The interplay of sulfur doping and surface hydroxyl in band gap engineering: Mesoporous sulfur-doped TiO2 coupled with magnetite as a recyclable, efficient, visible light active photocatalyst for water purification

- TiO2-S photocatalyst is prepared using titanium sulfate as a dual precursor.
- Fe3O4/TiO2-S with surface hydroxyls is an efficient visible light photocatalyst.
- A synergetic effect exists between doped sulfur and surface hydroxyl within TiO2.
- The electronic interaction between S and hydroxyls reduces the band gap of TiO2.
- Two-nonmetal modification is of benefit to band gap narrowing of a semiconductor.

Photocatalysis based on TiO2 offers a sustainable pathway to drive chemical reactions, such as water splitting and contaminants decomposition, while band gap engineering of TiO2 is necessary to achieve a visible light response. Herein, we prepare sulfur doped TiO2 (TiO2-S) photocatalyst by using titanium sulfate as a dual precursor for both of TiO2 and S in a one-pot synthetic strategy. Meanwhile, pre-synthesized Fe3O4 nanoparticles are coupled onto TiO2-S via a hydrothermal method. The resulting Fe3O4/TiO2-S composites with plenty of surface hydroxyl groups act as an efficient photocatalyst for decomposition of Rhodamine B and formaldehyde solution under visible light and solar light irradiation. On the basis of density functional theory (DFT) calculations and experimental observations, we suggest that the electronic interaction induced synergetic effect of doped sulfur and surface hydroxides can not only significantly narrow the band gap (individual surface hydroxyls or S-doping has no such a great effect), but also enhances the surface hydrophility of TiO2, ultimately making itself a robust visible light photocatalyst for organic pollutants decomposition. Thus, this dual nonmetal modification strategy is proved to exert an enormous function on band gap engineering of semiconductor photocatalyst. In addition, Fe3O4/TiO2-S photocatalyst is superparamagnetic and possesses excellent magnetic responsivity and redispersibility, which is advantageous to their photocatalytic applications.

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