Utilization of agricultural waste to herbicide removal: Magnetic BEA zeolite adsorbents prepared by dry-gel conversion using rice husk ash–derived SiO2 for paraquat removal.

[Display omitted] • Converting agricultural waste to an adsorbent for herbicide removal from water. • Use of rice husk ash-SiO 2 in dry-gel conversion to prepare magnetic BEA zeolite. • Adsorbent for paraquat removal with at least 4-cycle reusability is obtained. • Fe 3 O 4 addition allows magnetic collection while maintaining adsorption reusability. This study presents a method that will allow for the sustainable utilization of rice husk ash-SiO 2 (RHAS), an agricultural-waste – derived material, as a bulky solid SiO 2 source in the zeolite beta (BEA)/Fe 3 O 4 composite (magnetic RHAS-BEA) synthesis via a dry-gel conversion method for the removal of paraquat, a typical herbicide, from aqueous solutions. Ultrasonic waves were used to facilitate the formation of uniform Fe 3 O 4 -contained dry precursor gel before converting to the magnetic BEA zeolite composite for the first time. Magnetic RHAS-BEA was then characterized and compared with a non-magnetic sample (RHAS-BEA) using X-ray diffraction and field-emission scanning electron microscopy. In terms of adsorption, we found that paraquat had a high adsorption rate on the samples and conformed to a pseudo-second-order kinetic model. The adsorption behavior of paraquat on the synthesized RHAS-BEA and magnetic RHAS-BEA obeyed the Langmuir adsorption isotherm model. The synthesized adsorbents were reusable for at least four cycles, via thermal regeneration at 450 °C. The inclusion of Fe 3 O 4 particles in magnetic RHAS-BEA disrupted neither the crystallization of the BEA zeolite nor the adsorption of paraquat and enabled easy collection via an external magnet. [ABSTRACT FROM AUTHOR]