Highly improved adsorption performance of metal-organic frameworks CAU-1 for trace toluene in humid air via sequential internal and external surface modification

Trace volatile organic compounds (VOCs) such as aldehydes and aromatics significantly deteriorate the indoor air quality especially in newly-decorated buildings. The universal water vapor would greatly decrease the adsorption capacity of adsorbents for trace VOCs via competitive adsorption and capillary condensation. Herein, we developed a strategy to subsequently modify the internal and external surface of CAU-1, an aluminum-based metal-organic framework (MOF), to significantly improve its humidity resistance. First, anhydrides were used to transfer amino groups of CAU-1 into hydrophobic groups via amide reaction. Second, polydimethylsiloxane was used to form a hydorphobic coating on its external surface. The adsorption capacity of as-modified CAU-1 for 1 ppm toluene increased about 6 times under 50% relative humidity (RH) at 298 K, even much higher than those of common adsorbents including hydrophobic ZSM-5. In addition, it could be completely regenerated below 373 K, about 65 K lower than that required for regenerating ZSM-5 under the same condition, which not only greatly reduces the energy consumption but also improves the safety and feasibility of in-situ regeneration of adsorbents in indoor environment.