Ge1–x Sn x alloys are among a small class of benign semiconductors with composition tunable bandgaps in the near-infrared (NIR) spectrum. As the amount of Sn is increased, the band energy decreases and a transition from indirect to direct band structure occurs. Hence, they are prime candidates for fabrication of Si-compatible electronic and photonic devices, field effect transistors, and novel charge storage device applications. Success has been achieved with the growth of Ge1–x Sn x thin film alloys with Sn compositions up to 34%. However, the synthesis of nanocrystalline alloys has proven difficult, because of larger discrepancies (∼14%) in lattice constants. Moreover, little is known about the chemical factors that govern the growth of Ge1–x Sn x nanoalloys and the effects of quantum confinement on structure and optical properties. Herein, we report the synthesis of phase pure Ge1–x Sn x nanoalloys with sizes in the range of 15–23 and 3.4–4.6 nm and Sn compositions from x = 0.000–0.279, including the factors that have led to the elimination of undesired metallic impurities. The compositional dependence on lattice parameters has been studied using powder X-ray diffraction and Raman spectroscopy, which indicates a nonlinear expansion of the cubic Ge lattice with increasing Sn composition. Furthermore, the quantum size effects have resulted in bandgaps significantly blue-shifted from bulk Ge, for smaller Ge1–x Sn x nanoalloys (3.4–4.6 nm) with indirect energy gaps from 1.31 eV to 0.75 eV and direct energy gaps from 1.47 eV to 0.95 eV for x = 0.000–0.116 compositions. Remarkably, as-synthesized Ge1–x Sn x nanoalloys exhibit high thermal stability and moderate resistance against sintering up to 400–500 °C and are devoid of crystalline and amorphous Sn impurities.

Fischer−Tropsch synthesis (FTS) is a potentially attractive technology for the production of clean liquid fuels from synthesis gas. The efficiency and selectivity of FTS can be enhanced by the design of new active catalyst systems with improved selectivity for long-chain hydrocarbons and low methane production. In this paper, we introduce a new class of FT catalysts supported on the high surface area graphene nanosheets and report on their high activity and selectivity for the production of long-chain hydrocarbons. The chemical reduction of graphene oxide in water in the presence of the metal salts under microwave irradiation allows the deposition of well-dispersed surface-oxidized metal nanoparticles on the defect sites of the graphene nanosheets. The Fe−K-nanoparticle catalyst supported on graphene exhibits high activity and selectivity toward C 8 and higher hydrocarbons with excellent stability and recyclability. In comparison with other carbon supports, such as carbon nanotubes, the graphene support shows a unique tendency for minor formation of the low-value and undesirable products methane and carbon dioxide, respectively. The water-gas shift activity is reduced on the graphene support as compared with CNTs, and as a result, the formation of CO 2 is significantly reduced. Evidence is presented for the formation of the active Fe 5 C 2 iron carbide phase during the FTS on the graphenesupported Fe catalysts. The high activity and selectivity of the catalysts supported on graphene are correlated with the presence of defects within the graphene lattice that act as favorable nucleation sites to anchor the metal nanoparticles, thus providing tunable metal−support interactions. Given the activity, selectivity, and stability of the new graphene-supported, Fe-based nanoparticle catalysts, their industrial application appears to be promising. Controlling the nature and density of the defect sites in graphene could lead to improved understanding of the catalyst−graphene interactions and to further enhancement of the performance of these catalysts for the production of liquid fuels.

In the search for more efficient semiconductors with low to nontoxicity, Zn 3 P 2 has gained increasing interest for optoelectronic applications because of its direct band structure, high absorption coefficient, and long carrier diffusion lengths. However, the elucidation of the size-dependent optical properties in the quantum confinement regime has proven a difficult task. This report details a systematic study of the absorption and emission of alkyl-amine-passivated tetragonal Zn 3 P 2 crystallites with varying size (3.2 ± 0.6−8.8 ± 1.3 nm) produced via hot injection of diethyl zinc and tris(trimethylsilyl)phosphine in high boiling alkene/amine medium. The solid-state absorption spectra of nanocrystals (NCs) exhibit substantial blue shifts in the absorption onsets (2.11−2.73 eV) in comparison to the bulk counterpart (1.4−1.5 eV) and a clear red shift with increasing NC size, consistent with the expected quantum confinement effects. The emission properties of NCs were investigated as a function of growth temperature and time and indicate size-tunable maxima in the visible region (469−545 nm) with quantum yields of 0.35−1.6%. Structural and surface analyses of NCs suggest the presence of phase-pure tetragonal Zn 3 P 2 passivated with N−Zn and N−P bonds and the absence of metallic and metal oxide impurities.

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