The enhancement of WO3-catalyzed photodegradation of organic substances utilizing the redox cycle of copper ions

• Published in: Applied catalysis. B, Environmental Vol. 84; no. 1-2; pp. 42 - 47
• Main Authors: Arai, Takeo, Yanagida, Masatoshi, Konishi, Yoshinari, Ikura, Ami, Iwasaki, Yasukazu, Sugihara, Hideki, Sayama, Kazuhiro
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.10.2008; Elsevier
• Subjects: Catalysis; Chemistry; Copper redox; Exact sciences and technology; General and physical chemistry; Photochemistry; Photodegradation; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Substances; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Tungsten oxide; Photodegradation; Tungsten oxide; Substances; Copper redox; Heterogeneous catalysis; Catalytic reaction; Copper ion; Transition element compounds; Transition metal; Copper; Photochemical degradation; Environmental protection
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2008.03.002

WO3 is a visible-light-responsive photocatalyst and an n-type semiconductor photocatalyst, but its photocatalytic activity toward organic substances is low. We utilized several transition metal ions as redox mediators in attempts to improve the photoactivity of WO3, and a drastic improvement was observed only when Cu2+ ions were utilized for WO3-catalyzed photodegradation of organic substances. More specifically, the CO2 generation rates for the photodegradation of formaldehyde and methanol in the presence of Cu2+ ions were about 1000 and 150 times as high, respectively, as the rates in the absence of Cu2+ ions. We confirmed that Cu2+ was reduced to Cu+ through the transfer of a photoexcited electron from WO3 and that Cu+ was easily re-oxidized to Cu2+ by oxygen in air. This redox cycle could assist in the reduction of oxygen in the photocatalytic reaction, and the reaction was particularly efficient when Cu2+ was introduced to the system as a CuCl2 solution. Photodegradation was achieved with a WO3 photoelectrode in a two-compartment cell in which the Cu2+ solution was separated from wastewater containing organic substances by an ion-exchangeable membrane, simulating practical use. The anodic photocurrent generated by the photodegradation of organic substances was observed at the WO3 photoelectrode without applying any external bias.