Xiaodong Qian

In situ preparation of functionalized graphene oxide/epoxy nanocomposites with effective reinforcements

In order to obtain homogeneous dispersion and strong filler-matrix interface in epoxy resin, graphene oxide was functionalized via surface modification by hexachlorocyclotriphosphazene and glycidol and then incorporated into epoxy resin to obtain nanocomposites via in situ thermal polymerization. The morphology of nanocomposites was characterized by scanning electron microscopy and transmission electron microscopy, implying good dispersion of graphene nano-sheets. The incorporation of functionalized graphene oxide effectively enhanced various property performances of epoxy nanocomposites. The storage modulus of the epoxy nanocomposites was significantly increased by 113% (2% addition) and the hardness was improved by 38% (4% addition). Electrical conductivity was improved by 6.5 orders of magnitude. Enhanced thermal stability was also achieved. This work demonstrates a cost-effective approach to construct a flexible interphase structure, strong interfacial interaction and good dispersion of functionalized graphene in epoxy nanocomposites through a local epoxy-rich environment around graphene oxide sheets, which reinforces the polymer properties and indicates further application in research and industrial areas.

Novel organic–inorganic flame retardants containing exfoliated graphene: preparation and their performance on the flame retardancy of epoxy resins

In this work, a simple and efficient approach for the preparation of organic–inorganic hybrids flame retardants (FRs-rGO), aiming at improving the flame retardant efficiency was presented. The reduced graphite oxide (rGO) was incorporated into the flame retardants matrix by in situ sol–gel process, resulting in the formation of organic–inorganic hybrids flame retardants containing exfoliated rGO. The TEM results of FRs-rGO hybrids revealed that the rGO was previously exfoliated in the phosphorus and silicon containing FRs. Subsequently, the flame retardant (FRs-rGO) was incorporated into epoxy resins (EP). The previous exfoliation of rGO in the FRs allows rGO to be intimately mixed with epoxy resins, which can be confirmed by the TEM results of FRs-rGO/EP nanocomposites. With the incorporation of 5 wt% of FRs-rGO into EP, satisfied flame retardant grade (V0) and the LOI as high as 29.5 were obtained. The char residues of the FRs-rGO/EP nanocomposites were significantly increased in air as well as nitrogen atmosphere. Moreover, the peak heat release rate (pHRR) value of FRs-rGO/EP was significantly reduced by 35%, and the glass transition temperature (Tg) of FRs-rGO/EP nanocomposites shifted to higher temperature, compared to those of neat EP. The flame retardancy strategy of FRs-rGO combines condensed phase and gas phase flame retardant strategies such as the nanocomposites technique, phosphorus–silicon synergism systems in the condensed phase and DOPO flame retardant systems in the gas phase. Moreover, the flame retardants containing exfoliated graphene (FRs-rGO) provided a novel method to prepare organic–inorganic hybrids flame retardants and the as-prepared flame retardants exhibited high flame retardant efficiency.

Influence of g-C3N4 nanosheets on thermal stability and mechanical properties of biopolymer electrolyte nanocomposite films: a novel investigation.

A series of sodium alginate (SA) nanocomposite films with different loading levels of graphitic-like carbon nitride (g-C3N4) were fabricated via the casting technique. The structure and morphology of nanocomposite films were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis results suggested that thermal stability of all the nanocomposite films was enhanced significantly, including initial thermal degradation temperature increased by 29.1 °C and half thermal degradation temperature improved by 118.2 °C. Mechanical properties characterized by tensile testing and dynamic mechanical analysis measurements were also reinforced remarkably. With addition of 6.0 wt % g-C3N4, the tensile strength of SA nanocomposite films was dramatically enhanced by 103%, while the Youngs modulus remarkably increased from 60 to 3540 MPa. Moreover, the storage modulus significantly improved by 34.5% was observed at loadings as low as 2.0 wt %. These enhancements were further investigated by means of differential scanning calorimetry and real time Fourier transform infrared spectra. A new perspective of balance was proposed to explain the improvement of those properties for the first time. At lower than 1.0 wt % loading, most of the g-C3N4 nanosheets were discrete in the SA matrix, resulting in improved thermal stability and mechanical properties; above 1.0 wt % and below 6.0 wt % content, the aggregation was present in SA host coupled with insufficient hydrogen bondings limiting the barrier for heat and leading to the earlier degradation and poor dispersion; at 6.0 wt % addition, the favorable balance was established with enhanced thermal and mechanical performances. However, the balance point of 2.0 wt % from dynamic mechanical analysis was due to combination of temperature and agglomeration. The work may contribute to a potential research approach for other nanocomposites.

Functionalized graphene oxide/phosphoramide oligomer hybrids flame retardant prepared via in situ polymerization for improving the fire safety of polypropylene

A novel strategy based on functionalized graphene oxide (FGO)/phosphoramide oligomer flame retardant was developed to overcome the challenges of the dispersion of graphene sheets in polymer matrix and the ease of the burn-out of graphene under air atmosphere. Graphene oxide (GO) was modified by 4,4-diaminodiphenyl methane (DDM) and then in situ incorporated into phosphoramide oligomer, resulting in a nanocomposite flame retardant (FRs-FGO) containing exfoliated graphene. Subsequently, the flame retardant (FRs-FGO) was incorporated into polypropylene (PP) and simultaneously compatilized with PP-grafted maleic anhydride. TEM results showed that the FGO was dispersed more uniformly in PP than the bare GO because of the strong interfacial interaction and previous exfoliation of FGO in FRs before blending. The thermal properties investigated by thermogravimetric analysis (TGA) indicated that the addition of FRs-FGO into PP resulted in a significant improvement of thermal stability at elevated temperature with higher char yields. Moreover, the crystallization and fire safety properties of PP composites were also improved by the incorporation of FRs-FGO, including increased crystallization temperature (11.4 °C increase), reduced peak heat release rate (66.9% reduction) and decreased total heat release (24.4% decrease), and decreased fire growth rate index (73.0% decrease). The cone results indicated the simple blending of GO with FRs and exhibited less improvement in fire safety properties than FRs-FGO, which resulted from the improved dispersion and thermal stability of FGO sheets. The flame retardant mechanism was because of the shielding effect of FGO and char layers, which could reduce the release of combustible gases and inhibit the mass and heat transfer between the gas phase and condensed phase.

Ternary graphene–CoFe2O4/CdS nanohybrids: preparation and application as recyclable photocatalysts

Graphene (Gr)-based binary Gr–CoFe2O4 and Gr–CdS or ternary Gr–CoFe2O4/CdS nanohybrids were prepared via a facile solvothermal strategy. It was encouraging to find that the ternary Gr–CoFe2O4/CdS nanohybrids exhibited the highest photocatalytic degradation ability (80%) among all the photocatalysts. The significant enhancement in photodegradation under 40 W daylight lamp irradiation was attributed to graphene acting as a “bridge”, where electrons generated from CoFe2O4 were transferred to CdS by graphene and finally led to separation of electrons and holes. Interestingly, neat CoFe2O4 resulted in increasing concentration of methylene blue (MB) as the irradiation time increased. The phenomenon was ascribed to adsorption of MB molecules on CoFe2O4 in the dark and desorption from the photocatalyst during irradiation, confirmed by our ingenious experiment. Digital photos of the Gr–CoFe2O4/CdS hybrids in an external magnetic field indicated that the ternary photocatalyst could be easily separated from aqueous solution. The recycle measurements of the photocatalyst revealed that the ternary nanohybrids exhibited acceptable photocatalytic stability due to unstable decoration. This work would provide a new insight into the construction of visible light-responsive and magnetic separable photocatalysts with high performances.

An aqueous approach to ZnSe and CdSe semiconductor nanocrystals

With the use of elemental metals and selenium as resource materials, ZnSe and CdSe nanocrystals have been prepared through an aqueous method at temperature as low as 80°C in alkaline medium. The products were characterized by powder X-ray diffraction pattern (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectrum (XPS). Two kinds of chemical mechanisms for the formation of the products and the influence of experimental conditions are discussed.

Benzene-thermal preparation of nanocrystalline chromium nitride

Abstract Nanocrystalline CrN was successfully prepared through the liquid–solid reaction of anhydrous CrCl 3 and Li 3 N, via a benzene–thermal method in the temperature range of 350–420°C, which is much lower than that used in conventional methods. This process is simple and easy to control. X-ray diffraction (XRD) indicated that the compound was cubic CrN phase with cell constant a = 4.13 A. Transmission electron microscopy (TEM) images showed that the average particle size was about 25 nm. X-ray photoelectron spectroscopy (XPS) indicated that the as-prepared products contained a small amount (less than 20%) of amorphous carbon.

Silicon nanoparticle decorated graphene composites: preparation and their reinforcement on the fire safety and mechanical properties of polyurea

Reduced graphene oxide (rGO) was decorated with organic/inorganic nanoparticles through an in situ sol–gel process with various thicknesses. The presence of organic/inorganic nanoparticles made the rGO lipophilic, as evidenced by the good dispersion of the nanoparticles–rGO in dimethyl formamide solvent (DMF). The thickness of the nanoparticles–rGO could be varied by adjusting the amount of the silicane additive, as evidenced by the AFM results. The nanoparticles–rGO was then incorporated into polyurea in different ratios via in situ polymerization and the property enhancement of the nanocomposites was investigated. The TEM morphological study showed that, due to the good interfacial interaction between the nanoparticles–rGO and polyurea, nanoparticles–rGO was dispersed well in the polyurea matrix. Compared with the rGO, the nanoparticles could significantly improve the thermal stability and thermal conductivity of polyurea, implying that the good dispersion of rGO and the functional groups on the surface of rGO had a significant effect on the thermal stability and thermal conductivity of polyurea. The peak heat release rate (pHRR) of nanoparticles–rGO/polyurea nanocomposites was significantly reduced, which indicated that the combustible gas releasing rate of polyurea was reduced. Moreover, the storage modulus and tensile strength of the nanocomposites with 0.2 wt% have been enhanced by about 60% and 110% in comparison with those of neat polyurea, respectively. This simple and effective approach, decorating the rGO with organic/inorganic nanoparticles, is believed to offer possibilities for broadening the graphene applications in the polymer materials and make it possible to decorate the graphene with other functional groups and vary the aspect ratio of decorated graphene according to its application.

Preparation of nanocrystalline nickel powders through hydrothermal-reduction method

Nanocrystalline nickel powders were prepared in aqueous solution through a thermal-reduction process. The reductive atmosphere was produced from the disproportionation of white phosphorus in basic solution at 100°C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis were employed to characterize the products. XRD revealed that the nickel was single phase. TEM showed that the average particle size was about 26 nm. The purity of the as-prepared nickel was 99.6%, as determined from the spectrophotoscopy. The possible formation mechanism of nanocrystalline nickel is a reduction of nanocrystalline Ni(OH)2.

The preparation and phase transition of nanocrystalline iron sulfides via toluene-thermal process

A series of nanocrystalline iron sulfides have been successfully prepared via the reaction of FeSO4.7H2O and Na2S3 using the toluene-thermal method in the temperature range of 80–170°C. Two single phases of Fe3S4 and FeS2 were obtained. Transmission electron microscopy analyses indicate that Fe3S4 crystallite is about 25 nm and FeS2 is about 50 nm. The iron and sulfur contents are determined by spectrophotometric analysis. The ratios of Fe to S are Fe2.994S4 and Fe0.996S2, respectively. With the change of the reaction condition, the phase transition among iron sulfur was studied.