Magnetite Nanoparticles Loaded into Halloysite Nanotubes for Arsenic(V) Removal from Water

Groundwater contaminated by arsenic (As) is a serious concern because it poses a significant threat to millions of people reliant on both drinking and irrigation of farms. Hence, the low-cost and efficient treatment of these waters is of utmost importance. This study presents the ecofriendly synthesis of magnetite nanoparticles (Fe 3 O 4 NPs)-immobilized halloysite nanotube (HNT) composite (Fe 3 O 4 @HNT) for remediating arsenate [As(V)] from water. High-resolution transmission electron microscopy confirmed that ultrasmall Fe 3 O 4 NPs (4.52 ± 1.63 nm) were immobilized on the interior surface of HNT. Fe 3 O 4 @HNT possesses a larger surface area (82 ± 0.23 m 2 /g) and a higher thermal stability (7.1% weight loss at 950 °C) than a pristine HNT (47.23 ± 0.14 m 2 /g and 12.6%, respectively). Adsorption kinetics were best fitted with pseudo-second-order and intraparticle diffusion, while the isotherms results were best supported with the Freundlich model ( R 2 = 0.99 in each case). Therefore, it could be surmised that multiphase rate-controlling chemisorption occurred during adsorption. The thermodynamics data revealed the endothermic nature of As(V) adsorption by Fe 3 O 4 @HNT. Fourier transform infrared and X-ray photelectron spectroscopy analyses confirmed chemical bonding between As and Fe. In addition, Fe 3 O 4 @HNT was easily separable by an external magnet (the saturation magnetization value was 20 emu/g), which is an additional benefit of the material to be used on an industrial scale. The material was also reusable after regeneration for five rounds of consecutive sorption–desorption with excellent efficiency and no substantial loss of structural integrity. Furthermore, Fe 3 O 4 @HNT removed more than 99% As(V) from the groundwater, signifying its viability in real-case implementation. Cost-benefit analysis ensured that Fe 3 O 4 @HNT was cost-effective, while its biocompatibility test confirmed no detrimental impact on soil bacterial growth once the spent material had been disposed. Consequently, cheap, easily separable, reusable, and biocompatible Fe 3 O 4 @HNT may be a prospective composite for the sustainable eradication of As and other metallic toxicants from wastewater.