No abstract is available for this article.

No abstract is available for this article.

Discrete, unsupported nanoparticles of Ni₂P have been prepared by using a solution-phase method with bis(1,5-cyclooctadiene)nickel(0) [Ni(COD)₂] as the nickel source and trioctylphosphine (TOP) as the phosphorus source in the presence of the coordinating solvent trioctylphosphine oxide (TOPO). Ni₂P nanoparticles prepared at 345 °C have an average crystallite size of 10.2 ± 0.7 nm and are capped with TOP and/or TOPO coordinating agents. The surface of the Ni₂P nanoparticles can be modified by washing with CHCl₃ or by exchanging TOP/TOPO groups with mercaptoundecanoic acid (MUA). The surface areas of these nanoparticles are on the order of 30–70 m² g^–1. As-prepared and MUA-capped nanoparticles undergo a phase transformation at 370 °C under reducing conditions, but CHCl₃-washed Ni₂P nanoparticles retain the Ni₂P structure. CHCl₃-washed and MUA-capped nanoparticles exhibit higher HDS catalytic activity than as-prepared nanoparticles or unsupported Ni₂P prepared by temperature-programmed reduction of a phosphate precursor. The surface modifications have a clear effect on the catalytic activity as well as the thermal stability of Ni₂P nanoparticles under reducing conditions.

Abstract

Chalcogenide aerogels based entirely on semiconducting II-VI or IV-VI frameworks have been prepared from a general strategy that involves oxidative aggregation of metal chalcogenide nanoparticle building blocks followed by supercritical solvent removal. The resultant materials are mesoporous, exhibit high surface areas, can be prepared as monoliths, and demonstrate the characteristic quantum-confined optical properties of their nanoparticle components. These materials can be synthesized from a variety of building blocks by chemical or photochemical oxidation, and the properties can be further tuned by heat treatment. Aerogel formation represents a powerful yet facile method for metal chalcogenide nanoparticle assembly and the creation of mesoporous semiconductors.

A series of P/As mixed pnicogen phases of composition (CuI)₈P_12−xAs_x, in which x=2.4, 4.2, 4.8, 5.4, and 6.6, have been synthesized and characterized by X-ray single crystal and powder diffraction, solid-state NMR spectroscopy, thermal gravimetric analysis, and impedance spectroscopy. These materials are isostructural to (CuI)₈P₁₂ and consist of neutral, tubular P/As mixed pnicogen chains associated with Cu^I and I⁻ ions. The As is distributed throughout the pnicogen chains; however, the “roof” sites of the [P8] cage show preferred occupation by As relative to the other sites. Accordingly, the change in cell volume is not a linear function of the As incorporation. Solid-state ³¹P NMR spectroscopy of the 40 % As incorporated sample are consistent with the X-ray structural model, with extensive broadening due to ³¹P–⁷⁵As coupling and site disorder, and a change in the chemical shifts of the resonances due to the As substitution into the lattice. The degree of copper ion site disorder, probed by single-crystal X-ray diffraction, increases with increasing As content. Although very little change is observed in the copper ionic conductivity of polycrystalline samples, which ranges from 1.8–5.1×10⁻⁶ S cm⁻¹ for (CuI)₈P_12−xAs_x, x=0, 4.2, 5.4; a single crystal (x=4.8) measured along the needle axis has a conductivity of 1.7×10⁻³ S cm⁻¹ at 128 °C. This represents an order of magnitude improvement in conductivity over (CuI)₈P₁₂ at the same temperature.

Nanoparticulate transition-metal phosphides remain an unexplored, though emerging area of interest on the materials landscape, due principally to their promising magnetic and catalytic properties. This review describes synthetic strategies for the formation of both supported and unsupported transition-metal phosphide nanoparticles, provides a summary of their relevant magnetic and catalytic properties, and indicates new directions for exploration.