Evaluation of the O-2 and pH Effects on Probes for Surface Bound Hydroxyl Radicals
2014 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 15, 7971-7979 p.Article in journal (Refereed) Published
Interfacial reactions between H2O2 and metal oxides are important in several fields but are yet not fully understood. Recently, tris(hydroxymethyl)aminomethane (Tris) was used as a probe in detecting the intermediate hydroxyl radical (HO center dot) during such process via the formation of formaldehyde (CH2O). In this work, we evaluate two probes (methanol and Tris) for detection of surface bound HO center dot by investigating the O-2 and pH effects on the production of formaldehyde. Moreover, we also examine the pH effect on the production of formaldehyde from Tris in the catalytic decomposition of H2O2 on ZrO2. The influence of O-2 and pH on the yield of formaldehyde under homogeneous conditions was studied via gamma-radiolysis of water. The solution was either deoxygenated or saturated with gas containing 20% 02, and the pH was ranging from 7.0 to 9.0. In the gamma-radiolysis experiment, O-2 shows a strong impact on the yield of formaldehyde: 14-68% for methanol and 16-29% for Tris. However, during the catalytic decomposition of H2O2, O-2 only enables a 30% enhancement of the production of CH2O when using Tris as the scavenger. While for methanol, the O-2 effect is almost negligible, and the production of CH2O from Tris is much higher than that from methanol. For practical reasons, only Tris was studied when evaluating the pH effect. A significant increase in the production of formaldehyde is observed by increasing pH during gamma-radiolysis of water while an even more pronounced pH-dependent increase is observed in the catalytic decomposition of H2O2 on ZrO2. The former indicates that the scavenging yield is base-catalyzed while the latter indicates that the formation of HO center dot is also base-catalyzed. On the basis of the observed effects of O-2 and pH, we propose a mechanism for the production of formaldehyde from Tris. The mechanism accounts for the observed impacts of O-2 and pH on the yield of formaldehyde.
Place, publisher, year, edition, pages
2014. Vol. 118, no 15, 7971-7979 p.
Catalysis, Methanol, Petroleum tar, pH effects, Probes, Radiation chemistry, Radiolysis, Scavenging, Zirconium alloys, Catalytic decomposition, Homogeneous conditions, Hydroxyl radicals, Metal oxides, PH-dependent, Radiolysis of waters, Surface bounds, Trishydroxymethylaminomethane
IdentifiersURN: urn:nbn:se:kth:diva-145580DOI: 10.1021/jp412571pISI: 000334730300025ScopusID: 2-s2.0-84898997402OAI: oai:DiVA.org:kth-145580DiVA: diva2:723677
QC 201406112014-06-112014-05-232015-08-26Bibliographically approved