- Pune, Maharashtra, India
Pattayil Joy
National chemical laboratory, Physical & Materials Chemistry, Faculty Member
- Magnetism, Nanomaterials, Nanomagnetism, Magnetic nanoparticles, Nanofluids, Magnetism and Magnetic Materials, and 11 moreMagnetostrictive Materials, Magnetics, Magnetostriction, Energy Harvesting, Multiferroics, Solar Energy Materials, Graphene, Carbon Nanotubes, Nanoparticles, Nanorod, Quantum Dots, Nanoscience, and Nanotechnologyedit
To study the role of unsaturation in the surfactant molecule on the thermal conductivity of magnetite nanofluids, four different fatty acid (stearic, oleic, linoleic, and linolenic acids with different degree of unsaturation) coated... more
To study the role of unsaturation in the surfactant molecule on the thermal conductivity of magnetite nanofluids, four different fatty acid (stearic, oleic, linoleic, and linolenic acids with different degree of unsaturation) coated magnetite nanoparticles of comparable size are prepared and dispersed in toluene. It is found that the nanofluid with the saturated fatty acid coated nanoparticles show larger viscosity than the fluid with the unsaturated fatty acid coated particles at all concentrations. Thermal conductivity studies show enhancement only above a critical concentration for all fluids. The critical concentration for thermal conductivity enhancement varies with the surfactant, possibly due to the difference in the degree of aggregation of the nanoparticles in the fluid, because of the difference in the conformation of the surfactant molecules on the nanoparticle’s surface. The experimental thermal conductivity follows the Maxwell model at higher concentrations. From the overall studies, it is observed that the thermal conductivity of the fluids with aggregated or assembled nanoparticles shows slightly larger enhancement than that of the fluids with isolated particles. However, in the presence of a magnetic field, the fluids with isolated nanoparticles showed relatively larger enhancement, possibly due to the easy response of the isolated magnetite nanoparticles to the applied field.
Research Interests:
Thermal conductivity enhancement of nanofluids of oleic acid coated magnetite nanoparticles dispersed in four different base fluids (toluene, xylene, mesitylene, kerosene) is studied to understand the role of the solvent (base fluid).... more
Thermal conductivity enhancement of nanofluids of oleic acid coated magnetite nanoparticles dispersed in four different base fluids (toluene, xylene, mesitylene, kerosene) is studied to understand the role of the solvent (base fluid). From the correlation of the thermophysical properties of the base fluid with the thermal conductivity of the corresponding nanofluid, it is found that the nanofluid with the base fluid of lower intrinsic thermal conductivity and dielectric constant shows relatively larger enhancement in the thermal conductivity. A linear
increase in the thermal conductivity with increasing viscosity is observed for all four nanofluids studied. The concentration dependent thermal conductivity studies showed enhancement only above a particular concentration, within the sensitivity of the measurement, and this critical concentration is different for the different nanofluids. The nanofluid with kerosene showed the lowest critical concentration for thermal conductivity enhancement compared to the other nanofluids. The difference between the experimental thermal conductivity and the calculated value using the Maxwell model is found to depend on the critical concentration. By assuming the critical concentration as the zero concentration, it is found that all the studied nanofluids almost follow the Maxwell model of thermal conductivity. Thus, for the dispersions of the same oleic acid coated magnetite nanoparticles, the base fluid affects the critical concentration for thermal conductivity enhancement, probably due to the interfacial effects arising from the surfactant-solvent interactions.
increase in the thermal conductivity with increasing viscosity is observed for all four nanofluids studied. The concentration dependent thermal conductivity studies showed enhancement only above a particular concentration, within the sensitivity of the measurement, and this critical concentration is different for the different nanofluids. The nanofluid with kerosene showed the lowest critical concentration for thermal conductivity enhancement compared to the other nanofluids. The difference between the experimental thermal conductivity and the calculated value using the Maxwell model is found to depend on the critical concentration. By assuming the critical concentration as the zero concentration, it is found that all the studied nanofluids almost follow the Maxwell model of thermal conductivity. Thus, for the dispersions of the same oleic acid coated magnetite nanoparticles, the base fluid affects the critical concentration for thermal conductivity enhancement, probably due to the interfacial effects arising from the surfactant-solvent interactions.
Research Interests:
ABSTRACT
ABSTRACT
Page 1. The origin of ferromagnetism in the two different phases of LaMn0.5Co0.5O3: evidence from x-ray photoelectron spectroscopic studies This article has been downloaded from IOPscience. Please scroll down to see the full text article.... more
Page 1. The origin of ferromagnetism in the two different phases of LaMn0.5Co0.5O3: evidence from x-ray photoelectron spectroscopic studies This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2001 J. Phys.: Condens. ...
Research Interests:
Cobalt-ferrite (CoFe2O4) based materials are suitable candidates for magnetomechanical sensor applications owing to a strong sensitivity of their magnetostriction to an applied magnetic field. Zn-doped cobalt-ferrites, with nominal... more
Cobalt-ferrite (CoFe2O4) based materials are suitable candidates for magnetomechanical sensor applications owing to a strong sensitivity of their magnetostriction to an applied magnetic field. Zn-doped cobalt-ferrites, with nominal compositions CoFe2−xZnxO4 (x = 0–0.3), were synthesized by auto-combustion technique using Co- , Fe- , and Zn-nitrate as precursors. X-ray spectra analysis and Transmission electron microscopy studies revealed that the as-prepared powders were comprised of nano-crystalline (~25–30 nm) cubic-spinel phase with irregularly-shaped grains morphology along with minor impurity phases. Calcination (800 °C for 3 h) of the precursor followed by sintering (1300 °C for 12 h) resulted in a single phase cubic-spinel structure with average grain size ~2–4 μm, as revealed from scanning electron micrographs. The magnitude of coercive field decreases from ~540 Oe for x = 0 to 105 Oe for x = 0.30. Saturation magnetization initially increases and peaks to ~87 emu/g for x = 0...
Research Interests:
Research Interests:
ABSTRACT Tetrabutylammonium salt of [PW12O40](3-) and its transition metal (Mn2+, Fe2+, Co2+ and Cu2+) substituted compounds are characterized by elemental analysis, thermogravimetric and spectroscopic techniques. Thermal stability of... more
ABSTRACT Tetrabutylammonium salt of [PW12O40](3-) and its transition metal (Mn2+, Fe2+, Co2+ and Cu2+) substituted compounds are characterized by elemental analysis, thermogravimetric and spectroscopic techniques. Thermal stability of these compounds decreases after metal ion substitution, but the cobalt substituted compound is relatively more stable. The cobalt substituted compound is found to be a good catalyst for the oxidation of cyclohexanol and the catalytic activity of the transition metal substituted compounds decreases in the order: Co2+ much greater than Mn2+ > Fe2+ greater than or equal to Cu2+. Detailed studies of the reaction in the presence of Co2+ and Mn2+ substituted compounds reveal that the transition metal ions are initially oxidized to a higher oxidation state which then act as the catalytic centre for the reaction. The enhanced catalytic activity of Co2+ substituted compound is due its oxidation to Co4+ in the presence of H2O2 which is evidenced from EPR and UV-VIS spectroscopic studies.
Research Interests:
ABSTRACT The La–Zn substituted hexagonal strontium aluminate, Sr1−xLaxAl12−xZnxO19, with the magnetoplumbite structure and having five different coordination environments for Al with different symmetries, is investigated using 27Al... more
ABSTRACT The La–Zn substituted hexagonal strontium aluminate, Sr1−xLaxAl12−xZnxO19, with the magnetoplumbite structure and having five different coordination environments for Al with different symmetries, is investigated using 27Al solid-state NMR to get detailed information on the sites of substitution of Zn and the associated changes in the local coordination environments of Al. The objective of the study was to get information on the local structural variations in the isostructural La–Co substituted strontium ferrite, Sr1−xLaxFe12−xCoxO19, showing enhanced magnetic performance on substitution. The NMR studies on the aluminate give direct evidence for the sites of substitution and the changes in the local coordination environments. It is found that Zn is substituted at the 2a and 4f2AlO6 octahedral sites. However, an interesting observation from the NMR studies is the stabilization of the Al site occupancy at the penta-coordinated 2b site over the distorted tetrahedral 4eAl site, without any substitution at these sites. Large changes in the quadrupolar coupling constant of the 2a and 4e sites are observed between x = 0.2 and 0.3, corresponding to the compositional region showing higher performance in the case of Sr1−xLaxFe12−xCoxO19, indicating the role of distortion of local coordination environments on suitable substitution in controlling the performance parameters.
Research Interests:
Research Interests:
Research Interests:
Rapidly growing technological interests on colossal magnetoresistive (CMR) materials have stimulated scientists worldwide for a thorough investigation of the various aspects of physical properties of the rare-earth manganite system viz. R... more
Rapidly growing technological interests on colossal magnetoresistive (CMR) materials have stimulated scientists worldwide for a thorough investigation of the various aspects of physical properties of the rare-earth manganite system viz. R 1− x A x MnO 3 [1], [2], [3] and [4] ...
Research Interests:
ABSTRACT Core–shell bimetallic Au@Ni nanoparticles, with gold cores and thin nickel shells with overall size less than 10 nm, are synthesized and stabilized in pure cubic (fcc) and hexagonal (hcp) phase. Due to their unique crystal,... more
ABSTRACT Core–shell bimetallic Au@Ni nanoparticles, with gold cores and thin nickel shells with overall size less than 10 nm, are synthesized and stabilized in pure cubic (fcc) and hexagonal (hcp) phase. Due to their unique crystal, electronic, and geometric structure, they show interesting magnetic and chemical properties. The Au@Ni fcc is magnetic, whereas Au@Ni hcp is non-magnetic. Both the bimetallic nanostructures are stable to surface oxidation until 150 C and show excellent catalytic activity for p-nitrophenol reduction reaction.
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
ABSTRACT
Research Interests:
Studies on the magnetic properties of nanocrystalline ZnFe2O4 synthesized by an autocombustion method are reported. Superparamagnetic behavior is observed for the nanocrystalline materials with particle sizes of 8 nm and 17 nm, with... more
Studies on the magnetic properties of nanocrystalline ZnFe2O4 synthesized by an autocombustion method are reported. Superparamagnetic behavior is observed for the nanocrystalline materials with particle sizes of 8 nm and 17 nm, with superparamagnetic blocking temperatures of 65 K and 75 K, respectively. Magnetic hysteresis with very large coercivities of 533 Oe and 325 Oe, respectively, are observed at 12
Research Interests:
ABSTRACT
Research Interests:
Using vibrating sample magnetometery (VSM) 50MeV Li3+ ion irradiation effects on magnetic properties of single crystals of SrGaxInyFe12−(x+ y) O19 (where x= 0, 5, 7, 9; y= 0, 0.8, 1.3, 1.0), are reported. The substitution of Ga and In in... more
Using vibrating sample magnetometery (VSM) 50MeV Li3+ ion irradiation effects on magnetic properties of single crystals of SrGaxInyFe12−(x+ y) O19 (where x= 0, 5, 7, 9; y= 0, 0.8, 1.3, 1.0), are reported. The substitution of Ga and In in strontium hexaferrite crystals ...
Research Interests:
Research Interests:
Research Interests:
ABSTRACT
Research Interests:
The complex [Fe{HC(3-Mepz)(2)(5-Mepz)}(2)](BF(4))(2) (pz = pyrazolyl ring) has been prepared by the reaction of HC(3-Mepz)(2)(5-Mepz) with Fe(BF(4))(2) x 6 H(2)O. The solid state structures obtained at 294 and 150 K show a distorted... more
The complex [Fe{HC(3-Mepz)(2)(5-Mepz)}(2)](BF(4))(2) (pz = pyrazolyl ring) has been prepared by the reaction of HC(3-Mepz)(2)(5-Mepz) with Fe(BF(4))(2) x 6 H(2)O. The solid state structures obtained at 294 and 150 K show a distorted iron(II) octahedral N(6) coordination environment with the largest deviations arising from the restrictions imposed by the chelate rings. At 294 K the complex is predominately high-spin with Fe-N bond distances averaging 2.14 A, distances that are somewhat shorter than expected for a purely high-spin iron(II) complex because of the presence of an admixture of about 80% high-spin and 20% low-spin iron(II). At 294 K the twisting of the pyrazolyl rings from the ideal C(3v) symmetry averages only 2.2 degrees, a much smaller twist than has been observed previously in similar complexes. At 150 K the Fe-N bond distances average 1.99 A, indicative of an almost fully low-spin iron(II) complex; the twist angle is only 1.3 degrees, as expected for a complex with these Fe-N bond distances. The magnetic properties show that the complex undergoes a gradual change from low-spin iron(II) below 85 K to high-spin iron(II) at 400 K. The 4.2 to 60 K Mössbauer spectra correspond to a fully low-spin iron(II) complex but, upon further warming above 85 K, the iron(II) begins to undergo spin-state relaxation between the low- and high-spin forms on the Mössbauer time scale. At 155 and 315 K the complex exhibits spin-state relaxation rates of 0.36 and 7.38 MHz, respectively, and an Arrhenius plot of the logarithm of the relaxation rate yields an activation energy of 670 +/- 40 cm(-1) for the spin-state relaxation.
Research Interests:
... DOI: 10.1080/00150190903412408 S. Sagar a , PA ... The multiferroic nature of manganites Pr 0.6 Ca 0.4 MnO 3 , Nd 0.5 Ca 0.5 MnO 3 and Pr 0.7 Ca 0.3 MnO 3 is recently reported and the effect is explained by using the mixing of site... more
... DOI: 10.1080/00150190903412408 S. Sagar a , PA ... The multiferroic nature of manganites Pr 0.6 Ca 0.4 MnO 3 , Nd 0.5 Ca 0.5 MnO 3 and Pr 0.7 Ca 0.3 MnO 3 is recently reported and the effect is explained by using the mixing of site centered or bond centered charge ordering ...
Research Interests:
... [15] Terai T., Sasaki T., Kakeshita T., Fukuda T. and Saburi T., Phys. Rev. B, 61 (2000) 3488. [16] Wagh AA, Anil Kumar PS, Bhat HL and Suja Elizabeth, J. Phys.: Condens. Matter, 22 (2010) 026005. [17] Sagar S., Joy PA and... more
... [15] Terai T., Sasaki T., Kakeshita T., Fukuda T. and Saburi T., Phys. Rev. B, 61 (2000) 3488. [16] Wagh AA, Anil Kumar PS, Bhat HL and Suja Elizabeth, J. Phys.: Condens. Matter, 22 (2010) 026005. [17] Sagar S., Joy PA and Anantharaman MR, Ferroelectrics, 392 (2009) 13. ...
Research Interests:
ABSTRACT Magnetostriction characteristics of Mn substituted cobalt ferrite, CoFe2-xMnxO4 (0 <= x <= 0.3), sintered from nanocrystalline powders of average particle size of similar to 4 nm have been studied. Larger value of... more
ABSTRACT Magnetostriction characteristics of Mn substituted cobalt ferrite, CoFe2-xMnxO4 (0 <= x <= 0.3), sintered from nanocrystalline powders of average particle size of similar to 4 nm have been studied. Larger value of magnetostriction at lower magnetic field is achieved after substitution of Mn for Fe. The maximum value of magnetostriction coefficient is not much affected and the slope of the magnetostriction is increased with increasing Mn content. Higher maximum value of magnetostriction coefficient (lambda) of 234 ppm comparable to that of the unsubstituted composition with larger strain derivative (d lambda/dH) is obtained for x = 0.2 in CoFe2-xMnxO4. The magnetostriction coefficient is increased to 262 ppm with further enhancement in the strain derivative after annealing the sintered compact at 300 degrees C in a magnetic field of 400 kA/m for 30 min.
Research Interests:
Research Interests:
ABSTRACT The present work derives motivation from the so called surface/interfacial magnetism in core shell structures and commercial samples of Fe3O4 and g-Fe2O3with sizes ranging from 20 to 30 nm were coated with polyaniline using... more
ABSTRACT The present work derives motivation from the so called surface/interfacial magnetism in core shell structures and commercial samples of Fe3O4 and g-Fe2O3with sizes ranging from 20 to 30 nm were coated with polyaniline using plasma polymerization and studied. The High Resolution Transmission Electron Microscopy images indicate a core shell structure after polyaniline coating and exhibited an increase in saturation magnetization by 2 emu/g. For confirmation, plasma polymerization was performed on maghemite nanoparticles which also exhibited an increase in saturation magnetization. This enhanced magnetization is rather surprising and the reason is found to be an interfacial phenomenon resulting from a contact potential.
Research Interests:
Research Interests:
Research Interests:
In the work described in this paper, we have successfully fabricated flexible asymmetric supercapacitors (ASCs) based on transition-metal-oxide nanowire/single-walled carbon nanotube (SWNT) hybrid thin-film electrodes. These hybrid... more
In the work described in this paper, we have successfully fabricated flexible asymmetric supercapacitors (ASCs) based on transition-metal-oxide nanowire/single-walled carbon nanotube (SWNT) hybrid thin-film electrodes. These hybrid nanostructured films, with advantages of mechanical flexibility, uniform layered structures, and mesoporous surface morphology, were produced by using a filtration method. Here, manganese dioxide nanowire/SWNT hybrid films worked as the positive electrode, and indium oxide nanowire/SWNT hybrid films served as the negative electrode in a designed ASC. In our design, charges can be stored not only via electrochemical double-layer capacitance from SWNT films but also through a reversible faradic process from transition-metal-oxide nanowires. In addition, to obtain stable electrochemical behavior during charging/discharging cycles in a 2 V potential window, the mass balance between two electrodes has been optimized. Our optimized hybrid nanostructured ASCs exhibited a superior device performance with specific capacitance of 184 F/g, energy density of 25.5 Wh/kg, and columbic efficiency of approximately 90%. In addition, our ASCs exhibited a power density of 50.3 kW/kg, which is 10-fold higher than obtained in early reported ASC work. The high-performance hybrid nanostructured ASCs can find applications in conformal electrics, portable electronics, and electrical vehicles.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Water-dispersible magnetite nanoparticles functionalized with citric acid (CIT) modified β-cyclodextrin (CD) are prepared and curcumin (CUR) is loaded inside the cavity of CD. The CUR loading capacity of CD-CIT functionalized magnetite... more
Water-dispersible magnetite nanoparticles functionalized with citric acid (CIT) modified β-cyclodextrin (CD) are prepared and curcumin (CUR) is loaded inside the cavity of CD. The CUR loading capacity of CD-CIT functionalized magnetite nanoparticles is found to be much larger than that of CD alone as well as the CD-CIT conjugate. The release profile of curcumin is found to follow zero order kinetics at the physiological pH, and thus, can release CUR at a constant rate, after the initial burst release. Relaxivity studies using NMR showed that the functionalized nanoparticles are suitable for contrast enhancement in MRI. Thus, the water-dispersible, CIT modified β-CD functionalized magnetite nanofluid is an efficient carrier for water insoluble curcumin, and can be used for magnetic drug targeting/delivery as well as for contrast enhancement in MRI due to the superparamagnetic magnetite core.
Research Interests:
Superparamagnetic iron oxide nanoparticles of size ~5 nm surface functionalized with ascorbic acid (vitamin C) form a stable dispersion in water with a hydrodynamic size of ~30 nm. The anti-oxidant property of ascorbic acid is retained... more
Superparamagnetic iron oxide nanoparticles of size ~5 nm surface functionalized with ascorbic acid (vitamin C) form a stable dispersion in water with a hydrodynamic size of ~30 nm. The anti-oxidant property of ascorbic acid is retained after capping, as evidenced from the capability of converting methylene blue to its
reduced leuco form. NMR relaxivity studies show that the ascorbic-acid-coated superparamagnetic iron oxide aqueous nanofluid is suitable as a contrast enhancement agent for MRI applications, coupled with the excellent biocompatibility and medicinal values of ascorbic acid.
reduced leuco form. NMR relaxivity studies show that the ascorbic-acid-coated superparamagnetic iron oxide aqueous nanofluid is suitable as a contrast enhancement agent for MRI applications, coupled with the excellent biocompatibility and medicinal values of ascorbic acid.
Research Interests:
Research Interests:
High room temperature ferromagnetic moment with high Curie temperature (>700 K) for graphene oxide (GO) is obtained by a simple chemical activation using phosphoric acid followed by heat treatment at 800 oC. The field and temperature... more
High room temperature ferromagnetic moment with high Curie temperature (>700 K) for graphene oxide (GO) is obtained by a simple chemical activation using phosphoric acid followed by heat treatment at 800 oC. The field and temperature variations of the magnetization data indicate ferromagnetic, paramagnetic and diamagnetic contributions in the acid/heat treated sample. IR spectroscopic studies suggest hydrogenation (reduction) of GO after the acid and heat treatments. The results point to the role of defects, extent of hydrogenation, changes in the bonding characteristics and the nature of the functional
groups in determining the different magnetic contributions.
groups in determining the different magnetic contributions.