Fabrication of Core-Shell Nanoparticles

Metallic Cu and Au shells were fabricated around cobalt nanoparticles. A new technique to coat nanoparticles with carbon coatings and poly(methyl methacrylate) (PMMA) was developed. The copper shell formation is a self-limiting process. A thin copper shell (0.82 nm) around the cobalt nanoparticle (1.56 nm) enhanced the magnetic property by increasing the blocking temperature from 124 K to 235 K for nanoparticles with a copper shell. The formed gold shell (0.67 nm) enhanced the cobalt nanoparticle magnetic property by increasing the blocking temperature above room temperature. The magnetic moment in the Co-Cu and Co-Au core-shell nanoparticle is much higher than that of the pure cobalt nanoparticle. However, the copper shell (2.88 nm) around the FeCo alloy nanoparticle (0.87 nm) was fabricated and found to decrease the blocking temperature to 126 K. Complete displacement of Fe nanoparticle by copper ions was observed with a loss of the magnetic property. The electrochemical reaction rate was used to estimate the reaction rate in aqueous solutions between the cobalt, or iron nanoparticle, and the copper ions and was found to be similar: 0.0015 A/cm2 and 0.0022 A/cm2 for the Co-Cu and Fe-Cu systems. The annealing process has a dramatic effect on the behavior of the nanoparticles. The sizes were increased in all the nanoparticles, as expected. A phase change (from fcc to hcp) was found in the cobalt nanoparticles as the annealing temperature increased. Phase segregation and partial oxidation of the FeCo alloy nanoparticle under the annealing process was observed. A tight carbon shell was formed around the iron nanoparticle and protected the iron nanoparticle from oxidation in acid. Fe-C core-shell nanoparticles retained the magnetic property (i.e. saturation magnetization and coercivity) after exposure to acid. A resistance change with a variation of magnetic field is referred to as magnetoresistance (MR). Magnetoresistance was observed in the pressed Co-Au core-shell pellet. Both the fresh Co-Au and annealed core-shell nanoparticle followed the metallic conduction behavior. No MR was observed in the Co-Cu and FeCo-Cu core-shell nanoparticles

Reinforcement of Cu Nanoink Film with Extended Carbon Nanofibers for Large Deformation of Printed Electronics

poster abstractMetallic nanoparticle inks (nanoinks) have attracted great interest in the manufacturing of printed flexible electronics. However, micro-cracks and pores generated during the sintering process deteriorate mechanical and electrical characteristics of the sintered nanoink film. To alleviate these problems, we demonstrated the use of very long carbon nanofiber (CNF, average length 200 μm) to reinforce the sintered nanoink films. In this study, different weight fractions of CNFs are dispersed into the Cu nanoink to improve the mechanical bending characteristics. Scanning electron micrographs (SEM) shows improved dispersion of oxidized CNF in the nanoink compared to the as-received CNF. The composite nanoinks are stencil printed on polyethylene terephthalate (PET) film and sintered by intense pulsed light system using Xe-flash. The electrical measurements show 90 %, 65 %, and 66 % improved electrical conductivity in the composite nanoink film (0.7 % of oxidized CNF) compared to the pure Cu nanoink under the 75 mm, 50 mm, and 25 mm of bending radii, respectively

Lightweight conductive graphene/thermoplastic polyurethane foams with ultrahigh compressibility for piezoresistive sensing

Lightweight conductive porous graphene/thermoplastic polyurethane (TPU) foams with ultrahigh compressibility were successfully fabricated by using the thermal induced phase separation (TISP) technique. The density and porosity of the foams were calculated to be about 0.11 g cm−3 and 90% owing to the porous structure. Compared with pure TPU foams, the addition of graphene could effectively increase the thickness of the cell wall and hinder the formation of small holes, leading to a robust porous structure with excellent compression property. Meanwhile, the cell walls with small holes and a dendritic structure were observed due to the flexibility of graphene, endowing the foam with special positive piezoresistive behaviors and peculiar response patterns with a deflection point during the cyclic compression. This could effectively enhance the identifiability of external compression strain when used as piezoresistive sensors. In addition, larger compression sensitivity was achieved at a higher compression rate. Due to high porosity and good elasticity of TPU, the conductive foams demonstrated good compressibility and stable piezoresistive sensing signals at a strain of up to 90%. During the cyclic piezoresistive sensing test under different compression strains, the conductive foam exhibited good recoverability and reproducibility after the stabilization of cyclic loading. All these suggest that the fabricated conductive foam possesses great potential to be used as lightweight, flexible, highly sensitive, and stable piezoresistive sensors

Flexible polydimethylsiloxane/multi-walled carbon nanotubes membranous metacomposites with negative permittivity

Metacomposites with negative electromagnetic parameters can be promising substitute for periodic metamaterials. In this paper, we devoted to fabricating flexible metacomposite films, which have great potential applications in the field of wearable cloaks, sensing, perfect absorption and stretchable electronic devices. The conductivity and the complex permittivity were investigated in flexible polydimethylsiloxane (PDMS)/multi-walled carbon nanotubes (MWCNTs) membranous nanocomposites, which were fabricated via in-situ polymerization process. With the increase of conductive one-dimension carbon nanotubes concentration, there was a percolation transition observed in conduction due to the formation of continuous networks. The dielectric dispersion behavior was also analyzed in the spectra of complex permittivity. It is indicated that the conduction and polarization make a combined effect on the dielectric loss in flexible PDMS/MWCNTs composites. The negative permittivity with a dielectric resonance was obtained, and was attributed to the induced electric dipoles

Ionic liquid-assisted synthesis of Yb3+-Tm3+ codoped Y7O6F9 petal shaped microcrystals with enhanced upconversion emission

Petal-like Yb3+-Tm3+ codoped Y7O6F9 microparticles were achieved via ionic liquid-assisted (IL) hydrothermal process. The emission efficiency of Y7O6F9:Yb3+/Tm3+ powders is much stronger than that of Y2O3:Yb3+/Tm3+ sample. Under excitation at 980 nm with an unfocused laser beam under weak pump density of ∼0.1 W/cm2 (pump power 10 mW), the UC emission of the sample can been seen clearly. Four emission bands at 477, 540, 647 and 692 nm are observed and correspond to the 1G4 state to 3H6 state, 1D2 state to 3H5 state, 1G4 sate to 3F4 state, and 3F3 state to 3H6 state transition of Tm3+ ions. The enhanced UC emission is related to high crystallinity and lower effective phonon energy of oxyfluorides. The ionic liquid (IL) of [BMIM][BF4] is used both as the reaction medium and the source of F−

Electric Vehicle Revolution and Implications: Ion Battery and Energy

As record high heat waves sweep globally, global warming (caused by environmental pollution and greenhouse gas emissions) has turned into the primary concern, which put the non-renewable petrochemical energy and fuel vehicles on the chopping block. The development of new energy electric vehicles (EVs) leading by USA, EU and China has the potential to achieve zero-emissions. The innovation technologies of the corresponding rechargeable ion battery play the keys role. Thus, the EVs have profound impact on traditional energy, vehicles industries and the daily life

Flexible strain sensor enabled by carbon nanotubes-decorated electrospun TPU membrane for human motion monitoring

High-performance flexible strain sensors are gaining more and more attention with their bespoken detection range, excellent sensing performance and good stability, which are highly desired in the wearable electronics. Herein, a thermoplastic polyurethane elastomer (TPU) fibrous membrane was prepared as a flexible substrate by electrostatic spinning technology, then a coating of polydopamine was formed through fast synthesizing the dopamine on TPU fibrous membrane surface and loaded with CNTs to develop an extremely sensitive flexible strain sensor. The flexible sensor prepared by TPU fibrous membrane coated with polydopamine layer has an outstanding sensibility under the pulling force (GF of 10528.53 with 200 strain), rapid reaction time (188-221 ms), wide sensing range (up to 200), good stability and durability. The theoretical studies reveals that the underlying cause for the high sensitivity and the inherit relationship between the amount of conducting routes and the length between adjacent conducting fillers in the sensor. The demonstration of device shows a promising application to sense the human motion at various locations of body, with accurate and stable electrical signal output generated at corresponding motion

One-pot melamine derived nitrogen doped magnetic carbon nanoadsorbents with enhanced chromium removal

Novel nitrogen doped magnetic carbons (NMC), in-situ synthesized through facile pyrolysis-carbonization processes using Fe(NO3)3 and melamine as precursors, were demonstrated as excellent nanoadsorbents to remove Cr(VI) effectively. The achieved removal capacity in both neutral and acidic solution was 29.4 and 2001.4 mg g−1 respectively, much higher than the reported adsorbents so far. The unprecedented high adsorption performance can be attributed to the incorporation of the nitrogen dopant, which increased the negative charge density on the surface of adsorbent and thereby enhanced the interaction between the adsorbents and Cr(VI) ions. The density functional theory (DFT) calculation demonstrated that the nitrogen dopants can decrease the adsorption energy between the Cr(VI) ions and NMC (−3.456 kJ mol−1), lower than the undoped sample (−3.344 kJ mol−1), which boosted the adsorption behavior. Chemical rather than physical adsorption was followed for these magnetic nanoadsorbents as revealed from the pseudo-second-order kinetic study. Furthermore, the NMC showed high stability with recycling tests for the Cr(VI) removal