Morphological and textural features of various materials composed of porous or nonporous nanoparticles differently packed in secondary structures

摘要

Particulate morphology and texture of silicas (93 fumed and 56 porous silicas), carbons (230), and porous polymers (53) are analyzed using adsorption, SAXS, and microscopic methods. There are different correlations between pore volume (Vp) and specific surface area (SBET) for different material classes. A linear Vp - SBET approximation scatter decreases with increasing synthesis or treatment temperatures. Despite fumed silicas are composed of nonporous nanoparticles, but activated carbons (AC) are composed of porous nanoparticles weakly and strongly packed in secondary structures, respectively, there are general features of pore size distributions (PSD) for both, e.g., minimal contribution of narrow mesopores of 3-5 nm in radius. For AC produced using the same chars and activation agent but varied activation time, textural characteristics demonstrate smooth changes with the burn-off degree: nanopores transform into narrow mesopores with opposite PSD shifts of broad mesopores and macropores. Comparison of adsorption (open pores accessible for probes) and SAXS (both open and closed pores) data for carbons shows that the difference decreases with increasing burn-off degree due to decreasing contribution of closed pores. Most clear pictures on the particulate morphology and texture could be obtained in parallel applying the adsorption, SAXS, and microscopic methods with appropriate data treatments.