Faculty Publications
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Item Quantification and morphology studies of nanoporous alumina membranes: A new algorithm for digital image processing(2013) Choudhari, K.S.; Jidesh, P.; Sudheendra, P.; Kulkarni, S.D.A new mathematical algorithm is reported for the accurate and efficient analysis of pore properties of nanoporous anodic alumina (NAA) membranes using scanning electron microscope (SEM) images. NAA membranes of the desired pore size were fabricated using a two-step anodic oxidation process. Surface morphology of the NAA membranes with different pore properties was studied using SEM images along with computerized image processing and analysis. The main objective was to analyze the SEM images of NAA membranes quantitatively, systematically, and quickly. The method uses a regularized shock filter for contrast enhancement, mathematical morphological operators, and a segmentation process for efficient determination of pore properties. The algorithm is executed using MATLAB, which generates a statistical report on the morphology of NAA membrane surfaces and performs accurate quantification of the parameters such as average pore-size distribution, porous area fraction, and average interpore distances. A good comparison between the pore property measurements was obtained using our algorithm and ImageJ software. This algorithm, with little manual intervention, is useful for optimizing the experimental process parameters during the fabrication of such nanostructures. Further, the algorithm is capable of analyzing SEM images of similar or asymmetrically porous nanostructures where sample and background have distinguishable contrast. Copyright © Microscopy Society of America 2013.Item Ru–TiO2 semiconducting nanoparticles for the photo-catalytic degradation of bromothymol blue(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Kulkarni, R.M.; Malladi, R.S.; Hanagadakar, M.S.; Doddamani, M.R.; Santhakumari, B.; Kulkarni, S.D.Photo-catalytic degradation of bromothymol blue (BTB) in an aqueous medium by Ru–TiO2 using UVC (254 nm) irradiation was investigated for a pH range of 4.0–8.0. The liquid impregnation method was used to synthesize 0.2, 0.4 and 0.8 % ruthenium doped TiO2 (Ru–TiO2) nanoparticles. The characterizations of resulting nanoparticles were done using X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy analysis. The crystallite sizes of doped and undoped nanoparticles were determined from X-ray diffraction spectra using Scherrer equation. The average crystallite size of undoped TiO2 was found to be 17.00 nm, whereas the crystallite sizes of 0.2, 0.4 and 0.8 % Ru–TiO2 were 16.67, 15.70 and 14.40 nm respectively. The TEM images confirm the particle sizes to be 10–40 nm. Pseudo-first order rate constants (kobs) determined were found to decrease with increase in pH. The effect of BTB Concentration, catalyst dosage, a percentage of doping of photo catalyst, pH and UV light intensity of BTB on the degradation rate were also examined. © 2016, Springer Science+Business Media New York.Item Boronic Acid-Based n-Type Semiconductor for Electronic Device Application(Springer, 2022) Kagatikar, S.; Dhanya, D.; Kekuda, D.; Satyanarayana, M.N.; Kulkarni, S.D.; Karkera, C.Electron transporting, or n-type, semiconductors can serve as charge-transport materials, and are ideal for use in organic electronic devices. Boron-based small organic molecules have garnered immense research attention as the heteroatom can effectively alter the electronic structures leading to excellent photophysical and electrochemical properties. A luminescent Schiff base (E)-(4-((2-(2-hydroxybenzoyl)hydrazono)methyl)phenyl)boronic acid (SHB) was prepared by a one-pot condensation reaction between salicyloyl hydrazide and formylphenylboronic acid. The synthesized molecule was chemically characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, and mass spectrometry. The blue-emitting boronic acid-derived molecule displayed intramolecular charge transfer, high carrier concentration, good thermal stability, a reversible reduction tendency and formation of uniform amorphous thin films. A diode was successfully fabricated via a solution processing technique with an ideality factor of 7.76. Further, AC conductivity, dielectric constant, dielectric loss, and capacitance values in a frequency range of 10–1000 Hz were extracted from dielectric studies. The dielectric constant of SHB was found to be 9.71 with an AC conductivity of 6.34 × 10−9 Ω−1 cm−1 at 1000 Hz. Graphical Abstract: [Figure not available: see fulltext.] © 2022, The Author(s).Item Dual emissive water-based flexo ink from tapioca-derived carbon dots for anti-counterfeiting applications(Elsevier B.V., 2022) Ullal, N.; Lewis, P.M.; Dhanya, D.; Kulkarni, S.D.; P.j, A.; K, U.B.Counterfeiting of high-value items is a challenging menace worldwide, and luminescent nanoparticles-based security inks have promising applications while addressing this global issue. As Carbon dots (CDs) show attractive functional properties, hydrophilic CDs were prepared through hydrothermal approach from tapioca starch as an eco-friendly precursor. CDs with bluish-green fluorescence emission under 365 nm UV light illumination was obtained using column chromatography technique. TCSPC studies indicated the presence of blue and green emitters with average lifetimes of 1.12 and 1.61 ns, respectively. The graphitic and polycrystalline nature of CDs (~9 nm) with negatively charged surface groups was confirmed through ATR-IR, XPS, RS, XRD, SAED, DLS and TEM. An eco-friendly water-based security ink for flexography printing was formulated, and the influence of the ink components on the fluorescence of CDs were studied. The prints on UV dull paper displayed good abrasion resistance, densitometry and colorimetric values. The letters written using the invisible ink exhibited good security features including excellent covertness under daylight, and a bluish-green emission under 365 nm UV light. Moreover, a yellow emission was perceived using a yellow-orange pass filter under the same light source. The surface morphology and electrical property investigations suggested the use of flexo-ink in flexible printed electronics for anti-counterfeiting. These results propose that Tapioca-derived CDs can enable unique optical features in its eco-friendly ink formulation to demonstrate promising security applications. © 2022 Elsevier B.V.Item Pyrene-based chalcones as functional materials for organic electronics application(Elsevier Ltd, 2023) Kagatikar, S.; Dhanya, D.; Kekuda, D.; Satyanarayana, M.N.; Kulkarni, S.D.; Sudhakar, Y.N.; Vatti, A.K.; Sadhanala, A.Though new generation organic electronic devices have evolved from mere scientific perceptions to real-life marketed applications, considerably less research attention has been focused on n-type or electron transporting small molecule semiconductors. The present study is focused on the exploration of structural, thermal, electrochemical, electrical, and optical properties of two pyrene-based chalcones: PC1 and PC2, synthesized through Claisen Schmidt condensation reaction. The chalcones displayed good thermal stability and wide bandgap n-type semiconducting behaviour with high charge carrier concentration and dielectric constant. The experimental evidences including fluorescence measurements, nanoaggregate size, and morphology analysis, supported by DFT calculations and molecular dynamic simulations advocated the intramolecular charge transfer and aggregation-induced enhanced emission features of the molecules. Successful fabrication of a diode in combination with the current-voltage characteristics established the candidature of PC1 and PC2 for electro-optical devices. The dielectric studies were performed to measure dielectric constant and AC conductivity at different frequency ranges. The cyclic voltammetry and AC impedance response of PC2 differed from PC1 due to the inclusion of a fluorine atom in the molecular scaffold. Further, the functional implication of PC2 as an electrode material was explored by constructing a supercapacitor, which offered a specific capacitance of 220 Fg-1 at a scan rate of 10 mV s−1. Moreover, these chalcone-based organic semiconductors displayed high thermal and charge carrier concentration as well as compatibility with other layers in an OLED device. Hence PC1/PC2 can be further investigated as dopants along with other emissive layers as host materials in OLEDs. © 2022 Elsevier B.V.Item Improvement of third-order NLO properties of vacuum deposited Cd1-xPbxS nanostructured thin films for optoelectronic device applications(Elsevier Ltd, 2023) Bairy, R.; Vijeth, H.; Kulkarni, S.D.; Murari, M.S.; Bhat K, U.K.A polycrystalline nanostructured cadmium lead sulfide thin film was deposited using the thermal evaporation (PVD) technique (Cd1-xPbxS with x = 0.00, 0.01, 0.05 and 0.1 wt.% of Pb). Structural parameters of as-prepared Cd1-xPbxS thin films have been studied through X-ray diffraction. The optical investigation demonstrates that Cd1-xPbxS film's optical band gap (Eg) may be adjusted from the visible to the near-infrared region. (2.64 - 2.42 eV). The film is substantially more appropriate for absorbing layers in solar cells and optoelectronic applications due to the large decrease in ‘Eg.’ The enhanced Pb doping was found to have altered the surface morphology, verified by Field Emission Scanning Electron Microscopy (FESEM) images. The doped films also showed a significant red shift in the band edge and increased transmittance in the visible and NIR regions. The third-order nonlinear optical (TONLO) parameters of the samples were determined from the Q-switched Nd: YAG laser with 65-ps pulse duration at 1064 nm. The investigated TONLO components such as nonlinear absorption coefficient (β), nonlinear refractive index (n2) and the susceptibility χ(3)were found to be in the range from 1.16 × 10−3 to 4.12 × 10−3 (cmW−1), 1.06 × 10−8 to 3.32 × 10−8 (cm2 W−1) and 1.23 × 10−4 to 5.62 × 10−4 (esu) respectively. The results indicate that Pb-doping on CdS nanostructures on surface morphology can be used to modify NLO characteristics.Cd1-xPbxS thin film is a potential and able material for optoelectronic device applications, as seen by these encouraging NLO results. © 2023 Elsevier LtdItem Eco-friendly ink formulation of column purified carbon dots from GABA for anticounterfeiting applications(Elsevier B.V., 2023) Ullal, N.; Dhanya, D.; Kulkarni, S.D.; Sinha, R.K.; Anand, P.J.; Bhat K, U.K.Forgery of valuable products causes a negative impact on the society as well as the economy of the country. There is a growing demand to not only differentiate or authenticate genuine documents/products but also to protect their integrity. Carbon dots (CDs) are a class of fluorescent nanomaterials that are well-known for their facile synthesis, good photostability and less toxicity profile. The current research work focuses on the preparation of CDs via hydrothermal method using γ-aminobutyric acid (GABA) that contains amino and carboxylic groups. Column chromatography technique is adopted to purify the GABA-derived CDs from the reactants and by-products. The fourth fraction obtained after column purification containing CDs with fluorescence emission in the visible region is chosen for further studies. The presence of spherical CDs confirmed through TEM imaging are chemically characterised using SAED, EDS, DLS, FTIR, XPS, Raman and XRD spectroscopy. The blue (λem = 490 nm) and green (λem = 538 nm) emitting CDs present in the fourth fraction displayed a fluorescence lifetime of 1.90 ns and 2.02 ns. Theoretical studies are performed using B3LYP/6-31G(d,p) theory level on different plausible structures. The HOMO-LUMO band gap of 2.3 eV deduced using DFT calculation is in close agreement with the optical band gap of 2.6 eV derived from Tauc plot. A complex forming mechanism is proposed for the fluorescence quenching of CDs upon examining the EDS data of the precipitate obtained upon addition of cupric ions. Further, the CDs are used as pigments to formulate a water-based ink for flexographic printing on UV-dull paper substrate. The printed samples exhibited good colorimetric values, lightfastness, and rub resistance. The security features of the ink film include an UV-induced yellow fluorescence, which will be known to the forger and a secondary quenching of fluorescence when exposed to cupric ions, which can be used by the user to validate document/product authenticity. This stimulus responsive optical property is also explored in the design of ionochromic security paper based on cupric ion induced fluorescence quenching of CDs for data storage and decryption. Moreover, the lesser surface roughness and electrical parameter values obtained for the print proofs could be further explored for the potential application of CD-derived ink in electronic anticounterfeiting. © 2023 Elsevier B.V.Item Pistachio shell-derived carbon dots and their screen-printing formulation for anticounterfeiting applications(Springer, 2024) Chinmayi, H.D.; Ullal, N.; Dhanya, D.; Kulkarni, S.D.; Anand, P.J.; Udaya Bhat, K.In synergy with constructing a sustainable environment, facile reuse of carbon-rich biowastes as inexpensive precursors for the synthesis of value-added functional carbon dots (CDs) has garnered fruitful outcomes. Pistachio shells comprising cellulose, hemicellulose, and lignin were successfully utilized as a carbon source for the synthesis of CDs through carbonization and subsequent hydrothermal method. The methanolic fraction with desirable fluorescence in the visible region obtained after column purification of CDs was further characterized using TEM, EDS, SAED, FTIR, XPS, RS, XRD, and TCSPC techniques. The blue and green emitting CDs were used as colorants to prepare a water-based ink for screen printing. The screen prints on UV dull paper substrate exhibited good colorimetric and density values. The UV-induced yellow fluorescence of the ink film can be used as a security feature to authenticate genuine document/products and data storage. Graphical abstract: (Figure presented.). © American Coatings Association 2024.Item Yellow emissive and high fluorescence quantum yield carbon dots from perylene-3,4,9,10-tetracarboxylic dianhydride for anticounterfeiting applications(Royal Society of Chemistry, 2024) Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Bhat K, U.; Anand, P.J.Forged products are widespread in the market and there is an immediate need to counter this growing menace. Anti-counterfeit techniques using fluorescent materials with covert features that appear hidden under daylight and display characteristic fluorescence upon specific source irradiation have gained popularity. Carbon dots (CDs) that can be prepared through facile synthesis from various raw materials are a class of fluorescent materials that provide tremendous opportunities to combat counterfeiting. This work focuses on the fabrication of perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) derived CDs via the solvothermal approach and their subsequent purification using column chromatography. The fifth fraction obtained exhibited remarkable yellow emission (λem = 540 nm) with a high fluorescence quantum yield of 53.22% and a lifetime of 4 ns. The CDs appeared quasi-spherical during TEM imaging with an average diameter of 1-3 nm and appeared polycrystalline from the SAED pattern. The XPS and TEM-EDS results suggested carbon as the major element along with oxygen and nitrogen as the other heteroatoms. The water-based ecofriendly ink formulated using the CDs was printed on UV dull paper using the flexography technique. The print-proof paper samples appeared pale pink under daylight and fluorescent yellow upon 365 nm UV illumination. Moreover, the stability of the print was confirmed upon exposure to strong UV radiation cycles and abrasion resistance. Besides, the fluorescence emission remained unaltered even after 5 months of storage under room temperature conditions. The ink was used to print on PVC sheets and FBB boards with good stability against scuffing, suggesting its applicability in the packaging industry. The CDs could also serve as fluorescent markers for identifying post-consumer plastic packaging for a circular economy. © 2024 The Royal Society of Chemistry.Item 5,10,15,20-Tetrakis(p-tolyl)porphyrin derived carbon dots as colorant in flexo and screen inks with multi-level covert features for security printing(Elsevier B.V., 2024) Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Sinha, R.K.; Anand, P.J.; Udaya, B.K.Fluorescent inks with covert security features, which make it difficult for forgers to replicate, are highly sought after among the array of anti-counterfeit technologies. The present study focuses on the synthesis of Carbon dots (CDs) from 5,10,15,20-tetrakis(p-tolyl)porphyrin (TTP) via a solvothermal approach. The prepared CDs exhibit attractive emissive characteristics with an absolute fluorescence quantum yield of 38.85 %. Time-resolved fluorescence studies reveal the multiple exponential decay nature of the emitters, which could be due to the diverse chemical environment on the surface of the CDs. XPS analysis proves oxygen as the major element, along with carbon, sulfur, and nitrogen as minor elements. DFT studies on four optimized structures of CDs along with their respective UV and FT-IR plots are conducted. The theoretically derived photoluminescence plots corresponding to the 25-30th excited states coincide with the experimental emission peak. CDs demonstrate characteristic variations in fluorescence in the presence of water, attributed to ?-? stacking induced aggregation. Aggregate formation is also influenced by pH changes, affecting the surface functional groups in proximity to the solvent medium. CDs are used as colorants in the fabrication of both flexo and screen inks. Flexo ink retains the fluorescence features of the CDs, while screen ink offers multilevel security features. Exposing UV-dull paper to 365 nm UV light allows the ink inscribed letters to appear fluorescent blue, whereas the use of UV/green optical filters facilitates the visualization of green/yellow emissions. The introduction of multilevel features makes the duplication of the print difficult, protecting the integrity of the product and could be used for real-life applications. © 2024 The Author(s)