Revealing dual roles of g-C3N4 in Chlorella vulgaris cultivation

Booming graphitic carbon nitride (g-C3N4) photocatalyzed water splitting increases crisis of aquatic contamination. However, a controversial understanding regarding effect of g-C3N4 on growth of microalgae still exists. Accordingly, Chlorella vulgaris were cultured in 0-250 mg/L of g-C3N4 with biomass named as C-0, C-50, C-100, C-150, C-200, and C-250, respectively. g-C3N4 below 200 mg/L was beneficial to short-term cultivation of microalgae, while it was harmful to long-time cultivation. Protein factions of C-0, C-100, and C-250 were 41.4, 42.3, and 36.4 wt%, while their lipid factions varied from 21.5, 16.9, to 17.8 wt%, respectively. In short-term cultivation, superoxide dismutase's activity of C-0, C-150, and C-250 increased dramatically, while accumulated H2O2 led to increased activity of catalase. However, it started to decrease once antioxidant enzymes were per-oxidized, leading to increase of malondialdehyde content. In long-term cultivation, activities of superoxide dismutase, catalase and malondialdehyde content decreased dramatically owning to peroxidation of algae. Scavenger tests with tertiary butanol and triethanolamine implied that. OH was dominate parameter affecting growth of microalgae. This work indicates that g-C3N4 below 200 mg/L is propitious to short-term cultivation of microalgae, while it is bad to long-time cultivation of microalgae, revealing dual rules of g-C3N4 in Chlorella vulgaris cultivation.