Understanding the contribution of hydroxyl to the energy band of a semiconductor: Bi2O(OH)2SO4vs. Bi6S2O15

Abstract

It is still a big challenge to facilely tune the energy bands of a semiconductor. Herein, we have mainly investigated energy bands and photochemical properties of Bi₆S₂O₁₅ and Bi₂O(OH)₂SO₄, which have very similar layered structures. It is found that the hydroxyls have down shifted the conduction band (CB, 0.21 eV) and valence band (VB, 4.39 eV) of Bi₂O(OH)₂SO₄, compared with those (CB = 0 eV; VB = 3.36 eV) of Bi₆S₂O₁₅. Moreover, the main oxidative species of Bi₆S₂O₅ and Bi₂O(OH)₂SO₄ are holes (h⁺) and hydroxyl radicals (˙OH) for the degradation of rhodamine B (RhB) dye, respectively. This obvious difference has been mainly attributed to the hydroxyls, which have changed the energy band structure and the band gap. In addition, we have also investigated the morphology-dependent properties of Bi₂O(OH)₂SO₄. Under ultraviolet light irradiation (λ ≤ 420 nm), Bi₂O(OH)₂SO₄ microspheres show an activity 1.3 times and 2.2 times higher than the long flakes and straw sheaves for the degradation of (RhB), respectively. This study provides us a new idea that we can facilely tune the energy band of a semiconductor by introducing or removing hydroxyl or other anions.