Carbon-decorated iron oxide hollow granules formed using a silk fibrous template: lithium-oxygen battery and wastewater treatment applications

Hierarchical nanoarchitecture and phase control of iron oxides are important approaches for achieving multi-functionality for various applications. Herein, rice-grain-shaped iron oxide hollow structures were synthesized via a hydrothermal process using a silk fibrous template, and the crystalline phases (α-Fe 2 O 3 , Fe 3 O 4 ) were controlled by annealing. These structures were applied in a lithium-oxygen battery cathode and as adsorbents for wastewater treatment. The porosity, hollow interior, surface area, surface chemical composition and efficient carbon matrix of the C/Fe 3 O 4 hollow granules obtained by annealing under Ar atmosphere were favorable for enhancing the oxygen reduction and evolution kinetics when applied as an electrocatalyst for lithium-oxygen batteries, and also led to superior adsorption of organic pollutants (Rhodamine B) from an aqueous medium. The C/Fe 3 O 4 hollow granules were uniformly distributed and confined in the 3D nanoarchitecture; this morphology can offer rapid ion transport with improved electronic and chemical kinetics as well as superior adsorption of organic pollutants. Nanoarchitectures: Finding nano-treasures along the silk road Hollow nanoparticles of iron oxide can power up both batteries and water purification thanks to a silk-based synthetic strategy. Dong-Wan Kim from Korea University extracted fibroin proteins from silkworm cocoons to produce thin assemblies of beta sheets terminated by peptide chains. When mixed with an iron chloride precursor and heated in a sealed autoclave, the silk proteins aggregated into spherical micelles, which served as crystallization templates. Strong interactions between metal ions and micelles directed iron oxide to assemble into rice-grain-shaped structures that gradually ‘ripened’ with interior void spaces. Final annealing in an argon atmosphere produced carbon-magnetite composites with a large distribution of electrocatalytic sites useful for lithium-oxygen battery anodes. The three-dimensional hollow nanoarchitectures also proved efficient at removing carcinogenic rhodamine B dye from wastewater. Iron oxides were designed to the rice-grain-shaped hollow structures with hierarchical pores and highly aligned nano/micro-structures using silk fibrous templates to impose multi-functional materials for the electrocatalysts for Li-O 2 batteries and the adsorbents of organic pollutants.