Huai-Ping Cong

Macroscopic Multifunctional Graphene-Based Hydrogels and Aerogels by a Metal Ion Induced Self-Assembly Process

We report a one-step fabrication of macroscopic multifunctional graphene-based hydrogels with robust interconnected networks under the synergistic effects of the reduction of graphene oxide sheets by ferrous ions and in situ simultaneous deposition of nanoparticles on graphene sheets. The functional components, such as α-FeOOH nanorods and magnetic Fe(3)O(4) nanoparticles, can be easily incorporated with graphene sheets to assemble macroscopic graphene monoliths just by control of pH value under mild conditions. Such functional graphene-based hydrogels exhibit excellent capability for removal of pollutants and, thus, could be used as promising adsorbents for water purification. The method presented here is proved to be versatile to induce macroscopic assembly of reduced graphene sheets with other functional metal oxides and thus to access a variety of graphene-based multifunctional nanocomposites in the form of macroscopic hydrogels or aerogels.

Flexible graphene–polyaniline composite paper for high-performance supercapacitor

Free-standing graphene paper with a grey metallic luster has been fabricated for the first time, by a convenient one-step method on a large scale. Herein, the assembly of graphene oxide dispersion into ordered paper occurs simultaneously with the chemical reduction of graphene oxide to graphene. The graphene paper presents the advantages of good flexibility, low weight (0.2 g cm−3) and high electrical conductivity (15 Ω sq−1). Moreover, the size and shape of the graphene paper are freely exchanged for those of the Teflon substrate used. The flexible graphene–PANI paper subsequently exhibits excellent supercapacitor performance with an enhanced specific capacitance (763 F g−1) and good cycling stability by electropolymerization of PANI nanorods on the above graphene paper. The method presented here shows great promise for the development of low-cost electrode materials in potential energy storage devices.

Wet-spinning assembly of continuous, neat, and macroscopic graphene fibers

Graphene is now the most attractive carbon-based material. Integration of 2D graphene sheets into macroscopic architectures such as fibers illuminates the direction to translate the excellent properties of individual graphene into advanced hierarchical ensembles for promising applications in new graphene-based nanodevices. However, the lack of effective, low-cost and convenient assembly strategy has blocked its further development. Herein, we demonstrate that neat and macroscopic graphene fibers with high mechanical strength and electrical conductivity can be fluidly spun from the common graphene oxide (GO) suspensions in large scale followed with chemical reduction. The curliness-fold formation mechanism of GO fiber has been proposed. This wet-spinning technique presented here facilitates the multifunctionalization of macroscopic graphene-based fibers with various organic or inorganic components by an easy-handle in situ or post-synthesis approach, which builds the solid foundation to access a new family of advanced composite materials for the next practical applications.

Controlled Assemblies of Gold Nanorods in PVA Nanofiber Matrix as Flexible Free‐Standing SERS Substrates by Electrospinning

Under control: Controlled assemblies of gold nanorods in a poly(vinyl alcohol) (PVA) nanofiber matrix with tunable optical properties can be achieved by using electrospinning. The resultant assemblies can be used as substrates for surface-enhanced Raman spectroscopy (SERS). This work provides a facile way to control alignment of anisotropic nanostructures in a polymer nanofiber matrix and generates new assemblies with interesting properties.

Combining Nitrogen-Doped Graphene Sheets and MoS2: A Unique Film–Foam–Film Structure for Enhanced Lithium Storage

With a notable advantage in terms of capacity, molybdenum disulfide has been considered a promising anode material for building high-energy-density lithium-ion batteries. However, its intrinsically low electronic conductivity and unstable electrochemistry lead to poor cycling stability and inferior rate performance. We herein describe the scalable assembly of free-standing MoS2 -graphene composite films consisting of nitrogen-doped graphene and ultrathin honeycomb-like MoS2 nanosheets. The composite has a unique film-foam-film hierarchical top-down architecture from the macroscopic to the microscopic and the nanoscopic scale, which helps rendering the composite material highly compact and leads to rapid ionic/electronic access to the active material, while also accommodating the volume variation of the sulfide upon intercalation/deintercalation of Li. The unique structural merits of the composite lead to enhanced lithium storage.

The Electrochemistry with Lithium versus Sodium of Selenium Confined To Slit Micropores in Carbon

Substitution of selenium for sulfur in the cathode of a rechargeable battery containing Sx molecules in microporous slits in carbon allows a better characterization of the electrochemical reactions that occur. Paired with a metallic lithium anode, the Sex chains are converted to Li2Se in a single-step reaction. With a sodium anode, a sequential chemical reaction is characterized by a continuous chain shortening of Sex upon initial discharge before completing the reduction to Na2Se; on charge, the reconstituted Sex molecules retain a smaller x value than the original Sex chain molecule. In both cases, the Se molecules remain almost completely confined to the micropore slits to give a long cycle life.

Photocatalytic CO2 reduction highly enhanced by oxygen vacancies on Pt-nanoparticle-dispersed gallium oxide

Photocatalytic CO2 reduction on metal-oxide-based catalysts is promising for solving the energy and environmental crises faced by mankind. The oxygen vacancy (Vo) on metal oxides is expected to be a key factor affecting the efficiency of photocatalytic CO2 reduction on metal-oxide-based catalysts. Yet, to date, the question of how an Vo influences photocatalytic CO2 reduction is still unanswered. Herein, we report that, on Vo-rich gallium oxide coated with Pt nanoparticles (Vo-rich Pt/Ga2O3), CO2 is photocatalytically reduced to CO, with a highly enhanced CO evolution rate (21.0 μmol·h−1) compared to those on Vo-poor Pt/Ga2O3 (3.9 μmol·h−1) and Pt/TiO2(P25) (6.7 μmol·h−1). We demonstrate that the Vo leads to improved CO2 adsorption and separation of the photoinduced charges on Pt/Ga2O3, thus enhancing the photocatalytic activity of Pt/Ga2O3. Rational fabrication of an Vo is thereby an attractive strategy for developing efficient catalysts for photocatalytic CO2 reduction.

Shape‐Controlled Synthesis of Monodisperse PdCu Nanocubes and Their Electrocatalytic Properties

With increasing worldwide energy demand and environmental concerns, the need for sustainable sources is growing stronger and stronger. Among all attempts, fuel cells stand out as a practical and promising solution. At present, the state-of-the-art carbon-supported Pt nanocrystals are still the most commonly used electrocatalytic material for fuel cells because of both its activity and stability. 5] However, the high cost of Pt is one of the most important barriers that limits the large-scale commercialization of fuel cells. Therefore, economical and effective Pt-free catalysts are required and an alternative solution is needed. Among the metal-based catalysts studied to date, Pd and Pd alloys have been the focus of recent research for catalyst alternatives to Pt for the oxygen reduction reaction (ORR) and direct alcohol oxidation. Therefore, Pd-based bimetallic nanocrystals, that is, Pd alloys with less expensive secondary transition metals, have been proposed as substitutes for the fuel-cell catalysts. It has been found that upon appropriate modification of their surface atomic structure, Pd-based nanomaterials can become promising electrocatalysts by simultaneously decreasing material cost and enhancing performance. 8] In recent years, there has been considerable progress on searching for Pd-based bimetallic electrocatalysts, such as synthesizing Pd–Pt nanocomposites, 3] forming a Pd-monolayer on a second noble metal, or alloying Pd with less expensive 3d transition metals, including Fe, Co, Ni, and Cu, . Among the various bimetallic nanocrystals, PdCu nanocrystals have been intensively explored as catalytic materials for a variety of reactions such as generation of hydrogen, combustion, and CO oxidation. 17] Such noble-metal–non-noble-metal alloy nanocrystals might be the best economical catalyst with the desired performance. 19] Moreover, non-noble metallic Cu has received significant attention as an industrially important material and is considered as the ideal compromise between cost and excellent properties. Cu, with a full d band, has attracted a considerable amount of attention because of its extraordinary thermal conductivity. Recently, it has been reported that carbon-supported PdCu nanoparticles showed a high activity for ORR. 21] However, synthesis of PdCu nanocrystals with controlled morphologies still remains a great challenge. Herein, we describe a route to synthesize highly monodisperse PdCu nanocubes with an average size of 12 nm. PdCu nanocubes can be readily prepared by co-reduction of PdCl2 and [Cu(acac)2] (acac = acetylacetonate), with oleylamine (OAm) as both a solvent and a reductant and trioctylphosphine (TOP) as a stabilizer. The carbon-supported PdCu nanocubes displayed substantially enhanced ORR activity compared to that of spherical PdCu nanoparticles, Pd nanoparticles, and commercial Pt/C catalyst. The PdCu nanocubes were prepared from a 1:1 molar ratio of PdCl2 and [Cu(acac)2] in OAm as solvent and with TOP as stabilizer (see the Supporting Information for details). A typical scanning electron microscopy (SEM) image shows that the ob-

Bio-Inspired Fabrication of Hierarchical FeOOH Nanostructure Array Films at the Air–Water Interface, Their Hydrophobicity and Application for Water Treatment

Hierarchical FeOOH nanostructure array films constructed by different nanosized building blocks can be synthesized at the air-water interface via a bio-inspired gas-liquid diffusion method. In this approach, poly(acrylic acid) (PAA) as a crystal growth modifier plays a crucial role in mediating the morphology and polymorph of FeOOH crystals. With the increase of PAA concentration, the shape of the building blocks assembling into FeOOH films can be tailored from nanosheets, to rice spikes, then to branched fibers, and finally to nanowires. What is more, a low concentration of PAA will induce the formation of α-FeOOH, while a high one could stabilize FeOOH in the form of the γ-FeOOH phase. After being modified with a thin layer of polydimethylsiloxane (PDMS), the as-prepared FeOOH films exhibited strong hydrophobicity with water contact angles (CA) from 134° to 148° or even superhydrophobicity with a CA of 164° in the sample constructed by nanosheets. When the FeOOH nanostructures were dispersed in water by ultrasound, they displayed quite promising adsorption performance of heavy metal ions for water treatment, where the highest adsorption capacity can reach 77.2 mg·g⁻¹ in the sample constructed by nanowires. This bio-inspired approach may open up the possibilities for the fabrication of other functional nanostructure thin films with unique properties.

One-pot colloidal chemistry route to homogeneous and doped colloidosomes.

Colloidosomes are usually produced from a series of building blocks with different sizes ranging from several nanometers to micrometers or various shapes, such as particles, microrods, and quantum dots. Colloidosomes can possess a variety of characteristics in terms of photics, electrology, mechanical strength, and selective permeability, derived from their building blocks. However, poor mechanical stability and complicated synthesis processes have limited the applications of colloidosomes. Here, we report a new one-pot colloidal chemistry route to synthesize phenol formaldehyde resin (PFR), Ag@PFR, and Au@PFR colloidosomes with high yields. The method can be modified to synthesize different kinds of doped colloidosomes with different components, which will provide a new approach to design colloidosomes with different functions.