Chemical synthesis of highly stable PVA/PANI films for supercapacitor application

Polyvinyl alcohol (PVA)/polyaniline (PANI) thin films were chemically synthesized by adopting two step process: initially a thin layer (200 nm) of PVA was spin coated by using an aqueous PVA solution onto fluorine doped tin oxide (FTO) coated glass substrate, afterwards PANI was chemically polymerized from aniline monomer and dip coated onto the precoated substrate. The thickness of PANI layer was varied from 293 nm to 2367 nm by varying deposition cycles onto the precoated PVA thin film. The resultant PVA/PANI films were characterized for their optical, morphological and electrochemical properties. The FT-IR and Raman spectra revealed characteristic features of the PANI phase. The SEM study showed porous spongy structure. Electrochemical properties were studied by electrochemical impedance measurement and cyclic voltammetry. The electrochemical performance of PVA/PANI thin films was investigated in 1 M H₂SO₄ aqueous electrolyte. The highest specific capacitance of 571 Fg⁻¹ was observed for the optimized thickness of 880 nm. The film was found to be stable for more than 20,000 cycles. The samples degraded slightly (25% decrement in specific capacitance) for the first 10,000 cycles. The degradation becomes much slower (10.8% decrement in specific capacitance) beyond 10,000 cycles. This dramatic improvement in the electrochemical stability of the PANI samples, without sacrificing specific capacitance was attributed to the optimized PVA layer.     

Multilayer self-assembly of TiO₂ nanoparticles and polyaniline-grafted-chitosan copolymer (CPANI) for photocatalysis

A photocatalytic thin film of TiO? nanoparticles and polyaniline-grafted-chitosan (CPANI) was fabricated by layer-by-layer (LbL) approach. The growth of the self-assembly of polymer nanocomposite was monitored by UV-vis spectroscopy and the thin film morphology was analyzed from scanning electron microscopy (SEM). Poly(styrene sulfonate) (PSS) was used as a bridging layer between TiO? nanoparticles and CPANI. Incorporation of CPANI within the LbL self-assembly of polymer nanocomposites enhanced the dye degradation ability of the thin film. These results indicate that the presence of CPANI improves the adsorption of dye in the self-assembly. The effect of surface area and the amount of catalyst was also examined. The reusability of the thin films for dye degradation study ensures the stability of the self-assembly.     

Effect of impinging ion energy on the substrates during deposition of SiOx films by radiofrequency plasma enhanced chemical vapor deposition process

Radiofrequency (13.56 MHz) plasma enhanced chemical vapor deposition process is used for deposition of SiO_x films on bell metal substrates using Ar/hexamethyldisiloxane/O₂ glow discharge. The DC self-bias voltage developed on the substrates is observed to be varied from − 35 V to − 115 V depending on the RF power applied to the plasma. Plasma potential measurements during film deposition process are carried out by self-compensated emissive probe. The deposited films are characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, nano-scratch test and thermogravimetric analysis. The characterization results show strong dependency of the SiO_x films properties on the energy of the ions impinging on the substrates during deposition. Analysis of Raman spectra indicates an increase in vitreous silica content and reduction in defective Si-O-Si chemical structure in the deposited SiO_x films with increasing ion energy impinging on the substrates. The increase in inorganic (Si and O) content in the SiO_x films is further confirmed from XPS analysis. The growth of SiO_x films with more inorganic content and defect free chemical structure apparently contribute to the increase in their hardness and scratch resistance behavior. The films show higher thermal stability as the energy of the ions arriving at substrates increases with DC self-bias voltage. The possibility of using SiO_x films for surface protection of bell metal is also explored.     

Low temperature aqueous chemical synthesis of CdS sensitized ZnO nanorods

Cadmium sulfide nanoparticles (CNPs) sensitized zinc oxide nanorod arrays (ZNRs) were synthesized in the two step deposition process at relatively low temperature. The vertically aligned ZNRs were grown on the conducting glass substrates (FTO) using aqueous chemical method, followed by the deposition of CNPs at 70 °C using chemical bath deposition (CBD) technique. The samples were characterized by optical absorption, X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). Further, the photoelectrochemical (PEC) performance of ZNRs with and without CNPs sensitization was tested in Na₂S-NaOH-S and Na₂SO₄ electrolyte, respectively. When the CNPs are coated on the ZNRs, the optical absorption is enhanced and band edge is shifted towards visible region (525 nm) as compared with ZNRs (375 nm). The sample sensitized with CNPs shows higher photoelectrochemical (PEC) performance with maximum short circuit current of (I_sc) 2.60 mA/cm².     

Studies on Isolation and Characterization of Starch from Rajgeera Grains (Amaranthus paniculatus Lin.)

Isolation and some of the important physicochemical properties of starch from rajgeera grains have been investigated. The yield of starch was about 61.2%, on whole grain basis. The results on physicochemical properties revealed that it exhibited moderate swelling and higher solubility (55.5%) in water, as compared to other millet starches. An extensive solubility in dimethylsulphoxid (72.5%) of the starch indicated easy penetration of solvent in a granular matrix, may be due to labile and heterogenous bonding forces within the granules. Brabender viscoamylographic data on pasting characteristics revealed that it yielded low viscosity (448 B. U.) at concentration of 10% (w/v) and showed very little tendency to retrograde during cooling of the starch paste. The amylopectin content was 88.5% indicating the starch of rajgeera is probably waxy in nature. Amylolytic digestibility of native and gelatinized starch of rajgeera by human salivary α-amylase and glucoamylase was investigated.     

Kinetics of colour and texture changes in Gulabjamun balls during deep-fat frying

Gulabjamun, a popular Indian milk sweet, is prepared by deep-fat frying of balls of dough made of khoa, wheat flour and baking powder, and subsequent dipping in sugar syrup. Kinetics of colour and texture changes in gulabjamun balls were investigated with regard to frying temperature (120, 130, 140 °C). Crust colour was evaluated in terms of CIELAB parameters L*, a*, b*, and ΔE, and rheological properties in terms of hardness, stiffness and firmness. Frying-induced surface browning was reflected in a decreasing lightness value L* as well as the ratio of yellow hue index b* and red hue index a* and total colour expressed in terms of ΔE, L* following a zero-order change whereas the other parameters, a first-order change. Increase in the texture parameters hardness and firmness followed zero-order reaction kinetics whereas stiffness rise followed a first-order reaction. The temperature dependence of reaction constants could be explained by the Arrhenius equation. Activation energy was also obtained for both the colour and texture changes, which were in the range of 24.5-77.6 kJ/mol. High correlations between colour and texture parameters were observed and it was concluded that L* alone could be used to predict the firmness of deep-fat fried gulabjamun balls.