Mechanistic insights into a non-classical diffusion pathway for the formation of hollow intermetallics: a route to multicomponent hollow structures

Hollow nanostructures are used for various applications including catalysis, sensing, and drug delivery. Methods based on the Kirkendall effect have been the most successful for obtaining hollow nanostructures of various multicomponent systems. The classical Kirkendall effect relies on the presence of a faster diffusing species in the core; the resultant imbalance in flux results in the formation of hollow structures. Here, an alternate non-Kirkendall mechanism that is operative for the formation of hollow single crystalline particles of intermetallic PtBi is demonstrated. The synthesis method involves sequential reduction of Pt and Bi salts in ethylene glycol under microwave irradiation. Detailed analysis of the reaction at various stages indicates that the formation of the intermetallic PtBi hollow nanoparticles occurs in steps. The mechanistic details are elucidated using control experiments. The use of microwave results in a very rapid synthesis of intermetallics PtBi that exhibits excellent electrocatalytic activity for formic acid oxidation reaction. The method presented can be extended to various multicomponent systems and is independent of the intrinsic diffusivities of the species involved

Pristine nanomaterials: synthesis, stability and applications

Capping-free and linker-free nanostructures/hybrids possess superior properties due to the presence of pristine surfaces and interfaces. In this review, various methods for synthesizing pristine nanomaterials are presented along with the general principles involved in their morphology control. In wet chemical synthesis, the interplay between various reaction parameters results in diverse morphology. The fundamental principles behind the evolution of morphology including nanoporous aggregates of metals and other inorganic materials, 2D nanocrystals of metals is elucidated by capping-free methods in aqueous medium. In addition, strategies leading to the attachment of bare noble metal nanoparticles to functional oxide supports/reduced graphene oxide has been demonstrated which can serve as a simple solution for obtaining thermally stable and efficient supported catalysts with free surfaces. Solution based synthesis of linker-free oxide–semiconductor hybrids and capping-free metal nanowires on substrates are also discussed in this context with ZnO/CdS and ultrathin Au nanowires as examples. A simple and rapid microwave-assisted method is highlighted for obtaining such hybrids which can be employed for high-yield production of similar materials

Highly dispersed ultrafine Pt and PtRu nanoparticles on graphene: formation mechanism and electrocatalytic activity

We demonstrate a robust strategy for obtaining a high dispersion of ultrafine Pt and PtRu nanoparticles on graphene by exploiting the nucleation of a metal precursor phase on graphite oxide surfaces. Our method opens up new possibilities to engineer graphene-based hybrids for applications in multifunctional nanoscale devices

Nanoporous alloy aggregates: synthesis and electrocatalytic activity

Nanoporous structures are widely used for many applications and hence there have been several efforts directed towards their synthesis. While several template-based and template-less approaches are available for monometallic systems, there is no general method for the synthesis of nanoporous multicomponent systems/alloys. We present a general template-less strategy for the synthesis of nanoporous alloy aggregates by controlled aggregation of nanoparticles in the solution phase with excellent control over morphology and composition as illustrated using AuPt, AuPd, PdPt and PtRu systems as examples. The Pt-based nanoporous clusters exhibit excellent activity for methanol oxidation with good long-term stability and CO tolerance. We show that the method can be extended to produce ternary catalysts and hence we expect our method to be widely used for the synthesis of multifunctional nanoporous structures for catalysis, sensor and drug-delivery applications

Surface diffusion driven nanoshell formation by controlled sintering of mesoporous nanoparticle aggregates

We report a general method for the synthesis of hollow structures of a variety of functional inorganics by partial sintering of mesoporous nanocrystal aggregates. The formation of a thin shell initiates the transport of mass from the interior leading to growth of the shell. The principles are general and the hollow structures thus produced are attractive for many applications including catalysis, drug delivery and biosensing

Electron microscopy and spectroscopy studies of modified titanate nanostructures

Titanate nanotubes (TNTs), such as that of Na2Ti3O7, are investigated as alternatives to TiO2 for photocatalysis, as they combine the properties of TiO2 nanoparticles with the properties of layered titanates such as cation exchangeability and open mesoporous morphology with higher specific surface area. Recently spectroscopic investigations using XPS and Raman spectroscopy on cobalt modified TNT samples showed that the presence of the Co cations and its concentration influences the optical and photocatalytic properties. The structure, composition and morphology of the material play a significant role in their catalytic activity. In this work, aberration corrected electron microscopy (AC-TEM/STEM) along with the associated spectroscopic techniques, electron energy loss spectroscopy (EELS) and energy dispersive x-ray spectroscopy (EDS) are employed to study TNTs/cobalt modified TNTs to provide an accurate and in-depth understanding of their structure, composition and morphology of the specimen in a single experiment, from the same region, with high spatial resolution

Metformin Scavenges Methylglyoxal To Form a Novel Imidazolinone Metabolite in Humans

Methylglyoxal (MG) is a highly reactive dicarbonyl compound involved in the formation of advanced glycation endproducts (AGE). Levels of MG are elevated in patients with type-2 diabetes mellitus (T2DM), and AGE have been implicated in the progression of diabetic complications. The antihyperglycemic drug metformin (MF) has been suggested to be a scavenger of MG. The present work examined and characterized unequivocally the resulting scavenged product from the metformin–MG reaction. The primary product was characterized by ¹H, ¹³C, 2D-HSQC, and HMBC NMR and tandem mass spectrometry. X-ray diffraction analysis determined the structure of the metformin and MG-derived imidazolinone compound as (<i>E</i>)-1,1-dimethyl-2-(5-methyl-4-oxo-4,5-dihydro-1<i>H</i>-imidazol-2-yl)­guanidine (IMZ). A LC-MS/MS multiple reaction monitoring method was developed to detect and quantify the presence of IMZ in metformin-treated T2DM patients. Urine from >90 MF-treated T2DM patients was analyzed, with increased levels of MF directly correlating with elevations in IMZ. Urinary MF was detected in the range of 0.17 μM to 23.0 mM, and simultaneous measurement of IMZ concentrations were in the range of 18.8 nM to 4.3 μM. Since plasma concentrations of MG range from 40 nM to 4.5 μM, the level of IMZ production may be of therapeutic significance. Thus, in addition to lowering hepatic gluconeogenesis, metformin also scavenges the highly reactive MG <i>in vivo</i>, thereby reducing potentially detrimental MG protein adducts, with subsequent reductions in diabetic complications