Adsorption Properties of Nanocrystalline/Nanoporous Gallium Nitride Powders

A diverse pool of six semiconductor GaN nanopowders was synthesized by the thermally-driven pyrolysis of gallium imide at various temperatures. The XRD-derived average crystallite sizes for the nanopowders were in the range 1-17 nm. Standard nitrogen adsorption measurements at 77 K yielded the basic characteristics of the powder pore structures including the BET surface areas that spanned 23-287 m2/g. Rare studies of adsorption of water vapor, carbon dioxide, and hydrogen on the nitride nanopowders were carried out. The data on water vapor adsorption at 295 K supported chemisorption of water molecules on the primary adsorption centers and physisorption on the secondary centers. The data on carbon dioxide adsorption at 273 K and hydrogen adsorption at 77 K were used to determine the selectivity of adsorption for these gases defined as the ratio of the respective Henry’s constants calculated from the Langmuir equation. The GaN nanopowders showed remarkably diverse pore structure characteristics and adsorption properties that could be linked to the nitride’s average crystallite size and crystallite agglomeration, the latter supported by helium density data.