Effects of Adsorbed F, OH, and Cl Ions on Formaldehyde Adsorption Performance and Mechanism of Anatase TiO₂ Nanosheets with Exposed {001} Facets

Abstract

Formaldehyde (HCHO), as the main indoor air pollutant, is highly needed to be removed by adsorption or catalytic oxidation from the indoor air. Herein, the F^–, OH^–, and Cl^–-modified anatase TiO₂ nanosheets (TNS) with exposed {001} facets were prepared by a simple hydrothermal and post-treatment method, and their HCHO adsorption performance and mechanism were investigated by the experimental analysis and theoretical simulations. Our results indicated that the adsorbed F^–, OH^–, and Cl^– ions all could weaken the interaction between the HCHO and TNS surface, leading to the serious reduction of HCHO adsorption performance of TNS. However, different from F^– and Cl^– ions, OH^– ion could induce the dissociative adsorption of HCHO by capturing one H atom from HCHO, resulting in the formation of one formyl group and one H₂O-like group. This greatly reduced the total energy of the HCHO adsorption system. Thus, the adsorbed OH^– ions could provide the additional active centers for HCHO adsorption. As a result, the NaOH-treated TNS showed the best HCHO adsorption performance mainly because its surface F^– was replaced by OH^–. This study will provide new insight into the design and fabrication of high performance adsorbents for removing indoor HCHO and, also, will enhance the understanding of the HCHO adsorption mechanism