Shape-Selective Adsorption of Substituted Aniline Pollutants from Wastewater

ZSM-5 zeolite was used to treat wastewater containing aniline, 2-nitroaniline (2-NA), 3-nitroaniline (3-NA) and 4-nitroaniline (4-NA). Each molecule was removed from aqueous solution by Type I Langmuir adsorption onto ZSM-5. The quantities adsorbed varied greatly due to their shape-selective adsorption within the pores of ZSM-5. Aniline and 4-NA had maximum adsorption amounts of 161 and 265 mg g −1 , respectively, while the maximum amounts of 3-NA and 2-NA were 94.3 and 37.2 mg g −1 , corresponding to reductions of 64% and 86%, respectively, relative to 4-NA. This outcome was caused by the increase in the effective diameter for adsorption when the nitro group was located at the 2- and 3- positions of the molecule. This significantly reduced their ability to enter into, and diffuse through, the pores of ZSM-5. These findings underpin the importance of choosing the correct substrate when using such materials for water purification.