The creation of photocatalysts with controlled facets has become an important approach to enhance their activity. However, how the formation of heterojunctions on exposed facets could affect their photocatalytic performance ranking had not yet been investigated. In this study, Cu2O@TiO2 core-shell structures were created, and Cu2O/TiO2 p-n heterojunctions were formed on various exposed facets of Cu2O cubes, Cu2O cuboctahedra, and Cu2O octahedra, respectively. These Cu2O@TiO2 polyhedra demonstrated an enhanced photocatalytic degradation effect on Methylene Blue (MB) and 4-nitrophenol (4-NP) under visible light illumination, because of the enhanced charge carrier separation by the formation of Cu2O@TiO2 p-n heterojunctions. It was further found that their photocatalytic performance was also facet-dependent as pure Cu2O polyhedra, while the photocatalytic performance ranking of these Cu2O@TiO2 polyhedra was different with that of their corresponding Cu2O polyhedron cores. By the combination of optical property measurement and XPS analysis, the energy band alignments of these Cu2O@TiO2 polyhedra were determined, which demonstrated that Cu2O@TiO2 octahedra had the highest band offset for the separation of charge carriers. Thus, the charge-carrier-separation-driven force in Cu2O@TiO2 polyhedra was different from their corresponding Cu2O polyhedron cores, which resulted in their different surface photovoltage spectrum (SPS) responses and different photocatalytic performance rankings.

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A novel quasi-monodisperse, superparamagnetic Pd/Fe 3 O 4 catalyst was synthesized for effective catalytic bromate reduction. The catalyst was prepared by dispersing nanoparticles of Pd (weight percent up to 1%) on the surface of superparamagnetic Fe 3 O 4 microspheres with 300-500 nm in diameter and 10-20 nm in grain size. Complete reduction of bromate by this Pd/Fe 3 O 4 catalyst was demonstrated within a short period (<2 h) over a range of pH values, in the presence of a variety of co-existing ions, and after multiple cycles. In addition, the superparamagnetic nature of the catalyst enhanced its good dispersion in water during water treatment when there was no external magnetic field, and its high saturation magnetization allowed an easy magnetic separation from water when an external magnetic field was applied after the water treatment. Thus, it could be easily recycled and reused, further enhancing its application potential.

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