Chun Wei

Perpendicularly oriented few-layer MoSe2 on SnO2 nanotubes for efficient hydrogen evolution reaction

Maximizing the number of exposed active edges in newly emerged two-dimensional few-layer MoSe2 nanostructures is a key issue to fully realize the excellent electrochemical properties of MoSe2. In this work, a SnO2@MoSe2 nanostructure was successfully fabricated through a facile electrospinning technique combined with sintering and a solvothermal method. This rationally designed hierarchical architecture has perpendicularly oriented few-layered MoSe2 nanosheets uniformly and fully covering both inner and outer surfaces of SnO2 nanotubes, which exhibits excellent electrochemical activity as a hydrogen evolution reaction (HER) catalyst with a small onset potential of −0.11 V vs. reversible hydrogen electrode (RHE) and a small Tafel slope of 51 mV per decade. This excellent performance may originate from the unique hierarchical tubular structure with fully exposed active edges and open spaces for fast electron/electrolyte transfer, enabling their potential to replace Pt as a future electrocatalyst in HER.

Multihydroxy Dendritic Upconversion Nanoparticles with Enhanced Water Dispersibility and Surface Functionality for Bioimaging

Upconversion nanoparticle (UCNP) as a new class of imaging agent is gaining prominence because of its unique optical properties. An ideal UCNP for bioimaging should simultaneously possess fine water dispersibility and favorable functional groups. In this paper, we present a simple but effective method to the synthesis of a UCNP-based nanohybrid bearing a multihydroxy hyperbranched polyglycerol (HPG) shell by the combination of a grafting from strategy with a ring-opening polymerization technique. The structure and morphology of the resulting UCNP-g-HPG nanohybrid were characterized in detail by Fourier transform infrared, (1)H NMR, thermogravimetric analysis, and transmission electron microscopy measurements. The results reveal that the amount of grafted HPG associated with the thickness of the HPG shell can be well tuned. UCNP-g-HPG shows high water dispersibility and strong and stable upconversion luminescence. On the basis of its numerous surface hydroxyl groups, UCNP-g-HPG can be tailored by a representative fluorescent dye rhodamine B to afford a UCNP-g-HPG-RB nanohybrid that simultaneously presents upconversion and downconversion luminescence. Preliminary biological studies demonstrate that UCNP-g-HPG shows low cytotoxicity, high luminescent contrast, and deep light penetration depth, posing promising potential for bioimaging applications.

Polydopamine-derived porous carbon fiber/cobalt composites for efficient oxygen reduction reactions

Dopamine is an excellent and flexible agent for surface coating of various materials, with the high-concentration of amine groups serving as a facile stabilizer for some metallic nanoparticles. In this work, mesoporous composites of nitrogen-doped carbon fibers (NCFs) decorated with cobalt nanoparticles have been successfully fabricated via the combination of a mussel-inspired biomimetic polydopamine (PDA)-coating process using electrospun porous polystyrene fibers as templates, a simple solution deposition method and subsequent high-temperature carbonization. This rationally designed porous NCF–Co composite possesses a large surface area and numerous electrochemically active sites, which exhibits synergistically improved catalytic activity for oxygen reduction reactions (ORRs) with a relatively positive onset potential, large current density, as well as superior durability compared with the commercial platinum–carbon (Pt/C) catalyst, making it a promising noble-metal-free catalyst for practical ORR applications.

Study of Pickering emulsion stabilized by sulfonated cellulose nanowhiskers extracted from sisal fiber

Sulfonated cellulose nanowhiskers (sulfonated CNWs), a kind of needle-like colloidal particles, could be obtained through sulfuric acid hydrolysis of microcrystal cellulose extracted from sisal fibers. Here, stable Pickering emulsions were prepared using the sulfonated CNWs as a stabilizer. The effects of the sulfonated CNW concentration in aqueous phase, volume ratio of water to oil, oil type, and the pH value on the stability, type, and morphology of these emulsions were investigated. The average droplet size decreases with increasing sulfonated CNW concentration and volume ratio of water to oil. Many types of oil phase were stabilized by sulfonated CNWs to form stable oil-in-water (o/w) Pickering emulsion only by adjusting the pH value of water phase. In addition, poly(methyl methacrylate)PMMA/sulfnated CNW composite microspheres were fabricated by solvent volatilization of the as-prepared Pickering emulsion. Confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) studies confirmed that sulfonated CNWs adsorbed on the surface of the PMMA microparticles. With the interesting renewability and biodegradability of the sulfonated cellulose nanowhisker, these PMMA@sulfonated CNW composite microsphere could find great potential application in food, cosmetics, drug delivery, and biological tissue engineering, etc.

Synergistic effect of carbon nanotubes and layered double hydroxides on the mechanical reinforcement of nylon-6 nanocomposites

Synergistic effect in network formation of nylon-6 (PA6) nanocomposites containing one dimensional (1D) multi-walled carbon nanotubes (CNTs) and two dimensional (2D) layered double hydroxide (LDH) platelets on improving the mechanical properties has been studied. Mechanical tests show that, with incorporation of 1 wt% LDHs and 0.5 wt% CNTs, the tensile modulus, the yield strength as well as the hardness of the ternary composite are greatly improved by about 230%, 128% and 110% respectively, as compared with neat PA6. This is mainly attributed to the unique, strong interactions between the CNTs and the LDHs as well as the jammed network-like structure thus formed between the nanofillers, as confirmed by the morphological observations. As compared with the binary nanocomposites, a much enhanced solid-like behavior in the terminal region of the rheological curves can clearly be observed for the ternary system, which also indicates the formation of a percolating filler network.

Thermal and frictional properties of modified sisal fibre/phenolic resin composites

Abstract In order to enhance the bonding force of sisal fibres (SF) and polymer matrix, different surface modifiers (alkali, coupling agent and borax) were used to treat the fibres. The SF/phenol formaldehyde (PF) resin composites were prepared through compression moulding. Thermal properties of the treated SFs and fibre composites were studied by thermogravimetric analysis and thermal expansion analysis. The effect of SF modification on the friction and wear properties of composites was investigated using wear tester under dry condition. The treated fibre surface and the worn surfaces of SF/PF composites were observed by SEM. The results showed that the surface of SF became rough after borax treatment, and the initial decomposition temperature increased by 13·6°C, compared to untreated SF. Thermal stability and wear properties of the PF composites with treated fibre were obviously increased due to the fibre modification. For example, wear volume of the composites with sisal treated by borax decreased by 73·3%. Scanning electron microscopy photos showed that the wear mechanism changed from fatigue wear to slight plough wear.

Synthesis and characterization of organosoluble, transparent, and hydrophobic fluorinated polyimides derived from 3,3′-diisopropyl-4,4′-diaminodiphenyl-4′′-trifluoromethyltoluene

A novel aromatic fluorinated diamine monomer, 3,3′-diisopropyl-4,4′-diaminodiphenyl-4′′-trifluoromethyltoluene, was synthesized by coupling of 2-isopropylaniline and 4-(trifluoromethyl)benzaldehyde and its structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, elemental analysis, and mass spectrometry, and then used to prepare a series of fluorinated polyimides (FPIs) by polycondensation reaction with various commercial dianhydrides via conventional one-step method. The obtained FPIs present excellent solubility in most organic solvents and enough to cast into tough and flexible films. All the FPI films show good optical transparency and light color with the cutoff wavelengths in range of 307–362 nm and the average transmittance above 86%. These polymer films also exhibit high glass transition temperature in range of 261–331°C and thermal stability with 10% weigh loss above 463°C under nitrogen atmosphere. Furthermore, they exhibit outstanding mechanical properties with tensile strengths of 65.9–94.3 MPa, elongation at break of 11.4–13.8%, Young’s modulus of 1.6–1.9 GPa, and low dielectric constants in range of 2.75–3.10 at 1 MHz as well as prominent hydrophobicity with the contact angle in the range of 87.3–93.9°.

Studies on crystal transition of polyamide 11 nanocomposites by variable-temperature X-ray diffraction

Polyamide 11 (PA11) and its nanocomposites with different organoclay loadings were prepared by melt-compounding and subsequent pelletizing. The crystal phase transitions of PA11 and its clay nanocomposites were investigated by variable-temperature X-ray diffraction. It was found that the Brill transition of the nanocomposite was 20 K higher than that of the neat PA11 for both heating and cooling processes. The PA11 d-spacings of the nanocomposites were observed to be smaller than those of the neat PA11 for melt crystallization. The constraints imposed by the addition of layered clay, restricting the thermal expansion of the polymer chains, are probably responsible for such a reduction of the d-spacing.

Preparation, characterization, and properties of in situ formed graphene oxide/phenol formaldehyde nanocomposites

Graphene oxide (GO) has shown great potential to be used as fillers to develop polymer nanocomposites for important applications due to their special 2D geometrical structure as well as their outstanding mechanical, thermal, and electrical properties. In this work, GO was incorporated into phenol formaldehyde (PF) resin by in situ polymerization. The morphologies and structures of GO sheets were characterized by FTIR, XRD, and AFM methods. The structure and properties of the GO/PF nanocomposites were characterized using FTIR, XRD, DSC, and TGA methods. Effects of GO content, reactive conditions, and blending methods on the structure and properties of GO/PF nanocomposites were studied. It was found that due to the well dispersion of GO sheets in polymer matrix and the strong interfacial interaction between the GO sheets and PF matrix, the thermal stability and thermal mechanical properties of the GO/PF nanocomposites were greatly enhanced.

Aromatic polyimides with tertbutyl-substituted and pendent naphthalene units: synthesis and soluble, transparent properties

A novel non-coplanar aromatic diamine monomer, 3,3′-ditertbutyl-4,4′-diaminodiphenyl-4″-naphthylmethane (TAPN) was synthesized by a condensation reaction of 2-tertbutylaniline and 1-naphthaldehyde under catalyst hydrochloric acid. The structure of the monomer was confirmed by FTIR, NMR, elementary analysis and mass spectrometry. A series of aromatic polyimides (PIs) were synthesized via conventional one-step polycondensation from TAPN and various commercial aromatic dianhydrides. All of the PIs exhibit excellent solubility in common organic solvents, even in low boiling point solvents such as chloroform (CHCl3), tetrahydrofuran (THF) and acetone. The PIs present outstanding thermal stability with the glass transition temperature (Tg) ranged from 299 °C to 350 °C, and the temperature at 10% weight loss ranged from 490 °C to 504 °C, and high optical transparency with the cutoff wavelengths of 306–356 nm. Moreover, the flexible and tough PI films have prominent mechanical properties with tensile strengths in the range of 77.6–90.5 MPa, tensile modulus in the range of 1.8–2.4 GPa and elongation at break in the range of 6.3%–9.5%, as well as lower dielectric constant (2.89–3.12 at 1 MHz) and lower moisture absorption (0.35%–0.66%).