Differentiating between Acidic and Basic Surface Hydroxyls on Metal Oxides by Fluoride Substitution: A Case Study on Blue TiO₂ from Laser Defect Engineering

Abstract

Both oxygen vacancies and surface hydroxyls play a crucial role in catalysis. Yet, their relationship is not often explored. Herein, we prepare two series of TiO 2 (rutile and P25) with increasing oxygen deficiency and Ti 3 + concentration by pulsed laser defect engineering in liquid (PUDEL), and selectively quantify the acidic and basic surface OH by fluoride substitution. As indicated by EPR spectroscopy, the laser-generated Ti 3 + exist near the surface of rutile, but appear to be deeper in the bulk for P25. Fluoride substitution shows that extra acidic bridging OH are selectively created on rutile, while the surface OH density remains constant for P25. These observations suggest near-surface Ti 3 + are highly related to surface bridging OH, presumably the former increasing the electron density of the bridging oxygen to form more of the latter. We anticipate that fluoride substitution will enable better characterization of surface OH and its correlation with defects in metal oxides.

Mechanistic understanding of the thermal-assisted photocatalytic oxidation of methanol-to-formaldehyde with water vapor over Pt/SrTiO3

“…The latter originates from Ti 3+ -sites in disordered STO phases, where pronounced site-to-site disorder leads to a broad distribution of g-values (g-strain). 40,42,43 Furthermore a six line spectrum with a hyperfine splitting of 237 MHz is observed, which matches very well with reported values for Mn 2+ (S = 5/2, I = 5/2) substituting Ti 4+ sites. 44 UV light exposure in the absence of MeOH only led to minimal changes of the EPR spectrum (see Fig.…”

Introduction of TiO2 enhancing the catalytic performance of Ti(SO4)2/SiO2 for dimethyl ether oxidation

“…Moreover, the XPS results (Table S5, ESI †) show that Ti(SO 4 ) 2 /TS-400 1C has the highest number of surface hydroxyl groups, which is attributed to the presence of oxygen vacancies accompanied by the unsaturated Ti 3+ species. 27 It can be confirmed that the variable valence of Ti species and the generation of Ti 3+ species increases the acidity of the Ti(SO 4 ) 2 /TS catalyst, while the transformation between Ti 4+ and Ti 3+ also promotes the redox cycle of the DME oxidation reaction.…”

“…26 The presence of oxygen vacancies promotes the charge transfer between TiO 2 and Ti(SO 4 ) 2 , which may increase the electron density of the bridged oxygen and the proton affinity to form more –OH groups. 27 It has been reported that the structure of sulfate species significantly affects the acidic properties of the catalysts. From Fig.…”

Deep Photocatalytic Oxidation of Aromatic VOCs on ZnSn LDH: Promoting Role of Electron Enrichment of Surface Hydroxyl

“…Photocatalytic performance heavily relies on the formation of reactive oxygen species, where the hydroxyl radical (•OH) and superoxide anion (•O 2 – ) play a major role . Surface hydroxyl (OH) has been proven to effectively promote the generation of reactive oxygen species by enhancing charge separation in previous reports as well as our work. , Various methods have been proposed for regulating OH, such as pulsed laser irradiation, hydrothermal treatment, and solvent-controlled synthesis . However, these methods required complex treatments or rigorous synthesis.…”