M. Hassan Farooq

A novel Z-scheme WO3/CdWO4 photocatalyst with enhanced visible-light photocatalytic activity for the degradation of organic pollutants

A novel Z-scheme WO3/CdWO4 photocatalyst has been fabricated with sheet-like tungsten trioxide (WO3) hybridized by rod-like cadmium tungstate (CdWO4) via a hydrothermal and chemisorption method. The as-synthesized WO3/CdWO4 photocatalyst exhibited enhanced photocatalytic efficiency for the degradation of different organic dyes under visible light irradiation. It was found that the photocatalytic performance of the composite WO3/CdWO4 was much higher than that of either WO3 or CdWO4 for the degradation of each organic dye. The highest activity of the composite was recorded for the degradation of MB which was about 7 times greater than pure CdWO4 and 2.3 times that of pure WO3. The enhanced performance of the photocatalyst was mainly attributed to the increased surface area and introduction of WO3 into the composite sample, which can induce higher adsorption activity for organic dyes and increased electron–hole separation at the interface between two semiconductors by establishing an inner electric field.

Enhanced hydrogen storage performance for MgH2–NaAlH4 system—the effects of stoichiometry and Nb2O5 nanoparticles on cycling behaviour

Nowadays, the technological utilization of reactive hydride composites (RHC) as promising hydrogen storage materials is hampered by their reaction kinetics. In the present work, effects of reactant stoichiometry on ensuing hydrogen sorption properties and pathway of the MgH2–NaAlH4 (mole ratios 1:2, 1:1 and 2:1) system, both undoped and doped with Nb2O5 nanoparticles, were investigated. It was found that the as-prepared reactant stoichiometry of MgH2/NaAlH4 system had a profound impact on its dehydrogenation kinetics and reaction mechanism. Variable temperature dehydrogenation data revealed that undoped binary composites possessed enhanced hydrogen desorption properties compared to that of pristine NaAlH4 and MgH2. The use of Nb2O5 displayed superior catalytic effects in terms of enhancing dehydriding/rehydriding kinetics and reducing the dehydrogenation temperature of MgH2–NaAlH4 system. Isothermal volumetric measurements at 300 °C revealed that enhancements arising upon adding Nb2O5 were almost double that of undoped MgH2–NaAlH4 composites. The apparent activation energies for NaAlH4, Na3AlH6, MgH2, and NaH relevant decompositions in doped composite were found to be much lower than that for the undoped one. Moreover, Nb2O5 doping also markedly enhanced the reversible capacity of MgH2–NaAlH4 composites under moderate conditions, persisting well during three de/rehydrogenation cycles. XRD, XPS, and FESEM-EDS analyses demonstrated that reduction of Nb2O5 during first desorption was coupled to the migration of reduced niobium oxide species from the bulk to the surface of the material. It was suggested that these finely dispersed oxygen-deficient niobium species might contribute to kinetic improvement by serving as the active sites to facilitate hydrogen diffusion through the diffusion barriers both during dehydrogenation and rehydrogenation.

Growth of monodisperse nanospheres of MnFe2O4 with enhanced magnetic and optical properties

Highly dispersive nanospheres of MnFe2O4 are prepared by template free hydrothermal method. The nanospheres have 47.3-nm average diameter, narrow size distribution, and good crystallinity with average crystallite size about 22 nm. The reaction temperature strongly affects the morphology, and high temperature is found to be responsible for growth of uniform nanospheres. Raman spectroscopy reveals high purity of prepared nanospheres. High saturation magnetization (78.3 emu/g), low coercivity (45 Oe, 1 Oe = 79.5775 Acm−1), low remanence (5.32 emu/g), and high anisotropy constant 2.84 × 104 J/m3 (10 times larger than bulk) are observed at room temperatures. The nearly superparamagnetic behavior is due to comparable size of nanospheres with superparamagnetic critical diameter Dcrspam. The high value of Keff may be due to coupling between the pinned moment in the amorphous shell and the magnetic moment in the core of the nanospheres. The nanospheres show prominent optical absorption in the visible region, and the indirect band gap is estimated to be 0.98 eV from the transmission spectrum. The prepared Mn ferrite has potential applications in biomedicine and photocatalysis.

Controlled synthesis, phase formation, growth mechanism, and magnetic properties of 3-D CoNi alloy microstructures composed of nanorods

3-D flower like CoNi alloys nanostructures composed of nanorods have been synthesized by template free hydrothermal method at relatively low temperature (120 °C). The detailed characterizations confirm the formation of good crystalline fcc CoNi alloy, average crystallite size of 18.8 ± 1.0 nm, lattice parameter of 3.531 ± 0.01 A, and the nearly equiatomic composition (Co50Ni50). Highly uniform flower like nano structures are built up with nanorod of diameter about 100 nm and length in range of 200–400 nm. The nanorods (building blocks of flower) have single crystalline nature with [111] preferred growth direction. The concentration of NaOH plays a vital role in formation of alloys and high concentration promotes the formation of CoNi alloy at low temperature. The concentration of NaOH also affects the morphology remarkably by changing the growth/reaction rate of CoNi nanostructures and results in hollow spheres to nanoplate flower of CoNi alloys. Based on the evolution of the morphology of the products, a step wise growth mechanism is rationally proposed for flower like nanostructures by considering the effects of kinetic parameters on growth. Magnetic measurements show Co50Ni50 flower like nanostructure have high saturation magnetization, coercivity, remanent magnetization, and high effective anisotropy constant of value 101.3 emu g−1, 210.5 Oe, 16.2 emu g−1, and 4.457 × 104 J m−3 respectively. The enhancements of coercivity and effective anisotropy constant are attributed to nanoscale effects such as shape/surface anisotropy.

A facile one-step fabrication of novel WO3/Fe2(WO4)3·10.7H2O porous microplates with remarkable photocatalytic activities

Highly efficient visible-light-driven WO3/Fe2(WO4)3·10.7H2O porous microplates have been fabricated for the first time by a simple one-step hydrothermal method using sodium tungstate and iron chloride as precursors. The photocatalyst was characterized by employing X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV-VIS absorption, photoluminescence (PL), and Fourier transform infrared spectroscopy (FTIR). From the FESEM and TEM analysis, the size of as-prepared porous microplates was estimated to be ca. 2 μm. The as-prepared sample maintained a high specific surface area (96.906 m2 g−1) and showed remarkably high photocatalytic performance (k = 0.06771 min−1) for the degradation of methyl orange (MO) under visible light irradiation. The improved performance of the product was found to be 3.3 times greater than pure WO3 and about 6.7 times greater than that of P25 TiO2. The enhanced optical absorption in the visible region, large specific surface area, suitable band position and efficient separation of photogenerated electron–hole pairs at the heterojunction interface between the two materials were the key factors involved in the enhancement of the photocatalytic activity.

INTRINSIC ROOM TEMPERATURE FERROMAGNETISM OF SILICON-DOPED ZnO THIN FILMS

We report our study on the magnetic properties of Si-doped ZnO thin films fabricated by pulsed laser deposition technique. The Si-doped ZnO thin films show ferromagnetism at room temperature. The saturation magnetism increases from 0 to 2.4 emu/cc with the increasing of Si concentration up to 2%, and then decreases with further increasing of Si concentration. First-principles calculation demonstrates that the origination of ferromagnetism for Si-doped ZnO system is the two unpaired electrons of Si-2p. These unpaired electrons increase the magnetic moments which are responsible for the increasing ferromagnetism.

Facile Synthesis, Structural and Magnetic Properties of Hierarchical Tree-Leaf Like FeCo Alloy Microstructures

[Rafique, M. Yasir; Lqbal, M. Zubair; Javed, Qurat-ul-ain; Qiu, Hongmei; Guo Zhengang] Univ Sci & Technol Beijing, Dept Phys, Beijing 100083, Peoples R China. [Pan, Liqing] China Three Gorges Univ, Coll Sci, Yichang 443002, Peoples R China. [Pan, Liqing] China Three Gorges Univ, Inst New Energy, Yichang 443002, Peoples R China. [Farooq, M. Hassan] Univ Sci & Technol Beijing, Sch Mat Sci & Engn, Beijing 100083, Peoples R China. [Iqbal, M. Azhar] Univ Punjab, Dept Phys, Lahore 54590, Pakistan.