Ionothermal synthesis of black Ti³⁺-doped single-crystal TiO₂ as an active photocatalyst for pollutant degradation and H₂ generation

Abstract

A black Ti 3+ -doped single-crystal TiO 2 (Ti 3+ /TiO 2 ) was one-pot synthesized by treating metal Ti in an ionic liquid containing LiAc and HAc under mild ionothermal conditions. The ionic liquid(1-methyl-imidazolium tetrafluoroborate) supplied an environment enriched with fluoride ions for dissolving titanium foil at ionothermal condition, followed by reducing protons in acetic acid to form Ti 3+ ions, leading to Ti 3+ -doped single-crystal TiO 2 in black powder. EPR and XPS results indicated the high-concentrations of both Ti 3+ -dopants and oxygen vacancies. The Ti 3+ incorporated into TiO 2 lattice could narrow the energy band gap of TiO 2 via forming intermediate energy levels, leading to the visible photocatalyst. Meanwhile, the oxygen vacancies could inhibit the photoelectron-hole recombination. As expected, such a black Ti 3+ /TiO 2 exhibited high activity in photocatalytic degradation of organic pollutants and water splitting for H 2 production under irradiation with visible lights and/or simulated solar lights.

Striving Toward Noble-Metal-Free Photocatalytic Water Splitting: The Hydrogenated-Graphene–TiO2 Prototype

“…The coloration of TiO 2 (red, yellow, blue, grey, black) has sparked increasing research interest in recent years with the promise of overcoming the challenges of purely white TiO 2 itself. [41][42][43][44][45][46] The synthesis and functionality of such nanomaterials have been a very promising approach, not only to drastically enhance the activity by increasing the quantum efficiency but also to extend the optical absorption into the visible region by introducing a substantial amount of lattice disorder or defects. [41][42][43] In the light of these facts, investigating the hydrogen coverage via the extent of hydrogenation, on the coupling of TiO 2-x with hydrogenated graphene, graphone or graphane is a promising approach that possibly exhibits strong impact on the structural, physico-chemical, optical, electronic characteristics and even the catalytic activity of these materials.…”

Black Titanium Dioxide Nanomaterials in Photocatalysis

“…[55]. The ionic liquid enriched with fluorine and acetic acid play key roles in dissolving and oxidizing the Ti foil, respectively [55]. The in situ generated H 2 from the reaction between Ti foil and acetic acid could be strongly adsorbed onto the surface of TiO 2 and dissociated into H atom to form H-TiO 2-x disordered layer [55].…”

“…Copyright (2016) Nature Publishing Group. [55]. The ionic liquid enriched with fluorine and acetic acid play key roles in dissolving and oxidizing the Ti foil, respectively [55].…”

“…The ionic liquid enriched with fluorine and acetic acid play key roles in dissolving and oxidizing the Ti foil, respectively [55]. The in situ generated H 2 from the reaction between Ti foil and acetic acid could be strongly adsorbed onto the surface of TiO 2 and dissociated into H atom to form H-TiO 2-x disordered layer [55]. The Ti 3+ -rich black TiO 2 exhibited high activity in photocatalytic degradation of organic pollutants under visible light (λ > 420 nm) and also a high hydrogen evolution rate of 0.26 mmol·h −1 m −2 in water splitting under simulated solar light [55].…”

“…Oxygen vacancies are undetectable in most white TiO 2 nanomaterials, while oxygen vacancy is considered to be one of the feature defects in most black TiO 2 nanomaterials. Electron paramagnetic resonance (EPR) or electron spin resonance (ESR) spectroscope [37][38][39][40]52], Raman spectroscope [9,16,32,[53][54][55], and X-ray diffractometer [23,32,55] [30,33,37,41,52,55,57,59,60].…”