Papers by Velmurugan Thavasi
Journal of Physical Chemistry A, 2009
In this work we have demonstrated the free radical scavenging ability of two-hydroxy (catechol, h... more In this work we have demonstrated the free radical scavenging ability of two-hydroxy (catechol, hydroquinone, resorcinol) and three-hydroxy (phloroglucinol, pyrogallol, 1,2,4-benzenetriol) phenols against the diphenylpicrylhydrazyl radical at various temperatures (15-40°C) and in different solvent media. Kinetic measurements, made by the stopped-flow method, showed that the phenols with OH groups in the ortho positions have the largest rate coefficients compared to those with OH groups in the meta and para positions at all temperatures and in all solvent media. Among the ortho-structured phenols catechol, pyrogallol, and 1,2,4-benzenetriol, pyrogallol (three OH groups ortho to each other) had the greatest radical scavenging ability. This suggested that intramolecular hydrogen bonding in phenols controlled the rate of radical scavenging ability. The radical scavenging ability of phenols was fastest in methanol and slowest in THF, which emphasized the importance of the interactive behavior of the phenolic OH with the solvent. We concluded from our kinetic data together with our theoretically calculated OH bond dissociation enthalpies of phenols that the OH position played a crucial role in addition to the temperature and nature of the medium in determining the rate of the radical scavenging ability of polyphenols.
Journal of Physical Chemistry A, 2006
Recently, O-H bond dissociation enthalpies (BDEs) have been successfully used to express the free... more Recently, O-H bond dissociation enthalpies (BDEs) have been successfully used to express the free radical scavenging ability of polyphenolic antioxidants. In this work, the BDEs of phenol, catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, 1,2,4-benzenetriol, and 5-hydroxypyrogallol have been calculated at B3LYP/6-311G++(3df, 3pd) and used to elucidate the effect of OH groups. Increasing the number of OH groups in the adjacent (vicinal) position decreases the BDE of phenols. Increasing the number of O-H groups in the alternative position C(1,3) as in resorcinol and C(1,3,5) as in phloroglucinol does not show any notable change in the BDEs when compared to that of OH in C(1) as in phenol. 5-Hydroxypyrogallol has the smallest BDE (250.3 kJ mol -1 ) followed by pyrogallol (289.4 kJ mol -1 ), then 1,2,4-benzenetriol (294.8 kJ mol -1 ), and then catechol (312.8 kJ mol -1 ). Overall, our results indicated that the presence of ortho and para hydroxy groups reduces the BDEs. An intramolecular hydrogen bond (IHB) develops due to the ortho arrangement of OH's and plays a dominant role in decreasing the BDEs. This key study on phenols showed that the reactive order of OH position in the benzene ring is the following: 5-hydroxypyrogallol > pyrogallol > 1
Journal of Physical Chemistry A, 2009
In this work we have demonstrated the free radical scavenging ability of two-hydroxy (catechol, h... more In this work we have demonstrated the free radical scavenging ability of two-hydroxy (catechol, hydroquinone, resorcinol) and three-hydroxy (phloroglucinol, pyrogallol, 1,2,4-benzenetriol) phenols against the diphenylpicrylhydrazyl radical at various temperatures (15-40°C) and in different solvent media. Kinetic measurements, made by the stopped-flow method, showed that the phenols with OH groups in the ortho positions have the largest rate coefficients compared to those with OH groups in the meta and para positions at all temperatures and in all solvent media. Among the ortho-structured phenols catechol, pyrogallol, and 1,2,4-benzenetriol, pyrogallol (three OH groups ortho to each other) had the greatest radical scavenging ability. This suggested that intramolecular hydrogen bonding in phenols controlled the rate of radical scavenging ability. The radical scavenging ability of phenols was fastest in methanol and slowest in THF, which emphasized the importance of the interactive behavior of the phenolic OH with the solvent. We concluded from our kinetic data together with our theoretically calculated OH bond dissociation enthalpies of phenols that the OH position played a crucial role in addition to the temperature and nature of the medium in determining the rate of the radical scavenging ability of polyphenols.
Journal of Physical Chemistry A, 2006
Recently, O-H bond dissociation enthalpies (BDEs) have been successfully used to express the free... more Recently, O-H bond dissociation enthalpies (BDEs) have been successfully used to express the free radical scavenging ability of polyphenolic antioxidants. In this work, the BDEs of phenol, catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, 1,2,4-benzenetriol, and 5-hydroxypyrogallol have been calculated at B3LYP/6-311G++(3df, 3pd) and used to elucidate the effect of OH groups. Increasing the number of OH groups in the adjacent (vicinal) position decreases the BDE of phenols. Increasing the number of O-H groups in the alternative position C(1,3) as in resorcinol and C(1,3,5) as in phloroglucinol does not show any notable change in the BDEs when compared to that of OH in C(1) as in phenol. 5-Hydroxypyrogallol has the smallest BDE (250.3 kJ mol -1 ) followed by pyrogallol (289.4 kJ mol -1 ), then 1,2,4-benzenetriol (294.8 kJ mol -1 ), and then catechol (312.8 kJ mol -1 ). Overall, our results indicated that the presence of ortho and para hydroxy groups reduces the BDEs. An intramolecular hydrogen bond (IHB) develops due to the ortho arrangement of OH's and plays a dominant role in decreasing the BDEs. This key study on phenols showed that the reactive order of OH position in the benzene ring is the following: 5-hydroxypyrogallol > pyrogallol > 1
In this paper, ZnIn2S4 perpendicular nanosheet films have been directly deposited on FTO substrat... more In this paper, ZnIn2S4 perpendicular nanosheet films have been directly deposited on FTO substrates by a facile hydrothermal method and investigated as the electrode materials for solar cells. The crystal structure, morphology, and optical properties of the obtained ZnIn2S4 films were characterized by measurements such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectrum (EDS), X-ray photoelectron spectrum (XPS) and UV-vis spectra. The results revealed a uniform perpendicular ZnIn2S4 film with thickness of 4 μm and with an average nanosheet thickness of about 30 nm on FTO substrate, along with the band gap of 2.35 eV. The reaction conditions influencing the formation of ZnIn2S4 films, such as the substrate treatment and reaction time were investigated. A possible mechanism for the formation of ZnIn2S4 films on FTO substrates under hydrothermal conditions has been proposed. Furthermore, after heat treatment, the ZnIn2S4 film electrode exhibited a photoelectrical conversion efficiency of 0.23% in FTO/ZnIn2S4/polysulfide/Au liquid-junction solar cell under AM 1.5 (100 mW cm-2).In this paper, ZnIn2S4 perpendicular nanosheet films have been directly deposited on FTO substrates by a facile hydrothermal method and investigated as the electrode materials for solar cells. The crystal structure, morphology, and optical properties of the obtained ZnIn2S4 films were characterized by measurements such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectrum (EDS), X-ray photoelectron spectrum (XPS) and UV-vis spectra. The results revealed a uniform perpendicular ZnIn2S4 film with thickness of 4 μm and with an average nanosheet thickness of about 30 nm on FTO substrate, along with the band gap of 2.35 eV. The reaction conditions influencing the formation of ZnIn2S4 films, such as the substrate treatment and reaction time were investigated. A possible mechanism for the formation of ZnIn2S4 films on FTO substrates under hydrothermal conditions has been proposed. Furthermore, after heat treatment, the ZnIn2S4 film electrode exhibited a photoelectrical conversion efficiency of 0.23% in FTO/ZnIn2S4/polysulfide/Au liquid-junction solar cell under AM 1.5 (100 mW cm-2). Electronic supplementary information (ESI) available: XRD pattern, SEM images of the ZnIn2S4 precipitant product at the bottom of the autoclave. XRD pattern, SEM images, UV-vis spectra of ZnIn2S4 film on FTO substrates after heat treatment at 400 °C for 30 min in an Ar atmosphere. See DOI: 10.1039/b000000x
In this paper, ZnIn2S4 perpendicular nanosheet films have been directly deposited on FTO substrat... more In this paper, ZnIn2S4 perpendicular nanosheet films have been directly deposited on FTO substrates by a facile hydrothermal method and investigated as the electrode materials for solar cells. The crystal structure, morphology, and optical properties of the obtained ZnIn2S4 films were characterized by measurements such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectrum (EDS), X-ray photoelectron spectrum (XPS) and UV-vis spectra. The results revealed a uniform perpendicular ZnIn2S4 film with thickness of 4 μm and with an average nanosheet thickness of about 30 nm on FTO substrate, along with the band gap of 2.35 eV. The reaction conditions influencing the formation of ZnIn2S4 films, such as the substrate treatment and reaction time were investigated. A possible mechanism for the formation of ZnIn2S4 films on FTO substrates under hydrothermal conditions has been proposed. Furthermore, after heat treatment, the ZnIn2S4 film electrode exhibited a photoelectrical conversion efficiency of 0.23% in FTO/ZnIn2S4/polysulfide/Au liquid-junction solar cell under AM 1.5 (100 mW cm-2).In this paper, ZnIn2S4 perpendicular nanosheet films have been directly deposited on FTO substrates by a facile hydrothermal method and investigated as the electrode materials for solar cells. The crystal structure, morphology, and optical properties of the obtained ZnIn2S4 films were characterized by measurements such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectrum (EDS), X-ray photoelectron spectrum (XPS) and UV-vis spectra. The results revealed a uniform perpendicular ZnIn2S4 film with thickness of 4 μm and with an average nanosheet thickness of about 30 nm on FTO substrate, along with the band gap of 2.35 eV. The reaction conditions influencing the formation of ZnIn2S4 films, such as the substrate treatment and reaction time were investigated. A possible mechanism for the formation of ZnIn2S4 films on FTO substrates under hydrothermal conditions has been proposed. Furthermore, after heat treatment, the ZnIn2S4 film electrode exhibited a photoelectrical conversion efficiency of 0.23% in FTO/ZnIn2S4/polysulfide/Au liquid-junction solar cell under AM 1.5 (100 mW cm-2). Electronic supplementary information (ESI) available: XRD pattern, SEM images of the ZnIn2S4 precipitant product at the bottom of the autoclave. XRD pattern, SEM images, UV-vis spectra of ZnIn2S4 film on FTO substrates after heat treatment at 400 °C for 30 min in an Ar atmosphere. See DOI: 10.1039/b000000x
Polymer Reviews, 2011
Melt electrospinning is a technique for the production of micro and nanofibers which can be an in... more Melt electrospinning is a technique for the production of micro and nanofibers which can be an interesting alternative to conventional solvent electrospinning. In this process, the solvents are replaced by polymer melts. Despite its greater potential, the number of papers published and research groups working in the application of melt electrospinning for novel applications is significantly lower than that of solvent electrospinning. However, it is worth mentioning that attempts were made to improve the design and development of melt electrospinning and fabricate fibrous materials using the set up during the last few decades. A lack of interest in melt electrospinning is probably associated with the difficulty of melting the polymers at a precise temperature range. This report provides an overview on the various design setups employed to achieve melt electrospinning and a wide variety of polymers used.
Polymer Reviews, 2011
Melt electrospinning is a technique for the production of micro and nanofibers which can be an in... more Melt electrospinning is a technique for the production of micro and nanofibers which can be an interesting alternative to conventional solvent electrospinning. In this process, the solvents are replaced by polymer melts. Despite its greater potential, the number of papers published and research groups working in the application of melt electrospinning for novel applications is significantly lower than that of solvent electrospinning. However, it is worth mentioning that attempts were made to improve the design and development of melt electrospinning and fabricate fibrous materials using the set up during the last few decades. A lack of interest in melt electrospinning is probably associated with the difficulty of melting the polymers at a precise temperature range. This report provides an overview on the various design setups employed to achieve melt electrospinning and a wide variety of polymers used.
Sensors, 2009
We have prepared electrospun Nylon-6 nanofibers via electrospinning, and adsorbed multi-walled ca... more We have prepared electrospun Nylon-6 nanofibers via electrospinning, and adsorbed multi-walled carbon nanotubes (MWCNTs) onto the surface of Nylon-6 fibers using Triton ® X-100 to form a MWCNTs/Nylon-6 nanofiber composite. The dispersed MWCNTs have been found to be stable in hexafluoroisopropanol for several months without precipitation. A MWCNTs/Nylon-6 nanofiber composite based chemical sensor has demonstrated its responsiveness towards a wide range of solvent vapours at room temperature and only mg quantities of MWCNTs were expended. The large surface area and porous nature of the electrospun Nylon-6/MWCNT nanofibers facilitates greater analyte permeability. The experimental analysis has indicated that the dipole moment, functional group and vapour pressure of the analytes determine the magnitude of the responsiveness.
Sensors, 2009
We have prepared electrospun Nylon-6 nanofibers via electrospinning, and adsorbed multi-walled ca... more We have prepared electrospun Nylon-6 nanofibers via electrospinning, and adsorbed multi-walled carbon nanotubes (MWCNTs) onto the surface of Nylon-6 fibers using Triton ® X-100 to form a MWCNTs/Nylon-6 nanofiber composite. The dispersed MWCNTs have been found to be stable in hexafluoroisopropanol for several months without precipitation. A MWCNTs/Nylon-6 nanofiber composite based chemical sensor has demonstrated its responsiveness towards a wide range of solvent vapours at room temperature and only mg quantities of MWCNTs were expended. The large surface area and porous nature of the electrospun Nylon-6/MWCNT nanofibers facilitates greater analyte permeability. The experimental analysis has indicated that the dipole moment, functional group and vapour pressure of the analytes determine the magnitude of the responsiveness.
Materials Today, 2011
Nanotechnology has influenced the direction of research across the sciences, medicine, and engine... more Nanotechnology has influenced the direction of research across the sciences, medicine, and engineering. Carbon nanotubes (CNTs) and, more recently, protein nanotubes (PNTs) and protein-inorganic nanocomposites have received considerable attention due to their unique nanostructures that can be utilized as a scaffold to house proteins or create nanowires. A shift towards protein-inorganic interactions has numerous applications from biosensors to biofuel cells and bio-based nanodevices. We examine several systems where protein hot spots, the active domains on proteins and the interactive dynamics in them, play a critical role in the interactions at the interface of these unique systems.
Materials Today, 2011
Nanotechnology has influenced the direction of research across the sciences, medicine, and engine... more Nanotechnology has influenced the direction of research across the sciences, medicine, and engineering. Carbon nanotubes (CNTs) and, more recently, protein nanotubes (PNTs) and protein-inorganic nanocomposites have received considerable attention due to their unique nanostructures that can be utilized as a scaffold to house proteins or create nanowires. A shift towards protein-inorganic interactions has numerous applications from biosensors to biofuel cells and bio-based nanodevices. We examine several systems where protein hot spots, the active domains on proteins and the interactive dynamics in them, play a critical role in the interactions at the interface of these unique systems.
Acs Applied Materials & Interfaces, 2010
Mesophase ordering and structuring are carried out to attain optimized pore morphology, high crys... more Mesophase ordering and structuring are carried out to attain optimized pore morphology, high crystallinity, stable porous framework, and crack-free mesoporous titanium dioxide (TiO(2)) films. The pore structure (quasi-hexagonal and lamellar) can be controlled via the concentration of copolymer, resulting in two different types of micellar packing. The calcination temperature is also controlled to ensure a well-crystalline and stable porous framework. Finally, the synthesized mesoporous TiO(2) film is modified by adding P25 nanoparticles, which act as scattering centers and function as active binders to prevent formation of microcracks. Adding P25 nanoparticles into mesoporous structure helps to provide strong light-harvesting capability and large surface area for high -efficiency dye-sensitized solar cells (DSSC). The short-circuit photocurrent density (J(sc)) of the cell made from mixture of mesoporous TiO(2) and P25 nanoparticles displays a higher efficiency of approximately 6.5% compared to the other homogeneous films. A combination of factors such as increased surface area, introduction of light-scattering particles, and high crystallinity of the mesoporous films leads to enhanced cell performance.
Acs Applied Materials & Interfaces, 2010
Mesophase ordering and structuring are carried out to attain optimized pore morphology, high crys... more Mesophase ordering and structuring are carried out to attain optimized pore morphology, high crystallinity, stable porous framework, and crack-free mesoporous titanium dioxide (TiO(2)) films. The pore structure (quasi-hexagonal and lamellar) can be controlled via the concentration of copolymer, resulting in two different types of micellar packing. The calcination temperature is also controlled to ensure a well-crystalline and stable porous framework. Finally, the synthesized mesoporous TiO(2) film is modified by adding P25 nanoparticles, which act as scattering centers and function as active binders to prevent formation of microcracks. Adding P25 nanoparticles into mesoporous structure helps to provide strong light-harvesting capability and large surface area for high -efficiency dye-sensitized solar cells (DSSC). The short-circuit photocurrent density (J(sc)) of the cell made from mixture of mesoporous TiO(2) and P25 nanoparticles displays a higher efficiency of approximately 6.5% compared to the other homogeneous films. A combination of factors such as increased surface area, introduction of light-scattering particles, and high crystallinity of the mesoporous films leads to enhanced cell performance.
Journal of Photochemistry and Photobiology A-chemistry, 2011
This paper reports facile fabrication of polypyrrole (Ppy)/functionalized multiwalled carbon nano... more This paper reports facile fabrication of polypyrrole (Ppy)/functionalized multiwalled carbon nanotube (f-MWCNT) nanocomposite films on rigid fluorine-doped tin oxide (FTO) and flexible ITO-coated polyethylene naphthalate (PEN) substrates by a drop casting method, and their application as counter electrodes in dye-sensitized solar cells (DSSCs). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements of this solution processed Ppy/f-MWCNT nanocomposite film
Journal of Photochemistry and Photobiology A-chemistry, 2011
This paper reports facile fabrication of polypyrrole (Ppy)/functionalized multiwalled carbon nano... more This paper reports facile fabrication of polypyrrole (Ppy)/functionalized multiwalled carbon nanotube (f-MWCNT) nanocomposite films on rigid fluorine-doped tin oxide (FTO) and flexible ITO-coated polyethylene naphthalate (PEN) substrates by a drop casting method, and their application as counter electrodes in dye-sensitized solar cells (DSSCs). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements of this solution processed Ppy/f-MWCNT nanocomposite film
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2011
The integration of electrospinning and electrospraying to prepare the fibrous catalytic filter me... more The integration of electrospinning and electrospraying to prepare the fibrous catalytic filter membrane is demonstrated. The non-conductive polyethylene oxide (PEO) is blended with (±)-camphor-10-sulfonic acid (CSA) doped conductive polyaniline (PANi) for electrospinning. The conductive CSA/PANi-PEO composite fibers are produced upon electrospinning, which are used as the conductive collector for electrospraying process by which titanium dioxide (TiO 2 ) nanoparticles (NPs) are sprayed and allowed to adsorb on the fibers. The degree of adsorption and dispersion of nano TiO 2 catalysts on the surface of the CSA/PANi-PEO fibers exhibit a stronger dependence on weight percentage (wt%) of PANi in PEO solution and the strength of electrical conductivity of the fibers used during electrospraying. CSA/PANi-PEO fibers as collector reduce the wastage of TiO 2 NPs during electrospraying to lesser than 5%. Among the three different composition of PANi studied, PEO with 12 wt% PANi yields very uniform diameter and beads-free fibrous structure with higher electrical conductivity. 12 wt% CSA/PANi-PEO fibrous membrane is found to support for greater dispersion of TiO 2 NPs. The photocatalytic activity of the as-prepared TiO 2 -PANi-PEO catalytic membrane is tested against the toxicant simulant 2-chloroethyl phenyl sulfide (CEPS) under the ultraviolet light irradiation. It is observed that the TiO 2 nanoparticles catalysts embedded PANi-PEO fibrous membrane decontaminated the toxicant CEPS significantly, which is due to uniform dispersion of the catalysts produced by the methodology.
Materials Science and Engineering B-advanced Functional Solid-state Materials, 2011
The integration of electrospinning and electrospraying to prepare the fibrous catalytic filter me... more The integration of electrospinning and electrospraying to prepare the fibrous catalytic filter membrane is demonstrated. The non-conductive polyethylene oxide (PEO) is blended with (±)-camphor-10-sulfonic acid (CSA) doped conductive polyaniline (PANi) for electrospinning. The conductive CSA/PANi-PEO composite fibers are produced upon electrospinning, which are used as the conductive collector for electrospraying process by which titanium dioxide (TiO 2 ) nanoparticles (NPs) are sprayed and allowed to adsorb on the fibers. The degree of adsorption and dispersion of nano TiO 2 catalysts on the surface of the CSA/PANi-PEO fibers exhibit a stronger dependence on weight percentage (wt%) of PANi in PEO solution and the strength of electrical conductivity of the fibers used during electrospraying. CSA/PANi-PEO fibers as collector reduce the wastage of TiO 2 NPs during electrospraying to lesser than 5%. Among the three different composition of PANi studied, PEO with 12 wt% PANi yields very uniform diameter and beads-free fibrous structure with higher electrical conductivity. 12 wt% CSA/PANi-PEO fibrous membrane is found to support for greater dispersion of TiO 2 NPs. The photocatalytic activity of the as-prepared TiO 2 -PANi-PEO catalytic membrane is tested against the toxicant simulant 2-chloroethyl phenyl sulfide (CEPS) under the ultraviolet light irradiation. It is observed that the TiO 2 nanoparticles catalysts embedded PANi-PEO fibrous membrane decontaminated the toxicant CEPS significantly, which is due to uniform dispersion of the catalysts produced by the methodology.
Journal of Photochemistry and Photobiology C-photochemistry Reviews, 2010
Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis ha... more Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis has a great potential as can use clean and cheap sources-water and solar energy. In oxygenic photosynthetic microorganisms electrons and protons produced from water and redirected by the photosynthetic electron-transport chain via ferredoxin to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, e − and H + recombine and form molecular hydrogen. Hydrogenase activity can be very high but is extremely sensitive to the photosynthetically evolved O 2 that leads to reduced and unstable H 2 production. However, presently, several approaches are developed to improve the energetic efficiency to generate H 2 . This review examines the main available pathways to improve the photosynthetic H 2 production.
Journal of Photochemistry and Photobiology C-photochemistry Reviews, 2010
Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis ha... more Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis has a great potential as can use clean and cheap sources-water and solar energy. In oxygenic photosynthetic microorganisms electrons and protons produced from water and redirected by the photosynthetic electron-transport chain via ferredoxin to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, e − and H + recombine and form molecular hydrogen. Hydrogenase activity can be very high but is extremely sensitive to the photosynthetically evolved O 2 that leads to reduced and unstable H 2 production. However, presently, several approaches are developed to improve the energetic efficiency to generate H 2 . This review examines the main available pathways to improve the photosynthetic H 2 production.
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Papers by Velmurugan Thavasi