Concise, Single-Step Synthesis of Sulfur-Enriched Graphene: Immobilization of Molecular Clusters and Battery Applications

Metal-metal bonded pentamolybdate hybrids as electron storage materials

Two electron-rich, metal-metal bonded pentamolybdate hybrids, 2D-[MoIV3MoVI2O10Sr2(H2O)5(C6H4O7)2py3]·3.5H2O (1) and 1D-[MoIV3MoVI2O10Sr(H2O)3(C6H4O7)2py3]·py·2[NH2(CH3)2]·2H2O (2, py = pyridine), were prepared by the partial solvothermal oxidation of [MoIV3O2(O2CCH3)6(H2O)3]ZnCl4·8H2O and citric acid in py/H2O (for 1) or py/H2O/DMF (for 2). Both 1 and 2 feature a triangularly metal-metal bonded incomplete cuboidal [MoIV3O4] unit. Redox-active 6e-[MoIV3O4] units can serve as an "electron sponge" to store/release six electrons reversibly via Δ-bond breakage and re-formation during charging/discharging processes. 1 and 2 further form 3D and 2D supramolecular structures, respectively, through slipped π-π stacking interactions between the pyridine ligands. Both the incorporated 6e-redox active [MoIV3O4] unit and the 3D/2D supramolecular conductive networks in hybrid-POM 1/2 remarkably enhance the electronic conductivity and reversible multi-electron redox ability with the structural integrity retained. Consequently, 1 and 2 exhibited high discharge specific capacities of 236.0 and 277.0 mA h g-1 at 50 mA g-1, respectively, and a good cycling performance at high current density (121.8 mA h g-1, 2 A g-1 for 2), providing a new way for improving POM-based electrode materials.

Exfoliation of Al-Residual Multilayer MXene Using Tetramethylammonium Bases for Conductive Film Applications

This study describes the concise exfoliation of multilayer Ti₃C₂T_x MXene containing residual aluminum atoms. Treatment with tetramethylammonium base in a co-solvent of tetrahydrofuran and H₂O produced single-layer Ti₃C₂T_x, which was confirmed via atomic force microscopy observations, with an electrical conductivity 100+ times that of Ti₃C₂T_x prepared under previously reported conditions. The scanning electron microscopy and X-ray diffraction measurements showed that the exfoliated single-layer Ti₃C₂T_x MXenes were reconstructed to assembled large-domain layered films, enabling excellent macroscale electric conductivity. X-ray photoelectron spectroscopy confirmed the complete removal of residual Al atoms and the replacement of surface fluorine atoms with hydroxy groups. Using the exfoliated dispersion, a flexible transparent conductive film was formed and demonstrated in an electrical application.

Organo-Polyoxometalate-Based Hydrogen-Bond Catalysis

Several urea-inserted organo-polyoxometalates (POMs) derived from polyoxotungstovanadate [P₂ V₃ W₁₅ O₆₁ ]^9- were prepared. The insertion of the carbonyl into the polyoxometallic framework activates the urea toward Hydrogen-bond catalysis. This was shown on the Friedel-Crafts arylation of trans-β-nitrostyrene. Modelling shows that the most stable form of the organo-POMs features a cis-trans arrangement of the two N-H bonds, but that the likely catalytically active trans-trans form is accessible at room temperature. Finally, it is possible that the oxo substituents next to the vanadium atoms may help the approach of the nucleophile via H-bonding.

A Powerful One-Step Puffing Carbonization Method for Construction of Versatile Carbon Composites with High-Efficiency Energy Storage

Carbon materials play a critical role in the advancement of electrochemical energy storage and conversion. Currently, it is still a great challenge to fabricate versatile carbon-based composites with controlled morphology, adjustable dimension, and tunable composition by a one-step synthesis process. In this work, a powerful one-step maltose-based puffing carbonization technology is reported to construct multiscale carbon-based composites on large scale. A quantity of composite examples (e.g., carbon/metal oxides, carbon/metal nitrides, carbon/metal carbides, carbon/metal sulfides, carbon/metals, metal/semiconductors, carbon/carbons) are prepared and demonstrated with required properties. These well-designed composites show advantages of large porosity, hierarchical porous structure, high conductivity, tunable components, and proportion. The formation mechanism of versatile carbon composites is attributed to the puffing-carbonization of maltose plus in situ carbothermal reaction between maltose and precursors. As a representative example, Li₂ S is in situ implanted into a hierarchical porous cross-linked puffed carbon (CPC) matrix to verify its application in lithium-sulfur batteries. The designed S-doped CPC/Li₂ S cathode shows superior electrochemical performance with higher rate capacity (621 mAh g^-1 at 2 C), smaller polarization and enhanced long-term cycles as compared to other counterparts. The research provides a general way for the construction of multifunctional component-adjustable carbon composites for advanced energy storage and conversion.

General Synthesis of Ordered Mesoporous Carbonaceous Hybrid Nanostructures with Molecularly Dispersed Polyoxometallates

Hybrid nanomaterials with controlled dimensions, intriguing components and ordered structures have attracted significant attention in nanoscience and technology. Herein, we report a facile and green polyoxometallate (POM)-assisted hydrothermal carbonization strategy for synthesis of carbonaceous hybrid nanomaterials with molecularly dispersed POMs and ordered mesopores. By using various polyoxometallates such as ammonium phosphomolybdate, silicotungstic acid, and phosphotungstic acid, our approach can be generalized to synthesize ordered mesoporous hybrid nanostructures with diverse compositions and morphologies (nanosheet-assembled hierarchical architectures, nanospheres, and nanorods). Moreover, the ordered mesoporous nanosheet-assembled hierarchical hybrids with molecularly dispersed POMs exhibit remarkable catalytic activity toward the dehydration of tert-butanol with the high isobutene selectivity (100 %) and long-term catalytic durability (80 h).

A highly efficient bifunctional electrocatalyst (ORR/OER) derived from GO functionalized with carbonyl, hydroxyl and epoxy groups for rechargeable zinc–air batteries

A highly efficient bifunctional electrocatalyst, Co–N/S/rGO, was prepared via modifying the surface functional groups of GO, and it showed good application prospects in zinc–air batteries.

Synthesis and applications of amino-functionalized carbon nanomaterials

Carbon-based nanomaterials (CNMs) have attracted considerable attention in the scientific community both from a scientific and an industrial point of view. Fullerenes, carbon nanotubes (CNTs), graphene and carbon dots (CDs) are the most popular forms and continue to be widely studied. However, the general poor solubility of many of these materials in most common solvents and their strong tendency to aggregate remains a major obstacle in practical applications. To solve these problems, organic chemistry offers formidable help, through the exploitation of tailored approaches, especially when aiming at the integration of nanostructures in biological systems. According to our experience with carbon-based nanostructures, the introduction of amino groups is one of the best trade-offs for the preparation of functionalized nanomaterials. Indeed, amino groups are well-known for enhancing the dispersion, solubilization, and processability of materials, in particular of CNMs. Amino groups are characterized by basicity, nucleophilicity, and formation of hydrogen or halogen bonding. All these features unlock new strategies for the interaction between nanomaterials and other molecules. This integration can occur either through covalent bonds (e.g., via amide coupling) or in a supramolecular fashion. In the present Feature Article, the attention will be focused through selected examples of our approach to the synthetic pathways necessary for the introduction of amino groups in CNMs and the subsequent preparation of highly engineered ad hoc nanostructures for practical applications.

Concise, Single-Step Synthesis of Sulfur-Enriched Graphene: Immobilization of Molecular Clusters and Battery Applications

The concise synthesis of sulfur-enriched graphene for battery applications is reported. The direct treatment of graphene oxide (GO) with the commercially available Lawesson's reagent produced sulfur-enriched-reduced GO (S-rGO). Various techniques, such as X-ray photoelectron spectroscopy (XPS), confirmed the occurrence of both sulfur functionalization and GO reduction. Also fabricated was a nanohybrid material by using S-rGO with polyoxometalate (POM) as a cathode-active material for a rechargeable battery. Transmission electron microscopy (TEM) revealed that POM clusters were individually immobilized on the S-rGO surface. This battery, based on a POM/S-rGO complex, exhibited greater cycling stability for the charge-discharge process than a battery with nanohybrid materials positioned between the POM and nonenriched rGO. These results demonstrate that the use of sulfur-containing groups on a graphene surface can be extended to applications such as the catalysis of electrochemical reactions and electrodes in other battery systems.