Photocatalytic oxidation of sulfur dioxide in aqueous suspensions of .alpha.-iron oxide (Fe2O3)

Abstract

The kinetics and mechanism of the photoassisted autoxidation of S(IV) in aqueous colloidal suspensions of a-Fe203 have been studied over the pH range of 2-10.5. Similar kinetic behavior toward S(IV) was observed for colloidal suspensions of Ti02. Quantum yields, <j>, ranged from 0.08 to 0.3 with a maximum yield found at pH 5.7. Upon band-gap illumination conduction-band electrons and valence-band holes are separated; the trapped electrons are transferred either to surface bound dioxygen or to Fe(IlI) sites on or near the surface while the trapped holes accept electrons from adsorbed S(IV) to produce S(V). The formation of S(V) radicals indicates that the reaction proceeds via successive one-electron transfers. The relatively high quantum yields are attributed in part to the desorption of S03*" from the a-Fe203 surface and subsequent initiation of a homogeneous free radical chain autoxidation of S(IV) to S(VI). Kinetic and thermodynamic models for the photoassisted surface chemistry of S(IV) on a-Fe2Q3 are presented.

Sulfur isotope fractionation during heterogeneous oxidation of SO&lt;sub&gt;2&lt;/sub&gt; on mineral dust

“…Catalytic activity does not significantly change when the solid phase is filtered out of the leachate. This shows aqueous oxidation dominates over any surface effects of particles in the solution (Cohen et al, 1981;Rani et al, 1992), although, when aqueous iron and titanium oxide suspensions are irradiated, sulfate quantum yields 1 have been observed due to desorption of ·SO − 3 and initiation of a radical chain reaction (Hong et al, 1987;Faust et al, 1989).…”

Química atmosférica do enxofre (IV): emissões, reações em fase aquosa e impacto ambiental

“…Na reação catalisada por Fe(III), Kraft 103 encontrou uma maior quantidade de ditionato, para a reação conduzida na presença de oxigênio do que na ausência. Já Faust e col. 104 e Grgic e col. 12 não encontraram a presença de ditionato para a reação catalisada por Fe(III) em presença de ar. Brandt De acordo com Veprek-Siska e col. 106 , a reatividade do complexo metal-sulfito formado na etapa inicial do processo, é o principal fator que influencia os produtos da reação.…”

Nano-/microstructure improved photocatalytic activities of semiconductors

“…Several studies have already found that using size-quantized semiconductors can enhance photoefficiencies [80][81][82][83][84], although other works showed that photoactivities of size-quantized semiconductors decreased compared with their bulk-phase counterparts [81,85]. Such phenomenon should be attributed to the competition relationship between the positive effects of increased potential on quantum yields and the unfavourable surface speciation and surface defects formed during the preparation processes of semiconductor particles [86][87][88]. prepared [89][90][91][92].…”