Adsorption mechanism of typical VOCs on pristine and Al-modified MnO2 monolayer

Layered MnO2 is widely concerned due to its excellent adsorption performance of volatile organic compounds (VOCs). In this work, the first-principles calculations were carried out to thoroughly investigate the adsorption mechanism of typical VOCs (formaldehyde, benzene and methyl chloride) on pristine and Al-modified MnO2 monolayer surfaces. The result shows that there are weak physical interactions between VOCs molecules and MnO2 monolayer, however, the modification by Al atom dramatically enhance these interactions, which can be classified as chemical adsorption. Specifically, the best adsorption performance occurs in the adsorption process of benzene molecule on the Al-modified MnO2 monolayer (with the adsorption energy of 2.416 eV). Besides, the difference of adsorption energy (-2.044 eV, nearly 10 times increase) between pristine MnO2 monolayer and Al-modified MnO2 monolayer demonstrates that the Al atom used for surface modification can dramatically enhance the adsorption performance of MnO2 layer for formaldehyde. Additionally, the projected density of state and charge density difference results confirm that Al atom plays a role of tie to connect these VOCs and MnO2 monolayer. Therefore, the Al-modified MnO2 monolayer is expected to be a promising VOCs adsorbent.