Tobacco-waste homologous red-/blue-emitting carbon dots for enhancing photosynthesis

Abstract

Carbon dots (CDs), as a medium for enhancing photosynthesis, have attracted widespread attention, among which biomass-based CDs are ideal candidate materials owing to their multiple advantages. However, most of the biomass-based CDs are fabricated using a single synthesis strategy and employed directly, lacking rational classification and screening of diverse CD types within the products to identify homologous CDs that could maximize plant photosynthetic utilization efficiency. Hence, two types of CDs, blue (B-CDs) and red (R-CDs), were obtained from tobacco waste through a facile hydrothermal or solvothermal synthesis strategy. The prepared CDs proved to have tunable structures and properties, including tunable photoluminescence. The latter property matched well with the absorption spectra of chlorophyll and enabled the construction of chloroplast/CD hybrid photosynthesis systems. The 1 : 1 combination of B-CDs and R-CDs showed the most pronounced effect on the chloroplast photosynthetic activity, exhibiting a maximum increase of 367%. This significant improvement was attributed to CDs, which converted the energy of ineffective ultraviolet (B-CDs) and yellow-green light (R-CDs), thereby enhancing plant photosynthesis. Further in vivo studies showed that the 1 : 1 mixture of both CDs had a positive effect on light capture and absorption, acceleration of the electron transfer, CO₂ assimilatory power, chlorophyll content, photosynthetic activity, psbA gene expression, and Rubisco activity, all of which promoted plant photosynthesis. Improved accumulation of lettuce biomass and nutritional quality were other advantageous effects. In summary, both the developed CDs proved to be very efficient and highly applicable CD-based photosynthetic fertilizers.