Natural pollen exine-templated synthesis of photocatalytic metal oxides with high surface area and oxygen vacancies

• Synthesis of pollen exine-templated metal oxides (ZnO, CeO 2 , and Fe 2 O 3 ). • Unique morphology for high surface area and increased oxygen vacancies. • Rapid photocatalytic degradation of organic pollutants. Pollen grains in nature possess highly hierarchical structure been created through evolution process for over millions of years. Here, we report eco-friendly synthesis of highly photocatalytic metal oxides (ZnO, CeO 2 , and Fe 2 O 3 ) using sporopollenin exine capsules (SECs), the hard structure of pollen, as a template. We generate carboxylate groups on the SECs to induce electrostatic interactions between the metal ions in the precursor solution and the surface of the SECs. The pollen-templated metal oxide structure is synthesized by aggregating metal oxide nanoparticles with the size of 10–20 nm on the micro-sized SECs framework, which have maintained unique morphology of the pollen. These metal oxides display excellent performance of organic pollutants degradation under visible light, owing to high surface area and oxygen vacancies which allow higher reaction rates and promote separation of photogenerated electron-hole pairs.