Confinement effect-mediated adsorption enhancement of as(III)/as(V) by titanate nanotube-encapsulated nZVI

Arsenic contamination in water poses a severe threat to the environment and human health. Developing a green, low-cost, and highly efficient adsorbent for As(III)/As( V ) removal remains a great challenge. In this work, titanate nanotube-encapsulated nZVI (Fe@TNTs) and surface-supported nZVI (Fe/TNTs) were prepared. The confinement effect on arsenic adsorption was systematically investigated. A series of characterizations (TEM, XRD, XPS, etc.) and analyses (batch experiments, MD/DFT calculations) were conducted. Fe@TNTs exhibit superior adsorption capacities versus Fe/TNTs, along with excellent coexisting ion tolerance (excluding PO 4 3− ) and cyclic stability. As(III) is adsorbed via monolayer chemisorption, whereas As( V ) adsorption exhibits a heterogeneous surface adsorption behavior. MD simulations confirm confinement-induced arsenic enrichment in Fe@TNTs, and DFT calculations verify its lower arsenic adsorption energies. These advantages stem from confinement effect, which induces arsenic enrichment and promotes complexation, oxidation, and electrostatic interactions. This study provides a novel confinement engineering strategy for high-performance adsorbents, with great application potential in the treatment of arsenic-contaminated wastewater.