Surface diffusion driven nanoshell formation by controlled sintering of mesoporous nanoparticle aggregates
ABSTRACT 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.
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ABSTRACT: Engineered hollow nanoparticles have exhibited their potential in nanotechnology applications, but so far the investigation of the deformation mechanisms for these hollow particles during the sintering process has rarely been reported. Hence, a comparative study of both solid and hollow spherical silver nanoparticles with different sizes under different heating rates of laser sintering is conducted systematically in this paper, based on molecular dynamics simulations. An interesting phenomenon is observed where the temperature for fast neck growth shows an inverse trend in all the hollow nanoparticle pairs at an ultrahigh heating rate, which is quite different from that known in the solid particle cases. This finding implies that besides the size and heating rate, the nanoparticle geometry could also play an important role in the sintering process. At a low heating rate, the plastic deformation combined with structural reconfigurations induced by the lattice sliding in the hollow shells is found to be an important mechanism during the heating process. At an ultrahigh heating rate, the transition from fcc crystal directly to disordered structure from both outside and inside surfaces becomes more dominant than the structural reconfiguration with lattice defects, which is facilitated by the introduction of the inner free surfaces in hollow nanoparticles. The entire hollow particle pairs thus show an obvious tendency to coalesce and melt at a lower temperature level than with a low heating rate.Journal of Physics D Applied Physics 07/2013; 46(33):335302. DOI:10.1088/0022-3727/46/33/335302 · 2.52 Impact Factor
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ABSTRACT: 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.Particle and Particle Systems Characterization 07/2013; 30(7):590. DOI:10.1002/ppsc.201300022 · 0.54 Impact Factor
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ABSTRACT: The formation mechanism of SnO2 nanotubes (NTs) fabricated by generic electrospinning and calcining was revealed by systematically investigating the structural evolution of calcined fibers, product composition and released volatile by-products. The structural evolution of the fibers proceeded sequentially from dense fiber to wire-in-tube to nanotube. This remarkable structural evolution indicated a disparate thermal decomposition of poly-vinylpyrrolidone (PVP) in the interior and the surface of fibers. PVP on the surface of the outer of fibers decomposed completely at a lower temperature (<340°C), due to exposure to oxygen and SnO2 crystalized and formed a shell on the fiber. Interior PVP of the fiber were prone to loss of side substituents due to the oxygen-deficient decomposition, leaving only the carbon main chain. The rest Sn crystalized when the pores form resulting from the aggregated of SnO2 nanocrystals in the shell. The residual carbon chain did not decompose completely at temperatures less than 550°C. We proposed a PVP-assisted Ostwald ripening mechanism for the formation of SnO2 NTs. This work directs the fabrication of diverse nanostructure metal oxide by generic electrospinning method.Langmuir 08/2014; 30(37). DOI:10.1021/la5017559 · 4.38 Impact Factor