Facile synthesis of reduced graphene oxide-gold nanohybrid for potential use in industrial waste-water treatment

Here, we report a facile approach, by the photochemical reduction technique, for in situ synthesis of Au-reduced graphene oxide (Au-RGO) nanohybrids, which demonstrate excellent adsorption capacities and recyclability for a broad range of dyes. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) data confirm the successful synthesis of Au-RGO nanohybrids. The effect of several experimental parameters (temperature and pH) variation can effectively control the dye adsorption capability. Furthermore, kinetic adsorption data reveal that the adsorption process follows a pseudo second-order model. The negative value of Gibbs free energy (Delta G(0)) confirms spontaneity while the positive enthalpy (Delta H-0) indicates the endothermic nature of the adsorption process. Picosecond resolved fluorescence technique unravels the excited state dynamical processes of dye molecules adsorbed on the Au-RGO surface. Time resolved fluorescence quenching of Rh123 after adsorption on Au-RGO nanohybrids indicates efficient energy transfer from Rh123 to Au nanoparticles. A prototype device has been fabricated using Au-RGO nanohybrids on a syringe filter (pore size: 0.220 mu m) and the experimental data indicate efficient removal of dyes from waste water with high recyclability. The application of this nanohybrid may lead to the development of an efficient reusable adsorbent in portable water purification. GRAPHICS

Influence of calcination ambient and film thickness on the optical and structural properties of sol-gel TiO2 thin films

Influence of both calcination ambient and film thickness on the optical and structural properties of sol-gel derived TiO2 thin films have been studied. X-ray diffraction results show that prepared films are in an anatase form of TiO2. Films calcined in argon or in low vacuum (similar to 2 x 10(-1) mbar) are found to be smaller in crystallite size, more transparent at low wavelength region of similar to 300-450 nm, denser, have higher refractive index and band gap energy compared to air-calcined films. Scanning electron microscopic study reveals that surfaces of TiO2 films calcined in argon or in low vacuum are formed by densely packed nano-sized particulates. Presence of voids and signs of agglomeration can be seen clearly in the surface microstructure of air-calcined films. In the thickness range similar to 200-300 nm, band gap energy and crystallite size of TiO2 films remain practically unaffected with film thickness but refractive index of thinner film is found to be marginally higher than that of thicker film. In this work, it has been shown that apart from temperature and soaking time, partial pressure of oxygen of the ambient is also an important parameter by which crystallite size, microstructure and optical properties of the TiO2 films may be tailored during calcination perio

A simple spectrophotometric method for determination of the optical constants and band gap energy of multiple layer TiO2 thin films

Using sol-gel processing, TiO2 films have been prepared on microscopic glass slides by dip-coating technique. From X-ray diffractometric (XRD) and X-ray photoelectron spectroscopic (XPS) measurements, it has been confirmed that the deposited films are an anatase form of stoichiometric TiO2. Using either normal incidence transmittance or normal incidence reflectance data, a simple method for determining both film refractive index, n(lambda), and film thickness, d, has been proposed for a transparent film on a non-absorbing flat substrate. At same wavelength within visible region, a correlation between T-S and T-B has been established and verified. T-S and T-B represent the transmittances of single side and both sides coated films of same thickness, respectively, prepared at identical conditions. Average film thickness per coating at various withdrawal speeds (58-146 mm min(-1)) has been estimated. An empirical dispersion equation that describes the variation of n(lambda) of TiO2 films in the wavelength (lambda) range of similar to390-800 nm has been deduced. Band gap energy (E-g) has also been estimated for these films. It has been observed that E-g changes from similar to3.35 to 3.16 eV as the film thickness varies from similar to100 to 300 nm and it does not depend significantly upon film withdrawal speeds in the range 58-146 mm min(-1). (C) 2003 Elsevier B.V. All rights reserved

Influence of processing conditions on the structure, composition and ferroelectric properties of sputtered PZT thin films on Ti-substrates

PZT thin (similar to 500nm) films are synthesized on titanium (Ti) substrates by r.f. magnetron sputtering under various processing conditions. Present work aims to investigate the influence of working pressure and post-annealing temperature on the quality of the films. Phase evolution, surface morphology with local chemical composition and dielectric/ferroelectric properties of PZT films have been studied as the functions of working pressure and post-annealing temperature. A working pressure of similar to 0.7 Pa and a post-crystallization temperature of similar to 650 degrees C are found to be the optimum processing conditions for growing perovskite PZT films on Ti-substrates. Irrespective of processing conditions, however, all PZT films on Ti-substrates show poor electrical response. Depth dependent change in the chemical states of Pb, Zr, Ti and oxygen within the PZT films and across the PZT/Ti interfaces has also been scrutinized by XPS depth profiling. It is observed that within PZT films, Pb exists both in Pb2+ and Pb-0 (metallic-Pb) states. Surfaces of the PZT films are found to be enriched with a thin (similar to 60 nm) Pb-deficient and Zr-rich pyrochlore/fluorite (Py/Fl) phase. Existence of a thin titanium oxide layer in the form of a TiO2/TiO stack has also been confirmed at the PZT/Ti interface. Processing conditions dependant structural modifications have been correlated with the dielectric and ferroelectric properties of the films. (C) 2013 Elsevier B.V. All rights reserved

Effect of substrate temperature and annealing temperature on the structural, electrical and microstructural properties of thin Pt films by rf magnetron sputtering

Influence of both substrate temperature, T-s, and annealing temperature, T-a, on the structural, electrical and microstructural properties of sputtered deposited Pt thin films have been investigated. X-ray diffraction results show that as deposited Pt films (T-s = 300, 400 degrees C) are preferentially oriented along (1 1 1) direction. A little growth both along (2 0 0) and (3 1 1) directions are also noticed in the as deposited Pt films. After annealing in air (T-a = 500-700 degrees C), films become strongly oriented along (1 1 1) plane. With annealing temperature, average crystallite size, D, of the Pt films increases and micro-strain, e, and lattice constant, a(0), decreases. Residual strain observed in the as deposited Pt films is found to be compressive in nature while that in the annealed films is tensile. This change in the strain from compressive to tensile upon annealing is explained in the light of mismatch between the thermal expansion coefficients of the film material and substrate. Room temperature resistivity of Pt films is dependant on both the T-s and T-a of the films. Observed decrease in the film resistivity with T-a is discussed in terms of annihilation of film defects and grain-boundary. Scanning electron microscopic study reveals that as the annealing temperature increases film densification improves. But at an annealing temperature of similar to 600 degrees C, pinholes appear on the film surface and the size of pinhole increases with further increase in the annealing temperature. From X-ray photoelectron spectroscopic analysis, existence of a thin layer of chemisorbed atomic oxygen is detected on the surfaces of the as deposited Pt films. Upon annealing, coverage of this surface oxygen increases. (c) 2006 Elsevier B.V. All rights reserved

Influence of chemical composition, phase and thickness of TiO(x) (x <= 2) seed layer on the growth and orientation of the perovskite phase in sputtered PZT thin films

To study the influence of TiO(x) (x <= 2) seed layer on the formation of perovskite phase in lead zirconate titanate [Pb(Zr(0.52)Ti(0.48))O(3)] thin films, TiOx films of thickness similar to 20-480nm were prepared on coming-1737 glass substrates by r.f. magnetron sputtering and then post-annealed in air at different temperatures (350-650 degrees C). Depending mainly on seed layer thickness, TiO(x) films transform either into anatase or rutile TiO(2) after air-annealing. Thin PZT films (similar to 150 nm)were then deposited on substrates pre-coated with TiO(x) seed layers and air-annealed at 650 degrees C. It is found that thin TiO(2) seed layers (<= 150 nm) promote perovskite phase formation in PZT films. Anatase TiO(2) promotes the growth of randomly oriented perovskite PZT. A (101) textured rutile TiO(2) of thickness similar to 100 nm favours the growth of highly oriented perovskite phase along (100) and surface morphology of these PZT films shows dense rosette structures. A TiO or an amorphous TiO(x) seed film does not initiate perovskite growth. As the thickness of the TiO(x) seed layer exceeds similar to 150 nm, perovskite phase does not form readily irrespective of the crystalline form/phase of TiO(x). Thus, chemical composition, crystalline phase and thickness of the TiC(x) seed layer influence remarkably the crystalline phase, texture and surface morphology of the grown PZT films. (C) 2008 Elsevier B.V. All rights reserved

Crystallization trend in STO-seeded sputtered PZT thin films: Effects of seed layer thickness and post-annealing temperature

Based on the results of X-ray diffractometry (XRD) and analytical scanning/transmission electron microscopy (S/TEM), the crystallization trend and local chemistry of sputtered PZT films on SrTiO3 (STO) coated corning glass substrates have been scrutinized as functions of STO layer thickness (similar to 20-150 nm) and post-annealing temperature (450 C-650 degrees C). It is shown that as a seed layer, STO thin films promote perovskite PZT nucleation at the PZT/STO interface at a temperature of similar to 450 degrees C. Irrespective of STO seed layer thickness, PZT films evolve as a bi-layered structure comprising of tetragonal perovskite and disordered fcc fluorite upon post-annealing. The perovskite crystals are found to be enriched with Pb and lean in Zr and oxygen than fluorite structures. During the post-crystallization growth, Zr atoms get preferentially segregated from perovskite structures and accumulate in top fluorite zone resulting in Zr-enrichment in the latter. Thinner STO seed layers are observed to be more effective in realizing better perovskite growth while crystallographic orientation selection of perovskite is dependent on both seed layer thickness and post-annealing temperature. Transverse compositional homogeneity of the grown perovskite PZT and the level of Pb-diffusion from film to the seed layer and glass substrate are also observed to be seed layer thickness dependent. (C) 2014 Elsevier Ltd. All rights reserved

Multi-technique photoelectron spectrometer for micro-area spectroscopy and imaging

In this note we present the new multipurpose photoelectron spectroscopy facility installed recently at the CSIR-Central Glass and Ceramic Research Institute, Kolkata. Apart from the possibility of performing conventional X-ray and ultraviolet photoemission spectroscopic measurements, this instrument is also equipped with the necessary sources facilitating the performance of macro- as well as micro-area spectroscopy at varying temperatures along with the possibility of X-ray beam-induced secondary electron and chemical state imaging. We present here the details of the instrument along with some experimental results from various samples assessing the system performance

Near surface composition of some alloys by X-ray photoelectron spectroscopy

Chemical compositions of the alloys of CuNi (Cu0.10Ni0.90, Cu0.30Ni0.70, Cu0.70Ni0.30) and BiSb (Bi0.80Sb0.20, Bi0.64Sb0.34, Bi0.55Sb0.45) are determined by X-ray photoelectron Spectroscopy. The stoichiometries are determined and are compared with the bulk compositions. Possible sources of systematic errors contributing to the results are discussed. Errors arising out of preferential etching in these alloys have been investigated. It has been inferred from such studies that the preferential etching does not enrich the surface composition with a particular component for the two systems reported here. Quantitative results of CuNi system indicate that the surface regions of the Cu0.70Ni0.30 alloy is Cu-rich, although no such evidence is observed in case of BiSb system

A study on structural, optical, electrical and microstructural properties of thin TiO(x) films upon thermal oxidation: Effect of substrate temperature and oxidation temperature

Influences of both substrate temperature, T(s) (similar to 305, 473 K) and oxidation temperature, T(a)(similar to 623-973 K) on the structural, optical, electrical and microstructural properties of thin TiO(x) (x <= 2) films obtained by thermal oxidation of sputtered titanium thin films have been investigated. T(s) is found to be an important parameter that affects both the as deposited film morphology and phase evolution of TiO(x) films during oxidation. As deposited and oxidized films processed at T(a)similar to 623 K exist in TiO form. Formation of anatase (TiO(2)) phase takes place at T(a)similar to 723 K. As the T(a) increases above 723 K, degree of crystallinity of the film improves and rutile (TiO(2)) phase appears along with anatase phase at T(a)similar to 873 K. Further increase in the T(a) enhances the contribution of rutile phase at the expense of anatase contribution. Apparent crystallite size, L, and refractive index of the TiO(x) (x approximate to 2) films increase with T(a) but band gap energy, E(g) decreases from similar to 3.4 to 3.35eV. Scanning electron microscopic study reveals that both film densification and grain size improve with T(a). As the T(a) increases above 873 K, rutile phase contribution as well as grains of the oxidized films deposited at a lower T(s) grow at a faster rate than that of the TiO(x) films prepared at a higher T(s). Room temperature resistivity of the as deposited films is found to be dependent on T(s). Film-resistivity increases with oxidation temperature and at T(a)similar to 723 K, resistivity of the film increases drastically. Temperature coefficient of resistivity (TCR) for all the as deposited and oxidized films processed at T(a)similar to 623 K is found to be negative and lie between similar to 1.2 x 10(-3)-2.1 x 10(-3) K(-1). Thermal activation energy, E(a), of the as deposited and oxidized (T(a)similar to 623 K) TiO(x) (x approximate to 1) films is estimated to vary over the range similar to 0.015-0.027 eV. Observed change in the film electrical properties with T(a) is discussed in the light of oxygen incorporation in the TiO(x) structure. (C) 2009 Elsevier B.V. All rights reserved