Hydrophobic modification of UiO-66 by naphthyl ligand substitution for efficient toluene adsorption in a humid environment

Abstract

Adsorption method has been proved an effective method to remove low-concentration volatile organic compounds (VOCs) from the flue gas, however, it is challenged by the rapid deficiency of adsorption capacity under humid environment, due to the collapse of pore structure or more inclined adsorption for water than low-polarity VOCs such as BTEX. Therefore, developing adsorbents with high hydrothermal stability and hydrophobicity is urgently needed and very important. The outstanding chemical, thermal and structural stability enable UiO-66 a promising adsorbent candidate, however, hydrophobic modification is required to an obtain high adsorption capacity of BTEX in the humid flue gas. In this work, non-polar functional groups naphthyl groups were introduced into UiO-66 to increase hydrophobicity, so that the materials maintain stability and high adsorption efficiency in humid environments. UiO-66-NDC(X = 25,50,100) was synthesized by using 1,4-naphthalenedicarboxlic acid to substitute X percent terephthalic acid in a solvothermal process. Dynamic adsorption experiments were carried out to test the adsorption performance of toluene on UiO-66 and UiO-66-NDC(X). Compared with the pristine UiO-66, the modified adsorbent present improved adsorption capacity in varied humidity, especially, UiO-66-NDC (50) presents the highest toluene adsorption capacity at a relative humidity (RH) of 50%, increased by 69% compared with pristine UiO-66. Furthermore, the modified samples exhibited an excellent recyclability performance, which maintains a higher toluene adsorption capacity after five cycles, indicating that UiO-66-NDC (X) is an effective and regenerative adsorbent in humid environments. Mechanism diagram of UiO-66-NDC(X) adsorption of toluene in humid air. • UiO-66-NDC(X) was successfully synthesized with mixed organic ligands. • The non-polar group naphthyl group was successfully introduced into UiO-66. • UiO-66-NDC(X) shows excellent volatile organic compound adsorption performance in humid environments. • UiO-66-NDC(X) exhibited an excellent recyclability performance.