Sunirmal Jana

Characterization of oxygen deficiency and trivalent zirconium in sol-gel derived zirconia films

Abstract Zirconia films were prepared on silica glass substrates from the precursor solution of zirconium oxychloride octahydrate and acetic acid. The films were baked at 450 °C. The existence of oxygen deficiency and Zr(III) in the sol-gel derived zirconia films was characterized by UV and ESR spectral studies. The films baked in air, as well as in oxygen atmospheres, exhibited different UV absorption behaviours. The electronic transition at 5.45 eV of the air-baked film was identified with oxygen deficiency by studies of the functional dependence of the optical absorption coefficient on photon energy. The fundamental electronic transition at 5.80 eV of the films baked in different atmospheres was also identified by the same technique. The non-stoichiometric formula of zirconia (ZrO 1.63 ) was calculated from the relative change of the absorption coefficients (at 5.80 eV) of films of the same thickness 1818 ± 20 A cured in different atmospheres. The size of zirconia particles was determined by transmission electron microscopy (TEM) and found to be below 150 A. Electron diffraction patterns suggested that the structure of the metastable zirconia was cubic.

Optical characterization of in-situ generated Cu2O excitons in solution derived nano-zirconia film matrix

Abstract Cu2O excitons were generated in-situ in a nano-zirconia film matrix on silica glass substrate from the precursor solution containing Cu(II) nitrate trihydrate and zirconium oxychloride octahydrate. The films were annealed in the temperature range 200–1200 °C and characterized by transmission electron microscopy (TEM), UV-VIS-NIR and fluorescence spectroscopy. In the UV-VIS spectra of the films most of the UV and visible bands shifted towards longer wavelengths with increasing annealing temperature and the corresponding Cu2O microcrystallite size was evaluated from the shifting of the UV bands (271–371 nm). Wannier hydrogen-like excitonic transitions, e.g., blue, green, yellow series of Cu2O excitons were observed in the visible region. Excitation dependent fluorescence bands were observed in the visible region and the 400 nm excitation depicted two distinct fluorescence bands in the green (~ 525 nm) and red (~ 630 nm) regions. The intensity ratios of green and red fluorescences and vice versa were found to be dependent on the microcrystallite size. Tentative band assignments have been proposed from the excitonic absorption and fluorescence bands.

Sol–Gel-Based Titania–Silica Thin Film Overlay for Long Period Fiber Grating-Based Biosensors

An evanescent wave optical fiber biosensor based on titania-silica-coated long period grating (LPG) is presented. The chemical overlay, which increases the refractive index (RI) sensitivity of the sensor, consists of a sol-gel-based titania-silica thin film, deposited along the sensing portion of the fiber by means of the dip-coating technique. Changing both the sol viscosity and the withdrawal speed during the dip-coating made it possible to adjust the thickness of the film overlay, which is a crucial parameter for the sensor performance. After the functionalization of the fiber surface using a methacrylic acid/methacrylate copolymer, an antibody/antigen (IgG/anti-IgG) assay was carried out to assess the performance of sol-gel based titania-silica-coated LPGs as biosensors. The analyte concentration was determined from the wavelength shift at the end of the binding process and from the initial binding rate. This is the first time that a sol-gel based titania-silica-coated LPG is proposed as an effective and feasible label-free biosensor. The specificity of the sensor was validated by performing the same model assay after spiking anti-IgG into human serum. With this structured LPG, detection limits of the order of tens of micrograms per liter (10(-11) M) are attained.

Influence of Al doping on microstructural, optical and photocatalytic properties of sol–gel based nanostructured zinc oxide films on glass

Al doped nanostructured zinc oxide thin films (thickness, 165 ± 5 nm) on silica glass were prepared from zinc acetate based solutions of varying dopant content (0 to 10 at% with respect to Zn). X-ray diffraction confirmed the presence of nanocrystalline hexagonal ZnO. On increasing the doping level, we observed a change in ZnO morphology (spherical, hexagon and plate-shaped) under field emission scanning and transmission electron microscopes and a gradual decrease of ZnO crystallite size (14.0 to ∼10 nm) vis-a-vis an enhancement of direct band gap energy of the films. Root mean square film surface roughness and chemical state of elements were studied by atomic force microscopy and X-ray photoelectron spectroscopy respectively. In addition to common intrinsic defects in ZnO, a defect (designated as D˙ZA, appearing as a paramagnetic singly negatively charged oxygen vacancy) was identified up to 4% doping from the appearance of photoluminescence emission at 398 nm and measurement of paramagnetic property of the films. Film photocatalytic activity towards Rhodamine 6G dye decomposition was performed under UV (254 nm) irradiation and the film with 4% doping (A4ZO) showed the highest value of first order decomposition rate constant. On increasing Al content, the trend of change of defect concentration (oxygen vacancies) analyzed by Raman spectra was found to be identical with the dye photodecomposition activity (PA) of the films. A major role of DZA˙ towards the PA was explored under visible light. We proposed the reaction mechanism of PA based on the experimental results. The A4ZO would be expected to decompose micro-organisms under visible light.

Glass and glass-ceramic coatings, versatile materials for industrial and engineering applications

Among various coating systems for industrial and engineering applications, glass and glass-ceramic coatings have advantages of chemical inertness, high temperature stability and superior mechanical properties such as abrasion, impact etc as compared to other coating materials applied by thermal spraying in its different forms viz. PVD, CVD, plasma, etc. Besides imparting required functional properties such as heat, abrasion and corrosion resistance to suit particular end use requirements, the glass and glass-ceramic coatings in general also provide good adherence, defect free surface and refractoriness.Systematic studies covering the basic science of glass and glass-ceramic coatings, the functional properties required for a particular end-use along with the various fields of application have been reviewed in this paper.

Synthesis, characterization and antibacterial activity of Ag incorporated ZnO–graphene nanocomposites

The present work reports on the successful one-pot surfactant-free in situ synthesis of silver incorporated ZnO–chemically converted graphene (CCG) nanocomposites (AZG) by adopting a low temperature solution technique from zinc acetate dihydrate, silver nitrate and graphene oxide, and the varying silver content (up to 20% Ag with respect to Zn) in the precursors. X-ray diffraction and transmission electron microscopy studies confirmed the presence of Ag and ZnO nanoparticles (NPs), distributed uniformly with CCG. FTIR, Raman, UV-visible and X-ray photoelectron spectroscopic analyses confirmed the existence of interaction between CCG with the inorganic moieties (ZnO/Zn2+ and Ag NPs) of the AZG samples. In vitro cytotoxicity and quantitative cell viability of the human ovarian teratocarcinoma cell line (PA1) was studied up to a maximum sample concentration of 200 μg ml−1. Antibacterial activity was also measured on E. coli and S. aureus to confirm the efficiency of the nanocomposite, especially for killing bacterial cells without any major effect on the surrounding cells. Among the nanocomposites, the 10% Ag incorporated sample at a 6.25 μg ml−1 dose showed excellent antibacterial activity with negligible cytotoxicity. This simple strategy could be applied in the synthesis of Ag incorporated different metal oxide–CCG nanohybrids for antibacterial applications.

Yttria doped zirconia in glassy matrix useful for thermal barrier coating

Abstract Properties of thermal barrier coating (TBC) prepared from 3 wt.% yttria doped zirconia (YDZ) dispersed in a high temperature resistant alumino-borosilicate glassy phase in the system AO–B2O–C2O3–DO2 (where A=Ca, Mg, Ba; B=Na, K; C=Al; and D=Si) have been studied. The resultant coating compositions have been applied with good adherence on stainless steel (AISI-310) by simple and cost effective enameling technique. The thermal gradient of TBC with coating thickness of about 800 μm has been found to be within 175–180°C when it was exposed at 1000°C for 30 min. A significant improvement of the gradient to 650–675°C has been observed with a long exposure of coated surface at a temperature of 1000°C aided by a cooling system made of continuous flow of compressed air. Evaluation, characterisation, and microstructure studies have been reported in this paper.

Low temperature synthesis of graphene hybridized surface defective hierarchical core–shell structured ZnO hollow microspheres with long-term stable and enhanced photoelectrochemical activity

The present work reports on successful in situ synthesis of chemically converted graphene (CCG) hybridized, surface defective core–shell structured ZnO hollow microspheres (ZG-CSHM) from a surfactant/template free precursor by adopting a low temperature solution method. This special architecture has been synthesized as an intermediate product between solid and hollow microspheres via Ostwald ripening process by optimizing the reaction time, as observed by field emission scanning and transmission electron microscopic studies. The samples have also been characterized by X-ray photoelectron, FTIR and Raman spectral as well as X-ray diffraction analyses. From textural property measurement by BET N2 adsorption–desorption isotherms, it is seen that the ZG-CSHM possesses an enhanced specific surface area with narrow distribution of mesopores. Relatively higher photoelectrochemical activity with long term stability of ZG-CSHM is found compare to pristine core–shell structured ZnO hollow microspheres. The synergic effect of graphene hybridization and the presence of surface defects of ZnO nanoparticles in the mesoporous sample can play the key roles in advancing its photoelectrochemical activity. The surface defects can prolong the recombination rate of photogenerated charge carriers and the high surface area with narrow sized mesopore distribution can provide large number of active sites, make electrolyte diffusion and mass transportation easier. The ZG-CSHM sample also shows an improved photocurrent density compare to solid and hollow microspheres. Moreover, the existence of chemically interacted CCG with ZnO inhibits the photocorrosion, resulted long-term stable photoelectrochemical activity of ZG-CSHM. This facile process can create an avenue for synthesis of core–shell structured microspheres from different metal oxide semiconductors for improving their photoelectrochemical activity.

Chemical Behaviour of Zirconium Oxychloride Octahydrate and Acetic Acid in Precursor Solution for Zirconia Film Formation on Glass

Precursor solutions for zirconia films on soda lime silica glass substrate were prepared from zirconium oxychloride octahydrate (ZOO) and acetic acid (HOAC) maintaining the mol ratios, [HOAC]/[ZOO]=2, 4, 6, 8 and 10. A characteristic UV absorption band at ∼280 nm in the ∼120h aged precursor solutions was identified for acetate group of the zirconium acetato complexed species. The presence of acetate ligand coordinated with either ZrOOH+ or [Zr4(OH)8]8+ or with both was predicted by the studies of UV spectra of aged solutions and FTIR spectra of unbaked films on silicon wafer. Dipping technique was followed for film formation. Thicknesses and refractive indices of the baked (450°±5°C) films were in the ranges 1818±20 Å and 1.702–1.762 respectively. The positive SIMS experiment on two typical films baked at 450°±5°C derived from the precursors with [HOAC]/[ZOO]=2 and 6, detected the ionic species, Zr+, ZrO+, ZrO2+, Na+, Ca+, Fe+, H+ while the negative SIMS detected O− and Cl−. The relative contents of the ionic species with respect to Zr+ were dependent on the acid content of the precursors. Reflection (%) of the baked films in the UV region was also dependent on the acid content of the precursors. Electron diffraction pattern of the typical baked film derived from the precursor with [HOAC]/[ZOO]=2 exhibited meta-stable cubic phase of zirconia and the grains were found to be elongated (aspect ratio, 2.00–2.33).

Sol–gel based simonkolleite nanopetals with SnO2 nanoparticles in graphite-like amorphous carbon as an efficient and reusable photocatalyst

We report a new sol–gel nanocomposite (STC) having simonkolleite nanopetals (SC) and quasi-spherical tin oxide (SO) nanoparticles embedded in graphite-like amorphous carbon (C) as an efficient and reusable photocatalyst for the degradation of rhodamine 6G dye under UV (254 nm) illumination. The STC was synthesized using vacuum curing (450 °C) of precursor gel derived from a sol (Zn : Sn, 2 : 1) in 2-methoxyethanol with acetylacetone. The presence of tetragonal SO well decorated on rhombohedral SC forming nanoheterostructures in the carbon matrix was identified by X-ray diffraction, micro-Raman and X-ray photoelectron spectroscopy and electron microscopes (field emission scanning electron and transmission electron) studies. Carbon content and thermal weight loss behaviour in STC were studied by carbon determinator and thermogravimetry. The nanocomposite showed high photocatalytic activity (10−5 M dye solution degraded completely in 32 min). Reusability test of the photocatalyst exhibited about 95% of dye degradation after five successive recycles. In addition to accelerating photo-induced charge carrier separation and electron transport in the nanoheterostructures as revealed from electrochemical impedance spectroscopy response of the UV-exposed nanocomposite, an active role of the carbon at an optimum content (∼18%) was found for generating high BET specific surface area (∼143 m2 g−1). This simple synthesis strategy could open a new avenue to the development of sol–gel nanocomposites as efficient and reusable photocatalysts from various simonkolleite-based metal oxide semiconductors embedded in graphite-like amorphous carbon.