654 research outputs found
Sort by
Hydrolytic degradation of polylactic acid (PLA) and its composites
No full textBiodegradable polymers are seen as a potential solution to the environmental problems generated by plastic waste. In particular, the renewable aliphatic polyesters of poly(hydroxyacid)-type homopolymers and copolymers consisting of polylactic acid (PLA), poly(glycolic acid) (PGA), and poly(e-caprolactone) (PCL) constitute the most promising bioresorbable materials for applications in biomedical and consumer applications. Among those polymers, PLA has attracted particular attention as a substitute for conventional petroleum-based plastics. PLA is synthesized by the fermentation of renewable agricultural sources, including corn, cellulose, and other polysaccharides. Although some of its characteristics are disadvantageous (e.g., poor melt properties, mechanical brittleness, low heat resistance, and slow crystallization), there exist potential routes to resolve these shortcomings. These include copolymerization, blending, plasticization modification, or the addition of reinforcing phases (e.g., chitosan (Cs), cellulose, and starch). In this review, we discuss the degradation mechanisms of PLA and its modified form in the environment, current issues that hinder the achievement of good Cs/PLA combination, and ways to overcome some of these problems. Furthermore, our discussion is extended to cover the subjects of hydrolytic degradation and weathering effects with different Cs/PLA blends
Realization of all optical logic gates using universal NAND gates on photonic crystal platform
No full textIn this paper, the design of all-optical logic gates using the combination of universal NAND gates has been proposed. The photonic crystal structure consists of triangular lattice arrangement of air holes in silicon. Initially, the all optical NAND gate has been designed and optimized. Further, the optimized NAND gates have been used and arranged in a combination such that the combined structure behaves as an all-optical logic gate specifically, NOT, AND, OR, XOR and XNOR. The truth table for the designed all-optical logic gates has been verified at an operating wavelength of 1.55 μm. The proposed all optical gates exhibit a response period of 2.168 ps with a bit rate of 0.461 Tb/sec. Further, the contrast ratio for the designed gates has also been obtained
Selective electrochemical sensing for arsenite using rGO/Fe3O4 nanocomposites
No full textHerein, we report rGO/Fe3O4 nanocomposites (NCs) free from noble metals, synthesized by facile one step chemical reduction method, for electrochemical detection of arsenite in water by square wave anodic stripping Voltammetry (SWASV). The synthesized NCs were characterized for its optical, morphological and structural properties. The NCs modified glassy carbon (GCE), NCs/GCE, electrodes showed a higher sensitivity (0.281 μA/ppb) and lower LOD (0.12 ppb) under optimized experimental conditions. The proposed NCs/GCE electrodes show no interference towards arsenite species in the presence of common cationic interferants, namely, Cu(II), Pb(II), Ni(II), Co(II), Cd(II), Cr(II), Zn(II), etc. In addition, the proposed electrode demonstrates a good stability, reproducibility and potential practical application in electrochemical detection of arsenite
Experimental and theoretical study of hydroxyquinolines: hydroxyl group position dependent dipole moment and charge-separation in the photoexcited state leading to fluorescence
No full textOptical absorption and fluorescence (FL) spectra of 2-, 6-, 7-, 8-hydroxyquinolines (2-,6-,7- and 8-HQs) have been measured at room temperature in the wide range of solvents of different polarities, dielectric constant and refractive index. The ground state dipole moment (µ g) and excited state dipole moment (µ e) of 2-, 6-, 7- and 8-HQs were obtained using solvatochromic shift (SS) methods and microscopic solvent polarity parameters (MSPP). Change in the dipole moment (Δµ) between the ground and photo-excited states was estimated from SS and MSPP methods. DFT and TDDFT based theoretical calculations were performed for the ground and excited states dipole moments, and for vertical transitions. A significant enhancement in the excited state dipole moment was observed following photo-excitation. The large value of Δµ clearly indicates to the charge-separation in the photo-excited states, which in turn depends on the position of the hydroxyl group in the ring
Enhanced intrinsic fluorescence from carboxidized nano-sculptured thin films of silver and their application for label free dual detection of glycated hemoglobin
No full textEnhanced intrinsic fluorescence (~x103) from novel carboxidized nanosculptured thin films (CO-nSTFs) of silver is reported. The sources of intrinsic fluorescence, confirmed by X-ray photoelectron spectroscopy, are Ag2O grains and residual carbon formed on the outer layer of silver nSTFs when exposed to air, while the localized surface plasmons on silver nSTFs enhance this intrinsic fluorescence. The CO-nSTFs are optimized with respect to porosity for the maximum enhancement. A sensor developed by using the self-assembled monolayer technique on optimized CO-nSTF is used for the label free detection of glycated hemoglobin, performed by simultaneously using fluorescence imaging and spectroscopy. The specificity of the sensor is established from control experiments on hemoglobin. These novel nanorod like intrinsically fluorescent CO-nSTFs pose huge potential in label free biosensing, light sources, imaging and many more applications
Recent advances in liquid-phase microextraction techniques for the analysis of environmental pollutants
No full textThe liquid-phase microextraction (LPME) method is a sample pretreatment technique that uses small volumes of organic solvents to extract a wide variety of analytes from different matrices prior to instrumental analysis. The development of these techniques focuses on providing simple, inexpensive, and environmentally friendly extraction procedures for sample preparation or pretreatment. In this review, the most recent developments in LPME techniques for the analysis of various environmental pollutants are summarized after being categorized into several groups such as dispersive liquid–liquid microextraction (DLLME), ferrofluid-based microextraction, supramolecular-based liquid phase microextraction, and vortex-assisted liquid–liquid microextraction. Moreover, the extraction principles, the solvent production mechanism, and the historical development of the LPME techniques are also discussed. Finally, recent reports on the applications of these methodologies are reviewed
Selective electrochemical sensing for arsenite using rGO/Fe3O4 nanocomposites
No full textHerein, we report rGO/Fe3O4 nanocomposites (NCs) free from noble metals, synthesized by facile one step chemical reduction method, for electrochemical detection of arsenite in water by square wave anodic stripping Voltammetry (SWASV). The synthesized NCs were characterized for its optical, morphological and structural properties. The NCs modified glassy carbon (GCE), NCs/GCE, electrodes showed a higher sensitivity (0.281 μA/ppb) and lower LOD (0.12 ppb) under optimized experimental conditions. The proposed NCs/GCE electrodes show no interference towards arsenite species in the presence of common cationic interferants, namely, Cu(II), Pb(II), Ni(II), Co(II), Cd(II), Cr(II), Zn(II), etc. In addition, the proposed electrode demonstrates a good stability, reproducibility and potential practical application in electrochemical detection of arsenite
A convenient electrolytic assembly of graphene-MOF composite thin film and its photoanodic application
No full textIn the recent past, the metal organic frameworks (MOFs) have been recognized as attractive photosensitizer materials due to their hierarchically ordered structures and attractive light-harvesting characteristics. In this work, we report the application of a graphene-MOF composite as a potential photosensitizer material in dye-sensitized solar cells (DSSCs). A thin film of graphene-MOF hybrid composite was electrochemically assembled on a TiO2/FTO substrate and the different characteristics of the prepared film were investigated. This novel photoanode material hybrid structure demonstrated the potency of an alternative solid-state DSSC configuration. The 2.2% observed power conversion efficiency of the above graphene-MOF composite is a good basis for the further development of graphene-MOF composite-based photoanodes
Structural analysis of PVP capped silver nanoparticles synthesized at room temperature for optical, electrical and gas sensing properties
No full textAn aqueous-phase method for the synthesis of polyvinylpyrrolidone (PVP) capped silver nanoparticles (AgNPs) at room temperature was developed, followed by wet chemical reduction method. The nanoparticles thus prepared were investigated for their optical properties, structural, thermal and electrical behavior using transmission electron microscopy (TEM), X-ray powder diffraction (XRD), UV–Vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR) thermogravimetric analysis (TGA) and current–voltage (I–V) characteristic respectively. The structural analysis showed that synthesized material is face-centered cubic (fcc) and monodispersed within the PVP matrix with an average size of 22 nm. The controlled size of the synthesized nanoparticles reveals that PVP played a critical role in controlling the radius and dispersibility of the nanoparticles. Electrical response showed a conductive and metallic nature. Ammonium gas sensing of the synthesized nanoparticles were investigated. It was found that the fabricated PVP capped AgNPs thin film showed the maximum sensitivity towards ammonia gas
Deep Seated Negative Axicon in Selective Optical Fiber Tip and Collimated Bessel Beam
No full textIn this letter, we have demonstrated the fabrication of a deep seated negative axicon (DSNA) with micrometer dimensions inside a selective optical fiber tip for the generation of optical Bessel beams (BBs). The DSNA is prepared by simple chemical etching of the fiber tip in hydrofluoric acid under the influence of capillary action. The selective optical fiber has a high numerical aperture of 0.3 and a small core diameter of about 4 μm. The higher etching rate of the optical fiber core contributes to fabricate the DSNA, which converts Gaussian-like beam into BB. The central spot of the BB shows quasi-invariant spot-size over the propagation distance of sub-millimeter and centimeter range. The self-protected DSNA can be useful for scanning optical fiber endoscopy applications as well as can be integrated into systems, where non-diffracting BB is preferred