Synthesis and characterization of mesoporous ZnS with narrow size distribution of small pores

Abstract

Pure, nanocrystalline cubic ZnS forming a stable mesoporous structure was synthesized at room temperature by a non-toxic surfactant-assisted liquid–liquid reaction, in the 9.5–10.5 pH range of values. The appearance of an X-ray diffraction (XRD) peak in the region of very small angles (∼ 2°) reveals the presence of a porous material with a narrow pore size distribution, but with an irregular arrangement of the pores, a so-called worm hole or sponge-like material. The analysis of the wide angle XRD diffractograms shows the building blocks to be ZnS nanocrystals with cubic structure and average diameter of 2 nm. Transmission electron microscopy (TEM) investigations confirm the XRD results; ZnS crystallites of 2.5 nm with cubic (blende) structure are the building blocks of the pore walls with pore sizes from 1.9 to 2.5 nm, and a broader size distribution for samples with smaller pores. Textural measurements (N₂ adsorption–desorption isotherms) confirm the presence of mesoporous ZnS with a narrow range of small pore sizes. The relatively lower surface area of around 100 m²/g is attributed to some remaining organic molecules, which are filling the smallest pores. Their presence, confirmed by IR spectroscopy, seems to be responsible for the high stability of the resulting mesoporous ZnS as well.