The Influence of Fe 2 O 3 Nanoparticles on Chlorella spp. Growth and Biochemicals Accumulation

The addition of metal oxide nanoparticles (NPs) to microalgae cultures have become of great interest since they can directly and/or indirectly interact with microalgae resulting in enhanced production of biomass and high-value added products. The physicochemical characteristics of the NPs, i.e ., crystal phase, can differently influence microalgae metabolism, thus the synthesis of optimal NPs is mandatory to improve the value of microalgae biomass.This study aimed at assessing the effect of Fe 2 O 3 NPs on Chlorella spp. cultures with and without carbonate supplementation to confirm their beneficial effect. First, Fe 2 O 3 NPs were synthetized and two different annealing temperatures were implemented, 450 °C (Fe 2 O 3 -450) and 1000 °C (Fe 2 O 3 -1000), to obtain Fe 2 O 3 NPs with different crystal phases. The NPs crystal phase was analyzed by X-ray diffraction and the presence of the γ- and α- phases on both NPs were confirmed. However, the Fe 2 O 3 -450 NPs presented a higher content of the γ- phase. Subsequently, the effect of the crystal phase of Fe 2 O 3 NPs was assessed in Chlorella spp. cultures. The addition of Fe 2 O 3 -1000 NPs resulted in inhibition of Chlorella spp. On the other hand, the addition of Fe 2 O 3 -450 NPs recorded the carbohydrate enhancements > 91% in Chlorella spp. cultures. The indirect effect of the synthetized NPs was assessed in microalgae cultures without carbonate supplementation and the same tendency was observed. This study proves that Fe 2 O 3 -450 NPs directly and indirectly interact with microalgae, and can be used as a strategy to produce high-value biomass even in environments without carbonate supplementation. Graphical Abstract