Visible light photocatalysis of fullerol-complexed TiO₂ enhanced by Nb doping

By Lim, Jonghun; Monllor-Satoca, Damiàn; Jang, Jum Suk; Lee, Seockheon & Choi, Wonyong
Published in Applied Catalysis B: Environmental NULL 2014

Abstract

Visible light photocatalysis by TiO₂ nanoparticles modified with both fullerol complexation and Nb-doping (fullerol/Nb–TiO₂) demonstrated an enhanced performance. Nb-doped TiO₂ (Nb-TiO₂) was firstly prepared by a conventional sol–gel method, and subsequently fullerol was adsorbed on the surface of Nb–TiO₂. The physicochemical and optical properties of as-prepared fullerol/Nb-TiO₂ were analyzed by various spectroscopic methods (TEM, EELS, XPS, and DRS). The adsorption of fullerol on Nb–TiO₂ surface increased the visible light absorption through a surface-complex charge-transfer (SCCT) mechanism. Nb-doping enhanced the charge transport and induced the Ti cation vacancies that retarded the recombination of photo-generated charge pairs by trapping the electrons injected from the HOMO level of fullerol. Due to the advantage of simultaneous modification of fullerol and Nb-doping, the visible light photoactivity of fullerol/Nb–TiO₂ was more enhanced than either Nb–TiO₂ or fullerol/TiO₂. The photocatalytic activities of fullerol/Nb–TiO₂ for the reduction of chromate (CrVI), the oxidation of iodide, and the degradation of 4-chlorophenol were all higher than bare TiO₂ and singly modified TiO₂ (i.e., Nb–TiO₂ and fullerol/TiO₂) under visible light (λ > 420 nm). A similar result was also confirmed for their photoelectrochemical behavior: the electrode made of fullerol/Nb–TiO₂ exhibited an enhanced photocurrent under visible light. On the other hand, the decay of open-circuit potential of the fullerol/Nb–TiO₂ electrode after turning off the visible light was markedly slower than either that of Nb–TiO₂ or fullerol/TiO₂, which implies the retarded recombination of photo-generated charge pairs on fullerol/Nb–TiO₂. In addition, the electrochemical impedance spectroscopic (EIS) data supported that the charge transfer resistance is lower with the fullerol/Nb–TiO₂ than either Nb–TiO₂ or fullerol/TiO₂. This specific combination of the bulk (Nb-doping) and surface (fullerol complexation) modifications of titanium dioxide might be extended to other cases of bulk + surface combined modifications.

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