Fabrication of an Au25 -Cys-Mo Electrocatalyst for Efficient Nitrogen Reduction to Ammonia under Ambient Conditions.

Electrocatalysts for efficient production of ammonia from nitrogen reduction reaction (NRR) under ambient conditions are attracted growing interest in recent years, which demonstrate a great potential to replace the Haber-Bosch method which suffers the problems of the huge energy consumption and massive CO2 production. In this work, a novel electrocatalyst of Au25 -Cys-M is fabricated for NRR under ambient conditions, with transition metal ions (e.g., Mo6+ , Fe3+ , Co2+ , Ni2+ ) atomically decorated on Au25 nanoclusters via thiol bridging. The Au25 -Cys-Mo catalyst exhibits the highest Faradaic efficiency (26.5%) and NH3 yield (34.5 µg h-1  mgcat -1 ) in 0.1 m HCl solution. X-ray photoelectron spectroscopy analysis and high angle annular dark field image-scanning transmission electron microscopy characterization reveal that the electronic structure of Mo is optimized by forming the structure of Au-S-Mo and Mo acts as active sites for activating the nitrogen to promote the electrochemical production of ammonia. This work provides a new insight into the precise fabrication of efficient NRR electrocatalysts.

Photo-thermo Catalytic Oxidation over a TiO2 -WO3 -Supported Platinum Catalyst.

Photo-thermo catalysis, which integrates photocatalysis on semiconductors with thermocatalysis on supported nonplasmonic metals, has emerged as an attractive approach to improve catalytic performance. However, an understanding of the mechanisms in operation is missing from both the thermo- and photocatalytic perspectives. Deep insights into photo-thermo catalysis are achieved via the catalytic oxidation of propane (C3 H8 ) over a Pt/TiO2 -WO3 catalyst that severely suffers from oxygen poisoning at high O2 /C3 H8 ratios. After introducing UV/Vis light, the reaction temperature required to achieve 70 % conversion of C3 H8 lowers to a record-breaking 90 °C from 324 °C and the apparent activation energy drops from 130 kJ mol-1 to 11 kJ mol-1 . Furthermore, the reaction order of O2 is -1.4 in dark but reverses to 0.1 under light, thereby suppressing oxygen poisoning of the Pt catalyst. An underlying mechanism is proposed based on direct evidence of the in-situ-captured reaction intermediates.

Controlling CO2 Hydrogenation Selectivity by Metal-Supported Electron Transfer.

Tuning CO2 hydrogenation selectivity to obtain targeted value-added chemicals and fuels has attracted increasing attention. However, a fundamental understanding of the way to control the selectivity is still lacking, posing a challenge in catalyst design and development. Herein, we report our new discovery in ambient pressure CO2 hydrogenation reaction where selectivity can be completely reversed by simply changing the crystal phases of TiO2 support (anatase- or rutile-TiO2 ) or changing metal loadings on anatase-TiO2 . Operando spectroscopy and NAP-XPS studies reveal that the determining factor is a different electron transfer from metal to the support, most probably as a result of the different extents of hydrogen spillover, which changes the adsorption and activation of the intermediate of CO. Based on this new finding, we can not only regulate CO2 hydrogenation selectivity but also tune catalytic performance in other important reactions, thus opening up a door for efficient catalyst development by rational design.

High performance surface-enhanced Raman scattering from molecular imprinting polymer capsulated silver spheres.

Driven by the ultrasensitivity of the surface-enhanced Raman scattering (SERS) technique and the directive selection of molecular imprinting polymers (MIPs), core-shell silver-molecularly imprinted polymer (Ag@MIP) hybrid structure was synthesized to serve as a novel SERS platform. The results show that as prepared Ag@MIPs wrapped over a thin shell of MIPs are sensitive to the template molecule (Rhodamine 6G). To investigate the selectivity of Ag@MIPs, the structurally related molecules, such as Rhodamine B and crystal violet, were chosen as controls. Notably, the high sensitivity of Ag@MIPs is restrained by the non-specific recognition of Rhodamine B and crystal violet. This high SERS enhancement of the template molecule can be interpreted by the "gate effect" and/or "dummy hot spots". We believe that the sensitivity of SERS coupled with the selectivity of MIPs could induce a promising chemosensor or biosensor for practical applications.

Laser wavelength- and power-dependent plasmon-driven chemical reactions monitored using single particle surface enhanced Raman spectroscopy.

Plasmon-driven chemical reaction of p-nitrothiophenol (pNTP) dimerizing into p,p'-dimercaptoazobenzene (DMAB) has been monitored using single particle surface enhanced Raman spectroscopy, which provides laser wavelength- and power-dependent conversion rates of the reaction.

Mechanistic understanding of surface plasmon assisted catalysis on a single particle: cyclic redox of 4-aminothiophenol.

Surface plasmon assisted catalysis (SPAC) reactions of 4-aminothiophenol (4ATP) to and back from 4,4'-dimercaptoazobenzene (DMAB) have been investigated by single particle surface enhanced Raman spectroscopy, using a self-designed gas flow cell to control the reductive/oxidative environment over the reactions. Conversion of 4ATP into DMAB is induced by energy transfer (plasmonic heating) from surface plasmon resonance to 4ATP, where O2 (as an electron acceptor) is essential and H2O (as a base) can accelerate the reaction. In contrast, hot electron (from surface plasmon decay) induction drives the reverse reaction of DMAB to 4ATP, where H2O (or H2) acts as the hydrogen source. More interestingly, the cyclic redox between 4ATP and DMAB by SPAC approach has been demonstrated. This SPAC methodology presents a unique platform for studying chemical reactions that are not possible under standard synthetic conditions.

Highly sensitive surface-enhanced Raman spectroscopy (SERS) platforms based on silver nanostructures fabricated on polyaniline membrane surfaces.

Here, we demonstrate a facile synthesis of homogeneous Ag nanostructures fully covering the polyaniline (PANI) membrane surface simply by introducing organic acid in the AgNO(3) reaction solution, as an improved technique to fabricate well-defined Ag nanostructures on PANI substrates through a direct chemical deposition method [Langmuir2010, 26, 8882]. It is found that the chemical nature of the acid is crucial to create a homogeneous nucleation environment for Ag growth, where, in this case, homogeneous Ag nanostructures that are assembled by Ag nanosheets are produced with the assistance of succinic acid and lactic acid, but only scattered Ag particles with camphorsulfonic acid. Improved surface wettability of PANI membranes after acid doping may also account for the higher surface coverage of Ag nanostructures. The Ag nanostructures fully covering the PANI surface are extremely sensitive in the detection of a target analyte, 4-mercaptobenzoic acid (4-MBA), using surface-enhanced Raman spectroscopy (SERS), with a detection limit of 10(-12) M. We believe the facilely fabricated SERS-active substrates based on conducting polymer-mediated growth of Ag nanostructures can be promising in the trace detection of chemical and biological molecules.