Synthesis and characterization of Al2O3-C hybrid aerogels by a one-pot sol-gel method

Al2O3-C hybrid aerogels were prepared by a one-pot sol-gel method, supercritical n-hexane drying and carbonization using Al(NO3)3·9H2O as the Al2O3 source, resorcinol (R) and furfural (F) as carbon precursors, and propylene oxide (PO) as a gelation initiator. The effects of the Al2O3 contents, the R+F concentrations and the PO/Al molar ratios on the porosity of the hybrid aerogels were investigated using a constant R/F molar ratio of 0.5. It was found that the hybrid aerogels are all mesoporous with an average pore size below 20 nm. The crystalline structure of Al2O3 is γ-type, but its diffraction peaks are quite broad. The hybrid aerogels are monolithic when the Al2O3 content is below 5.31 wt% with an R+F concentration of 10 g/100 mL. The mesopore volume and size, BET surface area and external surface area all increase with increasing PO/Al molar ratio under otherwise identical conditions. The volume shrinkage decreases, carbonization yield increases and the density of the hybrid aerogel exhibits a maximum with an Al2O3 content of 4.93 wt%. The size and volume of the mesopores, and the external surface area decrease with the increasing R+F concentration at PO/Al ratios of 5 and 6, but increase with increasing R+F concentration at a PO/Al ratio of 4.