High-performance Er3+–TiO2 system: Dual up-conversion and electronic role of the lanthanide

• Published in: Journal of catalysis 2013-03, Vol.299, p.298-306
• Main Authors: Obregón, S., Kubacka, A., Fernández-García, M., Colón, G.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; chemical degradation; Chemical reactions; Chemistry; energy; Erbium; Exact sciences and technology; gases; General and physical chemistry; Hydrothermal; ions; irradiation; Luminescence; Metals; NIR; Phenol; Photocatalysis; photocatalysts; Photochemistry; Physical chemistry of induced reactions (with radiations, particles and ultrasonics); Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; TiO2; titanium dioxide; Toluene; ultraviolet radiation; Up-conversion
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2012.12.021

We propose a dual-type mechanism which could explain the improved photoactivities in Er3+-doped TiO2 systems. On the one hand, Er3+ improved the electronic charge separation process, enhancing the UV-photo-assisted process. An additional, small contribution of NIR photons in the overall mechanism due to an energy transfer process from erbium ions to TiO2. [Display omitted] ► By a simple hydrothermal method, we achieve the Er3+–TiO2 photoactive system. ► Synergetic mechanism involving photoluminescence and photocatalysis is evidenced. ► Er3+ aids to the charge separation increasing the efficiency of the photocatalyst. ► Er3+ provides extra UV photons from its luminescence upon NIR excitation. ► We show good performances for degradation of pollutants on gas and liquid phase. Erbium-doped TiO2 materials are synthesized by means of a surfactant-free hydrothermal method having good photoactivities for the liquid-phase degradation of phenol and MB and the gas phase of toluene. From the structural and morphological characterization, it has been stated that the presence of Er3+ induces a progressive anatase cell expansion due to its incorporation in the TiO2 lattice. The best photocatalytic performance was attained for the samples with 2at% of Er3+ irrespective of the chemical degradation reaction essayed. From activity and optical studies under different irradiation excitation conditions, a dual-type mechanism is proposed to be at the origin of the photocatalytic activity enhancement. On one hand, the improvement observed under UV irradiation occurs by the effective charge separation promoted by Er3+ species which would act as electron scavenger. Besides, the up-conversion luminescence process of Er3+ allows profiting the NIR range of the lamp and transferring energy in the UV range to the TiO2. The dual action of Er ions located at anatase networks will open up a wide roadway for the developing of an integral solar active photocatalyst.