C.A. Betty

CdS-sensitized TiO2 nanocorals: hydrothermal synthesis, characterization, application

Cadmium sulfide (CdS) nanoparticle-sensitized titanium oxide nanocorals (TNC) were synthesized using a two-step deposition process. The TiO(2) nanocorals were grown on the conducting glass substrates (FTO) using A hydrothermal process and CdS nanoparticles were loaded on TNC using successive ionic layer adsorption and reaction (SILAR) method. The TiO(2), CdS and TiO(2)-CdS samples were characterized by optical absorption, X-ray diffraction (XRD), FT-Raman, FT-IR, scanning electron microscopy (SEM) and contact angle. Further, their photoelectrochemical (PEC) performance was tested in NaOH, Na(2)S-NaOH-S and Na(2)S electrolytes, respectively. When CdS nanoparticles are coated on TNCs, the optical absorption is found to be enhanced and band edge is red-shifted towards visible region. The TiO(2)-CdS sample exhibits improved photoelectrochemical (PEC) performance with maximum short circuit current of (J(sc)) 1.04 mA cm(-2). After applying these TiO(2)-CdS electrodes in photovoltaic cells, the photocurrent was found to be enhanced by 2.7 and 32.5 times, as compared with those of bare CdS and TiO(2) nanocorals films electrodes respectively. Also, the power conversion efficiency of TiO(2)-CdS electrodes is 0.72%, which is enhanced by about 16 and 29 times for TiO(2), CdS samples.

Hydrothermal synthesis of rutile TiO2 nanoflowers using Brønsted Acidic Ionic Liquid [BAIL]: Synthesis, characterization and growth mechanism

Herein we report a facile method to synthesize rutile TiO2 nanoflowers (TNF) comprising a bunch of aligned nanorods with uniform size and shape via a hydrothermal method in Bronsted Acidic Ionic Liquid [BAIL] room temperature ionic liquid (RTIL). This method has some advantages: the process is simple and single step; the reaction can be performed under low temperature. The TNFs are highly crystalline and free of aggregation.

Hydrothermal synthesis of rutile TiO2 with hierarchical microspheres and their characterization

Novel rutile TiO2 films with primary microspheres and secondary nanospheres have been deposited on glass substrates via a hydrothermal process by using titanium(IV) butoxide in the presence of toluene and HCl at 160 °C and time period varying from 4 to 8 h. The TiO2 films were characterized using XRD, SEM, FT-Raman, etc. techniques.

Highly sensitive capacitive immunosensor based on porous silicon–polyaniline structure: Bias dependence on specificity

Porous silicon/polyaniline (PS/PANI) heterostructure has been prepared electrochemically which provides label free, real-time electrical detection with high sensitivity for the specific model biomolecules (mouse IgG/goat antimouse IgG). The sensor structures based on PS/PANI were prepared easily by directly immobilizing the biomolecule through gluteraldehyde coupler. These structures were used to detect specific biomolecule down to at least a picomolar concentration range and were found to be reusable. High sensitivity and easy processability of PS/PANI structures could be understood by the change in surface charge of the silicon channels in the PS structure that occurs by PANI deposition whilst providing covalent binding with biomolecules with its naturally occurring NH groups. The space charge layer in the PS/PANI channels get further modified by the surface charge change created by the specific analyte-antibody binding giving rise to high sensitivity. It was found that a substrate bias in the accumulation region of porous silicon gives the optimum sensitivity and specificity.

Room temperature gas sensitivity of ultrathin SnO2 films prepared from Langmuir-Blodgett film precursors

The authors report the room temperature gas sensitivity of ultrathin SnO2 films prepared by thermal decomposition of multilayer Langmuir-Blodgett (LB) films. The SnO2 films, which are characterized by various spectroscopic techniques and electrical measurements, have been shown to sense ammonia gas at room temperature with fast response and recovery. The presence of a large number of surface states in the ultrathin SnO2 film is responsible for the room temperature gas sensitivity. Present results demonstrate the potential of LB technique to fabricate high quality ultrathin oxide films useful for sensor applications.

From nanocorals to nanorods to nanoflowers nanoarchitecture for efficient dye-sensitized solar cells at relatively low film thickness: All Hydrothermal Process

Simple and low temperature hydrothermal process is employed to synthesize exotic nanostructures of TiO2. The nanostructures are obtained merely by changing the nature of the precursors and processing parameters. The chloride and isopropoxide salts of titanium are used to grow high quality thin films comprising anatase nanocorals, rutile nanorods and rutile nanoflowers respectively. A novel route of addition of room temperature ionic liquid (RTIL) is used to synthesize hitherto unexplored nano-morphologies. The Bronsted Acidic Ionic Liquid [BAIL] 0.01 M, 1: 3-ethoxycarbonylethyl-1-methyl-imidazolium chloride [CMIM][HSO4] RTIL directed growth of TiO2 flowers with bunch of aligned nanorods are obtained. The structural, optical and morphological properties of hydrothermally grown TiO2 samples are studied with the different characterization techniques. The influence of these exotic nano-morphologies on the performance of dye sensitized solar cells (DSSCs) is investigated in detail. It is found that [CMIM][HSO4] can facilitate the formation of novel nanoflower morphology with uniform, dense, and collectively aligned in regular petal like oriented TiO2 nanorods and hence improves the dye adsorption and the photovoltaic performance of DSSCs, typically in short-circuit photocurrent and power conversion efficiency. A best power conversion efficiency of 6.63% has been achieved on a DSSC based on nanoflowers (TNF) film obtained from a [CMIM][HSO4] solution.

Efficient dye-sensitized solar cells based on hierarchical rutile TiO2 microspheres

Dye-sensitized solar cells (DSSCs) are fabricated based on rutile TiO2 microspheres that are synthesized by a hydrothermal route. We found that, with increasing deposition time, semi microspheres get converted into microspheres. Our results show that the TiO2-based cells exhibit a noticeable improvement in the overall efficiency: maximum 3.81% versus 0.67% for the reference cell made of a rutile TiO2 semispherical nanocrystalline film. This extraordinary result is attributed to the effective light trapping and dye loading resulting in the highest efficiency 3.81%.

Electro-optical properties of copper phthalocyanines (CuPc) vacuum deposited thin films

Copper phthalocyanine (CuPc) thin films grown on glass substrates by the vacuum deposition method were investigated using photo absorption–transmission as well as photoreflectance spectroscopy with respect to different thickness. The surface morphology was investigated using scanning electron microscopy (SEM). Structural properties were studied by grazing angle XRD diffraction. The vibrational studies were carried out using Fourier transform infrared spectroscopy (FT-IR). The wettability was studied using a contact angle meter.

Pd–TiO2–SrIn2O4 heterojunction photocatalyst: enhanced photocatalytic activity for hydrogen generation and degradation of methylene blue

A novel heterojunction photocatalyst of TiO2–SrIn2O4 is found to be active for hydrogen generation from water as well as for the degradation of methylene blue under sunlight type radiation. Photocatalytic activity for hydrogen generation increases with increase in SrIn2O4 concentration and the optimum concentration is found to be 40% (by weight). The presence of a Pd co-catalyst enhances the photocatalytic activity and the catalyst is found to be stable after repeated cycles of photocatalysis experiments. A higher rate of degradation of methylene blue is observed when the composite is used as photocatalyst compared to pure TiO2 and SrIn2O4. Detailed characterization of the composite revealed that TiO2 exists as a dispersed phase on SrIn2O4 and the particle size of TiO2 and TiO2–SrIn2O4 is around 20 nm and 15 nm, respectively. Photocurrent experiments show a relatively higher current output for the composite compared to pure TiO2. The enhanced photocatalytic activity of the composite is attributed to a synergistic effect of the increased lifetime of the charge carriers in the composite and increased surface area of the sample. The dispersion of TiO2 nanoparticles on SrIn2O4 results in the formation of hetero-junctions between TiO2 and SrIn2O4 leading to efficient interfacial transfer of photogenerated electrons from TiO2 to SrIn2O4 and enhancing the lifetime of the charge carriers. The Pd co-catalyst enhances the activity of the composite further by increasing the availability of electrons in it and providing active sites for hydrogen evolution.

Nanostructured PdO Thin Film from Langmuir–Blodgett Precursor for Room-Temperature H2 Gas Sensing

Nanoparticulate thin films of PdO were prepared using the Langmuir-Blodgett (LB) technique by thermal decomposition of a multilayer film of octadecylamine (ODA)-chloropalladate complex. The stable complex formation of ODA with chloropalladate ions (present in subphase) at the air-water interface was confirmed by the surface pressure-area isotherm and Brewster angle microscopy. The formation of nanocrystalline PdO thin film after thermal decomposition of as-deposited LB film was confirmed by X-ray diffraction and Raman spectroscopy. Nanocrystalline PdO thin films were further characterized by using UV-vis and X-ray photoelectron spectroscopic (XPS) measurements. The XPS study revealed the presence of prominent Pd(2+) with a small quantity (18%) of reduced PdO (Pd(0)) in nanocrystalline PdO thin film. From the absorption spectroscopic measurement, the band gap energy of PdO was estimated to be 2 eV, which was very close to that obtained from specular reflectance measurements. Surface morphology studies of these films using atomic force microscopy and field-emission scanning electron microscopy indicated formation of nanoparticles of size 20-30 nm. These PdO film when employed as a chemiresistive sensor showed H2 sensitivity in the range of 30-4000 ppm at room temperature. In addition, PdO films showed photosensitivity with increase in current upon shining of visible light.