Lewis‐base sites have been widely applied to regulate the properties of Lewis‐acid sites in electrocatalysts for achieving a drastic technological leap of lithium‐oxygen batteries (LOBs). Whereas, ...the direct role and underlying mechanism of Lewis‐base in the chemistry for LOBs are still rarely elucidated. Herein, we comprehensively shed light on the pivotal mechanism of Lewis‐base sites in promoting the electrocatalytic reaction processes of LOBs by constructing the metal–organic framework containing Lewis‐base sites (named as UIO‐66‐NH2). The density functional theory (DFT) calculations demonstrate the Lewis‐base sites can act as electron donors that boost the activation of O2/Li2O2 during the discharged‐charged process, resulting in the accelerated reaction kinetics of LOBs. More importantly, the in situ Fourier transform infrared spectra and DFT calculations firstly demonstrate the Lewis‐base sites can convert Li2O2 growth mechanism from surface‐adsorption growth to solvation‐mediated growth due to the capture of Li+ by Lewis‐base sites upon discharged process, which weakens the adsorption energy of UIO‐66‐NH2 towards LiO2. As a proof of concept, LOB based on UIO‐66‐NH2 can achieve a high discharge specific capacity (12 661 mAh g−1), low discharged‐charged overpotential (0.87 V) and long cycling life (169 cycles). This work reveals the direct role of Lewis‐base sites, which can guide the design of electrocatalysts featuring Lewis‐acid/base dual centers for LOBs.
The Lewis‐base site of UIO‐66‐NH2 is capable of capturing Li+ during the discharge process, which can optimize the adsorption strength of UIO‐66‐NH2 towards LiO2 intermediates, thereby leading to the solution‐mediated growth of Li2O2 and ultimately improving the discharge capacity of the lithium‐oxygen battery. In addition, Lewis‐base site can promote the activation of O2 and Li2O2 to reduce the overpotential of the lithium‐oxygen battery.
Carbon nanotubes (CNTs) have attracted much attention from both academia and industry due to their unique mechanical, electrical and thermal properties. Many scholars have been devoted to pursuing ...its growth mechanism for more than three decades, which is the core of high quality and high yield preparation of CNTs. However, the requirement of exploring its growth mechanism is raised higher, and the combination and cross-use of in situ characterization and machine learning are the key techniques to explore its growth mechanism. The above technologies have important application prospects for the modification and performance enhancement of carbon fiber (CF) on the basis of exploring the growth mechanism of CNTs. And it has been possible to grow CNTs on CF with the trend of industrialization. Therefore, in-depth study of the growth mechanism of CNTs and their enhancement of CF properties is still a key concern and development direction in the future, which has important high-value applications in the manufacture of high-performance products and enhancement of interfacial properties of composite materials.
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•The role of machine learning in the study of carbon nanotubes is highlighted.•The importance of catalyst selection and temperature control is emphasized.•The in-situ modification of CNTs to CF was emphasized.
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•Synthesis of LC-ZSM-5 is optimized to achieve high adsorption capacity.•Agglomeration will occur as synthesis time of LC-ZSM-5 increases.•Thermodynamic study indicates a ...spontaneously physicochemical adsorption.•Adsorption mechanism includes electrostatic attraction and ligand exchange.•Adsorption capacity of LC-ZSM-5 maintains near 70% after 5 cycling runs.
High-efficiency phosphate removal from wastewater is crucial for protecting environmental stability. In this work, a lanthanum carbonate grafted ZSM-5 adsorbent (LC-ZSM-5) was prepared and optimized by a Box-Behnken design. The higher temperature, molar ratio of urea to lanthanum and initial lanthanum concentration are beneficial for LC-ZSM-5 synthesis, and the adsorption capacity of LC-ZSM-5 under optimistic conditions was 91.2 mg-PO43-/g. The growth mechanism indicates that the LC particles grow larger with synthesis time and finally agglomerate, and 12 h is the best synthesis time. The thermodynamic results show that phosphate adsorption over LC-ZSM-5 is a spontaneously exothermic and combined physicochemical adsorption process. Kinetic studies suggest that higher temperatures help increase the phosphate adsorption rate, and chemical adsorption plays an important role during adsorption with an activation energy Ea of 42.7 kJ/mol. The adsorption mechanism of the phosphate uptake process includes electrostatic attraction and ligand exchange, through which LC is changed to lanthanum phosphate (LP) during adsorption. Finally, the regeneration study revealed that LC-ZSM-5 still exhibited a high adsorption capacity after 5 cycles, showing its satisfactory regeneration ability and potential industrial application.
Bulk titanium and CoCr are the most common metals for use in orthopedic implants, but there are significant advantages in alternative substrates. Research in the last decade has focused on various ...alternatives; however, these materials are hindered by the adhesion of hydroxyapatite layers to non-bulk metal parts. Demonstrated in this work is the ability to grow hydroxyapatite on surfaces other than bulk metallic parts through the process and characterisation of coating properties. In this study, hydroxyapatite (HA) is grown from saturated solution onto thin titanium films and silicon substrates. Its efficacy is shown to be dependent on substrate roughness. The mechanism of the hydroxyapatite growth is investigated in terms of initial attachment and morphological development using SEM analysis. Characterisation of hydroxyapatite layers by XRD demonstrates how the hydroxyapatite forms from amorphous phases to preferential crystal growth along the 002 direction and TEM imagery confirms specific d-spacings. SEM-EDX and FTIR show adherence to known HA phases through elemental atomic weight percentages and bond assignment. All data are collated and reviewed through the lens of different substrates. The results suggest that once hydroxyapatite seeds, it grows identically regardless of substrate.
In this study, the PVD-ZrC ceramic was fabricated through magnetron sputtering, with a specific focus on its thickness-dependent growth and evolution of composition, microstructure, growth texture ...and mechanical properties. The relevance concerned with the process and growth structure/mechanisms in the controllable synthesis and properties of PVD-ZrC were analyzed.
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•Growth mechanisms regarding temperature and pressure were revealed.•Thickness-dependent evolution of structure and properties was analyzed.•Research results contribute to the fine-grained regulation of ZrC structure.•Mechanical properties were demonstrated through First-principles analysis.•Enriching the theoretical understanding of controlled preparation of ZrC ceramic.
The fine-tuning of controlled structure and property evolution of zirconium carbide (ZrC) ceramic is essential for its functional applications, especially with insufficient understanding of the size effect mechanisms. In this investigation, the physically vapor-deposited ZrC (PVD-ZrC) ceramic was fabricated through magnetron sputtering, with a specific focus on its thickness-dependent growth and evolution of composition, microstructure, growth texture and mechanical properties. As prepared PVD-ZrC presents a hybrid structure characterized by amorphous carbon and nanocrystalline ZrC, with diversity in crystallinity, crystallite size, and growth pattern determined by target power, gas-flow pressure and substrate temperature. Moreover, the PVD-ZrC ceramic deposited by directional deposition, exhibits a structure transition from equiaxed crystals to dense columnar fiber crystals and an isotropy-toward texture. As the thickness increases, the stress gradually shifts towards tensile stress with a weaker fracture toughness. Through the First-principle calculation, it is illustrated that the mechanical properties of bulk polycrystalline ZrC are evidently different from low-dimensional polycrystalline ZrC film. This mechanism of thickness-dependent structure and properties is dominant by the surface effect, size effect, grain boundary effect, and stress effects.
Mullite whiskers were synthesized based on the S-L-S growth mechanism at high temperatures using nano-alumina sol and nano-silica sol as the main materials and ammonium molybdate tetrahydrate as an ...additive. The effects of the silica-aluminum ratio, addition of ammonium molybdate catalyst, sintering temperature, and sintering time on the generation of mullite whiskers were systematically investigated to determine the optimal synthesis conditions. It was shown that the best raw material formulation was (3Al2O3·2.2SiO2)8(MoO3)2, which minimized the mass loss of precursor powder at 0–1200°C, with only 23.62%. The mullite whiskers generated by sintering for 1–3 h maintained good microforms without agglomeration. The optimal growth conditions were 1300°C sintering for 1 h. The resulting mullite whiskers grew along the 240 direction and had the largest aspect ratios up to 10.2–14.3. The highest generation rate was up to 94.5 wt% with a grain size of 81.6 nm. The BET surface area was 2.308 m2/g and the pore size was 5.44 nm. The mass loss at 0–1200°C was the least, only 1.32%, with good thermal stability. In addition, the effects of (xAl2O3·ySiO2)8(MoO3)2 (x:y=3:1.8, 3:2, 3:2.2) whiskers treated at 1300°C on the APSB adhesive and MSABS adhesive bonding were investigated in this paper, it was clear that whiskers with x:y=3:2.2 had the best enhancement effect. For APSB adhesive strength could be increased by up to 55% and the fracture displacement by 2.42 times. For MSABS adhesives, the strength could be increased by up to 47% and the fracture displacement by 1.49 times.
•The optimal growth condition is sintering precursor (3Al2O3·2.2SiO2)8(MoO3)2 at 1300°C for 1 h.•The whisker generation rate is 94.5%, with aspect ratio of 10.2–14.3, surface area of 2.038 m2/g.•The whiskers maintain whisker state for persistently at high temperatures.•The strength improvement rate of heat-resistant adhesive by adding the whisker is about 47–55%.
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•Brush–like SnO2@ZnO HNSs are hydrothermally synthesized.•The growth mechanism of SnO2@ZnO HNSs was investigated systematically.•The SnO2@ZnO based sensor shows highly sensitive and ...selective to NO2.•The minimum detection limit of SnO2@ZnO based sensor to NO2 was as low as 5 ppb.
The novel brush-like (B–) SnO2@ZnO hierarchical nanostructures (HNSs) are successfully synthesized by using a simple two–step hydrothermal method. The SnO2 nanowires (NWs) grow epitaxially on the non–polarized plane of ZnO nanorods (NRs) with a six–fold symmetry. The heterogeneous nucleation–growth processes of SnO2 and ZnO are discussed in detail based on the dissolution–recrystallization mechanism, growth kinetics and Ostwald ripening. The excellent sensing performances of B–SnO2@ZnO HNSs for NO2 gas sensor are developed, including good selectivity, ultrasensitive, fast response, broad detection range and low detection limits. The detection range of the sensor is measured from 5ppb to 10ppm, and the detection limit of the sensor is 5ppb at 150°C. The response and recovery time which reach 90% of the final signal is less than 60s, while retaining the low detection limit. The sensing mechanism is also discussed, and the unique structure of B–SnO2@ZnO is the dominating parameter for excellent sensing performances. The improved sensing performance of the HNSs also suggests the possibilities of other 1D materials combination for further sensing applications.
High-quality Si3N4 powder is a prerequisite for the preparation of high-performance Si3N4 ceramics. In this paper, Si3N4 powders with regular morphology were successfully prepared by pyrolysis of ...Si(NH)2 using silicon as a nucleation inducing agent. The mechanism of the silicon in regulating the morphology and particle size of Si3N4 powders was investigated. The results show that when Si(NH)2 is pyrolyzed directly at 1500 °C under N2 atmosphere, the products are mainly whiskers accompanied by some particles with irregular shape. In the presence of silicon, the powder particles exhibit a regular hexagonal prismatic morphology. With the increase of silicon content, the whisker content decreases obviously, and the whisker disappears completely when the silicon content exceeds 10 %. Furthermore, the particle size of Si3N4 powder decreases with the increase of silicon content, and the particle size is the smallest when the silicon content is 15 wt%, which is about 802 nm. The nucleation and growth process of Si3N4 powder particles can be divided into three stages. Firstly, silicon reacts with N2 to form Si3N4 nuclei. Then, amorphous Si3N4 partially decomposes to form Si(g) and SiO(g) and grows on the formed Si3N4 nuclei as the temperature increased. Finally, undecomposed amorphous Si3N4 spontaneously nucleates and grows of the solid-phase diffusion mechanism. Ultimately, all the powders show equiaxial regular morphology. Preferential nitridation of silicon to form Si3N4 nuclei provides nucleation sites for vapor-phase products, which is the key to inhibiting whisker formation and regulating the particle size of Si3N4 powders.
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Improving the tailorability of hydrochar synthesis is an effective way to enhance its performance and utilization efficiency. In this study, the growth rate, morphology, and molecular ...structure of hydrochar were controlled by regulating the pH and temperature of the hydrothermal carbonization process. Growth process analysis indicates that hydrochar has three growth periods: induction, rapid, and stable growth periods. It is mainly controlled by 5-hydroxymethylfurfural (HMF), which is formed by converting glucose and its transformation products. The regulation of acid can significantly shorten the induction period of hydrochar, even under low-temperature conditions (<180℃), and increase the growth rate of hydrochar. However, the degree of hydrochar adhesion varies: the lower the temperature, the greater the degree of its adhesion. Molecular structural analysis demonstrates that hydrochar mainly consists of furan structural domains and aromatic clusters, and its surface is rich in oxygen-containing functional groups. The degree at which hydrochar was aromatized was improved by increasing the reaction temperature (160–220℃); whereas the regulation of acid reduced it and increased the content of oxygen-containing functional groups on the hydrochar surface. Based on these results, it is proposed that hydrochar formation has five stages and three growth periods with or without acid regulation.
Nitric acid oxidation has been used to fabricate insulation coatings of the FeSiAl soft magnetic composites (SMCs). Growth mechanism of the coatings obtained with varied HNO3 concentration has been ...systematically studied based on careful analysis of the coating thickness, microstructure and composition. The oxidation process for the powders reacted with 10 wt% HNO3 corresponds to the steady-state passivation, while pitting corrosion occurs with raised HNO3 concentration of 30 wt%. Origin of the pitting corrosion has been analyzed based on the point defect model. Evolution of the coatings has been revealed under different growth conditions and correlated to the magnetic performance of the SMCs. The samples oxidized with 10 wt% HNO3 mainly form a thin and compact oxidation layer with dominating Al2O3, AlO(OH) and a small amount of Fe3O4, while increased HNO3 concentration (30 wt%) gives rise to mixed Al2O3, AlO(OH), Fe2O3 and Fe3O4 in the thicker coating layers. Enhanced magnetic performance of the FeSiAl SMCs can be achieved by optimized thickness and composition of the coatings (μe = 180.4, Pcv = 327.2 mW/cm3 for the SMCs oxidized by 10 wt% HNO3 and μe = 157.3, Pcv = 241.2 mW/cm3 via oxidization by 30 wt% HNO3 for 5 min).
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