We demonstrate molecular control of nanoscale composition, alloying, and morphology (aspect ratio) in CdS-CdSe nanocrystal dots and rods by modulating the chemical reactivity of phosphine-chalcogenide precursors. Specific molecular precursors studied were sulfides and selenides of triphenylphosphite (TPP), diphenylpropylphosphine (DPP), tributylphosphine (TBP), trioctylphosphine (TOP), and hexaethylphosphorustriamide (HPT). Computational (DFT), NMR ( 31 P and 77 Se), and high-temperature crossover studies unambiguously confirm a chemical bonding interaction between phosphorus and chalcogen atoms in all precursors. Phosphine-chalcogenide precursor reactivity increases in the order: TPPE < DPPE < TBPE < TOPE 1-x Se x quantum dots were synthesized via single injection of a R 3 PS-R 3 PSe mixture to cadmium oleate at 250 degree C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV/Vis and PL optical spectroscopy reveal that relative R 3 PS and R 3 PSe reactivity dictates CdS 1 -xSe x dot chalcogen content and the extent of radial alloying (alloys vs core/shells). CdS, CdSe, and CdS 1 -x Se x quantum rods were synthesized by injection of a single R 3 PE (E = S or Se) precursor or a R 3 PS-R 3 PSe mixture to cadmium-phosphonate at 320 or 250 degree C. XRD and TEM reveal that the length-to-diameter aspect ratio of CdS and CdSe nanorods is inversely proportional to R 3PE precursor reactivity. Purposely matching or mismatching R 3 PS-R 3 PSe precursor reactivity leads to CdS 1 -x Se x nanorods without or with axial composition gradients, respectively. We expect these observations will lead to scalable and highly predictable "bottom-up" programmed syntheses of finely heterostructured nanomaterials with well-defined architectures and properties that are tailored for precise applications. P reparative nanotechnology or "nanomanufacturing" is rapidly evolving toward fabrication of ever more complex materials with precise structure and properties. Tuning composition, relative configuration, and spatial arrangement of heterostructured nanomaterials can impact our ability to engineer and direct energy flows at the nanoscale. In the case of II 3 VI and IV 3 VI semiconductors, composition control has been demonstrated for homogeneously alloyed CdS 1Àx Se x , 1À4 CdS 1Àx Te x , 5 CdSe 1Àx Te x , 6 PbS x Se 1Àx , PbS x Te 1Àx , and PbSe x Te 1Àx 7 nanocrystals with size-and composition-tunable band gaps. 4,8,9 In some cases, a nonlinear relationship between composition and absorption/emission energies, called optical bowing, resulted in new properties not obtainable from the parent binary systems. 3 For example, CdS x Te 1Àx nanocrystals displayed small absorptionÀ emission spectral overlap, up to 150 nm Stokes shifts, and significantly red-shifted PL with respect to CdS and CdTe nanocrystals. 5 Controlling nanocrystal morphology is key to controlling nanocrystal properties. 10À14 A common technique to produce nanorods, for example, is to perform slow and/or subsequent reactant injections. 15À17 In i...

Metal-semiconductor heterostructures are promising visible light photocatalysts for many chemical reactions. Here, we use high-resolution superlocalization imaging to reveal the nature and photocatalytic properties of the surface reactive sites on single Au-CdS hybrid nanocatalysts. We experimentally reveal two distinct, incident energy-dependent charge separation mechanisms that result in completely opposite photogenerated reactive sites (e(-) and h(+)) and divergent energy flows on the hybrid nanocatalysts. We find that plasmon-induced hot electrons in Au are injected into the conduction band of the CdS semiconductor nanorod. The specifically designed Au-tipped CdS heterostructures with a unique geometry (two Au nanoparticles at both ends of each CdS nanorod) provide more convincing high-resolution single-turnover mapping results and clearly prove the two charge separation mechanisms. Engineering the direction of energy flow at the nanoscale can provide an efficient way to overcome important challenges in photocatalysis, such as controlling catalytic activity and selectivity. These results bear enormous potential impact on the development of better visible light photocatalysts for solar-to-chemical energy conversion.

Photocatalytic conversion of biomass is a potentially transformative concept in renewable energy. Dehydrogenation and hydrogenolysis of biomass-derived alcohols can produce renewable fuels such as H 2 and hydrocarbons, respectively. We have successfully used semiconductor-metal heterostructures for sunlightdriven dehydrogenation and hydrogenolysis of benzyl alcohol. The heterostructure composition dictates activity, product distribution, and turnovers. A few metal (M = Pt, Pd) islands on the semiconductor (SC) surface significantly enhance activity and selectivity and also greatly stabilize the SC against photoinduced etching and degradation. Under selected conditions, CdS-Pt favors dehydrogenation (H 2 ) over hydrogenolysis (toluene) 8:1, whereas CdS 0.4 Se 0.6 -Pd favors hydrogenolysis over dehydrogenation 3:1. Photochemically generated, surface-adsorbed hydrogen is useful in tandem catalysis, for example, via transfer hydrogenation. We expect this work will lead to new paradigms for sunlight-driven conversions of biomassrelevant substrates. KeywordsAlcohol dehydrogenation, Benzyl alcohol, CdS, photo-catalytic, photo-induced, product distributions, renewable energies, renewable fuels, semiconductor metals, tandem catalysis, transfer hydrogenations, biomass, cadmium compounds, hydrolysis ABSTRACT: Photocatalytic conversion of biomass is a potentially transformative concept in renewable energy. Dehydrogenation and hydrogenolysis of biomass-derived alcohols can produce renewable fuels such as H 2 and hydrocarbons, respectively. We have successfully used semiconductor-metal heterostructures for sunlight-driven dehydrogenation and hydrogenolysis of benzyl alcohol. The heterostructure composition dictates activity, product distribution, and turnovers. A few metal (M = Pt, Pd) islands on the semiconductor (SC) surface significantly enhance activity and selectivity and also greatly stabilize the SC against photoinduced etching and degradation. Under selected conditions, CdS-Pt favors dehydrogenation (H 2 ) over hydrogenolysis (toluene) 8:1, whereas CdS 0.4 Se 0.6 -Pd favors hydrogenolysis over dehydrogenation 3:1. Photochemically generated, surface-adsorbed hydrogen is useful in tandem catalysis, for example, via transfer hydrogenation. We expect this work will lead to new paradigms for sunlight-driven conversions of biomass-relevant substrates. SECTION: Energy Conversion and Storage; Energy and Charge Transport S olar-to-chemical energy conversion of biomass is a