Enhancing bioenergy production with carbon capture of microalgae by ultraviolet spectrum conversion via graphene oxide quantum dots

Microalgae play an important role in carbon sequestration by converting solar energy into biomass as an energy reserve. The conversion efficiency is often limited by light absorbed in the chloroplast. It is of great potential to enhance the photosynthesis capability by improving susceptibility of the light absorption by microalgae. Carbon-based quantum dots (QDs) are promising candidates for spectrum conversion, exhibiting remarkable biocompatibility, excellent water solubility, and customizable flexibility. Herein, we introduced graphene oxide quantum dots (GOQDs) with a blue light (465 nm) emission after ultraviolet (380 nm) excitation into the microalgae growth media. It is demonstrated that the ultraviolet light was effectively absorbed and utilized by the chlorophyll in the GOQDs-Chlorella pyrenoidosa system, resulting in a significantly increased photosynthetic activity. Moreover, a 20% improvement in carbon dioxide fixation and a 34% increase in bioenergy accumulation was found in the system. We further examined the microalgae metabolic pathways to reveal the biological response mechanism with GOQDs. Results verified that the GOQDs facilitated photosystem II (PSII) energy transfer to improve the photosynthesis of microalgae and upregulated the metabolites of lipid biosynthesis, resulting in a higher biomass and lipid content. This work suggested that using GOQDs as a promising approach for to improve the photosynthetic efficiency of microalgae, as well as a great potential for enhancing carbon capture and bioenergy production, especially in the environments with higher solar ultraviolet irradiation.