Browsing by Author "K, U.B."

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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.
Fluorene-vanillin hybrid: A multifunctional fluorophore for latent fingerprint detection and sustainable offset security ink development
(Elsevier B.V., 2025) K Jain, R.; P.j, A.; Dhanya, D.; Bhagavath, P.; Vatti, A.K.; Mahadeva Prasad, M.P.; K, U.B.; Alex, A.
Fluorophores play a pivotal role in forensic science and anticounterfeit applications due to their unique and distinct emission features, which enable visualization and authentication. In the pursuit for advanced fluorescent pigments, ortho vanillin-fluorene Schiff base (OAF) with bright orange fluorescence was synthesized using a cost-effective, simple, and one-step method. This fluorophore was highly effective in developing latent fingerprints (LFPs), enabling visualization of level 1–3 features on nonporous glass and semi-porous leather under 365 nm UV light. The interaction between glycine in the fingerprint residue on glass substrate and OAF was analyzed through computational studies and further validated using ATR-FTIR analysis. The FESEM images of the latent prints revealed detailed surface morphology and particle distribution on the ridges of the fingermarks. Further, fluorescent images of LFPs were successfully developed on sticky paint, moist glass, multicolored compact disc, and uneven leaf surface, demonstrating the material's versatility on challenging substrates. Moreover, the powder dusting of composite powder of OAF and JUP-AS120, a commercially available pigment enabled enhanced LFP visualization on glass under both 365 and 980 nm light sources for better contrast and minimal background fluorescence, while minimising degradation of fingerprint residues over time. In addition, an OAF spray was formulated using nitrocellulose resin, ethyl acetate and carbitol for broader forensic application, which facilitated LFP visualization down to fine minutiae details on porous, semi-porous and non-porous substrates. Furthermore, to address the growing rates of counterfeited products/banknotes/security documents, an ecofriendly composite security ink was formulated using OAF and JUP-AS120 to obtain offset prints with excellent resistance to photobleaching and scuffing on paper substrate. The ink film exhibited multilevel authentication features: orange fluorescence under a 365 nm light source, and green and red emissions without and with a 610 nm band pass filter, respectively under 980 nm laser source, enhancing security and making forgery more challenging. Additionally, biocompatible OAF can be incorporated in ink pads to offer a dual layer of validation for fingerprints on security documents: optical authentication by leveraging the ink's fluorescence properties and biometric recognition through fingerprint patterns. © 2025 The Author(s)
Investigation of column purified dye derived carbon nanomaterials for security printing and supercapacitor applications
(Elsevier B.V., 2024) Mehta, R.; Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Sudhakar, Y.N.; Abdul Salam, A.A.; K, U.B.; Anand, P.J.
Literature evidence reveals versatile applications of carbon dots (CDs), but generally mixtures of various types of carbon nanomaterials, molecular intermediates as well as side products are obtained upon hydrothermal treatment of the precursor material. This demands isolation of pure components and their complete characterization before these nano carbonaceous materials are chosen for suitable applications. In the present study, perylenetetracarboxylic dianhydride (PTCDA) is subjected to hydrothermal treatment and the mother liquor obtained is separated using column chromatography technique using dichloromethane-methanol solvent system to isolate fractions of various fluorescent carbonaceous nanostructures. The TEM imaging of nano carbonaceous particles of all five fractions indicated that the first and third fractions were composed of nanoribbons, while the latter two fractions largely contained quasi-spherical nanoparticles of both lesser (carbon quantum dots) and greater (carbon nanodots) than 10 nm dimensions. The XPS results of all the fractions suggested separation based on polarity difference. The ID/IG ratios obtained from Raman spectra implied the presence of several defects on the CDs. The time resolved fluorescence spectra of third, fourth and fifth fractions revealed mono-exponential decay of fluorophores with excitation independent average lifetime values. The fifth fraction exhibited good biocompatibility and the highest absolute fluorescence quantum yield of 58.47 % among all the isolated samples. As these CDs displayed a remarkable rise in the quantum yield to 88.60 % when dispersed in water, a water-based flexo-ink was formulated. The photostable pale yellow flexo print proofs obtained on UV dull paper exhibited a green fluorescence under 365 nm illumination, whereas a yellow glow when shined with blue light, which can serve as an authentication feature for security documents and currency notes. Moreover, as the third fraction constitutes mainly of carbon nanoribbons (CNRs), an optimized polymer electrolyte was prepared along with sodium alginate (SA), and MgCl2 to understand their potential use in energy storage application. A supercapacitor was fabricated and tested for its electrochemical performance such as cyclic voltammtery (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCD). An enhanced current window was observed in the CV of SA/CNRs compared to pure SA and SA/CNRs/Mg films, which indicated a structural interaction of CNRs with SA. The conductivity of SA/CNRs/Mg was lesser than SA/CNRs in EIS studies due to the presence of Mg ions, while pure SA showed lesser conductivity. The dual ionic interaction of Na and Mg along with enhanced structural stability due to doped CNRs favors its convenient supercapacitor application. The fabricated eco-friendly supercapacitor showed a specific capacitance of 84 F/g. The GCD of the device displayed pseudocapacitance behaviour and was quite stable for 2000 cycles with coulombic efficiency of 96 %. © 2024 The Author(s)
Neodymium doped graphene quantum dots/PANI composite for supercapacitor application
(Elsevier Ltd, 2025) Muhiuddin, M.; Bharadishettar, N.; Devi, N.A.; Gautam, A.; Chauhan, S.S.; Siddique, A.B.; Ahmad, M.I.; Satyanarayan, M.N.; K, U.B.; Akhtar, W.; Rahman, M.R.
The publication presents a streamlined and economical technique for fabricating advanced electrode materials to enhance the energy storage capabilities of supercapacitors (SCs). The focus is on synthesizing neodymium-doped graphene quantum dots (Nd-GQDs) via a microwave-assisted hydrothermal (MAH) process. This method uses microwave irradiation's rapid heating and efficient energy transfer under low pressure and minimal reaction time. The resulting Nd-GQDs exhibit enhanced electrochemical properties, including increased capacitance and improved charge storage, making this approach practical and effective for advancing supercapacitor technology. An exceptional specific capacitance of 618 F g?1 at a 5 mV s?1 scan rate is demonstrated using Nd-GQDs as the SC electrode material. Due to their high specific capacitance, Nd-GQDs, when combined with polyaniline (PANI), improve the energy and power density of SCs. Nd-GQDs/PANI composites with varying amounts of Nd-GQDs in symmetric SCs are fabricated to demonstrate their promising properties for SC applications. SCs fabricated with 20 mL of Nd-GQDs in the PANI matrix showed a superior specific capacitance of 354 F g?1 at a current density of 1 A g?1, while the energy density and power density were 49.15 Wh kg?1 and 2000 W kg?1, respectively. © 2025 Elsevier B.V.