-based catalysts for oxygen reduction reaction (ORR) to accelerate the industrialization of fuel cells (FCs). Herein, the nitrogen-doped three-dimensional reduced graphene oxide (N-3DrGO) catalysts have been prepared by a facile hydrothermal method using the raw materials of GO, melamine and formaldehyde. The N contents in N-3DrGO products vary from 3.12 to 9.69 at.% which can be easily regulated by adjusting the feed mass ratios of GO and melamine. It is found that a higher content of N does not necessarily result in enhanced electrocatalytic activity. Rather, with the highest total percentage of graphitic N and pyridinic N (69.2%), superior solvent dispersibility, as well as a smaller interfacial and charge-transfer resistance, the N-3DrGO catalyst obtained by a mass ratio of 1:1.5 between GO and melamine presents the most excellent activity towards ORR. As a catalyst using in FCs for ORR, the obtained N-3DrGO catalysts exhibit favorable electrocatalytic performance, excellent methanol tolerance and much enhanced durability compared with that of commercial Pt/C (20 wt%) catalyst in alkaline media. Furthermore, the above-mentioned approach is demonstrated to be a versatile method in fabricating N-3DrGO-based catalysts by introducing the foreign active atoms such as sulfur (S) to realize the N and S co-doping, which can further enhance the catalysts’ ORR activity.