Adsorption and sensing properties of volatile organic compound markers on Ti ₂ CO ₂ nanosheet decorated with Mn and Ru magnetic single atoms: a DFT perspective

Abstract The gas sensing response of semiconducting chemiresistors is governed by changes in electronic properties caused by molecular adsorption. These changes, such as in the band gap, work function, and density of states near the Fermi level, are often small when molecules are adsorbed on pristine materials, leading to low sensitivities. The decoration with single atoms is an effective strategy to enhance the sensitivity of the sensing material toward target molecules. Moreover, decoration-induced magnetism can lead to spin-dependent transport behavior that influences the sensing signal. In this work, by using density functional theory calculations, we investigate the adsorption behavior and sensing properties of selected Volatile Organic Compounds (VOCs), namely isopropanol (C 3 H 8 O), acetonitrile (C 2 H 3 N), toluene (C 7 H 8 ), and formaldehyde (CH 2 O), onto Ti 2 CO 2 MXene decorated with Mn and Ru single atoms. Our results show that these molecules preferentially adsorb on the single-atom sites, with adsorption energies ranging from −1.32 to −3.01 eV, ensuring strong immobilization essential for reliable detection. Electronic structure analysis reveals that Ru-decorated Ti 2 CO 2 maintains a semiconducting character with spin-dependent band gaps of 0.30/0.44 eV, which are slightly modified upon molecular adsorption. In contrast, Mn-decorated Ti 2 CO 2 shows half-metallic behavior with a spin-up gap of 0.34 eV and a metallic spin-down channel, while adsorption of toluene leads to a quenching of its magnetization and induces a transition to a semiconducting state with a band gap of 0.38 eV. Such a transition causes a significant drop in conductivity, which translates into a highly selective sensing response. These results demonstrate the superior sensing performance of the Mn-decorated MXene, which guarantees high sensitivity and selectivity along with reasonable recovery times, unlike the Ru-decorated MXene. This work also highlights the crucial role of magnetism in tuning the selectivity of semiconducting chemiresistors and provides valuable insights into designing efficient gas sensing platforms.