Manas K. Bhunia

Self-assembled TiO2 nanoparticles: mesoporosity, optical and catalytic properties

Herein, we explore the idea of self-assembly of nearly monodisperse nanoparticles as uniform building blocks to design highly crystalline mesoporous TiO(2) nanoparticles, through evaporation-induced self-assembly (EISA) and hydrothermal methods by using non-ionic Pluronic F127 and anionic surfactant SDS, respectively as structure directing agents. The small- and wide-angle powder X-ray diffraction and transmission electron microscopy (TEM) are used to characterize the mesophases. N(2) adsorption-desorption studies and high-resolution TEM results further reveal that mesopores are formed by the arrangement of the nanoparticles of size ca. 4.0-5.0 nm for SDS-templated and 8.0-9.0 nm for F127-templated TiO(2) nanoparticles with broad interparticle pore size distribution. Optical properties of these nanomaterials are studied by UV-visible diffuse-reflectance spectroscopy, photoluminescence (PL) and time-resolved fluorescence (TCSPC). These nanostructured titania exhibited excellent catalytic activity in the photodegradation of ecologically abundant dyes Methylene blue and Rose Bengal under UV-visible light irradiation.

Crystal engineering of zinc(II) metal–organic frameworks: role of steric bulk and angular disposition of coordinating sites of the ligands

Three novel 2D and 3D coordination polymers, [Zn(TPA)(H2MDP)]n (1), [Zn(IPA)(H2MDP)]n (2) and [Zn(HTMA)(H2MDP)]n (3) (H2MDP = methylenebis(3,5-dimethylpyrazole), H2TPA = terephthalic acid, H2IPA = isophthalic acid and H3TMA = trimesic acid), have been synthesized under hydrothermal conditions and structurally characterized by single crystal X-ray diffraction. For all three structures, the zinc atoms show a coordination number of four and adopt tetrahedral geometry, and subsequently form a diamondoid, a (2,4) and a (4,4) network. The employment of sterically hindered H2MDP ligand, on the other hand, successfully prohibits interpenetration among the 2D grids. The complex 1 features a metal–organic framework exhibiting a three-fold interpenetrated diamondoid network with linear dicarboxylate ligand (H2TPA) as an auxiliary ligand. The bent dicarboxylate ligands (H2IPA and H3TMA), on the other hand, lead to 2D non interpenetrative grid networks for 2 and 3. A comparative study of 2 and 3 underpins the importance of the hydrogen bond and π–π interaction in the synthesis of coordination polymers.

Hierarchical mesoporous Fe/ZSM-5 with tunable porosity for selective hydroxylation of benzene to phenol

Hierarchical mesoporous Fe–ZSM-5 zeolite with catalytically active surface Fe species is prepared by introduction of Fe3+ in the synthesis gel of mesoporous ZSM-5 and the material synthesised with the optimum Fe content and optimum porosity is highly active and selective for the hydroxylation of benzene to phenol with nitrous oxide. The porosity of the material is controlled by the synthesis gel composition (organosilane template concentration). Samples prepared at high template/Si ratio (0.11) show lower zeolitic crystallinity and lower micropore volume but higher strong acidity than the samples prepared with low template/Si ratio (0.036). Samples with very high surface area, high strong acidity, low zeolitic wall crystallinity and 0.93 wt% Fe content show 1.3 times higher phenol formation rate than a steamed H-ZSM-5 sample. Silylation of the mesoporous catalyst resulted in 2-fold increase in initial phenol formation rate compared to steamed microporous H-ZSM-5 which is attributed to improved hydrophobicity and reduced Lewis acid sites, resulting in better desorption of the phenol product from catalyst.

Multifunctional behaviour of mesoporous LiNbO3

Mesoporous LiNbO3 nanoparticles with BET surface area 185 m2 g−1 were synthesized by using Pluronic P123 as soft template. The samples showed three functionalities, viz., photoluminescence, ferroelectricity, and ferromagnetism. Room temperature photoluminescence was observed at 390 nm wavelength due to oxygen vacancy. The mesoporous LiNbO3 showed ferromagnetic behavior at room temperature. Ferroelectric behavior of the samples was confirmed from the P-E hysteresis loop measurement. The samples showed a magneto-dielectric effect with the dielectric constant increasing by ∼4.5% for an applied magnetic field of 10 kOe due to magnetostriction of the material which changed the lattice parameter to bring about an increase in the dipole moment of the unit cell.

Influence of chloro⋯chloro interaction and π–π stacking in 3D supramolecular framework construction

A series of 1D and 2D coordination polymers have been synthesized under solvothermal conditions using a terminal ligand, 3,5,6-trichlorosalicylic acid (H2TCSA) and different bipyridine based ligands, 2,2′-bipyridyl (2,2′-BIPY), 4,4′-bipyridyl (4,4′-BIPY), 4,4′-trimethylene bipyridine (TMBP) and trans-1,2-bis(4-pyridyl)-ethylene (TBPE). The major aim of this work was to study the influence of weak interactions in constructing 3D supramolecular frameworks. A two-step crystal engineering strategy has been adopted for generating 3D supramolecular frameworks. Firstly, various lower dimensional coordination networks have been achieved and then 3D supramolecular frameworks were constructed from the self-assembly of these networks via weak intermolecular interactions among the organic parts. The latter was achieved with the usage of ligand systems that are devoid of any conventional hydrogen bonding functional group. On the other hand, employment of a terminal ligand serves the purpose of generating different lower dimensional architectures, ranging from discrete zero dimensional coordination complexes to 1D, 2D coordination polymeric networks. We report herein, two 0D complexes, [Zn(HTCSA)2(TBPE)2] (1), [{Zn(TCSA)(2,2′-BIPY)}4] (2), five 1D coordination polymers, [Zn(TCSA)(4,4′-BIPY)0.5(DMF)]n(3), [Zn(HTCSA)2(4,4′-BIPY)]n(4), [Zn(HTCSA)2(TMBP)]n(5), [Zn(HTCSA)2(TMBP)]n (6), [Zn(HTCSA)2(TBPE)(H2O)]n (7), and two 2D polymeric networks, [Zn(TCSA)(4,4′-BIPY)]n (8) and [{Zn(TCSA)(TBPE)}·(TBPE)]n (9), and two related cobalt and nickel complexes, [{Co(TCSA)(TBPE)}·(TBPE)]n (10) and [Ni(HTCSA)(TBPE)1.5·(NO3)]n (11). For all the structures, π–π stacking and halogen bonding were found to be instrumental in bringing the additional dimensions to the self-assembly of the lower dimensional networks and lead to diverse 3D supramolecular frameworks.

Direct Synthesis of 2D-Hexagonal Mesoporous Iron Silicate and its Catalytic Activity for Selective Friedel-Crafts Alkylation

D-hexagonal mesoporous iron silicate (HMFeS) has been synthesized hydrothermally in the presence of a mixture of an amphiphilic triblock copolymer, pluronic F127 and 1,2,4-trivinylcyclohexane (TVCH) as swelling agent under acidic aqueous conditions. The direct incorporation of iron(III) into 2D-hexagonal silicate framework can be monitored in a optimized molar ratio of water and hydrochloric acid. The mesophase of the materials was investigated by using small-angle powder X-ray diffractions (PXRD), transmission electron microscopy (TEM) image analysis and nitrogen adsorption/desorption studies. TEM image and PXRD revealed that the material had 2D-hexagonal mesoporous architecture. The morphology of the material was investigated by using scanning electron microscope (SEM) and framework bonding by utilizing FT IR spectroscopy. The atomic absorption spectrophotometer (AAS) was used to estimate the incorporated iron sites within the silicate framework. BET surface area (780 m 2 g -1 ) and peak pore size of HMFeS (10.07 nm) is much higher than the pure silica SBA-15 (611 m 2 g -1 and peak pore size of 9.09 nm). This mesoporous material (HMFeS) acts as a very good catalyst in the Friedel Craft benzylation and benzoylation reactions of arenes under optimized reaction condition using benzyl chloride and benzoyl chloride as the bezylating and benzoylating agents, respectively.