Department of Electrical and Electronics Engineering

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Author: search.filters.author.Manjuladevi, V.

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    Structural and Optical Characterizations of Electrochemically Grown Connected and Free-Standing TiO2 Nanotube Array
    (Springer, 2014-05) Hazra, Arnab; Manjuladevi, V.; Gupta, Raj Kumar
    A TiO2 nanotube array was grown electrochemically by using single and mixed electrolyte/s with 20 V constant potential at room temperature. Anodization was carried out for 120 min using five different electrolytes, e.g., H3PO4, NH4F, HF, NH4F with H3PO4 and HF with H3PO4. Structural characterizations of the grown titania nanotubes were conducted by using x-ray diffraction and field emission scanning electron microscopy. Optical properties of the grown nanotubes were investigated through photoluminescence (PL) spectroscopy. In the case of the 4 M H3PO4 electrolyte, no perceptible growth of nanotubes was observed. The individual electrolytes of 0.3 M NH4F and 1 M HF resulted into the formation of the wall-connected nanotubes. In contrast, the mixed electrolytes comprising the strong (NH4F, HF) and weak (H3PO4) electrolytes have been found to be efficient for the growth of wall-separated titania nanotubes. The results of the PL spectroscopy have demonstrated that the free-standing nanotubes offer low PL intensity compared to its connected counterpart owing to the lower carrier recombination rate of free-standing nanotubes.
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    Detection of cadmium ion in aqueous medium by simultaneous measurement of piezoelectric and electrochemical responses
    (Elsevier, 2018-09) Gupta, Karunesh Kumar; Gupta, Raj Kumar; Manjuladevi, V.
    Cadmium is one of the important heavy metals which poses health hazards due to its consumption through potable water. Cadmium is known to form complexes with amine group and also it has good affinity towards carbon nanotubes. The octadecylamine functionalized single-walled carbon nanotubes (ODACNTs) can be employed for sensing cadmium ion in aqueous medium. A thin film of ODACNTs offers not only strong adsorption properties towards cadmium ion but also provides an enormous gain in surface to volume ratio, and good mechanical and chemical stability. Therefore, a sensing layer of ODACNTs was formed on the gold deposited quartz wafer and the sensing towards cadmium ion in the aqueous medium was performed. An experimental setup was designed to record the electrochemical and piezo-responses simultaneously. The piezo and electrochemical responses were found to be linear in the given concentration range. Interestingly, the piezoresponse modulates systematically and repeatedly from a maximum to minimum value due to voltage sweep during cyclic voltammetry indicating the interfacial phenomenon of adsorption and desorption.
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    Facile ultrathin film of silver nanoparticles for bacteria sensing
    (Elsevier, 2020-12) Gupta, Karunesh Kumar; Gupta, Raj Kumar; Manjuladevi, V.
    Silver nanoparticles (AgNPs) exhibit excellent anti-microbial and bactericidal properties. Due to bacterial abhorrence for AgNPs, it is difficult to develop a label-free, sensitive and low-cost bacteria sensor using them. In the present article, we report that an ultrathin and uniform Langmuir–Schaefer (LS) film of AgNPs can be employed for bacteria sensing effectively as compared to that of non-uniform and randomly distributed AgNPs in spin coated film. The uniformly distributed AgNPs in the LS film offer a relatively larger contact surface for bacteria as compared to that of spin coated film. Due to higher contact surface, adsorption of the bacteria on LS film is strongly preferable as compared to that of spin coated film leading to an enhanced sensing performance of the LS film than that of spin coated film. Soil bacteria was grown by the standard protocol and were utilized as model system for bacteria sensing application. The soil bacteria sensing was done by monitoring the piezoresponse and dissipation parameters using a quartz crystal microbalance, simultaneously. Our study indicates that the LS film of AgNPs not only facilitates the adsorption of the soil bacteria but also kills them.
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    Heavy Metal Ion Sensing using Ultrathin Langmuir-Schaefer Film of Tetraphenylporphyrin Molecule
    (IEEE, 2020) Gupta, Raj Kumar; Gupta, Karunesh Kumar; Manjuladevi, V.; Kumar, Dalip
    The exciting properties of porphyrin molecules can be employed for several applications like sensing, catalysis, photovoltaics and energy related fields. The assemblies of the molecules at interfaces can give rise to some unique physicochemical properties which can enhance the device performance. In this article, we report our studies on heavy metal ion sensing in aqueous medium using ultrathin film of tetraphenylporphyrin (TPP) molecules. The TPP molecules were synthesized and used for forming Langmuir monolayer at the air-water interface. The monolayer was transferred onto solid substrates by Langmuir-Schaefer (LS) method at different target surface pressure of deposition (πT). The morphological analysis of the films indicated supramolecular assembly of the molecules in the LS film deposited at πT = 30 mN/m. The LS films of TPP molecules were employed for sensing heavy metal cations viz. Pb 2+ , Hg 2+ , Co 2+ and Cd 2+ from the aqueous medium by measuring piezoresponse from a quartz crystal microbalance. The sensing performance was found to be the best with LS film deposited at πT = 30 mN/m. The sensitivity-towards Pb 2+ ion is found to be the highest. The sensing of the heavy metal cations using randomly oriented TPP molecules in spin coated thin film was found to be much inferior as compared to that of LS films of the molecule. The enhanced sensing performance by the LS film of TPP molecules may be attributed to the supramolecular assembly of the molecules. We report that the interference of the sensing measurement for the recognition of Cd 2+ and Pb 2+ ions is least and thus these species can be detected selectively with less errors. The cation species recognition features obtained from scanning electron microscope images and Raman spectroscopy were found to be remarkably different and therefore these cationic heavy metal species can be selectively detected using the LS film of TPP