Adsorption of S-containing gases on pristine, defective, and heteroatom doped stanene is studied for gas sensing applications by van der Waals corrected density functional theory. SO2 and H2S gas molecules are found to bind to pristine stanene too weakly to alter the electronic properties sufficiently for efficient gas sensing (binding energy of −0.20 and −0.33 eV, respectively). We demonstrate that vacancies and heteroatom doping can enhance the binding energy to −1.67 and −0.74 eV, respectively. It is found that presence of mono-vacancies, tri-vacancies, and In dopants at low concentrations in stanene results in considerable variations of the electronic properties in contact with S-containing gases, thus transforming stanene into an efficient sensing material.
A multi-scale approach is employed to design metal-organic frameworks (MOFs). The methane sorption properties are studied by grand canonical Monte Carlo simulations to reveal the structure-property relationship with respect to the methane total uptake and working capacity at different temperatures and pressures. We identify rhr-MOFs with outstanding gravimetric working capacity. For example, the BBB MOF (largest studied pore size) achieves a value of 60.7 wt% at 298 K and 5–65 bar.
High power K+ ion capacitors have great potential in various large-scale applications because of the cost advantages and the low redox potential of K/K+. However, the large ionic radius of potassium brings huge challenges for the development of suitable electrode materials. Here we demonstrate a general strategy for preparing porous MXene electrodes that can significantly enhance K+ storage performance. Using V2C MXene as a model system, we show that the K+ ion storage capacity can be greatly boosted by a simple sequential acid/alkali treatment. The resulting product, K–V2C, not only delivers a capacity of 195 mAh g−1 (in contrast to 98 mAh g−1 of pristine V2C) at 50 mA g−1, but also good rate performance. The charge storage mechanism was carefully studied and is shown to involve a solvent co-intercalation process. In addition, full cells were fabricated by coupling the K–V2C anode and Prussian blue analogous (KxMnFe(CN)6) cathode, which can work at a high average operating voltage of ~3.3 V within a wide range (0.01 V–4.6 V). Moreover, the devices can achieve a high energy density of 145 Wh kg−1 at a power density of 112.6 W kg−1, suggesting that K–V2C, and other porous MXenes prepared by our approach, are promising electrodes in mobile ion capacitors.
Ahmad, Rafiq; Majhi, Sanjit Manohar; Zhang, Xixiang; Swager, Timothy M.; Salama, Khaled N.(Advances in Colloid and Interface Science, Elsevier BV, 2019-05-22)[Article]
Vertically oriented zinc oxide (ZnO) nanomaterials, such as nanorods (NRs), nanowires (NWs), nanotubes (NTs), nanoneedles (NNs), and nanosheets (NSs), are highly ordered architectures that provide remarkable properties for sensors. Furthermore, these nanostructures have fascinating features, including high surface-area-to-volume ratios, high charge carrier concentrations, and many surface-active sites. These features make vertically oriented ZnO nanomaterials exciting candidates for gas sensor fabrication. The development of efficient methods for the production of vertically oriented nanomaterial electrode surfaces has resulted in improved stability, high reproducibility, and gas sensing performance. Moving beyond conventional fabrication processes that include binders and nanomaterial deposition steps has been crucial, as the materials from these processes suffer from poor stability, low reproducibility, and marginal sensing performance. In this feature article, we comprehensively describe vertically oriented ZnO nanomaterials for gas sensing applications. The uses of such nanomaterials for gas sensor fabrication are discussed in the context of ease of growth, stability on an electrode surface, growth reproducibility, and enhancements in device efficiency as a result of their unique and advantageous features. In addition, we summarize applications of gas sensors for a variety of toxic and volatile organic compound (VOC) gases, and we discuss future directions of the vertically oriented ZnO nanomaterials.
Chen, Long; Li, Zhi; Chen, Mingguang(Journal of Environmental Chemical Engineering, Elsevier BV, 2019-05-14)[Article]
Reduced graphene oxide (rGO) has broad applications based upon its superior electronic properties. In many cases, an additional antibacterial function of these materials requests physical or chemical modification, such as incorporating silver nanoparticles into rGO to produce silver-reduced graphene oxide (Ag/rGO) composite. Most of the previous methods of preparing Ag/rGO are top-down techniques starting from graphite exfoliation into graphene oxide (GO), to the reduction of a mixture of silver nitrate and GO into the Ag/rGO nanocomposite. This method is flawed by its high cost, tedious treatments, and heavy pollution from generated wastes. Herein, we manifest a novel bottom-up strategy of growing Ag/rGO totally from a cellulose acetate and silver nitrate precursor in one step without tedious solution exfoliation and chemical treatment steps. The produced Ag/rGO nanocomposite maintains highly effective antibacterial activity, which is ascribed to the synergy between the effect of rGO size and incorporated bactericidal silver nanoparticles. Our strategy is promising for industrial production from sustainability and cost-effectiveness perspectives.
We demonstrate a novel strategy to enhance sulfur loading and rate performance for Li–S battery by synchronously coupling a nanostructured cathode with an antifouling separator via a facile electrostatic self-assembly approach. The assembly of two dimensional (2D) MXene and positively charged 1D CNT-Polyethyleneimine was observed to controllably address the key issues of sluggish ionic transport, and produce an integrate cathode with dynamic crosslinking network. Moreover, an antifouling separator is proposed by this strategy for the first time, which features well-organized inter-lamellar porosity, dual polarity and high conductivity. The antifouling separator is found to play a pivotal role in: 1) low-order polysulfide activation, 2) high rate cyclability, and 3) Li dendrites inhibition. Our integrated design realizes a long-term capacity of 980 mAh g−1 at 5 mA cm−2 over 500 cycles (sulfur loading: 2.6 mg cm−2). Furthermore, a flexible self-assembled cathode with high loading (5.8 mg cm−2) and superb mechanical strength (13 MPa), demonstrates an appealing areal capacity of 7.1 mAh cm−2 and rate performance at nearly 10 mA cm−2.
Solution processable two-dimensional transition metal carbides, commonly known as MXenes, have drawn much interest due to their diverse optoelectronic, electrochemical and other useful properties. These properties have been exploited to develop thin and optically transparent microsupercapacitors. However, color changing MXene-based microsupercapacitors have not been explored. In this study, we developed titanium carbide--poly(3,4-ethylenedioxythiophene) (PEDOT) heterostructures by electrochemical deposition using a non-aqueous monomeric electrolytic bath. Planar electrodes of such hybrid films were carved directly using an automated scalpel technique. Hybrid microsupercapacitors showed five-fold areal capacitance and higher rate capabilities (2.4 mF cm−2 at 10 mV s−1, retaining 1.4 mF cm−2 at 1000 mV s−1) over the pristine MXene microsupercapacitors (455 μF cm−2 at 10 mV s−1, 120 μF cm−2 at 1000 mV s−1). Furthermore, the electrochromic behavior of PEDOT/Ti3C2Tx microsupercapacitors was investigated using in-situ UV–vis and resonant Raman spectroscopies. A high-rate color switch between a deep blue and colorless state is achieved on both electrodes in the voltage range of −0.6 to 0.6 V, with switching times of 6.4 and 5.5 s for bleaching and coloration, respectively. This study opens new avenues for developing electrochromic energy storage devices based on MXene heterostructures.
High-performance passivating contact is a prerequisite for high-efficiency crystalline silicon (c-Si) solar cells. In this work, an electron-conductive, hole-blocking contact based on titanium nitride (TiN) deposited by reactive magnetron sputtering is presented. Quasi-metallic TiN combined with an ultrathin SiO2 passivation layer (SiO2/TiN) is demonstrated to be an effective electron-selective contact on c-Si, featuring a low-contact resistivity of 16.4 mΩ.cm2 and a tolerable recombination current parameter of ∼500 fA/cm2. By implementing the dual-function SiO2/TiN contact, which acts simultaneously as a surface passivating layer and metal electrode, an efficiency of 20% is achieved by an n-type c-Si solar cell with a simple structure. This work not only demonstrates a way to develop efficient n-type c-Si solar cells with dual-function metal nitride contacts at a low cost but also expands the pool of available carrier transport materials, from metal oxides to metal nitrides, for photovoltaic devices.
Hajjaj, Amal; Nanaiah, Karumbaiah Chappanda; Batra, Nitin M; Hafiz, Md Abdullah Al; Da Costa, Pedro M. F. J.; Younis, Mohammad I.(Sensors and Actuators A: Physical, Elsevier BV, 2019-04-05)[Article]
Conventional pressure sensors rely on diaphragms with large surface areas, which deform in response to pressure. Down scalability of these devices is one of the major challenges of the technology along with reducing the overall actuation voltage and achieving ultra-high sensitivity. We present a sensitive miniature pressure sensor based on the change in the physisorbed gases with the pressure of the surrounding air. The sensor consists of a suspended individual multiwall carbon nanotube (MWCNT) clamped on Au electrodes by electron-beam-induced deposition (EBID) of Pt. The variation in the surrounding pressure is shown to be tracked by monitoring the change in the resistivity, hence resistance, of the MWCNT bridge structure due to the change in percentage of oxygen and humidity in the surrounding medium with pressure. The experimental data reveal the practicability and simplicity of the proposed pressure sensor.
Establishing an effective three-dimensional (3D) in vitro culture system to better model human neurological diseases is desirable, since the human brain is a 3D structure. Here, we demonstrated the development of a polydimethylsiloxane (PDMS) pillar-based 3D scaffold that mimicked the 3D microenvironment of the brain. We utilized this scaffold for the growth of human cortical glutamatergic neurons that were differentiated from human pluripotent stem cells. In comparison with the 2D culture, we demonstrated that the developed 3D culture promoted the maturation of human cortical glutamatergic neurons by showing significantly more MAP2 and less Ki67 expression. Based on this 3D culture system, we further developed an in vitro disease-like model of traumatic brain injury (TBI), which showed a robust increase of glutamate-release from the neurons, in response to mechanical impacts, recapitulating the critical pathology of TBI. The increased glutamate-release from our 3D culture model was attenuated by the treatment of neural protective drugs, memantine or nimodipine. The established 3D in vitro human neural culture system and TBI-like model may be used to facilitate mechanistic studies and drug screening for neurotrauma or other neurological diseases.
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