Unexpected ultra-fine nickel phyllosilicate nanofibers formed on the surface of Ni-encapsulated zeolite catalyst: Phase identification and independent synthesis

Abstract

During the study of hydrothermal synthesis of nickel-encapsulated zeolite catalyst using the ligand-protection method, uniform nanofibers (∼10 nm diameter, hundreds of nanometers long) were unexpectedly observed on the surface of zeolite crystals. These nanofibers were subsequently synthesized independently outside the zeolite synthesis system and were identified as nickel-kerolite, a kind of talc-like nickel phyllosilicate. An optimal synthesis approach of the nickel phyllosilicate fibers was realized via a hydrothermal method using a synthetic gel comprising a silicon source, sodium hydroxide, nickel nitrate, and ethylenediamine (EDA). It is found that the formation of the unique fibrous morphology of nickel phyllosilicate requires a sufficiently strong alkaline medium and the presence of EDA. Ethylenediamine was proven to be essential for achieving the nano-fibrous morphology, probably due to the anisotropic growth inhibition from both EDA and its nickel complex (Ni-EDA), which restrict crystal development predominantly along one direction.