Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Tungsten is the heaviest transition metal in the family of common transition metal dichalcogenides (TMDCs). Despite the essential similarities of TMDCs, the considerable differences in the size and charge of the building elements can make the typical 2D layered structure suitable for various applications. There is not much flexibility on the chalcogen side, as the popular elements are S and Se. Following the successful history of transition metal sulphides in various applications, transition metal selenides are now the rising stars. On the transition metal side, WS2 and WSe2 have recently attracted considerable attention. In comparison with the Mo counterparts, W is more abundant in the Earth's crust and thus cheaper, and less toxic. The significantly larger size of W atoms can substantially tune the TMDC properties. The popularity of molybdenum dichalcogenides has somehow overshadowed the potentials of tungsten dichalcogenides. This manuscript attempts to collect the recent reports on various applications of WS2 and WSe2 to provide a general overview of tungsten dichalcogenides. Due to the popularity of sulphides, the prime focus of the present review is on WSe2, which is an emerging member of this family. Although WTe2 is not a common material like all transition metal tellurides, it is also briefly reviewed as a member of this sub-family of TMDCs owing to its unique properties, which named it as a potential candidate for giant magnetoresistance and superconductivity.

Tungsten dichalcogenides (WS2, WSe2, and WTe2): materials chemistry and applications

Hollow porous CoNi/C composite nanomaterials derived from MOFs for efficient and lightweight electromagnetic wave absorber

Recent progress on carbon-based composite materials for microwave electromagnetic interference shielding

Graphene micro-supercapacitors (MSCs) are an attractive energy storage technology for powering miniaturized portable electronics. Despite considerable advances in recent years, device fabrication typically requires conventional microfabrication techniques, limiting the translation to cost-effective and high-throughput production. To address this issue, we report here a self-aligned printing process utilizing capillary action of liquid inks in microfluidic channels to realize scalable, high-fidelity manufacturing of graphene MSCs. Microstructured ink receivers and capillary channels are imprinted on plastic substrates and filled by inkjet printing of functional materials into the receivers. The liquid inks move under capillary flow into the adjoining channels, allowing reliable patterning of electronic materials in complex structures with greatly relaxed printing tolerance. Leveraging this process with pristine graphene and ion gel inks, miniaturized all-solid-state graphene MSCs are demonstrated to concurrently achieve outstanding resolution (active footprint: <1 mm2, minimum feature size: 20 µm) and yield (44/44 devices), while maintaining a high specific capacitance (268 µF cm–2) and robust stability to extended cycling and bending, establishing an effective route to scale down device size while scaling up production throughput.

Scalable, Self Aligned Printing of Flexible Graphene Micro Supercapacitors (Postprint)

The mechanical and thermal properties of epoxy composites were improved by using poly (allyl amine) (PAA) grafted graphene oxide (GO) as a toughening agent. The GO was first converted to GO-COOH where all the hydroxyl groups on the basal plane were converted to COOH containing groups. GO-COOH was reacted with PAA to yield GO-g-PAA. The effect of PAA grafted GO nanosheets as fillers on mechanical and thermal properties of aerospace grade epoxy was studied. Epoxy nanocomposites containing graphene oxide (GO) and GO-g-PAA nanosheets were fabricated by incorporating 0.35 to 1.4 wt% of filler. GO-g-PAA modified epoxy nanocomposites showed excellent improvement in flexural, compression and fracture properties compared to neat epoxy and GO modified epoxy. Fracture toughness increased from 0.94 MPa m to 1/2 for neat epoxy to 1.75 MPa m-1/2 (87%) for epoxy nanocomposites modified with 0.7 wt% of GO-g-PAA nanosheets. The temperature for 5% weight loss showed drastic improvement of 24 °C for epoxy nanocomposites modified with 0.7 wt% of GO-g-PAA nanosheets. The examination of fractured surfaces of modified epoxy nanocomposites showed better interaction of GO-g-PAA nanosheets with epoxy compared to GO nanosheets.

Toughening of high performance tetrafunctional epoxy with poly(allyl amine) grafted graphene oxide

In the present study, noncovalently functionalized tungsten disulfide (WS2) nanosheets were used as a toughening agent for epoxy nanocomposites. WS2 was modified with branched polyethyleneimine (PEI) to increase the degree of interaction of nanosheets with the epoxy matrix and prevent restacking and agglomeration of the sheets in the epoxy matrix. The functionalization of WS2 sheets was confirmed through Fourier transform infrared spectroscopy and thermogravimetric analysis. The exfoliation of the bulk WS2 was confirmed through X-ray diffraction and various microscopic techniques. Epoxy nanocomposites containing up to 1 wt % of WS2–PEI nanosheets were fabricated. They showed a remarkable improvement in fracture toughness (KIC). KIC increased from 0.94 to 1.72 MPa m–1/2 for WS2–PEI nanosheet loadings as low as 0.25 wt %. Compressive and flexural properties also showed a significant improvement as incorporation of 0.25 wt % of WS2–PEI nanosheets resulted in 43 and 65% increase in the compressive and flexura...

Noncovalently Functionalized Tungsten Disulfide Nanosheets for Enhanced Mechanical and Thermal Properties of Epoxy Nanocomposites

High-performance epoxy composites find application in the aerospace industry. Although epoxy is a high-performance polymer, its fracture toughness is compromised due to its highly cross-linked nature. Nanomaterials such as carbon nanotubes (CNTs), graphene derivatives, and inorganic 2-dimensional (2D) nanomaterials are being explored to improve epoxy composites' mechanical properties. Graphene is one of the most popular 2D nano-reinforcing agents for epoxy composites. Following graphene discovery, the research community's attention was brought to various other few-atom thick 2D nanomaterials. Hence, apart from graphene, inorganic nanosheets such as transition metal dichalcogenides (TMDs), hexagonal boron nitride (hBN), etc., are also being studied as modifiers for enhancing the mechanical performance of epoxy composites. Graphene, TMDs and hBN are known to possess a high aspect ratio, high specific surface area and inherently high mechanical strength and stiffness, contributing to a stronger and tougher composite. Despite that, the challenges associated with these nanomaterials, such as dispersion issues, lack of standardization, underlying health hazards, etc., have hampered their commercialization. It has been long past a decade since the discovery of graphene, yet there are concerns regarding the lab to industry scale-up, and health and environmental hazards associated with nanomaterials for the fabrication of aerospace composites. This review offers a comprehensive literature survey and a perspective into the possible ways of bridging the gaps between the laboratory research and industrialization of 2D nanosheet-filled epoxy composites.

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Mechanical properties of aerospace epoxy composites reinforced with 2D nano-fillers: current status and road to industrialization

This paper highlights the outstanding electromagnetic shielding efficiency achieved by constructing layer-wise assembly of polymer films containing CoNi (cobalt-nickel) micro flowers, rods, and microspheres. Following a hydrothermal approach, various CoNi microstructures were synthesized from their metal salt precursors using wet chemistry followed by dispersing them in a PVDF matrix along with conducting multiwalled carbon nanotubes (MWNT) and subsequently hot-compressing them into thin flexible films (of thickness less than 1 mm). Few films were also prepared by dispersing only MWNTs in PVDF to construct a layer-wise assembly following an approach wherein a reflector spacer (PVDF/MWNT composites) is sandwiched between n (n = 0,1,2,3) absorbers (PVDF/CoNi/MWNT composites). The film thickness was adjusted in such a way that the total thickness of each assembly is ca. 0.9 mm. This strategy wherein a reflecting layer is sandwiched between the absorbing layers resulted in an excellent total shielding efficiency (SET) of −41 dB. By careful control of different layers in this layer-wise assembly, we managed to facilitate significant magnetic losses coupled with conducting losses. Therefore, this paper offers a replacement of conventional metallic shields with unique CoNi-based polymer composites for suppressing EM radiation.

Tunable CoNi microstructures in flexible multilayered polymer films can shield electromagnetic radiation

A novel and highly sensitive sensing strategy for the detection of organophosphorus compounds (OPs) based on the catalytic reaction of acetylcholinesterase (AChE) and acetylcholine (ATCh) during the modulated synthesis of silver nanoparticles (AgNPs) has been developed. The enzymatic hydrolysis of ATCh by AChE yields thiocholine (TCh), which induces the aggregation of AgNPs during synthesis, and the absorption peak at 382 nm corresponding to AgNPs decreases. The enzymatic reaction can be regulated by OPs, which can covalently bind to the active site of AChE and decrease the TCh formation, thereby decreasing the aggregation and significantly enhancing the absorption peak at 382 nm. The proposed system achieved good linearity and limits of detection of 0.078 nM and 2.402 nM for trichlorfon and malathion, respectively, by UV-visible spectroscopy. Further, the sensitivity of the proposed system was demonstrated through the determination of OPs in different spiked real samples. The described work shows the potential application for further development of a colorimetric sensor for other OP pesticide detection during the synthesis of AgNPs using enzyme-based assays.

Developing acetylcholinesterase-based inhibition assay by modulated synthesis of silver nanoparticles: applications for sensing of organophosphorus pesticides

Megha Sahu

Papers

Toughening of high performance tetrafunctional epoxy with poly(allyl amine) grafted graphene oxide

Noncovalently Functionalized Tungsten Disulfide Nanosheets for Enhanced Mechanical and Thermal Properties of Epoxy Nanocomposites

Mechanical properties of aerospace epoxy composites reinforced with 2D nano-fillers: current status and road to industrialization

Tunable CoNi microstructures in flexible multilayered polymer films can shield electromagnetic radiation

Developing acetylcholinesterase-based inhibition assay by modulated synthesis of silver nanoparticles: applications for sensing of organophosphorus pesticides