Hydrothermal synthesis of zeolite A from alkali-activated sugarcane bagasse ash: influence of crystallization temperature and time on structure and properties

Sugarcane bagasse ash (SCBA), an abundant agro-industrial waste rich in silica and alumina, is a promising sustainable precursor for zeolite synthesis. However, the influence of precursor activation and hydrothermal crystallisation parameters on the structural evolution and physicochemical properties of SCBA-derived zeolites remains insufficiently understood. In this study, zeolite A was synthesised from alkali-activated SCBA via a hydrothermal method, and the effects of crystallisation temperature (100–200 °C) and time (6–8 h) were systematically investigated. SCBA was calcined at 600 °C and activated with 2 M NaOH to enhance silica and alumina dissolution. A synthesis gel with a Si/Al ratio of unity was subjected to hydrothermal treatment, producing zeolitic materials with varying crystallinity and morphology. XRD analysis revealed predominantly amorphous phases at 100 °C, whereas increasing the temperature to 150 and 200 °C enhanced crystallinity, reaching up to 88%. Crystallite sizes ranged from 10.36 to 19.77 nm, indicating progressive crystal growth. FTIR and SEM confirmed the transformation from amorphous aluminosilicate to well-defined zeolitic structures. EDS confirmed the presence of Na, Al, Si, and O, supporting sodium aluminosilicate formation. Zeta potential values (−2.13 to −12.8 mV) indicated negatively charged surfaces favourable for cation adsorption. Overall, lower temperatures favoured surface-active partially crystalline materials, whereas higher temperatures promoted crystallinity and structural ordering, demonstrating the potential of SCBA for tailoring zeolitic materials.