We study the freezing of CCl 4 in microporous activated carbon fibers ͑ACF͒, using Monte Carlo simulation and differential scanning calorimetry ͑DSC͒. Microporous activated carbon fibers are well characterized porous materials, having slit-shaped pores due to the voids formed between graphitic basal planes. They serve as highly attractive adsorbents for simple nonpolar molecules, the adsorbent-adsorbate interaction being mostly dispersive ͑of the van der Waals-type͒. Recent molecular simulation studies have predicted an upward shift in the freezing temperature (⌬T f ϭT f ,pore ϪT f ,bulk Ͼ0) for simple fluids confined in such highly attractive carbon slit pores. Our DSC experiments verify these predictions about the increase in T f. The results also indicate significant deviation from the prediction of ⌬T f based on the Gibbs-Thomson equation ͑simple capillary theory͒. We employ a recently developed free energy method to calculate the exact freezing temperature in these confined systems using molecular simulation, in order to address the failure of the simple capillary theory.

A polyacrylic acid (PAA)-protected platinum nanoparticle species (PAA-Pt) was prepared by alcohol reduction of hexachloroplatinate. The PAA-Pt nanoparticles were well dispersed and homogeneous in size with an average diameter of 2.0 +/- 0.4 nm (n = 200). We used electron spin resonance to quantify the residual peroxyl radical ([Formula: see text]) generated from 2,2-azobis (2-aminopropane) dihydrochloride (AAPH) by thermal decomposition in the presence of O(2) and a spectrophotometric method to quantify the residual 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. PAA-Pt scavenged these two radicals in a dose-dependent manner. Platinum was the functional component. PAA-Pt reduced the rate of oxygen consumption required for linoleic acid peroxidation initiated by [Formula: see text] generated from AAPH, indicating inhibition of the propagation of linolate peroxidation. A thiobarbituric acid test also revealed dose-dependent inhibition of the linolate peroxidation by PAA-Pt. Fifty micromolar platinum, as PAA-Pt, completely quenched 250 microM DPPH radical for 5 min. Even when twice diluted in half, the PAA-Pt still quenched 100% of the 250 microM DPPH radical. The scavenging activity of PAA-Pt is durable. These observations suggest that PAA-Pt is an efficient scavenger of free radicals.

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The freezing behavior of CCl 4 confined in graphitic micropores of activated carbon fibers (ACFs) was examined by use of differential scanning calorimetry over the temperature range of 180 to 320 K. For ACF of average pore width, w ) 1.1 nm, we observed a clear peak showing that the freezing temperature is 299 K. The freezing temperature was elevated by 57 K. However, the enthalpy of freezing was only 1.0% of that of the bulk liquid CCl 4 to an fcc solid phase. CCl 4 confined in micropores of w ) 0.80 nm had a more diffuse DSC peak, providing a similar elevation of the freezing temperature and an even smaller freezing enthalpy of 0.5% of the bulk value.