Tanmay Das

Disordered Mesoporous TiO2−xNx+Nano‐Au: An Electronically Integrated Nanocomposite for Solar H2 Generation

We report on H2 generation by photocatalysis driven by simulated white light by electronically integrated Au nanoparticles with multifunctional, disordered mesoporous TiO2−xNx (Au‐NT) nanocomposites. Solar H2 generation (1.5u2005mmolu2009h−1u2009g−1) from aqueous methanol has been demonstrated with Au‐NT nanocomposites. The water splitting activity of Au‐NT is attributed to the 21.1u2005ps lifetime of charge carriers observed from fluorescence lifetime measurements, which indicates a high electron‐injection efficiency from nano‐Au to the conduction band of TiO2, and hence charge separation as well as utilization. This is directly supported by the observation of a high photoluminescence emission intensity with Au‐NT that highlights the energy transfer from nano‐Au to TiO2. The p–n heterojunction observed between the Au (0u20090u20091) and TiO2 (1u20090u20091) facets helps towards the higher charge separation and their utilization. A low mesochannel depth (<10u2005nm) associated with disordered mesoporous TiO2−xNx helps the charge carriers to move towards the surface for redox reactions and hence charge utilization. Visible‐light absorption, as a result of the surface plasmon resonance of nano‐Au, is observed in a broad range between 500 and 750u2005nm, which helps in harvesting visible‐light photons. Finally, electronically integrated nano‐Au with TiO2−xNx in Au‐NT is evident from Raman and X‐ray photoelectron spectroscopy measurements. All of these factors help to achieve a high rate of H2 production. It is likely that a higher rate of H2 production than that reported here is feasible by strategically locating Au clusters in porous TiO2 to generate hot spots through electronic integration.

Emergence of nanoscale inhomogeneity in the superconducting state of a homogeneously disordered conventional superconductor

The notion of spontaneous formation of an inhomogeneous superconducting state is at the heart of most theories attempting to understand the superconducting state in the presence of strong disorder. Using scanning tunneling spectroscopy and high resolution scanning transmission electron microscopy, we experimentally demonstrate that under the competing effects of strong homogeneous disorder and superconducting correlations, the superconducting state of a conventional superconductor, NbN, spontaneously segregates into domains. Tracking these domains as a function of temperature we observe that the superconducting domains persist across the bulk superconducting transition, Tc, and disappear close to the pseudogap temperature, T*, where signatures of superconducting correlations disappear from the tunneling spectrum and the superfluid response of the system.

Conjugation of cytochrome c with hydrogen titanate nanotubes: novel conformational state with implications for apoptosis

We show that hydrogen titanate (H(2)Ti(3)O(7)) nanotubes form strongly associated reversible nano-bio-conjugates with the vital respiratory protein, cytochrome c. Resonance Raman spectroscopy along with direct electrochemical studies indicate that in this nano-bio-conjugate, cytochrome c exists in an equilibrium of two conformational states with distinctly different formal redox potentials and coordination geometries of the heme center. The nanotube-conjugated cytochrome c also showed enhanced peroxidase activity similar to the membrane-bound protein that is believed to be an apoptosis initiator. This suggests that such a nanotube-cytochrome c conjugate may be a good candidate for cancer therapy applications.

Anomalous enhancement in interfacial perpendicular magnetic anisotropy through uphill diffusion

We observed interfacial chemical sharpening due to uphill diffusion in post annealed ultrathin multilayer stack of Co and Pt, which leads to enhanced interfacial perpendicular magnetic anisotropy (PMA). This is surprising as these elements are considered as perfectly miscible. This chemical sharpening was confirmed through quantitative energy dispersive x-ray (EDX) spectroscopy and intensity distribution of images taken on high angle annular dark field (HAADF) detector in Scanning Transmission Electron Microscopic (STEM) mode. This observation demonstrates an evidence of miscibility gap in ultrathin coherent Co/Pt multilayer stacks.

Structure and chemistry across interfaces at nanoscale of a Ge quantum well embedded within rare earth oxide layers.

Structure and chemistry across the rare earth oxide-Ge interfaces of a Gd2O3-Ge-Gd2O3 heterostructure grown on p-Si (111) substrate using encapsulated solid phase epitaxy method have been studied at nanoscale using various transmission electron microscopy methods. The structure across both the interfaces was investigated using reconstructed phase and amplitude at exit plane. Chemistry across the interfaces was explored using elemental mapping, high-angle annular dark-field imaging, electron energy loss spectroscopy, and energy dispersive X-ray spectrometry. Results demonstrate the structural and chemical abruptness of both the interfaces, which is most essential to maintain the desired quantum barrier structure.

On-line Ammonia Sensor and Invisible Security Ink by Fluorescent Zwitterionic Spirocyclic Meisenheimer Complex

Ammonia is not only a highly important gas for civilization but also contribute significantly for climate change and human health hazard. Highly sensitive ammonia sensor has been developed from a fluorescent zwitterionic spirocyclic Meisenheimer complex. Moreover, formation of this Meisenheimer complex can also be utilized for selective as well as naked eye instant detection of nitro aromatic explosive picric acid. The presence of a quaternary nitrogen atom directly attached to the spiro carbon is the unique feature of this Meisenheimer complex. This excellent photoluminescent (PL) Meisenheimer complex has two distinct stimuli responsive sites. One is sensitive towards acid while the other one is towards the base. These two positions can be modulated by adding one equivalent acid and one equivalent base to result two new products which are non fluorescent. One of these two non fluorescent species was found very exciting because of its UV/Vis transparency. Utilizing this concept we have fabricated an on-line sensor for measuring ammonia in dry or humid and condensing sewer air. The sensor was robust against ambient temperature and humidity variation. We have also developed an invisible ink from this Meisenheimer complex, with potential application for security purpose.

A self-assembled peptide mimetic of a tubular host and a supramolecular polymer

Simple and efficient strategies for the generation of a supramolecular nanotube by self-assembly of acyclic modular building blocks and guest encapsulation remain an essentially unmet challenge. A tripeptide containing leucine, Aib and serine forms a rigid type-III′ β-turn structure stabilized by multiple intramolecular N–H⋯O and O–H⋯O hydrogen bonds. The modular building blocks self-assemble in a helical manner to develop a supramolecular nanotube. The formation of a self-assembled peptide mimetic of the nanotubular host has been proven with SEM, X-ray crystallography and other spectroscopic techniques. This supramolecular nanotube with a hydrophobic core has been used as the host for modular inclusion of designer hydrophobic guests to fabricate a supramolecular polymer. The interactions between the host and the guest were analyzed by using DLS and different spectroscopic techniques. The variable temperature NMR experiments show that with the increasing temperature the hydrophobic interactions between the host and the guest decrease, which indicates the sliding of the tubular host along the guest axle. Comparison of a coumarin based guest with a naphthalenediimide based guest shows that the latter have connected two tubular hosts and thus formed a supramolecular polymer. The formation of the supramolecular polymer has been proven with DLS, SEM and AFM and other spectroscopic techniques.

Formation of toroids by self-assembly of an α–α corner mimetic: supramolecular cyclization

An α-α corner mimetic self-assembles to form a rod-like supramolecular structure which bends and closes end-to-end like a cyclization reaction to form uniform toroids. Each peptide fragment containing l-leucine, α-aminoisobutyric acid (Aib) and l-tyrosine forms rigid 310 helical structures stabilized by multiple intramolecular N-HO hydrogen bonds. Two 310 helices are connected by the spacer 3-aminomethyl-benzylamine and maintain an angular distance of 120° and therefore mimic the α-α corner motif of a protein super secondary structure. The individual α-α corner subunits are themselves regularly interlinked through multiple water mediated intermolecular hydrogen-bonding interactions to form the rod-like supramolecular structure and toroids. The formation of the supramolecular structure has been proven with X-ray crystallography and other spectroscopic techniques. The cyclization of the supramolecular structure and toroid formation were studied by optical microscope, AFM and FE-SEM experiments. Despite other assignments such as exfoliation of graphene from graphite, the compound exhibits significant memory to finally produce the toroids.

Mopping up the Oil, Metal, and Fluoride Ions from Water

The recycle, cleaning, and reuse of water are highly important for environmental remediation. This issue is addressed by creating a fluorescent zwitterionic spirocyclic Meisenheimer complex with high chelating propensity for toxic metals using low-cost starting materials and a one-pot synthesis technique. The resulting material is able to detect fluoride up to 12.8 ppb level and remove 82% aqueous fluoride from 1000 mL of 100 ppm fluoride solution in a single contact. The material demonstrates rapid kinetics and is capable of dropping the toxic metal ion (Pb/Hg/Cd) concentration below 0.2 ppb within 10 min. A resin-free, precipitation-free, and reusable technique has been developed for the removal of toxic metal ions and fluoride from extremely polluted water. Moreover, utilizing its extreme hydrophobicity, polystyrene sponges have been coated with the Meisenheimer complex to mop up oil spill and organic solvents from a biphasic mixture.

Self-assembled peptide microspheres for sustainable release of sulfamethoxazole

The self-assembly of two peptides Boc-Phe-Aib-Gabu-OMe 1 and Boc-Tyr-Aib-Gabu-OMe 2 (Aib = α-aminoisobutyric acid, Gabu = γ-aminobutyric acid) containing a core of a conformationally rigid achiral amino acid and a conformationally flexible achiral amino acid at the C-terminus was studied to fabricate a sustainable delivery vehicle. From X-ray crystallography, peptide 1 with the Phe residue adopts a type II turn-like structure whereas the Tyr analogue 2 adopts a type II′ turn-like structure. However, peptide 1 self-associates to form four membered ring-like porous structures through multiple intermolecular hydrogen bonds but peptide 2 self-associates to form five membered ring-like porous structures by intermolecular hydrogen bonds. Field emission scanning electron microscopy (FE-SEM) revealed that both the peptides exhibit microsphere morphologies. Further, these microspheres were loaded with the bacteriostatic antibiotic sulfamethoxazole. The growth inhibition of E. coli is greater for the peptide 1-sulfamethoxazole formulation than for the peptide 2-sulfamethoxazole formulation which indicates that the formulation leads to sustained release of the encapsulated drug. The peptide 2 microspheres slowly release the encapsulated sulfamethoxazole, more so than the peptide 1 microspheres.