ESR‐Study of the Interaction of Oxygen Atoms with Clean Titanium Dioxide Surfaces

Abstract

Adsorption i Elektronenspinresonanz i Freie Radikale I Katalyse i Oberflachenerscheinungen Pure titanium dioxide, rutile, with well developed crystal faces was heated after pretreatment with oxygen in an ultrahigh vacuum system ( p i lo-' Torr) up to 1000°C. None of the ESR-signals were observed reported in the literature for less rigorously cleaned high surface area samples. This finding is discussed on the basis of the thermal disorder equilibrium. Reactions with oxygen atoms resulted in the formation of an adsorbed 0; -radical. This radical species occurs only after a few reaction steps for which a mechanism is discussed. Changes of the electronic energy levels on adsorption of the 0;-radical are evaluated from the g-tensor components (gl = 2.019, gz = 2.009, g, = 2.003).Reines Titandioxid, Rutil, mit gut ausgebildeten Kristallflachen, wurde nach Vorbehandlung mit Sauerstoff in einem Ultrahochvakuumsystem ( p < 10-' Torr) bis 1000°C erhitzt. Keines der ESR-Signale wurde beobachtet, die in der Literatur fiir weniger gut gereinigte Proben mit grol3er Oberfllche beschrieben wurden. Dieser Befund wurde auf der Basis des thermischen Fehlordnungsgleichgewichtes diskutiert.Reaktionen mit Sauerstoffatomen fiihrten zur Bildung eines adsorbierten 0; -Radikals. Dieses Radikal entsteht jedoch erst nach einigen Reaktionsschritten, wofur ein Mechanismus diskutiert wird. Anderungen der elektronischen Energieniveaus bei der Adsorption des 0,-Radikals werden aus den g-Tensor-Komponenten (gl = 2.019, 9, = 2.009, g3 = 2.003) bestimmt.

Photodegradation of Sulforhodamine-B Dye in Platinized Titania Dispersions under Visible Light Irradiation: Influence of Platinum as a Functional Co-catalyst

“…This electron transfer leads to efficient electron/hole separation and suppresses somewhat the recombination event (back electron transfer) between the SRB +• radical cations and the injected electrons. In turn, the electrons react with adsorbed O 2 to produce superoxide O 2 -• radical anions (Figure A) − and then • OH radicals (Figure B) 15,23 as evidenced by ESR spectroscopy in accord with earlier studies. Clarkson and McClellan have also reported similar formation of O 2 -• radical anions on gold, rhodium, and platinum supported on porous Vycor glass, whereas Bagghi and co-workers reported its formation on electrochemically reduced platinum electrodes.…”

Peptide-templated biomineralization of titanium dioxide toward improved light absorption and photodegradation activity

“…This electron transfer leads to an efficient separation of electrons and holes and slightly inhibits the recombination of the radical cation MB + ˙and the injected electron. In the third step, the injected electrons react with the adsorbed O 2 to produce superoxide O 2 − ˙radical anions [40][41][42][43][44] and ˙OH radicals. 45,46 In the fourth step, the generated ˙OH radicals degrade the MB adsorbed onto the peptide-TiO 2 surface.…”