Custard apple-shaped NaX zeolite with a large surface area derived from rice husk ash by a single-step template-free process

Abstract

Custard apple-shaped NaX zeolite with a large surface area was synthesized from rice husk ash without use of a templating agent via a single-step autoclave process at 90 °C/6h. The crystallinity of the particles was confirmed by XRD. An FTIR study shows the characteristic bands at 560 cm−1 for a double 6-membered ring (D6R), while a Raman shift at around 500 cm−1 indicates the bending mode of 4-membered ring fragments of NaX zeolite. The total BET surface area of the product was found to be 703 m2g−1 comprising a micrpore surface area of 623 m2g−1 and a mesopore surface area of 80 m2g−1. A hierarchical porous structure with micropores in the range of 0.72–1.76 nm and mesopores centred at 3.5 nm was obtained. FESEM and TEM images of NaX zeolite show a custard apple-like morphology (1–2 μm) of secondary particles which was formed by self-assembly of nanometer-sized (50–100 nm) primary particles. A proposed formation mechanism was illustrated.