Pollen as a template for synthesizing hierarchically structured metal oxides

Abstract

Pollen grains have represented promising biotemplates to fabricate 3D hierarchical structures due to their extremely resistant outer walls (exine) and uniform morphology in a given plant species. Here, we report a simple and green approach for the synthesis of metal oxides by using functionalized sporopollenin exine capsules (SECs) derived from Lycopodium clavatum as a novel template. After extracting the SECs, we generated carboxylates on the SECs through a facile NaOH treatment, to induce electrostatic interactions between the metal ions in the precursor solution and surface of the SECs. The prepared pollen-templated metal oxides (ZnO, CeO$_2$, and Fe$_2$O$_3$) successfully maintained the hierarchical shape of the pollen (Lycopodium) consisting of numerous nanoparticles and exhibited a larger surface area than that of commercial metal oxides. Results of the methylene blue degradation test under visible light showed that our pollen-templated metal oxides outperformed the commercial metal oxides in terms of the photocatalytic performance.