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Bakshi M.S.,Mount Saint Vincent University | Thakur P.,Guru Nanak Dev University | Khullar P.,Bbk Dav College For Women | Kaur G.,College of the Atlantic | Banipal T.S.,Guru Nanak Dev University
Crystal Growth and Design | Year: 2010

Lead selenide (PbSe) and copper selenide (CuSe) nanoparticles were synthesized in aqueous phase at a relatively mild temperature (85 C) in the presence of various cationic Gemini surfactants (12'2'12, 12'0'12, and 16'2'16) as capping/stabilizing agents. All nanoparticles exhibited clear core'shell (surfactant) morphologies. PbSe reactions produced predominantly platelike cubic morphologies along with long Se nanorods (NRs) as a reaction byproduct. CuSe particles were polyhedral thin plates with perforations. High resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD) measurements were used to characterize the shape and structure of the particles. HRTEM allowed us to measure the precise thickness of the surfactant shell around each nanocrystal (NC) which was in excellent agreement with the length of the surfactant hydrocarbon tail. Infrared spectroscopic (FT-IR) studies suggested a strong affinity of cationic surfactant for NC surface which was the driving force for the monolayer formation in the form of a shell. Energy dispersive X-ray spectroscopic (EDS) analysis demonstrated that PbSe and CuSe particles were always in 1:1 stoichiometry, and Se NRs were made up of only pure Se and no Pb contents were observed. Stronger interfacial adsorption of a surfactant with greater hydrophobicity controlled the morphology to produce platelike geometries. The size of PbSe and CuSe particles increased while the thickness decreased as the hydrophobicity of the surfactant increased in the order of 12'2'12 < 12'0'12 < 16'2'16. © 2010 American Chemical Society.

Khullar P.,BBK DAV College for Women | Mahal A.,BBK DAV College for Women | Singh V.,BBK DAV College for Women | Banipal T.S.,Guru Nanak Dev University | And 2 more authors.
Langmuir | Year: 2010

Aqueous micellar solutions of F68 (PEO78-PPO30- PEO78) and P103 (PEO17-PPO60-PEO17) triblock polymers were used to synthesize gold (Au) nanoparticles (NPs) at different temperatures. All reactions were monitored with respect to reaction time and temperature by using UV-visible studies to understand the growth kinetics of NPs and the influence of different micellar states on the synthesis of NPs. The shape, size, and locations of NPs in the micellar assemblies were determined with the help of TEM, SEM, and EDS analyses. The results explained that all reactions were carried out with the PEO-PPO-PEO micellar surface cavities present at the micelle-solution interface and were precisely controlled by the micellar assemblies. Marked differences were detected when predominantly hydrophilic F68 and hydrophobic P103 micelles were employed to conduct the reactions. The UV-visible results demonstrated that the reduction of gold ions into nucleating centers was channeled through the ligand-metal charge -transfer complex (LMCT) and carried out by the surface cavities. Excessive hydration of the surface cavities in the case of F68 micelles produced a few small NPs, but their yield and size increased as the micelles were dehydrated under the effect of increasing temperature. The results concluded that the presence of well-defined predominantly hydrophobic micelles with a compact micelle-solution interfacial arrangement of surface cavities ultimately controlled the reaction. © 2010 American Chemical Society.

Khullar P.,BBK DAV College for Women | Singh V.,BBK DAV College for Women | Mahal A.,BBK DAV College for Women | Dave P.N.,Krantiguru Shyamji Krishna Verma Kachchh University | And 5 more authors.
Journal of Physical Chemistry C | Year: 2012

Bovine serum albumin (BSA) conjugated gold (Au) nanoparticles (NPs) were synthesized to explore their applications as drug delivery vehicles in systemic circulation. They showed little hemolysis and cytotoxic responses essentially required for such applications. This study shows some of the important physiochemical aspects needed for an appropriate synthesis of BSA-conjugated NPs where unfolded BSA is an essential reaction component. Unfolding of BSA was carried out under different experimental conditions in the presence of different ionic/zwitterionic surfactants and monitored simultaneously by UV-visible studies. Cationic surfactants induced unfolding at relatively lower temperatures than anionic and zwitterionic surfactants due to stronger electrostatic interactions with BSA. TEM analysis revealed the presence of NPs with almost similar shapes and sizes for different samples, and all NPs were stabilized by a coating of unfolded BSA. Isoelectric point of unfolded BSA coating on NP surface was close to 4.7 in all cases, which was similar to that of unconjugated BSA. BSA free and cationic surfactant coated Au NPs were used as controls. They showed high hemolytic activity and very low cell viability under identical conditions. Thus, BSA coated NPs were considered to be the best vehicles for drug release and other possible biomedical applications. © 2012 American Chemical Society.

Singh V.,Bbk Dav College For Women | Khullar P.,Bbk Dav College For Women | Dave P.N.,Krantiguru Shyamji Krishna Verma Kachchh University | Kaura A.,Panjab University | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2014

Micelles of the star shaped block polymers "tetronics" were employed for the synthesis of gold (Au) nanoparticles (NPs) under the effect of pH and temperature variation. The presence of the diamine core in the tetronic macromolecule made its micelles highly pH responsive, thereby dramatically altering the physiochemical properties. Likewise, a high degree of hydration made the micelles temperature sensitive. UV-visible studies, transmission electron microscopy (TEM), gel electrophoresis, and structure optimization by energy minimization were applied to understand the physiochemical aspects of tetronic micelles and their further role in the synthesis of Au NPs. Synthesis of Au NPs was triggered by the surface cavities of the micelles and hence the NPs simultaneously adsorbed on the micelle surface. Low pH induced high hydration and temperature responsive well defined vesicular morphologies bearing Au NPs, while high pH produced mainly large and compact compound micelles carrying NPs. Both pH and temperature responsive behaviors of different tetronics significantly influenced the synthesis of Au NPs and thus demonstrated their ability to act as nanoreactors for the materials synthesis under different experimental conditions. © 2014 the Owner Societies.

Singh V.,Bbk Dav College For Women | Khullar P.,Bbk Dav College For Women | Dave P.N.,Krantiguru Shyamji Krishna Verma Kachchh University | Kaur G.,College of the Atlantic | Bakshi M.S.,Wilfrid Laurier University
ACS Sustainable Chemistry and Engineering | Year: 2013

Bioactive diethylaminoethyl dextran chloride (DEAE-D), a versatile polymer with numerous industrial applications, was used as a shape-directing agent for the synthesis of gold (Au) nanoparticles (NPs) in a typical green chemistry synthetic route. Shape-controlled growth was precisely directed by the quaternary amine functionalities of DEAE-D, while its polycationic nature provided simultaneous colloidal stabilization. Mechanistic aspects were drawn from different sets of reactions in which DEAE-D was directly used as a reducing agent with respect to reaction time and temperature. All reactions were simultaneously monitored with UV-visible studies, and NPs were characterized by TEM, SEM, and AFM analysis. Shape-controlled synthesis produced large extraordinarily thin microplates that were converted into small spherical NPs simply by switching the reaction to seed-growth (S-G) mode. DEAE-D-coated NPs thus produced were subjected to hemolysis for their possible use as drug release vehicles in systemic circulation so as to explore their possible biomedical applications. © 2013 American Chemical Society.

Bakshi M.S.,Wilfrid Laurier University | Kaur H.,Guru Nanak Dev University | Khullar P.,BBK DAV College for Women | Banipal T.S.,Guru Nanak Dev University | And 2 more authors.
Journal of Physical Chemistry C | Year: 2011

Bovine serum albumen (BSA) conjugated gold (Au) nanoparticles (NPs) were directly synthesized by using BSA as a weak reducing agent against HAuCl 4 in aqueous phase. A systematic variation in Au/BSA mole ratio showed a dramatic change in the size and shape of NPs which was very much dependent on the physical state of BSA. The nature of both colloidal NPs (due to surface plasmon resonance) and BSA (due to tryptophan residues) was monitored simultaneously by UV-visible measurements during the course of the reaction. A systematic variation in the reaction temperature from 20 to 70 °C demonstrated a clear denaturation process of BSA and how it influenced the synthesis of Au NPs. A predominantly native state of BSA that existed up to 40 °C proved to be a very mild reducing agent to convert Au(III) into Au(0). However, the reducing potential increased with unfolding of BSA beyond 40 °C and became maximum in the denaturation temperature range (i.e., 52-58 °C). Unfolded BSA conjugated NPs thus produced then started a seeding process with other similar NPs or free BSA to produce self-assembled colloidal assemblies in the form of soft film of BSA bearing NPs. SEM, TEM, and AFM studies were used to characterize the BSA conjugated NPs in the form of soft film. The soft film was used with water insoluble zein protein to produce very robust biodegradable protein films suitable for various food and pharmaceutical applications. Tensile strength and strain at failure measurements of zein protein films demonstrated that the film made with BSA conjugated NPs existed in the form of a soft film was much stronger and flexible in comparison to that made with nonaggregated NPs. © 2011 American Chemical Society.

Khullar P.,BBK DAV College for Women | Singh V.,BBK DAV College for Women | Mahal A.,BBK DAV College for Women | Kaur H.,Guru Nanak Dev University | And 4 more authors.
Journal of Physical Chemistry C | Year: 2011

Three block polymers, viz., L31, L64, and P123, were used as reducing agents for the synthesis of gold (Au) nanoparticles (NPs) to determine the effect of their micelle size, structure transitions, and environments on the mechanism of the reduction process leading to the overall morphology of Au NPs. Aqueous phase reduction was monitored with time at constant temperature and under the effect of temperature variation from 20 to 70 °C by simultaneous measurement of UV-visible spectra. The ligand to metal charge transfer (LMCT) band around 300 nm, due to a charge transfer complex formation between the micelle surface cavities and AuCl4 - ions, and Au NP absorbance around 550 nm, due to the surface plasmon resonance, were simultaneously measured to understand the mechanism of the reduction process and its dependence on the micelle structure transitions and environment of TBPs micelles. L64 micelles showed dramatic shift in the LMCT band from lower to higher wavelength due to an increase in the reduction potential of surface cavities induced by the structure transitions under the effect of temperature variations. This effect was not observed for micelles of either L31 or P123 and is explained on the basis of a difference in their micelle environments. The morphology of Au NPs thus evolved from the reduction process was studied with the help of TEM and SEM studies. Smaller micelle size with few surface cavities, as in L31, produced small NPs in comparison to large micelles with several surface cavities as in P123. Structure transitions of L64 demonstrated direct influence on the final morphology of NPs, and stronger transitions produced fused and deformed NPs in comparison to weaker transitions. The results showed that efficient reduction by the surface cavities and uninterrupted nucleation without structure transitions lead to well-defined morphologies in the presence of P123 micelles. © 2011 American Chemical Society.

Khullar P.,Bbk Dav College For Women | Singh V.,Bbk Dav College For Women | Mahal A.,Bbk Dav College For Women | Mahal A.,National Institute of Technology Jalandhar | And 3 more authors.
Journal of Physical Chemistry B | Year: 2013

Self-assembled gold (Au) nanoparticles (NPs) were synthesized in micelle surface cavities of a L121 block polymer in the presence of zwitterionic (viz. DPS, TPS, and HPS) and sugar surfactants (OG and DDM) in aqueous phase at 70 °C by using the surface cavities of L121 as reducing sites for converting Au(III) into Au(0). All reactions were monitored simultaneously by UV-visible spectroscopy to determine the growth kinetics in gold nucleating centers on the basis of surface plasmon resonance that also helped in tracing the structure micelle transitions over a wide temperature range of 10-70 °C. The surfactant/L121 mole ratio was changed systematically from 0.5 to 2.5 by keeping L121 and HAuCl4 concentrations constant at 10 and 0.25 mM, respectively, to determine the shape and size of the micelles and their relation to the self-assembled behavior of Au NPs. TEM studies were used to have a direct insight into the morphology of micelle templates and their shape and size for self-assembled NPs. L121 along with DPS (C12 carbon chain) produced well-defined micelles loaded with tiny NPs of 3-6 nm in the L121-rich region of the mixture, while large flower-like compound micelles with a clear core-shell morphology were produced in the DPS-rich region. TPS and HPS (C14 and C16 hydrocarbon chains, respectively) with stronger hydrophobicity than DPS also produced almost similar micelles loaded with tiny NPs in the L121-rich region, but they disappear in the surfactant-rich region. Replacement of zwitterionic with ionic surfactants did not yield micelle templates for self-assembled NPs. Results conclude that well-defined micelles of L121 are the fine templates for self-assembled NPs that can only be achieved in the presence of a neutral surfactant with low concentration and low hydrophobicity. © 2013 American Chemical Society.

Hastir A.,Guru Nanak Dev University | Kohli N.,BBK DAV College for Women | Singh R.C.,Guru Nanak Dev University
Sensors and Actuators, B: Chemical | Year: 2016

In the present work, influence of terbium doping on structural, morphological, optical and gas sensing properties of zinc oxide has been studied. A chemical route was adopted for synthesis of pure and terbium (Tb) doped zinc oxide. X-ray diffraction study confirmed the formation of hexagonal wurtzite structure for synthesized materials. Raman analysis revealed the shifting and broadening of peaks with increase in Tb concentration. The presence of terbium in ZnO and its oxidation states was confirmed using X-ray photoelectron spectroscopy. Photoluminescence emissions indicated increase in concentration of oxygen vacancies with introduction of dopant. Gas sensors were fabricated out of synthesized samples and it was observed that doped samples have significantly high sensing response, temperature dependent selectivity toward ethanol and acetone, and sensors were able to detect even low concentration (∼10 ppm) of these vapors. The temperature dependent selectivity of terbium doped ZnO depends on target gas which may be ascribed to interaction of target gas molecules and doped metal oxide surface at optimum operating temperature. It was found that 4% Tb doped ZnO sensor exhibited maximum sensor response toward ethanol and acetone. The enhanced sensing response has been attributed to increase in oxygen vacancies, reduction in particle size, large structural disorders and high surface basicity. © 2016 Elsevier B.V. All rights reserved.

Mohan S.,BBK DAV College for Women | Thind K.S.,Guru Nanak Dev University
Optical Materials | Year: 2016

Neodymium doped cadmium alkali borate glasses having composition 20CdO-20R2O-59.5H3BO3-0.5Nd2O3; (R = Li, Na and K) were prepared by conventional melt-quenching technique. The amorphous nature of the glasses was confirmed by X-ray diffraction studies. The physical properties such as density, refractive index, molar volume, rare earth ion concentration etc. were determined. Optical absorption and fluorescence spectra were recorded. The Judd-Ofelt theory was applied on the optical absorption spectra of the glasses to evaluate the three phenomenological intensity parameters Ω2, Ω4 and Ω6. These parameters were in turn used to predict the radiative properties such as the radiative transition probability (A), radiative lifetime (τR) and branching ratio (βR) for the fluorescent levels of Nd3+ ion in the present glass series. The lasing efficiency of the prepared glasses has been characterized by the spectroscopic quality factor (Ω4/Ω6), the value of which is in the range of 0.2-1.5, typical for Nd3+ in different laser hosts. The variation of Ω2 with the change in alkali oxide has been attributed to the changes in the asymmetry of the ligand field at the rare earth ion site. The shift of the hypersensitive bands, study of the oscillator strengths and the variation of the spectral profile of the transition 4I9/2 → 4F7/2 + 4S3/2 indicate a maximum covalency of Nd-O bond for glass with potassium ions. From the fluorescence spectra, peak wavelength (λp), effective line widths (Δλeff) and stimulated emission cross-section (σp) have been obtained for the three transitions 4F3/2 → 4I9/2, 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 of Nd3+ ion. The relatively high values of σp obtained for Nd3+ in present glass system suggest that these materials can be considered as suitable candidates for laser applications. The glass with potassium ions shows the highest value of the stimulated emission cross-section. © 2016 Elsevier B.V. All rights reserved.

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