An-Wu Xu

Noble-Metal-Free Fe–N/C Catalyst for Highly Efficient Oxygen Reduction Reaction under Both Alkaline and Acidic Conditions

In this work, we report the synthesis and assessment of a new non-precious-metal oxygen reduction reaction (ORR) catalyst from pyrolysis of an iron-coordinated complex which manifests superior activity in both alkaline and acidic media. 11,11-bis(dipyrido[3,2-a:2,3-c]phenazinyl) (bidppz) was selected as a ligand for the formation of a nitrogen-rich iron-coordinated coordination polymer (Fe-bidppz) which forms a self-supporting catalyst containing high densities of nitrogen and iron doping by pyrolysis. The catalyst pyrolyzed at 800 °C (Fe-N/C-800) shows the highest ORR activity with onset and half-wave potentials of 923 and 809 mV in 0.1 M KOH, respectively, which are comparable to those of Pt/C (half-wave potential 818 mV vs RHE) at the same catalyst loading. Besides, the Fe-N/C-800 catalyst has an excellent ORR activity with onset and half-wave potentials only 38 and 59 mV less than those of the Pt/C catalyst in 0.1 M HClO4. The optimal Fe-N/C-800 catalyst displays much greater durability and tolerance of methanol than Pt/C. We propose that the Fe-N/C-800 catalyst has a considerably high density of surface active sites because Fe-N/C-800 possesses excellent ORR activity while its specific surface area is not so high. Electrochemical measurements show that the Fe-N/C-800 catalyst in KOH and HClO4 follows the effective four-electron-transfer pathway.

Biomass-Derived Sponge-like Carbonaceous Hydrogels and Aerogels for Supercapacitors

As a newly developed material, carbon gels have been receiving considerable attention due to their multifunctional properties. Herein, we present a facile, green, and template-free route toward sponge-like carbonaceous hydrogels and aerogels by using crude biomass, watermelon as the carbon source. The obtained three-dimensional (3D) flexible carbonaceous gels are made of both carbonaceous nanofibers and nanospheres. The porous carbonaceous gels (CGs) are highly chemically active and show excellent mechanical flexibility which enable them to be a good scaffold for the synthesis of 3D composite materials. We synthesized the carbonaceous gel-based composite materials by incorporating Fe3O4 nanoparticles into the networks of the carbonaceous gels. The Fe3O4/CGs composites further transform into magnetite carbon aerogels (MCAs) by calcination. The MCAs keep the porous structure of the original CGs, which allows the sustained and stable transport of both electrolyte ions and electrons to the electrode surface, leading to excellent electrochemical performance. The MCAs exhibit an excellent capacitance of 333.1 F·g(-1) at a current density of 1 A·g(-1) within a potential window of -1.0 to 0 V in 6 M KOH solution. Meanwhile, the MCAs also show outstanding cycling stability with 96% of the capacitance retention after 1000 cycles of charge/discharge. These findings open up the use of low-cost elastic carbon gels for the synthesis of other 3D composite materials and show the possibility for the application in energy storage.

Highly Branched Concave Au/Pd Bimetallic Nanocrystals with Superior Electrocatalytic Activity and Highly Efficient SERS Enhancement†

Superstar: branched concave Au/Pd bimetallic nanocrystals were synthesized in high yield by seed-mediated co-reduction of Au and Pd metal precursors in an aqueous solution at room temperature. The branches are concave and have high-index facets on their surfaces. These nanocrystals show superior electrocatalytic activity for the oxidation of ethanol and highly efficient SERS enhancement.

Graphene oxide nanoribbons greatly enhance extracellular electron transfer in bio-electrochemical systems.

Bridging microbes and electrode to facilitate the extracellular electron transfer (EET) is crucial for bio-electrochemical systems (BESs). Here, a significant enhancement of the EET process was achieved by biomimetically fabricating a network structure of graphene oxide nanoribbons (GONRs) on the electrode. This strategy is universal to enhance the adaptability of GONRs at the bio-nano interface to develop new bioelectronic devices.

Terbium-based infinite coordination polymer hollow microspheres: preparation and white-light emission

Novel rare earth based 4,4′,4′′-benzene-1,3,5-triyl-tri-benzonate (RE-BTB) infinite coordination polymer (ICP) hollow microspheres have been successfully prepared via a facile surfactant-free mixed-solvothermal route, among which Tb-BTB was studied in detail. These as-prepared hollow microspheres using terbium as the central ion have diameters of 260–500 nm. Influential factors such as reaction temperature, reaction time, dosage of reagents, and solvent composition on the morphology and size of the Tb-BTB ICP hollow spheres have been systematically investigated. An inside-out formation mechanism was proposed for the hollow microspheres. The photoluminescence properties of the Tb-BTB hollow spheres have been systematically studied. It turns out that it is easy to tune the luminescent characteristics of the Tb-BTB ICP hollow spheres within a wide spectral range by simply varying the excitation lines or the doping concentration of Eu3+. Interestingly, white-light emission was realized in the Eu3+ doped Tb-BTB hollow spheres.

Coexistence of adsorption and coagulation processes of both arsenate and NOM from contaminated groundwater by nanocrystallined Mg/Al layered double hydroxides.

In this study, nanocrystallined Mg/Al layered double hydroxides (LDH-CO3) and chloridion intercalated nanocrystallined Mg/Al LDHs (LDH-Cl) were synthesized and used for simultaneous removal of arsenic and natural organic matter (NOM) from contaminated groundwater. Humic acid (HA) was selected as a model compound of NOM. The maximum adsorption capacities of arsenate (As(V)) on LDH-CO3 and LDH-Cl are 44.66 and 88.30 mg/g, respectively, and those of HA on LDH-CO3 and LDH-Cl are 53.16 and 269.24 mg/g, respectively. It was found that more than 98% of arsenic and 94% of NOM were eliminated by LDH-Cl from both arsenic and NOM-rich groundwater, which is used as drinking water in Togtoh County, Inner Mongolia, China. The arsenic concentration declined from 231 to 4 μg/L, which meets the drinking water standard. The adsorption mechanisms were determined by using X-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and extended X-ray absorption fine structure spectroscopy techniques (EXAFS). The results showed that the removal of HA was mainly via surface complexation as well as coagulation at the surface of LDHs, while the adsorption of As(V) was mainly via ion-exchange process. The presence of HA exhibited little inhibiting effect on As(V) adsorption by occupying partial binding sites on LDH surfaces. Nevertheless, it could not affect the ion-exchange process of As(V) with the interlayer anions of LDHs. The removal of As(V) and HA can be carried out independently due to the different adsorption mechanisms. By integrating the experimental results, it is clear that LDH-Cl can be potentially used as a cost-effective material for the purification of both arsenic and NOM contaminated groundwater.

Preparation of inorganic salts (CaCO3, BaCO3, CaSO4) nanowires in the Triton X-100/cyclohexane/water reverse micelles

Abstract Nanowires of inorganic salts (CaCO 3 , BaCO 3 , CaSO 4 ) were prepared in the nonionic surfactant reverse micelles (Triton X-100/cyclohexane/water) system. The growth process of CaCO 3 nanowire was monitored by the transmission electron microscopy (TEM) technique as a function of time. TEM images reveal that the CaCO 3 nanowires were formed in the reverse micelles by the directional aggregation process. The nanowires of CaCO 3 were 5–30xa0nm in diameter and had a length more than 10xa0μm.

Carbonaceous hydrogels and aerogels for supercapacitors

Carbonaceous hydrogels and aerogels are a large class of gels which have received much attention due to their multifunctional properties. The three-dimensional networks and porous structure of the carbonaceous gels can provide efficient diffusion of electrolyte ions and electrons, leading to promising applications in supercapacitors. This feature article gives an overview of the recent advances in the use of novel carbonaceous gels for supercapacitors. In particular, the synthetic methods for polymer derived carbonaceous gels, carbon nanotube based carbonaceous gels, graphene based carbonaceous gels and biomass derived carbonaceous gels are introduced, and their applications for supercapacitors are systematically discussed. Perspectives for the development of neotype carbonaceous gel based electrode materials for supercapacitors are given.

The biomimetic mineralization of double-stranded and cylindrical helical BaCO3 nanofibres

A facile biomimetic method is reported for the synthesis of novel BaCO(3) nanofibres with double-stranded and cylindrical helical morphologies via a phosphonated block co-polymer-controlled mineralization process.

Calcite Crystals with Platonic Shapes and Minimal Surfaces

Platonic solids are the five polyhedrons with equivalent facets composed of congruent convex regular polygons, in which the same number of facets meet at every vertex. The octahedron, with eight facets, is a platonic shape composed of triangles, and the dodecahedron, with 12 facets, is the only one with pentagonal facets. In nature, pyrite frequently occurs as octahedral or dodecahedral crystals. Certain viruses and radiolaria also routinely take the form of these regular polyhedral shapes. A number of synthetic inorganic crystals with platonic shapes have been reported recently, such as gold nanocrystals, mesoporous silicate dodecahedra and octahedra, SnO2 octahedra, [3d] In2O3 and Cu2O octahedra, [3e,f] as well as metallic alloy quasi-crystals. For the trigonal CaCO3 calcite crystal structure, the formation of platonic shapes is, owing to a too-low symmetry, not to be expected. Calcite pseudo-dodecahedra, nevertheless, were synthesized with a variety of additives, such as Mg, Co, simple organic acids, phosphate, carboxylate-rich polymers, amino acids, calcite-binding helical peptide, globular proteins, protein extracts isolated from aragonitic abalone shell nacre and from sea urchins. The mechanisms of crystal growth of these calcite pseudo-dodecahdra are additive adsorption on the {011} faces, the inhibiting effect of additives on step-growth, or the combination of the two functions. Calcite mesocrystals with pseudo-octahedral morphology and otoconia-like morphology were also described. However, a unified route towards more than one platonic calcite shape based on one same mechanistic approach has not yet been revealed. Herein, we present a nonclassical crystallization approach towards calcite with a platonic shape based on nanoparticle aggregation. We show that a commercial co-polyelectrolyte can be used to manoeuvre the crystallization of CaCO3 into meso-crystalline calcite structures with curved surfaces and platonic shapes. Significantly, the intermediates are consistent with rhombohedral primitive (P)surface morphology (see Supporting Information Figure S1)—one of the mathematical minimal surfaces, which were found in nature and in synthetic bicontinuous mesophases. The most striking example is the skeleton of Cidaris rugosa, in which self-assembled 3D networks have a continuous curvature. The importance of the P-surface structure was also recognized in other sea-urchin skeletal plates and has been connected with their functions in nutrient permeation, stress distribution, and their unique optical properties. 8] The platonic calcite crystals were generated by a simple gas-diffusion method in the presence of poly(4-styrenesulfonate-co-maleic acid) (PSS-co-MA). This polymer was chosen as it combines the maleic acid, which stabilizes {011} faces of calcite, with the mesocrystal-inducing properties of PSS in one molecule. Pseudo-dodecahedral crystals were obtained for a polymer concentration of 0.1 gL 1 and [CaCl2] = 1.25 mm after 2 weeks crystallization. Figure 1a and Figure 1b show the typical scanning electron microscopy (SEM) images of the pseudo-dodecahedral calcite microcrystals obtained. It can be seen that exclusively pseudododecahedral shapes were observed, with a relatively monodisperse size of approximately 20–30 mm. The transmission electron microscopy (TEM) image of an ultrathin section of the as-synthesized product (Supporting Information Figure S2) shows a remarkable large number of interstices within the bulk. The interstices suggest a crystallization