Shell Thickness Of Hollow Spheres Research Articles

Efficient N-doping of hollow core-mesoporous shelled carbon spheres via hydrothermal treatment in ammonia solution for the electrocatalytic oxygen reduction reaction

Nitrogen-doped hollow core-mesoporous shelled carbon spheres (NHMCSs) are successfully synthesized via a simple, scalable hydrothermal treatment of hollow mesoporous carbon spheres (HMCSs) with ammonia water as the nitrogen source. This strategy not only efficiently introduces nitrogen atoms into the carbon framework, but also causes the fracture of some spheres and increases the shell thickness of hollow spheres. The subsequent pyrolysis at 900 °C in Ar results in the transformation of pyrrolic-N to graphitic-N. The resulting NHMCS-900 has a high BET specific surface area (648 m2 g−1), large pore volume (1.06 cm3 g−1), hierarchical mesoporosity (2–8, 43.9 nm), uniform shells and large hollow cores. The electrochemical experiments indicate that NHMCS-900 as a metal-free electrocatalyst possesses the improved ORR activity with a close four-electron reaction pathway (∼3.88) and a peroxide yield lower than 10% over a wide potential range in alkaline solution. Contrary to commercial Pt/C, NHMCS-900 is unaffected by the methanol crossover effect and exhibits excellent long-term durability with 97.0% of the initial current density after 5.56 h of continuous operation. The excellent activity of NHMCS-900 is mainly attributed to the high relative content of pyridinic-N and graphitic-N. Besides, the superior activity is also ascribed to its unique structural properties, promoting fast and efficient mass transfer and providing inner and outer surfaces with N-relative active sites for ORR.

Gas Sensing Performance of Multiple-shell Hollow Silver and Hematite Composite Microspheres

In this report, multiple-shell hollow silver and hematite composite microsphere has been prepared by using carbonaceous saccharide microsphere as template. The products were characterized by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). The core size and shell thickness of hollow spheres obtained can be manipulated by changing the concentration of metal salt. The unique multiple-shell hollow silver and hematite composite microspheres may be potentially used as gas-sensor materials for detecting various toxic gases.DOI: http://dx.doi.org/10.5564/mjc.v12i0.163 Mongolian Journal of Chemistry Vol.12 2011: 7-15

One-pot controlled synthesis of single-crystal α-Fe2O3hollow nanostructure and its gas sensing properties

A series of single-crystal α-Fe2O3 nanostructures with tunable morphologies have been prepared via a simple one-pot solvothermal synthesis. The as-prepared nanoparticles were fully characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), selective area electron diffraction (SAED), N2 adsorption–desorption isotherms, and other techniques. The morphologies of the products can be easily adjusted by controlling the amount of NaAc added; with the amount of NaAc increasing the shell thickness of hollow spheres decreases, till the hollow structures disappeared and changed to nanoflower aggregates. Reaction temperature and the solvent ratio also play important roles in the synthesis of hollow nanospheres. The gas sensing properties of the as-prepared samples were also investigated. The results showed that the samples exhibited good gas sensing properties towards acetone vapor, and the gas sensing behavior was related to the morphologies of the samples.

Control of Shell Thickness of Hollow Silica-Alumina Composite Spheres and their Activity for Hydrolytic Dehydrogenation of Ammonia Borane

Herein, we investigated the influence of the shell thickness of hollow silica-alumina composite spheres on their activity for hydrolytic dehydrogenation of ammonia borane (NH3BH3). Silica-alumina composite shells were fabricated by coating on polystyrene (PS) template particles and then completely removing the PS by calcination. Based on the transmission electron microscopy images, the shell thicknesses of the hollow spheres prepared using 5, 10, and 15 g of PS suspensions and coating times of 24.0, 7.0, and 1.5 h were 20, 13, and 5 nm, respectively. The results indicated that the shell thickness of homogeneous hollow spheres was controlled by adjusting the amount of PS suspension and the coating time. In the presence of the hollow spheres with shell thicknesses of 5, 13, and 20 nm, 10.0, 9.5, and 9.0 mL of hydrogen was evolved from aqueous NH3BH3solutions for 13, 12, and 13 min, respectively. The molar ratios of the hydrolytically generated hydrogen to the initial NH3BH3in the presence of the hollow spheres with shell thicknesses of 5, 13, and 20 nm were 2.6, 2.5, and 2.3, respectively. From these results, it can be inferred that the activity for the hydrolytic dehydrogenation of NH3BH3increase with decrease of the shell thickness of the hollow spheres. The result of the temperature-programmed desorption profile of ammonia showed that in the number of amount of acid sites of the hollow spheres increase with decrease of the shell thickness of the hollow spheres. The results indicate the activity depends on the number of acid sites of the hollow spheres.

General Synthesis of Homogeneous Hollow Core−Shell Ferrite Microspheres

A general method has been developed for the synthesis of homogeneous hollow core−shell microspheres of spinel ferrites (MFe2O4, M = Zn, Co, Ni, Cd) by using carbonaceous saccharide microspheres as template. The products were characterized by X-ray powder diffraction, inductively coupled plasma-atomic emission spectroscopy, scanning electronic microscopy, transmission electron microscopy, and nitrogen sorption measurement. The effects of the concentration of metal salts have been studied using ZnFe2O4 as an example. Increasing the concentration of metal salts could avoid the generation of impurity phase. The core size and shell thickness of hollow spheres obtained can be manipulated by changing the concentration of metal salts. Gas-sensor investigations revealed the ZnFe2O4 hollow spheres used as gas-sensor materials possess high sensitivity and quick responses to organic gases such as ethanol.