Comparative life cycle assessment of graphitic carbon nitride synthesis routes

Abstract

AbstractGraphitic 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.