Adsorption–desorption behavior of gaseous formaldehyde on different porous Al2O3 materials

In this work, Al2O3 materials with different pore properties were synthesized using some kinds of surfactant templates including cationic (CTAB), anionic (SDS), nonionic (P123) and blank templates. The gaseous formaldehyde adsorption–desorption behavior was studied using adsorption breakthrough curves and temperature programmed desorption (TPD) methods. The addition of ionic surfactant template (containing anionic and cationic) in synthesized solution resulted in the decrease of the crystalline size of Al2O3 particles compared with Al2O3-Blank. The adsorption capacity for formaldehyde on the Al2O3 samples was as follows: Al2O3-P123 > Al2O3-Blank > Al2O3-SDS > Al2O3-CTAB, which was in direct proportion to the surface area and pore volume. A technique based on TPD was used for estimating the desorption activation energy (Ed) of HCHO from different porosity Al2O3 samples. Al2O3-CTAB exhibited the highest deception activation energy for HCHO, which was thought to be related to its narrowest pore size distribution. The presence of abundant surface hydroxyl groups for Al2O3-P123 would be in favor of the chemical adsorption with formaldehyde molecular, and then resulted in higher desorption activation energy even though its broadest pore size distribution.