This study focuses on investigating the effect of various solvents on the supercritical extraction of organic matter from Moroccan oil shales, with the goal of determining the optimal operating conditions that result ...This study focuses on investigating the effect of various solvents on the supercritical extraction of organic matter from Moroccan oil shales, with the goal of determining the optimal operating conditions that result in a high yield of high-quality oil rich in aromatic compounds. The results of this study demonstrate that the extraction yield and quality of the extracted oil heavily depend on the chosen operating conditions for supercritical or subcritical extraction of organic matter from oil shale. Additionally, the study found that phenol can effectively degrade oil shale and enable extraction of nearly all the organic matter, even under mild conditions (T = 390˚C, P = 1.2 MPa, Time = 2.5 h. Furthermore, the oils obtained through this extraction process are of high quality, with a rich content of maltenes, and a higher concentration of aromatic compounds and lower levels of sulfur than those obtained using other solvents.展开更多
This study focuses on investigating the effect of various solvents on the supercritical extraction of organic matter from Moroccan oil shales, with the goal of determining the optimal operating conditions that result ...This study focuses on investigating the effect of various solvents on the supercritical extraction of organic matter from Moroccan oil shales, with the goal of determining the optimal operating conditions that result in a high yield of high-quality oil rich in aromatic compounds. The results of this study demonstrate that the extraction yield and quality of the extracted oil heavily depend on the chosen operating conditions for supercritical or subcritical extraction of organic matter from oil shale. Additionally, the study found that phenol can effectively degrade oil shale and enable extraction of nearly all the organic matter, even under mild conditions (T = 390˚C, P = 1.2 MPa, Time = 2.5 h. Furthermore, the oils obtained through this extraction process are of high quality, with a rich content of maltenes, and a higher concentration of aromatic compounds and lower levels of sulfur than those obtained using other solvents.展开更多
A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol (PEG) (GEMINI protocol). Previous work provided evidence that this is i...A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol (PEG) (GEMINI protocol). Previous work provided evidence that this is in fact possible. Other fusogens might improve current results. In this study, we aimed to assess the effects of PEGylated graphene nanoribons (PEG-GNR, and called "TexasPEG" when prepared as lwt% dispersion in PEG600) versus placebo (saline) on locomotor function recovery and cellular level in a rat model of spinal cord transection at lumbar segment 1 (L1) level. In vivo and in vitro experiments (n -- 10 per experiment) were designed. In the in vivo experiment, all rats were submitted to full spinal cord transection at L1 level. Five weeks later, behavioral assessment was performed using the Basso Beattie Bresnahan (BBB) locomotor rating scale. Immunohistochemical staining with neuron marker neurofilament 200 (NF200) antibody and astrocyt- ic scar marker glial fibrillary acidic protein (GFAP) was also performed in the injured spinal cord. In the in vitro experiment, the effects of TexasPEG application for 72 hours on the neurite outgrowth of SH-SYSY cells were observed under the inverted microscope. Results of both in vivo and in vitro experiments suggest that TexasPEG reduces the formation of glial scars, promotes the regeneration of neurites, and thereby contributes to the recovery of locomotor function of a rat model of spinal cord transfection.展开更多
Dirac states composed of Px,y orbitals have been reported in many two-dimensional (2D) systems with honeycomb lattices recently. Their potential importance has aroused strong interest in a comprehensive understandin...Dirac states composed of Px,y orbitals have been reported in many two-dimensional (2D) systems with honeycomb lattices recently. Their potential importance has aroused strong interest in a comprehensive understanding of such states. Here, we construct a four-band tight-binding model for the Px,y-orbital Dirac states considering both the nearest neighbor hopping interactions and the lattice-buckling effect. We find that Px,y-orbital Dirac states are accompanied with two addi- tional narrow bands that are flat in the limit of vanishing n bonding, which is in agreement with previous studies. Most importantly, we analytically obtain the linear dispersion relationship between energy and momentum vector near the Dirac cone. We find that the Fermi velocity is determined not only by the hopping through n bonding but also by the hopping through ~ bonding of Px,y orbitals, which is in contrast to the case of pz-orbital Dirac states. Consequently, Px,y-orbital Dirac states offer more flexible engineering, with the Fermi velocity being more sensitive to the changes of lattice constants and buckling angles, if strain is exerted. We further validate our tight-binding scheme by direct first-principles calcula- tions of model-materials including hydrogenated monolayer Bi and Sb honeycomb lattices. Our work provides a more in-depth understanding of Px,y-orbital Dirac states in honeycomb lattices, which is useful for the applications of this family of materials in nanoelectronics.展开更多
The growing interest in functionalized nanoparticles and their implementa</span></span><span><span><span style="font-family:"">tion in oilfield applications (e.g., drilling...The growing interest in functionalized nanoparticles and their implementa</span></span><span><span><span style="font-family:"">tion in oilfield applications (e.g., drilling fluids and enhanced oil recovery</span></span></span><span><span><span style="font-family:""> (EOR)) facilitate the ongoing efforts to improve their chemical functionalization performance in stabilization of water based or hydrocarbon based nanofluids. Cyclic azasilanes (CAS), substituted 1-aza-2-silacyclopentanes, possess a strained 5-member ring structure. Adjacent Si and N atoms in the ring provide opportunity for highly ef</span></span></span><span style="font-family:Verdana;"></span><span><span><span style="font-family:"">ficient covalent surface functionalization of hydroxylated nanoparticles through a catalyst-free and byproduct-free click <span>reaction. In this work, hydroxylated silica, alumina, diamond, and carbon</span> coated iron core-shell nanoparticles have been studied for monolayer CAS <span>functionalization. Two cyclic azasilanes with different R groups at N atom</span>, such as methyl (CAS-1) and aminoethyl (CAS-2), have been utilized to func<span>tionalize nanoparticles. All reactions were found to readily proceed under</span> mild conditions (room temperature, ambient pressure) during 1 - 2 hours of sonication. CAS functionalized adducts of hydroxylated nanoparticles have been isolated and</span></span></span><span><span><span style="font-family:""> </span></span></span><span><span><span style="font-family:"">their microstructure, composition, solubility and thermal stability have been characterized. As a result, it has been demonstrated, for the first time, that covalent surface modification with cyclic azasilanes can be extended beyond the previously known porous silicon structures to hydroxylated silica, alumina and carbon nanoparticles. The developed methodology was also shown to provide access to the nanoparticles with the hydrophilic or hydrophobic surface functional groups needed to enable oilfield applications (e.g., EOR, tracers, drilling fluids) that require stable water based or hydrocarbon based colloidal systems.展开更多
Fresh and clean water is highly demanded throughout the world.To effectively address the need,nanomaterials enabled nanotechnology has been explored as a means of more efficient,reliable,and environmentally friendly a...Fresh and clean water is highly demanded throughout the world.To effectively address the need,nanomaterials enabled nanotechnology has been explored as a means of more efficient,reliable,and environmentally friendly approach towards water treatment practices.One concern in adopting nanomaterials is how to retrieve them from water body to avoid secondary contamination.In this work,the earth abundant and sustainable wood,e.g.,basswood,was selected and carbonized into porous carbon as host skeleton,and metal-organic frameworks(MOFs),e.g.,MOF-199 with extremely high surface area,were grown throughout all channels in the porous basswood carbon.Targeting the traditional organic pollutant,methyl orange(MO),the combination of MOFs and basswood carbon(MOFs@carbon)demonstrates a remarkable adsorption capacity,which is 243%and 454%higher than basswood carbon and MOF-199,respectively.Such an outstanding adsorption performance originates from that the positively charged carbon pulls MO molecules close to carbon surface,leading to a high MO molecule concentration,and then the concentration gradient drives the MO molecules to be stored inside MOFs,functioning like pockets.These findings highlight the potential application of coupled MOFs and biomass carbon in addressing water remediation.展开更多
Heterostructures from two-dimensional transition-metal dichalcogenides MX_2 have emerged as a hot topic in recent years due to their various fascinating properties. Here, we investigated the temperature dependent Rama...Heterostructures from two-dimensional transition-metal dichalcogenides MX_2 have emerged as a hot topic in recent years due to their various fascinating properties. Here, we investigated the temperature dependent Raman and photoluminescence(PL) spectra in vertical stacked WS_2/MoS_2 monolayer heterostructures. Our result shows that both E_(2g)~1 and A_(1g) modes of WS_2 and MoS_2 vary linearly with temperature increasing from 300 to 642 K. The PL measurement also reveals strong temperature dependencies of the PL intensity and peak position. The activation energy of the thermal quenching of the PL emission has been found to be equal to 69.6 meV. The temperature dependence of the peak energy well follows the bandgap shrinkage of bulk semiconductor.展开更多
A novel microfabrication process based on optimized photolithography combined with pyrolysis-reduction is proposed to fabricate interdigital porous carbon/tin quantum dots (C/Sn QDs) microelectrodes.C/Sn QDs active ...A novel microfabrication process based on optimized photolithography combined with pyrolysis-reduction is proposed to fabricate interdigital porous carbon/tin quantum dots (C/Sn QDs) microelectrodes.C/Sn QDs active microelectrodes are also employed as current collectors of a micro-supercapacitor (MSC).A uniform dispersion of Sn QDs (diameter of ~3 nm) in the carbon matrix is achieved using our facile and controllable microfabrication process.The as-fabricated C/Sn QDs MSC obtained by carbonization at 900 ℃ exhibits a higher areal specific capacitance (5.79 mF&#183;cm-2) than that of the pyrolyzed carbonbased MSC (1.67 mF&#183;cm-2) and desirable cycling stability (93.3% capacitance retention after 5,000 cyclic voltammetry cycles).This novel microfabrication process is fully compatible with micromachining technologies,showing great potential for large-scale fine micropatterning of carbon-based composites for applications in micro/nano devices.展开更多
Manipulation of light-matter interaction is critical in modern physics, especially in the strong coupling regime, where the generated half-light, half-matter bosonic quasiparticles as polaritons are important for fund...Manipulation of light-matter interaction is critical in modern physics, especially in the strong coupling regime, where the generated half-light, half-matter bosonic quasiparticles as polaritons are important for fundamental quantum science and applications of optoelectronics and nonlinear optics. Two-dimensional transition metal dichalcogenides (TMDs) are ideal platforms to investigate the strong coupling because of their huge exciton binding energy and large absorption coefficients. Further studies on strong exciton-plasmon coupling by combining TMDs with metallic nanostructures have generated broad interests in recent years. However, because of the huge plasmon radiative damping, the observation of strong coupling is significantly limited at room temperature. Here, we demonstrate that a large Rabi splitting (~300 meV) can be achieved at ambient conditions in the strong coupling regime by embedding Ag-WS2 heterostructure in an optical microcavity. The generated quasiparticle with part-plasmon, part-exciton and part-light is analyzed with Hopfield coefficients that are calculated by using three-coupled oscillator model. The resulted plasmon-exciton polaritonic hybrid states can efficiently enlarge the obtained Rabi splitting, which paves the way for the practical applications of polaritonic devices based on ultrathin materials.展开更多
Correlating mechanical performance with mesoscale structure is fundamental for the design and optimization of light and strong fibers(or any composites),most promising being those from carbon nanotubes.In all forms of...Correlating mechanical performance with mesoscale structure is fundamental for the design and optimization of light and strong fibers(or any composites),most promising being those from carbon nanotubes.In all forms of nanotube fiber production strategies,due to tubes’mutual affinity,some degree of bundling into liquid crystal-like domains can be expected,causing heterogeneous load transfer within and outside these domains,and having a direct impact on the fiber strength.By employing large-scale coarse-grained simulations,we demonstrate that the strength s of nanotube fibers with characteristic domain size D scales as s~1/D,while the degree of longitudinal/axial disorder within the domains(akin to a smectic↔nematic phase transition)can substantially mitigate this dependence.展开更多
The presence of defects/vacancies in nanomaterials influences the electronic structure of materials, and thus, it is necessary to study the correlation between the optoelectronic properties of a nanomaterial and its d...The presence of defects/vacancies in nanomaterials influences the electronic structure of materials, and thus, it is necessary to study the correlation between the optoelectronic properties of a nanomaterial and its defects/vacancies. Herein, we report a facile solvothermal route to synthesize three-dimensional (3D) SnS nanostructures formed by {131} faceted nanosheet assembly. The 3D SnS nanostructures were calcined at temperatures of 350, 400, and 450 ~C and used as counter electrodes, before their photocurrent properties were investigated. First principle computation revealed the photocurrent properties depend on the defect/vacancy concentration within the samples. It is very interesting that characterization with positron annihilation spectrometry confirmed that the density of defects/vacancies increased with the calcination temperature, and a maximum photocurrent was realized after treatment at 400 ℃. Further, the defect/vacancy density decreased when the calcination temperature reached 450℃ as the higher calcination temperature enlarged the mesopores and densified the pore walls, which led to a lower photocurrent value at 450℃ than at 400℃.展开更多
N-doped carbon-based single-atom catalysts(NC-SACs) are widely researched in various electrochemical reactions due to high metal atom utilization and catalytic activity.The catalytic activity of NC-SACs originates fro...N-doped carbon-based single-atom catalysts(NC-SACs) are widely researched in various electrochemical reactions due to high metal atom utilization and catalytic activity.The catalytic activity of NC-SACs originates from the coordinating structure between single metal site(M) and the doped nitrogen(N) in carbon matrix by forming M-N_(x)-C structure(1≤x≤4).The M-N4-C structure is widely considered to be the most stable and effective catalytic site.However,there is no in-depth research for the "x" modulation in Pt-Nx-C structure and the corresponding catalytic properties.Herein,atomically dispersed Pt on N-doped carbon(Pt-NC) with Pt-Nx-C structure(1≤x≤4),as a research model,is fabricated by a ZIF-8 template and applied to catalytic oxygen reduction.Different carbonization temperatures are used to control N loss,and then modulate the N coordination of Pt-Nx-C structure.The Pt-NC has the predictable low half-wave potential(E_(1/2)) of 0.72 V vs RHE compared to the Pt/C 20% of 0.81 V due to low Pt content.Remarkably,the Pt-NC shows a high onset potential(1.10 V vs RHE,determined for j=-0.1 mA cm^(2)) and a high current density of 5.2 mA cm^(-2),more positive and higher than that of Pt/C 20%(0.96 V) and 4.9 mA cm^(-2),respectively.As the structural characterization and DFT simulation confirmed,the reducing PtN coordination number induces low valence of Pt atoms and low free energy of oxygen reduction,which is responsible for the improved catalytic activity.Furthermore,the Pt-NC shows high mass activity(172 times higher than that of Pt/C 20%),better stability and methanol crossover resistance.展开更多
Exploration of structure-property relationships as a function of dopant concentration is commonly based on mean field theories for solid solutions.However,such theories that work well for semiconductors tend to fail i...Exploration of structure-property relationships as a function of dopant concentration is commonly based on mean field theories for solid solutions.However,such theories that work well for semiconductors tend to fail in materials with strong correlations,either in electronic behavior or chemical segregation.In these cases,the details of atomic arrangements are generally not explored and analyzed.The knowledge of the generative physics and chemistry of the material can obviate this problem,since defect configuration libraries as stochastic representation of atomic level structures can be generated,or parameters of mesoscopic thermodynamic models can be derived.To obtain such information for improved predictions,we use data from atomically resolved microscopic images that visualize complex structural correlations within the system and translate them into statistical mechanical models of structure formation.Given the significant uncertainties about the microscopic aspects of the material’s processing history along with the limited number of available images,we combine model optimization techniques with the principles of statistical hypothesis testing.We demonstrate the approach on data from a series of atomically-resolved scanning transmission electron microscopy images of Mo_(x)Re_(1-x)S_(2) at varying ratios of Mo/Re stoichiometries,for which we propose an effective interaction model that is then used to generate atomic configurations and make testable predictions at a range of concentrations and formation temperatures.展开更多
Sandwich structured graphene-wrapped FeS-graphene nanoribbons (G@FeS-GNIKs) were developed. In this composite, FeS nanoparticles were sandwiched between graphene and graphene nanoribbons. When used as anodes in lith...Sandwich structured graphene-wrapped FeS-graphene nanoribbons (G@FeS-GNIKs) were developed. In this composite, FeS nanoparticles were sandwiched between graphene and graphene nanoribbons. When used as anodes in lithium ion batteries (L1Bs), the G@FeS-GNR composite demonstrated an outstanding electrochemical performance. This composite showed high reversible capacity, good rate performance, and enhanced cycling stability owing to the synergy between the electrically conductive graphene, graphene nanoribbons, and FeS. The design concept developed here opens up a new avenue for constructing anodes with improved electrochemical stability for LIBs.展开更多
As one of the most important micro energy storage devices(MESDs),graphene-based micro-supercapacitors(G-MSCs)possess the advantages of excellent flexibility,long cycle life,affordability and high reliability.In most c...As one of the most important micro energy storage devices(MESDs),graphene-based micro-supercapacitors(G-MSCs)possess the advantages of excellent flexibility,long cycle life,affordability and high reliability.In most cases,constructing three-dimensional(3D)graphene networks is widely utilized to promote the permeation of electrolyte and enhance the utilization of active materials.In this work,conventional freeze-drying process is utilized in the fabrication of G-MSCs to constitute 3D interconnected networks micro-electrodes,and further by regulating the composition of inks,carbon spheres(CSs)at different mass loadings are introduced into the graphene scaffolds to further increase the active sites of the micro-electrodes.The fabricated all carbon-based MSC with the optimal mass loading of CSs(0.406 mg cm^(-2))exhibits a high specific areal capacitance of 17.01mF cm^(-2)at the scan rate of 10mV s^(-1)and a capacitance retention of 93.14%after 10000 cycles at the scan rate of 500 mV s^(-1).The proposed microfabrication process is facile and fully compatible with modern microtechnologies and will be highly suitable for large-scale production and integration.展开更多
Copper-decorated carbon nanotubes(CNTs) have important applications as precursors for ultraconductive copper wires. Tenorite-decorated CNTs(CuO-CNTs) are ideal candidates and are currently developed using laborious pr...Copper-decorated carbon nanotubes(CNTs) have important applications as precursors for ultraconductive copper wires. Tenorite-decorated CNTs(CuO-CNTs) are ideal candidates and are currently developed using laborious processes. For this reason, we have developed a facile and scalable method for the synthesis of CuO-CNTs from copper acetate. It was found that the optimal loading of copper acetate onto the CNTs was 23.1 wt% and that three 1-minute microwave treatments were sufficient for the decomposition of copper acetate to copper oxide. The loading of copper oxide onto the nanotubes was confirmed using X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and thermogravimetric analysis. The materials were characterised using X-ray diffraction and scanning electron microscopy.展开更多
New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries.While topography cues are known to promote attachment and direct pro...New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries.While topography cues are known to promote attachment and direct proliferation of many cell types,guided outgrowth of human neurites has been found difficult to achieve so far.Here,three-dimensional(3D)micropatterned carbon nanotube(CNT)templates are used to effectively direct human neurite stem cell growth.By exploiting the mechanical flexibility,electrically conductivity and texture of the 3D CNT micropillars,a perfect environment is created to achieve specific guidance of human neurites,which may lead to enhanced therapeutic effects within the injured spinal cord or peripheral nerves.It is found that the 3D CNT micropillars grant excellent anchoring for adjacent neurites to form seamless neuronal networks that can be grown to any arbitrary shape and size.Apart from clear practical relevance in regenerative medicine,these results using the CNT based templates on Si chips also can pave the road for new types of microelectrode arrays to study cell network electrophysiology.展开更多
Chemical vapor deposition(CVD)is one of the most versatile techniques for the controlled synthesis of functional nanomaterials.When multiple precursors are induced,the CVD process often gives rise to the growth of dop...Chemical vapor deposition(CVD)is one of the most versatile techniques for the controlled synthesis of functional nanomaterials.When multiple precursors are induced,the CVD process often gives rise to the growth of doped or alloy compounds.In this work,we demonstrate the self-assembly of a variety of‘phase-separated’functional nanostructures from a single CVD in the presence of various precursors.In specific,with silicon substrate and powder of Mn and SnTe as precursors,we achieved self-organized nanostructures including Si/SiOx core-shell nanowire heterostructures both with and without embedded manganese silicide particles,Mn11Si19 nanowires,and SnTe nanoplates.The Si/SiOx core-shell nanowires embedded with manganese silicide particles were grown along the<111>direction of the crystalline Si via an Au-catalyzed vapor-liquid-solid process,in which the Si and Mn vapors were supplied from the heated silicon substrates and Mn powder,respectively.In contrast,direct vapor-solid deposition led to particle-free<110>-oriented Si/SiOx core-shell nanowires and<100>-oriented Mn11Si19 nanowires,a promising thermoelectric material.No Sn or Te impurities were detected in these nanostructures down to the experimental limit.Topological crystalline insulator SnTe nanoplates with dominant{100}and{111}facets were found to be free of Mn(and Si)impurities,although nanoparticles and nanowires containing Mn were found in the vicinity of the nanoplates.While multiple-channel transport was observed in the SnTe nanoplates,it may not be related to the topological surface states due to surface oxidation.Finally,we carried out thermodynamic analysis and density functional theory calculations to understand the‘phase-separation’phenomenon and further discuss general approaches to grow phase-pure samples when the precursors contain residual impurities.展开更多
文摘This study focuses on investigating the effect of various solvents on the supercritical extraction of organic matter from Moroccan oil shales, with the goal of determining the optimal operating conditions that result in a high yield of high-quality oil rich in aromatic compounds. The results of this study demonstrate that the extraction yield and quality of the extracted oil heavily depend on the chosen operating conditions for supercritical or subcritical extraction of organic matter from oil shale. Additionally, the study found that phenol can effectively degrade oil shale and enable extraction of nearly all the organic matter, even under mild conditions (T = 390˚C, P = 1.2 MPa, Time = 2.5 h. Furthermore, the oils obtained through this extraction process are of high quality, with a rich content of maltenes, and a higher concentration of aromatic compounds and lower levels of sulfur than those obtained using other solvents.
文摘This study focuses on investigating the effect of various solvents on the supercritical extraction of organic matter from Moroccan oil shales, with the goal of determining the optimal operating conditions that result in a high yield of high-quality oil rich in aromatic compounds. The results of this study demonstrate that the extraction yield and quality of the extracted oil heavily depend on the chosen operating conditions for supercritical or subcritical extraction of organic matter from oil shale. Additionally, the study found that phenol can effectively degrade oil shale and enable extraction of nearly all the organic matter, even under mild conditions (T = 390˚C, P = 1.2 MPa, Time = 2.5 h. Furthermore, the oils obtained through this extraction process are of high quality, with a rich content of maltenes, and a higher concentration of aromatic compounds and lower levels of sulfur than those obtained using other solvents.
基金supported by a grant from the National Research Foundation(NRF)funded by the Korean government(NRF-2015M3A9C7030091 and NRF-2015R1C1A1A02037047)
文摘A sharply transected spinal cord has been shown to be fused under the accelerating influence of membrane fusogens such as polyethylene glycol (PEG) (GEMINI protocol). Previous work provided evidence that this is in fact possible. Other fusogens might improve current results. In this study, we aimed to assess the effects of PEGylated graphene nanoribons (PEG-GNR, and called "TexasPEG" when prepared as lwt% dispersion in PEG600) versus placebo (saline) on locomotor function recovery and cellular level in a rat model of spinal cord transection at lumbar segment 1 (L1) level. In vivo and in vitro experiments (n -- 10 per experiment) were designed. In the in vivo experiment, all rats were submitted to full spinal cord transection at L1 level. Five weeks later, behavioral assessment was performed using the Basso Beattie Bresnahan (BBB) locomotor rating scale. Immunohistochemical staining with neuron marker neurofilament 200 (NF200) antibody and astrocyt- ic scar marker glial fibrillary acidic protein (GFAP) was also performed in the injured spinal cord. In the in vitro experiment, the effects of TexasPEG application for 72 hours on the neurite outgrowth of SH-SYSY cells were observed under the inverted microscope. Results of both in vivo and in vitro experiments suggest that TexasPEG reduces the formation of glial scars, promotes the regeneration of neurites, and thereby contributes to the recovery of locomotor function of a rat model of spinal cord transfection.
基金Project supported by the National Key Research and Development Projects of China(Grant No.2016YFA0202300)the National Natural Science Foundation of China(Grant No.61390501)+1 种基金the Science Fund from the Chinese Academy of Sciences(Grant No.XDPB0601)the US Army Research Office
文摘Dirac states composed of Px,y orbitals have been reported in many two-dimensional (2D) systems with honeycomb lattices recently. Their potential importance has aroused strong interest in a comprehensive understanding of such states. Here, we construct a four-band tight-binding model for the Px,y-orbital Dirac states considering both the nearest neighbor hopping interactions and the lattice-buckling effect. We find that Px,y-orbital Dirac states are accompanied with two addi- tional narrow bands that are flat in the limit of vanishing n bonding, which is in agreement with previous studies. Most importantly, we analytically obtain the linear dispersion relationship between energy and momentum vector near the Dirac cone. We find that the Fermi velocity is determined not only by the hopping through n bonding but also by the hopping through ~ bonding of Px,y orbitals, which is in contrast to the case of pz-orbital Dirac states. Consequently, Px,y-orbital Dirac states offer more flexible engineering, with the Fermi velocity being more sensitive to the changes of lattice constants and buckling angles, if strain is exerted. We further validate our tight-binding scheme by direct first-principles calcula- tions of model-materials including hydrogenated monolayer Bi and Sb honeycomb lattices. Our work provides a more in-depth understanding of Px,y-orbital Dirac states in honeycomb lattices, which is useful for the applications of this family of materials in nanoelectronics.
文摘The growing interest in functionalized nanoparticles and their implementa</span></span><span><span><span style="font-family:"">tion in oilfield applications (e.g., drilling fluids and enhanced oil recovery</span></span></span><span><span><span style="font-family:""> (EOR)) facilitate the ongoing efforts to improve their chemical functionalization performance in stabilization of water based or hydrocarbon based nanofluids. Cyclic azasilanes (CAS), substituted 1-aza-2-silacyclopentanes, possess a strained 5-member ring structure. Adjacent Si and N atoms in the ring provide opportunity for highly ef</span></span></span><span style="font-family:Verdana;"></span><span><span><span style="font-family:"">ficient covalent surface functionalization of hydroxylated nanoparticles through a catalyst-free and byproduct-free click <span>reaction. In this work, hydroxylated silica, alumina, diamond, and carbon</span> coated iron core-shell nanoparticles have been studied for monolayer CAS <span>functionalization. Two cyclic azasilanes with different R groups at N atom</span>, such as methyl (CAS-1) and aminoethyl (CAS-2), have been utilized to func<span>tionalize nanoparticles. All reactions were found to readily proceed under</span> mild conditions (room temperature, ambient pressure) during 1 - 2 hours of sonication. CAS functionalized adducts of hydroxylated nanoparticles have been isolated and</span></span></span><span><span><span style="font-family:""> </span></span></span><span><span><span style="font-family:"">their microstructure, composition, solubility and thermal stability have been characterized. As a result, it has been demonstrated, for the first time, that covalent surface modification with cyclic azasilanes can be extended beyond the previously known porous silicon structures to hydroxylated silica, alumina and carbon nanoparticles. The developed methodology was also shown to provide access to the nanoparticles with the hydrophilic or hydrophobic surface functional groups needed to enable oilfield applications (e.g., EOR, tracers, drilling fluids) that require stable water based or hydrocarbon based colloidal systems.
基金J.W.W.,Z.Y.C.,and Y.C.Y.acknowledge the financial support from the USDA Forest Service(No.20-JV-11111124-035)Y.C.Y.and P.D.acknowledge the financial support from the Department of the Interior,Bureau of Reclamation(No.R19AC00116)Y.C.Y.thanks Dr.Y.Q.Meng in Idaho National Laboratory for helping on BET measurement.
文摘Fresh and clean water is highly demanded throughout the world.To effectively address the need,nanomaterials enabled nanotechnology has been explored as a means of more efficient,reliable,and environmentally friendly approach towards water treatment practices.One concern in adopting nanomaterials is how to retrieve them from water body to avoid secondary contamination.In this work,the earth abundant and sustainable wood,e.g.,basswood,was selected and carbonized into porous carbon as host skeleton,and metal-organic frameworks(MOFs),e.g.,MOF-199 with extremely high surface area,were grown throughout all channels in the porous basswood carbon.Targeting the traditional organic pollutant,methyl orange(MO),the combination of MOFs and basswood carbon(MOFs@carbon)demonstrates a remarkable adsorption capacity,which is 243%and 454%higher than basswood carbon and MOF-199,respectively.Such an outstanding adsorption performance originates from that the positively charged carbon pulls MO molecules close to carbon surface,leading to a high MO molecule concentration,and then the concentration gradient drives the MO molecules to be stored inside MOFs,functioning like pockets.These findings highlight the potential application of coupled MOFs and biomass carbon in addressing water remediation.
基金supported by the National Basic Research Program of China (2015CB932403)the National Natural Science Foundation of China (11674012, 61422501, 11374023, 11304054 and 61521004)+2 种基金Beijing Natural Science Foundation (L140007)Foundation for the Author of National Excellent Doctoral Dissertation of China (201420)National Program for Support of Top-notch Young Professionals
文摘Heterostructures from two-dimensional transition-metal dichalcogenides MX_2 have emerged as a hot topic in recent years due to their various fascinating properties. Here, we investigated the temperature dependent Raman and photoluminescence(PL) spectra in vertical stacked WS_2/MoS_2 monolayer heterostructures. Our result shows that both E_(2g)~1 and A_(1g) modes of WS_2 and MoS_2 vary linearly with temperature increasing from 300 to 642 K. The PL measurement also reveals strong temperature dependencies of the PL intensity and peak position. The activation energy of the thermal quenching of the PL emission has been found to be equal to 69.6 meV. The temperature dependence of the peak energy well follows the bandgap shrinkage of bulk semiconductor.
基金This work was supported by the National Key Research and Development Program of China (Nos. 2016YFA0202603 and 2016YFA0202604), the National Basic Research Program of China (No. 2013CB934103),the Programme of Introducing Talents of Discipline to Universities (No. B17034), the National Natural Science Foundation of China (Nos. 51502227, 51579198 and 51521001), the National Natural Science Fund for Distinguished Young Scholars (No. 51425204), the China Postdoctoral Science Foundation (No. 2015T80845), the Hubei Province Natural Science Fund (No. 2016CFB582), the Fundamental Research Funds for the Central Universities (WUT: 2016III001 and 2016III005). Prof. Liang He and Prof. Liqiang Mai gratefully acknowledged fi~andal support from China Scholarship Council (Nos. 201606955094 and 201606955096).
文摘A novel microfabrication process based on optimized photolithography combined with pyrolysis-reduction is proposed to fabricate interdigital porous carbon/tin quantum dots (C/Sn QDs) microelectrodes.C/Sn QDs active microelectrodes are also employed as current collectors of a micro-supercapacitor (MSC).A uniform dispersion of Sn QDs (diameter of ~3 nm) in the carbon matrix is achieved using our facile and controllable microfabrication process.The as-fabricated C/Sn QDs MSC obtained by carbonization at 900 ℃ exhibits a higher areal specific capacitance (5.79 mF&#183;cm-2) than that of the pyrolyzed carbonbased MSC (1.67 mF&#183;cm-2) and desirable cycling stability (93.3% capacitance retention after 5,000 cyclic voltammetry cycles).This novel microfabrication process is fully compatible with micromachining technologies,showing great potential for large-scale fine micropatterning of carbon-based composites for applications in micro/nano devices.
基金the National Key Research and Development Program of China (Grant No. 2017YFA0205700)National Basic Research Program of China (Grant No. 2015CB932403, 2017YFA0206000)+3 种基金National Natural Science Foundation of China (Grant Nos. 11674012, 61521004, 21790364, 61422501, and 11374023)Beijing Natural Science Foundation (Z180011, and L140007)Foundation for the Author of National Excellent Doctoral Dissertation of PR China (Grant No. 201420)National Program for Support of Top-notch Young Professionals (Grant No. W02070003).
文摘Manipulation of light-matter interaction is critical in modern physics, especially in the strong coupling regime, where the generated half-light, half-matter bosonic quasiparticles as polaritons are important for fundamental quantum science and applications of optoelectronics and nonlinear optics. Two-dimensional transition metal dichalcogenides (TMDs) are ideal platforms to investigate the strong coupling because of their huge exciton binding energy and large absorption coefficients. Further studies on strong exciton-plasmon coupling by combining TMDs with metallic nanostructures have generated broad interests in recent years. However, because of the huge plasmon radiative damping, the observation of strong coupling is significantly limited at room temperature. Here, we demonstrate that a large Rabi splitting (~300 meV) can be achieved at ambient conditions in the strong coupling regime by embedding Ag-WS2 heterostructure in an optical microcavity. The generated quasiparticle with part-plasmon, part-exciton and part-light is analyzed with Hopfield coefficients that are calculated by using three-coupled oscillator model. The resulted plasmon-exciton polaritonic hybrid states can efficiently enlarge the obtained Rabi splitting, which paves the way for the practical applications of polaritonic devices based on ultrathin materials.
基金This work was supported by the U.S.Department of Defense:Air Force Office of Scientific Research(AFOSR),Grant FA9550-17-1-0262Computer resources were provided by XSEDE,which is supported by NSF grant ACI-1548562,under allocation TG-DMR100029。
文摘Correlating mechanical performance with mesoscale structure is fundamental for the design and optimization of light and strong fibers(or any composites),most promising being those from carbon nanotubes.In all forms of nanotube fiber production strategies,due to tubes’mutual affinity,some degree of bundling into liquid crystal-like domains can be expected,causing heterogeneous load transfer within and outside these domains,and having a direct impact on the fiber strength.By employing large-scale coarse-grained simulations,we demonstrate that the strength s of nanotube fibers with characteristic domain size D scales as s~1/D,while the degree of longitudinal/axial disorder within the domains(akin to a smectic↔nematic phase transition)can substantially mitigate this dependence.
文摘The presence of defects/vacancies in nanomaterials influences the electronic structure of materials, and thus, it is necessary to study the correlation between the optoelectronic properties of a nanomaterial and its defects/vacancies. Herein, we report a facile solvothermal route to synthesize three-dimensional (3D) SnS nanostructures formed by {131} faceted nanosheet assembly. The 3D SnS nanostructures were calcined at temperatures of 350, 400, and 450 ~C and used as counter electrodes, before their photocurrent properties were investigated. First principle computation revealed the photocurrent properties depend on the defect/vacancy concentration within the samples. It is very interesting that characterization with positron annihilation spectrometry confirmed that the density of defects/vacancies increased with the calcination temperature, and a maximum photocurrent was realized after treatment at 400 ℃. Further, the defect/vacancy density decreased when the calcination temperature reached 450℃ as the higher calcination temperature enlarged the mesopores and densified the pore walls, which led to a lower photocurrent value at 450℃ than at 400℃.
基金financially supported by the National Natural Science Foundation of China (Nos. 51572124 and 51702162)the Natural Science Foundation of Jiangsu Province (No. BK20180154and BK20180490)+1 种基金the Fundamental Research Funds for the Central Universities (No. 30920130111003)A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD, China)。
文摘N-doped carbon-based single-atom catalysts(NC-SACs) are widely researched in various electrochemical reactions due to high metal atom utilization and catalytic activity.The catalytic activity of NC-SACs originates from the coordinating structure between single metal site(M) and the doped nitrogen(N) in carbon matrix by forming M-N_(x)-C structure(1≤x≤4).The M-N4-C structure is widely considered to be the most stable and effective catalytic site.However,there is no in-depth research for the "x" modulation in Pt-Nx-C structure and the corresponding catalytic properties.Herein,atomically dispersed Pt on N-doped carbon(Pt-NC) with Pt-Nx-C structure(1≤x≤4),as a research model,is fabricated by a ZIF-8 template and applied to catalytic oxygen reduction.Different carbonization temperatures are used to control N loss,and then modulate the N coordination of Pt-Nx-C structure.The Pt-NC has the predictable low half-wave potential(E_(1/2)) of 0.72 V vs RHE compared to the Pt/C 20% of 0.81 V due to low Pt content.Remarkably,the Pt-NC shows a high onset potential(1.10 V vs RHE,determined for j=-0.1 mA cm^(2)) and a high current density of 5.2 mA cm^(-2),more positive and higher than that of Pt/C 20%(0.96 V) and 4.9 mA cm^(-2),respectively.As the structural characterization and DFT simulation confirmed,the reducing PtN coordination number induces low valence of Pt atoms and low free energy of oxygen reduction,which is responsible for the improved catalytic activity.Furthermore,the Pt-NC shows high mass activity(172 times higher than that of Pt/C 20%),better stability and methanol crossover resistance.
文摘Exploration of structure-property relationships as a function of dopant concentration is commonly based on mean field theories for solid solutions.However,such theories that work well for semiconductors tend to fail in materials with strong correlations,either in electronic behavior or chemical segregation.In these cases,the details of atomic arrangements are generally not explored and analyzed.The knowledge of the generative physics and chemistry of the material can obviate this problem,since defect configuration libraries as stochastic representation of atomic level structures can be generated,or parameters of mesoscopic thermodynamic models can be derived.To obtain such information for improved predictions,we use data from atomically resolved microscopic images that visualize complex structural correlations within the system and translate them into statistical mechanical models of structure formation.Given the significant uncertainties about the microscopic aspects of the material’s processing history along with the limited number of available images,we combine model optimization techniques with the principles of statistical hypothesis testing.We demonstrate the approach on data from a series of atomically-resolved scanning transmission electron microscopy images of Mo_(x)Re_(1-x)S_(2) at varying ratios of Mo/Re stoichiometries,for which we propose an effective interaction model that is then used to generate atomic configurations and make testable predictions at a range of concentrations and formation temperatures.
文摘Sandwich structured graphene-wrapped FeS-graphene nanoribbons (G@FeS-GNIKs) were developed. In this composite, FeS nanoparticles were sandwiched between graphene and graphene nanoribbons. When used as anodes in lithium ion batteries (L1Bs), the G@FeS-GNR composite demonstrated an outstanding electrochemical performance. This composite showed high reversible capacity, good rate performance, and enhanced cycling stability owing to the synergy between the electrically conductive graphene, graphene nanoribbons, and FeS. The design concept developed here opens up a new avenue for constructing anodes with improved electrochemical stability for LIBs.
基金This work was supported by the National Natural Science Fund for Distinguished Young Scholars(51425204)the National Natural Science Foundation of China(51521001,51502227,51579198,51802239)+6 种基金the National Key Research and Development Program of China(2016YFA0202603,2016YFA0202604)the Programme of Introducing Talents of Discipline to Universities(B17034)the China Postdoctoral Science Foundation(2015T80845)the Yellow Crane Talent(Science&Technology)Program of Wuhan Citythe Wuhan Morning Light Plan of Youth Science and Technology(No.2017050304010316)the Fundamental Research Funds for the Central Universities(WUT:2017III005,2017III009,2018IVA091)the Students innovation and entrepreneurship training program(WUT:20171049701005).
文摘As one of the most important micro energy storage devices(MESDs),graphene-based micro-supercapacitors(G-MSCs)possess the advantages of excellent flexibility,long cycle life,affordability and high reliability.In most cases,constructing three-dimensional(3D)graphene networks is widely utilized to promote the permeation of electrolyte and enhance the utilization of active materials.In this work,conventional freeze-drying process is utilized in the fabrication of G-MSCs to constitute 3D interconnected networks micro-electrodes,and further by regulating the composition of inks,carbon spheres(CSs)at different mass loadings are introduced into the graphene scaffolds to further increase the active sites of the micro-electrodes.The fabricated all carbon-based MSC with the optimal mass loading of CSs(0.406 mg cm^(-2))exhibits a high specific areal capacitance of 17.01mF cm^(-2)at the scan rate of 10mV s^(-1)and a capacitance retention of 93.14%after 10000 cycles at the scan rate of 500 mV s^(-1).The proposed microfabrication process is facile and fully compatible with modern microtechnologies and will be highly suitable for large-scale production and integration.
基金the financial support provided by the Welsh Government Sêr Cymru National Research Network in Advanced Engineering and Materials (NRN-150)the Sêr Cymru Chair Programme (A.R.B.)+8 种基金the Sêr Cymru II Fellowship (C.E.G.)the Sêr Cymru II Recapturing Talent Fellowship (E.K.)partly funded by the European Regional Development Fund (ERDF)part of the Flexible Integrated Energy Systems (FLEXIS) and Reducing Industrial Carbon Emissions (RICE) research operations funded by the Welsh European Funding Office (WEFO)provided by the Engineering and Physical Sciences Research Council (EPSRC) UK, the Robert A. Welch Foundation (C-0002)King Saud Universitythe assistance provided by the Swansea University AIM Facility, which was funded in part by the EPSRC (EP/M028267/1)the European Regional Development Fund through the Welsh Government (80708)the Sêr Solar project via the Welsh Government
文摘Copper-decorated carbon nanotubes(CNTs) have important applications as precursors for ultraconductive copper wires. Tenorite-decorated CNTs(CuO-CNTs) are ideal candidates and are currently developed using laborious processes. For this reason, we have developed a facile and scalable method for the synthesis of CuO-CNTs from copper acetate. It was found that the optimal loading of copper acetate onto the CNTs was 23.1 wt% and that three 1-minute microwave treatments were sufficient for the decomposition of copper acetate to copper oxide. The loading of copper oxide onto the nanotubes was confirmed using X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy and thermogravimetric analysis. The materials were characterised using X-ray diffraction and scanning electron microscopy.
基金G.S.L.and L.Y-O.acknowledge the support from the Academy of Finland(Nos.320090,317437 and 286990,respectively)J.T.K.and T.J.acknowledge the support from the Finnish Cultural Foundation Pirkanmaa Regional Fund(No.50151501)+1 种基金the Central Fund(#00150312),respectively.S.N.,T.J.and M.K.acknowledge the support from the Academy of Finland(S.N.and T.J.No.312414 and M.K.No.312409)Business Finland(former Tekes,Human Spare Parts project).This work made use of the electron microscopy and clean-room facilities at the Centre of Microscopy and Nanotechnology,at the University of Oulu.The authors also acknowledge the Tampere Imaging Facility(TIF)and the Tampere CellTech Laboratories for their service.
文摘New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries.While topography cues are known to promote attachment and direct proliferation of many cell types,guided outgrowth of human neurites has been found difficult to achieve so far.Here,three-dimensional(3D)micropatterned carbon nanotube(CNT)templates are used to effectively direct human neurite stem cell growth.By exploiting the mechanical flexibility,electrically conductivity and texture of the 3D CNT micropillars,a perfect environment is created to achieve specific guidance of human neurites,which may lead to enhanced therapeutic effects within the injured spinal cord or peripheral nerves.It is found that the 3D CNT micropillars grant excellent anchoring for adjacent neurites to form seamless neuronal networks that can be grown to any arbitrary shape and size.Apart from clear practical relevance in regenerative medicine,these results using the CNT based templates on Si chips also can pave the road for new types of microelectrode arrays to study cell network electrophysiology.
基金This work was supported,in part,by the Indiana University Vice Provost for Research through the Faculty Research Support Program,National Science Foundation Research Experience for Undergraduates grant PHY-1757646,NSF-DMR-1350002We thank the Indiana University-Bloomington Nanoscale Characterization Facility(NCF)for the use of instruments(The XPS instrument at NCF was funded through grant NSF-DMR-1126394).
文摘Chemical vapor deposition(CVD)is one of the most versatile techniques for the controlled synthesis of functional nanomaterials.When multiple precursors are induced,the CVD process often gives rise to the growth of doped or alloy compounds.In this work,we demonstrate the self-assembly of a variety of‘phase-separated’functional nanostructures from a single CVD in the presence of various precursors.In specific,with silicon substrate and powder of Mn and SnTe as precursors,we achieved self-organized nanostructures including Si/SiOx core-shell nanowire heterostructures both with and without embedded manganese silicide particles,Mn11Si19 nanowires,and SnTe nanoplates.The Si/SiOx core-shell nanowires embedded with manganese silicide particles were grown along the<111>direction of the crystalline Si via an Au-catalyzed vapor-liquid-solid process,in which the Si and Mn vapors were supplied from the heated silicon substrates and Mn powder,respectively.In contrast,direct vapor-solid deposition led to particle-free<110>-oriented Si/SiOx core-shell nanowires and<100>-oriented Mn11Si19 nanowires,a promising thermoelectric material.No Sn or Te impurities were detected in these nanostructures down to the experimental limit.Topological crystalline insulator SnTe nanoplates with dominant{100}and{111}facets were found to be free of Mn(and Si)impurities,although nanoparticles and nanowires containing Mn were found in the vicinity of the nanoplates.While multiple-channel transport was observed in the SnTe nanoplates,it may not be related to the topological surface states due to surface oxidation.Finally,we carried out thermodynamic analysis and density functional theory calculations to understand the‘phase-separation’phenomenon and further discuss general approaches to grow phase-pure samples when the precursors contain residual impurities.