Removal of arsenic and mercury species from water by covalent triazine framework encapsulated γ-Fe2O3 nanoparticles

Abstract

The covalent triazine framework, CTF-1, served as host material for the in situ synthesis of Fe₂O₃ nanoparticles. The composite material consisted of 20 ± 2 m% iron, mainly in γ-Fe₂O₃ phase. The resulting γ-Fe₂O₃@CTF-1 was examined for the adsorption of As^III, As^V and Hg^II from synthetic solutions and real surface-, ground- and wastewater. The material shows excellent removal efficiencies, independent from the presence of Ca²⁺, Mg²⁺ or natural organic matter and only limited dependency on the presence of phosphate ions. Its adsorption capacity towards arsenite (198.0 mg g^-1), arsenate (102.3 mg g^-1) and divalent mercury (165.8 mg g^-1) belongs amongst the best-known adsorbents, including many other iron-based materials. Regeneration of the adsorbent can be achieved for use over multiple cycles without a decrease in performance by elution at 70 °C with 0.1 M NaOH, followed by a stirring step in a 5 m% H₂O₂ solution for As or 0.1 M thiourea and 0.001 M HCl for Hg. In highly contaminated water (100 μg L^-1), the adsorbent polishes the water quality to well below the current WHO limits.

Keywords: Arsenic; Covalent organic frameworks; Iron oxide nanoparticles; Mercury; Water treatment.