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Engineering the surface structure, together with the incorporation of a second metal, is an effective strategy for boosting the catalytic activities of Pt-based catalysts toward various reactions. Here, we report a facile approach to the synthesis of Pt–Ag octahedral and tetrahedral nanocrystals covered by concave surfaces. The presence of the Ag(I) precursor not only facilitated the reduction of the Pt(IV) precursor but also led to the formation of concaved facets on the Pt–Ag nanocrystals. Besides, poly(vinylpyrrolidone) (PVP) was demonstrated to serve as a co-reductant, in addition to its role as a colloidal stabilizer. Using PVP with different molecular weights, we were able to tune the size of the Pt–Ag nanocrystals in the range of 9–25 and 14–32 nm for the octahedral and tetrahedral shapes, respectively. The Pt–Ag nanocrystals exhibited 4.6- and 2.0-fold enhancements in terms of specific and mass activities, respectively, toward methanol oxidation, when benchmarked against the commercial Pt/C catalyst. After 1000 cycles of the accelerated tests, the specific and mass activities of the Pt–Ag nanocrystals were still 3.6 and 1.6 times as high as those of the original commercial Pt/C.
Semiconductor-based heterojunctions have been shown to be effective photocatalytic materials to overcome the drawbacks of low photocatalytic efficiency that results from a high rate of electron−hole recombination and narrow photo-response range. In this paper, we report on the study of heterojunctions made from visible light active, graphitic carbon nitride, g-C3N4), and UV light active, strontium pyroniobate, Sr2Nb2O7. Heterojunctions made from a combination of g-C3N4 and nitrogen-doped Sr2Nb2O7 obtained at different temperatures were also studied to determine the effect of N doping. The photocatalytic performance was evaluated by using photocatalytic hydrogen evolution reaction (HER)from water g under visible light irradiation. It was found that the photocatalytic activities of as prepared heterojunctions are significantly higher than that of individual components under similar conditions. Heterojunction formed from g-C3N4 and N-doped Sr2Nb2O7 at 700°C (CN/SNON-700) showed better performance than heterojunction made from g-C3N4 and Sr2Nb2O7 (CN/SNO). A plausible mechanism for the heterojunction enhanced photocatalytic activity is proposed based on, relative band positions, and photoluminescence data.
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