We report a study on hydrogen storage in Ca, Co, Fe, Ni, and Pd decorated multiwalled carbon nanotubes (MWCNTs) by using two techniques: volumetric and electrochemical. The results showed that hydrogen molecules are adsorbed on the defect sites and transported to the spaces between adjacent carbon via diffusion through both defect sites and opened tips into the layers. Hydrogen storage capacity can be improved in the decorated MWCNT by Co, Fe, Ni, and Ca metals in two approaches: (i) H 2 adsorption via Kubas interaction and (ii) dissociation of H 2 molecules on the metal particles. The results reveal that Pd are more effective catalyst for hydrogen storage process. It was found that dissociation of H 2 occurs on the Pd particle, and hydrogen atoms are entered into the spaces between adjacent carbon layers. They create loosely bonds of CH x species and PdÀCÀH x complex which can be decomposed easily at lower temperatures as compared to CÀH chemical bonds.

In this work, a novel technique is presented for the graphene fabrication based on the pulsed laser ablation of graphite target inside the cryogenic liquid using the pulsed nanosecond Q-switched Nd:Y3Al5O12 (Nd:YAG) laser at 1064 nm. Single-stage fabrication process is taken into account as a remarkable advantage without need to high vacuum devices and additional chemical components. The synthesis process is controllable by changing the laser properties and the irradiation conditions accompanying easy collection of the products.

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Abstract:In this research high-quality zinc oxide (ZnO) nanowires have been synthesized by thermal oxidation of metallic Zn thin films. Metallic Zn films with thicknesses of 250 nm have been deposited on a glass substrate by the PVD technique. The deposited zinc thin films were oxidized in air at various temperatures ranging between 450 °C to 650 °C. Surface morphology, structural and optical properties of the ZnO nanowires were examined by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and photoluminescence (PL) measurements. XRD analysis demonstrated that the ZnO nanowires has a wurtzite structure with orientation of (002), and the nanowires prepared at 600 °C has a better crystalline quality than samples prepared at other temperatures. SEM results indicate that by increasing the oxidation temperature, the dimensions of the ZnO nanowires increase. The optimum temperature for synthesizing high density, ZnO nanowires was determined to be 600 °C. EDX results revealed that only Zn and O are present in the samples, indicating a pure ZnO composition. The PL spectra of as-synthesized nanowires exhibited a strong UV emission and a relatively weak green emission.

In this work, Pd nanoparticles were synthesized by pulsed nanosecond laser ablation in deionized water using Q-switched Nd:YAG and ArF excimer lasers, independently. The aim is to investigate the wavelength dependence of nanoparticle formation mechanisms using IR and UV laser irradiations. Pd nanoparticles fabricated by a Q-switched Nd:YAG laser show a perfect spherical morphology, whereas those due to the ArF excimer laser undergo fragmental shapes. Furthermore, the production rate of Pd nanoparticles generated at IR is noticeably greater than that at UV wavelength. Moreover, the plasma temperature induced by the Nd:YAG laser is higher than that generated by the ArF laser mainly due to the stronger inverse Bremsstrahlung process at the IR region. It was shown that the ArF laser fabricates palladium oxide structure with much higher rate with respect to the Nd:YAG laser.