Abstract
Hydrogenated crystalized TiO2−x with oxygen vacant (OV) doping has attracted considerable attraction, owing to its impressive photoactivity. However, amorphous TiO2, as a common allotrope of titania, is ignored as a hydrogenated templet. In this work, hydrogenated amorphous TiO2−x (HAm-TiO2−x) with engineered surface OV and high surface area (176.7 cm2 g−1) was first prepared using a unique liquid plasma hydrogenation strategy. In HAm-TiO2−x, we found that OV was energetically retained in the subsurface region; in particular, the subsurface OV-induced energy level preferred to remain under the conduction band (0.5 eV) to form a conduction band tail and deep trap states, resulting in a narrow bandgap (2.36 eV). With the benefits of abundant light absorption and efficient photocarrier transportation, HAm-TiO2−x coated glass has demonstrated superior visible-light-driven self-cleaning performances. To investigate its formaldehyde photodegradation under harsh indoor conditions, HAm-TiO2−x was used to decompose low-concentration formaldehyde (~0.6 ppm) with weak-visible light (λ = 600 nm, power density = 0.136 mW/cm2). Thus, HAm-TiO2−x achieved high quantum efficiency of 3 × 10−6 molecules/photon and photoactivity of 92.6%. The adsorption capabilities of O2 (−1.42 eV) and HCHO (−1.58 eV) in HAm-TiO2−x are both largely promoted in the presence of subsurface OV. The surface reaction pathway and formaldehyde decomposition mechanism over HAm-TiO2−x were finally clarified. This work opened a promising way to fabricate hydrogenated amorphous photocatalysts, which could contribute to visible-light-driven photocatalytic environmental applications.
Highlights
As a promising and environmentally-friend photocatalyst, titanium dioxide (TiO2 )has gained widespread traction in the past few decades [1,2,3,4,5]
Hydrogenated amorphous TiO2−x (HAm-TiO2−x ) ought to have a narrower bandgap and more surface-oxygen vacant (OV) -induced active sites, which are the crucial factors for high-visible photoactivity
To complete all spin-polarization density functional theory (DFT) calculations, with the Perdew–Burke–Ernzerhof (PBE) formulation, the first-principles were employed within the generalized gradient approximation (GGA) [31,32,33]
Summary
As a promising and environmentally-friend photocatalyst, titanium dioxide (TiO2 ). Given the above challenges in the synthesis theory and technology, hydrogenation of pure amorphous phase TiO2 has so far scarcely succeeded Considering these aspects, the goal of this work is to prepare HAm-TiO2−x with an OV -doped disordered surface (disordered surface at the amorphous core) and, to reveal the fundamental mechanism of the correlation between OV concentration and distribution, electrical structure, optical response, reactive oxygen species (ROS) generation, and its photoactivity, which can discover uncommon electrical and optical properties of HAm-TiO2−x better than traditional hydrogenated crystalline TiO2−x. Current studies on photocatalytic formaldehyde photodegradation are mainly focused on reaction mechanisms, such as peculiar formaldehyde physicochemical adsorption models and complex reaction pathways They are focused on the synthesis of advanced photocatalysts with superior formaldehyde degradation performance under standard and ideal experimental conditions, including high power density of UV light source, high concentration formaldehyde, as well as high reaction temperature and pressure.
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