Dissociative Adsorption of H₂O₂ on the TiO₂(110) Surface for Advanced Oxidation Process

Abstract

Advanced oxidation processes (AOPs) involving the conjugation of H2O2 with metal oxide catalysts such as TiO2 have been studied for a long time because they enable efficient degradation of pollutants in wastewater. The combination of H2O2 and TiO2 is well known to generate oxidizing agents such as •OH and •O2 – radicals by catalytic reactions. However, the reaction mechanism for the production of these radicals is controversial. Here, we investigated the H2O2-dosed surface of rutile TiO2(110) by low-temperature scanning tunneling microscopy (LT-STM). We successfully probed the intermediate step of AOP at the single-molecule level. Ti–O–O–Ti peroxides were formed on the surface of aqueous H2O2 vapor-dosed TiO2(110), whereas H2O molecules were hardly found on the surface until the dosing concentration of H2O2 exceeded 0.04 Langmuir, although 30% aqueous H2O2 solution was used. H2O2 could be adsorbed only at the oxygen vacancy, which limited the number of Ti–O–O–Ti peroxide molecules. The formed peroxides could generate •OH radicals by further reaction with H2O molecules. Direct observation of the intermediate step of AOP upon adsorption of H2O2 molecules enabled us to understand the mechanism of the •OH radical-generating reaction.

Oxidative decomposition and mineralization of caffeine by advanced oxidation processes: The effect of hybridization

“…In the second heterogeneous hybrid process, we ran sono-photocatalysis (US/UVTiO 2 ) in the presence of 10 mg L −1 H 2 O 2 and the lowest test dose of the catalyst, (0.1 g L −1 ) and found that while the rate of reaction increased significantly (k = 0.39 min −1 ), the degree of mineralization was reduced from 75.4% without H 2 O 2 to 63.6% with it. The explanation for the rate enhancement is the strong adsorption of H 2 O 2 on the surface of the catalyst [48] . When such a surface is irradiated by UV, the photo-generated electrons react with H 2 O 2 leading to the formation of excess •OH via reductive dissociation [49] .…”

“…When such a surface is irradiated by UV, the photo-generated electrons react with H 2 O 2 leading to the formation of excess •OH via reductive dissociation [49] . It was also found that molecular H 2 O 2 is attached only on the oxygen vacancies at the surface of TiO 2 forming Ti–O–O–Ti peroxides [48] . Once all peroxides disappear from the surface by reductive dissociation, water molecules adsorb on Ti atoms and remain intact there [49] .…”

Accordion-like Multilayered Two-Dimensional Ti3C2Tx MXenes for Catalytic Elimination of Organic Dyes from Wastewater via the Fenton Reaction

“…This titanium peroxide further reacts with H 2 O and forms • OH radicals. 44 Figure 6c shows a schematic illustration of the MB dye degradation mechanism on the surface of m-TC40 in the presence of H 2 O 2 . Finally, to see if there was any trace of TiO 2 phase formation in the sample after the first cycle of reaction, we performed additional experiments, and we did not detect any peak related to the TiO 2 phase in XRD analysis (see Figure S10, Supporting Information).…”

“…Whereas the BE of Ti 4+ (459.02 eV) in Ti 2p, Ti–O (530.3 eV), and Ti–OH (531.8 eV) in O 1s XPS spectra matches well with the reported value of titanium peroxide (Ti–O–O–Ti). This titanium peroxide further reacts with H 2 O and forms • OH radicals Figure c shows a schematic illustration of the MB dye degradation mechanism on the surface of m-TC40 in the presence of H 2 O 2 .…”

“…Hence, it can be concluded that in the second stage, the contribution of the Ti 2+ valence state is greater than that in the first stage, making the degradation faster compared to the first stage. Another probable reason for the faster degradation in the second stage may be the formation of more • OH radicals due to the reaction of titanium peroxide (Ti 4+ ) and H 2 O.…”