Selective adsorption of volatile organic compounds in metal-organic frameworks (MOFs)

Volatile organic compounds (VOCs) are common air pollutants that are harmful to humans and to the environment, commonly originating as crude materials from various industrial chemical processes. It is increasingly important to develop cost-effective and highly adsorptive materials for VOC capture. To this end, metal-organic frameworks (MOFs) have been studied as a potentially effective class of adsorbents due to their flexible structure and pore size, large surface area, and adjustable chemical functionality. This review summarizes recent developments in the selective adsorption of four different classes of VOCs - aliphatic, aromatic, oxygenated, and sulfur-containing and their distinctive mechanisms of capture by MOFs. Aliphatic hydrocarbons form weaker Van der Waals dipolar interactions with MOF pore walls, while aromatic hydrocarbons predominantly form π-π host–guest interactions. Oxygenated volatile organic compounds rely on capture by the formation of polar interactions with suitable adsorption sites within MOFs. Lastly, sulfur-containing VOCs tend to form strong bonds with MOFs that contain unsaturated metal sites. Additionally, synthetic methods for enhancing the hydrophobicity of MOF micropores to improve their stability with respect to slow hydrolysis, in the presence of realistic, humid environments are presented. In this comprehensive review article, commercialization, scale-up, and nascent companies that utilize and/or produce MOFs are also discussed.