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The high surface activity and large specific surface area of metal halide perovskite materials create favorable conditions for improving the sensitivity and selectivity of gas sensors. Meanwhile, the high photoelectric conversion efficiency makes perovskite materials the best candidates for new self-powered gas sensing systems. Therefore, the adsorption mechanism of several volatile organic compounds (VOCs) on CsPbX3 (X = Cl, Br, and I) surfaces was investigated based on first-principles calculations and the non-equilibrium Green's function, including C2H6, CH4, CH3OH, and CH2O. The results show that CsPbBr3 (CPB) has excellent gas-sensing properties for CH2O molecules. The current-voltage (I-V) curves indicate that the transport properties of CH2O after adsorption on the CPB surface had a clear response. Moreover, the good mechanical response makes the adsorption process reversible and provides the possibility for flexible devices. Finally, the good absorption spectrum lays the foundation for the application of CPB in photovoltaic (PV) self-powered sensors. Therefore, we predict that CPB is expected to be a candidate for a CH2O gas sensor with high sensitivity and selectivity.
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Two-dimensional (2D) piezoelectric materials have attracted wide attention because they are of great significance to the composition of piezoelectric nanogenerators. In this work, we have systematically studied the piezoelectric properties of 2D LiAlTe2by using the first-principles calculation and found the 2D LiAlTe2monolayer exhibits both large in-plane piezoelectric coefficientd11(3.73 pm V-1) and out-of-plane piezoelectric coefficientd31(0.97 pm V-1). Moreover, the piezoelectric coefficients of 2D LiAlTe2are highly tunable by strain and stacking. When different uniaxial strains are applied,d11changes dramatically, butd31changes little. When 2% stretching is applied to 2D LiAlTe2monolayer along thex-axis,d11reaches 7.80 pm V-1, which is twice as large as the previously reported 2D piezoelectric material MoS2. Both AA stacking and AB stacking can enhance the piezoelectric properties of 2D LiAlTe2, but they have different effects on in-plane and out-of-plane piezoelectric coefficients. AA stacking can greatly increased31but has little impact ond11. In the case of four-layer AA stacking, thed31reaches 3.32 pm V-1. AB stacking can both increased11andd31, butd11grows faster thand31as the number of layers increases. In the case of four-layer AB stacking,d11reaches 18.05 pm V-1. The excellent and highly tunable piezoelectric performance provides 2D LiAlTe2greater potential for the application of piezoelectric nano-generators and other micro-nano piezoelectric devices.
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In this study, the adsorption of gas molecules, such as O2, NH3, CO, CO2, H2O, NOx (x = 1, 2) and SO2, on Janus Te2Se monolayer has been investigated by means of density functional theory (DFT) calculations. We show that Janus Te2Se monolayer is preferable for SO2 and NOx molecules with suitable adsorption strength and apparent charge transfers. We further calculated the current-voltage (I-V) curves using the nonequilibrium Green's function (NEGF) method. The transport feature exhibits distinct responses with a dramatic change of I-V curves before and after NOx (SO2) adsorption on Janus Te2Se. Thus, we predict that Janus Te2Se could be a promising candidate for SO2 and NOx sensors with high selectivity and sensitivity. Moreover, the effect of strain on the gas/substrate adsorption systems was also studied, implying that the strained Janus Te2Se monolayer could enhance the sensitivity and selectivity to SO2 and NO2. The adsorbed SO2 and NO2 on Janus Te2Se could escape by releasing the applied strain, which indicates that the capture process is reversible. Our study widens the application of Janus Te2Se not only as piezoelectric materials, but also as a potential gas sensor or capturer of SO2 and NOx with high sensitivity and selectivity.
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Nowadays, climate problems caused by greenhouse gases are becoming more and more serious. Motivated by reducing carbon dioxide emissions from fossil fuel power generation, scientists are devoting themselves to developing novel materials or technologies for capturing carbon dioxide. Nanostructure materials, which show great potential for this application, have come to the attention of scientists. Herein, the effects of doping an aluminum atom (replacing one boron atom by one aluminum one) on the adsorption of carbon dioxide on boron nitride nanosheets are theoretically investigated through computational analysis based on density functional theory. The results show that the binding between oxygen and aluminum atoms, which comes from classical Lewis base (CO2)-Lewis acid (Al) interactions, can provide a considerable gain to the mutual effect between the carbon dioxide molecule and the doped substrate. Compared with pristine boron nitride nanosheets, the adsorption energy value of the carbon dioxide molecule is markedly increased to 0.4784 eV (about 2.5-fold) after the doping process, which is in the range of the ideal adsorption energy of 0.415-0.829 eV. More importantly, the essence of physisorption signifies that carbon dioxide can be released by means of specific physical desorption, and, sequentially, this is more conducive for achieving reversible adsorption.
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Structural symmetry-breaking can lead to novel electronic and piezoelectric properties in two-dimensional (2D) materials. In this paper, we propose a 2D Janus tellurene (Te2Se) monolayer with asymmetric Se/Te surfaces and its derived multilayer structures. The band structure calculations show that the 2D Janus Te2Se monolayer is an indirect gap semiconductor, and the intrinsic mirror asymmetry combined with the spin-orbit coupling induces the Rashba spin splitting and the out-of-plane spin polarization. Moreover, the absence of both the inversion symmetry and out-of-plane mirror symmetry, together with flexible mechanical properties, results in large in-plane and out-of-plane piezoelectric coefficients that are valuable in 2D piezoelectric materials. Furthermore, the out-of-plane piezoelectric effects can exist in multilayer structures under different stacking sequences while the in-plane piezoelectric effect can only exist in some specific stacking patterns. The piezoelectric coefficients of the Janus Te2Se monolayer and multilayers exceed those of many Janus transition metal dichalcogenides and other well-known piezoelectric materials (e.g., α-quartz and wurtzite-AlN). The combination of the SOC-induced spin splitting and large piezoelectricity endows the Janus Te2Se structures with potential for applications in spintronics, flexible electronics and piezoelectric devices.
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Despite the good progress made in materials fabrication, it remains a big challenge to synthesize 2D sheets by assembling nanoflakes that are usually produced in experiments, and few theoretical studies have explored this topic. Based on the recent experimental synthesis of pentagonal graphene nanoflakes and the novel properties of penta-graphene, we report a series of 2D assembled carbon allotropes (CG568-80, CG568-180 and CG568-320) that have the following unusual properties: different from most other 2D carbon allotropes, the assembled carbon sheets have negative Gaussian curvatures, and exhibit ultra-softness and better chemical reactivity due to the curvature-induced misalignment of π-orbitals as compared with pristine graphene; all three studied carbon sheets are highly stable with binding energies comparable to those of phagraphene and ψ-graphene, and are semiconductors with tunable band gaps, displaying size-dependent carrier mobilities: â¼105 cm2 V-1 s-1 (CG568-80 and CG568-320) and â¼104 cm2 V-1 s-1 (CG568-180). These features indicate that assembling nanoflakes can effectively tune the structural morphology and properties to expand the family of 2D carbon materials for future applications.
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Efficient and rapid screening of target materials in a vast material space remains a significant challenge in the field of materials science. In this study, first-principles calculations and machine learning algorithms are performed to search for high out-of-plane piezoelectric stress coefficient materials in the MXene functional database among the 1757 groups of noncentrosymmetric MXenes with nonzero band gaps, which meet the criteria for piezoelectric properties. For the monatomic MXene testing set, the random forest regression (RFR), gradient boosting regression (GBR), support vector regression (SVR), and multilayer perceptron regression (MLPR) exhibit R2 values of 0.80, 0.80, 0.89, and 0.87, respectively. Expanding our analysis to the entire MXene data set, the best active learning cycle finds more than 140 and 22 MXenes with out-of-plane piezoelectric stress coefficients (e31) exceeding 3 × 10-10 and 5 × 10-10 C/m, respectively. Moreover, thermodynamic stabilities were confirmed in 22 MXenes with giant piezoelectric stress coefficients and 9 MXenes with both large in-plane (d11 > 15 pm/V) and out-of-plane (d31 > 2 pm/V) piezoelectric strain coefficients. These findings highlight the remarkable capabilities of machine learning and its optimization algorithms in accelerating the discovery of novel piezoelectric materials, and MXene materials emerge as highly promising candidates for piezoelectric materials.
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The development of wearable electronics has facilitated the growth of flexible energy storage systems, including micro-supercapacitors (MSCs). Thus, it is urgent to fabricate MSCs with both excellent mechanical strength and electrochemical performance. In this work, P-enriched laser-induced graphene (LIG) is fabricated for the first time on Kevlar textiles via the one-step laser direct writing process. Laser engraving is employed on polyvinyl alcohol (PVA)/H3PO4-coated Kevlar to obtain porous graphene and simultaneously in-situ dope phosphorus in pure LIG. The unreacted gel dopant could be removed by washing in hot water because of the thermal solubility of PVA, therefore the Janus LIG/Kevlar textiles keep well flexible and skin-friendly. Moreover, the phosphorus-doped LIG has optimized porous morphology compared to pure LIG, which benefits the interface between electrolyte and electrodes. The introduction of phosphorus contributes to the electrochemical performance attributed to the optimized porous morphology and pseudocapacitance brought by phosphorus doping. The obtained in-plane MSCs (PMSC-4) on Kevlar textiles present a high areal capacitance of 125.35 mF cm-2, good cycling stability (over 88% during 10,000 cycles), and flexibility. This work provides a facial and scalable method firstly to fabricate and optimize heteroatom-doping MSCs on Kevlar, showing potential for wearable electronics and electronic textiles.
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Grafite , Dispositivos Eletrônicos Vestíveis , Fósforo , Têxteis , LasersRESUMO
There has been a recent increase in the demand for wearable sensors for sweat glucose monitoring to facilitate diabetes management in a patient-friendly and non-invasive manner. To address this issue, the key challenge lies in the design of flexible sensors with high conductivity, miniaturized patterning, and environmental friendliness. Herein, we introduce a flexible electrochemical sensing system for glucose and pH detection based on one-step laser-scribed PtNPs nanostructured 3D porous laser-scribed graphene (LSG). The as-prepared nanocomposites can synchronously possess hierarchical porous graphene architectures, whereas PtNPs can significantly enhance their sensitivity and electrocatalytic activity. Benefiting from these advantages, the fabricated Pt-HEC/LSG biosensor exhibited a high sensitivity of 69.64 µA mM-1 cm-2 as well as a low limit of detection (LOD) of 0.23 µM at a detection range of 5-3000 µM (covering the glucose range in sweat). Moreover, the pH sensor was functionalized with polyaniline (PANI) on a Pt-HEC/LSG electrode, and it also exhibited high sensitivity (72.4 mV/pH) in the linear range of pH 4-8. The feasibility of the biosensor was confirmed by analyzing human perspiration during physical exercise. This dual-functional electrochemical biosensor displayed excellent performance, including a low detection limit, high selectivity, and great flexibility. These results confirm that the proposed dual-functional flexible electrode and fabrication process are highly promising for application in human sweat-based electrochemical glucose and pH sensors.
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Técnicas Biossensoriais , Grafite , Humanos , Glucose , Platina , Glicemia , Suor , Porosidade , Automonitorização da Glicemia , Técnicas Biossensoriais/métodos , Lasers , Concentração de Íons de Hidrogênio , Técnicas Eletroquímicas/métodosRESUMO
Two-dimensional (2D) materials composed of pentagon and Janus motifs usually exhibit unique mechanical and electronic properties. In this work, a class of ternary carbon-based 2D materials, CmXnY6-m-n (m = 2, 3; n = 1, 2; X, Y = B, N, Al, Si, P), are systematically studied by first-principles calculations. Six of 21 Janus penta-CmXnY6-m-n monolayers are dynamically and thermally stable. The Janus penta-C2B2Al2 and Janus penta-Si2C2N2 exhibit auxeticity. More strikingly, Janus penta-Si2C2N2 exhibits an omnidirectional negative Poisson ratio (NPR) with values ranging from -0.13 to -0.15; in other words, it is auxetic under stretch in any direction. The calculations of piezoelectricity reveal that the out-of-plane piezoelectric strain coefficient (d32) of Janus panta-C2B2Al2 is up to 0.63 pm/V and increases to 1 pm/V after a strain engineering. These omnidirectional NPR, giant piezoelectric coefficients endow the Janus pentagonal ternary carbon-based monolayers as potential candidates in the future nanoelectronics, especially in the electromechanical devices.
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With the rapid development of human-machine technology, self-powered pressure sensor integrated systems have been extensively studied. However, there are only a few reports on such multifunctional devices using a single active material. In this work, we report a flexible integrated system, which consists of flexible pressure sensors and supercapacitors. Both of the devices were fabricated based on layered porous Cu@Cu2O/graphitic carbon (Cu@Cu2O/GC) composites, which were obtained by a one-step simple polymer heat treatment method. Due to the discontinuous conductive paths and effective stress concentration relief in the composite, the pressure sensor shows a high sensitivity of 90 kPa-1 in a wide working range of 0-150 kPa, a fast response time of 90 ms, and a detection limit of 2.4 Pa. Moreover, the layered porous structure Cu@Cu2O/GC can not only maintain the integrity of the electrode material, but also promote the diffusion of electrons, enabling super capacitors to obtain excellent electrochemical performance. The specific capacitance of the super capacitor is 17.8 mF cm-2. More importantly, the flexible self-powered integrated system could be directly attached to the human body to detect human motions, showing its great potential application in wearable devices.
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Grafite , Humanos , Carbono , Porosidade , Capacitância Elétrica , EletrodosRESUMO
Transition metal nanoparticles-graphene nanocomposites incorporate the advantages of graphene and metal nanoparticles, which arouse extensive attention. Here, we design a novel, facile and versatile method for in-situ synthesis of laser-induced porous graphene (LIG) decorated with cobalt particles (Co). The LIG/Co nanocomposites are fabricated through one-step laser direct scribing on a customized film composed of polyimide (PI) powder, polyvinyl alcohol (PVA), and cobalt chloride (CoCl2·6H2O) precursors. Benefiting from the unique properties of Co nanoparticles embedded LIG, the obtained optimal in-plane micro-supercapacitors (IMSC) based on LIG/Co-1.5 possesses an excellent areal capacitance of 110.11 mF cm-2 and a superior energy density of 9.79 µWh cm-2, which are about 79 times that of pure LIG-based IMSCs. Simultaneously, the LIG/Co-1.5 MSCs also present good cycling stability, remarkable modular integration capability, and outstanding mechanical flexibility, showing potential for practical applications. Additionally, the density functional theory (DFT) calculations indicate that the decorating of cobalt particles elevates electron transfer. Moreover, the interaction between electrolyte and electrodes is also improved with the introduction of cobalt particles. Therefore, this strategy offers a new avenue for facile and large-scale manufacturing of various metallic atoms in-situ decorating in porous graphene.
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Two-dimensional Janus nanomaterials, due to their unique electronic, optical, and piezoelectric characteristics resulting from the antisymmetric structures, exhibit great prospects in multifunctional energy application to alleviate the energy crisis. Monolayer Janus Pb2SSe, with a black phosphorus-like structure and an indirect band gap of 1.59 eV as well as high carrier mobility (526-2105 cm2 V-1 s-1), displays outstanding potentials in the energy conversion between nanomechanical energy, solar energy, waste heat, and electricity, which has been comprehensively studied utilizing DFT-based simulations. The research results reveal that monolayer Pb2SSe not only possesses giant in-plane piezoelectricity of d11 = 75.1 pm V-1 but also superhigh out-of-plane piezoelectric coefficients (d31 = 0.5 pm V-1 and d33 = 15.7 pm V-1). Meanwhile, by constructing Pb2SSe bilayers, the out-of-plane piezoelectric coefficients can be significantly enhanced (d31 = 19.2 pm V-1 and d33 = 194.7 pm V-1). In addition, owing to the small conduction band offset, suitable donor band gap and excellent light absorption capability in the Pb2SSe/SnSe (Pb2SSe/GeSe) heterostructure, the power conversion efficiencies were calculated to be up to 20.02% (Pb2SSe/SnSe) and 19.28% (Pb2SSe/GeSe), making it a promising candidate for solar energy collection. Furthermore, from the thermoelectric electron and phonon transport calculations, it can be found that the Pb2SSe monolayer is an n-type thermoelectric material with ultrahigh ZT = 2.19 (1.52) at room temperature, which can be traced back to its ultralow κL = 0.78 (0.99) W m-1 K-1, and superhigh PF = 10.18 (8.25) mW m-1 K-2 along the x(y) direction at the optimal doping concentration at 300 K. The abovementioned versatile characteristics in the Janus Pb2SSe monolayer, along with its comprehensive stabilities (energy, dynamic, thermal, and mechanical stabilities), highlight its potential in clean energy harvesting.
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This study proposes an efficient, facile, and scalable strategy to synthesize in situ heteroatom-doped porous graphene via laser direct writing on the precursor-doped polyimide (PI) film, which is fabricated for the first time through incorporating PI powder and precursors with sodium carboxymethyl cellulose (CMC) binder by a drop-casting and low-temperature drying process. The resulting microsupercapacitors (MSCs) based on the as-prepared heteroatom-doped porous graphene exhibit remarkable capacitive performance. The typical boron-doped MSC prepared on borax-doped polyimide film possesses an ultrahigh areal capacitance of 60.6 mF cm-2 at 0.08 mA cm-2, which is approximately 20 times larger than that of undoped MSC. Furthermore, the boron-doped MSC has impressive cycling stability (with the capacitance retention of 96.3% after 20â¯000 cycles), exceptional mechanical flexibility, tunable capacitance, and voltage output through arbitrary modular serial and parallel integration. Besides, the nitrogen-doped porous graphene with excellent capacitive performance is also prepared by laser direct scribing on the sulfonated melamine-doped polyimide film, demonstrating excellent scalability and generality of this strategy. Hence, one-step laser direct writing on precursor-doped polyimide films can realize in situ heteroatom doping and generation of hierarchical porous graphene electrodes simultaneously, which opens a new avenue for the facile, cost-effective, and scalable fabrication of heteroatom-doped porous graphene, thus promising for MSCs and various flexible and wearable electronics at large-scale production.
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In this work, we predict two novel two-dimensional (2D) auxetic materials, BiSbX3 (X = S, Se) monolayers, through first-principles calculations. Attributed to their special braceletlike structure, the in-plane negative Poisson's ratio (NPR) of BiSbS3 and BiSbSe3 monolayers are as high as -0.25 and -0.26, respectively. The phonon dispersion calculations, ab initio molecular dynamics simulations, and elastic constants calculations demonstrate that these two monolayers possess excellent dynamic, thermal, and mechanical stabilities. The band gap values of BiSbS3 and BiSbSe3 calculated at the HSE level by considering the spin-orbit coupling (SOC) effect are 1.68 and 1.20 eV. The anisotropic carrier mobility and superior optical absorption indicate that they may shine in the next generation of electronic and optoelectronic devices. All of these discoveries not only enrich the types of auxetic materials but also provide a structural reference for designing new auxetic materials on the molecular level. Furthermore, they can provide theoretical guidance for future applications of BiSbX3 (X = S, Se) monolayers in various fields.
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Sensitivity and pressure range are two significant parameters of pressure sensors. Existing pressure sensors have difficulty achieving both high sensitivity and a wide pressure range. Therefore, we propose a new pressure sensor with a ternary nanocomposite Fe2O3/C@SnO2. The sea urchin-like Fe2O3 structure promotes signal transduction and protects Fe2O3 needles from mechanical breaking, while the acetylene carbon black improves the conductivity of Fe2O3. Moreover, one part of the SnO2 nanoparticles adheres to the surfaces of Fe2O3 needles and forms Fe2O3/SnO2 heterostructures, while its other part disperses into the carbon layer to form SnO2@C structure. Collectively, the synergistic effects of the three structures (Fe2O3/C, Fe2O3/SnO2 and SnO2@C) improves on the limited pressure response range of a single structure. The experimental results demonstrate that the Fe2O3/C@SnO2 pressure sensor exhibits high sensitivity (680 kPa-1), fast response (10 ms), broad range (up to 150 kPa), and good reproducibility (over 3500 cycles under a pressure of 110 kPa), implying that the new pressure sensor has wide application prospects especially in wearable electronic devices and health monitoring.
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Wearable devices with integrated alarm functions play a vital role in daily life and can help people prevent potential hazards. Although many wearable sensors have been extensively studied and proposed to monitor various physiological signals, most of them are needed to integrate with the external alarm elements to realize warning, such as light-emitting diodes and buzzers, resulting in the system complexity and poor flexibility. In this paper, an integrated sensing and warning multifunctional device based on the mechanical and thermal effect of porous graphene is proposed on a bilayer asymmetrical pattern of laser-induced graphene (LIG). Compared with the strain sensor with nonpatterned LIG, the mechanical performance is greatly improved with the highest gauge factor value of up to 950 for the strain sensor with mesh-patterned LIG. On the contrary, the heating performance of the heater with nonpatterned LIG is better than that with mesh-patterned LIG. Combining the performance differences of different LIG patterns, the integrated wearable device with a bilayer asymmetrical LIG pattern is demonstrated. It can generate enough heating energy to warn the person when the detected signal meets the threshold condition measured in real time by the ultrasensitive strain sensor. This work will provide a new way to construct an integrated wearable device for realizing multifunctional applications. This integrated multifunctional device shows great potential toward the applications in healthcare monitoring and timely warning.
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Grafite/química , Dispositivos Eletrônicos Vestíveis , Temperatura Corporal , Humanos , Lasers , Monitorização Fisiológica/instrumentação , Monitorização Fisiológica/métodos , PorosidadeRESUMO
Controlling the duration that information lasts on paper so that it disappears as desired is crucial for information security. However, this area is rarely studied. Here, we report [TEMA]2SbCl5 (1, TEMA+ = methyltriethylammonium), [TEA]2SbCl5 (2, TEA+ = tetraethylammonium), [TEBA]2SbCl5 (3, TEBA+ = benzyltriethylammonium), and [Ph4P]2SbCl5 (4, Ph4P+ = tetraphenylphosphonium) with structure-dependent reversible photoluminescent switching induced by the absorption and thermal release of small guest molecules including H2O, methanol, and ethylene glycol. Comparing the structural disorder levels, bond lengths, and luminescent Stokes shifts of the compounds aided in understanding their selective absorption behavior. Our results indicated that the information duration on the rewritable paper coated with the title compounds is easily tuned by changing the cation of the compounds, the type of guest molecules, and laser heating power. Our study opens previously unidentified avenues for information security and extends the potential applications of rewritable paper.
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Industrial production, environmental monitoring, and clinical medicine put forward urgent demands for high-performance gas sensors. Two-dimensional (2D) materials are regarded as promising gas-sensing materials owing to their large surface-to-volume ratio, high surface activity, and abundant surface-active sites. However, it is still challenging to achieve facilely prepared materials with high sensitivity, fast response, full recovery, and robustness in harsh environments for gas sensing. Here, a combination of experiments and density functional theory (DFT) calculations is performed to explore the application of tellurene in gas sensors. The prepared tellurene nanoflakes via facile liquid-phase exfoliation show an excellent response to NO2 (25 ppb, 201.8% and 150 ppb, 264.3%) and an ultralow theory detection limit (DL) of 0.214 ppb at room temperature, which is excellent compared to that of most reported 2D materials. Furthermore, tellurene sensors present a fast response (25 ppb, 83 s and 100 ppb, 26 s) and recovery (25 ppb, 458 s and 100 ppb, 290 s). The DFT calculations further clarify the reasons for enhanced electrical conductivity after NO2 adsorption because of the interfacial electron transfer from tellurene to NO2, revealing an underlying explanation for tellurene-based gas sensors. These results indicate that tellurene is eminently promising for detecting NO2 with superior sensitivity, favorable selectivity, an ultralow DL, fast response-recovery, and high stability.
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Motivated by the recent experimental exfoliation of ß-Cu2S thin films and the theoretical finding of a new phase labeled the δ-Cu2S monolayer, we carried out extensive studies on thermal conductivity and thermoelectric properties of the new phase using first principles combined with Boltzmann transport theory, focusing on the analysis of group velocities, Gruneisen parameters, three-phonon scattering rates, and the scattering phase space. Our results show that the δ-Cu2S monolayer exhibits an intrinsically ultralow lattice thermal conductivity of 0.10 W m-1 K-1 at 800 K. Such an ultralow lattice thermal conductivity leads to a high thermoelectric figure of merit ZT = 1.33 at 800 K in an optimum p-type doping concentration, which is not only larger than the value of 1.23 in In2S3 doped Cu2S at 850 K but also comparable with the value of 1.7 in Cu1.97S at 1000 K, exhibiting good potential in thermoelectric applications.