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Ascorbic acid (AA) is the most widely used reductant for noble metal nanoparticle (NP) synthesis. Despite the synthetic relevance, its aqueous chemistry remains misunderstood, due in part to various assumptions about its reduction pathway which are insufficiently supported by experimental evidence. This study aims to provide an understanding of the complex chemistry associated with AA under aqueous conditions. We demonstrate that (i) AA undergoes appreciable degradation in alkaline solution on a timescale relevant to NP synthesis, (ii) contrary to popular belief, AA does not degrade into dehydroascorbic acid (DHA), nor is DHA the oxidized product of AA under noble metal NP synthetic conditions, (iii) DHA, which readily degrades under alkaline conditions, can also effectively reduce metal salt precursors to metal NPs, (iv) neither ascorbate nor dehydroascorbate act as surface capping agents post‐synthetically on the NPs (v) AA degradation time greatly affects the morphology and polydispersity of the resultant NP. Results from our mechanistic investigation enabled us to utilize purposefully‐aged reductants to achieve control over shape yield and monodispersity in the seed‐mediated synthesis of Au nanorods. Our findings have important implications for achieving monodispersed products in the many metal NP synthesis reactions that make use of AA as a reducing agent. [ABSTRACT FROM AUTHOR]

EXAFS provides the capability to interrogate nanoparticle (NP) structure in atomistic detail without relying on long‐range crystallinity. There is a limitation in that EXAFS provides averaged structural information, making it difficult to separate a small amount of heterogeneous structure from bulk. In this work, models were developed to extract surface‐specific information from conventional EXAFS measurements collected on UO2 NPs of varying size. Specifically, the surface terminating species of UO2 NPs was determined from comparison of coordination numbers with geometric models while the origin of static disorder was interrogated from user‐defined simulations. Results show that the degree of oxygenation on the NP surface does not significantly deviate from bulk surface and that static disorder is highly enhanced in NP surface layers but cannot be attributed to surface relaxation effects alone. The approach described herein has the potential to be adapted to a range of inorganic NP systems to interrogate surface structure. [ABSTRACT FROM AUTHOR]

In this study we elucidate the structuraldistinctions betweenamorphous and crystalline Ni2P nanoparticles synthesizedusing tri-n-octylphosphine (TOP), through X-ray absorptionspectroscopy (XAS), X-ray diffraction (XRD), and inductively coupledplasma (ICP). We determine the differences in their chemical and atomicstructure, which have not been previously reported, yet are essentialfor understanding their potential as nanocatalysts. These structuralcharacteristics are related to the corresponding nanoparticle magneticproperties analyzed by performing magnetic measurements. XAS resultsreveal a significant P concentration in the amorphous nanoparticlesample – placing the stoichiometry close to Ni2P– despite XRD results that show only fcc Ni contributions.By comparing the long-range structural order from XRD to the short-rangeradial structure from EXAFS we conclude that both techniques are necessaryto obtain a complete structural picture of amorphous and crystallinenanoparticle phases due to the limitations of XRD amorphous characterization.We find that phases are amorphous with respect to XRD when their offsets(deviations) from bulk interatomic distances have a standard deviationas high as ∼4.82. Phases with lower standard deviation (e.g.,≲1.22), however, are detectable as crystalline through XRD.The possible presence of amorphous phases should be considered whenusing XRD alone for nanoparticle characterization. This is particularlyimportant when highly reactive reagents such as TOP are used in synthesis.By characterizing amorphous nickel phosphide nanoparticles that havea comparable stoichiometry to Ni2P, we confirm that TOPserves as a highly effective phosphorus source, even at temperaturesas low as 230 °C. Unintended amorphous structure domains maysignificantly affect nanoparticle properties, and in turn, their functionality. [ABSTRACT FROM AUTHOR]

We report the discovery of unintentional phosphorus (P) doping when tri-n-octylphosphine (TOP) ligands are used in Ni nanoparticle synthesis, which is the most common method for monodisperse Ni nanoparticle synthesis. The nanoparticles appear pure face-centered cubic (fcc) Ni in X-ray diffraction despite the surprisingly high level (5 atomic %) of P. We find that the P doping follows a direct relationship with increased reaction time and temperature and that the P doping can be estimated with the degree of lattice expansion shown from a peak shift in the XRD spectrum. Through EXAFS modeling and density-functional (DFT) calculations of defect formation energies we find that the P atoms are preferentially located on the fcc lattice as substitutional dopants with oxidation state of zero. Magnetic and catalytic properties are shown to be greatly affected by this doping; DFT calculations show magnetization losses in the Ni system, as well as in Fe and Co systems. These findings are likely relevant for other metal syntheses that employ phosphine ligands. [ABSTRACT FROM AUTHOR]