Wan Jiang

Amorphous TiO2 Shells: A Vital Elastic Buffering Layer on Silicon Nanoparticles for High‐Performance and Safe Lithium Storage

Smart surface coatings of silicon (Si) nanoparticles are shown to be good examples for dramatically improving the cyclability of lithium-ion batteries. Most coating materials, however, face significant challenges, including a low initial Coulombic efficiency, tedious processing, and safety assessment. In this study, a facile sol-gel strategy is demonstrated to synthesize commercial Si nanoparticles encapsulated by amorphous titanium oxide (TiO2 ), with core-shell structures, which show greatly superior electrochemical performance and high-safety lithium storage. The amorphous TiO2 shell (≈3 nm) shows elastic behavior during lithium discharging and charging processes, maintaining high structural integrity. Interestingly, it is found that the amorphous TiO2 shells offer superior buffering properties compared to crystalline TiO2 layers for unprecedented cycling stability. Moreover, accelerating rate calorimetry testing reveals that the TiO2 -encapsulated Si nanoparticles are safer than conventional carbon-coated Si-based anodes.

Preparation and thermoelectric properties of multi-walled carbon nanotube/polyaniline hybrid nanocomposites

In this work, a facile strategy for the fabrication of PANI/multi-walled carbon nanotube (MWCNT) nanocomposites without the assistance of a dispersant is introduced. MWCNTs and polyaniline were homogeneously mixed by cryogenic grinding (CG) and then consolidated via Spark Plasma Sintering (SPS). X-ray power diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and field-emission scanning electron microscopy (FESEM) were employed to characterize the as-prepared composites. The XRD results showed that cryogenic grinding can refine the grain size of PANI and induce more dislocations. The FTIR spectra data showed that the peaks of the PANI/MWNT composites displayed a red shift. In the high resolution FESEM image, the layer-by-layer structure and smooth surface can be observed. The thermoelectric properties of the as-prepared nanocomposites were investigated as a function of MWCNT content. The results showed that the electrical conductivity increased remarkably with the increasing MWCNT content, and the maximum power factor was 10.73 × 10−8 W mK−2, higher than pure PANI. Additionally, as the MWNT content increased from 10% to 30%, the electrical conductivity of the PANI/MWNT composite increased from 3.51 S m−1 to 1.59 × 102 S m−1. This work demonstrates a simple and effective method for improving the dispersity of carbon nanotubes and the thermoelectric properties of conducting polymers.

A Micelle Fusion–Aggregation Assembly Approach to Mesoporous Carbon Materials with Rich Active Sites for Ultrasensitive Ammonia Sensing

Nanostructured carbon materials have received considerable attention due to their special physicochemical properties. Herein, ordered mesoporous carbons (OMCs) with two-dimension (2D) hexagonal mesostructure and unique buckled large mesopores have successfully been synthesized via a micelle fusion-aggregation assembly method by using poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymers as a template and resorcinol-based phenolic resin as a carbon precursor. The obtained ordered mesoporous carbons possess unique fiber-like morphology, specific surface area of 571-880 m(2)/g, pore volume of 0.54 cm(3)/g and large mesopores (up to 36.3 nm) and high density of active sites (i.e., carboxylic groups) of 0.188/nm(2). Gas sensor based on the ordered mesoporous carbons exhibits an excellent performance in sensing NH3 at a low temperature with fast response (<2 min), ultralow limit of detection (<1 ppm), and good selectivity, due to the large pore sizes, high surface area and rich active sites in the carbon pore walls.

One-pot fabrication and thermoelectric properties of Ag nanoparticles–polyaniline hybrid nanocomposites

In this context, a one-pot and in situ strategy for fabrication of AgNPs (Ag nanoparticles)/PANI (polyaniline) nanocomposites in a micellar solution of dodecylbenzene sulfonic acid (DBSA, anionic surfactant) is introduced. Guided by this strategy, AgNPs were directly synthesized from silver nitrate. AgNPs/PANI hybrid nanocomposites with AgNPs were consolidated via spark plasma sintering (SPS). The phase structure and microstructure of the as-prepared composites were evaluated by several characterizations, and the growth mechanism of AgNPs was speculated. The thermoelectric properties of the samples with increasing silver nitrate content were systematically investigated. Compared with pure bulk PANI, the thermoelectric performance of AgNPs/PANI hybrid nanocomposites exhibits a distinct enhancement on the addition of AgNPs. The Seebeck coefficient (S) decreased slightly while the electric conductivity (σ) was found to increase remarkably. However, thermal conductivity (κ) remained unchanged with increasing silver nitrate content, which resulted in an obvious enhancement in the figure of merit (ZT) of the composites. Consequently, the maximum ZT of the AgNPs/PANI hybrid nanocomposites amazingly reached 5.73 × 10−5, which is about 3.8 times of the ZT of the pure PANI (1.503 × 10−5). This study suggests that the hybridization of organic/low-dimensional metal particles is promising to effectively improve the thermoelectric properties of conducting polymers.

Third-order nonlinear optical vitreous material derived from mesoporous silica incorporated with Au nanoparticles

Mesoporous silica SBA-15 encapsulated with Au nanoparticles was consolidated by spark plasma sintering. It turned out to be an original and facile preparation route for incorporating Au nanoparticles in silica glass. The incorporation of Au nanoparticles in a silica glass matrix made the obtained glass coloured dark wine-red due to the surface plasmon resonance effect of Au nanoparticles, although the concentration of Au nanoparticles was extremely low (about 0.05 wt%). Besides, the Z-scan method using a femtosecond laser pulse was employed to measure the nonlinear optical property of this mesoporous composite-derived glass, which exhibited self-focusing feature at 720 nm with saturable absorption. The third-order nonlinear refraction index n2 and absorption coefficient β were 1.74 × 10−18 m2 W−1 and −5.72 × 10−12 m W−1, respectively. We believe that this approach could be extended to disperse other metal or semiconductor nanoparticles in a glass matrix.

Hierarchical ordered macro/mesoporous titania with a highly interconnected porous structure for efficient photocatalysis

In this study, a 3-dimensional interconnected hierarchical ordered macro/mesoporous titania (HOPT) with thin walls, crystalline framework, large cavities (∼420 nm), uniform mesopores (3.7 nm) and high surface area (177 m2 g−1) was synthesized through a facile bi-template interface-directed deposition method using poly(propylene oxide)-block-poly(ethylene oxide)-block-poly(propylene oxide) (Pluronic P123) triblock polymer as a soft template and structure directing agent, titanium isopropoxide (TIPO) as a titania source and 3-dimensional ordered macroporous carbon (3DOMC) as the hard template and the nanoreactor. This was followed with a two-step thermal treatment in nitrogen and air. Under simulated sunlight irradiation at room temperature, the HOPT shows an ultrahigh photocatalytic activity for the degradation of Rhodamine B (RhB) with a fast reaction rate that is three times higher than commercial titania nanoparticles (P25).

Preparation of Graphene Nanosheet/Alumina Composites

Graphene nanosheet (GNS)/ Al2O3 composite powder with homogeneously distributed GNSs has been fabricated from wet ball milled expanded graphite and Al2O3, and then followed by the rotary evaporator at relatively low temperature to dry the mixture and the residual solvent was removed in atmosphere-vacuum pipe-type furnace accessing mixed gases of Argon and Hydrogen at 600 for 6h. During the process, homogeneously dispersed and mixed GNS/ Al2O3 composite powders with quite few damage of GNSs structure and properties have been obtained. The microstructures and grain sizes of GNS/ Al2O3 composite powders have been investigated. The results showed that the addition of GNSs had diminished the size of Al2O3 particles and also the as-prepared GNSs/ Al2O3 composite powders can be dispersed and mixed more homogeneously remarkably with the presence of GNSs.

Effects of Polarization on Mechanical Properties of Lead Zirconate Titanate Ceramics Evaluated by Modified Small Punch Tests

Pb(Zr,Ti)O3 (PZT) ceramics were prepared by the conventional mixed oxide method, and the strength of the resultant PZT ceramics was evaluated using modified small punch (MSP) tests. Load–displacement curve test results showed that the crack-initiation and fracture strengths of PZT ceramics decreased after polarization. The effect of the polarization accelerated the fatigue properties of PZT ceramics. Scanning electron microscopy (SEM) results showed that microcracks were formed before the maximum load in the MSP test, and the first load drop corresponded to crack initiation.

Preparation of TiB2/TiN Nanocomposites by SP

TiB2/TiN nanocomposites were in-situ fabricated by spark plasma sintering (SPS) technique using Ti and BN powders as starting materials. The phase constituents and microstructures of the samples were analyzed by X-ray diffraction (XRD) techniques, scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results showed that the average grain size of TiB2 and TiN was 1m and 300nm respectively. Furthermore, high resolution TEM analysis indicated that the as-prepared TiB2/TiN nanocomposites had very clean grain boundaries, and no amorphous phase or oxide layer was observed.

Comparison of the Luminescence Properties of PbS Quantum Dots Prepared by Different Methods

PbS quantum dots (QDs) were prepared through a two-phase approach and an aqueous method respectively. The reaction conditions of the two-phase approach were mild and highly controllable, but the as-prepared QDs were capped with oleic acid. Although the PbS QDs prepared by the aqueous method did not exhibit excellent photoluminescence properties, it was more facile and environmentally friendly, and furthermore the resulting PbS QDs were more promising in biological labeling without ligand exchange. We have investigated the absorption and luminescent properties of QDs prepared by the two methods. The results showed that the absorption shoulder of oil soluble PbS QDs was at 580nm and water soluble PbS QDs was at 600~700nm. And the emission peaks in the photoluminescence spectra were at 755nm and 970nm, respectively. XRD analysis confirmed that the PbS QDs were cubic phase. The TEM results showed that the size of both types of PbS QDs was smaller than the excitons Bohr radius (18nm).