Anirban Dandapat

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.

Installing Logic Gates in Permeability Controllable Polyelectrolyte-Carbon Nitride Films for Detecting Proteases and Nucleases

Proteases and nucleases are enzymes heavily involved in many important biological processes, such as cancer initiation, progression, and metastasis; hence, they are indicative of potential diagnostic biomarkers. Here, we demonstrate a new label free and sensitive electrochemiluminescent (ECL) sensing strategy for protease and nuclease assays that utilize target-triggered desorption of programmable polyelectrolyte films assembled on graphite-like carbon nitride (g-C3N4) film to regulate the diffusion flux of a coreactant. Furthermore, we have built Boolean logic gates OR and AND into the polyelectrolyte films, capable of simultaneously sensing proteases and nucleases in a complicated system by breaking it into simple functions. The developed intelligent permeability controlled enzyme sensor may prove valuable in future medical diagnostics.

Host-Mediated Synthesis of Cobalt Aluminate/γ-Alumina Nanoflakes: A Dispersible Composite Pigment with High Catalytic Activities

Cobalt aluminate/γ-alumina (CoAl(2)O(4)/γ-Al(2)O(3)) nanocomposite pigment with mesoporous structure has been synthesized. The method simply involves adsorption of Co(2+) ion on the surface of a commercially available boehmite (AlOOH) powder followed by the reaction of Co(2+) and AlOOH at relatively low temperature (500 °C) to obtain CoAl(2)O(4)/γ-Al(2)O(3) composite nanopowders. The formation of γ-Al(2)O(3) from boehmite induces the in situ generation of isostructural CoAl(2)O(4) (both crystallize as cubic spinel) at such a low temperature. The obtained intense blue powder of optimal composition (53.6 wt % CoAl(2)O(4) in γ-Al(2)O(3)) can be dispersed in glycerol and characterized by UV-visible, X-ray diffraction, Raman spectroscopy, TEM, and nitrogen sorption analyses. Raman studies confirm the formation of CoAl(2)O(4) phase in γ-Al(2)O(3). TEM studies reveal the formation of flake shaped (5-10 nm in width and 10-25 nm in length) nanopowders, and these flakes are assembled to form mesoporous structure. The specific surface area, total pore volume and average pore diameter of this powder are estimated to be ~118 m(2) g(-1), 0.1375 cm(3) g(-1), and 4.65 nm, respectively. This composite nanopowder has been used as an active catalyst for the decomposition of H(2)O(2) at room temperature and the decomposition follows the first order kinetics with rate constant value close to 2.3 × 10(-2) min(-1). This pigment nanopowder can be reused for several cycles without noticeable degradation of its original catalytic activity.

Hollow Au-Ag Nanoparticles Labeled Immunochromatography Strip for Highly Sensitive Detection of Clenbuterol

The probe materials play a significant role in improving the detection efficiency and sensitivity of lateral-flow immunochromatographic test strip (ICTS). Unlike conventional ICTS assay usually uses single-component, solid gold nanoparticles as labeled probes, in our present study, a bimetallic, hollow Au-Ag nanoparticles (NPs) labeled ICTS was successfully developed for the detection of clenbuterol (CLE). The hollow Au-Ag NPs with different Au/Ag mole ratio and tunable size were synthesized by varying the volume ratio of [HAuCl4]:[Ag NPs] via the galvanic replacement reaction. The surface of hollow Ag-Au NPs was functionalized with 11-mercaptoundecanoic acid (MUA) for further covalently bonded with anti-CLE monoclonal antibody. Overall size of the Au-Ag NPs, size of the holes within individual NPs and also Au/Ag mole ratio have been systematically optimized to amplify both the visual inspection signals and the quantitative data. The sensitivity of optimized hollow Au-Ag NPs probes has been achieved even as low as 2 ppb in a short time (within 15 min), which is superior over the detection performance of conventional test strip using Au NPs. The optimized hollow Au-Ag NPs labeled test strip can be used as an ideal candidate for the rapid screening of CLE in food samples.

Attomolar Level Detection of Raman Molecules with Hierarchical Silver Nanostructures Including Tiny Nanoparticles between Nanosized Gaps Generated in Silver Petals

We developed a route for synthesizing Ag nanostructures with tunable morphologies for ultrasensitive surface-enhanced Raman spectroscopy. Through the consecutive addition of three reducing agents (i.e., 4-mercaptobenzoic acid, trisodium citrate, and ascorbic acid) to an aqueous solution of silver nitrate, hierarchical flower-like Ag nanostructures were produced. The nanostructures had Ag petals in which nanosized gaps were generated, and small Ag nanoparticles were incorporated within the gaps. Theoretically, the nanostructures exhibited highly enhanced electric fields in the outer-shell regions where the small Ag nanoparticles were densely located. Combining the enhanced field effect with resonance effect of a Raman-active molecule (methylene blue) at a specific wavelength, measurable Raman signals were obtained at concentrations as low as 100 attomolar (10(-16) M; corresponding to 10(-21) mol). Key factors were discussed for the synthesis of the Ag nanostructures while finely controlling the morphologies of hierarchical Ag nanostructures, thereby modulating the intensity of surface-enhanced resonance Raman spectroscopy (SERRS) signals. Therefore, this synthetic method produces highly promising nanostructures for SERRS-based applications.

Spatially-controlled growth of platinum on gold nanorods with tailoring plasmonic and catalytic properties

We describe the synthesis of bimetallic dendritic platinum decorated gold nanorods (AuNRs) by the spatial control of Pt growth over gold nanorods using a heterogeneous seed-mediated growth method. The amounts of the Au seed and Pt-precursor were changed to achieve a tunable volume fraction of Pt coverage on the Au NRs surface. Pt nanostructures were spatially separated from each other, which was highly favorable for promising optical and catalytic properties. The dendritic-Pt decorated AuNRs with variable Au/Pt ratios were exploited to study their surface plasmonic properties and catalytic activities. Interestingly, the Pt decorated AuNRs showed strong surface plasmon resonance (SPR) peak due to noncompact dendritic Pt shell in contrast to the conventional core–shell Au@Pt nanoparticles (NPs). Moreover, the longitudinal peak of the AuNRs was finely tuned from 820 to 950 nm (NIR region) by controlling the volume fraction of the Pt decoration over the AuNRs. The catalytic activity of the dendritic-Pt decorated AuNRs on the reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH4) as reducing agent was studied and found to be superior to the activities compared to the monometallic Au NRs. Considering practical applications, dendritic-Pt decorated AuNRs nanostructures were immobilized successfully on the hydrophilic polyvinylidene difluoride (PVDF) film as an efficient reusable catalyst.

Development of Hybrid BiOClxBr1−x‐Embedded Alumina Films and Their Application as Highly Efficient Visible‐Light‐Driven Photocatalytic Reactors

A highly stable 75 wt % BiOClx Br1-x -loaded alumina composite film has been developed for the fabrication of glass-based photoreactors. A very simple approach has been adopted that does not involve the use of a special instrument and can be applied to all types of substrates irrespective to their size and shape. The structure and morphology of the films were well characterized by XRD, SEM, TEM, N2 -sorption, IR, Raman, and UV/Vis diffuse reflectance spectroscopy. BiOClx Br1-x microspheres (1-3 μm) with closely packed thin nanoplates (width ≈10 nm) were integrated within alumina to develop a hybrid film. The photocatalytic capacity of the films was evaluated for the decomposition of Rhodamine B (RhB) and naphthalene under visible-light irradiation. The composite films showed a remarkable photocatalytic activity and stability and have been reused for several cycles without any deterioration of their original activity.

Heterogemini surfactant assisted synthesis of monodisperse icosahedral gold nanocrystals and their applications in electrochemical biosensing

Icosahedral nanocatalysts (NCs) have shown very interesting physical and chemical properties owing to their multiply twinned nanostructures. Herein, we introduce a novel heterogemini surfactant (C10OhpNC8) assisted seed mediated growth approach for the synthesis of monodisperse icosahedral gold (Au) NCs in aqueous solution at room temperature. Very small shape impurities were observed in the resultant icosahedral Au NCs. Significantly improved monodispersity (relative standard deviation (RSD) of <10%) has been achieved by using a binary mixture of C10OhpNC8 and PVP as structure directing agents. Interestingly, the size of icosahedral Au NCs can be tuned ranging from 40 nm to 190 nm, which guides the surface plasmon resonance (SPR) peak to be tuned throughout the whole visible region and even to the near infrared (NIR) region. Furthermore, the developed icosahedral Au NCs specific probe has been designed to be applied as an easy electrochemical biosensor and successfully used to detect the bacteria Escherichia coli O157:H7 (E. coli O157:H7) with a detection limit of ∼10 colony forming units (CFU) mL−1. Notably, a much higher sensitivity of these icosahedral Au NCs probes has been achieved compared to the traditional colloidal gold immunochromatography (detection limit ∼103 CFU mL−1).

Pd-on-Au Supra-nanostructures Decorated Graphene Oxide: An Advanced Electrocatalyst for Fuel Cell Application

We report a very easy and effective approach for synthesizing unique palladium-on-gold supra-nanostructure (Au@Pd-SprNS)-decorated graphene oxide (GO) nanosheets. The SprNSs comprising Au nanorods as core and a unique close-packed assembly of tiny anisotropic Pd nanoparticles (NPs) as shell were homogeneously distributed on the GO surface via electrostatic self-assembly. Compared with the traditional one-pot method for synthesis of metal NPs on GO sheets, the size and shape of core-shell Au@Pd SprNSs can be finely controlled and uniformly distributed on the GO carrier. Interestingly, this Au@Pd-SprNSs/GO nanocomposite displayed high electrocatalytic activities toward the oxidation of methanol, ethanol, and formic acid, which can be attributed to the abundance of intrinsic active sites including high density of atomic steps, ledges and kinks, Au-Pd heterojunctions and cooperative action of the two metals of the SprNSs. Additionally, uniform dispersion of the SprNSs over the GO nanosheets prevent agglomeration between the SprNSs, which is of great significance to enhance the long-term stability of catalyst. This work will introduce a highly efficient Pd-based nanoelectrocatalyst to be used in fuel cell application.

A new mechanism for allylic alcohol isomerization involving ruthenium nanoparticles as a ‘true catalyst’ generated through the self-assembly of supramolecular triruthenium clusters

The primary objective of this study is to determine the ‘true catalyst’ in an allylic alcohol isomerization reaction involving μ3-oxo-triruthenium(III) acetate [Ru3O(OCOCH3)6(H2O)3][OCOCH3] as catalyst. This ruthenium-complex was previously presumed to act as a homogeneous catalyst. However, we have confirmed the heterogeneous nature of this catalytic reaction that proceeds through in situ-formed metallic nanoparticles. A new, five-step mechanism, where ruthenium nanoparticles are generated from the supramolecular triruthenium clusters during the reaction and guided the progress of the reaction, has been discovered. In this model, a stepwise reduction of ruthenium-centers within the complex is considered generating ruthenium nanoparticles during the reaction and those steps play a key role for the optimization process. Three autocatalytic steps have been proposed to obtain the best fitted profile for the reaction. The ‘true catalyst’ of the reaction has been identified as Ru0 nanoparticles having a certain size and geometry (described as ‘C’). In addition, the smaller sized particles (B) present in the reaction mixture are also believed to show some catalytic activity.