Peizhong Feng

One-pot synthesis of Bi24O31Br10/Bi4V2O11 heterostructures and their photocatalytic properties

Bi24O31Br10/Bi4V2O11 heterojunction photocatalysts were successfully prepared by a facile, one-pot solvothermal method. In the obtained heterojunctions, Bi4V2O11 nanoparticles were uniformly immobilized on or inlaid onto the surfaces of the Bi24O31Br10 nanosheets. They exhibited superior visible light photocatalytic activity towards the degradation of rhodamine B (RhB). Among them, the 25% Bi4V2O11 sample possessed the highest photocatalytic activity, the degradation rate of which was 4 and 6 times as fast as that of bare Bi24O31Br10 and Bi4V2O11, respectively. The enhanced photocatalytic activity could be attributed to the effective separation and transfer of photogenerated carriers. The trapping experiments confirmed that the photogenerated holes and ˙O2− radicals were the main active species responsible for the photodegradation of RhB.

One-pot synthesis of Bismuth Oxyhalide/Oxygen-rich bismuth oxyhalide Heterojunction and its photocatalytic activity

BiOBr/Bi24O31Br10 heterojunction photocatalysts were prepared by a facile solvothermal method for the first time. The X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), N2 sorption, UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence (PL) were applied to investigate the structures, morphologies, surface areas and photocatalytic properties of as-prepared samples. The photocatalytic activity of the samples was evaluated by the photocatalytic degradation of Rhodamine B under the visible-light irradiation. The results showed that BiOBr/Bi24O31Br10 heterojunctions with the different Bi24O31Br10 contents could be obtained by simply adjusting the amount of NaOH solution, all of which exhibited enhanced photocatalytic activity compared with bare BiOBr or Bi24O31Br10. Among them, the BiOBr/Bi24O31Br10 heterojunction prepared with 1.5ml of NaOH solution possessed the highest photocatalytic activity. The photogenerated holes and ·O2(-) radicals were confirmed to be the main active species responsible for the photodegradation of RhB. The mechanism of enhanced photocatalytic activity was discussed and the transfer process of the photogenerated charges carrier between BiOBr and Bi24O31Br10 was proposed on the basis of the estimated energy band positions.

Synthesis, microstructure and properties of Ti–Al porous intermetallic compounds prepared by a thermal explosion reaction

Ti–Al porous intermetallic compounds were prepared by a simple and energy-saving process of thermal explosion (TE) reactions. The effects of the Ti/Al molar ratios (including Ti : Al = 3 : 1, 2 : 1, 1 : 1, 1 : 2 and 1 : 3) on the temperature profiles, phase compositions, pore characteristics, density, expansion behaviors and oxidation resistance were investigated. The ignition temperatures were between 630–653 °C and the combustion temperatures were between 737–1161 °C, both of which are higher than the target furnace temperature. Porous Ti–Al alloys displayed a high open porosity of 35–56%. The pores were from non-fully dense green compacts and expansion behaviors of TE. When the target furnace temperature was set at 650 °C, the specimen with Ti and Al in a 1 : 2 ratio possessed the highest open porosity of 53.89% and the lowest density of 1.58 g cm−3. When the target furnace temperature was set at 700 °C, the specimen with Ti and Al in a 1 : 3 ratio possessed the highest open porosity of 56.27% and the lowest density of 1.44 g cm−3. The porous specimens with Ti and Al in a 1 : 3 ratio exhibited the best resistance to oxidation at 650 °C in air.

Facile synthesis, structure and enhanced photocatalytic activity of novel BiOBr/Bi(C2O4)OH composite photocatalysts

Novel composite photocatalysts BiOBr/Bi(C2O4)OH were successfully fabricated via a chemical etching method. After flower-like Bi(C2O4)OH microstructure assembled by nanorods was etched by KBr under an appropriate acidic condition, BiOBr nano-rods could be in-situ generated in nanorods, forming a heterostructure. The heterostructures exhibited a commendable photocatalytic performance toward the degradation of rhodamine B under the visible light irradiation. The effective separation and transfer of the photogenerated electrons and holes were believed to be the main factor for the enhanced activity, which resulted from the intrinsic characteristic of p-n junction. The responsible mechanism was detailedly discussed, and the photogenerated holes and O2- radicals were confirmed to be the main active species for the photodegradation of RhB.

Novel Fabrication and Enhanced Photocatalytic MB Degradation of Hierarchical Porous Monoliths of MoO 3 Nanoplates

Porous monoliths of MoO3 nanoplates were synthesized from ammonium molybdate (AHM) by freeze-casting and subsequent thermal treatment from 300 to 600 °C. Pure orthorhombic MoO3 phase was obtained at thermal treatment temperature of 400 °C and above. MoO3 monoliths thermally treated at 400 °C displayed bimodal pore structure, including large pore channels replicating the ice crystals and small pores from MoO3 sheets stacking. Transmission electron microscopy (TEM) images revealed that the average thicknesses of MoO3 sheet were 50 and 300 nm in porous monoliths thermally treated at 400 °C. The photocatalytic performance of MoO3 was evaluated through degradation of methylene blue (MB) under visible light radiation and MoO3 synthesized at 400 °C exhibited strong adsorption performance and best photocatalytic activity for photodegradation of MB of 99.7% under visible illumination for 60 min. MoO3 photocatalyst displayed promising cyclic performance, and the decolorization efficiency of MB solution was 98.1% after four cycles.

Effects of Raw Materials on Synthesis, Microstructure and Properties of MoSi2-10 Vol% SiC Composites

ABSTRACT MoSi2-10 vol% SiC composites have been prepared in situ by self propagating combustion synthesis from three different composite systems: Mo-Si-C, Mo-Si-Mo2C and Mo-Si-SiC. The combustion synthesis temperatures were all above 1800 K and the products were composed of MoSi2, SiC and trace Mo5Si3. MoSi2 and MoSi2-10 vol% SiC composites were consolidated by vacuum hot-pressing at 1400°C to produce monoliths with high density. A uniform dispersion of SiC particles was obtained in MoSi2 matrix composites. MoSi2-10 vol% SiC composites prepared by Mo-Si-SiC raw materials exhibited excellent mechanical properties: Vickers hardness 12.21 GPa, bending strength 773.4 MPa and fracture toughness 3.65 MPa m1/2. GRAPHICAL ABSTRACT

Synthesis and hydrogenation of anatase TiO2 microspheres composed of porous single crystals for significantly improved photocatalytic activity

Anatase microspheres composed of porous single crystals were successfully synthesized via a facile route without preseeding treatment and then further modified using a surface hydrogenation process. The porous materials obtained exhibit excellent photocatalytic activity and good recyclability leading to great potential in practical applications.

Aluminium matrix tungsten aluminide and tungsten reinforced composites by solid-state diffusion mechanism

In-situ processing of tungsten aluminide and tungsten reinforced aluminium matrix composites from elemental tungsten (W) and aluminium (Al) was investigated by thermal analysis and pulsed current processing (PCP). The formation mechanism of tungsten aluminides in 80 at.% Al-20 at.% W system was controlled by atomic diffusion. The particle size of W and Al in the starting powder mixture regulated the phase formation and microstructure. PCP of micron sized elemental Al and W resulted in formation of particulate reinforcements, W, Al4W and Al12W, dispersed in Al matrix. W particles were surrounded by a ~3 μm thick dual-layer structure of Al12W and Al4W. The hardness of Al matrix, containing Al12W reinforcements, was increased by 50% compared to pure Al, from 0.3 GPa to 0.45 GPa and W reinforcements showed a hardness of 4.35 GPa. On PCP of 80 at.% Al-20 at.% W mixture with particle size of W and Al ~70 nm, resulted in formation of Al4W as major phase along with small fractions of Al5W and unreacted W phase. This suggested strongly that the particle size of the starting elemental Al and W could be the controlling parameter in processing and tailoring of phase evolution, microstructure of particulate reinforced Al matrix composite.

Formation of Mo−Si−Ti Alloys by Self−propagating Combustion Synthesis

Test specimens with nominal compositions MoSi2, (Mo0.9Ti0.1)Si2, (Mo0.8Ti0.2)Si2, (Mo0.7Ti0.3)Si2, (Mo0.6Ti0.4)Si2, (Mo0.5Ti0.5)Si2 and (Mo0.4Ti0.6)Si2 were prepared by combustion synthesis. The combustion mode, propagation velocity of combustion wave, combustion temperature and product structure were investigated. Specimens MoSi2, (Mo0.9Ti0.1)Si2, (Mo0.8Ti0.2)Si2, (Mo0.7Ti0.3)Si2, underwent spontaneously self−propagating combustion synthesis. However, the (Mo0.6Ti0.4)Si2 and (Mo0.5Ti0.5)Si2 specimens required a sustainable energy supply to complete the combustion synthesis reaction. There was no combustion synthesis reaction in specimen (Mo0.4Ti0.6)Si2. The combustion wave propagated along a spiral trajectory from top to the bottom of the specimen compacts in a layer by layer mode. The propagation velocity of the combustion wave reduced with the addition of titanium. The X-ray diffraction analysis showed that the Cllb-MoSi2 and C40-(Mo,Ti)Si2 type phases were formed during combustion synthesis. The intensity of diffraction peaks of C40-(Mo,Ti)Si2 phase increased with Ti content.

Effect of heating rate on porous TiAl-based intermetallics synthesized by thermal explosion

ABSTRACT TiAl-based porous materials were synthesized by a novel process of thermal explosion (TE) reaction. The effects of heating rate on the expansion behavior of powder assemblies, phase compositions, and pore structures were investigated. Results showed that the actual temperature of specimen increased rapidly from 655 to 661°C (furnace temperature) to 1018–1136°C (combustion temperature) in a short time interval of 25–55 s, indicating that an obvious TE reaction occurred at different heating rates (1, 2, 5, and 10°C min−1). TE reaction in Ti/Al powder assemblies resulted in the formation of open-celled TiAl-based intermetallics. When the heating rate was set at 5°C min−1, the maximum open porosity of 59% was obtained in Ti-Al bodies, which experienced the highest combustion temperature (1136°C) and underwent maximum volume expansion (48%). The pore size distribution was uniform and pores were interconnected in TE products.