Effective, Low-Cost Recovery of Toxic Arsenate Anions from Water by Using Hollow-Sphere Geode Traps

Because of the devastating impact of arsenic on terrestrial and aquatic organisms, the recovery, removal, disposal, and management of arsenic-contaminated water is a considerable challenge and has become an urgent necessity in the field of water treatment. This study reports the controlled fabrication of a low-cost adsorbent based on microscopic C-,N-doped NiO hollow spheres with geode shells composed of poly-CN nanospherical nodules (100 nm) that were intrinsically stacked and wrapped around the hollow spheres to form a shell with a thickness of 500–700 nm. This C-,N-doped NiO hollow-sphere adsorbent (termed CNN) with multiple diffusion routes through open pores and caves with connected open macro/meso windows over the entire surface and well-dispersed hollow-sphere particles that create vesicle traps for the capture, extraction, and separation of arsenate (AsO₄ ³⁻) species from aqueous solution. The CNN structures are considered to be a potentially attractive adsorbent for AsO₄ ³⁻ species due to 1) superior removal and trapping capacity from water samples and 2) selective trapping of AsO₄ ³⁻ from real water samples that mainly contained chloride and nitrate anions and Fe²⁺, and Mn²⁺, Ca²⁺, and Mg²⁺ cations. The structural stability of the hierarchal geodes was evident after 20 cycles without any significant decrease in the recovery efficiency of AsO₄ ³⁻ species. To achieve low-cost adsorbents and toxic-waste management, this superior CNN AsO₄ ³⁻ dead-end trapping and recovery system evidently enabled the continuous control of AsO₄ ³⁻ disposal in water-scarce environments, presents a low-cost and eco-friendly adsorbent for AsO₄ ³⁻ species, and selectively produced water-free arsenate species. These CNN geode traps show potential as excellent adsorbent candidates in environment remediation tools and human healthcare.