Xiaohai Bu

Template-controlled fabrication of hierarchical porous Zn–Al composites with tunable micro/nanostructures and chemical compositions

The properties of materials are largely determined by the microstructures and components of materials. The design of layered double hydroxide (LDH) based composites has garnered much interest as a way of fabricating novel multiscale architectures with tunable micro/nanostructures and chemical compositions. The present study aims at exploiting the Zn–Al composites for controlled synthesis of multi-scale structures and multi-component materials. Firstly, microscaled Al2O3 fibers are successfully fabricated via a simple, convenient, and cost-effective biotemplate method employing paper fibers as bio-templates. Then, the multi-scale architectures are designed by an in situ growth method, which involves direct growth of nanoscaled LDH platelets on the surfaces of Al2O3 fibers. Finally, the multi-component LDH based materials are prepared based on the controlled crystal growth of LDHs and ZnO. The microstructure, morphology, and textural properties of the as-prepared samples are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption/desorption. The experimental results show that the longer reaction times are favorable for the crystal growth of LDHs, and the higher hydrothermal temperatures are favorable for the formation of ZnO. This study shows that the design of multi-scale structures and multi-components Zn–Al composites can be extended for the preparation of other hierarchical LDH based materials with controlled morphological and tunable chemical compositions for separation, catalysis, adsorption, sensor, and optical applications.

Two-dimensional ultrathin nanosheets of Ni–In-layered double hydroxides prepared in water: enhanced performance for DNA adsorption

This work describes a facile approach for the delaminating of Ni–In-layered double hydroxides (LDHs) by the intercalation of acetate anions in the LDHs gallery using co-precipitation method. The acetate-intercalated Ni–In LDHs exhibited swelling behavior in water and delaminated into semitransparent suspensions on the action of water. The transmission electron microscopy (TEM) and atomic force microscopic (AFM) observations revealed the formation of unilamellar LDHs nanosheets. This simple method did not need reflux at high temperatures, overcoming the deficiency of using organic solvents, resulting in a steady colloidal suspension of 2D nanosheets. The unique properties of 2D ultrathin nanosheets with full access to the positively charged activity sites make them attractive in terms of the improvement of DNA adsorption. The effect of dosage on the adsorption of DNA and the adsorption isotherm were investigated in detail. The equilibrium data were found to be well described by both the Langmuir and Freundlich models. Based on the mechanism of adsorption, the adsorption sites of exfoliated nanosheets can be easily occupied by highly negatively charged small anions through electrostatic interactions. The adsorbed DNA can be released via the addition of a hydrogen phosphate solution.

Novel design, facile synthesis and low infrared emissivity properties of single-handed helical polysilanes

The novel single-handed helical polysilanes (HPS), poly[di-n-hexylsilane-co-(methoxycarbonyl ethyl propyl ether)methylsilane] were synthesized by the Wurtz-type coupling of the chiral functional monomer, dichloro(methoxycarbonyl ethyl propyl ether)methylsilane (DCMMS). The monomer was prepared by the hydrosilylation reaction of methyl (S)-2-(allyloxy)propanoate. The chemical structure of HPS was confirmed by 1H, 13C and 29Si nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis) and circular dichroism (CD). The weight distributions and crystallinity of the polysilanes were demonstrated by gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and polarized light microscopy (POM), respectively. The single-handed helical characterization and polymerization degree of the new-typed polysilanes could be controlled by the co-monomers of DCMMS and di-n-hexyldichlorosilane (DCDHS), respectively. Furthermore, the infrared emissivity values (0.598 at 8–14 μm) of HPS were investigated by an Infrared Emissometer.

Preparation and Characterization of Micron-Sized PMMA/SiO2 Composite Microspheres

Micron PMMA microspheres which had PVP-g-PMMA graft polymers on the surface were prepared via a dispersion polymerization method by using the PVP K-30 as the dispersant. Because of the PVP-g-PMMA graft polymers, SiO2 nanoparticles were successfully introduced to the PMMA microsphere’s surface through the TEOS hydrolysis method. SEM and other tests suggested micron-sized PMMA/SiO2 composite microspheres were successfully synthesized. SiO2 nanoparticles could grow on the PMMA microspheres, probably because SiO2 was attracted chemically to the carbonyl bonds on the PVP molecules.

Design of micro–mesoporous zeolite catalysts for alkylation

Hierarchical zeolite Y was hydrothermally synthesized using ionic liquid 1-methyl-3-[3′-(trimethoxysilyl)propyl]imidazolium chloride, which was added into the conventional synthesis composition for crystalline microporous aluminosilicate as a mesopore-directing agent. An extremely short diffusion path length and abundant exposed acid sites in the hierarchical zeolite Y made it suitable for the catalytic transformation of bulky molecules. Then the catalytic performance of hierarchical zeolites Y was investigated using the alkylation of o-xylene with styrene. The ionic liquid directed hierarchical zeolite Y exhibited a remarkably high catalytic activity and long catalytic lifetime for the production of 1-phenyl-1-xylylethane via alkylation reaction, as compared with that of solely microporous zeolite Y. The distinct catalytic performances of the novel hierarchical zeolite Y could be attributed to the enhancement of medium strong acid amount and its micro–mesoporous structural properties which are favorable for the fast diffusion of products.

Helical polysilane wrapping onto carbon nanotube: preparation, characterization and infrared emissivity property study

A helical polysilane/multi walled carbon nanotubes composite was fabricated by wrapping helical HPS copolymer around the surface of modified nanotubes through surface oxidation. HPS was pre-polymerized by Wurtz-type coupling reaction in chloroform (CHCl3), demonstrating optical activity and adoption of a predominately signal-handed helical conformation. Various kinds of characterization including Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-vis), thermogravimetric analysis (TGA), circular dichroism (CD) and Raman spectroscopy have been utilized to demonstrate HPS noncovalently wrapped around the nanotubes to protect their original graphite structure. The wrapped HPS exhibited enhanced thermal stability and increased optical activity after wrapping. The infrared emissivity property of the composites at 8–14 μm was investigated as well. These results indicate the HPS/f-MWNTs composites possess a much lower infrared emissivity value (e = 0.576) than raw MWNTs, which resulted from synergistic effect of the particular helical conformation of HPS and improved interfacial interaction between the organic polymers and inorganic nanoparticles.

Preparation and Characterization of Optically Active Polyacetylene@CdTe Quantum Dots Composites with Low Infrared Emissivity

AbstractOptically active polyacetylene@CdTe Quantum Dots (HPA@CdTe and RPA@CdTe) composites have been prepared based on the surface modification of CdTe quantum dots (QDs). The as-prepared HPA@CdTe and RPA@CdTe were characterized by Fourier-transform infrared spectroscopy, UV–Vis absorption spectra, X-ray diffraction, thermogravimetric analysis, transmission electron microscopy and scanning electron microscopy. The infrared emissivity of HPA@CdTe and RPA@CdTe was also investigated. The results indicate that the polyacetylenes were successfully grafted onto the surfaces of the CdTe QDs without destroying the original crystalline structure of the CdTe QDs. Moreover, the infrared emissivity values of the HPA@CdTe and RPA@CdTe composites were reduced to 0.392 and 0.454, which possess much lower infrared emissivity values than those of the pure polymers and nanoparticles. The results are attributed to interfacial interactions between the organic and inorganic components. Furthermore, the helical conformation may also reduce the infrared emissivity due to the more ordered stereo structure and regular secondary structure.

Laterally-uniform Mn3O4 colloidal nanosheets: oriented growth and size-controlled synthesis

In this work, laterally-uniform Mn3O4 nanosheets with regular square-like shapes and tunable lateral dimensions are synthesized through an effective one-pot solvothermal chemical reaction. The formation pathway of the Mn3O4 nanosheets and sized-controlled methods are also investigated.