Crown-ether threaded covalent organic polyrotaxane framework (COPF) towards synergistic crown/Zn2+/photothermal/photodynamic antibacterial and infected wound healing therapy.

Controllable preparation of materials with new structure has always been the top priority of polymer materials science research. Here, the supramolecular binding strategy is adopted to develop covalent organic frameworks (COFs) with novel structures and functions. Based on this, a two-dimensional crown-ether ring threaded covalent organic framework (COF), denoted as Crown-COPF with intrinsic photothermal (PTT) and photodynamic (PDT) therapeutic capacity, was facilely developed using crown-ether threaded rotaxane and porphyrin as building blocks. Crown-COPF with discrete mechanically interlocked blocks in the open pore could be used as a molecular machine, in which crown-ether served as the wheel sliding along the axle under the laser stimulation. As a result, Crown-COPF combining with the bactericidal power of crown ether displayed a significant photothermal and photodynamic antibacterial activity towards both the Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus), far exceeding the traditional Crown-free COF. Noteworthily, the bactericidal performance could be further enhanced via impregnation of Zn2+ ions (Crown-COPF-Zn) flexible coordinated with the multiple coordination sites (crown-ether, bipyridine, and porphyrin), which not only endow the positive charge with the skeleton, enhancing its ability to bind to the bacterial membrane, but also introduce the bactericidal ability of zinc ions. Notably, in vivo experiments on mice with back infections indicates Crown-COPF-Zn with self-adaptive multinuclear zinc center, could effectively promote the repairing of wounds. This study paves a new avenue for the effectively preparation of porous polymers with brand new structure, which provides opportunities for COF and mechanically interlocked polymers (MIPs) research and applications.

Magnetic ε-Phosphorene for Sensing Greenhouse Gas Molecules.

It is critical for gas sensors that sense greenhouse gas molecules to have both good sensitivity and selectivity for water molecules in the ambient environment. Here, we study the charge transfer, IV curves, and electric field tuning of vanadium-doped monolayer ϵ-phosphorene as a sensor for NO, NO2, and H2O gas molecules via first-principle and transport calculations. We find that the paramagnetic toxic molecules of NO and NO2 have a high adsorption energy on V-ϵ-phosphorene, which originates from a large amount of charge transfer driven by the hybridisation of the localised spin states of the host with the molecular frontier orbital. Using the non-equilibrium Green's function, we investigate the IV responses with respect to the adsorption of different molecules to study the performance of gas molecule sensors. Our IV curves show a larger amount of changes in resistance of the paramagnetic NO and NO2 than nonmagnetic H2O gas molecules, suggesting both sensitivity and selectivity. Moreover, our calculations show that an applied external electric field (gate voltage) can effectively tune the amount of charge transfer. More charge transfer makes the sensor more sensitive to the molecule, while less charge transfer can reduce the adsorption energy and remove the adsorbed molecules, allowing for the repeated use of the sensor.

Ferromagnetic transition-metal dopedɛ-phosphorene.

Various stable 2D phosphorus allotropes have been experimentally synthesized or theoretically predicted, such as puckered blackα-, puckered blueß-, and buckledɛ-phosphorene. Here, we present a systematic study of the magnetic properties ofɛ-phosphorene doped with 3dtransition-metal (TM) atoms, as well as its gas-sensing capabilities, using first-principles and non-equilibrium Green's function formalism. Our results show that 3dTM dopants strongly bind ontoɛ-phosphorene. Sc, Ti, V, Cr, Mn, Fe, and Co-dopedɛ-phosphorene exhibit spin polarization with magnetic moments up to 6 µB, stemming from exchange and crystal-field splitting of the 3dorbital. Among them, V-dopedɛ-phosphorene exhibits the highest Curie temperature.

Chiral nanohelmet array films with Three-Dimensional (3D) resonance cavities.

Chiral nanohelmet array (NHA) films are prepared via an efficient and low-cost colloidal lithography and exhibit strong chiroptical properties. The chirality can be tailored by the opening-angle of the nanounits in the ultraviolet-visible light range, and optical g-factor reaches about 0.26. Such properties can be attributed to the dissymmetric charge oscillations and electric field distributions. Continuous chiral films can be facilely transferred onto other functional substrates and even, inverted in the transferring process, indicating more flexible application scenarios. Especially, benefiting from the three-dimensional (3D) resonance cavities, change of surrounding environment could further result in distinct surface plasmon (SP) modes, thus diverse chiroptical activities. Label-free enantiodiscrimination of biomolecules was demonstrated based on the chiral resonator with pronounced local superchiral fields. Overall, with strong chirality, excellent tunability, transferability and scalable fabrication, the chiral plasmonic NHA will benefit the study of chiral metamaterials and provide a reliable platform for various photonic applications and label-free chiral sensors.

A MOF derived bifunctional electrocatalyst Ni3ZnC0.7-Mo2C with enhanced performance for overall water splitting.

The efficiency and cost of electrocatalysts are critical factors restricting their application in water electrochemical decomposition. In recent years, transition metal carbides (TMCs) have been highlighted due to their unique characteristics for water splitting: good conductivity and stability. However, their electrochemical performance required further optimization. In this work, a distinct non-solvent method was utilized to achieve a Ni3ZnC0.7-Mo2C/Ni foam (NF) catalyst, which exhibited a nanoflower structure with efficient exposed active sites. Moreover, the synergistic effect between the Mo and Ni species greatly affected its HER and OER performance. Ni3ZnC0.7-Mo2C/NF showed excellent electrocatalytic performance with small overpotentials of 58 mV and 257 mV at 10 mA cm-2 for the HER and OER, respectively. To our delight, the overall water splitting could be driven by only 1.56 V. This work not only demonstrates an excellent bifunctional electrocatalyst for overall water splitting but also provides another method for polymetallic carbide preparation and activity optimization.

Bifunctional catalysts of Ni nanoparticle coupled MoO2 nanorods for overall water splitting.

The development of active and cost-effective bifunctional catalysts is crucial for water dissociation through electrolysis. In this study, bifunctional catalysts with Ni nanoparticles (NPs) anchored on MoO2 nanorods have been synthesized via in situ dissolution of NiMoO4-ZIF under an inert atmosphere without using hydrogen gas. The Ni-MoO2 catalyst exhibits high electrocatalytic activity by modulating the calcination temperature. Benefitingfrom the MOF transformation and accompanying Ni particles' outward diffusion, a precisely designed interface heterostructure between Ni and MoO2 was constructed. As a result, the optimized Ni-MoO2 catalyst achieves extremely low overpotentials of only 24 mV and 275 mV at 10 mA cm-2 for the hydrogen evolution reaction and oxygen evolution reaction, respectively. Furthermore, the catalyst required a small cell voltage of 1.55 V to deliver a current density of 10 mA cm-2 and remained stable over 20 h for overall water splitting. The proposed MOF-derived heterojunction protocol provides a general approach for designing and fabricating transition metal oxide catalysts for water electrolysis.

Ultrastable Zinc Anode by Simultaneously Manipulating Solvation Sheath and Inducing Oriented Deposition with PEG Stability Promoter.

Aqueous zinc-ion batteries are a low-cost and safe energy storage system, but suffer from detrimental side reactions and Zn dendrites due to the strong interactions between Zn2+ and water molecules in the electrolytes, and random Zn2+ deposition on the anode surface. Here, an electrolyte involving a dual-functional additive of polyethylene glycol (PEG) to bypass these issues is reported. The electrolyte can not only tailor the solvation sheath of Zn2+ but also enable favorably oriented deposition of Zn2+ on the anode surface. The dendrite-free Zn anode in Zn//Zn cells is obtained with high Columbic efficiency (98.8%) and long cycling lifespan (1500 h), six times longer than that of electrolyte without PEG at 0.25 mA cm-2 . What is more, the excellent cycling stability of the prepared batteries (Zn//V2 O5 ·1.6 H2 O) suggests that the developed tailoring strategy may propel a promising pathway for stabilizing Zn metal anodes.

Plasmonic Chiral Metamaterials with Sub-10 nm Nanogaps.

Sub-10 nm nanogaps are enantioselectively fabricated between two nanocrescents based on nanoskiving and show tailored circular dichroism (CD) activity. The mirror symmetry of the nanostructure is broken by subsequent deposition with different azimuthal angles. Strong plasmonic coupling is excited in the gaps and at the tips, leading to the CD activity. The dissymmetry g-factor of the chiral nanogaps with 5 nm gap-width is -0.055, which is 2.5 times stronger than that of the 10 nm gap-width. Moreover, the surface-enhanced Raman scattering (SERS) performance of l/d-cysteine absorbed on chiral nanogaps manifests as the emergence of enantiospecific Raman peaks and the appearance of distinct changes in SERS intensities, which affirms that chiral nanogaps can recognize specific cysteine enantiomers via standard Raman spectroscopy in the absence of circularly polarized light source and a chiral label molecule. The sub-10 nm chiral nanogaps with tailored chiroptical responses show great potential in a class of chiral applications, such as chiral sensing, polarization converters, label-free chiral recognition, and asymmetric catalysis.

Manipulation on active electronic states of metastable phase ß-NiMoO4 for large current density hydrogen evolution.

Non-noble transition metal oxides are abundant in nature. However, they are widely regarded as catalytically inert for hydrogen evolution reaction (HER) due to their scarce active electronic states near the Fermi-level. How to largely improve the HER activity of these kinds of materials remains a great challenge. Herein, as a proof-of-concept, we design a non-solvent strategy to achieve phosphate substitution and the subsequent crystal phase stabilization of metastable ß-NiMoO4. Phosphate substitution is proved to be imperative for the stabilization and activation of ß-NiMoO4, which can efficiently generate the active electronic states and promote the intrinsic HER activity. As a result, phosphate substituted ß-NiMoO4 exhibits the optimal hydrogen adsorption free energy (-0.046 eV) and ultralow overpotential of -23 mV at 10 mA cm-2 in 1 M KOH for HER. Especially, it maintains long-term stability for 200 h at the large current density of 1000 mA cm-2 with an overpotential of only -210 mV. This work provides a route for activating transition metal oxides for HER by stabilizing the metastable phase with abundant active electronic states.

Hierarchically porous polyimide/Ti3C2Tx film with stable electromagnetic interference shielding after resisting harsh conditions.

Polymer-based conductive nanocomposites are promising for electromagnetic interference (EMI) shielding to ensure stable operations of electronic devices and protect humans from electromagnetic radiation. Although MXenes have shown high EMI shielding performances, it remains a great challenge to construct highly efficient EMI shielding polymer/MXene composite films with minimal MXene content and high durability to harsh conditions. Here, hierarchically porous polyimide (PI)/Ti3C2Tx films with consecutively conductive pathways have been constructed via a unidirectional PI aerogel­assisted immersion and hot-pressing strategy. Contributed by special architectures and high conductivities, PI/Ti3C2Tx films with 2.0 volume % Ti3C2Tx have high absolute EMI shielding effectiveness up to 15,527 dB cm2 g−1 at the thickness of 90 µm. Superior EMI shielding performance can be retained even after being subjected to hygrothermal or combustion environments, cryogenic (−196°C) or high (250°C) temperatures, and rapid thermal shock (∆T = 446°C), demonstrating high potential as high-performance EMI shielding materials resisting harsh conditions.

A Polymer/Graphene Composite Cathode with Active Carbonyls and Secondary Amine Moieties for High-Performance Aqueous Zn-Organic Batteries Involving Dual-Ion Mechanism.

Aqueous zinc-ion batteries (AZIBs) are regarded as one of the most promising alternative technology to lithium-ion batteries on account of their low flammability and cost-benefits. Among various cathode materials in AZIBs, environment-friendly and sustainable organic electrode materials stand out owing to their structural diversity and tunability. However, their limited rate capability and cycle stability remain the obstacles to their further application in AZIBs. Herein, a mixed cathode design strategy including polymerization and carbon materials hybridization is adopted to assemble high-rate and durable AZIBs. Specifically, a polymer/graphene composite cathode with active carbonyls and secondary amine moieties is prepared to construct high-performance aqueous Zn-organic batteries. Furthermore, a hybrid energy storage mechanism involving dual-ion mechanism is confirmed by various ex situ characterization techniques, providing promising battery chemistry. Thus, this work opens up a new path to high performance AZIBs through a rational cathode design.

Chiral Plasmonic Metamaterials with Tunable Chirality.

Chiral hollow nanovolcano array (HNVA) film and chiral hollow nanoshells (HNSs) are simultaneously fabricated via a new strategy of colloidal lithography technique. The chirality of both chiral plasmonic nanostructures, which arises from the asymmetric charge oscillation and electric field distributions, can be well controlled by regulating the opening-angle of the nanounits during the metal depositions. The large-area HNVA films exhibit strong chiroptical responses in the ultraviolet-visible region with g-factor of 0.15 and possess remarkable transferability for better adaptability of different application situations. The chiral HNSs, which are simultaneously obtained during the deposition, is equipped with adjustable chirality and integrability. The obtained HNVA films were transferred to specific substrates, e.g., polydimethylsiloxane (PDMS), hydrogels, and high-curvature surfaces, maintaining the original chiroptical properties and excellent mechanical strength. Deformable chiral flexible metamaterial is obtained by incorporating the chiral HNSs in the hydrogel, enabling the ultrasensitive detection of water content in the hydrogel. Overall, this work will contribute to the study of chiral metamaterials by providing two kinds of newly developed chiral plasmonic metamaterials with tunable chirality and inspiring progressing ways for the flexible devices of artificial chirality.

Hierarchical Control of Plasmonic Nanochemistry in Microreactor.

A microreactor that can confine chemical reactions exclusively in tiny vessels with the volume of ∼0.015 µm3 is introduced. Aluminum inversed hollow nanocone arrays (IHNAs) are fabricated by a simple and efficient colloidal lithography method. Ag and Au nanoparticles (NPs), as well as polypyrrole, grow exclusively in the conic cavities under light illumination. The photocatalytic effect arising from the plasmonic enhanced electric fields (E-fields) of IHNAs boosts the reactions and is in charge of the submicrometer site-selectivity. By partially inhibiting light to IHNAs, various hierarchical patterns at the macro-, micro-, and sub-microscale are obtained, inspiring a facile patterning technique by varying the light source. In addition, the Al IHNA films are transferred to flexible and curved substrates with unchanged performances, showing high flexibility for wide applications. Microreactors based on the IHNAs will contribute to the control of chemical reactions at different dimensions and offer great potentials in developing novel nanofabrication techniques.

An in situ SERS study of plasmonic nanochemistry based on bifunctional "hedgehog-like" arrays.

An in situ SERS (surface-enhanced Raman scattering) study of plasmonic nanochemistry is realized on hierarchical Ag nanocone arrays ("hedgehog-like" arrays, denoted as HLAs) without any conventional catalyst. Ag nanocones are designed on 3D polystyrene (PS) microsphere arrays to provide a high density of hot spots within the laser-illumination area. Both experiments and numerical simulations demonstrate that the remarkable SERS and plasmonic catalytic performance of HLAs arise from the improved utilization rate of irradiation light in the third dimension and the tip enhancement effect of the nanocone arrays. On further combining their inherent SERS and catalytic properties, the in situ SERS study of plasmon-induced photocatalytic degradation reactions is realized. In this paper, not only the decomposition of methylene blue (MB) molecules is observed, but also the detailed molecular mechanisms of the reactions are revealed. Based on the bifunctional properties of the membrane-material interface, the HLAs are believed to be promising candidates in SERS and in situ SERS studies.

Free-Standing Plasmonic Chiral Metamaterials with 3D Resonance Cavities.

Hollow nanocone array (HNCA) films (cm × cm), composed of two Ag and Au nanoshells, are fabricated via a low-cost and efficient colloidal lithography technique. The relative position of the Ag and Au nanoshells can be controlled to generate various chiral asymmetries. A pronounced chiroptical response is observed in the ultraviolet-visible region with the anisotropy factor up to 10-1, which is rooted in the asymmetric current oscillations and electric field distributions. Beyond previous reports on plasmonic chiral metamaterials, the HNCA can be free-standing and further transferred to other functional and flexible substrates, such as polydimethylsiloxane (PDMS), highly curved surfaces, prepatterned films, and hydrogels, while keeping the original features. The good transferability would make HNCA more flexible in specific applications. Furthermore, the chiral HNCAs offer a series of chiral resonance cavities, which are conducive for the research of chiral sensing, confinement, chiral signal transmission, and amplification. Overall, this work provides a scalable metamaterial to tune the plasmonic chiral response, and HNCA would be a promising candidate of the components in chiral optical devices and sensors.

Preparation and characterization of silane-modified SiO2 particles reinforced resin composites with fluorinated acrylate polymer.

A series of fluorinated dental resin composites were prepared with two kinds of SiO2 particles. Bis-GMA (bisphenol A-glycerolate dimethacrylate)/4-TF-PQEA (fluorinated acrylate monomer)/TEGDMA (triethylene glycol dimethacrylate) (40/30/30, wt/wt/wt) was introduced as resin matrix. SiO2 nanopartices (30nm) and SiO2 microparticles (0.3µm) were silanized with 3-methacryloxypropyl trimethoxysilane (γ-MPS) and used as fillers. After mixing the resin matrix with 0%, 10%, 20%, 30% SiO2 nanopartices and 0%, 10%, 20%, 30%, 40%, 50% SiO2 microparticles, respectively, the fluorinated resin composites were obtained. Properties including double bond conversion (DC), polymerization shrinkage (PS), water sorption (Wp), water solubility (Wy), mechanical properties and cytotoxicity were investigated in comparison with those of neat resin system. The results showed that, filler particles could improve the overall performance of resin composites, particularly in improving mechanical properties and reducing PS of composites along with the addition of filler loading. Compared to resin composites containing SiO2 microparticles, SiO2 nanoparticles resin composites had higher DC, higher mechanical properties, lower PS and lower Wp under the same filler content. Especially, 50% SiO2 microparticles reinforced resins exhibited the best flexural strength (104.04 ± 7.40MPa), flexural modulus (5.62 ± 0.16GPa), vickers microhardness (37.34 ± 1.13 HV), compressive strength (301.54 ± 5.66MPa) and the lowest polymerization (3.42 ± 0.22%).

Synthesis, characterization and evaluation of a fluorinated resin monomer with low water sorption.

A fluorinated acrylate monomer (4-TF-PQEA) without BPA (bisphenol-A) structure was synthesized and mixed with triethylene glycol dimethacrylate (TEGDMA) to used as dental resin system in order to achieve lower water sorption and reduce human exposure to BPA derivatives. Double bond conversion (DC) was measured using Fourier transform infrared spectroscopy (FTIR). Water sorption (WS), water solution (WL) and depth of cure (DOC) were evaluated according to ISO 4049:2009. Water contact angle (CA) was measured using contact angle analyzer. Polymerization shrinkage (PS) was evaluated according to the Archimedes' principle and ISO 17304:2013. Flexural strength (FS) and flexural modulus (FM) were measured by three-point bending test with a universal testing machine according to ISO 4049:2009. Comprehensive strength (CS) and vickers microhardness (VM) were also investigated. Thermal stability test was measure by Thermogravimetric analyzer. Cytotoxicity of three resin systems was tested through MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromid) cytotoxicity method according to the ISO 10993-5:2009. Bisphenol-A glycidyl dimethacrylate (Bis-GMA)/ TEGDMA resin system was used as a control. The results show that 4-TF-PQEA/TEGDMA resin system had lower PS, lower WS and higher DC values than those of Bis-GMA/TEGDMA resin system except some mechanical properties, such as FS, FM and CS. Moreover, properties of other 4-TF-PQEA-containing resin systems were also comparable with those of Bis-GMA/TEGDMA resin system. In particular, the overall performance of resin system consisted of 4-TF-PQEA/Bis-GMA/TEGDMA is optimized when the mixture ratio is 30/40/30(wt/wt/wt). Therefore, the 4-TF-PQEA has potential to be used as resin monomer for dental resin composites to achieve lower water sorption.

Plasmonic Nanochemistry Based on Nanohole Array.

We show that the growth of Ag nanoparticles (NPs) follows the areas of maximum plasmonic field in nanohole arrays (NAs). We thus obtain Ag NP rings not connected to the metallic rim of the nanoholes. The photocatalytic effect resulting from the enhanced E-field of NAs boosts the reaction and is responsible for the site selectivity. The strategy, using plasmonics to control a chemical reaction, can be expanded to organic reactions, for example, synthesis of polypyrrole. After the NA film is removed, ordered ring-shaped Ag NPs are easily obtained, inspiring a facile micropatterning method. Overall, the results reported in this work will contribute to the control of chemical reactions at the nanoscale and are promising to inspire a facile way to pursue patterned chemical reactions.

Fluorescent and Electrochemical Supramolecular Coordination Polymer Hydrogels Formed from Ion-Tuned Self-Assembly of Small Bis-Terpyridine Monomer.

Herein, ditopic ligand DTA comprised of terpyridine and acetylene segments with only one aromatic π-conjugated building block was designed and synthesized. Driven by metal-ligand coordination interactions, we presented that the use of metal salts can direct the self-assembly of DTA in the generation of fluorescent and electrochemical polymers that entrapped water to form ambidextrous hydrogels. These were characterized by several approaches including fluorescent titrations, UV-vis, circular dichroism, and X-ray diffraction spectra as well as scanning electron microscopy and transmission electron microscopy experiments. DTA can selectively recognize Zn2+ ions and gelate water in the presence of ZnC6H10O6 (zinc lactate), giving Zn2+-specific fluorescent metallogels. Otherwise, DTA/Cu(OAc)2 forms nonfluorescent, electrochemical, and chiral hydrogel that responds to multiple stimuli such as heat, light, shearing, electrolysis, and reducer. The ion-controlled gelation approach, morphology, rheology, as well as fluorescent and chiroptical properties of DTA was studied in detail. Hence, our work demonstrated for the first time the crucial role of metal salts in the supramolecular polymerization and corresponding properties, in which symmetry breaking played an important role for the dynamic assembly difference.