Physiological and morphological responses of Chlorella pyrenoidosa to different exposure methods of graphene oxide...

Graphene oxide quantum dots (GOQDs) can convert the ultraviolet (200- 380 nm) into available wavelength (400- 700 nm) for microalgae cultivation. However, it has not been applied in large-scale microalgae culture due to its high cost and difficulties in recovery. This study proposed a new strategy for the sustainable use of GOQDs, namely, GOQDs solution was added to the outer sandwich of the reactor. Herein, the effects of direct and indirect exposure of different GOQDs concentrations (0, 100, and 1000 mg/L) on the microalgae culture were compared. When microalgae were directly exposed to the GOQDs, 100 mg/L of GOQDs increased the biomass production of microalgae by 24.0 %, while 1000 mg/L of GOQDs decreased biomass production by 31 %. High concentration of GOQDs (direct exposure) could cause extra oxidative stress in the microalgae cells and result in a significant reduction of pigment content. When microalgae were indirectly exposed to the GOQDs, the increased concentration of GOQDs enhanced the growth of microalgae. Compared to the blank group, 1000 mg/L of GOQDs increased the microalgae biomass production and bioenergy by 14.1 % and 40.17 %, respectively. The indirect exposure of GOQDs can effectively avoid photo-oxidation and organelle damage to the microalgae cells. Overall, the indirect exposure of GOQDs is a sustainable way for effectively promoting microalgae growth and reducing the application cost.