Photooxidation of Isoprene by Titanium Oxide Cluster Anions with Dimensions up to a Nanosize

Abstract

Titania (TiO 2 ) nanoparticles are active photocatalysts, and isoprene (C 5 H 8 ) is a biogenic volatile organic compound that contributes crucially to global particulate matter generation. Herein, the direct photooxidation of isoprene by titanium oxide cluster anions with dimensions up to a nanosize by both ultraviolet (UV) and visible (Vis) light excitations has been successfully identified through mass spectrometric experiments combined with quantum chemistry calculations. The potential role of "dry" titania in atmospheric isoprene oxidation has been revealed, and a clear picture of the photooxidation mechanism on titanium oxide nanoparticles has been provided explicitly at the molecular level. The adsorption of isoprene on the atomic oxygen radicals (O •− ) of titanium oxide clusters leads to the formation of the crucial interfacial state (IS) within the band gap of titanium oxides. This IS is demonstrated to be the significant factor in delivering the electron from the π orbital of C 5 H 8 to the Ti 3d orbital in the photooxidation process (C 5 H 8 + Ti 4+ −O •− → C 5 H 8 O + Ti 3+ ) and creating photoactivity in the Vis region. It is revealed that after the photogeneration of the O •− radicals by UV excitation on the TiO 2 particle surface, the subsequent reactions can be induced by Vis excitation through the IS. This multicolor strategy in both the UV and Vis regions can enhance the efficiency of solar energy harvesting and improve the product yield of the photocatalysis on TiO 2 nanoparticles. New insights have been provided into both the atmospheric chemistry of isoprene and the photochemistry of TiO 2 nanoparticles.

Single Ti3+ Ion Catalyzes NO Reduction on Stoichiometric Titanium Oxide Cluster Anions (TiO2)n– (n = 1–11)

“…Herein, the experimental and mechanistic studies on the (TiO 2 ) n – ( n = 1–11) clusters proposed that once the Ti 3+ ion is created on the surface of TiO 2 particles ( hv → h + + e – , Ti 4+ + e – → Ti 3+ ), NO can be easily trapped by such a Ti 3+ ion to form a highly reactive NO – radical that can capture and couple with another NO molecule in the surroundings to generate gas-phase N 2 O and the attached O •– radical on the resulting product (TiO 2 ) n O – . Note that the O •– radical is an important reactive species to drive multifarious oxidation reactions ,, (e.g., CO oxidation); therefore, the Ti 3+ ion can be regenerated (e.g., Ti 4+ –O •– + CO → Ti 3+ + CO 2 ), indicating that the cyclic utilization of the active species on the TiO 2 surface can be achieved, and the potential chemistry for NO removal driven by such a Ti 3+ ion should be considered for atmospheric processes. It is noteworthy that the existence of this localized Ti 3+ ion on the TiO 2 surface has been contradictorily discussed in the literature .…”

“…Confining individual active species on isolated atomic clusters that compositionally and chemically resemble the active sites on related condensed-phase materials is a widely accepted strategy to penetrate the essence of active species on the surface of catalysts. − Extensive efforts have been focused on the electronic properties − and reactivity − of titanium oxide clusters, and important implications that can be promising for the construction of bulk materials or surface of TiO 2 have been obtained. Available experiments have identified that (TiO 2 ) n O – ( n = 3–60) clusters with dimensions up to nanoscales still exhibit high reactivity in CO oxidation and C 5 H 8 photo-oxidation due to the presence of a highly reactive atomic oxygen radical (O •– ), ,, which can be abstracted during the reactions and leaves behind the stoichiometric (TiO 2 ) n – clusters (reaction ). These behaviors raise an important issue on how to regenerate the O •– radical on the residuary (TiO 2 ) n – clusters as well as the mechanisms that govern the reactions.…”

Nitrogen-doped biochar nanosheets facilitate charge separation of a Bi/Bi2O3 nanosphere with a Mott–Schottky heterojunction for efficient photocatalytic reforming of biomass

“…1 Meanwhile, to realize the efficient conversion of solar energy, semiconductors offer significant characteristics such as broadening of the light absorption range, which is conducive to increasing the capture of solar radiation. 3,4 As a popular photocatalyst, bismuth trioxide (Bi 2 O 3 ) has attracted considerable interest owing to its low cost, non-toxicity, high oxidation power, narrow bandgap and high efficiency. 5,6 Unfortunately, Bi 2 O 3 suffers from fast charge carrier recombination, which limits its practical application.…”

Theoretical insights into the gaseous and heterogeneous reactions of halogenated phenols with ˙OH radicals: mechanism, kinetics and role of (TiO2)nclusters in degradation processes

“…23,24 In particular, the structures and reactivity of different-size TiO 2 clusters have been extensively investigated [25][26][27][28] and found to facilitate the removal of oxygenated volatile organic compounds (VOCs). 29,30 Furthermore, small TiO 2 clusters are more reactive and perform better photocatalytically compared with their bulk counterpart, [31][32][33] so gas-phase (TiO 2 ) n clusters (n = 4, 6, 8, 12, and 16) have been selected as models to explore the effects of nanocluster catalysts and different surfaces [34][35][36][37][38][39][40] on pollutant removal and gain insight into the photocatalytic mechanism and kinetics at the molecular level.…”