Slightly hydrogenated TiO₂ with enhanced photocatalytic performance

Abstract

Slightly hydrogenated white TiO2 nanoparticles show enhanced photocatalytic performance due to their increased surface defects, while gray or black H-TiO2 nanoparticles display much worse catalytic performances due to the formation of bulk defects.

Black Titanium Dioxide Nanomaterials in Photocatalysis

“…It is likely that surface oxygen vacancies are responsible for the enhanced photocatalytic activity [39,70,75], while bulk oxygen vacancies act as trap states and charge carrier recombination centers [76]. Studies also showed that surface Ti 3+ defects could enhance hole trapping and thus facilitate the separation of photo-excited electrons and holes [57], while bulk Ti 3+ sites acted as charge annihilation centers, leading to enhanced nonradiative recombination and shorter lifetime of electrons and holes [57,60]. In addition, Ti 3+ ions with oxygen vacancies can improve the electrical conductivity of TiO 2 [73,77], which may enhance the charge transport and charge-transfer reaction [73].…”

“…More importantly, oxygen vacancies and/or Ti 3+ defects extend the photoresponse of TiO 2 from UV to visible light region, which leads to high visible-light photocatalytic activity [14,59,[67][68][69][70][71][72]. Note that high density of crystal defects, especially bulk defects, may accelerate electron-hole recombination as defects can International Journal of Photoenergy act as charge annihilation centers [57,73,74]. It is likely that surface oxygen vacancies are responsible for the enhanced photocatalytic activity [39,70,75], while bulk oxygen vacancies act as trap states and charge carrier recombination centers [76].…”

“…Black TiO 2 nanocrystals with the typical crystalline/ amorphous core/shell structure were prepared from hydrogen plasma treatment of commercial TiO 2 nanoparticles (Degussa P25) by Yan et al [57]. Surprisingly, the authors found that slightly hydrogenated TiO 2 nanocrystals without visible coloration exhibited enhanced photoactivity in both photocatalytic degradations of methylene blue and reduction of CO 2 with H 2 O, while gray and black TiO 2 showed worse photoactivity over pristine TiO 2 [57].…”

“…Black TiO 2 Nanomaterials by Hydrogen Plasma. Hydrogen plasma technology has attracted increasing interest owing to its effectiveness in engineering surface-disordered TiO 2 nanomaterials with a typical crystalline/amorphous core/shell structure [33,39,57,60]. Ti 3+ species and oxygen vacancies were reported to be the primary defects in some cases [57,58], while Ti-H groups and oxygen vacancies were believed to be the dominant defects in other cases [33,39].…”

“…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].…”