A Molecular Coordination Strategy for Regulating the Interface of MoS2 Field Effect Transistors.

Chemically modifying monolayer two-dimensional transition metal dichalcogenides (TMDs) with organic molecules provides a wide range of possibilities to regulate the electronic and optoelectronic performance of both materials and devices. However, it remains challenging to chemically attach organic molecules to monolayer TMDs without damaging their crystal structures. Herein, we show that the Mo atoms of monolayer MoS2 (1L-MoS2) in defect states can coordinate with both catechol and 1,10-phenanthroline (Phen) groups, affording a facile route to chemically modifying 1L-MoS2. Through the design of two isomeric molecules (LA2 and LA5) comprising catechol and Phen groups, we show that attaching organic molecules to Mo atoms via coordinative bonds has no negative effect on the crystal structure of 1L-MoS2. Both theoretical calculation and experiment results indicate that the coordinative strategy is beneficial for (i) repairing sulfur vacancies and passivating defects; (ii) achieving a long-term and stable n-doping effect; and (iii) facilitating the electron transfer. Field effect transistors (FETs) based on the coordinatively modified 1L-MoS2 show high electron mobilities up to 120.3 cm2 V-1 s-1 with impressive current on/off ratios over 109. Our results indicate that coordinatively attaching catechol- or Phen-bearing molecules may be a general method for the nondestructive modification of TMDs.

Blocking Metal Nanocluster Growth through Ligand Coordination and Subsequent Polymerization: The Case of Ruthenium Nanoclusters as Robust Hydrogen Evolution Electrocatalysts.

Metal nanoclusters providing maximized atomic surface exposure offer outstanding hydrogen evolution activities but their stability is compromised as they are prone to grow and agglomerate. Herein, a possibility of blocking metal ion diffusion at the core of cluster growth and aggregation to produce highly active Ru nanoclusters supported on an N, S co-doped carbon matrix (Ru/NSC) is demonstrated. To stabilize the nanocluster dispersion, Ru species are initially coordinated through multiple Ru─N bonds with N-rich 4'-(4-aminophenyl)-2,2:6',2''-terpyridine (TPY-NH2) ligands that are subsequently polymerized using a Schiff base. After the pyrolysis of the hybrid composite, highly dispersed ultrafine Ru nanoclusters with an average size of 1.55 nm are obtained. The optimized Ru/NSC displays minimal overpotentials and high turnover frequencies, as well as robust durability both in alkaline and acidic electrolytes. Besides, outstanding mass activities of 3.85 A mg-1 Ru at 50 mV, i.e., 16 fold higher than 20 wt.% Pt/C are reached. Density functional theory calculations rationalize the outstanding performance by revealing that the low d-band center of Ru/NSC allows the desorption of *H intermediates, thereby enhancing the alkaline HER activity. Overall, this work provides a feasible approach to engineering cost-effective and robust electrocatalysts based on carbon-supported transition metal nanoclusters for future energy technologies.

A Novel Anderson-Type POMs-Based Hybrids Flame Retardant for Reducing Smoke Release and Toxicity of Epoxy Resins.

Smoke emission and smoke toxicity have drawn more attention to improving the fire safety of polymers. In this work, a polyoxometalates (POMs)-based hybrids flame retardant (P-AlMo6 ) epoxy resin (EP) is prepared with toxicity-reduction and smoke-suppression properties via a peptide coupling reaction between POMs and organic molecules with double DOPO (bisDOPA). It combines the good compatibility of the organic molecule and the superior catalytic performance of POMs. Compared to pure EP, the glass transition temperature and flexural modulus of EP composite with 5 wt.% P-AlMo6 (EP/P-AlMo6 -5) are raised by 12.3 °C and 57.75%, respectively. Notably, at low flame-retardant addition, the average CO to CO2 ratio (Av-COY/Av-CO2 Y) is reduced by 33.75%. Total heat release (THR) and total smoke production (TSP) are lowered by 44.4% and 53.7%, respectively. The Limited Oxygen Index (LOI) value achieved 31.7% and obtained UL-94 V-0 rating. SEM, Raman, X-ray photoelectron spectroscopy, and TG-FTIR are applied to analyze the flame-retardant mechanism in condensed and gas phase. Outstanding flame retardant, low smoke toxicity properties are attained due to the catalytic carbonization ability of metal oxides Al2 O3 and MoO3 produced from the breakdown of POMs. This work advances the development of POMs-based hybrids flame retardants with low smoke toxicity properties.

Asymmetric Hydrophosphonylation of Imines to Construct Highly Stable Covalent Organic Frameworks with Efficient Intrinsic Proton Conductivity.

Imine-linked covalent organic frameworks (COFs) have received widespread attention because of their structure features such as high crystallinity and tunable pores. However, the intrinsic reversibility of the imine bond leads to the poor stability of imine-linked COFs under strong acid conditions. Also, their thermal stability is significantly lower than that of many other COFs. Herein, we report for the first time that the reversible imine bonds in the skeleton of COFs can be locked through the asymmetric hydrophosphonylation reaction of phosphite. The functionalized COFs not only retain the crystallinity and porous structure but also exhibit evidently improved chemical and thermal stabilities. In addition, the phosphorous acid groups generated by acidic hydrolysis attached to the skeleton endow the COFs with good intrinsic proton conductivity. Due to the diversity of phosphite derivatives and imine-linked COFs, this work may provide an avenue for extending the COF structures and functions through the asymmetric hydrophosphonylation reaction.

Metallopolymer Particle Engineering via Etching of Boronate Polymers toward High-Performance Overall Water Splitting Catalysts.

Metallopolymers combine the property features of both metallic compounds and organic polymers, representing a typical direction for the design of high-performance hybrid materials. Here, a highly adaptive etching method to create pores and cavities in the metallopolymer particles is established. Starting from boronate polymer (BP) and inorganic@BP core-shell particles, porous, hollow, and yolk-shell metallopolymer particles can be fabricated, respectively. By taking advantage of the easy control over composition and pore/cavity structure, these metallopolymer particles provide a universal platform for the fabrication of nitrogen, boron co-doped carbon nanocomposites loaded with metals (M-NBCs). The as-prepared M-NBCs exhibit remarkable catalytic activities toward oxygen evolution reaction and hydrogen evolution reaction. An alkaline overall water splitting cell assembled by using M-NBCs as the anode and cathode can be driven by a single AAA battery. The proposed strategy for the construction of metallopolymer composites may enlighten for the design of complex hybrid nanomaterials.

Self-activatable carbon nanotube@ruthenium-catechol coordination complex for hydrogen evolution reaction.

We report a simple metal ion-catechol coordination strategy to coat ruthenium-catechol polymer complex (TAC-Ru) on the surface of carbon nanotubes (CNT) to form a core-shell structure (abbreviated as CNT@TAC-Ru). This is achieved by firstly polymerizing catechol and boronic acid monomers on the surface of CNT to form a boronate ester polymer (BP) shell. Then, Ru3+is used to etch the BP shell, and cleave the dynamic boronate ester bond, leading to the formation of a CNT@ruthenium-catechol coordination complex based on the coordinative efficiency of the catechol group. The electrocatalytic property of the CNT@TAC-Ru composite can be activated through electrochemical cycling treatment. The as-activated CNT@TAC-Ru exhibits evidently improved hydrogen evolution reaction (HER) performance with an overpotential of 10 mV in 1.0 M KOH at a current density of 10 mA cm-2, which is better than that of commercial Pt/C (32 mV). And the long-term stability is also desirable. This work provides a pyrolysis-free method to form metal-polymer-carbon composite with high HER performance under the alkaline condition.

Molecular Exchange of Dynamic Imine Bond for the Etching of Polymer Particles.

The underlying trend of colloidal synthesis has focused on extending the structure and composition complexity of colloidal particles. Hollow and yolk-shell particles are successful examples that have potential applications in frontier fields. In this paper, a facile and controllable etching method based on the molecular exchange of the dynamic imine bond to generate cavities in polymer particles is developed. Starting from boronate ester polymer particles and inorganic@boronate core-shell particles with the imine bonds incorporated in the polymer networks, the etching method easily affords hollow and yolk-shell particles with tunable shell thicknesses. The molecular exchange dynamics analysis indicates that guest amine molecules cause the reconstruction of imine bonds and the leakage of molecular and oligomer fragments, resulting in the formation of the hollow structure. This molecular exchange-based etching method may be of interest in the construction of polymer architectures with increased composition and structure complexities.

Kinetics control over the Schiff base formation reaction for fabrication of hierarchical porous carbon materials with tunable morphology for high-performance supercapacitors.

Schiff base formation reaction is highly dynamic, and the microstructure of Schiff base polymers is greatly affected by reaction kinetics. Herein, a series of Schiff base cross-linked polymers (SPs) with different morphologies are synthesized through adjusting the species and amount of catalysts. Nitrogen/oxygen co-doped hierarchical porous carbon nanoparticles (HPCNs), with tunable morphology, specific surface area (SSA) and porosity, are obtained after one-step carbonization. The optimal sample (HPCN-3) possesses a coral reef-like microstructure, high SSA up to 1003 m2g-1, and a hierarchical porous structure, exhibiting a remarkable specific capacitance of 359.5 F g-1(at 0.5 A g-1), outstanding rate capability and cycle stability in a 1 M H2SO4electrolyte. Additionally, the normalized electric double layer capacitance (EDLC) and faradaic capacitance of HPCN-3 are 0.239 F m-2and 10.24 F g-1respectively, certifying its superior electrochemical performance deriving from coral reef-like structure, high external surface area and efficient utilization of heteroatoms. The semi-solid-state symmetrical supercapacitor based on HPCN-3 delivers a capacitance of 55 F g-1at 0.5 A g-1, good cycle stability of 86.7% after 5000 GCD cycles at 10 A g-1, and the energy density ranges from 7.64 to 4.86 Wh kg-1.

Oxygen reduction reaction performance of Fe-N/C catalysts from ligand-iron coordinative supramolecular precursors.

Simultaneous introduction of both transition metal and other inorganic elements into the carbon matrix has attracted great attention in the fabrication of carbon materials with high electrochemical properties. Herein, rational design of ligand-iron coordinative supramolecular precursors is achieved for the fabrication of Fe-N/C catalysts, which possess high oxygen reduction reaction (ORR) performance. A series of precursors are prepared by a simple coordination reaction between a three armed catechol monomer and iron ions. Particular interest is focused on tuning the doping species, surface area and morphology of the Fe-N/C catalysts through a simple selection of iron resources. We show that an Fe-N/C catalyst derived from Fe2(SO4)3 at a carbonization temperature of 800 °C, has the optimized ORR performance with an onset potential of 0.930 V and half-wave potential of 0.801 V. Detailed investigation indicates that the synergistic effect among doping elements of nitrogen and sulfur and the unique carbon structure determines the performance of the Fe-N/C catalysts. Our findings may be of significance for the fabrication of doped carbon materials using coordinative supramolecular polymers as precursors.

Predictable Particle Engineering: Programming the Energy Level, Carrier Generation, and Conductivity of Core-Shell Particles.

Core-shell structures are of particular interest in the development of advanced composite materials as they can efficiently bring different components together at nanoscale. The advantage of this structure greatly relies on the crucial design of both core and shell, thus achieving an intercomponent synergistic effect. In this report, we show that decorating semiconductor nanocrystals with a boronate polymer shell can easily achieve programmable core-shell interactions. Taking ZnO and anatase TiO2 nanocrystals as inner core examples, the effective core-shell interactions can narrow the band gap of semiconductor nanocrystals, change the HOMO and LUMO levels of boronate polymer shell, and significantly improve the carrier density of core-shell particles. The hole mobility of core-shell particles can be improved by almost 9 orders of magnitude in comparison with net boronate polymer, while the conductivity of core-shell particles is at most 30-fold of nanocrystals. The particle engineering strategy is based on two driving forces: catechol-surface binding and B-N dative bonding and having a high ability to control and predict the shell thickness. Also, this approach is applicable to various inorganic nanoparticles with different components, sizes, and shapes.

Orthogonally functionalized nanoscale micelles for active targeted codelivery of methotrexate and mitomycin C with synergistic anticancer effect.

The design of nanoscale drug delivery systems for the targeted codelivery of multiple therapeutic drugs still remains a formidable challenge (ACS Nano, 2013, 7, 9558-9570; ACS Nano, 2013, 7, 9518-9525). In this article, both mitomycin C (MMC) and methotrexate (MTX) loaded DSPE-PEG micelles (MTX-M-MMC) were prepared by self-assembly using the dialysis technique, in which MMC-soybean phosphatidylcholine complex (drug-phospholipid complex) was encapsulated within MTX-functionalized DSPE-PEG micelles. MTX-M-MMC could coordinate an early phase active targeting effect with a late-phase synergistic anticancer effect and enable a multiple-responsive controlled release of both drugs (MMC was released in a pH-dependent pattern, while MTX was released in a protease-dependent pattern). Furthermore, MTX-M-MMC could codeliver both drugs to significantly enhance the cellular uptake, intracellular delivery, cytotoxicity, and apoptosis in vitro and improve the tumor accumulation and penetration and anticancer effect in vivo compared with either both free drugs treatment or individual free drug treatment. To our knowledge, this work provided the first example of the systemically administrated, orthogonally functionalized, and self-assisted nanoscale micelles for targeted combination cancer chemotherapy. The highly convergent therapeutic strategy opened the door to more simplified, efficient, and flexible nanoscale drug delivery systems.

Composite polymer nanoarchitectures from a one-pot hydrothermal route.

Exploitation of facile and versatile synthetic approaches to polymeric nanoarchitectures is of great interest in polymer science and engineering. Herein, we show that a simple hydrothermal route using double-solvents as reaction media has the ability to generate polymer nanospheres with tunable morphologies and components. In this one-pot approach, condensation polymerization of a resol precursor and radical polymerization of styrene are allowed to occur simultaneously under hydrothermal treatment. The synergistic self-organization of phenol-formaldehyde crosslinked networks and polystyrene chains leads to the formation of well-defined hollow nanospheres with adjustable shell thickness or even Janus particles comprising a solid hemisphere and a hollow hemisphere. Furthermore, control over the composition of the hollow polymer nanospheres can be easily achieved by introducing a third monomer into the hydrothermal system.

Fluorescent polymeric assemblies as stimuli-responsive vehicles for drug controlled release and cell/tissue imaging.

Polymer assemblies with good biocompatibility, stimuli-responsive properties and clinical imaging capability are desirable carriers for future biomedical applications. Herein, we report on the synthesis of a novel anthracenecarboxaldehyde-decorated poly(N-(4-aminophenyl) methacryl amide-oligoethyleneglycolmonomethylether methacrylate) (P(MAAPAC-MAAP-MAPEG)) copolymer, comprising fluorescent chromophore and acid-labile moiety. This copolymer can assemble into micelles in aqueous solution and shows a spherical shape with well-defined particle size and narrow particle size distribution. The pH-responsive property of the micelles has been evaluated by the change of particle size and the controlled release of guest molecules. The intrinsic fluorescence property endows the micelles with excellent cell/tissue imaging capability. Cell viability evaluation with human hepatocellular carcinoma BEL-7402 cells demonstrates that the micelles are nontoxic. The cellular uptake of the micelles indicates a time-dependent behavior. The H22-tumor bearing mice treated with the micelles clearly exhibits the tumor accumulation. These multi-functional nanocarriers may be of great interest in the application of drug delivery.

Polymer crystallization dynamics investigated by synchronous scanning spectrum.

There is a cosine function between the reflected light intensity of a solid surface and its refractive index. And the mean squared fluctuation of refractive index is related to fluctuation of density and concentration. So some internal structures changes of materials can be reflected by changes in reflected light. Based on this theory, the synchronous scanning spectrum (SSS) technique was successfully applied to monitor melting and nonisothermal melt-crystallization of poly(ε-caprolactone) (PCL) film on a copper substrate. SSS can be implemented on a spectrofluorimeter by simultaneously scanning the excitation and emission monochromators (i. e, Δλ = λex-λem = 0 nm). In SSS of PCL films, two dominant peaks correlated to the light source spectrum of the spectrofluorimeter (at 467 and 473 nm) were used to characterize the macromolecular structure evolution during the melting and nonisothermal melt-crystallization processes. Detailed thermodynamic and crystallization kinetics parameters obtained by SSS method. The Avrami exponent n obtained by SSS method is in the range of 2.8-3.2 with an average of 3.13, illustrating a heterogeneous nucleation process followed by a three-dimensional spherulitic crystal growth mechanism. The crystallization activation energy is -158.2 kJ · mol(-1). These results are in agreement with values determined from differential scanning calorimetry (DSC) method. It indicates that SSS technique is a simple, effective in situ method for measuring the dynamic melting and crystallization process of polymers. Moreover, the SSS method is a universal spectroscopic technique based on a spectrofluorimeter for monitoring both luminescent and non-luminous solid polymers.

Carboxymethylcellulose hydrogels with stable carbon quantum dots: Enabling dynamic fluorescence modulation, automatic erasure, and secure information encryption.

Inspired by "disappear after reading", a time-modulated encryption hydrogel was synthesized by carboxymethyl cellulose with carbon quantum dots. Carboxymethyl cellulose in this system stabilized carbon quantum dots, which ensured the whole hydrogel worked well. The encryption/decryption of information depended on pH adjustment, application of EDTA and Cr (VI). Furthermore, an in-depth analysis of the fluorescence change mechanism uncovered that fluorescence quenching was potentially influenced by internal filtering effects and static quenching, which involved the amino, carboxyl, and hydroxyl groups present within the hydrogel.

Electrically weldable conductive elastomers.

Flexible and stretchable electronic devices are subject to failure because of vulnerable circuit interconnections. We develop a low-voltage (1.5 to 4.5 V) and rapid (as low as 5 s) electric welding strategy to integrate both rigid electronic components and soft sensors in flexible circuits under ambient conditions. This is achieved through the design of conductive elastomers composed of borate ester polymers and conductive fillers, which can be self-welded and generate welding effects to various materials including metals, hydrogels, and other conductive elastomers. The welding effect is generated through the electrochemical reaction-triggered exposure of interfacial adhesive promotors or the cleavage/reformation of dynamic bonds. Our strategy can ensure both mechanical compliance and conductivity at the circuit interfaces and easily produce welding strengths in the kilopascal to megapascal range. The as-designed conductive elastomers in combination with the electric welding technique provide a robust platform for constructing standalone flexible and stretchable electronic devices that are detachable and assemblable on demand.

Heterogeneous silver-polyaniline nanocomposites with tunable morphology and controllable catalytic properties.

This paper introduces not only a simple hydrothermal route to silver-polyaniline (Ag-PANI) nanocomposites with controllable morphology, but also a type of catalyst possessing tunable and switchable catalytic capability. Ag-PANI Janus nanoparticles (NPs) and Ag@PANI core-shell NPs have been constructed successfully at different hydrothermal temperatures. The diameter of both Ag and PANI hemispheres of Janus NPs, as well as the PANI shell thickness of core-shell NPs, was finely tuned via adjustment of the feed ratio. We also gained a deeper insight into the functionalities of PANI components in the catalytic capability of the heterogeneous catalysts, choosing catalytic reductions of nitrobenzene (NB) and 4-nitrophenol (4-NP) as model reactions. Our results showed that the catalytic capability of the nanocomposites was dependent on the PANI morphology and hydrophobicity. The PANI shell coating on Ag NPs can concentrate the lipophilic NB, thus leading to an enhanced catalytic capability of Ag@PANI core-shell NPs. However, this enhanced catalytic capability was not observed for Ag-PANI Janus NPs when catalytically reducing NB. More importantly, the catalytic capability of the core-shell NPs in the reduction of hydrophilic 4-NP is switchable by varying the PANI shell from an undoped to a doped state.

Graphene enhances the shape memory of poly (acrylamide-co-acrylic acid) grafted on graphene.

Acrylamide and acrylic acid are grafted on graphene by free-radical polymerization to produce a series of graphene-poly(acrylamide-co-acrylic acid) hybrid materials with different contents of graphene. The materials demonstrate shape memory effect and self-healing ability when the content of graphene is in the range of 10%-30% even though poly(acrylamide-co-acrylic acid) itself had poor shape memory ability. The permanent shape of the materials can be recovered well after 20 cycles of cut and self-healing. The result is attributed to the hard-soft design that can combine nonreversible "cross-link" by grafting copolymer on graphene and reversible "cross-link" utilizing the "zipper effect" of poly(acrylamide-co-acrylic acid) to form or dissociate the hydrogen-bond network stimulated by external heating.

A Novel P/N/Si-Containing Vanillin-Based Compound for a Flame-Retardant, Tough Yet Strong Epoxy Thermoset.

It is still extremely challenging to endow epoxy resins (EPs) with excellent flame retardancy and high toughness. In this work, we propose a facile strategy of combining rigid-flexible groups, promoting groups and polar phosphorus groups with the vanillin compound, which implements a dual functional modification for EPs. With only 0.22% phosphorus loading, the modified EPs obtain a limiting oxygen index (LOI) value of 31.5% and reach V-0 grade in UL-94 vertical burning tests. Particularly, the introduction of P/N/Si-containing vanillin-based flame retardant (DPBSi) improves the mechanical properties of EPs, including toughness and strength. Compared with EPs, the storage modulus and impact strength of EP composites can increase by 61.1% and 240%, respectively. Therefore, this work introduces a novel molecular design strategy for constructing an epoxy system with high-efficiency fire safety and excellent mechanical properties, giving it immense potential for broadening the application fields of EPs.

MoS2 @Polyaniline for Aqueous Ammonium-Ion Supercapacitors.

Ammonium-ion aqueous supercapacitors are raising notable attention owing to their cost, safety, and environmental advantages, but the development of optimized electrode materials for ammonium-ion storage still lacks behind expectations. To overcome current challenges, here, a sulfide-based composite electrode based on MoS2 and polyaniline (MoS2 @PANI) is proposed as an ammonium-ion host. The optimized composite possesses specific capacitances above 450 F g-1 at 1 A g-1 , and 86.3% capacitance retention after 5000 cycles in a three-electrode configuration. PANI not only contributes to the electrochemical performance but also plays a key role in defining the final MoS2 architecture. Symmetric supercapacitors assembled with such electrodes display energy densities above 60 Wh kg-1 at a power density of 725 W kg-1 . Compared with Li+ and K+ ions, the surface capacitive contribution in NH4 + -based devices is lower at every scan rate, which points to an effective generation/breaking of H-bonds as the mechanism controlling the rate of NH4 + insertion/de-insertion. This result is supported by density functional theory calculations, which also show that sulfur vacancies effectively enhance the NH4 + adsorption energy and improve the electrical conductivity of the whole composite. Overall, this work demonstrates the great potential of composite engineering in optimizing the performance of ammonium-ion insertion electrodes.