Efficient visible-light-driven photocatalytic degradation of nitrophenol by using graphene-encapsulated TiO2 nanowires.

In this work, a new hybrid nanocatalyst, namely titanium dioxide (TiO2) composite nanowires, encapsulated with graphene (G) and palladium nanoparticles (Pd NPs) (designated as G-Pd@TiO2-CNWs), was prepared. In preparing the nanowires, a combination of electrospinning and hydrothermal approaches was employed. The visible-light-driven photocatalytic performance of G-Pd@TiO2-CNWs was investigated using the reduction of 4-nitrophenol (4-NP) as a model reaction. The results showed that G-Pd@TiO2-CNWs converted nearly 100% of 4-NP under visible light irradiation. The reaction kinetics of the photocatalytic reduction of 4-NP was studied by UV-vis spectrophotometry and the apparent rate constant was determined and compared with those for other supported TiO2 catalysts. Furthermore, the spent G-Pd@TiO2-CNWs could be recovered by simple centrifugation and reused. The work is expected to shed new light on the development of G-incorporated hybrid nanostructures for harvesting light energy and on the development of new photocatalysts for the removal of environmental pollutants.

Nanodiamond based sponges with entrapped enzyme: a novel electrochemical probe for hydrogen peroxide.

A "modular approach" has been demonstrated for the preparation of nanodiamond (ND) based sponges (NS) with entrapped enzyme (horseradish peroxidase, HRP) (ND-NS(HRP)) and utilization as an electrochemical probe for detection of hydrogen peroxide (H2O2). ND-NS comprises ND, porous poly(aniline)-poly(2-acrylamido 2-methyl propane sulfonic acid) (PANI-PAMPSA) network and entrapped HRP. Field emission scanning electron microscope image of ND-NS(HRP) reveals sponge like suprastructure comprising interconnected nanospheres with numerous openings/pinholes/cavities. The entrapped HRP in ND-NS exhibits effective direct electron transfer with an electron transfer rate constant of 1.85 s(-1). ND-NS(HRP) exhibited excellent bioelectrocatalytic reduction of hydrogen peroxide (H2O2) with a wide linear concentration range (1-45 mM), quick response (5s), high sensitivity (129.6 µAM(-1)) and low detection limit 59 µM (S/N=3).

Large-scale preparation of polyaniline nanospheres anchored with thiol-stabilized gold nanoparticles.

Reported herein is the preparation of a new nanostructured composite consisting of PANI(SH) (where PANI(SH) is poly(aniline-co-4-aminothio phenol)) and gold nanoparticles (AuNPs)) via "seed"-induced bulk polymerization. The PANI(SH)-AuNPs composite was designated as PANI(SH)-Au-NS(P). The composite was characterized in terms of its morphology and structural, thermal, and electrochemical properties. The field emission scanning electron microscopy (FESEM) image of PANI(SH)-Au-NS(P) revealed the presence of PANI(SH) nanospheres (sizes: approximately 150-250 nm) with finely distributed AuNPs (approximately 10 nm). The usefulness of PANI(SH)-Au-NS(P) as an electrocatalyst towards the oxidation of methanol was tested.

Strategically functionalized carbon nanotubes as the ultrasensitive electrochemical probe for picomolar detection of sildenafil citrate (Viagra).

The present work demonstrates the utility of the functionalized carbon nanotubes, poly(4-aminobenzene sulfonic acid) (PABS) grafted multiwalled carbon nanotubes, MWNT-g-PABS, as an electrode modifier towards achieving ultrasensitive detection of a model drug, sildenafil citrate (SC). PABS units in MWNT-g-PABS interact with SC, pre-concentrate and accumulate at the surface. The electron transduction from SC to electrode is augmented via MWNT-g-PABS. As a result, the MWNT-g-PABS modified electrode exhibited ultrasensitive (57.7 µA/nM) and selective detection of SC with a detection limit of 4.7 pM. The present work provides scope towards targeting ultrasensitivity for the detection of biomolecules/drug through rational design and incorporation of appropriate chemical components to carbon nanotubes.

Preparation of poly(1,5 diamino naphthalene) nanobelts/nanodiscs through a "hard-soft combined templates" approach.

This is the first report on the preparation of nanobelts/nanodiscs of poly(1,5-diamino naphthalene) (PDAN-P) in bulk quantities through a "hard-soft combined templates" approach. PDAN was nanostructured within the channels of MCM-41 (hard template) in the presence of beta-napthalene sulfonic acid (beta-NSA) (soft template) and further used as the seed for the bulk preparation of pure PDAN nanobelts/nanodiscs of PDAN (PDAN-P). Field emision scanning electron microscope image reveals that a typical nanobelt has a length of approximately 3 microm, with a uniform breadth of approximately 150 nm and a thickness of approximately 50 nm. UV-Visible spectrum reveals that the electronic features of PDAN-P are different from PDAN prepared by conventional method (PDAN-C). The electrochemical and interfacial characteristics of PDAN-P were evaluated by cyclic voltammetry and impedance spectroscopy and compared with PDAN-C. The current density characteristics of ITO/PDAN-P and ITO/PDAN-C were also compared. The potential for the onset of current and the current densities beyond the onset potentials were higher at ITO/PDAN-P than for ITO/PDAN-C. Results from electrochemical imedance spectroscopy informed that the ac conductivity of PDAN-P is higher than PDAN-C. Thus, PDAN-P exhibits distinctly different electronic and electrochemical characteristics as compared to PDAN-C.

Preparation of poly(2-amino thiophenol) nanodiscs by a "combined hard-soft template" approach and characterization.

A seed induced chemical oxidative polymerization was used for the preparation of pure poly(2-amino thiophenol) nanodiscs (P2AT-NDs (P)). Two templates, (hard (MCM-41) and soft (ß-napthalene sulfonic acid), were utilized for the preparation of the seed, P2AT nanostructures loaded MCM-41. The field emission scanning electron microscopy reveals nanodisc morphology for P2AT (P). X-ray diffraction, current-potential characteristics and electrochemical impedance spectroscopy were used to evaluate the physicochemical properties of P2AT-ND (P). The P2AT-ND (P) exhibits semicrystalline behaviour, good electron transport and lesser charge transfer resistance at the interface as compared to simple P2AT prepared by conventional chemical route.

Nanomolar detection of dopamine at multi-walled carbon nanotube grafted silica network/gold nanoparticle functionalised nanocomposite electrodes.

This is the first report on ultrahigh sensitive and selective electrochemical detection of nanomolar concentrations of dopamine (DA) in the presence of ascorbic acid (AA) at a modified electrode fabricated with a new functional nanocomposite, comprising of multi-walled carbon nanotube (MWNT) grafted silica network (silica NW) and gold nanoparticles (Au NPs) (MWNT-g-silica NW/Au NPs). The fabrication of MWNT-g-silica NW/Au NPs modified electrodes involves two steps: covalent functionaliztion of MWNT with silica NW and deposition of Au NP. Cyclic voltammetry and differential pulse voltammetry experiments were performed for the individual and simultaneous electrochemical detection of DA (in nanomolar concentrations) and AA. Differential pulse voltammograms at ITO/MWNT-g-silica NW/Au NPs modified electrode (ME) revealed that the current response is linear for DA in the concentration range of 0.1 nM-30 nM with a detection limit of 0.1 nM. This is the lowest detection limit reported for DA. A plausible mechanism is presented for the excellent performance of ITO/MWNT-g-silica NW/Au NPs-ME towards nanomolar detection of DA. The results revealed that MWNT, silica NW and Au NPs in ITO/MWNT-g-silica NW/Au NPs-ME synergistically contribute to the ultrasensitivity and selectivity for the electrochemical detection of nanomolar concentrations of DA in the presence of coexisting species.

Covalently linked silica-multiwall carbon nanotube-polyaniline network: an electroactive matrix for ultrasensitive biosensor.

A three dimensional network comprising of covalently linked multi-walled carbon nanotubes (MWNT), silica and polyaniline chains (MWNT-Silica-PANI-NW) was prepared and used as the matrix for immobilization of an enzyme (horseradish peroxidase, HRP). MWNT-Silica-PANI-NW-HRP electrode showed superior performances over the individual components and their binary combinations, in terms of enzyme stability (minimum leaching to the medium), fast electron transfer from the enzyme to the electrode (2.11s(-1)), high sensitivity (58.1microAmM(-1)) and low detection limit (1pM) for the detection of hydrogen peroxide. The interconnected silica network provides open porous frame work for effective immobilization of the redox enzyme. The PANI units and MWNTs facilitate the electron transfer process and functions as molecular cable to "wire" the primary redox site of the enzyme (HRP) to the electrode. The improved performances for MWNT-Silica-PANI-NW arise from the synergistic contributions from conducting CNT, electron mediating PANI chains and porous silica network.

Fabrication of a novel layer-by-layer film based glucose biosensor with compact arrangement of multi-components and glucose oxidase.

Layer-by-layer (LbL) film based glucose biosensor was fabricated with alternative layers of a nanocomposite (comprising of multiwalled carbon nanotubes (MWNTs), Au nanoparticles (Au NPs) and thiol functionalized polyaniline (PANI(SH)) and glucose oxidase (GOx). The successful formation of multilayers was confirmed by UV-visible spectroscopy. The components in the nanocomposite provide adequate electron transfer path between GOx and the electrode. A high value for the rate constant of electron transfer process (27.84 s(-1)) was observed at [GOx/Au-(SH)PANI-g-MWNT](n)/ITO electrode. The [GOx/Au-(SH)PANI-g-MWNT](n) biosensor exhibited high sensitivity (3.97 microA/mM) for the detection of glucose over a concentration range of 1-9 mM with a low detection limit of 0.06 microM.

Electrochemical detection of celecoxib at a polyaniline grafted multiwall carbon nanotubes modified electrode.

A modified electrode is fabricated by grafting polyaniline (PANI) chains onto multiwall carbon nanotubes (MWNTs) and utilized for the adsorptive reduction of celecoxib (CEL). PANI-g-MWNTs modified electrode appreciably enhances the sensitive detection of CEL in extremely lower concentrations (1x10(-11)M). Square wave stripping voltammogram (SWSV) shows a reduction peak at -1.08V with a high peak current for SW frequency of 100Hz, amplitude of 25mV and step height of 6mV. The high surface area of PANI-g-MWNTs is effectively utilized for the adsorption of CEL to preconcentrate at the electrode. The PANI chains covalently linked to MWNTs mediate the electron transfer processes. The present finding open-up the scope for extending on the use of other conducting polymers grafted MWNTs modified electrodes for the detection of compounds that do not have surface-active properties at conventional electrodes.