Selective Access to Silacyclopentanes and Homoallylsilanes by La-Catalyzed Hydrosilylations of 1-Aryl Methylenecyclopropanes.

Methylenecyclopropanes (MCPs) have emerged as versatile building blocks in synthetic chemistry because of their unique reactivity. However, metal-catalyzed hydrosilylation of MCPs has met with very limited successes. In this paper, catalytic selective hydrosilylations of MCPs with some primary silanes using an ene-diamido lanthanum ate complex as the catalyst were described. The catalytic reactions resulted in the selective formation of silacyclopentanes and (E)-homoallylsilanes, respectively, depending on the substituents on MCPs. The formation of silacyclopentanes via a catalytic cascade inter- and intramolecular hydrosilylation mechanism is strongly supported by the control and deuteration-labeling experiments and DFT calculations. The unique reactivity and selectivity could be attributed to the large lanthanum ion and ate structure of the catalyst.

Density Functional Theory Study on the Mechanism of Nickel-Catalyzed 3,3-Dialkynylation of 2-Aryl Acrylamides Via Double Vinylic C-H Bond Activation.

The mechanisms of Ni-catalyzed 3,3-dialkynylation of 2-aryl acrylamide have been investigated by using density functional theory calculations. The result shows that this reaction includes double alkynylation, which involves sequential key steps of vinylic C-H bond activation, successive oxidative addition, and reductive elimination, with the second C-H bond activation being the rate-determining step. C-H and N-H bond activation occurs via the concerted metalation-deprotonation mechanism. The calculations show that no transition state exists in the first reductive elimination process, and a negative free energy barrier in the second reductive elimination process though a transition state is identified, indicating that the nickel-catalyzed vinylic C(sp2)-C(sp) bond formation does not require activation energy. Z-E isomerization is the prerequisite for the second alkynylation. In addition, our spin-flip TDDFT (SF-TDDFT) computational result discloses that the actual process of Z-E isomerization occurs on the potential energy surface of the first excited singlet state S1.

Computational Study of Iron-Catalyzed Intramolecular [2 + 2] Cycloaddition and Cycloisomerization of Enyne Acetates: Mechanism and Selectivity.

The mechanism of iron-catalyzed intramolecular [2 + 2] cycloaddition and cycloisomerization of enyne acetates has been investigated with DFT computations. Both mechanisms start the catalytic cycle from the stepwise 1,2-acyloxy migration to afford the iron carbene. The [2 + 2] cycloaddition mechanism involves subsequent key steps of [2 + 2] cycloaddition, 1,2-acyloxy migration, and reductive elimination to generate the azabicyclo [3.2.0] heptane product, with the reductive elimination being the rate-determining step. The cycloisomerization mechanism involves subsequent key steps of [2 + 2] cycloaddition, stepwise 1,4-acyloxy migration to produce the allenylpyrrolidine product, with the 1,4-acyloxy migration being the rate-determining step. Reaction potential energy surfaces for two model substrates that have or do not have alkene-terminal substituents have been investigated and the origins of the selectivities have been disclosed. Moreover, energy profiles with three possible spin states (SFe = 0, 1, 2) have been considered. The reaction is suggested to occur mainly on the singlet potential energy surface with a few spin crossovers between singlet and triplet states involved, which indicates that this reaction should have two-state reactivity (TSR).

Dual layer hollow fiber PVDF ultra-filtration membranes containing Ag nano-particle loaded zeolite with longer term anti-bacterial capacity in salt water.

Dual layer polyvinylidene fluoride (PVDF), antibacterial, hollow fiber, ultra-filtration composite membranes with antibacterial particles (silver (Ag) nano-particles loaded zeolite (Z-Ag)) in the outer layer were prepared with high water flux and desired pore sizes. The amounts of Ag(+) released from the composite membranes, freshly made and stored in water and salt solution, were measured. The result indicated that dual layer PVDF antibacterial hollow fiber containing Z-Ag (M-1-Ag) still possessed the ability of continuous release of Ag(+) even after exposure to water with high ionic content, showing a longer term resistance to bacterial adhesion and antibacterial activity than membrane doped with Z-Ag(+) (M-1). Results from an anti-adhesion and bacteria killing test with Escherichia coli supported that the antibacterial efficiency of dual hollow fiber PVDF membranes with Z-Ag was much higher than those with Z-Ag(+) after long time storage in water or exposure to phosphate buffered saline (PBS) solution. This novel hollow fiber membrane may find applications in constructing sea water pretreatment devices with long term antifouling capability for the desalination processes.

Development of Electromagnetic-Wave-Shielding Polyvinylidene Fluoride-Ti3C2Tx MXene-Carbon Nanotube Composites by Improving Impedance Matching and Conductivity.

Absorption-dominated electromagnetic interference (EMI) shielding is attained by improving impedance matching and conductivity through structural design. Polyvinylidene fluoride (PVDF)-Ti3C2Tx MXene-single-walled carbon nanotubes (SWCNTs) composites with layered heterogeneous conductive fillers and segregated structures were prepared through electrostatic flocculation and hot pressing of the PVDF composite microsphere-coated MXene and SWCNTs in a layer-by-layer fashion. Results suggest that the heterogeneous fillers improve impedance matching and layered coating, and hot compression allows the MXene and SWCNTs to form a continuous conducting network at the PVDF interface, thereby conferring excellent conductivity to the composite. The PVDF-MXene-SWCNTs composite showed a conductivity of 2.75 S cm-1 at 2.5% MXene and 1% SWCNTs. The EMI shielding efficiency (SE) and contribution from absorption loss to the total EMI SE of PVDF-MXene-SWCNTs were 46.1 dB and 85.7%, respectively. Furthermore, the PVDF-MXene-SWCNTs composite exhibited excellent dielectric losses and impedance matching. Therefore, the layered heteroconductive fillers in a segregated structure optimize impedance matching, provide excellent conductivity, and improve absorption-dominated electromagnetic shielding.

Structural design and preparation of Ti3C2Tx MXene/polymer composites for absorption-dominated electromagnetic interference shielding.

Electromagnetic interference (EMI) is a pervasive and harmful phenomenon in modern society that affects the functionality and reliability of electronic devices and poses a threat to human health. To address this issue, EMI-shielding materials with high absorption performance have attracted considerable attention. Among various candidates, two-dimensional MXenes are promising materials for EMI shielding due to their high conductivity and tunable surface chemistry. Moreover, by incorporating magnetic and conductive fillers into MXene/polymer composites, the EMI shielding performance can be further improved through structural design and impedance matching. Herein, we provide a comprehensive review of the recent progress in MXene/polymer composites for absorption-dominated EMI shielding applications. We summarize the fabrication methods and EMI shielding mechanisms of different composite structures, such as homogeneous, multilayer, segregated, porous, and hybrid structures. We also analyze the advantages and disadvantages of these structures in terms of EMI shielding effectiveness and the absorption ratio. Furthermore, we discuss the roles of magnetic and conductive fillers in modulating the electrical properties and EMI shielding performance of the composites. We also introduce the methods for evaluating the EMI shielding performance of the materials and emphasize the electromagnetic parameters and challenges. Finally, we provide insights and suggestions for the future development of MXene/polymer composites for EMI shielding applications.

Robust and Multifunctional 3D Graphene-Based Aerogels Reinforced by Hydroxyapatite Nanowires for Highly Efficient Organic Solvent Adsorption and Fluoride Removal.

In view of the serious perniciousness and complex diversity of actual wastewater systems, exploiting a robust and multifunctional adsorbent material featuring high sorption efficiency, broad-spectrum applicability, and excellent recyclability in treating multifarious pollutants in water (such as oils and fluoride ions) is highly required; however, it is still a daunting goal to pursue to date. In this work, novel mechanically robust and exceptional graphene oxide/hydroxyapatite nanowire (GO/HAPNW) aerogels (RGHAs/polydopamine (PDA)@RGHAs) with adjustable surface wettability were developed through a facile sol-gel self-assembly technology and subsequently optional bioinspired hydrophilic modification. Thanks to the reinforcing effect of HAPNWs with higher aspect ratio, a remarkably improved mechanical robustness (including superior compressibility and superelasticity) was acquired for the resulting aerogels. Based on the cooperative effect of the favorable selective wetting properties (i.e., hydrophobic/oleophilic for RGHAs) and the excellent mechanic stability, the aerogels displayed an outstanding sorption performance for diverse oils/organic solvents accompanied with a prominent recyclability. Specifically, a fairly high adsorption capacity of as high as 191 times of its own mass (for pump oil) was achieved based on a fast adsorption kinetic process. More importantly, superamphiphilic three-dimensional (3D) PDA@RGHAs revealed an extraordinary removal capability for water-soluble fluoride ions, exhibiting a superior equilibrium adsorption capacity (qe, 9.93 mg/g), which is distinctly superior to those of low-dimensional fluorine adsorbent materials recently reported. Accordingly, the as-prepared 3D aerogels combining both superior oil/organic solvent adsorption and excellent defluorination capability reveal a competitive application prospect toward effective intricate oily wastewater purification.

Robust Graphene/Poly(vinyl alcohol) Janus Aerogels with a Hierarchical Architecture for Highly Efficient Switchable Separation of Oil/Water Emulsions.

Given the complexity and diversity of actual oily sewages, developing multifunctional separation materials with features of high separation efficiency and low energy consumption for separating diverse oil/water emulsions is urgently needed, yet it remains a formidable challenge till now. Herein, a superior graphene/poly(vinyl alcohol) Janus aerogel (J-CGPA), showing an intriguing three-dimensional (3D) hierarchical architecture (a dense skin-layer and a larger internal cell network) and desirable asymmetric wettability, was exploited via a simple direct freeze-shaping technique and subsequent mussel-inspired hydrophilic modification. Benefiting from the controlled unilateral decoration of dopamine, the resultant aerogels displayed completely opposite superwettability on two antithetic sides, i.e., one side is highly hydrophobic (water contact angle (WCA), 143°), whereas the other side is superhydrophilic. On the basis of the favorable 3D hierarchical structure and binary cooperative superwetting properties, the Janus aerogels achieved a remarkable switchable separation performance for both highly emulsified oil-in-water and water-in-oil emulsions as well as stratified oil/water mixtures accompanied with outstanding separation efficiencies. Particularly, an ultrahigh permeation flux of 1306 L m-2 h-1 along with a high rejection efficiency of 99.7% was acquired solely under the driving of gravity (<1 kPa), which is 1-2 order of magnitude higher than that of pioneering two-dimensional Janus polymeric/inorganic membranes recently reported. Moreover, together with robust reusability, this novel 3D Janus aerogel indicates a promising practical application for high-performance oily wastewater remediation.

Facile fabrication of long-chain alkyl functionalized ultrafine reduced graphene oxide nanocomposites for enhanced tribological performance.

Due to their ultrathin 2D laminated structure as well as excellent mechanical and thermal stabilities, ultrafine graphene-based nanoparticles exhibit fascinating advantages as highly-efficient lubricant additives. However, it remains a daunting challenge to achieve good and durable dispersion of these graphene-based nanoparticles in lubricating oils. Herein, we report a facile and efficient integration strategy involving particle size miniaturization, surface grafting with octadecyl alcohol (OA), and partial chemical reduction to prepare a novel long-chain alkyl functionalized ultrafine reduced graphene oxide (RGO-g-OA) with highly-dispersive capacity and superior tribological performance. The chemical composition and structural characteristics, microstructural morphology, and particle size distribution of RGO-g-OA were systematically investigated. Combining significantly improved lipophilicity derived from the long-chain alkyl grafting and partial chemical reduction with the small-size effect gave rise to outstanding long-term dispersion stability (as long as one month) of RGO-g-OA in the finished oil. Moreover, the friction coefficient and wear volume of finished oil with merely 0.005 wt% RGO-g-OA greatly reduced to 0.065 and 10 316 µm3, decreased by 9.7% and 44%, respectively, compared to those of pristine finished oil, demonstrating remarkable friction reduction and anti-wear performances. Consequently, owing to the characteristics of facile fabrication, durable dispersion stability, and superior tribological performance at an extremely low content, this novel nanoadditive shows a promising application potential in the tribology field.

Facile construction of gas diode membrane towards in situ gas consumption via coupling two chemical reactions.

Controlling the bubbles' behavior on a solid surface is significant for exploring more related applications and thus recently has attracted increased investigations. Based on this, a Janus poly (l-lactic acid) (PLLA) membrane with definitely opposite water wettability in air and opposite bubble wettability underwater was successfully fabricated in this work. The obtained Janus membrane exhibited unidirectional transport for air bubble underwater from the superaerophilic side to superaerophobic side, meanwhile prevented the permeation of water medium from both sides under low pressure. This special membrane was designed to couple two chemical reactions. During the designed chemical reaction process, the feature of bubble unidirectional transport allowed the carbon dioxide (CO2) produced in one reaction system to transport through the resultant membrane into another reaction system, wherein it could be consumed. Meanwhile, the anti-water-permeation function of the membrane guaranteed that the two chemical reactions could be performed independently. We believe that the present research could broaden the potential applications of membranes with super-wetting character for gas bubbles.

Flexible Polydimethylsilane Nanocomposites Enhanced with a Three-Dimensional Graphene/Carbon Nanotube Bicontinuous Framework for High-Performance Electromagnetic Interference Shielding.

High-performance electromagnetic interference (EMI)-shielding materials featuring lightweight, flexibility, excellent conductivity, and shielding properties, as well as superior mechanical robustness, are highly required, yet their development still remains a daunting challenge. Here, a flexible and exceptional EMI-shielding polydimethylsilane/reduced graphene oxide/single-wall carbon nanotube (PDMS/rGO/SWCNT) nanocomposite was developed by a facile backfilling approach utilizing a preformed rGO/SWCNT aerogel as the three-dimensional (3D) conducting and reinforcement skeleton. Pristine SWCNTs acting as secondary conductive fillers showed intriguing advantages, whose intrinsically high conductivity could be well preserved in the composites because of no surface acidification treatment. The robust and interconnected 3D network can not only serve as fast channels for electron transport but also effectively transfer external load. Accordingly, a prominent electrical conductivity of 1.2 S cm-1 and an outstanding EMI-shielding effectiveness of around 31 dB over the X-band frequency range were achieved for the resultant composite with an ultralow loading of 0.28 wt %, which is among the best results for currently reported conductive polymer nanocomposites. Moreover, the composite displayed excellent mechanical properties and bending stability; for example, a 233% increment in the compression strength was obtained compared with that of neat PDMS. These observations indicate the unrivalled effectiveness of 3D rGO/SWCNT aerogel as a reinforcement to endow the polymer composites with outstanding conductive and mechanical properties toward high-performance EMI-shielding application.

Tunable adhesion of superoleophilic/superhydrophobic poly (lactic acid) membrane for controlled-release of oil soluble drugs.

Superhydrophobic membranes with tunable adhesion have attracted intense interests for various engineering applications. In this work, superhydrophobic sustainable poly (lactic acid) (PLA) porous membrane with tunable adhesive force from 101µN to 29µN was successfully fabricated via one-step phase separation method. The incorporation of Perfluoro-1-decene (PFD) into the PLLA/PDLA membrane via the in situ polymerization can facilely tune the PLLA/PDLA stereocomplex crystallization during phase inversion, which consequently caused the unique morphology blooming evolution from bud to full-blown state. The resulted membrane showed tunable pore size, porosity, surface area, surface roughness and superhydrophobicity, which enabled the membrane with controlled-release of oil soluble drugs.