Degradation and decomposition of poisonous and noxious organic compounds using photocatalytic oxidation technique has been studied extensively [1]. TiO 2 as an efficient and active photocatalyst has only been used largely for wastewater purification and organic pollutants degradation under UV irradiation [2]. In order to utilize solar light efficiently, exploitation of high active, stable, novel and visible-light-induced photocatalysts becomes urgent and indispensable. One of the promising methods is to modify TiO 2 on the surface or in the bulk, mainly doping by nonmetal (N, C, S, P), transition metals (Fe, Co, Ni, Cu, Zn), rare earth (Sm, Pr, La, Gd, Nd) or noble metals (Au, Pt, Pd) [3][4][5][6][7][8][9][10]. It has demonstrated that the photocatalysts modified with co-catalysts were active under solar light irradiation. Another method is to design and produce novel and efficient non-TiO 2 visible-lightactivated photocatalysts. Recently, much effort has been made to develop novel visible-light-driven non-TiO 2 catalysts and many compounds have been exploited, such as CdIn 2 S 4 [11], Ag 3 VO 4 [12], BiVO 4 [13], InNbO 4 [14], InVO 4 [15] and so on.
BiVO 4 with scheelite structure was found to possess photocatalytic activity for O 2 evolution and 4-nonylphenol degradation under visible light irradiation [16,17]. However, the activity of the neat BiVO 4 was still low owing to its poor adsorption ability [18]. In order to enhance the photocatalytic activity of the host BiVO 4 , the transition metal and noble metal co-catalysts had been used to modify the neat BiVO 4 , such as Co 3 O 4 /BiVO 4 [18], Pd/BiVO 4 [19], Pt/ BiVO 4 [20], Cu-BiVO 4 [21], Fe-BiVO 4 [22] and Ag-BiVO 4 [23-25].
Recently, several literatures indicated that rare earth ions could be regarded as active co-catalysts and dopants [8]. It was demonstrated that doping of Ce 3+ [26], La 3+ [27] and Gd 3+ [9] could enhance the photocatalytic activity of TiO 2 . However, in our best knowledge, the photocatalytic properties of rare earth-loaded BiVO 4 had not yet been reported. In this work, rare earth-loaded BiVO 4 (RE 3+ -BiVO 4 , RE = La, Ce, Ho, Yb, Eu, Sm, Nd and Gd) were synthesized by impregnation method and methylene blue (MB) was used as a model compound to evaluate the photocatalytic activity of the samples under visible light irradiation. The RE 3+loaded BiVO 4 photocatalysts were characterized by XRD, BET, DRS, SEM-EDS and XPS, and the relationship between activity and structure of the samples was also discussed.
Experimental
2.1. Preparation of catalysts
Preparation of BiVO 4 had been reported in detail elsewhere [23,24]. Aqueous solution of 0.04 mol (19.4 g) of Bi(NO 3 )ร5H 2 O was