Abstract
The hydrogenation and introducing oxygen vacancies (VO) can lead to surface lattice disorder in TiO2, which is a new form of TiO2 named black TiO2, with excellent visible-light photocatalytic activity, but this TiO2 is easy to failure because oxidation makes the concentration of surface VO decrease rapidly in a short time. In this work, black TiO2 nanoparticles with VO almost concentrated inside nanoparticles were fabricated under ultrafast hydrogen flow. These bulk VO shortened the bandgaps of black TiO2, enhanced its visible light absorption, and meanwhile provided extremely strong stability. The location of VO in black TiO2 was evident from EPR, XPS with HRTEM investigation, and other characteristics of black TiO2 were obtained by XRD, UV-Vis, SEM, PL, and photocurrent techniques. The degradation experiments on Cr6+ or rhodamine B demonstrated the good visible-light photocatalytic performance of our material. After 18 months of natural aging treatment (in the air), our samples showed no discoloration and maintained 89.5% photocatalytic efficiency, and further study exhibited that this black TiO2 also contained excellent acid resistance and moderate alkaline resistance. This work could help design lattice disorder to obtain more stable and practical black TiO2.
Highlights
TiO2 has been widely studied in dealing with environmental and energy problems since its photocatalytic property of decomposing water was discovered in 1972 [1,2,3]
The main phase of samples hydrogenated at different temperatures all maintained rutile TiO2, and no obvious change was observed among 700°C-H-TiO2, 750°C-H-TiO2, 800°C-H-TiO2, and white TiO2
Higher hydrogenation temperatures led to the formation of suboxide titanium, reflecting as tiny splits in the main diffraction peak (27.4°), and a reconstruction process induced by titanium suboxides during reduction processes brought other effects which were detailed discussed in supporting information [25, 26]
Summary
TiO2 has been widely studied in dealing with environmental and energy problems since its photocatalytic property of decomposing water was discovered in 1972 [1,2,3]. Reported a material called "black TiO2" with an amazing narrowed bandgap (1.54 eV) and significantly improved visible-light photocatalytic activities compared to white TiO2 [9], quickly attracting public eyes. These TiO2 nanoparticles changed from white to black after being reduced in a hydrogen atmosphere with high pressure, but their phase kept TiO2. The generation of VO was often considered to be accompanied by the appearance of Ti3+ [20, 21], and they could both promote the separation of photogenerated electron-hole pairs Other defects such as surface hydroxyl groups had been reported to be responsible for the formation of black TiO2 with its excellent visible-light photocatalytic performance. The natural aging process of 18 months indicated 3 times longer shelf life of our samples than traditional black TiO2, besides, an acid-alkali resistance experiment further investigating the stability of black TiO2
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