Iron(III) oxyhydroxide and oxide monoliths with controlled multiscale porosity: synthesis and their adsorption performance

Iron(III) oxyhydroxide and oxide monoliths with controlled multiscale porosity have been successfully fabricated via the sol-gel process accompanied by phase separation. The size of macropores was controlled by synthesis parameters such as starting compositions. The as-dried iron(III) oxyhydroxide monoliths were amorphous and possessed surface areas over 340 m(2) g(-1), of which mesostructures could be further controlled by a heat-treatment at 250-350 degrees C without collapse of macrostructures and monolithic forms. When the as-dried gel was heated at 300 degrees C, the resultant gel transformed to crystalline alpha-Fe2O3 and exhibited a specific surface area of 124 m(2) g(-1). Heat-treatment at 350 degrees C resulted in the broadened size distribution of mesopores. The adsorption behavior of Congo red has revealed that the interconnected macroporous structure contributed to faster diffusion and better accessibility in a continuous flow-through set up, and the crack-free monolithic forms accounted for an advantageous use of the flow-through adsorbents.