Haoyang Wu

Combustion synthesis and excellent photocatalytic degradation properties of W18O49

In this paper, one-dimensional W18O49 nanopowders were fabricated by a one-step solution combustion method using glycine as the fuel and a metal acid radical ion as the metal source. The morphologies and non-stoichiometric single-crystal phase of W18O49 can be controlled by changing the amount of the fuel. The nanoneedles had a large amount of defects such as oxygen vacancies. This characteristic resulted in an excellent visible light-driven photocatalytic performance that took about 50 min to degrade methylene blue (100 mL; 40 mg L−1) under visible light. The interesting reaction mechanism of such needle-like W18O49 and the photocatalytic mechanism are studied in this paper.

Synthesis of Mesoporous Single Crystal Co(OH)2 Nanoplate and Its Topotactic Conversion to Dual-Pore Mesoporous Single Crystal Co3O4

A new class of mesoporous single crystalline (MSC) material, Co(OH)2 nanoplates, is synthesized by a soft template method, and it is topotactically converted to dual-pore MSC Co3O4. Most mesoporous materials derived from the soft template method are reported to be amorphous or polycrystallined; however, in our synthesis, Co(OH)2 seeds grow to form single crystals, with amphiphilic block copolymer F127 colloids as the pore producer. The single-crystalline nature of material can be kept during the conversion from Co(OH)2 to Co3O4, and special dual-pore MSC Co3O4 nanoplates can be obtained. As the anode of lithium-ion batteries, such dual-pore MSC Co3O4 nanoplates possess exceedingly high capacity as well as long cyclic performance (730 mAh g(-1) at 1 A g(-1) after the 350th cycle). The superior performance is because of the unique hierarchical mesoporous structure, which could significantly improve Li(+) diffusion kinetics, and the exposed highly active (111) crystal planes are in favor of the conversion reaction in the charge/discharge cycles.

The formation of CuO porous mesocrystal ellipsoids via tuning the oriented attachment mechanism

We report a new chemical reaction route to synthesizing CuO porous mesocrystal ellipsoids via decomposition of copper vanadium oxide under hydrothermal conditions. By finely tuning the oriented attachment growth mechanism of CuO, a porous mesocrystal structure was synthesized. Structural and morphological evolutions of the CuO product were investigated and the formation of CuO porous mesocrystal ellipsoids here was essentially determined by the amount of ammonium metavanadate. An oriented nanoparticle aggregation with tailoring of the structure, including compact mesocrystals and porous mesocrystals, could be achieved in different concentrations of reactants. The strategy of constructing the structure via an oriented attachment growth mechanism could be applied to the synthesis of other nanomaterials with complex structures.

Thermal Stability of Non-Equilibrius Microstructure in Microalloyed Steel During Reheating

Cooled in water after isothermal relaxation of deformed austenite for different times, an Nb-bearing microalloyed steel always exhibits synthetic microstructures, in which bainitic ferrite dominates. Dislocation configurations and distributions of strain induced precipitates inside bainitic ferrite of samples relaxed for different times were distinct. When compared with the austenite model steel, which maintained fcc structure even at room temperature, the strain induced precipitates were not found in the sample without relaxation whereas these were distributed outside dislocations in sample relaxed for 1000s. Most of the strain induced precipitates distribute along dislocations and pin dislocations in sample relaxed for appropriate time. After bainitic transformation, the dislocations formed in deformed austenite remain to be pinned by the precipitates. When these samples were reheated to and held at 650 or 700 °C, the non-equilibrious microstructures tended to evolve into equilibrious ones. The sample relaxed for 60s displayed the highest thermo-stability, whereas microstructure evolution was the quickest in the sample relaxed for 1000s even though it was the softest prior to reheating. Dislocations inside laths got rid of pinning of precipitates, and their polygonization became the precursor to the evolution of microstructures during reheated and held, followed by gradual disappearance of lath boundaries caused by dislocation climbing. Finally, recrystallization occurred and polygonal ferrite appeared. By hardness measurement, it was found that softening is not a single process occurring during reheated, in which hardness fluctuates with time. There were two peaks in the hardness-time curve of each sample having undergone relaxation, while single peak occured in the curve of the sample not being relaxed. These results indicated that the thermo-stability of microstructures was determined by their history of formation to a considerable degree.

Facile solution combustion synthesis of MoO2 nanoparticles as efficient photocatalysts

Foam-like MoO2 assembled from nanoparticles was fabricated by a solution combustion synthesis method using hexaammonium molybdate, ammonium nitrate (NH4NO3) and glycine as the precursors. The effect of the glycine/NH4NO3 ratio (Φ = 0.25, 0.50, 0.75, 1.0 and 1.25) on the physicochemical properties of the final products was systematically studied. The Φ value was found to display significant roles in the final phases and morphologies of the products. With a Φ value of 0.50, the foam-like product consisting of MoO2 nanoparticles with an average size of about 20–30 nm was synthesized. The photocatalytic activities of the foam-like MoO2 towards degradation of several contaminants, including methyl orange (MO), methylene blue (MB), rhodamine B (Rh B) and phenol, were investigated. The foam-like MoO2 offered excellent capability and stability toward photocatalytic degradation of the studied contaminants. The results reported here demonstrated that rational design of MoO2-based photocatalysts might be able to improve their properties in energy conversion and environmental preservation.

A Self-standing Silver/Crosslinked-Poly(vinyl alcohol) Network with Microfibers, Nanowires and Nanoparticles and Its Linear Aggregation

Silver/polymer nanocomposites have made inroads into the fields of electronic devices, thermally conductive materials, antimicrobial agents and sensors. Here, we present the hydrothermal synthesis of a novel three-dimensional self-standing silver/crosslinked-poly(vinyl alcohol) (Ag/crosslinked-PVA) hybrid network constructed by linking three different subunits, namely, microfibers, nanowires and nanoparticles. One-dimensional crosslinked-PVA-based microfibers act as the skeleton of the sponge. Ag nanoparticles are uniformly embedded in the interior of the microfibers, and Ag nanowires grow outward from the interior of the microfibers. This Ag/crosslinked-PVA multi-architecture has not be observed or reported in current state-of-the-art studies. We simultaneously carry out two types of reactions, chemical reduction of Ag+ ions and intermolecular crosslinking of PVA chains, in the synthesis under hydrothermal conditions. Ag nanoparticles are formed and dispersed in the crosslinked-PVA microspheres. Then, these Ag/crosslinked-PVA microspheres bridge each other, forming microchains and microfibers. Ultimately, linear aggregation, which has rarely been mentioned in the literature, occurs in some adjacent Ag nanoparticles in the microfibers, and the Ag nanoparticles reorganize into nanowires. The Ag/crosslinked-PVA network is shown to be converted into a Ag/C composite through annealing, which exhibits electrocatalytic activity for glucose oxidation and can be used as a self-supporting electrode in an antibacterial nonenzymatic glucose sensor.

Ultrafast synthesis of amorphous VOx embedded into 3D strutted amorphous carbon frameworks–short-range order in dual-amorphous composites boosts lithium storage

Crystalline vanadium oxides have some unique advantages, including abundant material sources, high energy density, and a typical layered structure, making them promising anode candidates for lithium-ion batteries. However, the intrinsic low electrical conductivity and volume expansion side effects severely limit their capacity and cyclability at high charge/discharge rates. Herein, unique dual-amorphous composites with 3D strutted amorphous carbon sheet framework encapsulated amorphous vanadium oxide particles have been prepared by an ultrafast (within one minute), ultralow temperature (172 °C), one-step and large-scale combustion synthesis method. We demonstrate that the dual-amorphous VOx/C composites provide a large number of accessible active sites and defects for lithium ion intercalation/deintercalation and are self-accommodative to tolerate volume expansion. Another noteworthy point is the short-range ordered atomic arrangement observed in amorphous VOx that exhibits a larger interlayer spacing (d(001) = 4.80 A) than other crystalline vanadium oxides. This particular structure has the potential to accommodate more lithium ions and tolerate the volume expansion. Meanwhile the 3D hierarchical porous sheet-like structure facilitates the transfer of electrons and lithium ions. The electrochemical measurements show excellent lithium storage performance with high capacity, good rate capability and long-term cycling stability of the composites.