Spinel type CoFe oxide porous nanosheets as magnetic adsorbents with fast removal ability and facile separation

Adsorption is often time consuming due to slow diffusion kinetic. Sizing he adsorbent down might help to accelerate adsorption. For CoFe spinel oxide, a magnetically separable adsorbent, the preparation of nanosheets faces many challenges including phase separation, grain growth and difficulty in preparing two-dimensional materials. In this work, we prepared porous CoFe oxide nanosheet with chemical formula of Co2.698Fe0.302O4 through topochemical transformation of a CoFe precursor, which has a layered double hydroxide (LDH) analogue structure and a large interlayer spacing. The LDH precursor was synthesized from a cheap deep eutectic solvent (DES) system. The calcined Co2.698Fe0.302O4 has small grain size (10–20 nm), nanosheet morphology, and porous structure, which contribute to a large specific surface area of 79.5 m2 g−1. The Co2.698Fe0.302O4 nanosheets show fast removal ability and good adsorption capacity for both organic waste (305 mg g−1 in 5 min for Congo red) and toxic heavy metal ion (5.27 mg g−1 in 30 min for Cr (VI)). Furthermore, the Co2.698Fe0.302O4 can be separated magnetically. Considering the precursor can be prepared through a fast, simple, surfactant-free and high-yield synthetic strategy, this work should have practical significance in fabricating adsorbents.

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