Mechanistic insights into different types of typical VOC adsorption on monolayer MoS2 via first-principles approaches

Abstract

Volatile organic compounds (VOCs) in the atmosphere emitted from industrial activities are stirring concern due to the serious threats to human health and global environmental over the recent years. Among the available VOC abatement options, adsorption technology has emerged as an appealing candidate for VOC removal from the contaminated air, yet little is known about the variation in adsorption trends and the underlying adsorption mechanism for different types of VOC species. Herein, the adsorption of eight typical types of VOCs (C ≤ 8 atoms) emitted from the petrochemical industry was investigated by density functional theory (DFT) calculations at the electronic and atomic level on monolayer MoS2, including alkanes, alkenes, alkynes, alcohols, aldehydes, carboxylic acids, ketones and aromatic hydrocarbons. Our research aims to investigate the adsorption behaviors of various types of VOCs, including those with different carbon chain lengths within the same VOC category. It shows that the unique structural properties of MoS2 monolayer not only provide excellent adsorption capabilities but also exhibited distinct responses to the eight aforementioned VOC types. The adsorption energy of VOCs exhibits a distinct hierarchical order: alkanes < aromatic hydrocarbons < alkynes < aldehydes < ketones < alkene < alcohols< carboxylic acids, with the adsorption energy spanning from -0.25 to -1.19 eV. For different VOC adsorption systems, the distance between the rightmost peak of the density of states (DOS) and the Fermi level ranges from -1.42 to -0.17 eV. Additionally, for a given type of VOCs, it was observed that an increase in the carbon chain length correlates with an increase in adsorption energy, while a predictive fitting curve was derived for the adsorption energy of VOCs, expressed as Eads/eV = -0.13X - 0.12 with X being the number of carbon atoms. Through a comprehensive analysis involving charge density differences, DOS and Mulliken charge analysis, we elucidated the underlying mechanisms that correlate adsorption energy with both the specific VOC species and the carbon chain length. Our research highlights the potential and feasibility of MoS2 as a promising candidate for selective VOC adsorption, while also providing a theoretical framework for the development of high-performance VOC adsorbents.