Synthesis of nanostructured transition metal sulfides is of particular interest in providing new methods to control their porosity and improve their surface area because those sulfides hold promising applications in high-energy density devices. Significant challenges remain currently to prepare metal sulfides having three-dimensional (3-D) continuous mesoporous structures, known to be critical for increasing their active surface sites and enhancing ion transport. We herein present a facile solid-phase sulfurization method to synthesize 3-D continuous mesoporous CoS2, NiS2, and their binary sulfides in a two-step nanocasting using bicontinuous KIT-6 as hard templates. The solid-phase sulfurization taking place at 400 °C yields mesoporous sulfides with highly crystalline frameworks and a stoichiometric ratio of metal-to-sulfur, 1:2 (mol), within 30 min. Elemental sulfur as an inexpensive sulfur source can be directly used for the solid-phase sulfurization of mesoporous oxides of Co3O4, NiO, and their binary oxides. This facile synthetic method is highly efficient to prepare mesoporous sulfides in the gram-scale production at a very low cost. Mesoporous sulfides are demonstrated to be superior electrode materials for pseudo-supercapacitors, given their high surface area and accessible bicontinuous mesopores, the suitable crystalline sizes, and the enhanced ion transport capability. The use of binary mesoporous sulfides presents interesting synergetic effect where the doping of metal ions can significantly enhance the capacitive performance of single-component sulfides. The binary sulfides of mNi0.32Co0.68S2 show a specific capacitance up to 1698 F g–1 at a current density of 2 A g–1. The supercapacitor device of mNi0.32Co0.68S2 has a high energy density of 37 Wh kg–1 at a power density of 800 W kg–1. We believe that the reported solid-phase synthesis offers a universal method toward the conversion of mesoporous oxides materials into various useful and functional forms for energy conversion and storage applications.Keywords: mesoporous sulfides; metal oxides; metal sulfides; solid-phase sulfurization; supercapacitors;

Metal-containing single chain polymeric nanoparticles (SCPNs) can be used as synthetic mimics of metalloenzymes. Currently, the role of the folded polymer backbones on the activity and selectivity of metal sites is not clear. Herein, we report our findings on how polymeric frameworks modulate the coordination of Cu sites and the catalytic activity/selectivity of Cu-containing SCPNs mimicking monophenol hydroxylation reactions. Imidazole-functionalized copolymers of poly(methyl methacrylate-co-3-imidazolyl-2-hydroxy propyl methacrylate) were used for intramolecular Cu-imidazole binding that triggered the self-folding of polymers. Polymer chains imposed steric hindrance which yielded unsaturated Cu sites with an average coordination number of 3.3. Cu-containing SCPNs showed a high selectivity for the hydroxylation reaction of phenol to catechol, >80%, with a turnover frequency of >870 h–1 at 60 °C. The selectivity was largely influenced by the flexibility of the folded polymer backbone where a more flexible polymer backbone allows the cooperative catalysis of two Cu sites. The second coordination sphere provided by the folded polymer that has been less studied is therefore critical in the design of active mimics of metalloenzymes.

A general synthetic methodology is reported to grow ultrafine cobalt-based nanoparticles (NPs, 2–7 nm) within high-surface-area mesoporous carbon (MC) frameworks. Our design strategy is based on colloidal amphiphile (CAM) templated oxidative self-polymerization of dopamine. The CAM templates consisting of a hydrophobic silica-like core and a hydrophilic PEO shell can coassemble with dopamine and template its self-polymerization to form polydopamine (PDA) nanospheres. Given that PDA has rich binding sites such as catechol and amine to coordinate metal ions (e.g., Co2+), PDA nanospheres containing Co2+ ions can be converted into hierarchical porous carbon frameworks containing ultrafine metallic Co NPs (Co@MC) using high-temperature pyrolysis. The CAM templates offer strong “nanoconfinements” to prevent the overgrowth of Co NPs within carbon frameworks. The yielded ultrafine Co NPs have an average size of <7 nm even at a very high loading of 65 wt %. Co@MC can be further converted into various oxides and sulfides, e.g., CoO, Co3O4, CoS2 and transition-metal doped bimetallic CoxM1–xS2, without significantly changing the size of NPs. As a proof-of-concept application, the porous Co-based NPs@MC hybrids were used as electrode materials for supercapacitors, which exhibit excellent supercapacitive performance with outstanding long-term cycling stability, due to the features such as ultrafine size, controllable chemical compositions, hierarchical porous structures, and full coverage of conductive carbons.Keywords: cobalt nanoparticles; electrode materials; mesoporous carbon; supercapacitors; ultrafine nanoparticles;

Loading catalytically active, aggregation-free and thermally stable metal nanoparticles (NPs) on a high surface area support represents a major interest in heterogeneous catalysis. Current synthetic approaches to these hybrid catalysts, however, still lack controllability in the thermal stability of metal NPs, particularly at high temperatures in the absence of organic ligands. We herein report a facile “co-assembly” methodology to prepare aggregation-free, ligand-free and thermally stable mesoporous hybrid nanocatalysts of metal–oxides and metal–carbons. Immobilization of catalytically active gold NPs (AuNPs) within high surface area mesoporous frameworks was achieved via the polymer-directed co-assembly of chemically and structurally equivalent Pluronic P-123 and poly(ethylene oxide)-modified metallic gold NPs (AuNP-PEO) as co-structure-directing-agents. The in situ immobilization of AuNPs partially embedded into periodically ordered mesoporous frameworks imposed a three-dimensional “nanoconfinement” effect and essentially enhanced the long-term thermal stability of AuNPs up to 800 °C. The mesoporous hybrids retained a high surface accessibility of AuNPs and they had a fantastic high-temperature catalytic durability (>130 h at 375 °C) confirmed by two model catalytic reactions, including aerobic oxidation of benzyl alcohol and CO oxidation, respectively. Our results may offer a new realm of possibilities for the rational applications of thermally stable nanocatalysts in renewable energy technology and high-temperature catalysis.

Cross-linking that defines the three-dimensional networks in hydrogels has a significant impact on their physiochemical properties. The cross-linking of hydrophilic polymers via post-polymerization reactions is an ideal way to manufacture hydrogels with high reproducibility and without monomer residuals. We herein report the use of Ag(I)-catalyzed oxidative decarboxylation to cross-link poly(acrylic acid) (PAA) and a family of COOH-containing hydrophilic polymers. Our method is based on the radical-mediated elimination reaction to remove COOH group(s) and generate alkyl radical(s) simultaneously, in the presence of AgNO3 and persulfates. The further intermolecular radical coupling is demonstrated to be very effective in inducing cross-linking and gelation of COOH-containing hydrophilic polymers. The cross-linking reaction can be readily achieved by simply mixing a small amount of AgNO3 (as low as 0.03 wt%) and persulfates with polymers at room temperature in air. Rheological measurements show that the gelation occurs in 20–30 min. The applications of oxidative decarboxylation in the preparation of hydrogels of COOH-containing hydrophilic copolymers and their interpenetrating polymer network (IPN) hydrogels are further validated. Finally, the residual Ag(I) ions in hydrogels are discussed in terms of how Ag(I) ions further change the mechanical and optical properties of hydrogels by photoreduction of Ag(I) to Ag nanoparticles. We expect that this Ag(I)-catalyzed oxidative decarboxylation chemistry can not only serve as a facile and general strategy to produce hydrogels through post-polymerization, but also enrich the toolbox of cross-linking chemistries of COOH-containing polymers in all forms (e.g. films, colloids and dispersions).

We report a robust, universal “soft” nitriding method to grow in situ ligand-free ultrasmall noble metal nanocatalysts (UNMN; e.g., Au, Pd, and Pt) onto carbon. Using low-temperature urea pretreatment at 300 °C, soft nitriding enriches nitrogen-containing species on the surface of carbon supports and enhances the affinity of noble metal precursors onto these supports. We demonstrated sub-2-nm, ligand-free UNMNs grown in situ on seven different types of nitrided carbons with no organic ligands via chemical reduction or thermolysis. Ligand-free UNMNs supported on carbon showed superior electrocatalytic activity for methanol oxidation compared to counterparts with surface capping agents or larger nanocrystals on the same carbon supports. Our method is expected to provide guidelines for the preparation of ligand-free UNMNs on a variety of supports and, additionally, to broaden their applications in energy conversion and electrochemical catalysis.

Two-dimensional (2-D) layered inorganic materials with ultra-high surface area and mechanical strength have shown impressive photo-/electro-catalytic activities. We herein report a facile synthetic strategy to grow monodispersed 2-D MnO2 nanosheet on an individual gold nanoparticle (AuNP@MnO2 nanosheet), and demonstrate that the strongly interacted AuNP and MnO2 nanosheet could greatly improve the electrocatalytic activity of the MnOx family for electrocatalytic oxygen reduction reactions (ORRs). AuNP@MnO2 nanosheets were prepared using a hydrothermal reduction of KMnO4 by citrate ligands capped on AuNPs. Because of the metastability of the layered MnO2 nanosheets, we observed unconventional structural and morphological transitions of amorphous MnO2 nanosheets to δ-MnO2 nanoflakes, and eventually to α-MnO2 nanorods under hydrothermal conditions. The layered MnO2 nanosheets underwent a structural expansion to nanoflakes before the curling and re-folding of layered MnO2 nanosheets occurred. The intermediate states and structural transitions via a “layer compression”, for the first time, were experimentally recorded at a single-NP scale using electron microscopy. Moreover, we found the electrocatalytic activity of AuNP@MnO2 nanosheets was enhanced roughly 30–40 times, compared to that of pure MnO2 nanosheets and AuNPs. The strong interaction of metal–oxide interfaces (MnO2 nanosheets and AuNPs) was likely responsible for the improved electrocatalytic activity. This interaction of MnO2 and AuNPs was weakened in the course of hydrothermal treatment where partially positively charged Au+ was reduced at elevated temperatures, accompanying with the decrease of ORR activity. This insight into the effect of topological nanostructures and metal–oxide interactions on the electrocatalytic performance of the MnOx family is believed to illustrate an alternative pathway to develop new efficient electrocatalysts.

We report a colloidal amphiphile-templating approach to preparing nanosized Fe3C encapsulated within mesoporous nitrogen-doped carbon nanospheres (Fe3C@mCN). The obtained Fe3C@mCN hybrids having a high surface area and ultrafine Fe3C nanocrystals exhibited superior activity and durability for oxygen reduction.

We report a facile approach to designing multiblock thermoplastic elastomers using a two-step thiol–ene polyaddition reaction. It is based on the utilization of intermolecular hydrogen bonding of widely available and cost-effective monomer of N,N′-methylenebis(acrylamide) (MBAm) as physical cross-links. Thiol-terminated “soft” prepolymers were first prepared using ethylene glycol dimethacrylate (EGDMA) and an excess of 1,6-hexanedithiol (HDT); subsequently, the thiol-terminated prepolymers were further reacted with MBAm as a chain-extension reaction to yield the multiblock thermoplastic elastomers. The prepolymers with oligo(ethylene glycol) segments had a low glass-transition temperature, acting as elastic “soft” blocks; while MBAm units could form up to 4 hydrogen bonds that serve as physical networks to endow the elasticity to multiblock polymers. Proton nuclear magnetic resonance spectroscopy and gel permeation chromatography indicated the occurrence of the two-step thiol–ene reactions. The reaction kinetics of thiol–ene reactions was found to be highly dependent on the molecular weights of monomers. The first thiol–ene reaction of EGDMA and HDT could reach >90% conversion of both monomers within 5 min; while the kinetics of the second chain extension reaction was relatively slow and it took approximately 7 h to reach 90% conversion. The formation of the intermolecular hydrogen bonding between amide groups of MBAm units was confirmed by variable-temperature Fourier transform infrared spectroscopy and differential scanning calorimetry. The viscoelasticity and elasticity of the thermoplastic elastomers were found to be largely determined by the content of MBAm. With a molar ratio of 15% MBAm relative to EGDMA, the maximum elongation at break of elastomers reached >400%. Our synthetic method has the advantages of mild reaction conditions, high conversion and adjustable mechanical properties of elastomers; additionally, it does not involve heavy syntheses and expensive monomers/catalysts. Our findings conceivably stand out as a new tool to synthesize and engineer thermoplastic elastomers using the combination of thiol–ene chemistry and supramolecular interaction.

We report a general strategy to conceptualize a new design for the pH-programmable self-assembly of plasmonic gold nanoparticles (AuNPs) tethered by random copolymers of poly(styrene-co-acrylic acid) (P(St-co-AA)). It is based on using pH as an external stimulus to reversibly change the surface charge of polymer tethers and to control the delicate balance of interparticle attractive and repulsive interactions. By incorporating –COOH moieties locally within PSt hydrophobic segments, the change in the ionization degree of –COOH moieties can dramatically disrupt the hydrophobic attraction within a close distance. pH acts as a key parameter to control the deprotonation of –COOH moieties and “programs” the assembled nanostructures of plasmonic nanoparticles in a stepwise manner. At a higher solution pH where –COOH groups of polymer tethers became highly deprotonated, electrostatic repulsion dominated the self-assembly and favored the formation of end-to-end, anisotropic assemblies, e.g. 1-D single-line chains. At a lower pH, the less deprotonated –COOH groups led to the decrease of electrostatic repulsion and the side-to-side aggregates, e.g. clusters and multi-line chains of AuNPs, became favorable. The pH-programmable self-assembly allowed us to engineer a “manual” program for a sequential self-assembly by changing the pH of the solution. We demonstrated that the two-step pH-programmable assembly could generate more sophisticated “multi-block” chains using two differently sized AuNPs. Our strategy offers a general means for the programmable design of plasmonic nanoparticles into the specific pre-ordained nanostructures that are potentially useful for the precise control over their plasmon coupling.

This Communication highlights the facet-dependent electrocatalytic activity of MnO nanocrystals for OERs/ORRs. The MnO(100) facets with higher adsorption energy of O species can largely promote the electrocatalytic activity.

We report the preparation and self-assembly of amphiphilic hybrid nano building blocks (NBBs) with surfactant-mimicking structures. These NBBs, composed of hydrophilic silica-like heads tethered with well-defined one or two hydrophobic polystyrene (PS) tails, were prepared by efficient intramolecular cross-linking via silane chemistry. Using a series of “AB” diblock copolymers (BCPs) and “ABA” tri-BCPs of PS and poly(tert-butyl acrylate-co-3-(trimethoxysilyl)propyl methacrylate) (P(tBA-co-TMSPMA)), the intramolecular self-folding of P(tBA-co-TMSPMA) blocks and the deprotection of tert-butyl groups were demonstrated to be an efficient method to prepare amphiphilic NBBs with a hydrophilic silica head tethered by one or two PS tails. The formation of NBBs was carefully studied by gel permeation chromatography, nuclear magnetic resonance spectroscopy, and transmission electron microscopy. The self-assembly of these amphiphilic NBBs was further investigated by fixing the molecular weight of PS tails and varying the size of hydrophilic heads. The intramolecular cross-linking of hydrophilic heads that shifted the hydrophilic/hydrophobic balance of polymers resulted in morphological transitions from bilayered vesicles to spherical micelles. Spherical micelles prepared from NBBs with large hydrophilic heads were found to have surface protrusions that differed from the self-assembly of linear BCPs. We also observed that the chain conformation of PS tails was critical for the self-assembly of NBBs, where the bitailed NBBs with highly stretched PS tails favored bilayered vesicle structures.

The catalytic oxidation reaction of CO has recently attracted much attention because of its potential applications in the treatment of air pollutants. The development of inexpensive transition metal oxide catalysts that exhibit high catalytic activities for CO oxidation is in high demand. However, these metal oxide catalysts are susceptible to moisture, as they can be quickly deactivated in the presence of trace amounts of moisture. This article reports a facile synthesis of highly active Co3O4@CNT catalysts for CO oxidation under moisture-rich conditions. Our synthetic routes are based on the in situ growth of ultrafine Co3O4 nanoparticles (NPs) (∼2.5 nm) on pristine multiwalled CNTs in the presence of polymer surfactant. Using a 1% CO and 2% O2 balanced in N2 (normal) feed gas (3–10 ppm moisture), a 100% CO conversion with Co3O4@CNT catalysts was achieved at various temperatures ranging from 25 to 200 °C at a low O2 concentration. The modulation of surface hydrophobicity of CNT substrates, other than direct surface modification on the Co3O4 catalytic centers, is an efficient method to enhance the moisture resistance of metal oxide catalysts for CO oxidation. After introducing fluorinated alkyl chains on CNT surfaces, the superhydrophobic Co3O4@CNT exhibited outstanding activity and durability at 150 °C in the presence of moisture-saturated feed gas. These materials may ultimately present new opportunities to improve the moisture resistance of metal oxide catalysts for CO oxidation.Keywords: carbon nanotube; CO oxidation; Co3O4 nanoparticles; hydrophobic catalysts; metal oxide catalysts; superhydrophobicity

Nano building blocks (NBBs) decorated with well-defined polymer tethers have emerged as a promising type of building blocks for constructing hierarchical materials through programmable self-assembly. We present a general and facile strategy for preparing hybrid NBBs composed of silica-like heads decorated with well-defined polymer tethers by the self-collapse of polymer single chains. Using amphiphilic block copolymers (BCPs) of poly(ethylene oxide)-block-[poly(methyl methacrylate)-co-poly(3-(trimethoxysilyl)propyl methacrylate)] (PEO-b-P(MMA-co-TMSPMA)), the intramolecular hydrolysis and polycondensation of silane moieties led to the formation of hybrid NBBs with silica-like heads and PEO tethers. The formation of hybrid NBBs was carefully characterized by gel permeation chromatography, nuclear magnetic resonance spectroscopy, transmission electron microscopy, and static/dynamic light scattering. In a mixed solvent of THF/water, amphiphilic NBBs could assemble into spherical micelles, vesicles, and large compound micelles, depending on the size of silica heads and the initial concentrations. The intramolecular cross-linking of P(MMA-co-TMSPMA) blocks significantly altered the assembly behavior of linear BCPs. The rigid hydrophobic heads of NBBs could not be stretched/compressed, and the self-assembly of NBBs behaved surfactant-like. Furthermore, we observed that the mismatched dimensions of NBBs and linear BCPs would give rise to the formation of unprecedented phase-separated bilayer vesicles when coassembling two amphiphiles. Our study of NBBs may bridge the study of nanoparticles and polymeric building blocks and offer new opportunities to synthesize hybrid NBBs with controlled functionalities for use in novel functional materials and devices.

This Communication highlights the facet-dependent electrocatalytic activity of MnO nanocrystals for OERs/ORRs. The MnO(100) facets with higher adsorption energy of O species can largely promote the electrocatalytic activity.

Two-dimensional (2-D) layered inorganic materials with ultra-high surface area and mechanical strength have shown impressive photo-/electro-catalytic activities. We herein report a facile synthetic strategy to grow monodispersed 2-D MnO2 nanosheet on an individual gold nanoparticle (AuNP@MnO2 nanosheet), and demonstrate that the strongly interacted AuNP and MnO2 nanosheet could greatly improve the electrocatalytic activity of the MnOx family for electrocatalytic oxygen reduction reactions (ORRs). AuNP@MnO2 nanosheets were prepared using a hydrothermal reduction of KMnO4 by citrate ligands capped on AuNPs. Because of the metastability of the layered MnO2 nanosheets, we observed unconventional structural and morphological transitions of amorphous MnO2 nanosheets to δ-MnO2 nanoflakes, and eventually to α-MnO2 nanorods under hydrothermal conditions. The layered MnO2 nanosheets underwent a structural expansion to nanoflakes before the curling and re-folding of layered MnO2 nanosheets occurred. The intermediate states and structural transitions via a “layer compression”, for the first time, were experimentally recorded at a single-NP scale using electron microscopy. Moreover, we found the electrocatalytic activity of AuNP@MnO2 nanosheets was enhanced roughly 30–40 times, compared to that of pure MnO2 nanosheets and AuNPs. The strong interaction of metal–oxide interfaces (MnO2 nanosheets and AuNPs) was likely responsible for the improved electrocatalytic activity. This interaction of MnO2 and AuNPs was weakened in the course of hydrothermal treatment where partially positively charged Au+ was reduced at elevated temperatures, accompanying with the decrease of ORR activity. This insight into the effect of topological nanostructures and metal–oxide interactions on the electrocatalytic performance of the MnOx family is believed to illustrate an alternative pathway to develop new efficient electrocatalysts.