Chenrayan Senthil

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.

Micelle-templated synthesis of Pt hollow nanospheres for catalytic hydrogen evolution

As an alternative to galvanic replacement reactions and hard-template strategies, we report an efficient, mild and simple synthesis strategy for fabrication of colloidal platinum (Pt) hollow nanospheres. An aqueous asymmetric triblock copolymer poly(styrene-b-vinyl-2-pyridine-b-ethylene oxide) [PS(20.1k)–PVP(14.2k)–PEO(26.0)] micelle with core–shell–corona architecture has been found to be an efficient soft scaffold for the synthesis of Pt hollow nanospheres using K2PtCl6 as a metal precursor and NaBH4 as a reducing agent. In the core–shell–corona type micelles, the core serves as a template for void volume creation, the shell domain acts reaction site for inorganic precursors, and the corona stabilizes the composite particles. The polymer/Pt composite particles were solvent-extracted by refluxing with dimethyl formamide (DMF) at 160 °C to remove polymeric materials and obtain hollow particles. Investigation of precursor concentrations suggested that the wall-structures become irregular and uneven as the molar ratio of PVP/Pt(IV) increases from 1 : 12 to 1 : 25, whereas the use of polymers with large PS block length [PS(45k)–PVP(16k)–PEO(8.5)] results in the formation of spherical particles with slightly increased hollow void-space diameters. The polymeric micelles and Pt hollow nanospheres were thoroughly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), infra-red (FT IR), thermal (TG/DTA) and nitrogen sorption analyses. The catalytic activity of the Pt hollow nanospheres was investigated for hydrogen liberation from ammonia–borane (AB) by hydrolysis reaction at room temperature. The catalytic activity of the Pt hollow nanospheres reveals that they can serve as a promising heterogeneous catalyst towards hydrogen generation system using AB as solid hydrogen storage materials.

An efficient mesoporous carbon nitride (g-C3N4) functionalized Pd catalyst for carbon–carbon bond formation reactions

Metal nanoparticles in pristine form without any stabilizing agents and free from agglomeration are very critical for their function and diverse catalytic applications. With the goal to accomplish a molecularly defined Pd-based heterogeneous C–C bond forming catalyst, highly ordered mesoporous nitrogen-rich carbon nitride (MCN) polymers with extended three-dimensional π-conjugation have been used as solid supports. Here, palladium nanoparticles ca. Pd(II) and Pd(0) were dispersed onto MCN and used in a surface-exposed state that renders them with inherently high catalytic activity. The catalysts were thoroughly investigated by a series of characterization techniques such as small-angle XRD, TEM, EDAX, SEM, 13C MAS NMR, 1H NMR, FTIR, N2 sorption, and CHN analyses. The XRD, N2 sorption isotherms and TEM show that Pd-catalysts maintain a hexagonal mesoporous structure with a high surface area (355.9 m2 g−1) and pore volume of 0.63 mL g−1. 13C MAS NMR and FTIR spectroscopy confirmed the presence of triazine ring, NH2 and NH groups in the polymeric graphitic carbon nitrides. Both Pd(II) and Pd(0) catalysts exhibited good catalytic activities and product selectivities in the copper- and phosphine-free Sonogashira cross-coupling reaction between aryl iodide and aryl alkynes. Hot filtration tests confirmed the heterogeneity of the catalysts and the catalysts were reused for six successive reactions with negligible change in the conversion.