Zinc Oxide Nanocrystals Stabilized by Alkylammonium Alkylcarbamates

Abstract

Nearly monodispersed, spherical ZnO nanocrystals were synthesized from the reaction of an amide precursor, [Zn(N(i)Bu(2))(2)](2), with hexylamine followed by reactions of the as-formed solution in a moist air flow. Extensive experiments were conducted to optimize the synthesis and to characterize the nanocrystals. The room temperature reactions led to 3.3-5.3 nm nanocrystals with the sizes increasing in direct proportion to the relative humidity. Purification afforded high yields of free-flowing nanocrystals that were dispersible in nonpolar solvents. The overall synthesis requires several days, but it results in multigram quantities of stable, redispersible nanocrystals. The nanocrystals were characterized using elemental analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), solution and solid-state NMR, IR, UV-vis absorption, and photoluminescence spectroscopies. In addition to providing H(2)O to serve as the source of oxygen in the ZnO, the air flow adds CO(2) that converts the alkylamine into an alkylammonium alkylcarbamate, which serves as the surfactant. Elemental analysis, TGA, and XPS results established that the total number of N-hexyl fragments on a 3.7 nm nanocrystal was 200, where they exist as an equal number of anionic carbamates and cationic ammonium ions. The addition of pure hexylammonium hexylcarbamate to ZnO nanocrystals prepared by literature methods resulted in the formation of a product that was similar to the ZnO formed using [Zn(N(i)Bu(2))(2)](2). Larger nanocrystals up to 7.3 nm were also obtained by heating smaller nanocrystals in a mixture of hexylamine and toluene at 119 degrees C.

Hydrolysis of organometallic and metal–amide precursors: synthesis routes to oxo-bridged heterometallic complexes, metal-oxo clusters and metal oxide nanoparticles

“…184 Gladfelter and co-workers also showed that moisture was the major reagent in the reaction of Zn(N i Bu2)2 under air. 189 The ZnO NP size increased as the humidity level was increased, while only amorphous products were formed under dry conditions. The presence or absence of O2 may still be important in the hydrolysis reaction: for example, the reaction of Fe(N(SiMe3)2)2 with water forms wüstite Fe1-yO NPs; 168,169 whilst under air the iron becomes oxidised, instead forming maghemite Fe2O3 NPs.…”

“…Hydrolysis of reactive metal precursors can take place under air, where both water vapour and O2 can act as the oxygen source (vide infra). Several studies have indicated that water vapour is typically the key reagent under these conditions, 184,189 however, the presence of oxygen may affect the products, especially where an oxidisable metal precursor is used (e.g. Fe(N(SiMe3)2)2 or Ni(4-C8H12)2).…”

Electrostatic Induced Molecular Tilting in Self-Assembled Monolayers of n-Octadecylamine on Mica

“…The same conclusion species. 18,26,30,31,32,33,34 The N 1s peaks have been fitted using these components and a progressive increment of the -NH 3 + /-NH 2 ratio is observed along the ripening process (see Table S1 and Figure S2 in supporting information). Furthermore, carbamation seems to be constant along the ODA/mica SAM exposition to air, as indicated by the evolution of the 400.2 eV component in Figure 3.…”

Synthesis and application of palladium stearates as precursors for the preparation of palladium nanoparticles

“…It is known that carbamates or carbamic acids could be formed in ambient or supercritical conditions from the reaction between amines and CO 2 . The carbamates were reported as efficient stabilizers which not only could improve the stability and uniformity of the nanoparticles but also could reduce the size as well as manipulate the shape of the nanoparticles . On the other hand, the addition of CO 2 would lead to a volume expansion of the solvent, thus forming a CO 2 ‐expanded liquid (CXL) system .…”