Mechanistic insights into the adsorption of different types of VOCs on monolayer MoS2via first-principles approaches†

Abstract

Emissions from industrial activities have led to the significant accumulation of volatile organic compounds (VOCs) in the atmosphere, raising substantial concerns due to their serious threats to human health and the global environment in recent years. Among the various strategies for VOC abatement, adsorption technology has emerged as a promising approach for effectively removing VOCs from contaminated air. However, the adsorption behavior and mechanisms for different VOC species remain poorly understood. Herein, the adsorption characteristics of eight typical VOC categories (C ≤ 8 atoms) commonly emitted by the petrochemical industry were systematically investigated using density functional theory (DFT) calculations at the electronic and atomic levels on monolayer MoS₂. The VOC categories analyzed include alkanes, alkenes, alkynes, alcohols, aldehydes, carboxylic acids, ketones and aromatic hydrocarbons. Our research was aimed at investigating the adsorption behaviors of various types of VOCs, including those with varying carbon chain lengths within the same category. Results demonstrated that the unique structural properties of the MoS₂ monolayer not only provided excellent adsorption capabilities but also exhibited distinct responses to the eight aforementioned VOC categories. The adsorption energies of the VOCs followed a distinct hierarchical order, alkanes < aromatic hydrocarbons < alkynes < aldehydes < ketones < alkenes < alcohols < carboxylic acids, with the values ranging from −0.25 to −1.19 eV. In different VOC adsorption systems, the distance between the rightmost peak of the density of states (DOS) and the Fermi level ranged from −1.42 to −0.17 eV. Additionally, for a given VOC category, it was observed that an increase in carbon chain length correlated with an increase in adsorption energy. A predictive fitting curve for the adsorption energy of VOCs was derived and expressed as E_ads (E_v) = −0.13X − 0.12, where X represents the number of carbon atoms. Through comprehensive analyses involving charge density differences, DOS and Mulliken charge analysis, the underlying mechanisms correlating adsorption energy with both VOC species and carbon chain length were elucidated. Our research highlights the potential of MoS₂ as a promising candidate for selective VOC adsorption and provides a theoretical framework for the development of high-performance VOC adsorbents.