Graphene–TiO2 composite photocatalysts, which are very promising in many fields such as optoelectronics, electrode materials and lithium-ion batteries, have attracted much attention in recent years. However, a proper design of graphene–TiO2 photocatalysts requires a systematic study of graphene functions for photocatalytic activity enhancement. It is evident that the enhancement may depend on the structural of graphene, the graphene–TiO2 interface, the nanoscale morphologies, surface area and more. These factors are highly dependent on the preparation method. Herein, in this article, we show two synthetic strategies with three routes to prepare the graphene–TiO2 composite films with spray coating method. The effects of structural differences of graphene and the preparation strategies on the microstructure and the photocatalytic performance of the graphene–TiO2 composite films under the same condition were systematically investigated. The results showed that both of the structure characteristics of graphene including the electron transport ability and specific surface area, and the interfacial contact between graphene nanosheets and TiO2 nanoparticles have important effects on the photocatalytic properties of materials. It is hoped that these experimental results can be applied as a background source to understand the underlying mechanism of the photocatalytic activity enhancement and construct more efficient graphene–TiO2 photocatalysts.

A novel multifunctional structural supercapacitor based on graphene and geopolymer infused with 2 M KOH electrolyte was fabricated. Metakaolin-based geopolymers, which were first applied as structural separators in this paper, were prepared with metakaolin and different moduli of alkaline activator solution. The widespread pores in geopolymer matrix provide enough channels for ion storage and motion. The effects of alkaline activator solution modulus and curing age on the electrochemical properties were analyzed. The results revealed the ideal capacitive behavior of structural supercapacitor. The samples with modulus of 2.0 exhibited the highest specific capacitance of 36.5 F g−1 at curing age of 28 days. A possible mechanism was proposed to explain the factors that influence the specific capacitance of geopolymer-based structural supercapacitor. The result of multifuncitonality analysis showed that samples with modulus of 1.6 exhibited the best level of multifunctionality, with compressive strength of 33.85 MPa and specific capacitance of 33.4 F g−1 at curing age of 28 days. It achieved a balance between mechanical property and electrochemical performance.

Graphene nanoplatelets(GNP)/cement composites were prepared using three types of GNP with different structures. In order to investigate the effects of GNP and styrene-acrylate emulsion on properties of GNP/cement composites, GNP with different addition (0-2.0 wt%) and styrene-acrylate emulsion (10 wt%) were mixed into cement through the method of mechanical stirring. Electrical performance and the pressure-sensitive property of GNP/cement composites were studied. The results showed that the addition of GNP to cement would lead to a significant drop of resistivity and make composites manifest pressure sensitivity. In addition, the structure (C/O atomic ratio) of GNP greatly affected the properties of the GNP/cement composites. A distinct enhancement in pressure sensitivity was found when emulsion was added to GNP/cement composites. The gauge factor of emulsion modified GNP/cement composites reached a peak value of 7.783, which was 1 order of magnitude higher than composites without emulsion. This work offered a new opportunity to make use of traditional cement materials combining with GNP.

•Graphene-TiO2 composite film with multifunctionality was prepared.•A drastic synergetic effect in graphene-TiO2 composite film was found.•Effects of TiO2 on the structure and properties of graphene film were studied.In this study, reduced graphene oxide-TiO2 (rGO-T) composite films fabricated by a spray coating method are proposed to develop a multifunctional material with transparent conductive, photocatalytic and strain sensing properties. In the presence of SDBS, well-dispersed reduced graphene oxide solutions were prepared by mixing graphene oxide dispersions with hydrazine hydrate. A drastic synergetic effect was found simply by mixing reduced graphene oxide dispersions with TiO2 solutions. The obtained multifunctional rGO-T composite films showed relatively high optical transmittance, excellent strain sensing property with tunable gauge factors (GF) of 11–21 and enhanced photocatalytic property. The remarkable performance could be attributed to the combination of the excellent electrical and mechanical properties of graphene nanosheets and photocatalytic performance derived from TiO2 nanoparticles. Overall, this work could provide new insights into the research of the graphene-TiO2 composite materials and facilitate their application in a broad range.Download high-res image (139KB)Download full-size image

•Three-dimensional graphene network/1-hexadecanol composite was prepared by one-pot method.•The composite PCMs exhibited enhanced thermal conductivity and electrical conductivity.•The composite PCMs have desirable phase change enthalpy and excellent shape stability.In this paper, three-dimensional graphene network encapsulating 1-hexadecanol composite was prepared by one-pot method, which is based on Pickering emulsion template. The composite phase change materials (PCMs) showed enhanced thermal conductivity and electrical conductivity due to the interconnected graphene network in PCMs. In addition, the composite PCMs exhibited excellent shape stability, which prevented the leakage of PCMs during phase change. This novel shape-stable PCM can be used in thermal energy storage and conversion.

In this study, reduced graphene oxide-TiO2 (rGO-T) composite films fabricated by a spray coating method are proposed to develop a multifunctional material for the application of strain sensing and photodegradation. This work provides a simple and versatile approach to prepare rGO-T as a multifunctional material. The drastic synergy effect was found simply by mixing graphene oxide with TiO2. The obtained multifunctional rGO-T composite films showed relatively high optical transmittance (around 60% at a 550 nm wavelength), excellent strain sensing property with gauge factors (GF) of 12–23 and enhanced photocatalytic property. The remarkable performance could be attributed to the combination of electrical and mechanical properties of rGO nanosheets and photocatalytic performance derived from TiO2 nanoparticles. Overall, this work could provide new insights into the research of the graphene-TiO2 composite materials and facilitate their application in a broad range.

We develop a simple approach to fabricate graphene–TiO2 films both on rigid and flexible substrates by the spray coating technique. A drastic synergetic effect was found simply by mixing graphene with TiO2. The composite films were conductive and showed enhanced photocatalytic activities. More significantly, the graphene–TiO2 composite films which could sustain a large tensile deformation (5% strain) demonstrated high sensitivity to mechanical strain with tunable gauge factors (GF) of 14–35. The remarkable performance could be attributed to the combination of photocatalytic performance derived from TiO2 nanoparticles and the electrical and mechanical properties of graphene nanosheets. Based on the observed results, a plausible mechanism was proposed. Overall, this work could provide new insights into the research of the graphene–TiO2 composite materials and facilitate their application in a broad range.

The reduction of graphene oxide (GO) is a promising route to bulk produce graphene-based sheets. Different reduction processes result in reduced graphene oxide (RGO) with different properties. In this paper three reduction methods, chemical, thermal and electrochemical reduction, were compared on three aspects including morphology and structure, reduction degree and electrical conductivity by means of scanning electron microscopy (SEM), X-ray diffraction(XRD), the Fourier transform infrared spectroscopy (FT-IR) spectrum, X-ray photoelectron spectroscopy (XPS) and four-point probe conductivity measurement. Understanding the different characteristics of different RGO by preliminary comparison is helpful in tailoring the characteristics of graphene materials for diverse applications and developing a simple, green, and efficient method for the mass production of graphene.

A free-standing graphene thin film is prepared by a simple electrochemical method applying positive and negative pulse electric signal, followed by air drying and being peeled off from the electrodes. During the process, formation and reduction of graphene oxide film have been simultaneously achieved. The free-standing graphene thin film obtained is characterized by X-ray diffraction, X-ray photoelectron and electrochemistry. The results show that the electrical conductivity and reduction of free-standing graphene film are influenced by pulse characteristic duty ratio and time of reaction. Their capacitive behavior is investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy using the two-electrode symmetric capacitor test. The free-standing flexible graphene film prepared under duty ratio 60% for 3 h exhibits a specific capacitance of 157 F g−1 and good cycling stability. In addition, energy density and power density can reach to 3.36 W h kg−1 and 20.5 kW kg−1, respectively, at a discharge of 100 A g−1. This approach opens up the possibility of fabrication of high-performance flexible electrode materials.

•We proposed a one-pot strategy for the fabrication of 3D framework graphene.•The GO was not only been reduced but also been exfoliated via pulse electrical field.•The formation mechanism of 3D framework graphene has also been investigated.•Graphene dendrite firstly found in our article was used as building blocks.A one-pot approach of producing three-dimensional (3D) framework graphene was reported. The proposed method is based on exfoliation and reduction of graphite oxide in electrochemical reaction using pulse wave. The formation mechanism of 3D framework graphene has been investigated. The results show that graphene dendrite firstly found in our article were used as building blocks, the growing evolution of which might follow the pattern of deposition of the diffusion-limited aggregation (DLA). The flexible graphene dendrite in different structural levels overlapped or coalesced with each other, resulting in formation of cross-linking 3D framework ultimately. The 3D framework graphene as an electrode material exhibits high specific capacitance (140 F/g at 5 A g−1) in an aqueous electrolyte.

Phase-change nanocapsule particles are successfully synthesized by the two-step miniemulsion polymerization method. Urea–formaldehyde resin is used as the shell material. Hexadecane is used as the core material. The particle size distribution and the surface morphology of nanocapsules are characterized by laser particle size analyzer, optical and scanning electron microscopy. The thermal properties are investigated by differential scanning calorimeter. The effects of the amounts of surfactant (AS) on the properties of prepared nanocapsules are also investigated. The results indicated that the nanocapsules have smooth surface and the mean particle size is about 270 nm; nano-structure of capsules has not changed dramatically after being heated at 100 °C for 72 h; The phase-change enthalpy of nanocapsules increases from 114.6 to 143.7 J/g with the increasing of the AS, but the mean particle diameter decreases from 285 to 253 nm; The degree of undercooling of hexadecane decreases about average 94% after being encapsulated in capsules.

Aqueous colloids of graphene oxide nanosheets were produced from exfoliation of graphite oxide using a magnetic stirrer and heat treatment in the absence of ultrasonication. Laser particle measurements showed that the particle size distribution of graphite oxide dispersed in de-ionized water was significantly influenced by treatment time indicating an increasing exfoliation level of graphite oxide. Atomic force microscopy (AFM) confirmed that single-layer graphene oxide nanosheets with a thickness of ~1 nm were obtained after 72 h of magnetic stirring and heat treatment. These findings provide a new methodology for preparation of single-layer graphene oxide nanosheet colloids.

Reduced graphene oxide (RGO) nanosheets were produced by chemical reduction of exfoliated graphite oxide. Atomic force microscopy (AFM) images show that the obtained RGO nanosheets vary greatly in lateral-dimensional sizes, ranging from less than 100  100 nm to more than 2000  2000 nm. In order to separate these nanosheets, one simple and low-cost method mainly based on magnetic-stirring and centrifugation treatments was proposed. Preliminary statistical analysis of RGO nanosheets, based on AFM images, shows that the dot-like RGO nanosheets (with lateral dimensions less than 100  100 nm) and leaf-like RGO nanosheets (with lateral dimensions more than 500  500 nm) were effectively separated by this simple method.