Photoinduced reactivity of titanium dioxide

The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .

An overview of semiconductor photocatalysis

Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.

Catalytic Properties of Ceria and CeO2-Containing Materials

http://repository.ias.ac.in/39608/1/49_pub.pdf

A review of imperative technologies for wastewater treatment I: oxidation technologies at ambient conditions

A surface science perspective on TiO2 photocatalysis

Chemiluminescence during the catalysis of carbon monoxide oxidation on a thoria surface

The problems raised by the immobilization (or anchoring) of a photocatalyst, namely TiO2, on a support are reviewed, from the standpoints of the procedure itself and of the structure, adherence, morphology and photocatalytic activity of the deposit. Some new experimental findings are also reported. It is concluded that the immobilized photocatalyst absorbs all the actinic light that it can, but the immobilization treatment generally lowers its activity. It would therefore be advisable to tailor a treatment which would at least maintain this activity, and even increase it, possibly by size quantization.

On the “immobilization” of titanium dioxide in the photocatalytic oxidation of spent waters

Catalysis of carbon monoxide oxidation by cerium dioxide: I. Correlations between catalytic activity and electrical conductivity

Acetic acid is oxidized by oxygen in the presence of UV light, TiO2 and dissolved copper ions being the catalysis. The reaction rate is zeroth order with respect both to acetic acid and to dissolved oxygen, and is proportional to the absorbed light intensity, with a quantum yield of 0.06. The variation in reaction rate with the concentrations of the different copper species present in the solution, i.e. free ions, Cu(CH3COO)+ and Cu(CH3COO)2, leads us to propose the second of these as the reactive species adsorbed on the TiO2 surface, the diacetato complex (or neutral salt) also being adsorbed on the TiO2 surface, but as a poison. These results extend those already obtained for formic acid and are a part of a general scheme of photo-oxidation of carboxylic acids in the presence of these catalysts.

The photo-oxidation of acetic acid by oxygen in the presence of titanium dioxide and dissolved copper ions

Photocatalytic activity of TiO2 in the oxidation by oxygen of formic acid is considerably enhanced by the presence of dissolved copper ions. The role of oxygen transfer between the gas phase and the slurry is examined. The kinetic results obtained in the absence of mass transfer limitations lead to a mechanism based upon a redox cycle between Cu2+ and Cu+ species adsorbed on the surface of TiO2.

Bernard Claudel

Papers

Chemiluminescence during the catalysis of carbon monoxide oxidation on a thoria surface

On the “immobilization” of titanium dioxide in the photocatalytic oxidation of spent waters

Catalysis of carbon monoxide oxidation by cerium dioxide: I. Correlations between catalytic activity and electrical conductivity

The photo-oxidation of acetic acid by oxygen in the presence of titanium dioxide and dissolved copper ions

Photo-oxidation of formic acid by oxygen in the presence of titanium dioxide and dissolved copper ions: oxygen transfer and reaction kinetics