A mixture of bulk hexagonal boron nitride (h-BN) with hydrazine, 30% H(2)O(2), HNO(3)/H(2)SO(4), or oleum was heated in an autoclave at 100 °C to produce functionalized h-BN. The product formed stable colloid solutions in water (0.26-0.32 g L(-1)) and N,N-dimethylformamide (0.34-0.52 g L(-1)) upon mild ultrasonication. The yield of "soluble" h-BN reached about 70 wt%. The dispersions contained few-layered h-BN nanosheets with lateral dimensions in the order of several hundred nanometers. The functionalized dispersible h-BN was characterized by IR spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV/Vis spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). It is shown that h-BN preserves its hexagonal structure throughout the functionalization procedure. Its exfoliation into thin platelets upon contact with solvents is probably owing to the attachment of hydrophilic functionalities.
In
this work, we tried to combine the advantages of microemulsion
and emulsion synthesis to obtain stable concentrated organosols of
Ag nanoparticles, promising liquid-phase materials. Starting reagents
were successively introduced into a micellar solution of sodium bis-(2-ethylhexyl)sulfosuccinate
(AOT) in n-decane in the dynamic reverse emulsion
mode. During the contact of the phases, Ag+ passes into
micelles and Na+ passes into emulsion microdroplets through
the cation exchange AOTNaOrg + AgNO3
Aq = AOTAgOrg + NaNO3
Aq. High concentrations
of NaNO3 and hydrazine in the microdroplets favor an osmotic
outflow of water from the micelles, which reduces their polar cavities
to ∼2 nm. As a result, silver ions are contained in the micelles,
and the reducing agent is present mostly in emulsion microdroplets.
The reagents interact in the polar cavities of micelles to form ∼7
nm Ag nanoparticles. The produced nanoparticles are positively charged,
which permitted their electrophoretic concentration to obtain liquid
concentrates (up to 30% Ag) and a solid Ag–AOT composite (up
to 75% Ag). Their treatment at 250 °C leads to the formation
of conductive films (180 mOhm per square). The developed technique
makes it possible to increase the productivity of the process by ∼30
times and opens up new avenues of practical application for the well-studied
microemulsion synthesis.
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