Manickam Sasidharan

Triazine functionalized ordered mesoporous polymer: a novel solid support for Pd-mediated C–C cross-coupling reactions in water

A new functionalized mesoporous polymer (MPTAT-1) has been synthesized via organic–organic radical polymerization of 2,4,6-triallyloxy-1,3,5-triazine (TAT) in aqueous medium in the presence of an anionic surfactant (sodium dodecyl sulfate) as template. Powder XRD and TEM image analysis suggests the presence of ordered 2D-hexagonal arrangement of pores in the material. N2 sorption analysis reveals a moderately good surface area 135 m2 g−1 for this mesoporous polymer. The template free MPTAT-1 acts as an excellent support for immobilizing Pd(II) at its surface and the resulting material showed very good catalytic activity in several C–C cross-coupling reactions like Mizoroki–Heck, Sonogashira and Suzuki–Miyaura in an environmentally benign reaction medium, water. The catalyst exhibits very high catalytic activity for the coupling of various aryl halides including aryl chlorides with alkenes or alkynes and the sodium salt of (trihydroxy)phenylborate. Due to strong binding with the functional groups of the polymer, the anchored Pd(II) could not leach out from the surface of the mesoporous catalyst during the reaction and it has been reused several times without appreciable loss in catalytic activity.

Optical sensor for the visual detection of mercury using mesoporous silica anchoring porphyrin moiety

A low cost, solid optical sensor for the rapid detection of low concentrations of Hg2+ in aqueous media was prepared by the monolayer functionalization of mesoporous silica with 5,10,15,20-tetraphenylporphinetetrasulfonic acid (TPPS), anchored by N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride (TMAC). The detection is based on the color change of TPPS from orange to green as a result of the formation of a charge-transfer complex with Hg2+. The intensity of the charge-transfer band varies linearly with Hg2+ in the concentration range from zero to 2.5 x 10(-7) mol dm(-3). The lower detection limit observed for Hg2+ concentration is 1.75 x 10(-8) mol dm(-3). The material exhibits good chemical and mechanical stability, and did not show any degradation of TPPS for a period of eight months. The sensor was applied for the analysis of various environmental samples. The effects of pH, sample volume, reaction time, amount of material, and the presence of foreign ions on the detection method are discussed.

Synthesis, characterization and application for lithium-ion rechargeable batteries of hollow silica nanospheres

Hollow silica nanospheres with uniform size of about 30 nm have been successfully synthesized using a template of ABC triblock copolymer micelles of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS–PVP–PEO) with a core–shell–corona architecture. In this type of triblock copolymers, the PS block (core) works as a template of the void space of hollow silica, the PVP block (shell) acts as a reaction field for the sol–gel reaction of tetramethoxysilane (TMOS), and the PEO block (corona) stabilizes the polymer/silica composite particles. Use of polymers with different chain lengths of PS, PVP, and PEO led to hollow silica with tunable cavity size and wall thickness. The obtained hollow particles were thoroughly characterized by X-ray diffraction (XRD), thermal (TG/DTA) and nitrogen sorption analyses, infra-red (FT IR) and nuclear magnetic resonance (29Si MAS NMR) spectroscopies, and transmission electron microscopy (TEM). The efficiency of hollow silica nanospheres for lithium-ion rechargeable batteries is demonstrated for the first time. The hollow silica nanoparticles exhibited high cycle performance of up to 500 cycles in the lithium rechargeable batteries through the alloying/dealloying process. The tiny grain size of hollow nanospheres results in less volume expansion and/or contraction during charge/discharge cycles.

In-situ polymerization of grafted aniline in the channels of mesoporous silica SBA-15

Monolayer N-propylaniline functionalized mesoporous silica SBA-15 (MFMS) has been successfully used for the grafting of polyaniline moieties through in-situ polymerization in the presence of ammonium peroxodisulfate (APS) as oxidant. For comparison, siliceous SBA-15 has been used to prepare non-grafted polyaniline (PANI) nanocomposites. The SBA-15, MFMS, and PANI nanocomposites were thoroughly characterized through powder XRD, TEM, SEM, FTIR, TG-DTA and N2 sorption measurements. The powder XRD pattern and TEM image of MFMS show a hexagonal (p6mm) structure. The FTIR, TG-DTA and N2 sorption studies confirm the presence of lattice bound N-propylaniline groups in MFMS material. The decrease in mesopore volume of MFMS from 0.89 to 0.61 ml g−1 after polymerization indicates that the polymers are well packed inside the channels of SBA-15. The thermal analysis further reveals that covalently grafted polyaniline decomposes at much higher temperature than the non-grafted analogue. The increased electrical conductivity of grafted polyaniline compared to non-grafted composites is attributed to the presence of more counter ions and the increased intensity of the “electronic-like absorption’ band at 1155 cm−1 of the former. The grafted PANI exhibits electrorheological effects with an increased shear viscosity under an applied electric field compared with the non-grafted polyaniline nanocomposite.

Selective catalytic oxidation of cyclohexylbenzene to cyclohexylbenzene-1-hydroperoxide: a coproduct-free route to phenol

A method is described for the highly selective oxidation of cyclohexylbenzene to cyclohexylbenzene-1-hydroperoxide. In the presence of 0.5 mol% N-hydroxyphthalimide (NHPI) and 2 mol% of the hydroperoxide product, without solvent, a selectivity of ca. 98% to the desired product was obtained at 32% conversion. The use of NHPI increases the selectivity for initial H-abstraction from the 1-position, vs the other positions in the cyclohexyl ring, suppresses byproduct formation via transannular hydrogen abstraction and increases the overall rate of reaction.

Micelle templated NiO hollow nanospheres as anode materials in lithium ion batteries

Nano-sized nickel oxide (NiO) hollow spheres of size 28 ± 2 nm have been synthesized by a soft-template self-assembly process. ABC triblock copolymeric micelles of poly(styrene-b-acrylic acid-b-ethylene oxide) (PS–PAA–PEO) with core–shell–corona architecture serve as an efficient colloidal-template for fabrication of NiO hollow nanospheres. In the above polymeric template, the PS block (core) acts as a template of hollow void space, the PAA block (shell) with negative charges serves as the reaction site for metal ion interactions, and the corona domain stabilizes organic/inorganic composite particles. The PS–PAA–PEO template micelles as well as the NiO hollow nanospheres were thoroughly characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermal analysis (TG/DTA), FTIR spectroscopy, and nitrogen adsorption/desorption analyses. The XRD and TEM techniques confirmed the hollow spherical morphology and phase purity of nickel oxide nanoparticles. The NiO hollow nanospheres were further investigated as anode materials for lithium ion rechargeable batteries for the first time. The nanostructured electrode delivers a high capacity of 393 mA h g−1 after 50 cycles of charge–discharge at a rate of 0.3 C. More importantly, the hollow spherical electrode maintains the structural integrity and excellent cycling stability even after subjecting to a high rate of 10 C (high current density). The high electrochemical performance is attributed to hollow void space coupled with a nanosized NiO shell domain that facilitates fast lithium diffusion kinetics.

Synthesis of mesoporous hollow silica nanospheres using polymeric micelles as template and their application as a drug-delivery carrier

Mesoporous hollow silica nanospheres with uniform particle sizes of 31-33 nm have been successfully synthesized by cocondensation of tetramethoxysilane (TMOS) and alkyltrimethoxysilanes [RSi(OR)3], where the latter also acts as a porogen. ABC triblock copolymer micelles of poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-PVP-PEO) with a core-shell-corona architecture have been employed as a soft template at pH 4. The cationic shell block with 2-vinyl pyridine groups facilitates the condensation of silica precursors under the sol-gel reaction conditions. Phenyltrimethoxysilane, octyltriethoxysilane, and octadecyltriethoxysilanes were used as porogens for generating mesopores in the shell matrix of hollow silica and the octadecyl precursor produced the largest mesopore among the different porogens, of dimension ca. 4.1 nm. The mesoporous hollow particles were thoroughly characterized by small-angle X-ray diffraction (SXRD), thermal (TG/DTA) and nitrogen sorption analyses, infra-red (FTIR) and nuclear magnetic resonance ((13)C-CP MAS NMR and (29)Si MAS NMR) spectroscopies, and transmission electron microscopy (TEM). The mesoporous hollow silica nanospheres have been investigated for drug-delivery application by an in vitro method using ibuprofen as a model drug. The hollow silica nanospheres exhibited higher storage capacity than the well-known mesoporous silica MCM-41. Propylamine functionalized hollow particles show a more sustained release pattern than their unfunctionalized counterparts, suggesting a huge potential of hollow silica nanospheres in the controlled delivery of small drug molecules.

A facile and selective synthesis of β-keto esters via zeolite catalysed transesterification

Crystalline microporous aluminosilicates (zeolites) efficiently catalyse the transesterification of β-keto esters with high selectivity under environmentally safe reaction conditions.

Tailor-Made Hollow Silver Nanoparticle Cages Assembled with Silver Nanoparticles: An Efficient Catalyst for Epoxidation

A novel approach toward the synthesis of hollow silver nanoparticle (NP) cages built with building blocks of silver NPs by layer-by-layer (LbL) assembly is demonstrated. The size of the NP cage depends on the size of template used for the LbL assembly. The microcages showed a uniform distribution of spherical silver nanoparticles with an average diameter of 20 ± 5 nm, which increased to 40 ± 5 nm when the AgNO3 concentration was increased from 25 to 50 mM. Heat treatment of the polyelectrolyte capsules at 80 °C near their pKa values yielded intact nano/micro cages. These cages produced a higher conversion for the epoxidation of olefins and maintained their catalytic activity even after four successive uses. The nanocages exhibited unique and attractive characteristics for metal catalytic systems, thus offering the scope for further development as heterogeneous catalysts.

Novel and mild synthetic strategy for the sulfonic Acid functionalization in periodic mesoporous ethenylene-silica.

A new postsynthetic method has been developed for sulfonic acid functionalization of hybrid periodic mesoporous organosilica (PMO) materials containing carbon-carbon double bonds (-C═C-) located in mesoporous wall structures. Hexagonal mesoporous ethenylene-silicas (HME) with different pore sizes were synthesized by using P123, Brij76, and Brij56 surfactants and investigated for postsynthetic functionalization. The present functionalization strategy involves epoxidation of double bonds at -5 °C followed by conversion of the resulting epoxide with bisulfite ions at 65 °C and involves neither the use of well-known mercaptol/H2O2 nor harsh concentrated H2SO4 reagents during the course of -C═C- functionalization. The epoxidation step plays a crucial role in determining the amount of -SO3H groups functionalized onto the silica support which is optimized with respect to different synthesis parameters. The ethenylene-silicas both before and after chemical modification were thoroughly characterized by powder XRD, TEM, N2 adsorption, Raman spectroscopy, 13C and 29Si MAS NMR, and catalytic test reactions. X-ray powder diffraction measurements and sorption data indicated that the mesostructure was intact during the postsynthetic chemical modification. Raman spectra exhibited two strong bands at 1567 and 1290 cm(-1) for ethenylene-silica attributed to -C═C and -C-H stretching vibrations, respectively; whereas after epoxidation and sulfonation, new bands were observed at 1215 and 1035 cm(-1) corresponding to the epoxide and -SO3 stretching vibrations, respectively. 13C CP MAS NMR of surfactant extracted ethenylene-silica exhibits a signal at 146 ppm along with signals at 16.4 and 17.4 ppm. The appearance of new signals at 47.7 and 46.5 ppm is attributed to carbon atom with ≡C-OH and ≡C-SO3H groups, respectively. 29Si MAS NMR spectra exclusively showed T2 and T3 species at -73 and -82 ppm, respectively both before and after chemical modification and negligible amount of Q3 or Q4 species confirms the stability of Si-C bonds during the functionalization. The sulfonic acid-functionalized mesoporous ethenylene-silicas show high catalytic activity in esterification of acetic acid with ethanol under liquid-phase reaction conditions.