Microalgae biomass is a sustainable source with the potential to produce a range of products. However, there is currently a lack of practical and functional processes to enable the high-efficiency utilization of the microalgae. We report here a hydrothermal process to maximize the utilizability of microalgae biomass. Specifically, our concept involves the simultaneous conversion of microalgae to (i) hydrophilic and stable carbon quantum dots and (ii) porous carbon. The synthesis is easily scalable and eco-friendly. The microalgae-derived carbon quantum dots possess a strong two-photon fluorescence property, have a low cytotoxicity and an efficient cellular uptake, and show potential for high contrast bioimaging. The microalgae-based porous carbons show excellent CO2 capture capacities of 6.9 and 4.2 mmol g(-1) at 0 and 25 C respectively, primarily due to the high micropore volume (0.59 cm(3) g(-1)) and large specific surface area (1396 m(2) g(-1)). (C) 2017 Elsevier Inc. All rights reserved.