Engineering topics
Publications and source records attributed to Li, Tao.
The dendron-shaped macromolecules AB n crystallize into well-ordered pyramid-like structures from mixed solvents, which is on the contrary to spherical motifs with curved structures in bulk.
Atomically dispersed Cu catalyst was designed for highly efficient hydroxylation of aryl iodides under mild conditions.
Almost all surfaces sensitive to the ambient environment are covered by water, whereas the impacts of water on surface-dominated colloidal quantum dot (CQD) semiconductor electronics have rarely been explored. Here, strongly hydrogen-bonded water on hydroxylated lead sulfide (PbS) CQD is identified. The water could pilot the thermally induced evolution of surface chemical environment, which significantly influences the nanostructures, carrier dynamics, and trap behaviors in CQD solar cells. The aggravation of surface hydroxylation and water adsorption triggers epitaxial CQD fusion during device fabrication under humid ambient, giving rise to the inter-band traps and deficiency in solar cells. To address this problem, meniscus-guided-coating technique is introduced to achieve dense-packed CQD solids and extrude ambient water, improving device performance and thermal stability. Our works not only elucidate the water involved PbS CQD surface chemistry, but may also achieve a comprehensive understanding of the impact of ambient water on CQD based electronics.
Abstract Background Plasmodium falciparum (Pf) sporozoites (PfSPZ) can be administered as a highly protective vaccine conferring the highest protection seen to date. Sanaria® PfSPZ vaccines are produced using aseptically reared Anopheles stephensi mosquitoes. The bionomics of sporogonic development of P. falciparum in A. stephensi to fully mature salivary gland PfSPZ is thought to be modulated by several components of the mosquito innate immune system. In order to increase salivary gland PfSPZ infections in A. stephensi and thereby increase vaccine production efficiency, a gene knock down approach was used to investigate the activity of the immune deficiency (IMD) signaling pathway downstream effector leucine-rich repeat immune molecule 1 ( LRIM1 ), an antagonist to Plasmodium development. Methods Expression of LRIM1 in A. stephensi was reduced following injection of double stranded (ds) RNA into mosquitoes. By combining the Gal4/UAS bipartite system with in vivo expression of short hairpin (sh) RNA coding for LRIM1 reduced expression of LRIM1 was targeted in the midgut, fat body, and salivary glands. RT-qPCR was used to demonstrate fold-changes in gene expression in three transgenic crosses and the effects on P. falciparum infections determined in mosquitoes showing the greatest reduction in LRIM1 expression. Results LRIM1 expression could be reduced, but not completely silenced, by expression of LRIM1 dsRNA. Infections of P. falciparum oocysts and PfSPZ were consistently and significantly higher in transgenic mosquitoes than wild type controls, with increases in PfSPZ ranging from 2.5- to tenfold. Conclusions Plasmodium falciparum infections in A. stephensi can be increased following reduced expression of LRIM1. These data provide the springboard for more precise knockout of LRIM1 for the eventual incorporation of immune-compromised A. stephensi into manufacturing of Sanaria’s PfSPZ products.
Catalytic transformation of light alkanes could have considerable practical value, yet remains one of the most challenging areas in catalysis research due to the inertness of the C–H bond. Here, we proposed an efficient ammodehydrogenation (ADeH) catalytic system for the direct C–N linkage between light alkanes and ammonia for CH 3 CN and H 2 (CO x free) production. This breakthrough is achieved over bifunctional metal-modified HZSM-5 catalysts, through the tandem dehydrogenation–amination–dehydrogenation mechanism. We show that ethane ADeH over the Pt/HZSM-5 catalyst can be realized under atmospheric pressure at temperatures as low as 350 °C. The specific rate of CH 3 CN is ~60 μmol/(g min), and the selectivity is up to 99% under such mild conditions. The yield of CH 3 CN increases with increasing temperature; however, the selectivity decreases due to the formation of HCN, C 2 H 4 , and CH 4 . Additionally, the Pt/HZSM-5 catalyst is coke-resistant during the ADeH owing to the strong interaction between NH 3 and the acid sites of the catalyst. So, we anticipate that the proposed ADeH could be extended for the transformation of various n/iso-alkanes with tunable selectivity to alkene and nitriles.
Enzyme immobilization techniques are widely researched due to their wide range of applications. Polymer–protein core–shell nanoparticles (CSNPs) have emerged as a promising technique for enzyme/protein immobilization via a self-assembly process. Based on the desired application, different sizes and distribution of the polymer–protein CSNPs may be required. This work systematically studies the assembly process of poly(4-vinyl pyridine) and bovine serum albumin CSNPs. Average particle size was controlled by varying the concentrations of each reagent. Particle size and size distributions were monitored by dynamic light scattering, ultra-small-angle X-ray scattering, small-angle X-ray scattering and transmission electron microscopy. Results showed a wide range of CSNPs could be assembled ranging from an average radius as small as 52.3 nm, to particles above 1 µm by adjusting reagent concentrations. In situ X-ray scattering techniques monitored particle assembly as a function of time showing the initial particle growth followed by a decrease in particle size as they reach equilibrium. The results outline a general strategy that can be applied to other CSNP systems to better control particle size and distribution for various applications.
Battery degradation results from multiple factors that usually correlate with each other. Electrochemical corrosion of the current collector is one of the main reasons for battery failure, leading to poor internal electrical contact and the dissolution of harmful ions into electrolytes. This phenomenon is especially evident in lithium bistrifluoromethanesulfonimidate (LiTFSI)-based electrolytes, although they have many advantages over conventional lithium hexafluorophosphate (LiPF 6 )-based electrolytes, such as low viscosity, good thermal stability, and stable to water. Recently, highly concentrated electrolytes are found hopeful of inhibiting aluminum's corrosion and boosting new electrolyte development. Here we discuss the solvation structures of liquid electrolytes and decouple the degradation mechanisms of using LiTFSI-based electrolytes in Li(Ni 0.8 Co 0.1 Mn 0.1 )O 2 /Li metal batteries. The results suggest although concentrated electrolytes inhibit the Al corrosion, the growth of lithium dendrites and the protection of the cathode-electrolyte interphase are not significantly improved. Furthermore, this paper provides a paradigm to evaluate the performance of electrolytes comprehensively.
Abstract Heme enzymes, with the pentacoordinate heme iron active sites, possess high catalytic activity and selectivity in biosensing applications. However, they are still subject to limited catalytic stability in the complex environment and high cost for broad applications in electrochemical sensing. It is meaningful to develop a novel substitute that has a similar structure to some heme enzymes and mimics their enzyme activities. One emerging strategy is to design the Fe‐N‐C based single‐atomic site catalysts (SASCs). The obtained atomically dispersed Fe‐N x active sites can mimic the active sites of heme enzymes effectively. In this work, a SASC (Fe‐SASC/NW) is synthesized by doping single iron atoms in polypyrrole (PPy) derived carbon nanowire via a zinc‐atom‐assisted method. The proposed Fe‐SASC/NW shows high heme enzyme‐like catalytic performance for hydrogen peroxide (H 2 O 2 ) with a specific activity of 42.8 U mg −1 . An electrochemical sensor based on Fe‐SASC/NW is developed for the detection of H 2 O 2 . This sensor exhibits a wide detection concentration range from 5.0 × 10 −10 m to 0.5 m and an excellent limit of detection (LOD) of 46.35 × 10 −9 m . Such excellent catalytic activity and electrochemical sensing sensitivity are attributed to the isolated Fe‐N x active sites and their structural similarity with natural metalloproteases.
Nonaqueous redox flow batteries use liquid electrolytes containing redox-active organic molecules (redoxmers) as their energy storage medium. To maximize energy density, the redoxmer concentration needs to be maximized while maintaining low viscosity and high ionic conductivity. During charge, a redoxmer molecule pairs with an ion in the electrolyte while another ion migrates across the membrane to maintain electric neutrality. In a crowded electrolyte, this reconstitution changes physical and chemical properties of the solution. To explore these behaviors, a phenothiazine redoxmer fully miscible with acetonitrile was used, and electrochemical charge was mimicked by chemical oxidation. The solutions were examined using small-angle X-ray scattering, nuclear magnetic resonance, and conductometry and modeled using classical molecular dynamics. Overall, our study indicates that physical and structural properties of redoxmer solutions in both states of charge make it exceedingly difficult to increase the redoxmer concentrations over 2 M at any temperature without compromising dynamic properties of such solutions. The cause for this limitation is proximity to a gel-like regime in which fluidity, diffusivity, and ionic conductivity exponentially decrease with increasing concentration. This tendency is compounded by non-Arrhenius behavior of the electrolyte: a small increase in the concentration outruns gains in fluidity and conductivity at a higher temperature. Thus the properties of crowded electrolytes generally make it impossible to operate when gel-like behavior sets in. Pushing the redoxmer concentration to 2.5-3 M might be possible for small redoxmer molecules, but it would require the use of ionic liquid electrolytes at 340-360 K. (C) 2021 Elsevier B.V. All rights reserved.
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Li–O 2 batteries have recently emerged to meet nowadays elevated electric energy demands. Redox mediators (RMs) for solution-inducing decomposition of discharge products are one approach to increase energy efficiency and reduce high overpotentials in these batteries. However, multiple obstacles hinder their usage such as redox shuttling, capacity fading, electrolyte degradation, etc. Herein, we present a new chemistry based on a combination of LiNO 3 , TEGDME and an ionic liquid that enables LiI (1 M) to lower the charge potential (3.5V) with a long cycle life of 270 cycles. 0.1 M LiI increases the cyclability up to 500 with a slightly increased charge potential (~4V) for a fixed capacity of 1000 mAh/g. Up to 100 cycles, this battery system retained ~95% Li 2 O 2 capacity with a ~0.8 V charge-discharge polarization gap. The addition of LiNO 3 to the electrolyte provides a protective solid electrolyte interface (SEI) on anode that works in synergy with the LiI RM. Moreover, we found that this electrolyte blend results in domain formation of ionic and neutral species enhancing the discharge and charge processes. Finally, DFT calculations provide a better understanding of the role of the anode SEI layer and the Li 2 O 2 decomposition promoted by the LiI during charge on the cathode.
We report the direct Z-scheme heterojunction has been recently emerging as an appealing architecture for photocatalysts design. Its efficiency depends on the interfacial and structural features of the photocatalysts. Herein, the two-dimensional ZnIn 2 S 4 nanosheets are grown on the surface of CdS hollow cubes to construct the CdS@ZnIn 2 S 4 hierarchical hollow photocatalysts with chemically bonded interface. The visualized measurements based on spatial-resolved surface photovoltage spectroscopy, combined with other spectroscopic and simulation investigations, clearly disclose that the CdS@ZnIn 2 S 4 hollow cubes constitute a highly efficient direct Z-scheme system. This accounts for the stoichiometric generation of H 2 and H 2 O 2 from pure water observed for the CdS@ZnIn 2 S 4 sulfide-only photocatalysts under visible light irradiation with an apparent quantum efficiency of 1.63 % at 400 nm. The present work demonstrates an effective protocol to achieve comprehensive insights into the charge transfer route at semiconductor heterojunction, and offers a viable way for constructing efficient sulfide-only photocatalysts for driving water splitting reaction.
Doped metal oxide nanocrystals (NCs) exhibit tunable localized surface plasmon resonances (LSPRs) in the infrared spectral region. Compared to the binary oxides commonly studied, plasmonic NCs derived from ternary oxides remain far less explored primarily due to the difficulty of controlling NC phase-purity and stoichiometry. Here, we report the synthesis of inverse spinel-type cadmium stannate (Cd 2 SnO 4 ) NCs, for which cation-exchange reactions were developed to tailor their composition and LSPR properties. X-ray absorption spectroscopy studies revealed that the inequivalent tetrahedrally and octahedrally coordinated Cd 2+ can be selectively exchanged for Cu + and In 3+ ions, respectively, enabling broadband tunable LSPR and Cu-mediated cation-exchange with lanthanide ions that are otherwise difficult to incorporate. Here, our work paves the way for systematic compositional engineering to accelerate the design of complex metal oxide NCs with emerging plasmonic, electronic, and magnetic properties.
Single-atom and subnanocluster catalysts (SSCs) represent a highly promising class of low-cost materials with high catalytic activity and high atom-utilization efficiency. However, SSCs are susceptible to undergo restructuring during the reactions. Exploring the active sites of catalysts through in situ characterization techniques plays a critical role in studying reaction mechanism and guiding the design of optimum catalysts. In situ X-ray absorption spectroscopy/small-angle X-ray scattering (XAS/SAXS) is promising and widely used for monitoring electronic structure, atomic configuration, and size changes of SSCs during real-time working conditions. Unfortunately, there is no detailed summary of XAS/SAXS characterization results of SSCs. The recent advances in applying in situ XAS/SAXS to SSCs are thoroughly summarized in this review, including the atomic structure and oxidation state variations under open circuit and realistic reaction conditions. Furthermore, the reversible transformation of single-atom catalysts (SACs) to subnanoclusters/nanoparticles and the application of in situ XAS/SAXS in subnanoclusters are discussed. To conlcude, the outlooks in modulating the SSCs and developing operando XAS/SAXS for SSCs are highlighted.
Supported metal nanoparticle (SMN) catalysts are enormously crucial for many catalytic applications. However, catalyst deactivation, caused by sintering and coke formation, is a ubiquitous problem that significantly undermines catalytic processing economics. The application of material overcoating onto supported metal nanoparticles by atomic layer deposition (ALD) offers the solution to inhibit catalyst deactivation. Herein, we discuss examples in which ALD has been used to stabilize SMN catalysts in gaseous and aqueous-phase reactions. We highlight the ALD tools and methods in coating high-surface-area catalysts. Besides, various techniques are introduced to understand better how to characterize the overcoating layer and the catalyst itself. Finally, the outlook for new techniques to characterize the ALD overcoated catalytic materials is discussed.
“Water-in-salt” electrolytes with excellent electrochemical and physical properties have been extensively investigated. However, the structural understanding of the lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in water is still lacking. Here, we perform synchrotron X-ray scattering to systemically study the structural variation of TFSI anions in an aqueous solution under a variety of concentrations and temperatures. There are two different solvation structures in the solution: TFSI - solvated structure and TFSI - network. As the concentration increases, the TFSI - solvated structure gradually disappears while the TFSI - network gradually forms. Even at relatively low concentrations, the TFSI - network can be observed. Our experimental results show that these two structures can coexist at a particular concentration, and temperature changes will lead to one structure’s formation or disappearance. Also, the TFSI - network is the key to obtain a stable electrochemical window under relatively high temperatures.
Using ab initio molecular dynamics (AIMD) simulations, classical molecular dynamics (CMD) simulations, small-angle X-ray scattering (SAXS), and pulsed-field gradient nuclear magnetic resonance (PFG-NMR), the solvation structure and ion dynamics of magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI) 2 ) aqueous electrolyte at 1, 2, and 3 m concentrations are investigated. From AIMD and CMD simulations, the first solvation shell of an Mg 2+ ion is found to be composed of six water molecules in an octahedral configuration and the solvation shell is rather rigid. The TFSI - ions prefer to stay in the second solvation shell and beyond. Meanwhile, the comparable diffusion coefficients of positive and negative ions in Mg(TFSI) 2 aqueous electrolytes have been observed, which is mainly due to the formation of the stable [Mg(H 2 O) 6 ] 2+ complex, and, as a result, the increased effective Mg ion size. Finally, the calculated correlated transference numbers are lower than the uncorrelated ones even at the low concentration of 2 and 3 m, suggesting the enhanced correlations between ions in the multivalent electrolytes. This work provides a molecular-level understanding of how the solvation structure and multivalency of the ion affect the dynamics and transport properties of the multivalent electrolyte, providing insight for rational designs of electrolytes for improved ion transport properties.