ABSTRACT
2D transition metal carbides and nitrides (MXenes) suggest an uncommonly broad combination of important functionalities amongst 2D materials. Nevertheless, MXene suffers from facile oxidation and colloidal instability upon conventional water-based processing, thus limiting applicability. By experiments and theory, It is suggested that for stability and dispersibility, it is critical to select uncommonly high permittivity solvents such as N-methylformamide (NMF) and formamide (FA) (εr = 171, 109), unlike the classical solvents characterized by high dipole moment and polarity index. They also allow high MXene stacking order within thin films on carbon nanotube (CNT) substrates, showing very high Terahertz (THz) shielding effectiveness (SE) of 40-60 dB at 0.3-1.6 THz in spite of the film thinness < 2 µm. The stacking order and mesoscopic porosity turn relevant for THz-shielding as characterized by small-angle X-ray scattering (SAXS). The mechanistic understanding of stability and structural order allows guidance for generic MXene applications, in particular in telecommunication, and more generally processing of 2D materials.
ABSTRACT
MXenes are emerging sensing materials due to their metallic conductivity and rich surface chemistry for analytes; they, however, suffer from poor stability. Incorporation with functional polymers can largely prevent the performance decay and enhance the sensing performance. Herein, we demonstrate a core-shell composite, Ti3C2Tx@croconaine (poly(1,5-diaminonaphthalene-croconaine), PDAC) prepared by a facile in situ polymerization reaction, suitable for NH3 detection. Compared to pristine Ti3C2Tx, the sensor made of a Ti3C2Tx-polycroconaine composite exhibits a significantly enhanced sensitivity of 2.8% ppm-1 and an estimated achievable limit of detection of 50 ppb. The improved sensing performance could be attributed to the presence of PDAC facilitating the adsorption of NH3 and changing the tunneling conductivity between Ti3C2Tx domains. Density functional theory (DFT) calculations reveal that the adsorption energy of NH3 on PDAC is the highest among the tested gases, which supports the selectivity of the sensor to this analyte. Benefiting from the protection conferred by the PDAC shell, the composite has a reliable operation period of at least 40 days. In addition, we demonstrated a flexible paper-based sensor of the Ti3C2Tx@PDAC composite, without attenuated performance upon mechanical deformation. This work proposed a novel mechanism and a feasible methodology to synthesize MXene-polymer composites with improved sensitivity and stability for chemical sensing.
ABSTRACT
The synthesis of low-dimensional transition metal nitride (TMN) nanomaterials is developing rapidly, as their fundamental properties, such as high electrical conductivity, lead to many important applications. However, TMN nanostructures synthesized by traditional strategies do not allow for maximum conductivity and accessibility of active sites simultaneously, which is a crucial factor for many applications in plasmonics, energy storage, sensing, and so on. Unique interconnected two-dimensional (2D) arrays of few-nanometer TMN nanocrystals not only having electronic conductivity in-plane, but also allowing transport of ions and electrolyte through the porous nanosheets, which are obtained by topochemical synthesis on the surface of a salt template, are reported. As a demonstration of their application in a lithium-sulfur battery, it is shown that 2D arrays of several nitrides can achieve a high initial capacity of >1000 mAh g-1 at 0.2 C and only about 13% degradation over 1000 cycles at 1 C under a high areal sulfur loading (>5 mg cm-2 ).
ABSTRACT
The use of abundant solar energy for regeneration and desalination of water is a promising strategy to address the challenge of a global shortage of clean water. Progress has been made to develop photothermal materials to improve the solar steam generation performance. However, the mass production rate of water is still low. Herein, by a rational combination of photo-electro-thermal effect on an all-graphene hybrid architecture, solar energy can not only be absorbed fully and transferred into heat, but also converted into electric power to further heat up the graphene skeleton frame for a much enhanced generation of water vapor. As a result, the unique graphene evaporator reaches a record high water production rate of 2.01-2.61 kg m-2 h-1 under solar illumination of 1 kW m-2 even without system optimization. Several square meters of the graphene evaporators will provide a daily water supply that is enough for tens of people. The combination of photo-electro-thermal effect on graphene materials offers a new strategy to build a fast and scalable solar steam generation system, which makes an important step towards a solution for the scarcity of clean water.
ABSTRACT
Recycling of plastic waste has commercial value and practical significance for both environmental safety and recovery of resources. To realize trash recycling, a cheap, simple, and safe solid-state chemical vapor deposition method has been developed to convert a series of daily plastic wastes to a high quality graphene foil (GF) at a large scale. The GF possesses a high electrical conductivity of 3824 S·cm-1, which is much higher than that of the conventional free-standing graphene film treated at an extremely high temperature of 2200-2500 °C. Further, the GF can act as various flexible elements such as a free-standing electrode in a foldable lithium-ion battery, which shows stable electrochemical performances. On the other hand, it presents a fast and ultra low-voltage responsivity to be used as a flexible electrothermal heater, which generates a temperature of up to 322.6 °C at a low input voltage of only 5 V. The convenient trash-to-treasure conversion of plastics to GF provides a unique pathway for waste recycling and opens new application possibilities of graphene in various fields.
ABSTRACT
Polymer/graphene-based materials with interesting physical and chemical properties have been attracting considerable attention and have been shown to have great potential as active materials in the field of energy conversion and storage. In this review, we focus on recent significant advances in the fabrication and application of polymer/graphene hybrids as electrocatalysts and electrode materials. Synthetic strategies and application of these materials in energy conversion and storage are presented, particularly in devices such as fuel cells, actuators, and supercapacitors, accompanied with a discussion of the challenges and research directions necessary for the future development of polymer/graphene hybrids.
ABSTRACT
Vertically, carbon nanotube (CNT) arrays were successfully fabricated on hexagon patterned Si substrates through radio frequency plasma-enhanced chemical vapor deposition using gas mixtures of acetylene (C2H2) and hydrogen (H2) with Fe/Al2O3 catalysts. The CNTs were found to be graphitized with multi-walled structures. Different H2/C2H2 gas flow rate ratio was used to investigate the effect on CNT growth, and the field emission properties were optimized. The CNT emitters exhibited excellent field emission performance (the turn-on and threshold fields were 2.1 and 2.4 V/µm, respectively). The largest emission current could reach 70 mA/cm(2). The emission current was stable, and no obvious deterioration was observed during the long-term stability test of 50 h. The results were relevant for practical applications based on CNTs.
