Kingsuk Mukhopadhyay

Facile reduction of para-nitrophenols: catalytic efficiency of silver nanoferns in batch and continuous flow reactors

The catalytic efficiency of silver-nanoferns (Ag-NFs) decorated on carbon microfiber surfaces has been investigated. The Ag-NFs were grown on carbon microfibers employing electrodeposition technique using an electrolytic solution of aqueous silver nitrate and boric acid. The structure of grown Ag-NFs has nanoscaled sub-branches of sizes ≤50 nm that could be controlled by applied voltage and electrodeposition time. Using a specially designed home-made glass reactor, the catalytic efficiency of the Ag-NFs grown over carbon microfibers (cAg-NF) has been measured and tested for a model catalytic reaction of para-nitrophenol reduction mediated by sodium borohydride, both in batch and continuous flow modes of operation. The cAg-NFs have shown excellent catalytic activity with a normalized rate constant κ = 3.42 s−1 g−1. The reusability for the cAg-NFs has been observed up to seven cycles of operation without much degradation in the catalytic efficiency. The integrated c-Ag-NF catalyst system and the designed reactors are simple and can be easily incorporated for facile effluent treatment or in other applications where catalytic reduction may be required.

Immobilization of individual nanotubes in graphitic layers for electrical characterization

A simple route is followed to produce an abundance of individual carbon nanotubes (CNTs) immobilized in graphitic layers to counter the challenge of locating individual CNTs and restrict the lateral displacement of CNTs due to the high electrostatic force exerted by a scanning tunnelling microscope tip for electrical characterization. Graphitic layers are selected for the embedding matrix as graphite and the nanotubes have a similar work function and hence would not perturb the electrical configuration of the nanotube. Solvent mediated exfoliation of graphite layers to insert the nanotubes was preferred over oxidative expansion, as oxidation could perturb the electrical configuration of graphite. During the exfoliation of graphite the optimized amount of nanotubes was introduced into the medium such that an individual nanotube could be immobilized in few-layer graphene followed by precipitation and centrifugation. The dose and the time of sonication were optimized to ensure that damage to the walls of the nanotubes is minimized, although the ultrasonication causes scissoring of the nanotube length. This procedure for immobilizing nanotubes in graphitic layers would be equally applicable for functionalized CNTs as well. The capability of embedding individual nanotubes into a similar work function material in an organic solvent, which could then be transferred onto a substrate by simple drop casting or spin coating methods, has an added advantage in sample preparation for the STM characterization of CNTs.

A Real Time Analysis of the Self-Assembly Process Using Thermal Analysis Inside the Differential Scanning Calorimeter Instrument

The supramolecular assembly of the regioregular poly-3-hexylthiophene (rr-P3HT) in solution has been investigated thoroughly in the past. In the current study, our focus is on the enthalpy of nanofiber formation using thermal analysis techniques by performing the self-assembly process inside the differential scanning calorimetry (DSC) instrument. Thermogravimetric analysis (TGA) was carried out to check the concentration of the solvent during the self-assembly process of P3HT in p-xylene. Ultraviolet visible (UV-vis) spectophotometric technique, small-angle X-ray scattering (SAXS) experiment, atomic force microscopic (AFM), and scanning electron microscopic (SEM) images were used to characterize the different experimental yields generated by cooling the reaction mixture at desired temperatures. Comparison of the morphologies of self-assembled products at different fiber formation temperatures gives us an idea about the possible crystallization parameters which could affect the P3HT nanofiber morphology.

Engineering the physical parameters for continuous synthesis of fullerene peapods

Previous efforts to insert fullerenes into a carbon nanotube (CNT) involved the isolated synthesis of CNTs and fullerenes and then annealing CNTs and fullerenes together for encapsulation. We demonstrated the process for the continuous production of fullerene peapods inside the arc instrument by modifying the conventional arc ablation system, which can be repeated to obtain the desired mass scale product. Inside the arc discharge unit, by using the tunable external magnetic field, the double-walled CNTs (DWCNTs) were first synthesized and then directed to deposit onto the water cooled aluminium (Al) plate. The openings were created on DWCNTs by controlled heating of the Al plate and then fullerenes were synthesized and deposited on DWCNTs. In the arc instrument, fullerenes were finally directed to enter into DWCNTs from the defect sites by heating the Al plate in a vacuum. The formation of the peapod was established by the structure-property studies despite the huge deposition of metal catalyst nanoparticles and fullerenes on the surface of the nanotube which were a serious challenge for molecular level characterization of the grown peapod structures.