• Asim Bhaumik

      Articles written in Journal of Chemical Sciences

    • Mesoporous titanium phosphates and related molecular sieves: Synthesis, characterization and applications

      Asim Bhaumik

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      Titanium (IV) phosphates TCM-7 and -8 with mesoporous cationic framework topologies using both cationic and anionic surfactants have been synthesized. Experimental data suggest the stabilization of the tetrahedral state of Ti in TCM-7/8 (O-P-O-Ti-O-, at Ti/P = 1:1)vis-à-vis the most stable octahedral state of Ti in the rutile/anatase or pure mesoporous TiO2. Mesoporous TCM-7 and-8 show anion exchange capacity due to the framework phosphonium cation and cation exchange capacity due to defective P-OH groups. Grafting the organic functionality in the surface or bridging the organic moiety in between the inorganic phosphorus precursors can enhance hydrophobicity of these materials similar to that of mesoporous silica materials. The high catalytic activity in the liquid phase partial oxidation of cyclohexene over such organically surface modified mesoporous titanium phosphate using a dilute H2O2 oxidant supports the tetrahedral coordination of Ti in these materials. These materials also show excellent photocatalytic activity in the production of H2 by photo-reduction of water under UV light irradiation.

    • Facile Growth of Multi-twined Au Nanostructures

      Raj Kumar Bera Asim Bhaumik C Retna Raj

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      We describe a facile growth of chain-like Au nanostructures and their spontaneous transformation to multi-twined nanostructure using a mild reducing agent bisphenol A (BPA). The growth Au nanostructures involves the chemical reduction of HAuCl4 by BPA in the presence of cetyltrimethylammonium bromide (CTAB) as capping agent in alkaline condition without any seeds. Wire and chain-like Au nano-network structures with diameter in the range of 4 to 9 nm are obtained in the initial stage of the reaction. These chainlike nanostructures undergo spontaneous transformation into multi-twined nanostructures within 24 h. These nanocrystalline multi-twined structures have an average size of 80-90 nm. X-ray and selected area electron diffraction measurements reveal that the Au nanoparticles have (111), (200), (220) and (311) planes of a face centered cubic structure. High resolution transmission electron microscopic measurement shows that the nanostructures are mainly composed of (111) lattice plane with twin boundaries. The concentration of HAuCl4, BPA and CTAB has pronounced effect in the growth of nanostructures. The multi-twined nanostructures are highly stable at room temperature over a period of one month and can be used for catalytic applications.

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