Crystal transformation of 2D tungstic acid H2WO4 to WO3 for enhanced photocatalytic water oxidation

Abstract

New photocatalytic materials for stable reduction and/or oxidization of water by harvesting a wider range of visible light are indispensable to achieve high practical efficiency in artificial photosynthesis. In this work, we prepared 2D WO3•H2O and WO3 nanosheets by an one-pot hydrothermal method and sequent calcination, focusing on the effects of crystal transformation on band structure and photocatalytic performance for photocatalytic water oxidation in the presence of electron acceptors (Ag +) under simulated solar light irradiation. The as-prepared WO3 nanosheets exhibit enhanced rate of photocatalytic water oxidation, which is 6.3 and 3.6 times higher than that of WO3•H2O nanosheets and commercial WO3, respectively. It is demonstrated that the releasing of water molecules in the crystal phase of tungstic acid results in transformation of the crystal phase from orthorhombic WO3•H2O to monoclinic WO3, significantly improving the activity of photocatalytic water oxidation in the presence of Ag + because the shift-up of conduction band of WO3 matches well with the electrode potential of Ag + /Ag(s), leading to efficient separation of photoinduced electrons and holes in pure WO3 nanosheets.

Tungsten oxide-based visible light-driven photocatalysts: crystal and electronic structures and strategies for photocatalytic efficiency enhancement

“…94 The relationships between E VB , E CB and E g follow the equations: (1) E CB = χ − E e − 0.5E g and ( 2) E g = E VB − E CB , where χ is Mulliken's electronegativity of the material (6.59 eV for WO 3 ) and E e is the energy of a free electron on the hydrogen scale (4.5 eV). 85 This indicates that the positions of the VB and the CB for a specific material are influenced directly by the bandgap E g . Bulk WO 3 has a typical E g of 2.6 eV at room temperature, corresponding to a light absorption threshold at 477 nm determined by λ = 1240/E g and E VB and E CB at +3.39 eV and +0.79 eV, respectively.…”

“…90 projection of cubic pyrochlore-type WO 3 •0.5H 2 O in the [110] direction (small circles represent water molecules) (c), 91 As for WO X •nH 2 O photocatalysts, they generally show smaller E g than their dehydrated counterparts due to the weaker binding energy, thus exhibiting larger light absorption ranges. 41,85…”

Nanostructured Ternary Metal Tungstate-Based Photocatalysts for Environmental Purification and Solar Water Splitting: A Review

“…However, the TiO 2 photocatalyst possesses a wide band gap of ~ 3.2 eV that can only absorb ultraviolet (UV) light, which is a small fraction (~ 5%) of solar light, thereby hardly harvesting the remaining solar energy [ 26 , 27 ]. To efficiently utilize the majority of the solar spectrum, Fe 2 O 3 - [ 28 ], WO 3 - [ 29 , 30 ], Bi 2 WO 6 - [ 31 ], ZnO- [ 32 ], Bi 2 O 3 - [ 33 ], and NiO-based semiconductors [ 34 ] have been widely developed as photocatalysts for environmental treatment and solar water splitting (Fig. 1 ).…”

Nanocarbon-Enhanced 2D Photoelectrodes: A New Paradigm in Photoelectrochemical Water Splitting

“…The above-discussed GCN and TMDs materials are mainly utilized to assemble 2D photocathodes for PEC-HER. Correspondingly, the efficient 2D photoanodes for the PEC-OER are fabricated by using LDHs [121][122][123] and metal oxides [124][125][126]. Particularly, as a typical 2D material, LDHs have a layered stacking structure, where six oxygen atoms are situated at six corners and one transition metal atom is located at the center of an octahedron, denoted as MO 6 .…”