Controlling the selectivity of catalytic oxidation of styrene over nanocluster catalysts

The water is discovered to control the selectivity by changing the surface composition of Au nanocluster or the valence state of Ag nanocluster.

PPyNT-Im-PtAu alloy nanoparticle hybrids with tunable electroactivity and enhanced durability for methanol electrooxidation and oxygen reduction reaction

Polypyrrole nanotubes (PPyNTs)/PtAu alloy nanoparticle (NP) hybrids were synthesized in gram-scale by using covalently attached imidazolium moieties as a linker. The approach involves the surface functionalization of PPyNTs with pendant imidazolium moieties (PPyNT-Im), anion-exchange with Pt and Au precursors, and followed by the reduction of metal ions to produce the PtAu alloy NPs on the surface of PPyNTs. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and elemental mapping showed that both Pt and Au were atomically distributed in the PtAu alloy NPs without phase segregation. The composition of the PtAu alloy NPs can be simply controlled by adjusting the feed ratio in the metal precursor solution. The electrocatalytic properties of prepared PPyNT-Im-PtxAuy (the suffixes x and y represent the relative molar ratio of Pt and Au in the feed, respectively) NP hybrids were determined by the composition of alloy NPs. The Pt-rich NP hybrids, PPyNT-Im-Pt8Au2, showed highly electrocatalytic activity and stability toward the methanol oxidation in both acidic and alkaline solutions, whereas the Au-rich NP hybrids, PPyNT-Im-Pt2Au8, showed an enhanced catalytic activity and durability upon oxygen reduction. The present study provided a simple and effective approach for the preparation of PtAu alloy catalysts with controllable composition for high-performance fuel cells and electrochemical sensors.

Design of nanoporous metals with bimodal pore size distributions for enhanced biosensing

Nanoporous gold (np-Au) has shown great potential in catalysis, plasmonics, sensing, etc. In this work, by two-step dealloying a well-designed AuAgAl ternary precursor alloy, np-Au with bimodal ligament/pore size distributions is successfully fabricated. The first dealloying in HCl solution removes Al and generates a nanoporous AuAg alloy which would be mildly annealed at 200 °C for 30 min to homogenize the alloy ligament and enlarge the ligament/pore size. Next, the nanoporous AuAg alloy is further dealloyed in a HNO(3) solution to etch Ag and fabricate np-Au with a hierarchical microstructure. This novel bimodal np-Au is demonstrated to exhibit enhanced electrocatalytic activity towards H(2)O(2) reduction and be a better support for the fabrication of an oxidase-based biosensor compared with normal np-Au, with a uniform pore/ligament size of 30-40 nm. In a proof-of-concept study, a sensitive glucose biosensor with a linear range up to 21 mM is fabricated by immobilization of glucose oxidase on the bimodal np-Au.