Synthesis, Characterization, and Adsorption Studies of Nanocrystalline Aluminum Oxide and a Bimetallic, страница 4

the presence of remaining strongly chemisorbed species.

Destructive Adsorption of Diethyl 4-Nitrophenyl Phosphate.

A 0.100 g sample was placed into a 250 mL round-bottom flask

that had been flushed with argon, 100 mL dry pentane was

then added to the flask, and stirring commenced. Then 8 ÌL

of Paraoxon was added to the flask, and ultraviolet/visible

spectroscopy (SIM Aminco Milton Roy 3000 array) was used

to monitor the disappearance of Paraoxon at 270 nm wavelength,

by extracting samples at desired intervals. This

reaction was monitored every 20 min for 3 h and then at 20 h.

The powder was then filtered and FTIR was then used to

detect adsorbed species on the solid. The used solid was also

washed with 10 mL portions of CH2Cl2, and the IR spectra of

the extracts showed that no adsorbed species were removed.

Additional studies have been previously conducted with the

actual chemical warfare agents.36


Preparation of the Aluminum Oxide. Several

experiments were conducted varying the starting materials,

solvents, and stirring time, and all were found

to have an effect on the surface area of the resulting

sample. Some of the results are shown in Table 1.

It can be seen the best results were obtained for

sample number eight, using aluminum tri-tert-butoxide

as the starting material. The data support earlier

findings that report that branched alkyl molecular

precursors lead to higher surface area samples. Time

was also found to be a factor in the surface area, enough

had to be allowed for hydrolysis, but too much resulted

in lowering the surface areas. The amount of solvent

used was also studied and found to have an important

role in the surface area. In samples 8, 10, and 11 it can

be seen that decreasing the amount of toluene from 100

to 50 mL had a significant decrease in surface area,

going from 786 to 673 m2/g.

Activation of the Aluminum Oxide (Thermal

Dehydration). Aluminum oxide was activated under

both argon flow and dynamic vacuum, and it was found

that the surface area is significantly higher for samples

activated under dynamic vacuum. During activation, the

surface area increases, then goes through a maximum,

and then decreases. This small decrease in surface area

at temperatures above 400 °C can be explained by


Aluminum Oxide Characterization. By careful

characterization of the Al2O3 samples it became clear

that the NC-Al2O3 samples had different textural

properties from that of the commercial (CM) Al2O3


Brunauer-Emmet-Teller Method (BET). Commercial

Al2O3 is most commonly prepared by high-temperature

methods, and CM-Al2O3 typically had surface areas

within the range 100-110 m2/g. Our NC-Al2O3 samples

typically possessed surface areas within the range of

790-810 m2/g after heat treatment at 500 °C. When

heated at higher temperatures, the crystallites began

to sinter, and surface areas decreased slightly.

Using BET, it was also possible to obtain data on the

pore structures (Table 2). The average NC-Al2O3

sample after heat treatment possessed pores that were

10 nm in diameter, held 2.05 cm3/g volume and had a

cylindrical pore structure that was open at both ends,

Table 1. Nanocrystalline Aluminum Oxide Preparation Variables

sample no. starting material solvent stirring time (h) surface area (m2/g)

1 aluminum triethoxide toluene/ethanol 2 352

(100 mL/40 mL)

2 aluminum triethoxide toluene/ethanol 10 385

(100 mL/40 mL)

3 aluminum isoproproxide toluene/2-propanol 2 224

(100 mL/40 mL)

4 aluminum isoproproxide toluene/2-propanol 10 243

(100 mL/40 mL)

5 aluminum tributoxide toluene/butanol 2 392

(100 mL/40 mL)

6 aluminum tributoxide toluene/butanol 10 369

(100 mL/40 mL)

7 aluminum tri-tert-butoxide toluene/tert-butanol 2 743

(100 mL/40 mL)