Design and Synthesis of Reusable Nanoparticles for Reversible Chemisorption of Hexavalent Chromium Anions from Aqueous Media and Catalysis

Abstract

A magnetically active nanocomposite material has been synthesized from the reaction mixture of magnetite core iron nano-particles electrostatically coated with SiO2, hydrotalcite nanosheets ([Eu8 (OH) 20 (H2O)n] 4+), and decatungstophosphate anion ([α-PW10O367−]). The resulting nanocomposite material, denoted as Fe34@SiO2@LEuH@PW10, is demonstrated to effectively adsorb chromate anions from aqueous solutions, the adsorption isotherms fit the Langmuir model with a capacity of 23 mmol·g−1 after 42 minutes at 25°C, the reaction is spontaneous at room temperature with 44.22 kJ·mol−1of activation energy required. In addition, heating the chromate-adsorbed nanocomposite material at 40°C results in dissociation of the chromate anions from the nanocomposite material. As such, the recycled adsorbent Fe3O4@SiO2@LEuH@PW10 is reused for chromate removal in aqueous solutions for at least ten times without obvious loss of activity. This spontaneous reversible chemisorption mechanism for chromate adsorption provides a new pathway for separation and cleaning of industrial wastewater contaminated with chromate ions, the robust catalytic activity of the nanocomposite is also demonstrated.