Design of Hierarchal 3D Metal Oxide Structures for Water Oxidation and Purification

Nanostructure materials have witnessed tremendous progression toward their use in various applications due to their unique properties. However, their incorporation and fabrication into prototype devices remain a challenge mainly due to the limited ability to form hierarchical three dimensional (3D) structures on a large scale, low cost, and simple process. Herein, we address this challenge and demonstrate the growth of unique hierarchical structures by coating calcareous foraminiferal shells with inorganic materials. Foraminifera is highly diverse and abundant marine unicellular protists that possess vastly complex, porous, hierarchical and large (from 0.1 mm to more than 200 mm) shells. Surprisingly, despite their unique structures, they have not been used as templates to grow inorganic or organic materials. Coating the scaffold was simply conducted via thermal decomposition of single source precursors at moderate temperatures to form a metal and metal oxide directly on the surfaces of foraminiferal templates, Sorites was chosen as prototype species. These hierarchal structures were investigated in electrochemical water oxidation reaction, and water purification processes of metal ions contaminate. For water oxidation, Sorites@Co and Sorites@NiO present a remarkable performance for oxygen evolution, 154.6 mA/cm² and 73.5 mA/cm² at 1 V vs. Ag/AgCl and an onset potential of ~0.55 V vs. Ag/AgCl, respectively. For water purification process, Sorites@Fe(OH)_x structures were used as an active material for removing of contaminants without using any external pressure. The superior performance of the prototype filter was achieved where the concentration of the contaminants after filtration, such as Pb²⁺, Cd²⁺, and Cu²⁺ was reduced by 99.98%, 99.99 %, and 99.99%, respectively.