Carbon-supported, Pt and PtCo nanocrystals (NCs) with controlled size and composition were synthesized and examined for hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF). Experiments in a continuous flow reactor with 1-propanol solvent, at 120 to 160 °C and 33 bar H2, demonstrated that reaction is sequential on both Pt and PtCo alloys, with 2,5-dimethylfuran (DMF) formed as an intermediate product. However, the reaction of DMF is greatly suppressed on the alloys, such that a Pt3Co2 catalyst achieved DMF yields as high as 98%. XRD and XAS data indicate that the Pt3Co2 catalyst consists of a Pt-rich core and a Co oxide surface monolayer whose structure differs substantially from that of bulk Co oxide. Density functional theory (DFT) calculations reveal that the oxide monolayer interacts weakly with the furan ring to prevent side reactions, including overhydrogenation and ring opening, while providing sites for effective HDO to the desired product, DMF. We demonstrate that control over metal nanoparticle size and composition, along with operating conditions, is crucial to achieving good performance and stability. Implications of this mechanism for other reactions and catalysts are discussed

The synthesis of colloidal III–V quantum dots (QDs), particularly of the arsenides and antimonides, has been limited by the lack of stable and available group V precursors. In this work, we exploit accessible InCl3- and pnictogen chloride-oleylamine as precursors to synthesize III–V QDs. Through coreduction reactions of the precursors, we achieve size- and stoichiometry-tunable binary InAs and InSb as well as ternary alloy InAs1–x Sb x QDs. On the basis of structural, analytical, optical, and electrical characterization of the QDs and their thin-film assemblies, we study the effects of alloying on their particle formation and optoelectronic properties. We introduce a hydrazine-free hybrid ligand-exchange process to improve carrier transport in III–V QD thin films and realize InAs QD field-effect transistors with electron mobility > 5 cm2/(V s). We demonstrate that III–V QD thin films are promising candidate materials for infrared devices and show InAs1–x Sb x QD photoconductors with superior short-wavelength infrared (SWIR) photoresponse than those of the binary QD devices.

We report direct photocatalytic hydrogen evolution from substoichiometric highly reduced tungsten oxide (WO x ) nanowires (NWs) using sacrificial alcohol. WO x NWs are synthesized via nonaqueous colloidal synthesis with a diameter of about 4 nm and an average length of about 250 nm. As-synthesized WO x NWs exhibit a broad absorption across the visible to infrared regions attributed to the presence of oxygen vacancies. The optical band gap is increased in these WO x NWs compared to stoichiometric bulk tungsten oxide (WO 3 ) powders as a result of the Burstein−Moss shift. As a consequence of this increase, we demonstrate direct photocatalytic hydrogen production from WO x NWs through alcohol photoreforming. The stable H 2 evolution on platinized WO x NWs is observed under conditions in which platinized bulk WO 3 and bulk WO 2.9 powders either do not show activity or show very low rates, suggesting that increased surface area and specific exposed facets are key for the improved performance of WO x NWs. This work demonstrates that control of size and composition can lead to unexpected and beneficial changes in the photocatalytic properties of semiconductor materials.

X-ray atomic pair distribution functions (PDFs) were collected from a range of canonical metallic nanomaterials, both elemental and alloyed, prepared using different synthesis methods and exhibiting drastically different morphological properties. Widely applied shape-tuned attenuated crystal (AC) fcc models proved inadequate, yielding structured, coherent, and correlated fit residuals. However, equally simple discrete cluster models could account for the largest amplitude features in these difference signals. A hypothesis testing based approach to nanoparticle structure modeling systematically ruled out effects from crystallite size, composition, shape, and surface faceting as primary factors contributing to the AC misfit. On the other hand, decahedrally twinned cluster cores were found to be the origin of the AC structure misfits for a majority of the nanomaterials reported here. It is further motivated that the PDF can readily differentiate between the arrangement of domains in these multiply twinned motifs. Most of the nanomaterials surveyed also fall within the sub-5 nm size regime where traditional electron microscopy cannot easily detect and quantify domain structures, with sampling representative of the average nanocrystal synthesized. The results demonstrate that PDF analysis is a powerful method for understanding internal atomic interfaces in small noble metallic nanomaterials. Such core cluster models, easily built algorithmically, should serve as starting structures for more advanced models able to capture atomic positional disorder, ligand induced or otherwise, near nanocrystal surfaces.

Hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) was examined over well-defined and uniform, Pt-Ni, Pt-Zn and Pt-Cu alloyed nanocrystals (NCs) supported on carbon, at 33 bar and between 160 and 200 °C. Pt-Ni alloy catalysts were prepared in three different Pt:Ni ratios, Pt6Ni, Pt3Ni, and PtNi. While all of the Pt-Ni alloys were more selective for producing 2,5-dimethylfuran (DMF) than were Pt or Ni monometallic catalysts, the Pt3Ni catalyst was superior to the other compositions, exhibiting a yield of 98% due to its optimum surface composition. Similarly high yields were obtained on catalysts prepared from Pt2Zn and PtCu NCs. Possible reasons are given for why each of the Pt-alloy catalysts is highly selective

We report a generalized wet-chemical methodology for the synthesis of transition-metal (M)-doped brookite-phase TiO2 nanorods (NRs) with unprecedented wide-range tunability in dopant composition (M = V, Cr, Mn, Fe, Co, Ni, Cu, Mo, etc.). These quadrangular NRs can selectively expose {210} surface facets, which is induced by their strong affinity for oleyl­amine stabilizer. This structure is well preserved with variable dopant compositions and concentrations, leading to a diverse library of TiO2 NRs wherein the dopants in single-atom form are homogeneously distributed in a brookite-phase solid lattice. This synthetic method allows tuning of dopant-dependent properties of TiO2 nanomaterials for new opportunities in catalysis applications.

The selective hydrodeoxygenation (HDO) of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) is an important step in cellulosic biomass upgrading to biofuels, where bimetallic oxophilic catalysts have shown promising performance. Well controlled bimetallic NiCu and NiCu3 nanocrystals supported on carbon are shown to give high yields and selectivities to DMF. To shed light on the active phase, near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to characterize the surface composition of these highly selective base-metal catalysts under reducing conditions relevant to the HDO reaction. Reactions were performed in a continuous flow reactor under reasonable conditions of 33 bar and 180 °C. The Ni alloys were significantly more selective for DMF compared to monometallic Ni or Cu catalysts. With a well-controlled surface composition, the nanocrystal NiCu3/C catalyst exhibited a maximum DMF yield of 98.7%. NAP-XPS characterization showed that the Ni–Cu nanocrystals were completely reduced below 250 °C in H2; this, together with bulk thermodynamic calculations, implies that the catalysts were completely reduced under the reaction conditions. NAP-XPS also indicated that the NiCu3 nanocrystal structure consisted of a Cu-rich core and a 1 : 1 molar Ni : Cu shell

Controlling nanoparticles’ (NPs) surface polarity, colloidal stability, and self-assembly into well-defined complex architectures is of paramount importance for emergent nano- and biotechnologies, and each depends strongly on the ligand shell composition and chemical nature. In this study, a series of dendritic ligands with hydrophobic, hydrophilic, and Janus surface groups was synthesized, grafted onto Au NPs, and their effects on the self-assembly behavior and surface polarity of the corresponding hybrid materials were investigated. A generalized, flexible strategy was utilized for ligand synthesis that independently introduces dendritic end groups, responsible for the surface polarity and colloidal properties, and specific surface NPs binding groups, reducing the number of synthetic steps. The dendritic ligands obtained were grafted onto NP surfaces through solution phase ligand-exchange, and the resulting NP–dendron hybrids were studied using a variety of techniques such as transmission electron microscopy, UV–vis, and small-angle X-ray scattering. When the solvent evaporation rate during self-assembly is controlled, these dendronized Au hybrids self-organize into highly ordered thin films comprised of close-packed arrays of NPs where the interparticle separation can be varied as a function of the dendritic generation and end group chemistry. Moreover, contact angle and colloidal observations revealed the strong dependence of the dendron end-group and generation on the NP surface polarity. Uniquely, the hybrid material of Au NPs and the Janus dendron exhibits controlled surface wetting, where the surface polarity is dependent on solvent exposure, revealing a surface polarity memory effect, making this material a model system for surfaces that demonstrate switchable wettability.