Experimental

To avoid inorganic impurities from the raw materials, microporous-activated carbons were prepared from a polymer precursor and chemically modified by oxidation with nitric acid. Granular activated carbon (APET) was prepared from poly(ethylene terephthalate) (PET) pellets [12]. Steam-activated carbon, obtained at 900°C, was treated for 3 h with room temperature (APETA) and boiling (APETB) concentrated nitric acid to obtain different degrees of surface functionalization. Before use, the samples were thoroughly washed with distilled water until neutral pH was attained. The morphology and surface chemistry of these carbons have been characterized elsewhere [13, 14]. Relevant characteristic data are listed in Table 1.

TABLE 1. Characteristic data derived from the low temperature nitrogen adsorption* and x-ray photoelectron spectroscopy (XPS).

APETW

APETA

APETB

SBET

m2/g

1,156

1,114

304

Wo/Vtot

0.96

0.96

0.86

WDR

A

8.4

8.6

11.0

dHe

g/cm3

1.74

1.82

1.50

O/C

Atomic ratio

0.064

0.098

0.27

*£BET: surface areas from BET and Dubinin-Radushkevich (DR) models; Vtot, W0: total and micropore volume, resp.; wDR: average micropore width; dHe: true density from helium pycnometry.

*£BET: surface areas from BET and Dubinin-Radushkevich (DR) models; Vtot, W0: total and micropore volume, resp.; wDR: average micropore width; dHe: true density from helium pycnometry.

The powdered samples, inserted into 1.5 mm diameter glass capillaries, were heated to 110°C for 24 h. The capillaries were equilibrated in air containing water vapour at various degrees of relative humidity (RH) and then sealed. Other samples were exposed either to liquid hexane or to hexane vapour at 40% partial vapour pressure at 20°C for 2 weeks, before sealing.

The SAXS responses were measured on the BM2 beam line at the European Synchrotron Radiation Facility (ESRF), Grenoble, France, in the wave vector range 6 x 10"3 A-1 < q < 6 A"1, using an indirect illumination CCD detector. Data were corrected for grid distortion, dark current, sample transmission and background scattering. In the wide-angle x-ray scattering region (1 A-1 < q < 6 A-1) no sign of Bragg scattering peaks was detected, indicating that the carbons are fully amorphous. Intensities were normalized with respect to a standard (lupolen), assuming an effective sample thickness of 1 mm to account for the filling factor of the powder in the capillary tubes. The SAXS measurements were made at the same temperature as the sample preparation (20°C).

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