Ultrastrong Graphene Sheets Assembled with Nanoconfined Water.

Highly ordered assembly of two-dimensional (2D) nanoplatelets plays a key role in enhancing the mechanical properties of layered nanocomposites. Layer-by-layer (LbL) assembly, vacuum-assisted filtration, and blade coating have been used to fabricate layered nanocomposites. However, the intrinsic wrinkles of 2D nanoplatelets and defects derived from assembling approaches make it difficult to align 2D nanoplatelets. Recently, the team of Prof. Qunfeng Cheng at Beihang University and their collaborator, Prof. Ray H. Baughman at the University of Texas at Dallas developed a novel approach for aligning graphene and Ti3C2Tx MXene nanoplatelets by nanoconfined assembly through continuous vacuum-assisted filtration. The resultant MXene-bridged sheet has ultrastrong mechanical properties and low porosity, providing a new concept for assembling 2D nanoplatelets into aligned and compact high-performance layered nanocomposites.

Aqueous Dispersion of Aramid Nanofibers Achieved by Using Tannic Acid for Ultrahigh Strength Films.

Polymer nanofibers have established a robust foundation and possess immense potential in various emerging fields such as sensors and biotechnology. In this study, aqueous dispersions of aramid nanofibers (ANFs) were successfully prepared by using tannic acid (TA). Morphological analysis revealed that TA effectively prevented self-aggregation of ANFs, and preserved the nanofiber structure during TA-assisted solvent exchange. Subsequently, the ANF and TA/ANF films were fabricated using casting and vacuum-assisted filtration techniques. Notably, the tensile strength of the casting TA/ANF film reached 393.8 MPa, exhibiting a remarkable improvement of 41.3% compared to that of the pure ANF film. These exceptional mechanical properties can be attributed to the well-dispersed nanostructures, hydrogen-bonding interactions, zigzag structures, and fiber-bridging effects. Furthermore, the TA/ANF film demonstrated superior ultraviolet (UV) shielding capabilities, visible transparency properties, and excellent resistance to chemical reagents. The above-mentioned interesting findings demonstrate its potential as a nanofiber-reinforced material for poly(vinyl alcohol) (PVA) composites.

SERS Performance of Ti3C2Tx MXene-Based Substrates Correlates with Surface Morphology.

The surface-enhanced Raman scattering (SERS) properties of low-dimensional semiconducting MXene nanoflakes have been investigated over the last decade. Despite this fact, the relationship between the surface characteristics and SERSing performance of a MXene layer has yet to be comprehensively investigated and elucidated. This work shows the importance of surface morphology on the overall SERS effect by studying few-layer Ti3C2Tx MXene-based SERS substrates fabricated by vacuum-assisted filtration (VAF) and spray coating on filter paper. The VAF deposition results in a dense MXene layer suitable for SERS with high spot-to-spot and substrate-to-substrate reproducibility, with a significant limit of detection (LoD) of 20 nM for Rhodamine B analyte. The spray-coated MXenes film revealed lower uniformity, with a LoD of 50 nM for drop-casted analytes. Moreover, we concluded that the distribution of the analyte deposited onto the MXene layer is affected by the presence of MXene aggregates created during the deposition of the MXene layer. Accumulation of the analyte molecules in the vicinity of MXene aggregates was observed for drop-casted deposition of the analyte, which affects the resulting SERS enhancement. Ti3C2Tx MXene layers deposited on filter paper by VAF offer great potential as a cost-effective, easy-to-manufacture, yet robust, platform for sensing applications.

Liquid Shear Exfoliation of MoS2: Preparation, Characterization, and NO2-Sensing Properties.

2D materials possess great potential to serve as gas-sensing materials due to their large, specific surface areas and strong surface activities. Among this family, transition metal chalcogenide materials exhibit different properties and are promising candidates for a wide range of applications, including sensors, photodetectors, energy conversion, and energy storage. Herein, a high-shear mixing method has been used to produce multilayered MoS2 nanosheet dispersions. MoS2 thin films were manufactured by vacuum-assisted filtration. The structural morphology of MoS2 was studied using ς-potential, UV-visible, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). The spectroscopic and microscopic analyses confirm the formation of a high-crystalline MoS2 thin film with good inter-sheet connectivity and relative thickness uniformity. The thickness of the MoS2 layer is measured to be approximately 250 nm, with a nanosheet size of 120 nm ± 40 nm and a number of layers between 6 and 9 layers. Moreover, the electrical characteristics clearly showed that the MoS2 thin film exhibits good conductivity and a linear I-V curve response, indicating good ohmic contact between the MoS2 film and the electrodes. As an example of applicability, we fabricated chemiresistive sensor devices with a MoS2 film as a sensing layer. The performance of the MoS2-chemiresistive sensor for NO2 was assessed by being exposed to different concentrations of NO2 (1 ppm to 10 ppm). This sensor shows a sensibility to low concentrations of 1 ppm, with a response time of 114 s and a recovery time of 420 s. The effect of thin-film thickness and operating temperatures on sensor response was studied. The results show that thinner film exhibits a higher response to NO2; the response decreases as the working temperature increases.

Effect of L-Ascorbic Acid Solution Concentration on the Thermoelectric Properties of Silver Selenide Flexible Films Prepared by Vacuum-Assisted Filtration.

Currently, there are several thermoelectric materials, such as Ag2Te, Bi2Te3, and Sb2Te3, that have been investigated for thermoelectric applications. However, the toxicity and rarity of most of these materials make them unsuitable for practical applications. In contrast, silver selenide (Ag2Se) is an abundant and environment-friendly thermoelectric material. This study provides a facile synthetic approach for preparing high-performance, low-cost, and flexible Ag2Se thermoelectric films. Ag2Se nanomaterials were prepared based on the chemical template method, and the reaction solution concentration was varied to systematically investigate the effects of reaction solution concentration on the characterization and thermoelectric properties of Ag2Se nanomaterials. For convenience of testing, the flexible Ag2Se films were prepared on porous nylon membranes using vacuum-assisted filtration. The prepared thermoelectric films were tested using an X-ray diffractometer, scanning electron microscope, Seebeck coefficient tester, and Hall tester. The film prepared from the solution with the lowest concentration (18.0 mM) demonstrated the best thermoelectric performance, with a maximum power factor of 382.18 µW∙m-1∙K-2 at ~400 K. Additionally, a cold-pressing treatment could effectively enhance the electrical conductivity of the film, without damaging the substrate, as the conductivity of the film remained at 90% of the original value after 1500 bending cycles.

Vacuum-assisted bilayer PEDOT:PSS/cellulose nanofiber composite film for self-standing, flexible, conductive electrodes.

Sustainable cellulose nanofiber (CNF)-based composites as functional conductive materials have garnered considerable attention recently for their use in soft electronic devices. In this work, self-standing, highly flexible, and conductive PEDOT:PSS-CNF composite films were developed using a simple vacuum-assisted filtration method. Two different composite films were successfully fabricated and then tested: 1) a single-layer composite composed of a mixture of PEDOT:PSS and CNF phases and 2) a bilayer composite composed of an upper PEDOT:PSS membrane layer and a CNF matrix sub-layer. The latter composite was constructed by electrostatic/hydrogen bonding interactions between PEDOT:PSS and CNFs coupled with sequential vacuum-assisted filtration. Our results demonstrated that the resultant bilayer composite film exhibited a competitive electrical conductivity (ca. 22.6Scm-1) compared to those of previously reported cellulose-based composites. Furthermore, decreases in the electrical properties were not observed in the composite films when they were bent up to 100 times at an angle of 180° and bent multiple times at an angle of 90°, clearly demonstrating their excellent mechanical flexibility. This study provides a straightforward method of fabricating highly flexible, lightweight, and conductive films, which have the potential to be used in high-performance soft electronic systems.