Comparative life cycle assessment of graphitic carbon nitride synthesis routes

Graphitic carbon nitride (g-C3N4) has gained great interest as a visible-light-activated photocatalyst. As an emerging nanomaterial for environmental applications, its competitive performance and environmentally responsible synthesis are critical to its success. A powerful tool for informing material development with reduced environmental impacts is life cycle assessment (LCA). In this study, LCA is used to evaluate the environmental impacts of g-C3N4 nanosheet produced via eight existing synthesis routes. The results reveal electricity as the main contributor to the cumulative impacts of all eight g-C3N4 syntheses. There are opportunities to reduce energy demand, and consequently the synthesis impacts, by revising synthesis procedures (i.e., removing or reducing time of use of a piece of equipment), optimizing the calcination step (i.e., faster heating rate, lower heating time, lower temperature), and moving to cleaner electricity sources. Further, benchmarking the environmental impacts of g-C3N4 nanosheets to a well-established metal-based photocatalyst, titanium dioxide nanoparticles (nano-TiO2), reveals mixed comparative results. The synthesis method substantially influences the comparative impacts. Considering use-phase benefits of activating g-C3N4 with visible wavelength light emitting diodes compared to ultraviolet (UV) wavelengths for nano-TiO2 results in a 52% energy demand reduction (in kWh). Performance of g-C3N4 compared to a high-energy disinfection approach (i.e., conventional UV) reveals an inability to meet drinking water disinfection standards for viral load reduction (4-log reduction) with any mass of g-C3N4, given its high embodied resource footprint. This work establishes a foundation to inform and direct g-C3N4 nanosheets toward improved sustainable development.

Duke Scholars

Author Leanne Gilbertson Civil and Environmental Engineering