Rehan Danish

Morphological evolution of ZnO nanostructures and their aspect ratio-induced enhancement in photocatalytic properties

This work presented controllable growth of ZnO nanostructures with different aspect ratios by the microwave irradiation method and investigated the photocatalytic degradation of methyl red (MR). X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) measurements showed that all ZnO nanostructures were of a hexagonal phase structure. It was revealed by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images that the morphology of ZnO can be effectively controlled as sheet-like, rod-like, brush-like, flower-like, prism-like, and pyramid-like only by changing the molar ratio (zinc acetate: KOH) and reaction time. With the increase of molar ratio and reaction time, modification in the E2(high) and E1(LO) Raman modes was observed. The energy band gap was found to be tuned by the aspect ratio of ZnO nanostructures. Photoluminescence spectroscopy revealed the low-intensity NBE emission and high and broad defect-related emission for high aspect ratio (14) nanorods. BET surface area porosity analysis confirmed the presence of a mesoporous network in all the nanostructures, showed high surface area and a uniform pore-size distribution for high aspect ratio nanorods. A terephthalic acid assay study confirmed the formation of hydroxyl radicals (OH) in MR dye solution treated with a ZnO nanostructures photocatalyst. The photodegradation of MR under UV light irradiation showed that ZnO nanorods with a high aspect ratio of ∼14 showed superior photodegradation (∼98% degradation of MR within 60 min) than that of the lower aspect ratio nanostructures. The apparent reaction rate constant for high aspect ratio (14) nanorods was higher than that of the lower aspect ratio nanostructures. The enhancement in photocatalytic performance could be due to the high surface area and enhanced charge separation and transfer efficiency of photoinduced charge carriers in the high aspect ratio nanorods.

Study of A-Site Disorder Dependent Structural, Magnetic, and Magnetocaloric Properties in La0.7-xSmxCa0.3MnO3 Manganites

We report studies on the magnetocaloric effect of samarium doped lanthanum manganites with different Sm-concentrations. Polycrystalline La0.7-xSmxCa0.30MnO3 (0≤x≤0.3) samples were prepared using the conventional solid-state reaction method with phase purity and structure confirmed using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal first order ferromagnetic transition in parent sample and second order ferromagnetic transition in doped sample with Curie temperature decreasing progressively with increasing Sm concentration from ~182 K for x = 0.05 to 109 K for x = 0.30. A large magnetic entropy change (~1.75 J kg-1 K-1 at 0.5 T) has been observed in La0.7Ca0.3MnO3 sample, and is greatly suppressed as a function of disorder caused by Sm doping. This is ascribed to the gradual loss of first-order ferromagnetic transition. This investigation suggests that La0.7-xSmxCa0.30MnO3 compounds can be used as a potential magnetic refrigerating material with wide range of temperature.

Facile synthesis of single-crystalline rutile TiO2 nano-rods by solution method

Abstract A convenient and scalable technique for the synthesis of rutile titanium dioxide (TiO2) nano-rods was presented by using bulk TiO2 powder, sodium hydroxide (NaOH) and distilled water as raw materials. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) studies indicate that the prepared sample is crystalline and free from any impurities, however, it has no distinct shape and possesses a huge degree of agglomeration, and the average crystal size is around 40 nm. After annealing the sample at 600 °C for 2 h, it is observed through FESEM that nano-rods are formed. And XRD analysis shows that the nano-rods are single crystalline with distinct and smooth surfaces in different sizes with average length of about 1 µm and diameter of about 80 nm. Further UV-visible spectroscopy and Raman studies were conducted for the prepared sample and the band gap of the final product is found to be 3.40 eV.

Facile Synthesis of ZnO Nanoparticles Using Mechanochemical Route and their Structural, Morphological and Thermal Properties

In the present work, we have prepared ZnO nanoparticles by a two-step mechanochemical synthesis method. The reaction was carried out in a paste state at room temperature with a short grinding time of 20 min. The prepared ZnO nanoparticles were characterized by using x-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis-differential thermal analysis (TGA/DTA). XRD and TEM results demonstrated that ZnO have a single phase nature with wurtzite structure with high crystallinity. The lattice parameters calculated from XRD pattern are a= 3.25 Å and c= 5.248 Å and the average grain size of the ZnO nanoparticles was found to be ~ 20 nm (TEM) or ~22 nm (XRD). FTIR spectra demonstrated the peak at ~455 cm-1 which correspond to stretching mode of ZnO.

Effect of Precursor Concentration on the Structural, Morphological, and Optical Properties of TiO 2 Nano-Flowers

The effect of precursor concentration on the structural, morphological, and optical properties of nano-flowers was investigated in this study. An increase in crystallite size was observed with an increase in the concentration of the precursor (titanium butoxide). The FE-SEM micrographs of the as-prepared samples show a three-dimensional flower-like morphology. The flowers consist of several nanorods coming out of a single core and have very sharp edges. Also, the variation in the aspect ratio of the nanostructure was observed with the concentration of the precursor. The photocatalytic properties of the samples show that the sample that has a high aspect ratio (AR~9) has a much better photocatalytic activity compared to the nano-crystal with a low aspect ratio (AR~6.1). It is believed that the excellent photocatalytic performance and short time synthesis of nano-flowers using the microwave hydrothermal method can have potential applications in the field of photocatalysis.

Relationship Between Structural, Morphological, Optical and Magnetic Properties of Transition Metal (TM)-Doped ZnO Nanostructures Prepared by Microwave-Hydrothermal.

In this work, pure and 3% TM (Co, Ni, and Cu)-doped ZnO nanostructures were prepared by microwave-hydrothermal method. The striking similarities between changes in the lattice volume, bandgap energy, morphology and saturation magnetization indicated a strong correlation between these properties. XRD, SAED and HRTEM analyses revealed that all the TM-doped ZnO nano-structures have wurtzite structure and no secondary phase was detected. FESEM and TEM results confirmed a higher aspect ratio and highly crystalline nature of nanostructures. Raman spectra revealed that no defect related mode was observed which indicated that the nanostructures have high quality and negligible defects. The value of bandgap was found to decrease with the increase in atomic number of TM dopants. RTFM was observed in all the TM-doped ZnO nanostructures and the value of Ms and Mr were decreased with TM dopants.

Effect of concentration on the growth of rutile TiO2 nanocrystals.

In the following study we present an easy and scalable method for the synthesis of Rutile Titanium Dioxide (TiO2) nano-rods by using bulk TiO2 powder, Sodium Hydroxide (NaOH), distilled water and ethanol. We demonstrated the effects of concentration on the size, morphology and band gap of the finally obtained nanostructures. X-ray diffraction pattern (XRD) studies indicated that the samples were crystalline and were free from any impurities with a little hint of anatase at the lower concentrations and the average crystal size ranges between 20 nm to 41 nm, FESEM studies revealed that nano structures are rod like. Further UV-Visible Spectroscopy and Raman studies were conducted of the prepared samples and the band gap of the samples was found to be ranging from 3.5 eV to 3.8 eV. The photo-catalytic degradation of methyl orange was done by the sample prepared in the presence of UV source and was compared with the degrading capacity of bulk TiO2 and was inferred that the Methyl orange is degraded much efficiently with the use of the synthesized sample. The central feature of the presented approach being the use of simple technique and instruments like hot plate, economical and easily accessible chemical like NaOH as a reactant, and a facilitator for the growth of nano-rods and with the reaction being carried out at very low temperatures and less reaction times makes this technique highly feasible for being used in mass production of Rutile TiO2 nano-rods and the fact that the morphology and size can be tuned by varying the concentration of the NaOH.