Journal of Photochemistry and Photobiology A: Chemistry 159 (2003) 281–287 Phthalocyanine modified TiO 2 or WO 3 -catalysts for photooxidation of sulfide and thiosulfate ions upon irradiation with visible light V. Iliev ∗ , D. Tomova, L. Bilyarska, L. Prahov, L. Petrov Institute of Catalysis, Bulgarian Academy of Sciences, Akad. G. Bontchev Str., Bl. 11, 1113 Sofia, Bulgaria Received 10 March 2003; received in revised form 10 March 2003; accepted 31 March 2003 Abstract The photooxidation of Na 2 S or Na 2 S 2 O 3 , catalyzed by Al 2 O 3 , TiO 2 or WO 3 superficially modified with metal-free phthalocyanine complex (Pc), cobalt phthalocyanine complex (CoPc) and copper phthalocyanine complex (CuPc), has been studied upon irradiation with visible light. The rates of the substrate photooxidation, catalyzed by the phthalocyanine complexes supported on TiO 2 or WO 3 , are much higher than those registered with the same complexes, anchored on Al 2 O 3 . The high photocatalytic activity of the samples is explained by an electron transfer from the conduction band of the excited phthalocyanine semiconductor particles to the conduction band of the TiO 2 or WO 3 supports. The increase of the quantum yield of the photocatalytic redox process comes as a result of the additional formation of superoxide radicals on the TiO 2 or WO 3 conduction bands. A complete oxidation of Na 2 S or Na 2 S 2 O 3 to sulfates has been registered in the presence of the studied photocatalysts. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Photocatalytic detoxification; Phthalocyanine semiconductors; Oxide semiconductors; Sulfide; Thiosulfate; Visible light 1. Introduction Semiconductor photocatalysis is an advanced oxidation process to eliminate organic pollutants in water. During the last two decades, there have been a number of studies on this process and it has recently been reviewed [1–3]. Photoin- duced electrons and holes can reduce and oxidize species adsorbed on the semiconductor particles during photocat- alytic processes [3]. The semiconductors, most widely used as photocatalysts, triggering off the oxidative destruction and mineralization of organic substrates, are TiO 2 , WO 3 and SnO 2 . Due to the width of the band gap (E G ) of these pho- tocatalysts (TiO 2 , E G = 3.2 eV; WO 3 , E G = 2.8 eV; SnO 2 , E G = 3.6 eV) [2], the processes of catalytic oxidative de- struction are accomplished upon irradiation with light of the UV region. The photocatalytic processes do not occur ef- fectively during the irradiation with solar light as only ap- proximately 4% of the total radiation of the solar spectrum is in ultraviolet region. One disadvantage of the particulate systems upon band gap excitation of the semiconductors is the high degree of recombination between the photogener- ated charge carriers. As a results of this recombination the ∗ Corresponding author. Tel.: +359-2-9792514; fax: +359-2-9712967. E-mail address: iliev@ic.bas.bg (V. Iliev). photocatalyst effectivity is decreased as well as the quantum yield of the redox process. In order to overcome this disadvantage, semiconductors [4,5] or coupled semiconductor systems (heterotype “photo- chemical diodes”) are used, in which one of the components is excited upon visible light irradiation [6,7]. Applying pho- tocatalysts, obtained by coupling two different semiconduc- tor phases, an efficient charge separation can be achieved [7,8]. The anchoring of pigments, especially phthalocyanine complexes on wide-band gap semiconductors [5,9–13], is an alternative method, in which a dye (sensitizer), adsorbed on the support surface, gets excited by absorbing visible light and an intercomponent electron transfer is realized in the couple molecular semiconductor–oxide semiconductor. It was shown in previous studies [12,13] that the rates of the sodium sulfide or phenols photooxidation, catalyzed by the metal-free 29H-, 31H-phthalocyanine complexes, sup- ported on TiO 2 , are much higher than those registered with the same complexes, anchored on Al 2 O 3 . The catalytic activity of the metal-free phthalocyanine complex (Pc), the cobalt phthalocyanine complex (CoPc) and the copper phthalocyanine complex (CuPc) supported on Al 2 O 3 , TiO 2 or WO 3 , is studied in the present work upon irradiation of the samples with visible light. The oxidation of Na 2 S and that of Na 2 S 2 O 3 have been chosen as model reactions. The thiosulfates are the main final products in the 1010-6030/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1010-6030(03)00170-9