3D architecture reduced graphene oxide-MoS2 composite: Preparation and excellent electromagnetic wave absorption performance

High-performance electromagnetic absorbers with wide absorption band, strong absorption and lightweight are necessary for industry and military application. To obtain the desired materials, two-dimensional (2D) atomic layers structure nanosheets, such as graphene and graphene-like, were adopted due to its unique structure and properties. Here, 3D architecture reduced graphene oxide-molybdenum disulfide (RGO-MoS₂) composite was prepared by one-pot hydrothermal reaction. MoS₂ generated on graphene oxide intercalation through hydrothermal process and rGO is obtained in the meanwhile. 3D architecture RGO-MoS₂ composite can effectively prevent two-dimensional nanosheets re-stacked and can be applied in electromagnetic wave absorption field. In this paper, composites consist of RGO and various MoS₂ were prepared and their electromagnetic performances were investigated for the first time. Maximum absorption bandwidth (R_L < −10 dB) is 5.92 GHz with thickness of 2.5 mm. We may reasonably conclude that RGO-MoS₂ composite can serve as excellent light-weight electromagnetic wave absorbers and can be widely used in practice.     

Preparation of aligned Fe3O4@Ag-nanowire/poly(vinyl alcohol) nanocomposite films via a low magnetic field

Aligned Fe₃O₄@Ag-nanowire (Ag-NW)/poly(vinyl alcohol) (PVA) nanocomposite films are prepared via a magnetic field-assisted method under a low magnetic field (B < 0.1 T) induction. The effects of the mass ratio (MR) of Fe₃O₄ to Ag-NWs and the Ag-NW content are systematically studied on the composite electrical conductivity (EC). The preferential alignment of Ag-NWs brings about a significant increase in the EC of the oriented composite in the parallel direction along the magnetic field. The optimal MR is determined to be equal to 0.15 at which the random composite has a good EC meanwhile the oriented composite shows a good response to the applied magnetic field. The oriented composite with the 20 wt% Ag-NWs shows a high EC anisotropy of ca. 6.6 and a very high EC of 4500 S/cm via the external magnetic field. In addition, the introduction of Ag-NWs leads to an obvious improvement in the thermal stability of PVA composites.     

Enhanced microwave absorption properties of flake-shaped FePCB metallic glass/graphene composites

A novel kind of composite absorber, i.e. FePCB/graphene composite, with excellent microwave absorption properties was successfully fabricated by a simple and scalable ball milling method. After being milled, the FePCB particles displayed flaky morphology with large aspect ratio. The complex permittivity and permeability of the flaky FePCB distinctly increased compared with those before milling. Furthermore, with the introduction of graphene, the flaky FePCB/graphene composite exhibited excellent microwave absorption performance with strong absorption and wide absorption band. In particular, for FePCB/graphene composite with an absorber thickness of 2 mm, the reflection loss (RL) reached a minimum of −45.3 dB at 12.6 GHz and the effective absorption bandwidth (RL < −10 dB) covered 5.4 GHz. The enhanced microwave absorption performance of the FePCB/graphene composite was attributed to the high magnetic loss and improved impedance matching which were closely related to the flake-shaped FePCB particles and the introduction of graphene sheets.     

Enhanced mechanical,thermal and flame retardant properties by combining graphene nanosheets and metal hydroxide nanorods for Acrylonitrile–Butadiene–Styrene copolymer composite

Three metal hydroxide nanorods (MHR) with uniform diameters were synthesized, and then combined with graphene nanosheets (GNS) to prepare acrylonitrile–butadiene–styrene (ABS) copolymer composites. An excellent dispersion of exfoliated two-dimensional (2-D) GNS and 1-D MHR in the ABS matrix was achieved. The effects of combined GNS and MHR on the mechanical, thermal and flame retardant properties of the ABS composites were investigated. With the addition of 2 wt% GNS and 4 wt% Co(OH)₂, the tensile strength, bending strength and storage modulus of the ABS composites were increased by 45.1%, 40.5% and 42.3% respectively. The ABS/GNS/Co(OH)₂ ternary composite shows the lowest maximum weight loss rate and highest residue yield. Noticeable reduction in the flammability was achieved with the addition of GNS and Co(OH)₂, due to the formation of more continuous and compact charred layers that retarded the mass and heat transfer between the flame and the polymer matrix.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Magnetically-sensitive shape memory polyurethane composites crosslinked with multi-walled carbon nanotubes

Magnetically-sensitive polyurethane composites, which were crosslinked with multi-walled carbon nanotubes (MWCNTs) and were filled with Fe₃O₄ nanoparticles, were synthesized via in situ polymerization method. MWCNTs pretreated with nitric acid were used as crosslinking agents. Because of the crosslinking of MWCNTs with polyurethane prepolymer, the properties of the composites with a high content of Fe₃O₄ nanoparticles, especially the mechanical properties, were significantly improved. The composites showed excellent shape memory properties in both 45 °C hot water and an alternating magnetic field (f = 45 kHz, H = 29.7 kA m⁻¹). The shape recovery time was less than one minute and the shape recovery rate was over 95% in the alternating magnetic field.     

Synthesis and characterization of carbon-coated Fe3O4 nanoflakes as anode material for lithium-ion batteries

The carbon-coated Fe₃O₄ nanoflakes were synthesized by partial reduction of monodispersed hematite (Fe₂O₃) nanoflakes with carbon coating. The carbon-coated Fe₃O₄ nanoflakes were characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and galvanostatic charge/discharge measurements. It has been demonstrated that Fe₂O₃ can be completely converted to Fe₃O₄ during the reduction process and carbon can be successfully coated on the surface of Fe₃O₄ nanoflakes, forming a conductive matrix. As anode material for lithium-ion batteries, the carbon-coated Fe₃O₄ nanoflakes exhibit a large reversible capacity up to 740 mAh g⁻¹ with significantly improved cycling stability and rate capability compared to the bare Fe₂O₃ nanoflakes. The superior electrochemical performance of the carbon-coated Fe₃O₄ nanoflakes can be attributed to the synthetic effects between small particle size and highly conductive carbon matrix.     

Tunable BT@SiO2 core@shell filler reinforced polymer composite with high breakdown strength and release energy density

Barium titanate@silicon dioxide (BT@SiO₂) core@shell fillers with an average diameter of 100 nm were prepared by a facile sol–gel synthesis. The thickness of SiO₂ shell can be easily tuned by varying different mass ratio of BT to tetraethyl orthosilicate (TEOS). Polyvinylidene fluoride (PVDF) based composite films reinforced by BT and BT@SiO₂ were fabricated via a solution casting method. The effects of SiO₂ shell on morphology structure, wettability, interfacial adhesion, dielectric, electrical and energy performances of composites were investigated. Compared with BT/PVDF, BT@SiO₂/PVDF composites show significantly increased breakdown strength due to enhanced interfacial adhesion and suppressed charge carrier conduction. Benefiting from enhanced breakdown strength and reduced remnant polarization induced by SiO₂ shell, BT@SiO₂/PVDF shows increased release energy density (energy density which can be fully discharged and applicable). Especially, BT@SiO₂/PVDF with SiO₂ thickness of 4 nm exhibits the highest release energy density of 1.08 J/cm³ under applied electric field of 145 kV/mm.     

SnO2/α-Fe2O3 hierarchical nanostructure: Hydrothermal preparation and formation mechanism

In this paper, we reported a simple solution method to assemble SnO₂ nanorods hierarchically on the surface of α-Fe₂O₃ nanosheets using Fe₃O₄ nanosheets as precursor. The product was characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM). Our experimental results show that the lattice mismatch at the interface of SnO₂ nanorods with α-Fe₂O₃ nanosheets played an important role in determining the growth direction of SnO₂ nanorods. The interface prefers to take the least lattice mismatch and thus the preferential growth direction of SnO₂ nanorods was along [1 0 1] direction. The result may have important impact on the understanding of the nucleation growth process in a heterogeneous system.     

The measurement of the adhesion force between ceramic particles and metal matrix in ceramic reinforced-metal matrix composites

This paper presents the method for measurement of the adhesion force and fracture strength of the interface between ceramic particles and metal matrix in ceramic reinforced-metal matrix composites. Three samples with the following Cu to Al₂O₃ ratio (in vol.%) were prepared: 98.0Cu/2.0Al₂O₃, 95.0Cu/5.0Al₂O₃ and 90Cu/10Al₂O₃. Furthermore, microwires which contain a few ceramic particles were produced by means of electro etching. The microwires with clearly exposed interface were tested with use of the microtensile tester. The microwires usually break exactly at the interface between the metal matrix and ceramic particle. The force and the interface area were carefully measured and then the fracture strength of the interface was determined. The strength of the interface between ceramic particle and metal matrix was equal to 59 ± 8 MPa and 59 ± 11 MPa in the case of 2% and 5% Al₂O₃ to Cu ratio, respectively. On the other hand, it was significantly lower (38 ± 5 MPa) for the wires made of composite with 10% Al₂O₃.     

The influence of nano/micro hybrid structure on the mechanical and self-sensing properties of carbon nanotube-microparticle reinforced epoxy matrix composite

Nano/micrometer hybrids are prepared by chemical vapor deposition growth of carbon nanotubes (CNTs) on SiC, Al₂O₃ and graphene nanoplatelet (GNP). The mechanical and self-sensing behaviors of the hybrids reinforced epoxy composites are found to be highly dependent on CNT aspect ratio (AR), organization and substrates. The CNT–GNP hybrids exhibit the most significant reinforcing effectiveness, among the three hybrids with AR1200. During tensile loading, the in situ electrical resistance of the CNT–GNP/epoxy and the CNT–SiC/epoxy composites gradually increases to a maximum value and then decreases, which is remarkably different from the monotonic increase in the CNT–Al₂O₃/epoxy composites. However, the CNT–Al₂O₃ with increased AR ⩾ 2000 endows the similar resistance change as the other two hybrids. Besides, when AR < 3200, the tensile modulus and strength of the CNT–Al₂O₃/epoxy composites gradually increase with AR. The interrelationship between the hybrid structure and the mechanical and self-sensing behaviors of the composites are analyzed.     

Effect of silica coating thickness on the thermal conductivity of polyurethane/SiO2 coated multiwalled carbon nanotube composites

Silica coated multiwalled carbon nanotubes (SiO₂@MWCNTs) with different coating thicknesses of ∼4 nm, 30–50 nm, and 70–90 nm were synthesized by a sol–gel method and compounded with polyurethane (PU). The effects of SiO₂@MWCNTs on the electrical properties and thermal conductivity of the resulting PU/SiO₂@MWCNT composites were investigated. The SiO₂ coating maintained the high electrical resistivity of pure PU. Meanwhile, incorporating 0.5, 0.75 and 1.0 wt% SiO₂@MWCNT (70–90 nm) into PU, produced thermal conductivity values of 0.287, 0.289 and 0.310 W/mK, respectively, representing increases of 62.1%, 63.3% and 75.1%. The thermal conductivity of PU/SiO₂@MWCNT composites was also increased by increasing the thickness of the SiO₂ coating.     

Highly mechanical strength and thermally conductive bismaleimide–triazine composites reinforced by Al2O3@polyimide hybrid fiber

Bismaleimide–triazine (BT) resins have received a great deal of attention in microelectronics due to its excellent thermal stability and good retention of mechanical properties. Thereafter, developing BT based composites with high mechanical strength, thermal conductivity and dielectric property simultaneously are highly desirable. In this study, one hybrid fiber of Al₂O₃ nanoparticle (200 nm) supported on polyimide fiber (Al₂O₃@PI) with core–shell structure was introduced into BT resin to prepare promising Al₂O₃@PI–BT composite. The results indicated that the resultant composites possessed high Young’s modulus of 4.06 GPa, low dielectric constant (3.38–3.50, 100 kHz) and dielectric loss (0.0102–0.0107, 100 kHz). The Al₂O₃@PI hybrid film was also conductive to improve thermal stability (T_d5% up to 371 °C), in-plane thermal conductivity (increased by 295% compared to that of the pure BT resin). Furthermore, the Al₂O₃@PI–BT composite were employed to fabricate a printed circuit substrate, on which a frequency “flasher” circuit and electrical components worked well.     

High T2-relaxation and biocompatible magnetic nanofluids with poly(amino acid) coating

A facile one-pot method has been developed to prepare poly(amino acid) functionalized, water-stable, biocompatible, and superparamagnetic iron oxide nanoparticles (NPs) with small diameters of ∼10 nm. The obtained biocompatible magnetic nanoparticles capped with polyaspartic acid (PASP) exhibit a relatively high saturation magnetization (57.1 emu/g) and a much strong magnetic resonance (MR) T₂ relaxation effect with the transverse relaxivity coefficient (r₂) as high as 302.6 s⁻¹ mM⁻¹. Interestingly, the as-prepared Fe₃O₄@PASP NPs are highly stable in aqueous solution and demonstrate the property of magnetic nanofluids. The high T₂ effect, good water-stability, superparamagnetization, biocompatibility and bioconjugatability render the as-synthesized Fe₃O₄@PASP NPs great desirable for bioapplications such as magnetic resonance imaging (MRI), bioseparation, targeted drug delivery, and so on.     

Multi-step microwave reduction of graphite oxide and its use in the formation of electrically conductive graphene/epoxy composites

The multi-step MW reduction technique was developed in this study to obtain reduced graphene oxides; EG, RGO-1, and RGO-2 with MW irradiation time of 1, 2, and 3 min, respectively. Results of TGA, IR, and elemental analysis demonstrated that the degree of reduction of GO increased with increasing the MW irradiation time. Overall, 3 min of MW irradiation of GO in 3 steps was sufficient to obtain highly reduced GO (C/O ratio 10.38 by elemental analysis). The electrical percolation threshold of composites was observed as 1 wt% and 0.3 wt% for RGO-1 and RGO-2, respectively. Even at 0.5 wt% loading of RGO-2 in epoxy, the T_g value of the composite increased by 10 °C, indicating a strong interfacial interaction between graphene and epoxy resin.     

Ordered multiphase polymer nanocomposites for high-performance solid-state supercapacitors

Multilayered ordered nanostructures were fabricated by assembling in-situ grown polyaniline nanowire arrays with graphene oxide nanosheets. As-fabricated nanostructure was subsequently impregnated with the (H₃PO₄–Nafion)/polyvinyl alcohol solution to create a multiphase composite, which was used as a solid-state supercapacitor where graphene oxide/polyaniline nanowires served as electrode and (H₃PO₄–Nafion)/polyvinyl alcohol served as solid electrolyte. The ordered polyaniline (PANI) nanostructures facilitated the charge transfer and resulted in the specific capacitance of 83 F/g even if the discharge current was 5 A/g. The efficient charge transportation and electrode–electrolyte interaction resulted in small equivalent series resistance as low as 5.83 Ω, and thus outstanding electrochemical performance. The charge transfer resistance was much smaller than other commonly used solid-state electrolyte and almost negligible. As a result only 7% capacitance loss was found when the frequency increased from 100 to 1000 Hz. The energy density was as high as 26.5 Wh/kg while the power density was ∼3600 W/kg. The energy storage performance was also very stable since 82% specific capacitance was maintained after 1000 cycles.     

The effect of interfacial state on the thermal conductivity of functionalized Al2O3 filled glass fibers reinforced polymer composites

Rapidly increasing packaging density of electronic devices puts forward higher requirements for thermal conductivity of glass fibers reinforced polymer (GFRP) composites, which are commonly used as substrates in printed circuit board. Interface between fillers and polymer matrix has long been playing an important role in affecting thermal conductivity. In this paper, the effect of interfacial state on the thermal conductivity of functionalized Al₂O₃ filled GFRP composites was evaluated. The results indicated that amino groups-Al₂O₃ was demonstrated to be effective filler to fabricate thermally conductive GFPR composite (1.07 W/m K), compared with epoxy group and graphene oxide functionalized Al₂O₃. It was determined that the strong adhesion at the interface and homogeneous dispersion of filler particles were the key factors. Moreover, the effect of interfacial state on dielectric and thermomechanical properties of GFRP composites was also discussed. This research provides an efficient way to develop high-performance GFRP composites with high thermal conductivity for integrated circuit packaging applications.     

Synthesis and functionalization of SiO2 coated Fe3O4 nanoparticles with amine groups based on self-assembly

The purpose of this research was to synthesize amino modified Fe₃O₄/SiO₂ nanoshells for biomedical applications. Magnetic iron-oxide nanoparticles (NPs) were prepared via co-precipitation. The NPs were then modified with a thin layer of amorphous silica. The particle surface was then terminated with amine groups. The results showed that smaller particles can be synthesized by decreasing the NaOH concentration, which in our case this corresponded to 35 nm using 0.9 M of NaOH at 750 rpm with a specific surface area of 41 m² g^? 1 for uncoated Fe₃O₄ NPs and it increased to about 208 m² g^?1 for 3-aminopropyltriethoxysilane (APTS) coated Fe₃O₄/SiO₂ NPs. The total thickness and the structure of core-shell was measured and studied by transmission electron microscopy (TEM). For uncoated Fe₃O₄ NPs, the results showed an octahedral geometry with saturation magnetization range of (80–100) emu g^?1 and coercivity of (80–120) Oe for particles between (35–96) nm, respectively. The Fe₃O₄/SiO₂ NPs with 50 nm as particle size, demonstrated a magnetization value of 30 emu g^?1. The stable magnetic fluid contained well-dispersed Fe₃O₄/SiO₂/APTS nanoshells which indicated monodispersity and fast magnetic response.     

Doping of iron phosphate glasses with Al2O3, SiO2 or B2O3 for improved thermal stability

The effects of doping 60 P₂O₅–40 Fe₂O₃ (mol%) glasses with 5–10 mol% SiO₂, Al₂O₃ or B₂O₃ on their thermal stability, iron environments and redox were investigated. Thermal stability improved markedly with 5% dopant addition in the order Al₂O₃ > SiO₂ > B₂O₃ ≫ base glass. Solubility of pro rata additions when melted at 1150 °C was 5–10% SiO₂, <5% Al₂O₃, and >10% B₂O₃. It was possible to dissolve 5% Al₂O₃ by replacing Fe₂O₃. These additions generally had little effect on dilatometric measurements and iron environments, however the Fe²⁺/ΣFe redox ratio increased in the order base glass < Al₂O₃ < SiO₂ < B₂O₃. This behaviour was broadly consistent with the effects of glass basicity. The increased thermal stability of these glasses may improve their suitability for applications such as waste immobilisation or sealing.     

Synthesis of polyaniline-modified Fe3O4/SiO2/TiO2 composite microspheres and their photocatalytic application

Polyaniline-modified Fe₃O₄/SiO₂/TiO₂ composite microspheres have been successfully synthesized by sol–gel reactions on Fe₃O₄ microspheres followed by the chemical oxidative polymerization of aniline. The synthesized multilayer-structured composites were characterized by TEM, XRD, TGA, UV–vis diffuse reflectance spectra and magnetometer. The photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light. The effect of polyaniline (PANI) amounts on the photocatalytic activity was investigated. The photocatalytic activity results show that the Fe₃O₄/SiO₂/TiO₂ composites with about 2.4 wt.%–4.1 wt.% PANI could show higher photocatalytic efficiency than that of Fe₃O₄/SiO₂/TiO₂. Furthermore, the PANI-Fe₃O₄/SiO₂/TiO₂ photocatalyst could be easily recovered using a magnet.