RESUMO
Zeolites are among the most important heterogeneous catalysts, widely employed in separation reaction, fine chemical production, and petroleum refining. Through rational design of the frameworks, zeolites with versatile functions can be synthesized. Local imaging of zeolite structures at the atomic scale, including the basic framework atoms (Si, Al, and O) and extra-framework cations, is necessary to understand the structure-function relationship of zeolites. Herein, we implemented electron ptychography into direct imaging of local structures of two zeolites, Na-LTA and ZSM-5. Not only all the framework atoms but also extra-framework Na+ cations with only 1/4 occupation probabilities in Na-LTA were directly observed. Local structures of ZSM-5 zeolites having guest molecules among channels with different orientations were also unraveled using different reconstruction algorithms. The approach presented here provides a new way to locally image zeolites structure, and it is expected to be an essential key for further studying and tuning zeolites active sites at the atomic level.
RESUMO
Hexagonal boron nitride (h-BN) is regarded as one of the most efficient catalysts for oxidative dehydrogenation of propane (ODHP) with high olefin selectivity and productivity. However, the loss of the boron component under a high concentration of water vapor and high temperature seriously hinders its further development. How to make h-BN a stable ODHP catalyst is one of the biggest scientific challenges at present. Herein, we construct h-BNâxIn2O3 composite catalysts through the atomic layer deposition (ALD) process. After high-temperature treatment in ODHP reaction conditions, the In2O3 nanoparticles (NPs) are dispersed on the edge of h-BN and observed to be encapsulated by ultrathin boron oxide (BOx) overlayer. A novel strong metal oxide-support interaction (SMOSI) effect between In2O3 NPs and h-BN is observed for the first time. The material characterization reveals that the SMOSI not only improves the interlayer force between h-BN layers with a pinning model but also reduces the affinity of the B-N bond toward O⢠for inhibiting oxidative cutting of h-BN into fragments at a high temperature and water-rich environment. With the pinning effect of the SMOSI, the catalytic stability of h-BNâ70In2O3 has been extended nearly five times than that of pristine h-BN, and the intrinsic olefin selectivity/productivity of h-BN is well maintained.
RESUMO
The rational design and controllable synthesis of hollow nanoparticles with both a mesoporous shell and an asymmetric architecture are crucially desired yet still significant challenges. In this work, a kinetics-controlled interfacial super-assembly strategy is developed, which is capable of preparing asymmetric porous and hollow carbon (APHC) nanoparticles through the precise regulation of polymerization and assembly rates of two kinds of precursors. In this method, Janus resin and silica hybrid (RSH) nanoparticles are first fabricated through the kinetics-controlled competitive nucleation and assembly of two precursors. Specifically, silica nanoparticles are initially formed, and the resin nanoparticles are subsequently formed on one side of the silica nanoparticles, followed by the co-assembly of silica and resin on the other side of the silica nanoparticles. The APHC nanoparticles are finally obtained via high-temperature carbonization of RSH nanoparticles and elimination of silica. The erratic asymmetrical, hierarchical porous and hollow structure and excellent photothermal performance under 980 nm near-infrared (NIR) light endow the APHC nanoparticles with the ability to serve as fuel-free nanomotors with NIR-light-driven propulsion. Upon illumination by NIR light, the photothermal effect of the APHC shell causes both self-thermophoresis and jet driving forces, which propel the APHC nanomotor. Furthermore, with the assistance of phase change materials, such APHC nanoparticles can be employed as smart vehicles that can achieve on-demand release of drugs with a 980 nm NIR laser. As a proof of concept, we apply this APHC-based therapeutic system in cancer treatment, which shows improved anticancer performance due to the synergy of photothermal therapy and chemotherapy. In brief, this kinetics-controlled approach may put forward new insight into the design and synthesis of functional materials with unique structures, properties, and applications by adjusting the assembly rates of multiple precursors in a reaction system.
RESUMO
The impact of airborne molecular contaminants (AMCs) on the lifetime of fused silica UV optics in high power lasers (HPLs) is a critical issue. In this work, we demonstrated the on-line monitoring method of AMCs concentration based on the Sagnac microfiber structure. In the experiment, a Sagnac microfiber loop with mesoporous silica coating was fabricated by the microheater brushing technique and dip coating. The physical absorption of AMCs in the mesoporous coating results in modification of the surrounding refractive index (RI). By monitoring the spectral shift in the wavelength domain, the proposed structure can operate as an AMCs concentration sensor. The sensitivity of the AMCs sensor can achieve 0.11 nm (mg/m3). By evaluating the gas discharge characteristic of four different low volatilization greases in a coarse vacuum environment, we demonstrated the feasibility of the proposed sensors. The use of these sensors was shown to be very promising for meeting the requirements of detecting trace amounts of contaminants.
RESUMO
Here we use low-temperature scanning tunneling microscopy and spectroscopy to reveal the roles of the narrow electronic band in two 1T-TaS_{2}-related materials (bulk 1T-TaS_{2} and 4H_{b}-TaS_{2}). 4H_{b}-TaS_{2} is a superconducting compound with alternating 1T-TaS_{2} and 1H-TaS_{2} layers, where the 1H-TaS_{2} layer has a weak charge density wave (CDW) pattern and reduces the CDW coupling between the adjacent 1T-TaS_{2} layers. In the 1T-TaS_{2} layer of 4H_{b}-TaS_{2}, we observe a narrow electronic band located near the Fermi level, and its spatial distribution is consistent with the tight-binding calculations for two-dimensional 1T-TaS_{2} layers. The weak electronic hybridization between the 1T-TaS_{2} and 1H-TaS_{2} layers in 4H_{b}-TaS_{2} shifts the narrow electronic band to be slightly above the Fermi level, which suppresses the electronic correlation-induced band splitting. In contrast, in bulk 1T-TaS_{2}, there is an interlayer CDW coupling-induced insulating gap. In comparison with the spatial distributions of the electronic states in bulk 1T-TaS_{2} and 4H_{b}-TaS_{2}, the insulating gap in bulk 1T-TaS_{2} results from the formation of a bonding band and an antibonding band due to the overlap of the narrow electronic bands in the dimerized 1T-TaS_{2} layers.
RESUMO
Stretchable optical fiber sensors (SOFSs), which are promising and ultra-sensitive next-generation sensors, have achieved prominent success in applications including health monitoring, robotics, and biological-electronic interfaces. Here, we report an ultra-sensitive multi-functional optical micro/nanofiber embedded with a flexible polydimethylsiloxane (PDMS) membrane, which is compatible with wearable optical sensors. Based on the effect of a strong evanescent field, the as-fabricated SOFS is highly sensitive to strain, achieving high sensitivity with a peak gauge factor of 450. In addition, considering the large negative thermo-optic coefficient of PDMS, temperature measurements in the range of 30 to 60 °C were realized, resulting in a 0.02 dBm/°C response. In addition, wide-range detection of humidity was demonstrated by a peak sensitivity of 0.5 dB/% RH, with less than 10% variation at each humidity stage. The robust sensing performance, together with the flexibility, enables the real-time monitoring of pulse, body temperature, and respiration. This as-fabricated SOFS provides significant potential for the practical application of wearable healthcare sensors.
Assuntos
Nanofibras , Dispositivos Eletrônicos Vestíveis , Eletrônica , Frequência Cardíaca , TemperaturaRESUMO
Exfoliation of non-layered (structurally) bulk materials at the nanoscale is challenging because of the strong chemical bonds in the lattice, as opposed to the weak van der Waals (vdW) interactions in layered materials. We propose a top-down method to exfoliate ϵ-MnO2 nanosheets in a family of charge-ordered La1-x AEx MnO3 (AE=Ca, Sr, Ba) perovskites, taking advantage of the Jahn-Teller disproportionation effect of Mn3+ and bond-strength differences. ϵ-MnO2 crystallized into a nickel arsenide (NiAs) structure, with a thickness of 0.91â nm, displays thermal metastability and superior water oxidation activity compared to other manganese oxides. The exfoliation mechanism involves a synergistic proton-induced Mn3+ disproportionation and structural reconstruction. The synthetic method could also be potentially extended to the exfoliation of other two-dimensional nanosheet materials with non-layered structures.
RESUMO
The formation of laser-induced periodic surface structures (LIPSS) on two different dielectrics of K9 glass and fused silica upon irradiation in ambient conditions and in vacuum with multiple femtosecond (fs) laser pulse sequences at different pulse durations (35 fs, 260 fs, and 500 fs) was studied experimentally. Three types of LIPSS, so-called high-spatial-frequency LIPSS (HSFL), low-spatial-frequency LIPSS (LSFL), and supra-wavelength periodic surface structures (SWPSS) with different spatial periods and orientations were identified. The appearance was characterized with respect to the experimental parameters of laser fluence and number of laser pulses per spot. The crater morphologies - including nanoripples, periodic microgrooves, quasiperiodic microspikes, and central smooth zone - were observed by scanning electron microscope (SEM). The supra-wavelength structures exhibit periodicities, which are markedly, even multiple times, higher than the laser excitation wavelength. The SWPSS were formed with a broader range of laser fluences, upon the longer laser pulse durations (260 fs and 500 fs) and/or on the lower band-gap dielectrics (K9 glass), due to the deeper effective light penetration depths and thicker viscous surface layers formation. The HSFL were observed on the higher band-gap dielectrics (fused silica) and within a certain narrow laser parameter window. The formation mechanisms of LIPSS were also discussed.
RESUMO
The synthesis of intermetallic antimonides usually depends on either the high-temperature alloying technique from high-purity metals or the flux method in highly poisonous Pb-melt. In this paper, we introduced a soft-chemical method to synthesize intermetallic antimonides from ternary chalcogenide precursors under an argon atmosphere below 200 °C. Powder X-ray diffraction and compositional analysis clearly indicate that a new phase of the Ag3Sb nanocrystal was synthesized from the Ag3SbS3 precursors. Three types of trialkylphosphines (TAPs) were applied as desulfurization agents, and the transformation mechanism was elucidated. The capability of the desulfurization agent follows the sequence of triphenylphosphine (TPP) > tributylphosphine (TBP) > trioctylphosphine (TOP). Besides, this TAP-driven desulfurization route to synthesize the intermetallic phase could also be possible for AgSbSe2 and Sb2S3. Therefore, this paper provides an efficient and mild technique for the fabrication of intermetallic nanocrystals.
RESUMO
A simple and convenient means of fabricating concave microlens arrays direct on silica glass by using the local fictive temperature modification of fused silica is presented. This method is based on the fact that an increased fictive temperature results in a much higher HF acid etching rate of fused silica. Combining the abrupt local fictive temperature enhancement by the CO2 laser pulse and the subsequent etching by the HF acid solution, concave microlens arrays with high fill factors, excellent smoothness, and optical performance are generated on fused silica.
RESUMO
The Li+/H+ cation exchange reactions occur when the cathode is exposed to water and can cause the degradation of battery performance, posing a significant challenge in the preparation of cathode aqueous electrodes. In this study, kh570 [3-(trimethoxysilyl)propyl methacrylate] is used to coat and modify the surface of LiNi0.5Co0.2Mn0.3O2 cathode particles. During the coating process, kh570 undergoes hydrolysis to generate silanol groups, which are subsequently bonded onto the surface of cathode particles and undergo self-polymerization through condensation reactions. As a result, a coating layer forms on the surface of the cathode. This change alters the surface properties of the cathode particles from hydrophilic to hydrophobic, thereby increasing their resistance to water. The coating layers reduce direct contact with water and minimizes internal particle microcracks formation in aqueous electrode processing. After the preparation of aqueous electrodes, the modified cathode exhibits lower transfer resistance and lower polarization, improving both the current rate performance and the cycling performance of the battery.
RESUMO
Herein, we achieved reactive oxygen species manipulation using transition metal spinel ferrites (NixCo1-xFe2O4, x = 0, 0.5, 1) as Fenton-like agents. Specifically, NiFe2O4 mainly produced 1O2 and high-valence metals, while CoFe2O4 mainly produced ËOH, from H2O2 activation. With bisphenol A as a model pollutant, the NiFe2O4/H2O2 system exhibited good resistance to ion interference.
RESUMO
Metastable noble metal nanocrystals may exhibit distinctive catalytic properties to address the sluggish kinetics of many important processes, including the hydrogen evolution reaction under alkaline conditions for water-electrolysis hydrogen production. However, the exploration of metastable noble metal nanocrystals is still in its infancy and suffers from a lack of sufficient synthesis and electronic engineering strategies to fully stimulate their potential in catalysis. In this paper, we report a synthesis of metastable hexagonal Pt nanostructures by coherent growth on 3d transition metal nanocrystals such as Ni without involving galvanic replacement reaction, which expands the frontier of the phase-replication synthesis. Unlike noble metal substrates, the 3d transition metal substrate owns more crystal phases and lower cost and endows the hexagonal Pt skin with substantial compressive strains and programmable charge density, making the electronic properties particularly preferred for the alkaline hydrogen evolution reaction. The energy barriers are greatly reduced, pushing the activity to 133 mA cmgeo-2 and 17.4 mA µgPt-1 at -70 mV with 1.5 µg of Pt in 1 M KOH. Our strategy paves the way for metastable noble metal catalysts with tailored electronic properties for highly efficient and cost-effective energy conversion.
RESUMO
China's progress in decarbonizing its transportation, particularly vehicle electrification, is notable. However, the economically effective pathways are underexplored. To find out how much cost is necessary for carbon neutrality for the light-duty vehicle (LDV) sector, this study examines twenty decarbonization pathways, combining the New Energy and Oil Consumption Credit model and the China-Fleet model. We find that the 2060 zero-greenhouse gas (GHG) emission goal for LDVs is achievable via electrification if the battery pack cost is under CNY483/kWh by 2050. However, an extra of CNY8.86 trillion internal subsidies is needed under pessimistic battery cost scenarios (CNY759/kWh in 2050) to eliminate 246 million tonnes of CO2-eq by 2050 ensuring over 80% market penetration of battery electric vehicles (BEVs) in 2050. Moreover, the promotion of fuel cell electric vehicles is synergy with BEVs to mitigate the carbon abatement difficulties, decreasing up to 34% of the maximum marginal abatement internal investment.
RESUMO
Aerosol particle contamination in high-power laser facilities has become a major cause of internal optical component damage resistance and service life reduction. In general, contaminating particles primarily originate from stray light; therefore, it is crucial to investigate the mechanism and dynamics of the dynamic contaminating particle generation to control the cleanliness level. In this study, corresponding research was conducted on experiments and theory. We investigated the particle generation and surface composition modification under the action of a laser. We employed various surface analytical methods to identify the possible variations in the aluminum alloy surface during laser irradiations. A theoretical model for particle ejection from aluminum alloy surfaces was established by taking the adhesion force and laser cleaning force (due to thermal expansion) into account. The results show that the threshold energies for contamination particle generation and damage are around 0.1 and 0.2 J/cm2, respectively. Subsurface impurities are the primary source of particles, and particle adhesion density is related to surface roughness. Pollution particle generation and splashing processes include temperature increases, phase changes, impact diffusion, and adhesion. The results provide a reference for the normal operation of high-energy laser systems. The results also suggest that the laser irradiation pretreatment of aluminum alloy surfaces is essential to improve the cleanliness level.
RESUMO
Incorporating plasticizers is an effective way to facilitate conduction of ions in solid polymer electrolytes (SPEs). However, this conductivity enhancement often comes at the cost of reduced mechanical properties, which can make the electrolyte membrane more difficult to process and increase safety hazards. Here, a novel crosslinking strategy, wherein metal-alkoxy-terminated polymers can be crosslinked by precisely controlling the content of H2 O as an initiator, is proposed. As a proof-of-concept, trimethylaluminum (TMA)-functionalized poly(ethylene oxide) (PEO) is used to demonstrate that ultrafine Al-O nanoclusters can serve as nodes to crosslink PEO chains with a wide range of molecular weights from 10 000 to 8 000 000 g mol-1 . The crosslinked polymer network can incorporate a high concentration of plasticizers, with a total weight percentage over 75%, while still maintaining excellent stretchability (4640%) and toughness (3.87 × 104 kJ m-3 ). The resulting electrolyte demonstrates high ionic conductivity (1.41 mS cm-1 ), low interfacial resistance toward Li metal (48.1 Ω cm2 ), and a wide electrochemical window (>4.8 V vs Li+ /Li) at 30 °C. Furthermore, the LiFePO4 /Li battery shows stable cycle performance with a capacity retention of 98.6% (146.3 mAh g-1 ) over 1000 cycles at 1C (1C = 170 mAh g-1 ) at 30 °C.
RESUMO
A new strategy was established for the degradation of wastewater-based organic pollutants. Laser-induced plasma (LIP) was used as an alternative UV light source to realise rapid photodegradation of methylene blue (MB), an organic pollutant. A conventional 1064 nm Nd:YAG laser was used for plasma excitation to degrade MB solutions. The results show that the LIP effectively degraded the organic matter, and the degradation efficiency was related to the UV component with wavelength less than 400 nm. The compositions of the plasma excited by different dielectric substrates are different owing to various mechanisms involving moderate heat dissipation and sonoluminescence. However, metallic substrates, especially Fe, can enhance the proportion of UV light and accelerate the degradation efficiency. In the process of methylene blue degradation, solution parameters, such as initial dye concentration, pH, irradiation time and hydrogen peroxide concentration, will affect the degradation efficiency. The conditions of effective degradation of methylene blue (10 mg L-1 MB-1 concentration, 50 mL L-1 H2O2 concentration, pH = 3 and P = 60 mW) were obtained in this study, which can provide reference for practical application.
RESUMO
The research on plasma chemistry involved in the formation and dissociation of abundant chemical bonds is fundamental to developing plasma cleaning. To understand the influence of reactive oxygen species' concentration and ambient temperature on the evolution behavior of the chemical bond during plasma cleaning, microscopic reaction models between organic contaminants and reactive oxygen species were established and performed by reactive molecular dynamics. Dibutyl phthalate, as a representative organic contaminant, was selected as the research object. The simulation results suggested that hydrogen bonds between hydroxyl radicals reduced the mobility of reactive species, resulting in the cleaning ability of hydroxyl radicals being much lower than atomic oxygen and ozone radicals. The concentration of reactive species dominated the efficiency of plasma cleaning, and the increase in ambient temperature further improved the cleaning ability. C-H, C-C and C-O bonds were gradually oxidized to C[double bond, length as m-dash]C, C-O, C[double bond, length as m-dash]O and O-H bonds by hydrogen abstraction reaction during the reaction of reactive species with organic contaminants. An increase in ambient temperature induced the possibility of benzene ring destruction under the action of reactive species, which was considered a method of complete dissociation of aromatic hydrocarbons.
RESUMO
Electron microscopy has been widely used in the structural analysis of proteins, pharmaceutical products, and various functional materials in the past decades. However, one fact is often overlooked that the crystal structure might be sensitive to external environments and response manners, which will bring uncertainty to the structure determination and structure-property correlation. Here, we report the atomic-level ab initio structure determinations of microcrystals by combining 3D electron diffraction (3D ED) and environmental transmission electron microscope (TEM). Environmental conditions, including cryo, heating, gas and liquid, have been successfully achieved using in situ holders to reveal the simuli-responsive structures of crystals. Remarkable structural changes have been directly resolved by 3D ED in one flexible metal-organic framework, MIL-53, owing to the response of framework to pressures, temperatures, guest molecules, etc.
Assuntos
Elétrons , Proteínas , Microscopia EletrônicaRESUMO
Exsolution is an ingenious strategy for the in situ construction of metal- or alloy-decorated oxides and, due to its promising energy related catalysis applications, has advanced from use in perovskites to use in spinels. Despite its great importance for designing target composites, the ability to identify whether active metal ions at octahedral or tetrahedral sites will preferentially exsolve in a spinel remains unexplored. Here, an inverse spinel NiFe2O4 (NFO) was employed as a prototype and FeNi/NFO composites were successfully constructed via exsolution. The preferential breaking of octahedral metal-oxygen bonds in the spinel oxide was directly observed using Mössbauer and X-ray absorption spectroscopy. This was further verified from the negative segregation energies calculated based on density-functional theory. One exsolved FeNi/NFO composite exhibits enhanced electrochemical activity with an overpotential of 283 mV at 10 mA cm-2 and a long stability time for the oxygen evolution reaction. This work offers a unique insight into spinel exsolution based on the preferential breaking of chemical bonds and may be an effective guide for the design of new composite catalysts where the desired metal ions are deliberately introduced to octahedral and/or tetrahedral sites.