Characteristics of GaPO4-LTA: Unique phase transition into amorphous cubic particles by long-term soaking in water

Abstract

The transformation of as-synthesized gallophosphate crystals with an LTA structure (GaPO4-LTA) into an amorphous phase was induced simply by soaking the crystals in water. The obtained amorphous gallophosphate (am-GaPO) particles maintained the characteristic initial cubic morphology of GaPO4-LTA but with no molecules of dipropylamine (DPA), which acts as an organic structure-directing agent for the crystal synthesis. Am-GaPO incorporates many water molecules in place of DPA. The removal of DPA enables the water molecules to contact the GaPO4-LTA framework, which degrades the crystallinity. Though am-GaPO was expected to be a porous material due to its many water molecules, the square-shaped submicron holes on the particle surface, and light scattering from the particle interior, only a small surface area of 6 m2/g was estimated by the Brunauer–Emmett–Teller method. The accessible holes were distributed mainly on the particle surface, and it was concluded that the incorporated water molecules were chemisorbed.