Transformation of Proteins to interconnected G-CF for water purification.
Illustration of the seamlessly interconnected porous G-CF architecture.Proteins in egg white can be transformed into ultralightweight carbon aerogels to make highly efficient water purification materials, researchers report [Ozden et al., Materials Today (2022), https://doi.org/10.1016/j.mattod.2022.08.001 ]. The team from Princeton University, Aramco Research Center-Houston, Institute of Chemistry and Organometallic Compounds (CNR-ICCOM), Istituto Nanoscienze-CNR, NEST-Scuola Normale Superiore, University of Trento, and Queen Mary University of London led by Craig B. Arnold and Sehmus Ozden took a multidisciplinary approach involving experimental and computational chemistry techniques.
The researchers’ approach seamlessly integrates covalently bonded 2D graphitic carbon sheets (G) with 1D carbon nanofibers (CF) to form a new type of carbon structure with hierarchical porosity, high surface area, and very low density. Currently, freeze-drying or templating are used to produce hierarchical porous carbon structures but while the latter can produce controlled and tunable pore sizes and shapes, template removal can be complex. Starting materials like proteins, however, offer an attractive alternative because of their intrinsically hierarchical structure and the possibilities of self-assembly via polypeptide chain folding.
“The inspiring principle here was that interactions occurring in macromolecular protein aggregates offer a special opportunity to design and manufacture complex porous materials without the need for external templates and costly post-processing,” explains Ozden, first author of the study.
The structural complexity and sustainability of natural egg white proteins is exploited to fabricate interconnected hierarchical G-CF aerogels via freeze-drying without any templates. When pyrolyzed (at 900°C under N2 gas), the egg white proteins in the form of alpha-helices and beta-sheets transform into amyloid-type beta-sheet components in the carbonized aerogel. Pores form as gases are released during the high temperature process, while nanoscale porosity is provided by various defects and vacancies in the hexagonal lattice making up the G-sheets. The resulting ultralightweight, low density aerogels have largely flat surfaces made up of G-sheets with micron-sized pores.
The G-CF aerogels show promising results for water purification and desalination, removing over 98% of ionic impurities (or salts) and 99.99% of nano/microplastic contamination from seawater. The low-cost, ready availability, mechanical stability and robustness of egg-derived G-CF aerogels hold potential for a range of other uses from energy storage, energy conversion, separation technologies, and environmental remediation to catalysis and thermal applications.
“We are currently working on the scale-up of the process and investigating approaches to improve the stability, selectivity, and efficiency of the aerogel structure for water purification and clean energy applications,” says Ozden.