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1.
Adv Mater ; : e2007549, 2021 Jan 27.
Artigo em Inglês | MEDLINE | ID: mdl-33506541

RESUMO

The shuttle effect of lithium polysulfides (LiPS) and potential safety hazard caused by the burning of flammable organic electrolytes, sulfur cathode, and lithium anode seriously limit the practical application of lithium-sulfur (Li-S) batteries. Here, a flame-retardant polyphosphazene (PPZ) covalently modified holey graphene/carbonized cellulose paper is reported as a multifunctional interlayer in Li-S batteries. During the discharge/charge process, once the LiPS are generated, the as-obtained flame-retardant interlayer traps them immediately through the nucleophilic substitution reaction between PPZ and LiPS, effectively inhibiting the shuttling effect of LiPS to enhance the cycle stability of Li-S batteries. Meanwhile, this strong chemical interaction increases the diffusion coefficient for lithium ions, accelerating the lithiation reaction with complete inversion. Moreover, the as-obtained interlayer can be used as a fresh 3D current collector to establish a flame-retardant "vice-electrode," which can trap dissolved sulfur and absorb a large amount of electrolyte, prominently bringing down the flammability of the sulfur cathode and electrolyte to improve the safety of Li-S batteries. This work provides a viable strategy for using PPZ-based materials as strong chemical scavengers for LiPS and a flame-retardant interlayer toward next-generation Li-S batteries with enhanced safety and electrochemical performance.

2.
Mikrochim Acta ; 188(1): 18, 2021 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-33404778

RESUMO

A new method based on coordination polymer nanoparticles (CPNs) derived from nucleotides and Tb3+ ions (GMP/Tb) for the selective and sensitive determination of aqueous 2,4,6-trinitrophenol (TNP) (picric acid) is established. The fluorescence of GMP/Tb nanoparticles is effectively quenched by TNP via photo-induced charge transfer (PCT), thus achieving its selectivity toward TNP over other nitroaromatic explosives. The decreased fluorescence of GMP/Tb shows a good linear relationship to the concentrations of TNP ranging from 5.0 to 40.0 µM, and the limit of detection is 26.0 nM (5.96 ppb). The proposed GMP/Tb probe also achieves satisfactory results in real samples. The obtained recoveries of this method in river water samples are in the range 93.15-106.10%. The relative standard deviation (RSD) are 0.57 to 1.01% based on three repeated determinations. This fabricated detector provides a feasible path for determination of ppb-level TNP in natural water samples, which can help humans to avoid TNP-contaminated drinking water. Graphical abstract.

3.
Nanoscale ; 2021 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-33404574

RESUMO

Metal-organic frameworks (MOFs) have emerged as attractive materials for energy and environmental-related applications owing to their structural, chemical and functional diversity over the last two decades. It is known that the poor carrier mobility and low electrical conductivity of ordinary MOFs severely limit their utility in practical applications. In the past 10 years, several MOF materials with high carrier mobility and outstanding electrical conductivity have received a worldwide upsurge of research interest and many techniques and strategies have been used to synthesize such MOFs. In this critical review, we provide an overview of the significant advances in the development of conductive MOFs reported until now. Their theoretical and synthetic design strategies, conductive mechanisms, electrical transport measurements, and applications are systematically summarized and discussed. In addition, we will also give some discussions on challenges and perspectives in this exciting field.

4.
Anal Chem ; 2020 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-33284581

RESUMO

Understanding the structure and composition of aluminate complexes in extremely alkaline systems such as Bayer liquors has received enormous attention due to their fundamental and industrial importance. However, obtaining direct molecular information of the underlying ion-ion interactions using traditional approaches such as NMR spectroscopy or Raman spectroscopy is challenging due to the weakness of these interactions and/or their complex overlapping spectral signatures. Here, we exploit in situ liquid secondary-ion mass spectrometry (SIMS) as a new approach and show how it enables new insights. In contrast with traditional techniques, using SIMS we succeeded in acquiring information on dominant ion clusters in these alkaline systems. In Na+/K+ mixed alkaline aluminate solutions, we clearly observe preferential formation of Na+-anion clusters over K+-anion clusters. Evaluation of these clusters by density functional theory (DFT) calculations shows that these structures are stable and that their relative bond energies are consistent with their observed SIMS signal intensity differences. This demonstrates a key advantage of in situ liquid SIMS for overcoming ambiguities obscuring important information in these systems on constituent molecular clusters defined by relatively weak ion-pair competition and ion-solvent interactions.

5.
J Am Chem Soc ; 2020 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-33295765

RESUMO

We propose a dynamic covalent chemistry (DCC)-induced linker exchange strategy for the structural transformation between covalent organic frameworks (COFs) and cages for the first time. Studies have shown that the COF-to-cage and cage-to-COF transformations were realized by using borate bonds and imine bonds, respectively, as linkages. Self-sorting experiments suggested that borate cages and imine COFs are thermodynamic minimum compounds. This research builds a bridge between discrete and polymeric organic scaffolds and broadens the knowledge of chemistry and materials for porous materials science.

6.
Acc Chem Res ; 53(10): 2443-2455, 2020 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-33003700

RESUMO

ConspectusFlexible and wearable electronics have recently sparked intense interest in both academia and industry because they can greatly revolutionize human lives by impacting every aspect of our daily routine. Therefore, developing compatible energy storage devices has become one of the most important research frontiers in this field. Particularly, the development of flexible electrodes is of great significance when considering their essential role in the performance of these devices. Although there is no doubt that transition metal oxide nanomaterials are suitable for providing electrochemical energy storage, individual oxides generally cannot be developed into freestanding electrodes because of their intrinsically low mechanical strength.Two-dimensional sheets with genuine unilamellar thickness are perfect units for the assembly of freestanding and mechanically flexible devices, as they have the advantages of low thickness and good flexibility. Therefore, the development of metal oxide materials into a two-dimensional sheet morphology analogous to graphene is expected to solve the above-mentioned problems. In this Account, we summarize the recent progress on two-dimensional molecular sheets of transition metal oxides for wearable energy storage applications. We start with our understanding of the principle of producing two-dimensional metal oxides from their bulk-layered counterparts. The unique layered structure of the precursors inspired the exploration of their interlayer chemistry, which helps us to understand the processes of swelling and delamination. Rational methods for tuning the chemical composition, size/thickness, and surface chemistry of the obtained nanosheets and how physicochemical properties of the nanosheets can be modulated are then briefly introduced. Subsequently, the orientational alignment of the anisotropic sheets and the origins of their liquid-crystalline characteristics are discussed, which are of vital importance for their subsequent macroscopic assembly. Finally, macroscopic electrodes with geometric diversity ranging from one-dimensional macroscopic fibers to two-dimensional films/papers and three-dimensional monolithic foams are summarized. The intrinsically low mechanical stiffness of metal oxide sheets can be effectively overcome by wisely designing the assembly mode and sheet interfaces to obtain decent mechanical properties integrated with superior electrochemical performance, thereby providing critical advantages for the fabrication of wearable energy storage devices.We expect that this Account will stimulate further efforts toward fundamental research on interface engineering in metal oxide sheet assembly and facilitate wide applications of their designed assemblies in future new-concept energy conversion devices and beyond. In the foreseeable future, we believe that there will be a big explosion in the application of transition metal oxide sheets in flexible electronics.

7.
ACS Appl Mater Interfaces ; 12(36): 40433-40442, 2020 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-32812729

RESUMO

Carbon nitride has drawn widespread attention as a low-cost alternative to metal-based materials in the field of photocatalysis. However, the traditionally synthesized carbon nitrides always suffer a bulky architecture, which limits their intrinsic activities. Here, a cycloaddition reaction is proposed to synthesize a triazine-based precursor with implanted sodium and cyano groups, which are mostly retained in the resulting carbon nitride after the following polymerization. Incorporated sodium and cyano defects can not only tune the band structure of the carbon nitride but also provide more additive active sites. The optimized properties enable it an adorable photocatalytic hydrogen evolution rate of 1070 µmol h-1 g-1, varying by almost an order of magnitude from the pristine carbon nitride (79 µmol h-1 g-1). Moreover, a sequential self-assembly strategy has been adopted to further improve its architecture. As a consequence, a three-dimensional (3D) porous carbon nitride microtube cluster is constructed, indicating abundant exposed active sites and the faster separation of charge carriers. The corresponding photocatalytic hydrogen evolution rate is 1681 µmol h-1 g-1, which is very competitive compared with the reported pure carbon nitride photocatalysts. Briefly, this new approach may offer opportunities to fabricate task-specific carbon- and nitrogen-based materials from the molecular level.

8.
J Am Chem Soc ; 142(33): 14357-14364, 2020 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-32787252

RESUMO

The development of anhydrous proton-conducting materials is critical for the fabrication of high-temperature (>100 °C) polymer electrolyte membrane fuel cells (HT-PEMFCs) and remains a significant challenge. Covalent organic frameworks (COFs) are an emerging class of porous crystalline materials with tailor-made nanochannels and hold great potential for ion and molecule transport, but their poor chemical stability poses great challenges in this respect. In this contribution, we present a bottom-up self-assembly strategy to construct perfluoroalkyl-functionalized hydrazone-linked 2D COFs and systematically investigate the effect of different lengths of fluorine chains on their acid stability and proton conductivity. Compared with their nonfluorous parent COFs, fluorinated COFs possess structural ultrastability toward strong acids as a result of enhanced hydrophobicity (water contact angle of 144°). Furthermore, the superhydrophobic 1D nanochannels can serve as robust hosts to accommodate large amounts of phosphonic acid for fast and long-term proton conduction under anhydrous conditions and a wide temperature range. The anhydrous proton conductivity of fluorinated COFs is 4.2 × 10-2 S cm-1 at 140 °C after H3PO4 doping, which is 4 orders of magnitude higher than their nonfluorous counterparts and among the highest values of doped porous organic frameworks so far. Solid-state NMR studies revealed that H3PO4 forms hydrogen-boding networks with the frameworks and perfluoroalkyl chains of COFs, and most of the H3PO4 molecules are highly dynamic and mobile while the frameworks are rigid, which affords rapid proton transport. This work paves the way for the realization of the target properties of COFs through predesign and functionalization of the pore surface and highlights the great potential of COF nanochannels as a rigid platform for fast ion transportation.

9.
Nanoscale ; 12(18): 9958-9963, 2020 May 14.
Artigo em Inglês | MEDLINE | ID: mdl-32356547

RESUMO

Identifying novel 2D semiconductors with promising electronic properties and transport performances for the development of electronic and optoelectronic applications is of utmost importance. Here, we show a detailed study of the electronic properties and ballistic quantum transport performance of a new 2D semiconductor, SbSiTe3, based on density functional theory (DFT) and non-equilibrium Green's function (NEGF) formalism. Promisingly, monolayer SbSiTe3 owns an indirect band gap of 1.61 eV with a light electron effective mass (0.13m0) and an anisotropic hole effective mass (0.49m0 and 1.34m0). The ballistic performance simulations indicate that the 10 nm monolayer SbSiTe3 n- and p-MOSFETs display a steep subthreshold swing of about 80 mV dec-1 and a high on/off ratio (106), which indicate a good gate-controlling capability. As the channel length of SbSiTe3 decreases to 5 nm, its p-MOSFET also effectively suppresses the intra-band tunneling. Therefore, 2D SbSiTe3 is a potential semiconductor for future nanoelectronics.

10.
Chem Commun (Camb) ; 56(51): 7005-7008, 2020 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-32441719

RESUMO

Restacking of 2D nanomaterials is often deemed to be detrimental to their applications. In contrast to this common notion, here we demonstrate that tightly packed stacked MoS2 exhibits a higher electrocatalytic activity for hydrogen evolution than the more loosely stacked ones.

11.
Small ; 16(8): e1907043, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-32003933

RESUMO

Conjugated coordination polymers (CPs) with designable and predictable structures have drawn tremendous attention in recent years. However, the poor electrical conductivity and low structural stability seriously restrict their practical applications in electronic devices. Herein, the rational design and synthesis of a hierarchically structured 2D bimetallic CoNi-hexaaminobenzene CPs derived from Co(OH)2 are reported as an efficient oxygen evolution reaction (OER) self-supported electrode. The as-obtained electrode possesses high electrochemical surface area and intrinsic activity, exhibiting high electrochemical catalytic activity, favorable reaction kinetics performance, and strong durability compared with those of the powder catalysts. As a result, the electrode delivers low overpotential of 219 mV @ 10 mA cm-2 and Tafel slope of 42 mV dec-1 as well as 91.3% retention of current density after 24 h of reaction time. The results of density functional theory computations reveal that the synergistic effect of Co and Ni plays an important role in OER. This work not only presents a strategy to fabricate advanced self-supported electrodes with abundant and dense active sites, but also promotes the development of conjugated CPs for electrocatalysis.

12.
Nat Commun ; 11(1): 845, 2020 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-32051407

RESUMO

Encapsulation strategies are widely used for alleviating dissolution and diffusion of polysulfides, but they experience nonrecoverable structural failure arising from the repetitive severe volume change during lithium-sulfur battery cycling. Here we report a methodology to construct an electrochemically recoverable protective layer of polysulfides using an electrolyte additive. The additive nitrogen-doped carbon dots maintain their "dissolved" status in the electrolyte at the full charge state, and some of them function as active sites for lithium sulfide growth at the full discharge state. When polysulfides are present amid the transition between sulfur and lithium sulfide, nitrogen-doped carbon dots become highly reactive with polysulfides to form a solid and recoverable polysulfide-encapsulating layer. This design skilfully avoids structural failure and efficiently suppresses polysulfide shuttling. The sulfur cathode delivers a high reversible capacity of 891 mAh g-1 at 0.5 C with 99.5% coulombic efficiency and cycling stability up to 1000 cycles at 2 C.

13.
ACS Nano ; 14(2): 2436-2444, 2020 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-31986009

RESUMO

Metal clusters, an emerging category of materials with molecular metal dispersity, have been proposed for versatile applications. In this work, we show an unexpected function of metal clusters, which can contribute to preparing 2D/2D superlattice-like heterostructures. The key step is to use metal clusters to adjust the surface charge of 2D nanosheets and, consequently, match the charge negativities per surface area for different 2D nanosheets, which facilitate the electrical-driven assembly of these nanosheets into a superlattice-like heterostructure in aqueous solutions. Accordingly, iron-cluster-directed cationic Fe-N-C nanosheets (Zeta potential: +30.4 mV) have been assembled with anionic MXene (Zeta potential: -39.7 mV) to produce a superlattice-like heterostructure characteristic of a lateral size of around tens of nanometers, a surface area of 30 m2 g-1, and ultrathickness of several nanometers with repeated dimensions of 0.4 and 2.1 nm. Potential application of the synthesized Fe-N-C/MXene heterostructure has been demonstrated for electrocatalytic oxygen reduction reaction (ORR) that shows a positive onset potential of 0.92 V, four-electron transfer pathway, and strong durability of 20 h in alkaline electrolyte. This work suggests that metal clusters can assist the assembly of low-dimensional architectures for energy-related applications.

14.
IEEE Trans Neural Netw Learn Syst ; 31(3): 1010-1021, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31199272

RESUMO

The cooperative control problem of nonlinear multiagent systems is studied in this paper. The followers in the communication network are subject to unmodeled dynamics. A fully distributed neural-networks-based adaptive control strategy is designed to guarantee that all the followers are asymptotically synchronized to the leader, and the synchronization errors are within a prescribed level, where some global information, such as minimum and maximum singular value of graph adjacency matrix, is not necessarily to be known. Based on the Lyapunov stability theory and algebraic graph theory, the stability analysis of the resulting closed-loop system is provided. Finally, an numerical example illustrates the effectiveness and potential of the proposed new design techniques.

15.
ACS Appl Mater Interfaces ; 11(30): 27226-27232, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31286761

RESUMO

Graphitic carbon nitride (g-C3N4), characterized with a suitable bandgap, has aroused great interest as a robust and efficient catalyst for solar energy utilization. Herein, we introduce a new strategy to fabricate a three-dimensional (3D) porous g-C3N4 by a facile NaCl-assisted ball-milling strategy. The porous structure-induced advantages, such as a higher specific surface area, more efficient charge separation, and faster electron-transfer efficiency, enable the 3D porous g-C3N4 to achieve impressive properties as a bifunctional catalyst for both photocatalytic hydrogen evolution and electrocatalytic oxygen evolution reaction (OER). As a result, the 3D porous g-C3N4 exhibits a hydrogen evolution rate of 598 µmol h-1 g-1 with an apparent quantum yield of 3.31% at 420 nm for photocatalytic H2 generation, which is much higher than that of the bulk g-C3N4. Simultaneously, the porous g-C3N4 also presents an attractive OER performance with a low onset potential of 1.47 V (vs reversible hydrogen electrode) in an alkaline electrolyte after rational cobalt-doping. Accordingly, the NaCl-assisted ball-milling strategy paves the way to the rational design of a controllable porous structure.

16.
Nanoscale ; 11(1): 178-184, 2018 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-30525158

RESUMO

Pyrite-type FeS2 is regarded as a promising anode material for sodium ion batteries. The synthesis of FeS2 in large quantities accompanied by an improved cycling stability, as well as retaining high theoretical capacity, is highly desirable for its commercialization. Herein, we present a scalable and simple strategy to prepare a foam-like FeS2 (F-FeS2) nanostructure by combining solution combustion synthesis and solid-state sulfurization. The obtained F-FeS2 product is highly uniform and built from interconnected FeS2 nanoparticles (∼50 nm). The interconnected feature, small particle sizes and porous structure endow the product with high electrical conductivity, good ion diffusion kinetics, and high inhibition capacity of volume expansion. As a result, high capacity (823 mA h g-1 at 0.1 A g-1, very close to the theoretical capacity of FeS2, 894 mA h g-1), good rate capability (581 mA h g-1 at 5.0 A g-1) and cyclability (754 mA h g-1 at 0.2 A g-1 with 97% retention after 80 cycles) can be achieved. The sodium storage mechanism has been proved to be a combination of intercalation and conversion reactions based on in situ XRD. Furthermore, high pseudocapacitive contribution (i.e. ∼87.5% at 5.0 mV s-1) accounts for the outstanding electrochemical performance of F-FeS2 at high rates.

17.
ACS Appl Mater Interfaces ; 10(44): 37773-37778, 2018 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-30346690

RESUMO

Though 2D transition metal dichalcogenides have attracted a lot of attention in energy-storage applications, the applications of NbSe2 for Li storage are still limited by the unsatisfactory theoretical capacity and uncontrollable synthetic approaches. Herein, a controllable oil-phase synthetic route for preparation of NbSe2 nanoflowers consisted of nanosheets with a thickness of ∼10 nm is presented. Significantly, a part of NbSe2 can be further replaced by orthorhombic CoSe2 nanoparticles via a post cation exchange process, and the predominantly 2D nanosheet-like morphology can be well-maintained, resulting in the formation of CoSe2-decorated NbSe2 (denoted as CDN) nanosheets. More interestingly, the CDN nanosheets exhibit excellent lithium-ion battery performance. For example, it achieves a highly reversible capacity of 280 mAh g-1 at 10 A g-1 and long cyclic stability with specific capacity of 364.7 mAh g-1 at 5 A g-1 after 1500 cycles, which are significantly higher than those of reported pure NbSe2.

18.
IEEE/ACM Trans Comput Biol Bioinform ; 15(6): 2086-2093, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29993838

RESUMO

This paper investigates the gene circuit control design problem of time-delayed genetic regulatory networks. In the genetic regulatory networks, the time delays are unknown constants, and the genetic regulatory is not conventional SUM regulatory logic and can be modeled to be an unknown nonlinear function of the time-delayed states of the other genes in a cell. By Lyapunov stability, a novel adaptive gene circuit control design approach is proposed for the genetic regulatory networks, where the unknown time delays are estimated online by adaptive algorithms and the unknown regulatory functions are approximated by neural networks. The design approach in this paper is delay-dependent and has less conservatism than the delay-independent approach. From theoretical analysis, the closed-loop system is asymptotically stable and all the signals in the system converge to an adjustable neighborhood of the origin. Finally, a numerical example is given to show the effectiveness of the new design approach.


Assuntos
Redes Reguladoras de Genes , Algoritmos , Biologia Computacional , Simulação por Computador , Modelos Genéticos
19.
Photochem Photobiol ; 94(5): 942-954, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-29797582

RESUMO

CH3 COO(BiO) (denoted as BiOAc) is one of the most easily obtained bismuth compounds and was for the first time proposed by our group as an effective UV light photocatalyst. Herein, BiOCl1- x Brx (x refers to the feeding atomic ratio) were obtained using a facile solid state milling and subsequent water washing. More importantly, all of the as-prepared BiOCl1- x Brx possessed better visible light photocatalytic activity to the corresponding ones obtained by previously reported solution route. Especially at an optimal x value of 0.5, the solid solution showed the highest photodegradation efficiency (~100%) for rhodamine B (RhB) with a concentration of 30 mg L-1 , whereas the degradation efficiency was only 63% over that obtained by solution route. Furthermore, the as-prepared BiOCl0.5 Br0.5 also exhibited excellent photodegradation activity for malachite green (MG). The superior photocatalytic performance of the as-prepared BiOCl0.5 Br0.5 could be attributed to its thinner sheetlike structures and highly exposed (001) facets, which enable effective separation of the photogenerated electrons and holes along the [001] direction. In addition, the as-prepared BiOCl0.5 Br0.5 revealed dramatic adsorption capacity for cationic dyes like MG, RhB and methylene violet (MV), as well as anion (Cr2 O7 )2- owing to electrostatic interaction between cationic dyes and negatively charged surface of BiOCl0.5 Br0.5 , and positively charged surface in K2 Cr2 O7 solution (pH ≈ 3).

20.
Nanoscale ; 10(4): 1766-1773, 2018 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-29308801

RESUMO

The exploration of highly active catalysts for hydrogen evolution reaction (HER) is beneficial to realize high catalytic activity and enhance kinetics for water splitting. Herein, flower-like molybdenum disulfide/carbon nitride (MoS2/C3N4) nanosheets with thickness of 4.6 nm and enlarged interlayer spacing of 0.64 nm were synthesized via a facile hydrothermal method. As expected, the ultrathin thickness endowed MoS2/C3N4 with abundant active sites, ensuring outstanding catalytic activity and excellent stability for HER in alkaline electrolyte. MoS2/C3N4 nanocomposites can offer an onset overpotential of 153 mV versus reversible hydrogen electrode (RHE). Notably, the Tafel slope value is only 43 mV dec-1, which is significantly better than those of reported MoS2-based hydrogen evolution catalysts, revealing superior HER performance of MoS2/C3N4, particularly in catalytic kinetics. More significantly, density functional theory (DFT) calculations further verify that rich active sites confined in ultrathin nanostructure of g-C3N4 nanolayers could increase the activity of MoS2/C3N4 and result in enhanced HER efficiency. This study indicates that rational interaction between two different 2D materials can significantly facilitate H2 generation, which endows extraordinary HER activity.

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