Chunlai Ma

Preparation of nanocrystalline metal oxide powders with the surfactant-mediated method

Abstract Nanocrystalline metal oxides (ZnO, NiO, and SnO2) powders with an average particle diameter of 18–55 nm have been successfully prepared with the surfactant-mediated method. The cationic surfactant (cetyltrimethylammonium bromide, CTAB) and the hydrous metal chlorides (ZnCl2·2H2O, NiCl2·6H2O, and SnCl4·5H2O) appear to be the good candidates for obtaining a high yield of nanoparticles. The resultant products have been characterized by thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). The resulting powders are highly crystalline and largely monodisperse oxide particles. The surfactant-mediated method turned out to be suited for the preparation of the nanocrystalline oxide powders. Through this method, it is possible to obtain nanocrystalline metal oxide powders.

Preparation and characterization of SnO2 nanoparticles with a surfactant-mediated method

Using a surfactant-mediated method, tin dioxide nanoparticles with a high surface area were generated within the template of the cationic surfactant (cetyltrimethylammonium bromide) micelle assembly from the hydrous metal chloride (SnCl4 ? 5H2O). The as-synthesized product was amorphous and transformed into crystalline calcined at 500?C for 2 h, and exhibited a higher Brunauer?Emmet?Teller surface area of 69.2 m2 g?1. The resulting particles were highly crystalline and largely monodisperse oxide particles in the nanometre range (15?25 nm). Thermogravimetric analysis, x-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and x-ray photoelectron spectroscopy were used to characterize the final products.

Preparation and characterization of MnOOH and β-MnO 2 whiskers

Abstract MnOOH and β-MnO 2 whiskers are obtained for the first time in our work. MnOOH whiskers are chemically synthesized in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB). The product is obtained under extremely low surfactant concentrations under basic conditions, using MnSO 4 ·H 2 O as the manganese source and ethylamine as the alkali source. After the subsequent heat treatment of MnOOH at 300 °C for 1 h, β-MnO 2 whiskers retaining the similar morphologies are obtained. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and thermogravimetry analysis (TGA) are used to characterize the products.

Synthesis of mesoporous structured material based on tin oxide

Abstract Mesoporous structured tin oxide with high specific surface area was synthesized under acidic conditions at ambient temperature in this study. The synthesis of this material was accomplished using a cationic surfactant (cetyltrimethylammonium bromide: CH 3 (CH 2 ) 15 N + (CH 3 ) 3 Br − ) as the organic supramolecular template and the hydrous tin chloride (SnCl 4 ·5H 2 O) and NH 4 OH as the inorganic precursor and counterion source. X-ray diffraction, thermogravimetric analysis and transmission electron microscopy have been used to characterize the mesostructures formed at room temperature as well as calcined at different temperature. The synthesis procedure strongly influenced the formation of the mesophase. The pore diameters and the surface areas of materials, evaluated from the N 2 -sorption isotherms, indicate average pore diameters of about 22 and 24 A and surface areas about 368 and 343 m 2 /g for calcination at 300 and 350 °C respectively. The formation of the tin oxide mesostructured material was proposed due to the presence of the hydrogen-bonding interactions between supramolecular template and inorganic precursors Sn 4+ and OH − , which were supposed to self-assemble around the cationic surfactant molecules.

Controlled crystallization of calcium phosphate under stearic acid monolayers

Controlled crystallization of calcium phosphate from supersaturated solutions by using stearic acid monolayers has been investigated by scanning electron microscopy, transmission electron microscopy with selected-area diffraction, and X-ray diffraction. Whereas crystallization in the absence of a monolayer results in minuscule spheric octacalcium phosphate (OCP) particles distributed randomly in the solution, the presence of organized monolayers gives rise to (0001) oriented hydroxyapatite (HAp) nuclei across the organic substrate. This result has been explained by the molecular recognition effect of the electrostatic interactions and lattice matching between the inorganic-organic interface. Subsequent growth results in OCP platelets with (010) preferred orientation on the HAp crystals due to a nearly coherent relationship existing on the interface of the two phases and suitable solution conditions.

Synthesis and characterization of amorphous TiO2 with wormhole-like framework mesostructure

Abstract Using neutral amine surfactant (dodecylamine) as an organic template and neutral inorganic material (tetrabutyl titanate) as a precursor, amorphous TiO2 with wormhole-like framework mesostructure was synthesized with the variation of surfactant-to-Ti alkoxide ratios. Powder X-ray diffraction (XRD), thermogravimetric analysis, Fourier transformed infrared spectra, transmission electron microscopy (TEM), nitrogen adsorption–desorption, and X-ray photoelectron spectroscopy (XPS) have been used to characterize the TiO2 mesostructure. The interaction between surfactant and titanium dioxide was displayed by XPS. The samples exhibit a wormhole-like framework from XRD patterns and TEM images, and high surface area (221 m2/g) for the sample calcined at 450 °C for 2 h. The formation of the titanium oxide mesostructure is proposed to be due to the presence of the interactions between surfactant head group and inorganic precursors prior to hydrolysis, and the condensation under condition favorable for liquid crystal formation.

Oriented growth of hydroxyapatite on (0001) textured titanium with functionalized self-assembled silane monolayer as template

A highly (0001) textured hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 , HA] coating on polycrystalline titanium plate is successfully synthesized by a biomimetic process mimicking biomineralization. To simulate the first stage of biomineralization, that is, supramolecular preorganization, a template surface with highly organized arrangement of carboxyl (–COOH) and alcoholic hydroxyl (–1OH) groups is prepared through self-assembly of vinyltriethoxysilane [(C 2 H 5 O) 3 SiCH=CH 2 , VTS] on hydroxylated titanium with strong (0001) texture, followed by oxidation of the vinyl groups (–1CH=CH 2 ) with dilute KMnO 4 solution into alcoholic hydroxyl and then into carboxyl groups. The functionalized substrate can induce oriented nucleation and growth of HA with (0001) planes parallel to the substrate surface from supersaturated HA solution through interfacial molecular recognition. The mechanisms of molecular recognition are also discussed.

The functionalization of titanium with EDTA to induce biomimetic mineralization of hydroxyapatite

A new process is developed to functionalize an inorganic substrate with an organic polycarboxylic chelating agent to obtain a biomimetic template for mimicking biomineralization for the synthesis of films or coatings. A titanium plate is first placed in ethylenediaminetetracetic acid (EDTA) solution to effect chemisorption and self-assembly of EDTA molecules on the plate. The plate is then aged in supersaturated hydroxyapatite [(Ca 10 (PO 4 ) 6 (OH) 2 , HA] solution to mimic biomineralization. The functionalization process is found to be very effective in creating a surface with an organized arrangement of carboxylate ions (–COO – ) with the orientation of lone pairs of electrons on O perpendicular to or radiating from the substrate surface. The coating is formed through the plate-like outgrowth of HA grains along the [001] direction under the mediation of the functionalized surface, giving rise to the coexistence of two kinds of microstructural patterns in coating. One is a parallel arrangement of the plate-like HA grains with (001) planes preferably parallel to the substrate surface, the other is a radial arrangement of the plate-like HA grains with the [001] direction radiating from one surface core and the (111) planes preferably parallel to the surface. The mineralization mechanism is discussed on the basis of the conformation of the self-assembled EDTA molecules and the interfacial molecular recognition, analogous to the biomineralization, including electrostatic interactions, hydrogen bonding, stereochemical arrangement and geometrical correspondence.

Neutral templating route to mesoporous structured TiO2

A neutral templating route for preparing mesoporous structured TiO2 with high surface area is demonstrated based on self-assembly between a neutral amine surfactant (dodecylamine) and neutral inorganic precursor (tetrabutyl titanate). X-ray diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron micrographs (TEM) have been used to characterize the mesostructure that forms at room temperature as well as the calcined materials. The pore diameters and the surface areas of materials, evaluated from the N2-sorption isotherms, indicate average pore diameter of about 29.8 A and surface areas about 246 m2/g for calcination at 300 °C.

Synthesis of mesostructured SnO2 with CTAB and hydrous tin chloride

Abstract Mesostructured SnO 2 was synthesized using a cationic surfactant (cetyltrimethylammonium bromide, CTAB) as the organic supramolecular template and the hydrous tin chloride (SnCl 4 ·5H 2 O) and NH 4 OH as the inorganic precursor and counterion source under acidic conditions and room temperature. The resultant products have been examined with X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The formation of the tin oxide mesostructured material was proposed due to the presence of the hydrogen bonding interactions between supramolecular template and inorganic precursors Sn 4+ and OH − , which was supposed to self-assemble around the cationic surfactant molecules.