Atomically thin MXene/WSe2Schottky heterojunction towards enhanced photogenerated charge carrier.

Two-dimensional materials garner increasing interest in next-generation electronics and optoelectronic devices due to their atomic-thin nature and distinctive physical properties. Building on these advances, we present the successful synthesis of a heterostructure composed of the semi-metallic Ti3C2-MXene and the semiconducting WSe2, in which the atomic layers are vertically aligned. The wet impregnation method effectively synthesizes an atomically thin Ti3C2-MXene/WSe2heterostructure characterized by atomic force microscopy, Raman and time-resolved photoluminescence (TRPL) analysis. In addition, the current-voltage characteristics at the heterostructure reveal the Schottky junction probed by the scanning tunnelling microscopy and the conductive atomic force microscopy tip. The Schottky heterojunction also exhibits enhanced photocatalytic properties by improving the photogenerated charge carriers and inhibiting recombination. This work demonstrates the unique 2D-2D Ti3C2-MXene/WSe2vertical heterojunction possesses superior photon trapping ability and can efficiently transport photogenerated charge carriers to the reaction sites to enhance photocatalysis performance.

Schiff base crosslinked graphene/oxidized nanofibrillated cellulose/chitosan foam: An efficient strategy for selective removal of anionic dyes.

A versatile foam based on Schiff base crosslinking of oxidized nanofibrillated cellulose (ONFC) with amino modified graphene oxide (NGO) and chitosan (CS) was prepared for the efficacious selective removal of anionic dyes. (3-aminopropyl) triethoxysilane (APTES) was employed as a surface modifier to yield an amino modified graphene oxide (NGO). Meanwhile, ONFC was obtained via a periodate oxidation process to produce dialdehyde groups. Thus, the Schiff base crosslinking of ONFC with NGO and CS enabled to be readily accomplished, producing a versatile NGO/ONFC/CS foam. Systematical characterizations confirmed the successful covalent crosslinking and formation of NGO/ONFC/CS foams. Selective adsorption of Allura Red (AR) and orange G (OG) over cationic dye methylene blue (MB) by NGO/ONFC/CS was confirmed. It was found the maximum adsorption capacities of AR and OG at 303 K were 416.7 and 300.5 mg g-1, while it was 14.60 mg g-1 for MB. Thus, the new Schiff base crosslinked NGO/ONFC/CS paves the way for developing versatile graphene based foams in the applications of water treatment.

Designing Supertough and Ultrastretchable Liquid Metal-Embedded Natural Rubber Composites for Soft-Matter Engineering.

Functional elastomers with incredible toughness and stretchability are indispensable for applications in soft robotics and wearable electronics. Furthermore, coupled with excellent electrical and thermal properties, these materials are at the forefront of recent efforts toward widespread use in cutting-edge electronics and devices. Herein, we introduce a highly deformable eutectic-GaIn liquid metal alloy-embedded natural rubber (NR) architecture employing, for the first time, industrially viable solid-state mixing and vulcanization. Standard methods of rubber processing and vulcanization allow us to fragment and disperse liquid metals into submicron-sized droplets in cross-linked NR without compromising the elastic properties of the base matrix. In addition to substantial boosts in mechanical (strain at failure of up to ∼650%) and elastic (negligible hysteresis loss) performances, the tearing energy of the composite was enhanced up to 6 times, and a fourfold reduction in the crack growth rate was achieved over a control vulcanizate. Moreover, we demonstrate improved thermal conductivity and dielectric properties for the resulting composites. Therefore, this work provides a facile and scalable pathway to develop liquid metal-embedded soft elastomeric composites that could be instrumental toward potential applications in soft-matter engineering.

Weathering of Antibacterial Melt-Spun Polyfilaments Modified by Pine Rosin.

For many antibacterial polymer fibres, especially for those with natural functional additives, the antibacterial response might not last over time. Moreover, the mechanical performance of polymeric fibres degrades significantly during the intended operation, such as usage in textile and industrial filter applications. The degradation process and overall ageing can lead to emitted volatile organic compounds (VOCs). This work focused on the usage of pine rosin as natural antibacterial chemical and analysed the weathering of melt-spun polyethylene (PE) and poly lactic acid (PLA) polyfilaments. A selected copolymer surfactant, as an additional chemical, was studied to better integrate rosin with the molecular structure of the plastics. The results reveal that a high 20 w-% of rosin content can be obtained by surfactant addition in non-oriented PE and PLA melt-spun polyfilaments. According to the VOC analysis, interestingly, the total emissions from the melt-spun PE and PLA fibres were lower for rosin-modified (10 w-%) fibres and when analysed below 60 ℃. The PE fibres of the polyfilaments were found to be clearly more durable in terms of the entire weathering study, i.e., five weeks of ultraviolet radiation, thermal ageing and standard washing. The antibacterial response against Gram-positive Staphylococcus aureus by the rosin-containing fibres was determined to be at the same level (decrease of 3-5 logs cfu/mL) as when using 1.0 w-% of commercial silver-containing antimicrobial. For the PE polyfilaments with rosin (10 w-%), full killing response (decrease of 3-5 logs cfu/mL) remained after four weeks of accelerated ageing at 60 ℃.

Recent advances in graphene and its metal-oxide hybrid nanostructures for lithium-ion batteries.

Today, one of the major challenges is to provide green and powerful energy sources for a cleaner environment. Rechargeable lithium-ion batteries (LIBs) are promising candidates for energy storage devices, and have attracted considerable attention due to their high energy density, rapid response, and relatively low self-discharge rate. The performance of LIBs greatly depends on the electrode materials; therefore, attention has been focused on designing a variety of electrode materials. Graphene is a two-dimensional carbon nanostructure, which has a high specific surface area and high electrical conductivity. Thus, various studies have been performed to design graphene-based electrode materials by exploiting these properties. Metal-oxide nanoparticles anchored on graphene surfaces in a hybrid form have been used to increase the efficiency of electrode materials. This review highlights the recent progress in graphene and graphene-based metal-oxide hybrids for use as electrode materials in LIBs. In particular, emphasis has been placed on the synthesis methods, structural properties, and synergetic effects of metal-oxide/graphene hybrids towards producing enhanced electrochemical response. The use of hybrid materials has shown significant improvement in the performance of electrodes.

Reduced graphene oxide (RGO)-supported NiCo2O4 nanoparticles: an electrocatalyst for methanol oxidation.

The design and development of cheap, highly active, and durable non-platinum (Pt)-based electrocatalysts for methanol electrooxidation is highly desirable, but is a challenging task. In this paper, we demonstrate the application of a hydrothermally synthesized NiCo2O4-reduced graphene oxide (RGO) composite as an electrocatalyst for the electrochemical oxidation of methanol in alkaline pH. The physicochemical properties of the NiCo2O4-RGO composite were investigated via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The physical characterization methods confirm the deposition of NiCo2O4 nanoparticles on the RGO surface. The TEM image shows that the NiCo2O4 nanoparticles with an average size of ∼10 nm are distributed over the RGO surface. Compared to RGO and NiCo2O4 nanoparticles, the NiCo2O4-RGO-based electrode shows excellent electrocatalytic activity for the oxidation of methanol in alkaline pH. On the NiCo2O4-RGO-based electrode, the oxidation of methanol occurs at ∼0.6 V with a higher catalytic current density, and the response is highly stable. The excellent electrocatalytic activity of the NiCo2O4-RGO composite is attributed to the synergistic effects between the NiCo2O4 nanoparticles and RGO. Since the NiCo2O4-RGO composite shows a highly stable response during methanol oxidation reaction, it is a very promising material to be used as an electrocatalyst in the development of high performance non-Pt based alkaline fuel cells.

Fluorescence resonance energy transfer from sulfonated graphene to riboflavin: a simple way to detect vitamin B2.

We have prepared sulfonated graphene (SG) by diazonium coupling technique and it has been characterized by UV-vis absorption spectroscopy, Raman spectroscopy, electron microscopy, energy-dispersive spectroscopy (EDS), EDS elemental mapping, X-ray photoelectron spectroscopy (XPS), and FTIR spectroscopy. The photoluminescence (PL) property of SG at different pH (pH 4, 7, and 9.2) has been investigated and SG shows highest PL-intensity and quantum yield at pH 4 compared to those at higher pH and that of GO at pH 4. Due to the strong overlap between the emission spectrum of SG and absorption spectrum of riboflavin (RF, vitamin B2) at pH 4, it has been tactfully used as donor for the fluorescence resonance energy transfer (FRET) process. However, graphene oxide (GO) does not exhibit any FRET with RF at an identical condition due to its much lower quantum yield. We have demonstrated a selective detection of vitamin B2 in presence of nucleic acid (DNA, RNA), protein (BSA), amino acid (Lysine) and other water-soluble vitamins (Becosules, Zevit capsules) based on the spontaneous FRET from PL-active SG (donor) to RF (acceptor). The calibration curve indicates excellent affirmation to detect vitamin B2 using FRET and it is superior to the ordinary fluorescence method of detecting RF in presence of different biomolecules.

Highly fluorescent graphene oxide-poly(vinyl alcohol) hybrid: an effective material for specific Au3+ ion sensors.

We have developed a new highly fluorescent graphene oxide (GO)/poly(vinyl alcohol) (PVA) hybrid (GO-PVA) in an acidic medium (pH 4). Fourier transform infrared (FTIR) spectra indicate the formation of hydrogen bonds between the hydroxy group of PVA and the hydroxy groups of GO. The hybrid is highly fluorescent, because of passivation by hydrogen bonding, as evident from Raman spectra. The quantum yields of GO-PVA hybrids are higher than that of GO. The fluorescent microscopic images of the hybrids exhibit a fibrillar morphology, and all of them emit highly intense green light. Field-emission scanning electron microscopy (FESEM) micrographs also show a fibrillar morphology, which is produced due to the supramolecular organization of GO-PVA complex. The highly fluorescent GO-PVA1 hybrid has been used as a fascinating tool for selective sensing of Au(3+) ions in aqueous media with a detectable limit of ~275 ppb. The sensitivity of the Au(3+) ion (300 µM) in the presence of 600 µM concentrations of each ion (Cu(2+), Ag(+), Mg(2+), Ca(2+), Zn(2+), K(+), Pb(2+), Co(2+), Ni(2+), Pd(2+), Fe(2+), Fe(3+), and Cr(3+)), taken together, is unique, exhibiting a quenching efficiency of 76%. The quenching efficiency in the presence of a biologically analogous mixture (d-glucose, d-lysine, BSA, Na(+), K(+), Ca(2+), Mg(2+), Zn(2+)) (600 µM each) is 73%, which suggests that the GO-PVA1 hybrid is an efficient sensor of Au(3+) ions. The average lifetime of GO at pH 4 increases in the GO-PVA1 hybrid, indicating the formation of a more stable excited state but the increase in lifetime value after addition of Au(3+) salt solution to the hybrid solution indicates dynamic quenching. The selectivity of sensing of Au(3+) is attributed to its reduction potential being higher than that of other metal ions and XPS data of GO-PVA1 hybrid with 300 µM Au(3+) substantiate the reduction of Au(3+) to Au(0), because of the transfer of excitons from the hybrid facilitating the selective photoluminescence (PL) quenching.

Ethidium bromide-adsorbed graphene templates as a platform for preferential sensing of DNA.

Sulfonated graphene (SG) and graphene oxide (GO) are used as an ethidium bromide (EtBr, E) binding platform, to preferentially sense DNA (D) among the other biomolecules such as RNA (R), bovine serum albumin (BSA, P) and glucose (G) using spectroscopic techniques. EtBr loses its intrinsic fluorescence property after binding with SG. DNA can "turn on" the quenched fluorescence of an SG-EtBr hybrid to a greater extent compared to the RNA, BSA, and glucose. UV-vis absorption spectra and circular dichroism (CD) spectra also support the higher ability of DNA to release adsorbed EtBr from the SG surface in comparison to the above-mentioned biomolecules. Compared to GO-EtBr, the SG-EtBr hybrid is superior to preferentially sense DNA, as the enhancement of fluorescence intensity is 16 times in the later but it is 4.5 times in the former from their respective complexes. An analysis of Raman spectral data indicates that the interaction of EtBr in its adsorbed state on an SG template is greater with DNA than with RNA.