Abstract
Black TiO2 has triggered worldwide research interest due to its excellent photocatalytic properties. However, the understanding of its structure–property relationships and a more effective, facile and versatile method to produce it remain great challenges. We have developed a facile approach to synthesize black TiO2 nanoparticles with significantly improved light absorption in the visible and infrared regions. The experimental results show that oxygen vacancies are the major factors responsible for black coloration. More importantly, our black TiO2 nanoparticles have no Ti3+ ions. These oxygen vacancies could introduce localized states in the bandgap and act as trap centers, significantly decreasing the electron–hole recombination. The photocatalytic decomposition of both rhodamine B and methylene blue demonstrated that, under ultraviolet light irradiation, better photocatalytic performance is achieved with our black TiO2 nanoparticles than with commercial TiO2 nanoparticles.
Highlights
Since the pioneering work of Fujishima and Honda in 1972 [1], titanium dioxide (TiO2) has attracted extensive interest as a widely used semiconductor photocatalyst in the fields of hydrogen production, photocatalytic water-splitting [2], environmental protection technologies [3] and photocatalytic reduction of carbon dioxide [4].Especially in the area of environmental protection, textile dyes and other industrial dye stuffs constitute one of the largest group of organic compounds that represent an increasing environmental danger
Inspired by the above-mentioned considerations, we have developed a facile technique for synthesizing black TiO2 nanoparticles, for the first time by low-temperature annealing in a Nanomaterials 2018, 8, 245 vacuum-tube furnace
No color change was observed for the black TiO2 (B-TiO2) nanoparticles over one year after they were synthesized and stayed black even when annealed at 200 ◦C in air for 3 days
Summary
Since the pioneering work of Fujishima and Honda in 1972 [1], titanium dioxide (TiO2) has attracted extensive interest as a widely used semiconductor photocatalyst in the fields of hydrogen production, photocatalytic water-splitting [2], environmental protection technologies [3] and photocatalytic reduction of carbon dioxide [4].Especially in the area of environmental protection, textile dyes and other industrial dye stuffs constitute one of the largest group of organic compounds that represent an increasing environmental danger. A hydrogenated black TiO2 (B-TiO2) material was reported by Mao and co-workers, having a narrow bandgap of ~1.5 eV with increased light harvesting efficiency in the visible and infrared regions and enhanced photocatalytic activity [15] This discovery has triggered worldwide research interest in black TiO2 nanomaterials, which represent a major breakthrough for TiO2 in photocatalysis. Sinhamahapatra et al developed a controlled magnesiothermic reduction to synthesize reduced black TiO2 under a 5% H2/Ar atmosphere, with an optimum bandgap and band position, oxygen vacancies, surface defects and charge recombination centers and showing significantly improved optical absorption in the visible and infrared regions [23]. High-concentration of oxygen vacancies, Ti3+ ions, Ti-OH groups and Ti-H bands have been found in some black TiO2 and explain their color change, enhancement of light absorption and photocatalytic activity. The resultant B-TiO2 nanoparticles showed superior photocatalytic activity, far beyond that of commercial white TiO2 nanoparticles
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