Preparation of paramagnetic ferroferric oxide-calcined layered double hydroxide core-shell adsorbent for selective...

Adsorption is one of the most common methods of pollution treatment. The selectivity for pollutants and recyclability of adsorbents are crucial to reduce the treatment cost. Layered double hydroxide (LDH) materials are one type of adsorbent with poor recyclability. Prussian blue (PB) is a sturdy and inexpensive metal-organic framework material that can be used as the precursor for synthesizing paramagnetic ferroferric oxide (Fe₃O₄). It is intriguing to build some reusable adsorbents with magnetic separation by integrating LDH and PB. In this work, paramagnetic Fe₃O₄-calcined LDH (Fe₃O₄@cLDH) core-shell adsorbent was designed and prepared by the calcination of PB-ZnAl layered double hydroxide (PB@LDH) core-shell precursor, which exhibits high anionic dyes selectivity in wastewater solutions. The paramagnetism and adsorption capability of Fe₃O₄@cLDH come from the Fe₃O₄ core and calcined ZnAl-LDH shell, respectively. Fe₃O₄@cLDH shows an adsorption capacity of 230 mg g^-1 for acid orange and a high selectivity for anionic dyes in cation-anion mixed dye solutions. The regeneration process indicates that the high selectivity for anions is related to the specific hydration recovery process of ZnAl-LDH. The synergistic effect of the paramagnetic Fe₃O₄ core and calcined ZnAl-LDH shell makes Fe₃O₄@cLDH an excellent magnetic separation adsorbent with high selectivity to anions.