EDTA-Assisted Synthesis of Nitrogen-Doped Carbon Nanospheres with Uniform Sizes for Photonic and Electrocatalytic Applications

We report a robust method for the facile synthesis of N-doped carbon nanospheres with uniform and tunable sizes. Instead of involving a surfactant or other templates, this synthesis relies on the incorporation of ethylenediaminetetraacetic acid (EDTA) into the emulsion droplets of phenolic resin oligomers. The EDTA provides a high density of surface charges to effectively increase the electrostatic repulsion between the droplets and thereby prevent them from coalescing into irregular structures during polymerization-induced hardening. The EDTA-loaded polymer nanospheres are highly uniform in terms of both size and shape for easy crystallization into opaline structures. While maintaining good uniformity, the diameters of the resultant N-doped carbon nanospheres can be readily tuned from 100 to 375 nm, allowing for the fabrication of opaline lattices with brilliant structural colors. The EDTA also serves as an additional nitrogen source to promote the formation of graphitic-N, making the N-doped carbon nanospheres highly active, metal-free bifunctional electrocatalysts toward oxygen reduction and oxygen evolution reactions.

Automated summary

We developed a simple method for synthesizing N-doped carbon nanospheres with uniform and tunable sizes. The synthesis involves the incorporation of EDTA into the emulsion droplets of phenolic resin oligomers, providing surface charges to prevent the coalescing of the droplets. The resulting N-doped carbon nanospheres have highly uniform sizes and shapes, and can be crystallized into opaline structures for fabricating opaline lattices with brilliant colors. The EDTA also promotes the formation of graphitic-N, making the nanospheres highly active electrocatalysts.