Jisha J. Pillai

Bio: Jisha J. Pillai is an academic researcher from Cochin University of Science and Technology. The author has contributed to research in topics: Photocurrent & Quenching (fluorescence). The author has an hindex of 3, co-authored 6 publications receiving 27 citations.

Photoluminescence and optical nonlinearity of CdS quantum dots synthesized in a functional copolymer hydrogel template

Abstract: A hydrogel template assisted synthesis was employed to prepare CdS quantum dots (QDs) in poly(methyl methacrylate-co-acrylic acid), p(MMA-co-AAc), for the ultimate formation of a nanocomposite. The copolymer hydrogelates in an aqueous solution of precursor reagents and acts as a template for the absorption of Cd2+ ions, which is followed by CdS QD formation. The CdS QDs are positioned inside the core of the micelles in the copolymer hydrogel. The ultraviolet-visible (UV-vis) absorption and band edge emission of the composite solution are blue shifted relative to bulk CdS. The composition of acrylic acid (AAc) in the copolymer has an influence on the size as well as on the surface effect of the CdS QDs, which is reflected in the photoluminescence (PL) of the composite. The copolymer is capable of passivating CdS QDs for intense band edge emission with weak defect state emission. The z-scan technique gives an exhibition of the nonlinear refraction and absorption of the composite, which are determined by the AAc content and thus the size of the CdS QDs present in the composite. The composites show self defocusing phenomena for their negative nonlinear refraction. The magnitude of nonlinear refractive index increases with the CdS QD size. The copolymer with a large number of AAc units forms a CdS QD composite with reverse saturable absorption (RSA) near the focus and saturable absorption (SA) at the focus. The RSA behavior of the composites shows that they can be used in optical limiting devices.

Stretching the sensitivity and stability of an acrylamide based photopolymer material with mixture of dyes

Abstract: The limited absorption range of photopolymers in the visible region was always a matter of concern due to their wide-spread application in the field of holography. The present work has investigated the possibility of extending the limited absorption range towards the entire visible range by simple modifications in the photopolymer composition so that panchromaticity can be invoked in the material. Here modification was done on already developed photopolymer material by adding another photosensitizer. Studies showed that holographic performance was improved to a great extent. It was possible to record gratings with blue, green and red wavelengths in 130 µm thick films with more than 80% diffraction efficiency (DE) creating a refractive index modulation of ∼1.7 × 10−3 at exposure energy of 50 mJ/cm2. This material will be a good candidate for data storage and color holographic applications. One of the remarkable findings was that the storage and shelf life of the material could be extended compared to other photopolymer materials. This material could be used to write gratings with 70% DE even after 12 months of storage. Thus, addition of a second photosensitizer not only extended the absorption range, but also the shelf life of the photopolymer.

An in situ approach for the synthesis of a gum ghatti-g-interpenetrating terpolymer network hydrogel for the high-performance adsorption mechanism evaluation of Cd(II), Pb(II), Bi(III) and Sb(III)

Abstract: Herein, gum ghatti-g-(N-isopropylacrylamide-co-3-(N-isopropylacrylamido) propanoic acid-co-sodium acrylate) (GTINIAMSA), a novel interpenetrating terpolymer network hydrogel with unprecedented thermomechanical and physicochemical properties and excellent recyclability, was synthesized via the grafting of gum ghatti (GTI) and the in situ strategic protrusion of 3-(N-isopropylacrylamido) propanoic acid (NIPAMPA) during the solution polymerization of sodium acrylate (SA) and N-isopropylacrylamide (NIPAm) using N,N′-methylenebisacrylamide (MBA) and potassium persulfate (PPS)/sodium bisulfite (SBS) as a cross-linker and redox pair of initiators, respectively, through the systematic multistage optimization of the constituents and the reaction temperature for a comprehensive understanding of the superadsorption mechanism of hazardous metal ions, i.e. M(II/III), like Cd(II), Pb(II), Bi(III) and Sb(III). The unorthodox in situ attachment of NIPAMPA, grafting of GTI into NIPAm-co-NIPAMPA-co-SA (NIAMSA) matrix and the superadsorption mechanism were systematically investigated via extensive unloaded and/or loaded microstructural analyses by FTIR, 1H-/13C-NMR, C 1s-/O 1s-/Cd 3d5/2,3/2-/Pb 4f7/2,5/2-/Bi 4f7/2,5/2-/Sb 3d3/2-XPS, TGA, XRD, FESEM and EDX, along with the measurements of the %gel content (% GC), pH at point of zero charge (pHPZC), % graft ratio (% GR) and network parameters of the hydrogels. The prevalence of ionic (I) and variegated coordinative interactions, such as monodentate (M), bidentate bridging (BB) and bidentate chelation (BC), between GTINIAMSA and M(II/III) were also investigated by FTIR and the fitting of kinetics data to a pseudo-second-order model as well as by the measurements of the activation energies of adsorption. The equilibrium adsorption data of M(II/III) were fitted excellently to the Langmuir isotherm model. The thermodynamically spontaneous chemisorption processes showed the excellent maximum adsorption capacities (ACs) of 1477.83, 1568.81, 1582.38 and 1518.09 mg g−1 for Cd(II), Pb(II), Bi(III), and Sb(III), respectively, at 303 K with an adsorbent dose of 0.02 g and initial concentration of M(II/III) = 500–800 ppm.

Tetrapolymer Network Hydrogels via Gum Ghatti-Grafted and N-H/C-H-Activated Allocation of Monomers for Composition-Dependent Superadsorption of Metal Ions.

Abstract: Herein, gum ghatti (GGTI)-g-[sodium acrylate (SA)-co-3-(N-(4-(4-methyl pentanoate))acrylamido)propanoate (NMPAP)-co-4-(acrylamido)-4-methyl pentanoate (AMP)-co-N-isopropylacrylamide (NIPA)] (i.e., GGTI-g-TetraP), a novel interpenetrating tetrapolymer network-based sustainable hydrogel, possessing extraordinary physicochemical properties and excellent recyclability, has been synthesized via grafting of GGTI and in situ strategic protrusion of NMPAP and AMP during the solution polymerization of SA and NIPA, through systematic multistage optimization of ingredients and temperature, for ligand-selective superadsorption of hazardous metal ions (M(II)), such as Sr(II), Hg(II), and Cu(II). The in situ allocation of NMPAP and AMP via N-H and C-H activations, grafting of GGTI into the SA-co-NMPAP-co-AMP-co-NIPA (TetraP) matrix, the effect of comonomer compositions on ligand-selective adsorption, crystallinity, thermal stabilities, surface properties, swellability, adsorption capacities (ACs), mechanical properties, and the superadsorption mechanism have been apprehended via extensive microstructural analyses of unloaded and/or loaded GGTI-g-TetraP1 and GGTI-g-TetraP2 bearing SA/NIPA in 8:1 and 2:1 ratios, respectively, using Fourier transform infrared (FTIR), 1H/13C/DEPT-135 NMR, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, differential scanning calorimetry, X-ray diffraction, field emission scanning electron microscopy, rheological analysis, and energy-dispersive X-ray spectrometry, along with measuring % gel content, pH at point of zero charge (pHPZC), and % graft ratio. The thermodynamically spontaneous chemisorption has been inferred from FTIR, XPS, fitting of kinetics data to pseudo-second-order model, and activation energies. The chemisorption data have exhibited excellent fitting to the Langmuir isotherm model. For Sr(II), Hg(II), and Cu(II), ACs were 1940.24/1748.36, 1759.50/1848.03, and 1903.64/1781.63 mg g-1, respectively, at 293 K, 0.02 g of GGTI-g-TetraP1/2, and initial concentration of M(II) = 500-1000 ppm.