Synthesis and characterization of neodymium oxide modified nafion membrane for direct alcohol fuel cells

Nafion composite membranes were prepared by incorporating neodymium oxide (Nd₂O₃), a hygroscopic rare earth oxide and a dopant for H⁺ ion conduction, into the nafion structure. Five different loadings of Nd₂O₃ were used to fabricate Nd₂O₃/nafion composite membranes and characterized extensively for possible use in direct alcohol fuel cells. The proton conductivity, ion exchange capacity, water uptake, tensile strength, and oxidation stability of the composite membrane were higher than pure cast nafion membrane. Nd₂O₃/nafion composite membrane exhibited reduced methanol and ethanol crossover as compared to pure cast nafion membrane and thus has potential to use in direct alcohol fuel cells.     

Investigation into hybrid configuration in electrospun nafion/silica nanofiber

Organic–inorganic composites with nanostructure could exhibit a diverse range of multi-functional properties. In this study, nafion/silica composite nanofibers were successfully fabricated by using electrospinning technique with nafion coated surface. The tunable wettability of composite nanofiber was controlled by addition of nafion or flame-treatment. The thermal stability of nafion has been improved as it hybridized with silica nanofiber. Interestingly, the hydrophobic behavior still existed after heat-treatment with 500 °C for 2 h. The fire resistant property of composite nanofiber has been characterized. The effect of nafion polymer and post treatment on the morphology and wettability of composite nanofiber was evaluated. The mechanism of formation of nafion/silica composite nanofiber during electrospinning process has been proposed. The results of this study improve the understanding of the structure rearrange in organic–inorganic sols during high voltage field.     

Visible light induced photocatalytic performance of Mn-SnO2@ZnO nanocomposite for high efficient cationic dye degradation

In this work, we have synthesized Mn-doped SnO₂@ZnO nanocomposite for photo degradation of Methylene blue and Rhodamine B dyes upon visible light irradiation. The crystal structure, functional group, optical absorption, defect related emission, morphology, purity and binding energy state of synthesized samples were identified by using various analytical tools. The crystal structure revealed the rutile tetragonal, hexagonal wurtzite for SnO₂ and ZnO samples and the average crystal sizes were found in the range of 23.3 nm to 16.7 nm for the synthesized samples. The optical absorption peaks were shifted to higher wavelength side and optical band gap values were found between 3.52 eV and 2.77 eV which confirm the formation of hetero-junction of SnO₂@ZnO composites. The field emission scanning electron spectroscopy (FESEM) revealed the spherical grain morphology for pure and composite samples. The energy dispersive spectra (EDS) and element mapping confirms the purity of the synthesized samples. The X-ray photoelectron spectroscopy (XPS) revealed that the composition and energy state of Mn⁴⁺, Sn⁴⁺ and Zn²⁺ for composite samples. The photocatalytic degradation results clearly indicate that the Mn-doped SnO₂@ZnO nanocomposite has higher degradation efficiency of 98% and 92% for the Methylene blue and Rhodamine B dyes, respectively and is higher than the other synthesized samples. The present study reveals a low cost and highly efficient photo-catalyst which works up on visible light irradiation for the purification of waste water from industries.

     

Organic dyes containing fluorenylidene functionalized phenothiazine donors as sensitizers for dye sensitized solar cells

Two new organic sensitizers featuring fluorenylidene decoration on the phenothiazine donor have been synthesized and characterized as sensitizers for nanocrystalline TiO₂-based dye sensitized solar cells (DSSCs). The dyes possess cyanoacrylic acid as acceptor/anchoring group and a conjugation pathway composed of fluorene and thiophene. Introduction of the fluorenylidene moiety on phenothiazine enhances the optical density of the dyes while the extension of conjugation by thiophene insertion red-shifts the absorption peak originating from the intramolecular charge transfer from phenothiazine to cyanoacrylic acid. The ground and excited state oxidation potentials of the fluorenylidene-containing dyes are upwardly shifted when compared to the parent dyes indicating a π-delocalized donor segment. The electronic properties were supported by density functional theoretical computations. Among the DSSCs fabricated, the dye (5a) having fluorene and thiophene in the spacer resulted higher power conversion efficiency (3.31 %) than the corresponding bithiophene analog (5b, 2.83 %) attributable to the relatively high electron life time and enhanced resistance for recombination in the former.     

Transfer of molybdenum sulphide coating material onto corundum balls in fretting wear tests

Transfer films on corundum balls from sulfur deficient molybdenum disulfide (MoS_x) coatings with different crystallographic orientations were investigated after fretting tests performed in ambient air of different humidity levels. The morphology of wear tracks on MoS_x coatings and of transfer films on corundum balls were investigated by light optical microscopy with Normarski contrast. The thickness of transfer films was measured by scanning white light and optical phase-shifting interferometry, and their composition was analyzed by X-ray photoelectron spectroscopy. The effect of relative humidity in fretting tests on the composition of the transfer films as well as the effect of the transfer film on the tribological performance of MoS_x coatings in fretting wear tests is discussed.     

Acridine-1, 8-diones – A new class of thermally stable NLOphores: Photophysical, (hyper)polarizability and TD-DFT studies

Linear and non-linear optical properties of a series of new acridine-1, 8-dione derivatives are investigated in different solvents by using solvatochromic and computational methods. Values of first-order hyperpolarizabilities (β_CT or β₀) obtained using solvatochromic and computational methods are compared with the reported values for urea and 3-aminoxanthone. The new materials under study show first hyperpolarizability values 2.3 to 5.6 times larger than that of urea and 2 to 15.6 times more than that of 3-aminoxanthone. The dyes possess very high thermal stabilities. The dyes are prepared using one pot multicomponent reaction between dimedone, various aromatic aldehydes and amino acids, and characterized by spectroscopic techniques.     

Effect of annealing temperature on structural,optical and humidity sensing properties of indium tin oxide (ITO) thin films

Tin doped indium oxide (ITO) thin films were prepared by sol–gel spin coating method with In (NO₃)·3H₂O and SnCl₄·5H₂O as indium and tin sources, respectively. The as deposited samples were annealed at various temperature such as, 300, 400, 500 and 600?°C for 2 h in ambient atmosphere. The grown ITO thin films are polycrystalline in nature with cubic structure of In₂O₃ with the space group La3 and the results are in good agreement with the standard JCPDS data (card no#06-0416). In addition crystalline size increases with increasing annealing temperature from 25 to 55 nm. Polycrystalline with uniform smooth surface was observed by SEM micrographs. The optical band gap energy was found to be decreased from 3.85 to 3.23 eV as the annealing temperature is increased from 300 to 600?°C. The humidity sensing performance (high sensitivity and fast response time) was significantly improved for 600?°C thin films samples, which is probably due to smaller energy band gap and physisorption between the water molecules and the surface of the thin films. The films were further characterized by PL and EDS analysis. The effect of temperature on humidity sensing mechanism of ITO thin films is also discussed.     

Polyvinyl chloride seal layer for improving the durability of electrochromic switchable mirrors based on Mg-Ni thin film

Electrochromic switchable mirrors consisting of a multilayer of Mg₄Ni/Pd/Al/Ta₂O₅/H_XWO₃/indium tin oxide on a glass substrate degrade when subjected to changes in humidity and temperature. Polyvinyl chloride was applied as a seal layer to such a device in an attempt to improve its durability. The optical switching properties of the device were investigated through an accelerated degradation test conducted at a constant temperature of 30 °C and a relative humidity of 80%. Although the device with a seal layer was thicker, it showed superior optical switching properties with a transmittance as high as 54% in the transparent state due to interference at the multilayer. Furthermore, the device with a seal layer exhibited higher durability after 35 days in an accelerated degradation environment, as well as higher switching durability.     

High performance humidity sensing properties of indium tin oxide (ITO) thin films by sol–gel spin coating method

The tin doped indium oxide (ITO) thin films prepared by sol–gel spin coating method with In(NO₃)3H₂O and SnCl₄·5H₂O as indium and tin sources respectively is presented. The as deposited samples were annealed at 500 °C for 2 h in order to improve the crystallinity. The structural, morphological and optical properties of the films were analysed by using X-ray diffraction, scanning electron microscope (SEM), UV–Vis transmission spectra and photoluminescence, spectra analysis. The SEM images ensure the uniform and smooth surface of the as prepared and annealed film. The optical transmittance of more than 85 % has been observed in the UV–Vis region with a band gap of 3.91 and 3.73 eV for the as prepared and annealed films of ITO respectively. The PL spectra reveal that the optical properties were significantly improved due to the annealing effect. The annealed film shows high sensitivity for humidity approximately two order changes in the resistance and the sensitivity increases for different relative humidity from 10 to 90 % due to the physisorption between the water molecules and the surface of the thin films.     

An electroanalytical study of chemiplated thin films of copper sulphide

Thin films of copper sulphide have been deposited from aqueous solution onto glass, platinum and cadmium sulphide by two new methods: first, chemiplated Cu₂O films have been subjected to anion exchange with S_2- ions and second, copper (I) thiourea complexes have been hydrolysed in sodium tetraborate solution. The copper sulphide films Cu _x S have been analysed electrochemically andx has been found to have values within the range 1.83 to 1.93. The dominance of the digenite phase (Cu_1.8S) in these films has been confirmed by optical measurements.     

New configuration of optical photosensitizers for dye-sensitized solar cells: combination of carbazole and xantone

Novel organic dyes system containing responsible group for using in dye-sensitized solar cells and effective anchoring group for improving interaction between dye (photosensitizers) and nanolayer were designed and prepared. All intermediates and organic dyes were purified and analyzed using analytical techniques. The results confirmed the structure of intermediates and organic dyes. Dye-coated TiO₂ and ZnO semiconductors were used for the preparation of the photoanode. The synthesized dyes were trapped in J-aggregation, reflected J-aggregation, and red shift in UV–Vis spectra of dyes in solution relative to the coated on nanomaterials. Cyclic voltammetry and DFT methods were used to evaluate the energy levels of the synthesized compounds. Dye-sensitized solar cells were also prepared and evaluated under standard conditions, using the synthesized compounds. The efficiency of Dye 8 as photosensitizer on TiO₂ and ZnO was 6.65% and 6.37%, respectively.

     

The influence of alizarin and fluorescein on the photoactivity of Ni,Pt and Ru-doped TiO2 layers

The doping with different metal ions and sensitization with organic compounds are two well known methods used to improve the photoactivity of TiO₂. In this respect, the metallic ions-doped TiO₂ samples were prepared by embedding Ni, Pt and Ru ions into TiO₂ crystalline network and then, each sample was sensitized with alizarin and fluorescein dyes. The qualitative evaluation of prepared TiO₂-based materials was made by: UV–vis spectroscopy, spectrofluorimetry, FT/IR spectroscopy and microscopy, X-ray diffraction and N₂ physisorption measurements. The optoelectronic properties investigated by UV–vis spectroscopy show that the optical response of Ni-doped TiO₂ layer shifts to visible. The X-ray spectra do not show peaks of nickel, platinum and ruthenium oxide crystals or pure metals. The FT/IR spectra proved the presence of dye molecules adsorbed on titania nanoparticles surface. These results demonstrated that the studied dopants and dyes have potential to promote modified TiO₂-based materials as good candidates to be used in photolectrocatalytic processes.     

A hybrid humidity sensor using optical waveguides on a quartz crystal microbalance

In this study, slab and ridge optical waveguides (OWGs) made of fluorinated polyimides were deposited on a quartz crystal microbalance (QCM), and hybrid sensors using OWG spectroscopy and the QCM technique were prepared. Polyvinyl alcohol (PVA) film with CoCl₂ was deposited on the OWGs, and the characteristics of humidity sensing were investigated. A prism coupler was used to enter a He–Ne laser beam (λ = 632.8 nm) to the slab OWG. The output light intensity markedly changed due to chromism of the CoCl₂ as a result of humidity sorption, and this change was dependent on the incident angle of the laser beam to the slab OWG. During the measurement of output light, the QCM frequency was simultaneously monitored. The humidity dependence of the sensor with the slab OWG was also investigated in the range from 15 to 85%. For the sensor with the ridge OWG, white light was entered by butt-coupling, and the characteristics of humidity sensing were investigated by observing the output light spectrum and the QCM frequency.     

Evanescent wave optical-fiber sensing (temperature, relative humidity, and pH sensors)

Sensitive and versatile evanescent wave-sensing systems featuring polished optical fiber-based sensor designs with low-cost light sources have been developed for temperature, relative humidity, and pH measurements. The work herein contained describes the fabrication of three types of sensors based on standard silica, single-mode fibers previously subjected to a lateral polishing of the cladding. Temperature sensing through oils whose refractive index varied linearly with temperature showed applicability with up to 5 dB//spl deg/C for a 5/spl deg/ range. Polyvinyl alcohol films on the fibers showed almost 10-dB linear variation from 70% to 90% relative humidity. Sol-gel trapped dyes as thin films on the polished surface were capable of performing 15-dB output variation (although not linearly) for pH ranging from 2 to 11.     

Monitoring of Corrosion Under Insulations by Acoustic Emission and Humidity Measurement

We simultaneously monitored humidity and AE from active corrosion under insulation (CUI). For humidity monitoring, we developed an optical fiber sensor based on the moisture dependency of absorption of laser light by connecting coating of polyvinyl alcohol and CoCl₂ coating and pullulan coating in series on the fiber as a cladding layer. The sensor could be used to measure humidity of 65–95% RH at 80°C. The temperature dependence of the sensor was as small as 2.5% RH/10°C. We monitored active CUI by the acoustic emission technique and humidity sensing under wetting and drying cycles. Most AE signals were produced during the drying process in each wetting and drying cycle, and the AE rate increased with the time of wetness (period of humidification).     

Structural,optical and excellent humidity sensing behaviour of ZnSnO<Subscript>3</Subscript> nanoparticles: effect of annealing

The chemi-resistive humidity sensing behaviour of as prepared and annealed fcc-ZnSnO₃ nanoparticles synthesized using wet chemical synthesis method is reported here. The effect of annealing on the evolution of varied nano-morphology of ZnSnO₃ is in accordance to Ostwald’s ripening law. The optical energy bandgap energy change from 4.64 to 3.84 eV for annealed samples confirms the role of annealing over improved sensing performance. At room temperature, an excellent humidity sensitivity of 4155% and response/recovery time of 19/22 s. is observed for 500 °C annealed ZnSnO₃ sample within 08–97% relative humidity range. The experimental data observed over the entire range of RH values well fitted with the Freundlich adsorption isotherm model, and revealing two distinct water adsorption regimes. This indicates that with an increase in annealing temperature the samples show improved adsorption capacity and strength. The excellent humidity sensitivity observed in the annealed nanostructures is attributed to Grotthuss mechanism considering the availability and distribution of available adsorption sites. This present result proposes utilization of low cost synthesis technique of ZnSnO₃ holds the promising capabilities as a potential candidate for the fabrication of next generation humidity sensors.     

Preparation and piezoelectric catalytic performance of HT-Bi2MoO6 microspheres for dye degradation

HT-Bi₂MoO₆ microspheres were prepared by hydrothermal method and applied in piezoelectric catalytic degradation of dye. The crystallinity, morphology, optical property, and the surface chemical state of Bi₂MoO₆ catalyst were characterized by XRD, SEM, UV–vis and XPS techniques, respectively. The effects of catalyst preparation method, catalyst amount, dyes type and reaction conditions were investigated on the piezoelectric catalytic performance. The highest degradation ratio of 98.9% was achieved with 10 mg of HT-Bi₂MoO₆ catalyst after 45 min of piezoelectric catalytic vibration. In addition, a possible piezoelectric catalytic mechanism over HT-Bi₂MoO₆ catalyst has been proposed by active species trapping experiment. ·O₂⁻ and h⁺ are suggested to be the main active species in the piezoelectric catalytic process. These research results show that the HT-Bi₂MoO₆ catalyst with flower-like microspheres morphology consisting of nanosheets can effectively transform mechanical energy into electrical energy by vibration to generate reactive species for the degradation of dyes.     

Improvement of photon collection in Cu(In,Ga)Se2 solar cells and modules by fluorescent frequency conversion

Fluorescent photon down conversion for the improvement of the blue response of ZnO/CdS/Cu(In,Ga)Se₂ heterojunction solar cells and modules is investigated. Fluorescent dyes of the series Lumogen® F are analyzed by optical transmission and reflection as well as by photoluminescence measurements. A spectral transfer matrix formalism is introduced that allows to predict the suitability of a luminescent dye as a down-converter for a given solar cell from its absorption/emission properties. We find that Lumogen® F Violet 570 and Lumogen® F Yellow 083 as well as a combination of both yields improvements for Cu(In,Ga)Se₂ solar modules. Particularly, we find that the short circuit current density of a Cu(In,Ga)Se₂ mini-module is improved by 1.5 mA cm^− 2 when applying a varnish with a combination of Lumogen® F Violet and Yellow. About 0.5 mA cm^− 2 of this improvement is due to a reduced overall reflectance and an improvement of 1 mA cm^− 2 results from the frequency conversion by the dyes.     

Nitrogen‐Doped Single Graphene Fiber with Platinum Water Dissociation Catalyst for Wearable Humidity Sensor

Humidity sensors are essential components in wearable electronics for monitoring of environmental condition and physical state. In this work, a unique humidity sensing layer composed of nitrogen‐doped reduced graphene oxide (nRGO) fiber on colorless polyimide film is proposed. Ultralong graphene oxide (GO) fibers are synthesized by solution assembly of large GO sheets assisted by lyotropic liquid crystal behavior. Chemical modification by nitrogen‐doping is carried out under thermal annealing in H₂(4%)/N₂(96%) ambient to obtain highly conductive nRGO fiber. Very small (≈2 nm) Pt nanoparticles are tightly anchored on the surface of the nRGO fiber as water dissociation catalysts by an optical sintering process. As a result, nRGO fiber can effectively detect wide humidity levels in the range of 6.1–66.4% relative humidity (RH). Furthermore, a 1.36‐fold higher sensitivity (4.51%) at 66.4% RH is achieved using a Pt functionalized nRGO fiber (i.e., Pt‐nRGO fiber) compared with the sensitivity (3.53% at 66.4% RH) of pure nRGO fiber. Real‐time and portable humidity sensing characteristics are successfully demonstrated toward exhaled breath using Pt‐nRGO fiber integrated on a portable sensing module. The Pt‐nRGO fiber with high sensitivity and wide range of humidity detection levels offers a new sensing platform for wearable humidity sensors.     

On the optical limiting and Z-scan of hexamethylin-dotricarbocyanine perchlorate dye

Measurement of Reverse Saturable Absorption (RSA) and optical limiting response in hexamethylin-dotricarbocyanine perchlorate (HITC perchlorate) is reported for the first time and results are compared with C₆₀ and various other dyes under the nanosecond pulse excitation. HITC perchlorate shows better optical limiting than well known C₆₀ and results reveal that photo-excited triplet state absorption cross-section is higher than the ground state absorption cross-section, suggesting the presence of Reverse Saturable Absorption (RSA) in these materials. Limiting threshold for HITC perchlorate is 0.45 J/cm² (at 70% linear transmission), which is lower than C₆₀ (1.2 J/cm², at 70% linear transmission). Z-scan shows negative nonlinearity (self-defocusing) for HITC perchlorate. Ethanol soluble and low cost HITC perchlorate displaying better optical limiting as compared to other conventional materials. Absence of photochemical or photothermal destruction processes in the studied materials suggests their perspective application as a stable optical limiter in photonic devices.