Green and Sustainable Zeolite Synthesis: A Review of Waste-Derived Feedstocks and Energy-Efficient Methods

Abstract

Conventional zeolite manufacturing incurs escalating environmental and economic costs driven by costly reagent-grade precursors, energy-intensive autoclaved heating, and organic structure-directing agents requiring high-temperature calcination, which collectively generate significant waste and emissions. To address these issues, zeolites—defined as crystalline microporous aluminosilicates with well-defined pore architectures that underpin their widespread industrial utility as catalysts, adsorbents, and ion exchangers—are the focus of recent advancements. This review critically examines green and sustainable synthesis by focusing on two interconnected strategies: waste-derived aluminosilicate feedstocks such as coal fly ash, volcanic ash, kaolin, and waste glass as sustainable silica and alumina sources; and energy-efficient synthesis routes including microwave-assisted, solvent-free, and seed-assisted methods that dramatically lower crystallization time and energy consumption. Furthermore, the review analyzes the vital roles of alkaline fusion pre-treatment, structure-directing agents, Si/Al ratios, and gel compositions in precisely controlling framework type and crystallinity under sustainable constraints. Ultimately, a comprehensive comparative assessment of all major synthesis routes is provided alongside future research directions aimed at achieving scalable, template-free, and waste-valorizing zeolite production.