Zeolite beta films synthesized from basic and near-neutral precursor solutions and gels

Abstract

Zeolite Beta films were grown on silicon wafers from clear aluminosilicate solutions in alkaline media or from aluminium free gels in near-neutral nonalkaline (F −) media. Colloidal zeolite Beta seeds were preliminary deposited onto the substrates by either electrostatic adsorption or spin coating. The seeded wafers were then vertically placed in polypropylene reactors or autoclaves and hydrothermally treated with the synthesis solutions or gels at 100 °C or 150 °C. The products crystallized in the bulk solution and the corresponding zeolite films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), dynamic light scattering (DLS) and thermogravimetric analysis (TGA). In addition, the crystal orientation along the films depth was studied by grazing incidence X-ray diffraction (GID) using synchothron X-ray radiation. The BEA films prepared from clear solutions in alkaline media were relatively homogeneous, built up by crystals with a size of ca. 80 nm and with an overall thickness of ∼200 nm. The zeolite Beta films prepared in fluoride media were very rough with a thickness exceeding 20 μm and were composed of well-faceted uniform 2.5–3 μm truncated square dipyramidal crystals. The different composition of the films in terms of aluminium content resulted in different hydrophilicity/hydrophobicity of the zeolite Beta crystals building up the films. The GID analysis showed that the crystals of the zeolite Beta films grown from the two types of precursor synthesis mixtures were randomly oriented.