Designing Nanofluidic Channels of Boron Nitride Nanosheets/Aramid Nanofibers/Covalent Organic Frameworks Nanofiltration Membrane for Ultrafast Mass Transport.

2D lamellar nanofiltration membrane is considered to be a promising approach for desalinating seawater/brackish water and recycling sewage. However, its practical feasibility is severely constrained by the lack of durability and stability. Herein, a ternary nanofiltration membrane via a mixed-dimensional assembly of 2D boron nitride nanosheets (BNNS) is fabricated, 1D aramid nanofibers (ANF), and 2D covalent organic frameworks (COF). The abundant 2D and 1D nanofluid channels endow the BNNS/ANF/COF membrane with a high flux of 194 L·m‒2·h‒1. By the synergies of the size sieving and Donnan effect, the BNNS/ANF/COF membrane demonstrates high rejection (among 98%) for those dyes whose size exceeds 1.0 nm. Moreover, the BNNS/ANF/COF membrane also exhibits remarkable durability and mechanical stability, which are attributed to the strong adhesion and interactions between BNNS, ANF, and COF, as well as the superior mechanical robustness of ANF. This work provides a novel strategy to develop robust and durable 2D lamellar nanofiltration membranes with high permeance and selectivity simultaneously.

Formation Mechanisms of Hexagonal Boron Nitride Nanosheets in Solvothermal Exfoliation.

Solvothermal techniques are widely used to exfoliate many two-dimensional materials, but the formation mechanisms of these nanomaterials have not been clearly revealed. Herein, we discovered the dissociation of hexagonal boron nitride (h-BN) in solvothermal exfoliation evidenced by the formation of B(OH)3, NH4B5O8·4H2O, and (NH4)2B10O16·8H2O. In the selected solvents, the lateral sizes of the formed boron nitride nanosheets (BNNSs) are increased in the order of N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), acetonitrile (MeCN), and isopropanol (IPA), suggesting the decreased dissolving abilities of these solvents to h-BN in turn. The dissociation behaviors are the properties of solvents themselves, but the inclusion of lithium chloride (LiCl) and cetyltrimethylammonium bromide (CTAB) can elevate the dissociation degree and yield BNNSs with smaller lateral sizes due to the intercalating effects. The cation-π interactions make CTAB more effective in obtaining uniform BNNSs than using the neutral halogenated hydrocarbons as assistant reagents. The dissociation abilities of the solvents have strong relationships with the surface tension, Hansen solubility parameters distances (Ra), and polarities, whereas there is little relevance with the pressures. Meanwhile, we also observed the cracking of CTAB and the polymerization of MeCN in these reactions. Our findings indicate that the impurities are prone to be attached to the BNNSs exfoliated by the solvothermal route.

Ammonium-tungstate-promoted growth of boron nitride nanotubes.

Ammonium tungstate ((NH4)10W12O41 · xH2O) is a kind of oxygen-containing ammonium salt. The following study proves that it can be successfully used as a metal oxide alternative to produce boron oxide (B2O2) by oxidizing boron (B) in a traditional boron oxide chemical vapor deposition (BOCVD) process. This special oxidant promotes the simplistic fabrication of boron nitride nanotubes (BNNTs) in a conventional horizontal tube furnace, an outcome which may have resulted from its strong oxidizability. The experimental results demonstrate that the mole ratio of B and (NH4)10W12O41 · xH2O is a key parameter in determining the formation, quality and quantity of BNNTs when stainless steel is employed as a catalyst. We also found that Mg(NO3)2 and MgO nanoparticles (NPs) can be used as catalysts to grow BNNTs with the same precursor. The BNNTs obtained from the Mg(NO3)2 catalyst were straighter than those obtained from the MgO NP catalyst. This could have been due to the different physical forms of the catalysts that were used.

Polyvinyl alcohol-mediated splitting of Kevlar fibers and superior mechanical performances of the subsequently assembled nanopapers.

In this work, a composite of aramid nanofibers (ANFs) and polyvinyl alcohol (PVA) was prepared by PVA-assisted splitting of macro Kevlar fibers, which assures the uniform wrapping of PVA chains on the surface of ANFs, thus leading to an enhanced interfacial bonding strength between ANFs and PVA. The morphological characterizations manifest the enhanced diameters of the ANFs after PVA wrapping. The subsequently assembled ANFs/PVA paper shows a strength of 283.25 MPa and a toughness of 32.41 MJ m-3, which are increased by 57% and 152% compared to the pure ANF paper, respectively. The superior mechanical properties are attributed to the strong interfacial bonding strength, enhanced hydrogen bonding interactions, the densification of the materials, and curved fracture paths. Meanwhile, the ANFs/PVA paper also shows robust UV shielding and visible transparency properties, as well as excellent environmental stabilities, especially at high and low temperatures.

Improved mechanical and ultraviolet shielding performances of hydroxyethyl cellulose film by using aramid nanofibers as additives.

Recently, aramid nanofibers (ANFs) have drawn the attention of scientist due to the high mechanical strength, high-temperature resistance, and high electrical and thermal insulation properties. In this work, we aimed at improving the mechanical and ultraviolet shielding properties of hydroxyethyl cellulose (HEC) film by using ANFs as additives. Mechanical results show that the 1.0 % ANFs could improve the tensile strength of pure HEC film by 176.6 %. Meanwhile, the ANFs additives can also enable the HEC film excellent ultraviolet (UV) shielding and visible light transmittance, as well as high UV radiation resistance ability. It is believed that the high mechanical strength of the HEC/ANFs composites is derived from the rearrangement of HEC chains along the tensile direction after the addition of hard ANFs and the enhanced hydrogen bonds between HEC and ANFs.

The MgB2-catalyzed growth of boron nitride nanotubes using B/MgO as a boron containing precursor.

With the development of preparation technology, obtaining boron nitride nanotubes (BNNTs) is no longer difficult, but it is still not easy to balance the quality and purity of the obtained products using existing methods. In this work, we investigated a previously reported MgB2 catalyst to explore the synthesis of BNNTs at a higher temperature in a conventional chemical vapor deposition (CVD) system from a classic B/MgO precursor. Various characterization methods showed the high activity of MgB2 at 1400 °C and the superiority of the as-grown BNNTs in terms of purity and quality. Further reference experiments and element characterization measurements were also performed to verify the role of MgB2 in the growth of the BNNTs, finding that B/MgO/MgB2 is a simple and efficient precursor.

All cellulose composites prepared by hydroxyethyl cellulose and cellulose nanocrystals through the crosslink of polyisocyanate.

In this work, all cellulose composite (ACC) films were prepared through a blocked polyisocyanate (BPIC) induced cross-linking of hydroxyethyl cellulose (HEC) and cellulose nanocrystals (CNC). The chemical characterization indicates that the covalent bonds have been formed between HEC and CNC. Mechanical test shows that the addition of 4 % CNC into the HEC matrix improves the tensile strength by 120.2 % compared to the neat HEC film. The further incorporation of 10 % BPIC into the above ACC film can enhance the tensile strength by 280.2 %. The water contact angles of the ACC film that constituted by 4 % CNC and 10 % BPIC is increased to 100.1° while the thermal decomposition temperature is up to 210 °C. The morphological analysis suggests that the CNC is beneficial to the dispersion of the cross-linked HEC, which increases the elongation at break and maintains the excellent tensile strength meanwhile.

Magnesium-induced preparation of boron nitride nanotubes and their application in thermal interface materials.

The effective growth of boron nitride nanotubes (BNNTs) by boron oxide chemical vapor deposition (BOCVD) is extremely challenging, especially in a horizontal tube furnace. Herein, we propose a novel Mg-induction strategy, which is low cost and efficiently generates BNNTs by separating Mg from diverse boron sources (B2O3, H3BO3, borates, and so on). After careful analysis and discussion of the prepared BNNTs, the corresponding in situ generation of MgB2, an effective catalyst for the growth of BNNTs, was proposed and verified. This contribution will provide a low-cost, highly efficient and large-scale method for the preparation of BNNTs with the CVD method. The prepared BNNTs can be widely used in thermal interface materials, as demonstrated by the high thermal conductivity of the poly-vinyl alcohol (PVA) composite filled with these BNNTs. Therefore, our work offers a new strategy that is low cost and highly efficient for large-scale fabrication of BNNTs, and demonstrates that the prepared BNNTs have great potential applications in thermal interface materials.

Growth of boron nitride nanotubes from magnesium diboride catalysts.

The difficulty in synthesizing boron nitride nanotubes (BNNTs) in a conventional horizontal tube furnace by chemical vapor deposition (CVD) may be ascribed to the failure to identify suitable catalysts and nucleation particles. This report demonstrates that magnesium diboride (MgB2) can effectively catalyze the growth of BNNTs in such a tube furnace from various boron sources, including boron oxide (B2O3), boric acid (H3BO3), and a mixture of boron (B) and calcium oxide (CaO). This catalyst is more efficient than the possible magnesium oxide (MgO) or magnesium nitride (Mg3N2) catalysts. MgB2 efficiently catalyzes the formation of BNNTs by maintaining a liquid state and showing a dissolving capacity for B2O3 at the growth temperature, thus satisfying the criteria for the vapor-liquid-solid (VLS) mechanisms of one-dimensional nanomaterials. First-principles simulations demonstrate that B2O3 can be dissolved into the MgB2 nanoparticle. We believe that the strong catalytic behavior of MgB2 can be attributed to its robust nucleation for BNNTs and dissolubility for B2O3.

In Situ Generation of Photosensitive Silver Halide for Improving the Conductivity of Electrically Conductive Adhesives.

Electrically conductive adhesives (ECAs) can be regarded as one of the most promising materials to replace tin/lead solder. However, relatively low conductivity seriously restricts their applications. In the present study, we develop an effective method to decrease the bulk electrical resistivity of ECAs. KI or KBr is added to replace the lubricant and silver oxide layers on silver flakes and to form photosensitive silver halide. After exposure to sunlight, silver halide can photodecompose into silver nanoparticles that will sinter and form metallic bonding between/among flakes during the curing process of ECAs, which would remarkably reduce the resistivity. The modified micro silver flakes play a crucial role in decreasing the electrical resistivity of the corresponding ECAs, exhibiting the lowest resistivity of 7.6 × 10-5 Ω·cm for 70 wt % loaded ECAs. The obtained ECAs can have wide applications in the electronics industry, where high conductance is required.