Tuning fermi level and band gap in Li4Ti5O12 by doping and vacancy for ultrafast Li+ insertion/extraction

Li₄T_i5O₁₂ (LTO) attracts great interest due to the “zero strain” during cycles but the poor electronic and ionic conductivity critically impede the practical application. Herein, we report a synergy strategy of tuning localized electrons to shift Fermi level and band gap by Mg/Zr co-doping and oxygen vacancy incorporation, which significantly improves Li⁺ and electronic transport. More importantly, the intrinsic synergistic mechanism has been revealed by neutron diffraction, X-ray absorption spectra, and first-principles calculations. The “elastic effect” of lattice induced by Mg/Zr co-doping allows LTO to accommodate more oxygen vacancies to a certain degree without a severe lattice distortion, which largely improves the electronic conductivity. Mg/Zr co-doping and oxygen vacancy incorporation effectively enhanced the dynamic characteristics of LTO electrode, achieving the excellent rate performance (90 mAh/g at 20C) and cycle stability (96.9% after 500 cycles at 10C). First-principles calculations confirm Fermi level shifts to the conduction band, and the band gap becomes narrowed due to the synergistic modulation, and the intrinsic mechanism of the enhanced electronic and Li-ion conductivity is clarified. This study offers some insights into achieving the fast Li⁺ insertion/extraction by tuning the crystal and electronic structure with lattice doping and oxygen vacancy engineering.     

Polyethylenimine-modified sugarcane bagasse cellulose as an effective adsorbent for removing Cu(II) from aqueous solution

Polyethylenimine-modified sugarcane bagasse cellulose (SBCMP), as a new adsorbent, was synthesized by the reaction of polyethylenimine (PEI) with sugarcane bagasse cellulose and glutaraldehyde. The adsorption of Cu(II) by SBCMP was pH-dependent, and the higher removal efficiency of Cu(II) appeared in the range of pH 3.0–6.0. The adsorption isothermal data fitted well with the Langmuir model, and the maximum adsorption capacity of SBCMP was up to 107.5 mg/g. The adsorption kinetics was best described by the pseudo-second-order kinetic. The adsorption of Cu(II) by SBCMP was unfavorable at high temperatures, and thermodynamic analyses implied that the adsorption of Cu(II) by SBCMP was an exothermic reaction. Fourier transform infrared spectroscopy (FT-IR) combined with X-ray photoelectron spectroscopy (XPS) revealed that Cu(II) adsorption on SBCMP mainly controlled by the nitrogen atoms of  NH group in PEI. The results of regeneration cycles showed that SBCMP was suitable for reuse in the adsorption of Cu(II) from aqueous solution. These experimental results suggested that SBCMP is expected to be a new biomass adsorbent with high efficiency in removing Cu(II) from wastewater.     

Effect of special structure of clam shell powder on structure and properties of castor oil-based composites

Castor oil (CO) is an environmentally friendly renewable green resource and ideal alternative to petroleum resources. The preparation of high strength and high toughness castor oil-based polyurethane prepolymer (COPU) composites has significant applications such as supporting material and engineering plastic sheet. In this study, unmodified clam shell powder (CSP) with a unique CaCO₃-proteoglycan structure was used as a filler to prepare compatible reinforced COPU composite materials. Investigation of the mechanical properties revealed that the elastic modulus of the composite COPU reinforced with 50 wt% of CSP had increased to 5859.0 ± 8.4 MPa representing 187.77% to obtain stiffer and stronger material over pure COPU (2036.6 ± 196.9 MPa). Moreover, the scanning electron microscopy, thermogravimetric analysis and contact angle results demonstrated that the reinforced COPU composites have better compatibility, thermal stability, and water resistance than pure COPU. This work will promote the application prospects of CO-based polyurethane.     

Study on performance characteristics of fused deposition modeling 3D-printed composites by blending and lamination

Component contacting degree in a composite material is an important reference for evaluation the performance characteristics. In this article, two composite material systems involving polylactic acid (PLA) with acrylonitrile butadiene styrene (ABS) and PLA with thermoplastic polyurethane (TPU) were prepared by blending and laminating through fused deposition modeling (FDM) 3D printing technology. The mechanical and thermal properties of the as-prepared composite materials were examined. The results indicated that PLA and TPU played a dominant role in tensile strength and breaking elongation, respectively, in individual composite material. ABS and TPU changed the glass transition peek, crystallinity, and modulus of PLA. The results also suggested that although the processing design of the blending method was more suitable for the contact between two components, but the mechanical properties of laminated composites were closer to theoretical predictions. The structural design and processing technology provide a comparative method and reference basis for studying the performance characteristics of composite materials.     

Enhancing flame retardant and antistatic properties of polyamide 6 by a grafted multiwall carbon nanotubes

In order to improve the flame retardancy and antistatic properties of polyamide 6 (PA6) at as low amount of additives as possible, an integrated-functional additive was synthesized by 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and multiwalled carbon nanotubes (MWCNTs). The results showed 2 wt% of DOPO-MWCNTs distributed in PA6 formed an electric network and decreased volume resistivity sharply to 3.1 × 10⁸ Ω cm. In other words, it helped PA6 to get to the percolation threshold of semiconductor. By using of 3 wt% DOPO-MWCNTs, the severe dripping in burning of PA6 was almost controlled. The possible reason was also ascribed to the network formed by evenly dispersed DOPO-MWCNTs, which strengthened the char structure and held severe dripping of PA6. As a result, the heat and smoke release were also suppressed obviously. The most important is that CO release was about half cut in CONE test.     

Structure and properties of bio-based polyurethane coatings for controlled-release fertilizer

Two kinds of bio-based polyurethane coatings for controlled-release urea were prepared by in-situ polymerization used castor oil and liquefied starch as raw materials, respectively. Scanning electron microscopy (SEM) showed that the section morphology of castor oil based polyurethane (Castor-PU) coating was uniform and dense, and that of liquefied starch based polyurethane (Starch-PU) coating had certain proportion of microporous. Infrared spectroscopy (IR) showed that the two coatings had typical urethane characteristic structure, but the difference was that the Starch-PU had obvious unreacted isocyanate structure. Differential scanning calorimetry (DSC) showed that the glass transition temperature of the two coatings was around 58°C, but the Castor-PU had a crystallization domain with obvious crystallization melting peak at 130°C. Thermogravimetric analysis (TG) showed that the thermal stability of Castor-PU was significantly higher than that of Starch-PU. The controlled-release property test showed that when the coating ratio was 2.8%, the nutrient release longevity of urea coated with Castor-PU was 49 days and that of urea coated with Starch-PU was 14 days. The reasons for the poor controlled-release performance of Starch-PU were analyzed, which probably caused by concentrated sulfuric acid and hydrophilic dispersant added in the liquefied starch.     

Atomistic simulations of functionalization of aramid fiber-epoxy nanocomposite

Owing to its high degree of crystallinity and orientation, the surface of aramid fiber is smooth, causing its low bonding strength with polymer matrix. This has restricted the application of aramid fiber in reinforced polymer materials. Effective methods are by introducing functional groups through surface modification and by increasing its surface roughness thereby greatly improving its bonding strength with the polymer. In this work, molecular dynamics (MD) simulation study fiber functionalized with hydroxyl (OH), carboxyl (COOH), and the silane coupling agent as nanofillers for polymer nanocomposites. The interfacial characteristics and the mechanical behavior of polymer nanocomposites are investigated. The results show that the functionalization can enhance the interfacial shear stress and tensile strength. The functional group not only provides a stronger interface, but also provides additional mechanical interlocking effect, which effectively improves load-bearing transmission capacity. The analysis of the micro-mechanism from the energy level also provides new insights for the functionalized design of nanocomposites.     

Hierarchically porous N-doped carbon nanofibers derived from ZIF-8/PAN composites for benzene adsorption

Coupling with electrospinning technique, metal–organic-frameworks (MOFs)-derived porous carbon fibers exhibit a great potential application in the adsorption of volatile organic compounds (VOCs) because of their huge surface area, high porosity, as well as sufficient heteroatom-doped active sites. In this work, the hierarchically porous N-doped carbon nanofibers are obtained after the pyrolysis of zeolite imidazole framework-8 and polyacrylonitrile (ZIF-8/PAN) composite fibers synthesized by electrospinning method. The N-doped carbon nanofibers fabricated in N₂ atmosphere (N-CF-N₂) present an enhanced adsorption capacity of 694 mg/g for benzene because of the synergistic effect of the hierarchically porous structure and the abundant N-species-containing active sites. It is also interesting that the N-doped hierarchical carbon nanofibers fabricated in Ar atmosphere (N-CF-Ar) exhibit a low benzene adsorption as compared with the N-CF-N₂, which can be attributed to the porous structure damage caused by the bombardment of heavy Ar atoms on the pore shells during the pyrolysis. These results not only show a promising application of the as-fabricated N-CF-N₂ in adsorption of VOCs for air purification due to its merit of cost-efficient, large-scale production, and excellent adsorption capacity, but also expand the potential of electrospinning technology and composite fibers in volatile organic gas adsorption.     

Antibacterial self-healing anticorrosion coatings from single capsule system

It is highly desirable to develop self-healing anticorrosion coatings with enhanced antibacterial function to prevent the scratched area to be fouled or corroded in harsh environments. Herein, we report antibacterial self-healing anticorrosion coatings via the simple incorporation of the easily synthesized single polymer microcapsule system. Well-defined polymer microcapsules containing isophorone diisocyanate (IPDI) as a healing agent and 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) as antibacterial molecules were synthesized by one-pot polymerization. The diameter and core fraction were around 30 μm and 90%, respectively. The active DCOIT content in the core material could be precisely controlled by adjusting the DCOIT/IPDI feeding ratio. The DCOIT/IPDI microcapsules-embedded protective coating exhibits an adaptive self-healing anticorrosion property, as shown by electrochemical test under the condition of the salt-water immersion. Furthermore, the self-healing coating showed efficient antibacterial function against Escherichia coli and Pseudomonas aeruginosa, which is due to the released active biocide molecules on the damaged surfaces. In contrast to other systems, this single capsule system without any catalyst is perspective for extending the service time of the antibacterial self-healing materials in harsh environment.