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Evaluation of the O-2 and pH Effects on Probes for Surface Bound Hydroxyl Radicals
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.ORCID iD: 0000-0003-0663-0751
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
Abstract [en]

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.
Keyword [en]
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
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-145580DOI: 10.1021/jp412571pISI: 000334730300025Scopus ID: 2-s2.0-84898997402OAI: oai:DiVA.org:kth-145580DiVA: diva2:723677
Note

QC 20140611

Available from: 2014-06-11 Created: 2014-05-23 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Radiation Induced Processes at Solid-Liquid Interfaces
Open this publication in new window or tab >>Radiation Induced Processes at Solid-Liquid Interfaces
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the thesis, the reactions between water radiolysis products—H2O2, HO• and O2—with metals and metal oxides utilized in nuclear industry are studied. The reactions include not only surface reactions, e.g. redox reactions and catalytic decomposition of H2O2, but also solution reactions (Haber-Weiss reactions). To study the interfacial reactions, it is crucial to monitor the dissolution of the solid material, reactivity of H2O2 and formation of the intermediate hydroxyl radicals.Hydroxyl radicals are captured by probe (Tris or methanol) to generate CH2O which can be quantified by the modified Hantzsch method. The results from γ-irradiation experiments on homogeneous system show that the conversion yield of CH2O from hydroxyl radicals is affected by O2 and pH. A mechanism of CH2O production from Tris is proposed.Besides, the consumption rate of H2O2 in the H2O2/ZrO2/Tris system is found to be influenced by Tris. A mechanism for the catalytic decomposition of H2O2 upon ZrO2 surface is proposed which includes independent surface adsorption sites for H2O2 and Tris. Moreover, it is demonstrated that the deviation of detected CH2O concentration by the modified Hantzsch method from actual concentration increases with increasing [H2O2]0/[CH2O]0.The inhibition of sulfide on the radiation induced dissolution of UO2 is confirmed and is dependent on sulfide concentration. And the inhibition of sulfide is independent to that of H2/Pd.It is found that the reactivity of H2O2 and dynamics of CH2O formation are different for the studied materials in the H2O2/MxOy/Probe system. The kinetic parameters, such as rate constant, activation energy, frequency factors are determined.Both surface and solution reactions are observed in the aqueous W(s)/H2O2/Tris system. It is also demonstrated that Haber-Weiss reactions which produce HO• continuously are dominating. Furthermore, it is found that hydroxyl radicals are formed simultaneously during the dissolution of W in aerobic aqueous system.The knowledge conveyed by the thesis is relevant to nuclear technological applications, as well as the applications related in photocatalysis, biochemistry, corrosion science, catalysis and optics/electronics.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xii, 74 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:39
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-172421 (URN)978-91-7595-656-5 (ISBN)
Public defence
2015-09-18, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20150826

Available from: 2015-08-26 Created: 2015-08-21 Last updated: 2015-08-26Bibliographically approved

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