Surface engineering of diatomite using nanostructured Zn compounds for adsorption and sunlight photocatalysis

Abstract

Diatomite, composed of amorphous macroporous hydrated silica, has generated increasing attention as an attractive raw material for elimination of heavy metal, while suffering low surface activity. Herein, easily separable diatomite adsorbents modified by Zn compounds are developed for effective adsorption of Pb(II), Cu(II) and Cd(II) ions and sunlight photoreduction of toxic Cr(VI) to low-toxic Cr(III). The micro-structure and functionality are characterized through energy spectrum and spectroscopic analysis. Sulfion S2− or carbonyl COO− interlinked networks on the modified diatomite are effective for capturing Pb(II), Cu(II) and Cd(II) ions, and are capable of being oxidized to generate diatomite@ZnO directly at 450 °C in air atmosphere. Significantly, by recycling the used diatomite@ZnS (Dt@ZnS) adsorbents loaded by Cu(II) and Cd(II) ions, Cu or Cd doped ZnO photocatalysts can be fabricated on diatomite to vary band gap energy of ZnO for more efficient absorption of visible light for Cr(VI) photoreduction under sunlight irradiation. Although the derivatives exhibit weakened Cr(VI) photoreduction capacity compared with Dt@ZnS precursor, probably owing to the influence of surface deposits of Cu(II) or Cd(II) on doping efficiency and light absorption, this idea offers a promising solution to convert the used adsorbents loaded by poisonous heavy metals into photocatalysts for secondary utilization in waste water purification, thus making it possible to produce tailor-made materials for specific requirements alternative by the reutilization of discarded heavy metal adsorbents.