Molecular Chemistry to the Fore: New Insights into the Fascinating World of Photoactive Colloidal Semiconductor Nanocrystals

Colloidal semiconductor nanocrystals possess unique properties that are unmatched by other chromophores such as organic dyes or transition-metal complexes. These versatile building blocks have generated much scientific interest and found applications in bioimaging, tracking, lighting, lasing, photovoltaics, photocatalysis, thermoelectrics, and spintronics. Despite these advances, important challenges remain, notably how to produce semiconductor nanostructures with predetermined architecture, how to produce metastable semiconductor nanostructures that are hard to isolate by conventional syntheses, and how to control the degree of surface loading or valence per nanocrystal. Molecular chemists are very familiar with these issues and can use their expertise to help solve these challenges. In this Perspective, we present our group\u27s recent work on bottom-up molecular control of nanoscale composition and morphology, low-temperature photochemical routes to semiconductor heterostructures and metastable phases, solar-to-chemical energy conversion with semiconductor-based photocatalysts, and controlled surface modification of colloidal semiconductors that bypasses ligand exchange

Formate as a surface probe for ruthenium nanoparticles in solution 13C NMR spectroscopy

Formic acid adsorption on ruthemium nanoparticles of different sizes allows differentiation of differently bound formate species by solution 13C NMR spectroscopy (see picture). The chemical shifts are comparable to those of organometallic analogues, thus indicating that formate can act as a probe to distinguish surface features of metallic nanoparticles in solution with good quantification and resolution. © 2009 Wiley-VCH Verleg GmbH and Co. KgaA

Prominent electronic and geometric modifications of palladium nanoparticles by polymer stabilizers for hydrogen production under ambient conditions.

A remarkable effect from the modification of electronic and geometric properties of Pd nanoparticles by the use of polymer pendant groups bound to the surface of palladium nanoparticles is reported. The degree of electron promotion to the Pd nanoparticles under ambient conditions was found to be dependent on the availability of the lone pair electrons of the pendant groups

Electron promotion by surface functional groups of single wall carbon nanotubes to overlying metal particles in a fuel-cell catalyst.

A remarkable promotion: Functional groups added onto single-wall carbon nanotubes (SWNTs) can significantly influence the activity of a noble metal for formic acid oxidation. Phenolate groups on SWNTs under alkaline conditions can double the activity of 20 % w/w Pd compared to unmodified SWNTs. This catalyst has 14 times higher activity than the commercial benchmark catalyst (10 % w/w Pd on Vulcan)

Promotion of Direct Methanol Electro-oxidation by Ru Terraces on Pt by using a Reversed Spillover Mechanism

By examining Pt-core-Ru-shell nanocatalysts of different compositions for the electro-oxidation of methanol, a volcano activity response is revealed according to Ru coverage. This activity profile can be accounted for by a bifunctional mechanism of spilling over the hydroxy species from Ru to Pt in close proximity with supplemental electronic and structural promotions. At high surface coverage of Ru on Pt, it is revealed that a new 'direct' pathway of Ru terraces on Pt sites in close vicinity can provide synergetic catalysis. Pt sites activate the methoxy surface species, which migrate to the Ru terrace to react with its surface oxygenates, from water dissociation, for accelerated CO2 formation through a 'reversed' spillover mechanism. This non-CO electro-oxidation route to CO2 on a Ru surface requires a lower potential to take place than the corresponding process on a Pt surface. © 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

¹³C NMR guides rational design of nanocatalysts via chemisorption evaluation in liquid phase.

The search for more efficient heterogeneous catalysts remains critical to the chemical industry. The Sabatier principle of maximizing catalytic activity by optimizing the adsorption energy of the substrate molecule could offer pivotal guidance to otherwise random screenings. Here we show that the chemical shift value of an adsorbate (formic acid) on metal colloid catalysts measured by (13)C nuclear magnetic resonance (NMR) spectroscopy in aqueous suspension constitutes a simple experimental descriptor for adsorption strength. Avoiding direct contact between the (13)C atom and the metal surface eliminates peak broadening that has confounded prior efforts to establish such correlations. The data can guide rational design of improved catalysts, as demonstrated here for the cases of formic acid decomposition and formic acid electro-oxidation reactions

Morphology-dependent interactions of ZnO with Cu nanoparticles at the materials' interface in selective hydrogenation of CO2 to CH3OH.

A good face: The (002) polar facet of platelike ZnO nanoparticles gives a much stronger electronic interaction with Cu nanoparticles than other facets (see picture; CB=conductance band; VB=valence band) and shows higher selectivity in the catalytic hydrogenation of CO2 to methanol. This finding provides the basis for the rational design of new nanocatalysts for CO 2 hydrogenation. © 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim