We report here a series of nontoxic and stable bismuth-based perovskite nanocrystals (PeNCs) with applications for photocatalytic reduction of carbon dioxide to methane and carbon monoxide. Three bismuth-based PeNCs of general chemical formulas A 3 Bi 2 I 9 , in which cation A + = Rb + or Cs + or CH 3 NH 3 + (MA + ), were synthesized with a novel ultrasonication top-down method. PeNC of Cs 3 Bi 2 I 9 had the best photocatalytic activity for the reduction of CO 2 at the gas−solid interface with formation yields 14.9 μmol g −1 of methane and 77.6 μmol g −1 of CO, representing a much more effective catalyst than TiO 2 (P25) under the same experimental conditions. The products of the photocatalytic reactions were analyzed using a gas chromatograph coupled with a mass spectrometer. According to electron paramagnetic resonance and diffuse-reflectance infrared spectra, we propose a reaction mechanism for photoreduction of CO 2 via Bi-based PeNC photocatalysts to form CO, CH 4 , and other possible side products.

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Highly crystalline and surface-modified Zr-doped TiO(2) nanorods were successfully prepared using a nonhydrolytic sol-gel method that involves the condensation of metal halides with alkoxides in anhydrous trioctylphosphine oxide (TOPO) at either 320 or 400 degrees C. In addition, the interaction of the cross-condensation between the Ti and Zr species was studied by characterizing the morphologies, crystalline structures, chemical compositions, surface properties, and band gaps of the nanocrystals obtained at different reaction temperatures and Zr-to-Ti stoichiometric ratios. Increases in the concentration of Zr(4+) and in the reaction temperature led to large nanorods and regular shapes, respectively. In addition, only the anatase form was observed in the Zr-doped TiO(2) nanorods. The Zr-to-Ti ratios obtained ranged from 0.01 to 2.05, all of which were far below the stoichiometric ratios used during the preparation of the samples (0.25-4). Moreover, the Zr(4+) units accumulated mainly at the surface of the TiO(2) nanocrystals. The band gaps of the Zr-doped TiO(2) nanorods ranged from 2.8 to 3.8 eV, which are smaller than those of pure TiO(2) (3.7 eV) or ZrO(2) (5.2 eV). The Zr-doped anatase TiO(2) nanorods prepared at 400 degrees C at an initial stoichiometric Zr-to-Ti ratio of 2:3 exhibited the highest photoactivities for the decomposition of rhodamine B because of the presence of trace amounts of Zr(4+) (Zr/Ti = 0.03) in the TiO(2) and the regular shapes of these particles. DSC analysis indicated that the temperatures for forming nanocrystalline TiO(2) and ZrO(2) were 207 and 340 degrees C, respectively. Moreover, the reactivities of condensation between the Ti species were reduced when Zr species were involved in the NHSG reactions. The results obtained in this study clearly demonstrate that the faster kinetics for the generation of TiO(2) controls the material properties as well as the photoactivities of the nonhydrolytic sol-gel-derived nanocrystals.

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