M. Jayachandran

Spray pyrolysis growth and material properties of In2O3 films

Indium oxide (In2O3) thin films have been prepared by spray pyrolysis using a very low concentration of indium precursor. The spray process parameters like the concentration of precursor in spray solution, ethanol+water, air-flow rate, substrate–nozzle distance and substrate temperature have been optimized for obtaining optically transparent, conducting and device-quality In2O3 films. The material properties are reported by studying the structural, electrical and optical properties of the In2O3 films prepared at a relatively lower temperature of 380°C. The surface morphology has been studied by scanning electron microscopy and atomic force microscopy. A possible film growth mechanism has been proposed for preparing device-quality In2O3 films using lower substrate temperatures.

Electrodeposition of Sn, Se, SnSe and the material properties of SnSe films

Abstract A detailed account of the electrochemistry involved in the deposition of Sn, Se and SnSe films is presented. The redox reactions and the polarization curves of Sn and Se were studied to fix the pH and potential values V (NHE) to get uniform deposition. Films were cathodically deposited at 55°C. XRD studies show an orthorhombic structure. Films showed an indirect band-gap of 1.05 eV. Surface morphological studies were carried out using SEM, and the stoichiometry was estimated from XPS analysis. Effect of annealing in air at 200°C has been reported.

Photoelectrochemical characteristics of brush plated tin sulfide thin films

Abstract Thin films of tin sulfide find wide applications in optoelectronic devices and window materials for heterojunction solar cells. Thin films of p-SnS were brush plated onto tin oxide coated glass substrates from aqueous solution containing SnCl 2 and Na 2 S 2 O 3 . Deposits have been characterized with XRD and SEM for structural analysis. Hot probe method showed invariably p-type nature for all the brush plated SnS films. The variation of space charge capacitance, C sc , with applied potential, V , was recorded for the PEC cell with p-SnS/Fe 3+ , Fe 2+ /Pt system. The spectral response of the PEC cell formed with SnS photoelectrode was studied and reported.

Investigation of x-ray photoelectron spectroscopic (XPS), cyclic voltammetric analyses of WO3 films and their electrochromic response in FTO/WO3/electrolyte/FTO cells

Electrochromic thin films of tungsten oxide (WO3) were prepared on transparent conducting oxide substrates, i.e., fluorine doped tin oxide coated (FTO or SnO2:F) glass and microscopic glass substrates by the electron beam evaporation technique using pure WO3 (99.99%) pellets at various substrate temperatures (i.e., Tsub = room temperature (RT, 30 °C), 100 °C and 200 °C). The films were prepared under vacuum of the order of 1 × 10−5 mbar. The room temperature prepared films were further post-heat-treated (Tanne) at 200 and 300 °C for about 1 h in the vacuum environment. The prepared films are in monoclinic phase. The chemical composition has been characterized by using the XPS technique. The W 4f and O 1s core levels of WO3 films have been studied on the samples. The obtained core level binding energies revealed the WO3 films contained six-valent tungsten (W6+). The electrochemical nature of the films was studied by a three-electrode electrochemical cell in the configuration of FTO/WO3/H2SO4/Pt, SCE, using the cyclic voltammetry (CV) technique. Electrochromic devices (ECDs) of the general type FTO/WO3/electrolyte/FTO were studied. The films produced at higher substrate temperature show smaller modulation of the visible spectrum, compared with the films produced at lower temperatures. The significant chemical bonding nature associated with the coloring/bleaching process which follows the H+ ion incorporation in the film is studied by FTIR analysis. The W–O–W framework peak was observed at 563 cm−1 and confirms the stability of the films in the electrochemical analysis. The results obtained from cyclic voltammetry technique and ECD cell characterization are used to emphasize the suitability for some applications of the solar control systems.

Formation of shape-selective magnetic cobalt oxide nanowires: environmental application in catalysis studies

A new route for the formation of shape-selective CoO nanowires has been developed using a simple microwave (MW) heating method. The reduction of Co(II) ions was done using a new reducing agent alkaline 2,7-dihydroxy naphthalene (2,7-DHN) in cetyltrimethylammonium bromide (CTAB) micellar media. The reaction mixture was irradiated using MW for a total time of 6 min. The process exclusively generates CoO nanowires of different lengths and having diameter ∼5 ± 2 nm to 15 ± 2 nm range just by tuning the metal-ion-to-surfactant molar ratios and changing the other reaction parameters. Magnetization measurements indicate that there is no observable coercivity for the short nanowires, but the coercivity increases as the length of the nanowires increases although the magnetic moment values at the maximum applied magnetic field of 2 T decreased with an increase in the length of the nanowires. The synthesized CoO nanowires are found to serve as an effective catalyst for the mineralization of several organic dye molecules in the presence of NaBH4 in a short reaction time. The process assists the room temperature mineralization of the dyes and provides a cleanup measure of dye contaminated water bodies even in the presence or in the absence of light. The yield of the CoO nanowires with uniform shapes is found to be significantly high (>95%) and the nanowires are stable for more than a month under ambient conditions. The proposed synthesis method is efficient, straightforward, reproducible, and robust. Other than in catalysis, the cobalt oxide nanomaterials can also be applied for making pigments, lithium-ion battery materials, solid state sensors, or as anisotropy source for magnetic recording.

The self-assembling of DNA-templated Au nanoparticles into nanowires and their enhanced SERS and catalytic applications

A simple photochemical technique is described for the synthesis of organized assemblies of Au nanoparticles (NPs) on a DNA template in a shorter time scale. The smaller Au nanoparticles (NPs) are initially formed in the DNA solution, self-assembled together, and generate the nanowire structures. The diameter and the length of the nanowires can be tuned by controlling the different reaction parameters. The average diameters of the individual Au NPs could be varied in the range of 10–50 nm, whereas their lengths could be extended to the level of several micrometres. The mechanism for the formation of the self-assembled structure of Au NPs on DNA is elaborated upon. The DNA–Au nanowire shows a highly stable and reproducible signal in surface enhanced Raman scattering (SERS) studies. The SERS activity was examined with Rhodamine 6 G (R6G) as a model dye molecule and the observed enhancement factor (EF) was ∼106. The catalytic activity was tested for the reduction of 4-nitroaniline (4-NA) with sodium borohydride in aqueous solution. The synthesized Au nanowires were found to be stable for more than six months under ambient conditions at room temperature without any change of the optical properties. The superior SERS and catalytic activities of the material might be useful in future for different applications in organic catalysis reactions and in a variety of SERS based detections of bio-molecules, as sensors etc.

Structural, electrochromic and FT-IR studies on electrodeposited tungsten trioxide films

Abstract Tungsten trioxide (WO3) has been found to be a very versatile material for electrochromic (EC) devices. It behaves as a mixed ion conductor and hence it has recently attracted much interest in the field of solid state ionics. When the intercalation of the film is taken in the cyclic voltammograms for various concentrations (0.1, 0.5 and 1.0 N) of H2SO4, the voltage is recorded for the peak current. The powder X-ray diffraction pattern is taken and the peaks are compared with the JCPDS values. It is found to be the triclinic structure. The FT-IR spectra are taken for the WO3 films electrodeposited at different deposition current densities (0.25, 0.50, 0.65 and 0.75 mA/cm2) keeping the other deposition parameters like pH of the solution, concentration of the electrolyte and temperature of the bath constant. The film exhibits a broad peak from 3780 to 3500 cm−1 which indicated the OH–H stretching vibration. The peak at 3543 cm−1 depends upon the coloration increase in the electrodeposited tungsten trioxide film. A little amount of molecular water may exist in the electrodeposited WO3 film, which corresponds to a broad peak at 2500 cm−1. A small peak at 820 cm−1 exhibits W–O stretching. After ion intercalation the peak positions are slightly changed.

Organic free low temperature direct synthesis of hierarchical protonated layered titanates/anatase TiO2 hollow spheres and their task-specific applications

Layered protonated titanates and corresponding anatase TiO2 shapes, specifically the hollow spheres, are the most important functional materials and have attracted much attention because of their superior performance. Here, a facile organic substrate (both as solvent or surfactant) free, low temperature aqueous solution based chemical protocol for the direct synthesis of 3D arranged hierarchical hollow spheres of protonated layered dititanate (H2Ti2O5·H2O), is proposed. The spheres had a high surface area (as high as 334 m2 g−1), and were prepared through hydrothermal treatment of freshly prepared peroxo titanium carbonate complex in the presence of ammonium hydroxide. Ammonium hydroxide is crucial in the formation of spherical arrangement of titanate sheets and the size of the spheres is tunable by changing the amount of ammonium hydroxide. The titanate spheres can easily be converted to pure anatase TiO2 with identical morphology on subsequent calcination. The synthesized titanate spheres showed very high removal capacity for toxic heavy metals like Pb2+ and methylene blue from aqueous solution. Corresponding anatase TiO2 spheres manifested as a brilliant anode material for lithium ion batteries with excellent cyclability. TiO2 spheres also showed good photocatalytic activity.

Influence of alloying additives on the performance of commercial grade aluminium as galvanic anode in alkaline zincate solution for use in primary alkaline batteries

The self-corrosion of different grades of commercial aluminium such as 2S, 3S, 26S and 57S in 4 M NaOH containing 0.6 M ZnO has been determined by weight loss measurements. It is found that 26S and 57S aluminium exhibit negligible corrosion rates in the range 0.05–0.06 mg cm−2 min−1, which can be attributed to the formation of a zincate coating on the aluminium surface. The influence of zincating on the performance of binary and ternary alloys of 26S and 57S aluminium obtained by incorporating alloying elements such as zinc, indium, thallium, gallium and tin as galvanic anode in 4 M NaOH containing 0.6 M ZnO has been examined by studying self corrosion, steady state open circuit potential, galvanostatic polarization and anode efficiency. It is found that zincated ternary alloys of 26S and 57S aluminium containing zinc and indium can serve as good galvanic anodes in alkaline medium. AC impedance measurements and X-ray diffraction studies have been carried out to understand the nature of the film formed on the aluminium surface.

CeO2 nanowires with high aspect ratio and excellent catalytic activity for selective oxidation of styrene by molecular oxygen

CeO2 is a most promising oxidation catalyst and its superior oxidation performance is highly dependent on the extent of its Ce4+/Ce3+ redox cycle, shape, surface area and surface structure. Herein, a simple, efficient and aqueous solution based hydrothermal synthetic route for uniform CeO2 nanowires (NWs), with high aspect ratio and surface area, using an aqueous solution of cerium ammonium carbonate complex as precursor and poly(ethylene glycol) (PEG) as structure directing agent, is described. Cobalt incorporated CeO2 NW (Co–CeO2) were also synthesized by impregnation followed by calcination. Structural and morphological characterization by XRD, SEM and TEM showed that synthesized CeO2 NWs are of cubic fluorite crystal structure, with approximately 7 ± 2 nm width and several micrometers in length, bundled, grown through the (110) surface keeping the active (100) surface exposed. XPS and TPD analysis revealed the presence of both Ce3+ and Ce4+ with higher amount of Ce3+ as well as Co2+ and Co3+ species. The amount of PEG is crucial for the synthesis of uniform CeO2 wires and other varying shapes. A probable formation mechanism of wires through the (110) surface is proposed. Synthesized CeO2 shapes were employed as catalyst for selective oxidation of styrene to styrene oxide using molecular oxygen as oxidant. Shape selective catalytic studies revealed that the synthesized Co–CeO2 NWs showed excellent catalytic activity. Kinetic study revealed that the oxidation reaction followed the Langmuir–Hinshelwood model. The synthesized CeO2 NW catalysts are recyclable with no significant loss in catalytic activity in subsequent cycles.