Soumitra Satapathi

Sensitive Detection of Nitroaromatics With Colloidal Conjugated Polymer Nanoparticles

We observe more than two orders of magnitude enhancement of fluorescence quenching in colloidal conjugated polymer nanoparticles by nitroaromatic analytes compared to solution of the same polymer in organic solvents. This observation is surprising as the quantum efficiency of fluorescence of the polymer solution is significantly higher. The colloidal nanoparticle dispersions of substituted polythiophene derivative are fabricated by the surfactant-assisted mini-emulsion technique. Stern–Volmer constants are determined using both one-photon and two-photon excitation methods. We believe strong analyte–nanoparticle interaction results in the large value of the Stern–Volmer constants measured. The nanoparticle-based sensor described here is suitable for developing a field-based sensory device for detecting a broad class of nitroaromatics in solution.

Enhanced Sensory Response of Quaterthiophene Bearing 1,2,3-Triazole Moiety to Explosives

Quaterthiophene (QT) with a 1,2,3-triazole moiety was found to have a high sensory response in solution toward a broad class of nitroaromatics, including DNT and TNT, and nitro esters, such as RDX and PETN. Fluorescence quenching in QT thin films was also high for vapors containing DNT or TNT in ppb levels. These results were unexpected based our earlier report that a polythiophene with triazole moiety as a side group does not show fluorescence quenching in solution with the same explosives. Remarkably, QT bearing a 1,2,3-triazole moiety, the oligomeric analog, shows fluorescence quenching in solution and in the solid state when exposed to nitroaromatic molecules used as explosives. We attribute the enhanced quenching observed in the oligomer in solution and in solid state to its lower aggregation propensity and thus enhanced access of the quenching sites to the analytes.

Fabrication of Dye-sensitized Solar Cells and Fluorescence Quenching Study Using Thiophene Based Copolymers

Photovoltaic performance of dye sensitized solar cells fabricated with a commercially available thiophene based copolymer was investigated. Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(bithiophene)], a highly soluble polythiophene, was used as a sensitizer. An open-circuit voltage of 0.64 V and a short-circuit current density of 0.36 mA/cm2 were measured. The incident photon to current conversion efficiency for the polymer was measured. Fluorescence from the other polythiophene, poly(3,3′-didodecyl quarter thiophene) was found to be quenched when blended with phenyl C61 butyric acid methyl ester (PCBM) (1:1 wt ratio), indicating the charge transfer from the conjugated polymer to PCBM.

Utilization of Naturally Occurring Dyes as Sensitizers in Dye Sensitized Solar Cells

Dye sensitized solar cells (DSSCs) were fabricated with four naturally occurring anthocyanin dyes extracted from naturally found fruits/juices (viz., Indian jamun, plum, black currant, and berries) as sensitizers. Extraction of anthocyanin was done using acidified ethanol. The highest power conversion efficiencies (η) of 0.55% and 0.53% were achieved for the DSSCs fabricated using anthocyanin extracts of blackcurrant and mixed berry juice. Widespread availability of these fruits and juices, high concentration of anthocyanins in them, and ease of extraction of anthocyanin dyes from these commonly available fruits render them novel and inexpensive candidates for solar cell fabrication. Anthocyanins are naturally occurring biodegradable and nontoxic molecules that are extracted using techniques that involve negligible low cost to the environment and therefore can provide ecofriendly alternatives to synthetic dyes for DSSC production.

Reusable graphene oxide nanofibers for enhanced photocatalytic activity: a detailed mechanistic study

Abstract Water pollution due to indiscriminate disposal of industrial dyes poses serious environmental hazards nationally and internationally. Some of the dyes are potentially carcinogenic and may induce mutagenicity and genotoxicity. Recently, graphene-based nanocomposite has attracted considerable interest for photocatalysis-based wastewater treatment. Here, we report the production of graphene-oxide-based hydrophobic PAN/GO nanofibers using electrospinning technique for photocatalytic degradation of Rhodamine 6G dye under natural sunlight illumination. The synthesized nanofibers were characterized using X-ray diffraction, EDX, field emission scanning electron microscopy and FTIR spectroscopy. Dye removal efficiency was investigated by monitoring UV–Vis absorption intensity over time. Structural change in dye was studied using FTIR analysis. Kinetics of dye degradation reaction was monitored through pseudo-first-order and pseudo-second-order kinetics model. Effects of nanofiber weight and initial dye concentration on the degradation efficiency were investigated in detail. Reusability and stability of these synthesized nanofibers in dye solution have been studied using scanning electron microscopy and FTIR spectroscopy. A comparative study for dye degradation was also performed using TiO2-coated nanofibers under visible light and UV light illumination. These large-area reusable graphene oxide nanofibers provide a scalable and novel route for photocatalytic degradation of carcinogenic dyes from industrial water.

Local Optoelectronic Characterization of Solvent-Annealed,Lead-Free, Bismuth-Based Perovskite Films

Traditional organolead-halide perovskite-based devices have shown rapid improvements in their power conversion efficiency in less than a decade, yet challenges remain for improving stability and film uniformity, as well as the elimination of lead to address toxicity issues. We fabricated lead-free methylammonium bismuth iodide (MBI) perovskite films and studied the effect of solvent annealing with dimethylformamide (DMF) on both (1) the crystallinity and structure of the films with X-ray diffraction and scanning electron microscopy and (2) the local optoelectronic properties of the films as measured via (photo)conductive atomic force microscopy. We found that solvent annealing leads to improved crystallinity and increased grain size in the MBI films as compared to the thermally annealed films. Furthermore, solvent-annealed MBI films show significantly increased electrical conductivity in the out-of-plane direction. Photoconductivity in both solvent-annealed and thermally annealed MBI films was increased in the grain interiors versus the grain boundaries. It was observed that DMF-induced solvent annealing impacts charge transport through the film, which can be a unique design parameter for optimizing local optoelectronic properties. By studying how solvent annealing affects the MBI film structure and changes the ways in which charges are transported through the film, we have developed a better understanding of how local optoelectronic properties are affected by DMF annealing.

Effect of functional groups on sensitization of dye-sensitized solar cells (DSSCs) using free base porphyrins

Dye-sensitized solar cells (DSSCs) were fabricated with six meso-substituted A3B and A4 free base porphyrin dyes having different functional groups, as sensitizers. The two step synthesis and the effect of different functional groups and their positions on the photosensitization properties of these porphyrin dyes are reported. The highest power conversion efficiencies (η) of 3.26%, 2.94% and 2.84% were achieved for the DSSC fabricated using 5,10,15-tris(4′-pyridyl)-20-(4′-carboxyphenyl)porphyrin (H2TriPyMCPP), 5,10,15,20-tetrakis(4′-aminophenyl)porphyrin (H2TAPP) and 5-(4′-pyridyl)-10,15,20-tris(4′-carboxyphenyl)porphyrin (H2MPyTriCPP) dyes, respectively. The electron donating amino group is shown to enhance the power conversion efficiency while pyridyl appended porphyrin sensitizers are shown to be superior sensitizers as compared to carboxyphenylporphyrins. The investigation of effect of functional group and position of functional group of porphyrin dye on DSSC can serve as an important tool to guide further selection and synthesis of potential candidates as sensitizers.

Systematic investigation and in vitro biocompatibility studies on implantable magnetic nanocomposites for hyperthermia treatment of osteoarthritic knee joints

The inefficacy of the currently used treatment modalities for osteoarthritis has elicited considerable research interest in the exploration of alternative methods. Hyperthermia treatment, generally used in the case of lesions, maybe considered as a viable solution owing to the economic and ergonomic factors involved. In the present study, Cr-doped Fe2O3 embedded in PVDF matrix is proposed as the biocompatible magnetic-dielectric composite to provide thermo-regulated prolonged treatment. A systematic study was carried out to characterize the physical properties of the prepared formulation. Further, cellular uptake studies were done to ensure bioviability. Finite element method studies using COMSOL were used to simulate the hyperthermia treatment of osteoarthritic knee joint. The approach proposed here may be used further to develop a novel class of therapeutic devices for the treatment of osteoarthritis.

Two-photon active polymeric nanoparticles for high contrast in vitro imaging

Two water dispersible and two-photon (TP) active polymer nanoparticles were synthesized from poly[2-(3-thienyl) ethanol n-butoxy carbonyl methyl-urethane] and poly(3,3′′′-didodecyl quarter thiophene) polymers using a simple miniemulsion technique. Strong TP fluorescence was observed from each of these nanoparticles using a femtosecond laser operated at 800 nm. Interestingly, these polymeric nanoparticles were found to be non-toxic in dose dependent cell viability studies for 24 h nanoparticle incubation time period. TP microscopic imaging and Z-stacking confirmed cellular internalization of TP active nanoparticles by human macrophage THP-1 cells. These fluorescent polymer nanoparticles could be suitable candidates for in vitro TP bioimaging.

Sensory Response and Two-Photon-Fluorescence Study of Regioregular Polythiophene Nanoparticles

Nanoparticles of a regioregular and soluble polythiophene were fabricated by mini-emulsion technique. The fabricated nanoparticles were characterized by optical spectroscopy and dynamic light scattering. The fluorescence quenching of these fabricated nanoparticles with 2,4-dinitrotolune (DNT) in aqueous and organic solutions was investigated. Significant fluorescence quenching was observed. The Stern-Volmer constants were determined to be higher than that of the bulk polymer in solution, indicating that the nanoparticles provide better sensitivity in DNT sensing. Strong two-photon-induced fluorescence was measured from these nanoparticles.