Huige Wei

Advanced micro/nanocapsules for self-healing smart anticorrosion coatings

Smart self-healing coatings for corrosion protection of metallic substrates (steel, magnesium, and aluminium, and their alloys) have attracted tremendous interest due to their capability to prevent crack propagation in the protective coatings by releasing active agents from micro/nanocapsules, that is, micro/nano particles consisting of a coating layer or a shell (micro/nanocontainers) and core material (solids, droplets of liquids or gases), in a controllable manner. This paper aims to give a concise review on the most recent advances in preparing micro/nanocapsules based on different types of micro/nanocontainers, i.e., organic polymer coatings, inorganic clays, mesoporous silica nanoparticles, polyelectrolyte multilayers, etc. for smart coatings with self-healing properties. The state-of-the-art design and preparation of micro/nanocapsules are highlighted with detailed examples.

Mesoporous magnetic carbon nanocomposite fabrics for highly efficient Cr(VI) removal

We have demonstrated that magnetic carbon nanocomposite fabrics prepared by microwave assisted heating are advanced adsorbents in the removal of Cr(VI) with a much higher removal capacity of 3.74 mg g−1 compared to 0.32 mg g−1 for cotton fabrics and 0.46 mg g−1 for carbon fabrics. The enhanced Cr(VI) removal is attributed to the highly porous structure of the nanocomposites. The adsorption kinetics follow the pseudo-second-order model, which reveals a very large adsorption capacity and high adsorption rate. The removal process takes only 10 min, which is much faster than conventional adsorbents such as activated carbon and biomass that often requires hours of operation. The significantly reduced treatment time and the large adsorption capacity make these nanocomposite fabrics promising for the highly efficient removal of heavy metals from polluted water.

Electrically Conductive Polypropylene Nanocomposites with Negative Permittivity at Low Carbon Nanotube Loading Levels

Polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites were prepared by coating CNTs on the surface of gelated/swollen soft PP pellets. The electrical conductivity (σ) studies revealed a percolation threshold of only 0.3 wt %, and the electrical conductivity mechanism followed a 3-d variable range hopping (VRH) behavior. At lower processing temperature, the CNTs formed the network structure more easily, resulting in a higher σ. The fraction of γ-phase PP increased with increasing the pressing temperature. The CNTs at lower loading (0.1 wt %) served as nucleating sites and promoted the crystallization of PP. The CNTs favored the disentanglement of polymer chains and thus caused an even lower melt viscosity of nanocomposites than that of pure PP. The calculated optical band gap of CNTs was observed to increase with increasing the processing temperature, i.e., 1.55 eV for nanocomposites prepared at 120 °C and 1.70 eV prepared at 160 and 180 °C. Both the Drude model and interband transition phenomenon have been used for theoretical analysis of the real permittivity of the nanocomposites.

Polymer nanocomposites for energy storage, energy saving, and anticorrosion

Polymer nanocomposites exhibit unique physicochemical properties that cannot be obtained with individual components acting alone. Polymer nanocomposites have attracted significant research interests due to their promising potential for versatile applications ranging from environmental remediation, energy storage, electromagnetic (EM) absorption, sensing and actuation, transportation and safety, defense systems, information industry, to novel catalysts, etc. In particular, polymer nanocomposites have attracted intensive research interest for solving both energy and environmental issues. This review paper mainly focuses on the most recent advances in polymer nanocomposites for energy storage (i.e., electrochemical capacitors and batteries), energy saving (i.e., electrochromic devices and carbon dioxide capture), and anticorrosion (conductive and non-conductive polymer nanocomposite anticorrosive coatings) applications.

Anticorrosive conductive polyurethane multiwalled carbon nanotube nanocomposites

Conductive polyurethane (PU) nanocomposite coatings filled with multiwalled carbon nanotubes (MWNTs) fabricated by employing an in situ surface-initiated-polymerization (SIP) method were tested for corrosion prevention of stainless steel (SS). The nanocomposites exhibited a good response of electrical conductivity change to the strain during the cyclic tensile strain test. The anticorrosion properties of these nanocomposite coatings on the SS surface were evaluated in 3.0 wt% NaCl aqueous solution by monitoring the open circuit potential (Eocp) and tracing quasi-stationary polarization (Tafel) of the nanocomposite-coated stainless steel (MWNT/PU–SS) electrode. Electrochemical impedance spectroscopy (EIS) was also obtained to give an insight into the anticorrosion protection of SS. The nanocomposite displayed a good chemical stability over long immersion in a corrosive environment. A significant positive shift of nearly 1.0 V in the Eocp was observed from the Eocp–time curve. Extrapolation of Tafel plots gave a much more positive corrosion potential (Ecorr) and a lower corrosion current (Icorr). A protection efficiency as high as 97.70% was obtained. An equivalent circuit of the coating was proposed to fit the EIS data, confirming an effective corrosion protection for SS. The results indicate that the polyurethane matrix combined with the well dispersed MWNT reinforcements provided a significant physical barrier against the attack of corrosive ions in the solution for SS while providing a channel for the conductivity.

Polyaniline coating on carbon fiber fabrics for improved hexavalent chromium removal

Carbon fabrics (CFs) loaded with 5.0, 10.0, 15.0 and 20.0 wt% polyaniline (PANI) (PANI/CF) prepared by soaking carbon fiber fabrics in 1.0 wt% PANI m-cresol solution have demonstrated superior hexavalent chromium (Cr(VI)) removal performance compared to the as-received CFs. The PANI/CF nanocomposites were noticed to remove Cr(VI) from solutions with an initial Cr(VI) concentration of 1.0 mg L-1 within 15 min, which is faster than the conventional active carbon (6 h) and the as-received CFs (>1 h). A better Cr(VI) removal efficiency was observed in the acidic solutions than in the basic solutions. A pseudo-second-order behavior was justified for the PANI/CF with a much higher removal rate (0.06 g mg-1 min-1) than the reported ~0.03 g mg-1 min-1 for the active carbon. The adsorption isotherm study demonstrated that the adsorbents follow the Langmuir model with a calculated maximum adsorption capacity of 18.1 mg g-1 for the 10.0 wt% PANI/CF. The Cr(VI) removal mechanisms explored by FT-IR and XPS involve the reduction of Cr(VI) to Cr(III) by PANI. The PANI/CF adsorbents have demonstrated easy recycling capability for up to five cycles with a Cr(VI) removal rate at above 91%.

Polypyrrole doped epoxy resin nanocomposites with enhanced mechanical properties and reduced flammability

For the liquid epoxy nanosuspensions with both fibril and spherical polypyrrole (PPy) nanostructures, a stronger PPy nanofibers/epoxy interaction and more temperature stable behavior with a lower flow activation energy of nanosuspensions with nanofibers (54.34 kJ mol−1) than that with nanospheres (71.15 kJ mol−1) were revealed by rheological studies. As well as the common enhancing mechanism of limiting crack propagation in the polymer matrix, the nanofibers further initiated the shear bands in the epoxy resin to give a higher tensile strength (90.36 MPa) than that of pure epoxy (70.03 MPa) and even that of the epoxy nanocomposites with nanospheres (84.53 MPa). With a larger specific surface area, the nanofibers rather than nanospheres were observed to reduce the flammability of epoxy more efficiently by assisting more char formation of the epoxy resin. The hydroxyl groups formed between the protons of the doped acid in the PPy nanofillers and the epoxy broke the conjugate structure of PPy, leading to a higher bandgap in the nanocomposites (Eg1 = 3.08 eV for 1.0 wt% PPy nanofibers) than that of pure nanofillers (1.8 eV for PPy nanofibers and 1.2 eV for PPy nanospheres). Due to the high aspect ratio, the PPy nanofibers could form the conductive path more easily than the PPy nanospheres to provide a lower percolation threshold value. The real permittivity was observed to increase with increasing the PPy nanofiller loading, and the enhanced permittivity was interpreted by the interfacial polarization.

Strengthened Magnetoresistive Epoxy Nanocomposite Papers Derived from Synergistic Nanomagnetite-Carbon Nanofiber Nanohybrids.

Novel papers based on epoxy nanocomposites with magnetite and carbon nanofiber (CNF) nanohybrids, without any surface modification to the nanofillers, show combined conductive, magnetic, and magnetoresistive properties. Negative magnetoresistance (MR) is observed in synthesized epoxy nanohybrid papers for the first time. These papers have potential applications for flexible electronics, magnetoresistive sensors, and the printing industry.

Multifunctional Carbon Nanostructures for Advanced Energy Storage Applications

Carbon nanostructures—including graphene, fullerenes, etc.—have found applications in a number of areas synergistically with a number of other materials.These multifunctional carbon nanostructures have recently attracted tremendous interest for energy storage applications due to their large aspect ratios, specific surface areas, and electrical conductivity. This succinct review aims to report on the recent advances in energy storage applications involving these multifunctional carbon nanostructures. The advanced design and testing of multifunctional carbon nanostructures for energy storage applications—specifically, electrochemical capacitors, lithium ion batteries, and fuel cells—are emphasized with comprehensive examples.

Electropolymerized polyaniline/manganese iron oxide hybrids with an enhanced color switching response and electrochemical energy storage

Polyaniline (PANI) nanocomposites embedded with manganese iron oxide (MnFe2O4) nanoparticles were prepared as thin films by electropolymerizing aniline monomers onto indium tin oxide (ITO) glass slides pre-spin-coated with MnFe2O4 nanoparticles. The shift of the characteristic peaks of PANI/MnFe2O4 in UV-visible absorption spectra and Fourier transform infrared (FT-IR) spectra indicates the formation of composite films and the chemical interaction between the PANI matrix and MnFe2O4 particles. A coloration efficiency of 92.31 cm2 C−1 was obtained for the PANI/MnFe2O4 nanocomposite film, higher than that of the pristine PANI film, 80.13 cm2 C−1, suggesting a synergistic effect between the MnFe2O4 particles and the PANI matrix. An enhanced areal capacitance of 4.46 mF cm−2 was also achieved in the PANI/MnFe2O4 nanocomposite film compared with 3.95 mF cm−2 in the pristine PANI film by CV at a scan rate of 5 mV s−1. The enhanced performances of the composite films were attributed to the pseudocapacitive properties of MnFe2O4 and rougher morphology caused by the embedment of MnFe2O4 particles into the PANI matrix. Finally, the sulfuric acid (H2SO4) concentration and temperature effects on the supercapacitive behavior of the pristine PANI and PANI/MnFe2O4 nanocomposite films were studied, suggesting the positive effects of decreasing H2SO4 concentration and increasing temperature in a low temperature range; higher temperatures can destroy the PANI structure and cause the degradation of PANI.