Debrina Jana

Anisotropic gold nanoparticle doped mesoporous boehmite films and their use as reusable catalysts in electron transfer reactions.

Anisotropic Au nanoparticle (NP) doped mesoporous and oriented boehmite films of about 2 microm in thickness were prepared and used as reusable catalysts. The films were characterized by grazing incidence X-ray diffraction (GIXRD), field emission scanning electron and transmission electron microscopies, optical absorptions and surface area and pore size measurements. GIXRD of the doped films showed a preferential growth of boehmite crystallites in the (020) plane. The electron microscopy studies revealed existence of dispersed anisotropic Au NPs of approximately 15-40 nm size range and irregular Au aggregates of approximately 200-300 nm inside the mesoporous boehmite films. The optical absorption of the films showed Au-plasmon bands at 605 nm and broad absorption covering the near-infrared (NIR) region due to the anisotropic Au nanostructures. These films showed excellent catalytic activities in both the organic (p-nitrophenol to p-aminophenol by sodium borohydride) and inorganic (ferricyanide to ferrocyanide by thiosulphate) electron transfer (redox) reactions in aqueous solutions with high rate constant values. The films can be easily separated after the reaction and reused several times without any significant degradation of their original catalytic activity.

Synthesis of Thick Mesoporous γ-Alumina Films, Loading of Pt Nanoparticles, and Use of the Composite Film as a Reusable Catalyst

Nanocrystalline mesoporous gamma-Al2O3 film of high thickness has been developed and characterized. The films were prepared on ordinary glass substrates by a single dip-coating method using boehmite (AlOOH) sols derived from aluminum tri-sec-butoxide in presence of cetyltrimethylammonium bromide (CTAB) as structure-directing agent. The dried films were heat-treated at 500 degrees C in air to remove the organics and strengthen the network. The GIXRD of the heat-treated (500 degrees C) film shows a broad peak in the low-angle region supporting the formation of worm-hole-like disordered mesostructures. The high-angle GIXRD, FTIR, and TEM of the films confirm the formation of gamma-Al2O3. N2 adsorption-desorption analyses showed that the heat-treated (500 degrees C) film has a BET surface area of 171 m(2) g(-1) with a pore volume of 0.188 cm(3) g(-1) and mean pore diameter 4.3 nm. Pt nanoparticles (NPs) (approximately 2.7 mol % with respect to the equivalent AlO(1.5)) were generated inside the mesopores of the heat-treated films simply by soaking H2PtCl6 solutions into it, and followed by thermal decomposition at 500 degrees C. The surface area and pore volume of the Pt-incorporated film have been reduced to 101 m(2) g(-1) and 0.119 cm(3) g(-1) respectively, confirming the inclusion of Pt NPs inside the pores. FESEM and TEM studies revealed uniform distribution of Pt NPs (2-8.5 nm; average diameter 4.9 nm) in the films. Catalytic properties of the Pt-incorporated films were investigated in two model (one inorganic and other organic) systems: reduction of hexacyanoferrate(III) ions by thiosulfate to ferrocyanide, and p-nitrophenol to p-aminophenol. In both the cases, the catalyst showed excellent activities, and the reduction reactions followed smoothly, showing isosbestic points in the UV-visible spectra. The catalyst films can be separated easily after the reactions and reused several times.

High Raman Enhancing Shape-Tunable Ag Nanoplates in Alumina: A Reliable and Efficient SERS Technique

Shape-tunable Ag nanoplates in alumina enable very strong SERS performances showing Raman enhancement factor >1 × 10(9), and allows for easy detection of analyte methylene blue having a concentration in the picomolar range. Raman enhancements have been systematically studied during the Ag nanoparticle-shape evolution from spherical nanoparticles to hexagonal nanoplates with sharp corners to truncated triangular nanoplates in alumina sol. Large SERS enhancement has been observed because of the uniform dispersion and embedment of Ag nanoplates in a relatively high dielectric alumina network where analyte molecules are held. This new approach gives uniform and strong SERS signal with reproducibility.

Spontaneous generation and shape conversion of silver nanoparticles in alumina sol, and shaped silver nanoparticle incorporated alumina films

Stable and well-dispersed Ag nanoparticles were generated by spontaneous reduction of AgNO3 in the partially acetylacetonato complexed aluminium tri-sec-butoxide solution without using any additional reducing agent. The addition of higher concentration of AgNO3 caused agglomeration of Ag nanoparticles resulting in precipitation. Use of polyvinylpyrrolidone as capping agent not only prevents the agglomeration but also causes a controlled growth of Ag nanoparticles in different shapes in alumina sol. The addition of varying concentrations of polyvinylpyrrolidone caused transformation of yellow alumina sol to green and blue coloured sol. These changes were due to the conversion of spherical (yellow) to a mixture of hexagonal and triangular (green), and finally truncated/filleted triangular (blue) Ag nanoparticles. These yellow, green and blue coloured alumina sols were used to prepare different shaped Ag nanoparticle doped optically transparent amorphous alumina films on glass substrates. The shape conversions of the Ag nanoparticles were studied systematically by UV/visible spectrometry, transmission electron microscopy and grazing incidence X-ray diffraction, and a mechanism of growth of the Ag nanoparticles in alumina sol was established.

Capping Agent-Free Gold Nanostars Show Greatly Increased Versatility and Sensitivity for Biosensing

We report the first assessment of the plasmonic biosensing capabilities of capping agent-free gold nanostars. Capping agent removal was carried out using aqueous solutions of sodium borohydride, which yielded a refractive index sensitivity of 474 nm/RIU for the polyvinylpyrrolidone (PVP)-free nanostars compared with 98 nm/RIU for PVP-coated gold nanostars. Following PVP removal, biotinylated thiol and streptavidin protein were added to the nanostars, which resulted in red shifts as large as 51 nm and a limit of detection as low as 0.1 pM. Refractive index-based sensing of prostate specific antigen (PSA) both in buffer and serum was then carried out and was shown to yield shifts as large as 127 nm and have a limit of detection of 100 pM in serum. Last, a sandwich assay involving PSA was developed to aggregate the nanostars together for greater sensitivity. The sandwich assay did, indeed, give shifts close to 200 nm and was capable of detecting 10(-17) M PSA in serum. The greatly increased sensitivity and amenability to functionalization of PVP-free gold nanostars should prove useful in applications ranging from catalysis to drug delivery.