Characterisation of the porosity of polymer and carbon aerogels containing Fe, Ni or Cu prepared from 2,4-dihydroxybenzoic acid by n-nonane pre-adsorption and density functional theory

Abstract

Polymer aerogels were prepared from 2,4-dihydroxybenzoic acid (DHBA) and formaldehyde (F) using synthesis mixtures containing up to 17% solids content and Fe, Cu or Ni introduced by ion exchange. Carbon aerogels were then obtained by carbonisation. The materials were characterised by TEM and N2 adsorption at 77 K. The results show that increasing solids content lowered the mesopore volumes and diameters of the polymer aerogels. The mesopore volumes and diameters of carbon aerogels obtained from DHBA/F polymer aerogels in the acid form were lower than those of the parent polymer aerogel. On the other hand, in the presence of metals, new mesoporosity was formed and there was an overall increase in mesopore volume and the appearance of a second peak on the mesopore size distribution. The n-nonane pre-adsorption method was successfully applied to characterise the microporosity and lead to values in the range 0.15–0.27 cm3 g_1 and 0.47–0.65 nm for the micropore volume and width, respectively, depending on the metal present and the % solids used during synthesis. For metal free samples, excellent agreement was given by application of the quenched solid density functional theory method. In the presence of metals both QSDFT and NLDFT gave higher micropore volumes which may have been due to a strong N2–metal interaction.