Influence of saline water sources on the crystallographic and morphological criteria of organic-template-free eco-synthesized zeolites

Abstract

This study novelly investigates the influence of saline water sources in the ecofriendly synthesis of zeolites, employing economical materials like aluminum scraps, and commercial sodium silicate, within an organic-template-free crystallization system. The type of dissolved anions significantly influences the crystallographic and morphological properties of zeolites. Initially, mordenite forms in distilled water, then transforms into P zeolite and eventually the more stable analcime phase. Saline waters significantly slowed down the phase transformation of the zeolites. At prolonged reaction time, pure analcime, exhibiting varying degrees of aggregation, was observed using distilled, tap, and synthetic saline waters containing Cl⁻ or CO₃²⁻. However, mixtures of well-defined crystals consisting of 82.3% P zeolite and 17.7% analcime, or 65.3% P zeolite and 34.7% mordenite, were obtained using waters containing SO₄²⁻ or HCO₃⁻, respectively. When Mediterranean seawater was utilized, a mixture comprising 30.9% mordenite and 69.1% analcime was produced. Conversely, the high salinity of the Red seawater impeded zeolite formation. While distilled water follows classical nucleation and layer-by-layer deposition, saline waters influenced crystallography and morphology, with anions playing a pivotal role. HCO₃⁻ suppressed transformation, while surface-adsorbed Cl⁻ and SO₄²⁻ ions facilitated reverse crystal growth mechanism akin to organic-directing agents. Preliminary tests reveal zeolites’ affinity for removing Cu²⁺ and Fe³⁺ ions, warranting further research. This study opens new avenues for sustainable materials and environmental remediation.

Graphical abstract