A general route to modify diatomite with niobates for versatile applications of heavy metal removal

Abstract

A general solution-phase strategy is developed to synthesize nanostructure niobates such as MnNb₂O₆, SnNb₂O₆ and ZnNb₂O₆ on natural mineral diatomite for water environmental remediation. (NH₄)₂C₂O₄ aqueous solution is the key to achieve a scalable and controllable synthesis of niobate/diatomite hybrid systems, which generates NH₃·H₂O for surface etching activation of diatomite, and H₂C₂O₄ for complexation dissolution of Nb₂O₅, enabling the heterogeneous crystallization process to proceed with controllable growth kinetics. First principle calculations indicate that both niobium atom and niobium–oxygen species have the lowest adsorption energy on SiO₂ surface, and then induce the nucleating process of Nb–O–Mn (or Zn, Sn) networks. Cr(VI), Fe(III), and Pb(II) ions are taken as target pollutants to evaluate the water-cleaning ability of the niobate-modified diatomite. Possible mechanisms for the photoreduction of Cr(VI), physical adsorption of Fe(OH)₃ colloids, and chemisorption of Pb(II) ions are proposed on the basis of experimentally investigations. The possibility of combining the advantages of natural mineral diatomite and nanostructured niobates provides a highly robust and potential material system with versatile functionalities of heavy metal ion removal, demonstrating great promise for a wide range of water purification.