Chemically controlled particulate properties of zeolites: Towards the face-less particles of zeolite A. Part 1. Influence of the batch molar ratio [SiO2/Al2O3]b on the size and shape of zeolite A crystals

Influence of the batch molar ratio, y ≡ [SiO2/Al2O3]b, on the size and shape of zeolite A crystals at three different molar ratios [SiO2/H2O]b and [Na2O/H2O]b was investigated. Four different morphological entities of zeolite A, namely regular cubic crystals with sharp edges and apexes, cubic crystals with truncated edges, cubic crystals with “rounded” edges and apexes and pseudo-spherical, face-less particles, were observed in the crystalline end products obtained by hydrothermal treatment (heating at 80 °C) of the hydrogels having 1.0 ⩽ [SiO2/Al2O3]b ⩽ 2.2, 0.006 ⩽ [SiO2/H2O]b ⩽ 0.0186 and 0.0136 ⩽ [Na2O/H2O]b ⩽ 0.0424. The chemical conditions with respect to the values of [SiO2/Al2O3]b, [SiO2/H2O]b and [Na2O/H2O]b for obtaining the particular morphological entities of zeolite A are defined, and the possible mechanisms of their formation are discussed. The influence of the mentioned factors on the crystal size and the surface properties of crystallized zeolites is also considered.

Graphical abstractScanning-electron micrograph (magnification: 33.000 times) of the particles of the fully crystalline face-less particles of zeolite A (zeolite FLA), showing their pseudo-spherical shape and rough surfaces.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► Scanning-electron micrograph of the particles of crystalline face-less particles of zeolite FLA. ► Pseudo-spherical shape and rough surfaces are obtained. ► Produced using batch molar ratios A = [Na2O/H2O] 0.037, tsc = [SiO2/H2O] 0.0162 and y = [SiO2/Al2O3] 1.3. ► Absorption ability is about 2.8 times higher than the one of the “standard” morphological forms of zeolite A.