Boosting biological hydrogen production by integrating functionally symbiotic bacteria/algae with engineered nitrogen-doped carbon dots

Abstract

Although biological hydrogen (bioH₂) represents a promising green energy source, its production faces significant challenges, including non-spontaneous generation in heterotrophic microorganisms, inhibition of hydrogenases and inefficient photoelectron transfer in photoautotrophic microorganisms. In this study, spontaneous and solar-driven bioH₂ production was achieved through functional symbiosis between Chlorella pyrenoidosa and Lactobacillus plantarum, which was further enhanced by engineered nitrogen-doped carbon dots (N-CDs). Both C. pyrenoidosa and L. plantarum produce bioH₂, via photosynthesis and fermentation, respectively. A mutualistic interaction was designed within the C. pyrenoidosa–L. plantarum system, where L. plantarum produces lactic acid that facilitates aggregation of C. pyrenoidosa under hypoxic conditions, allowing activation of the hydrogenase. L. plantarum also generates bioelectricity, which supports bioH₂ production. C. pyrenoidosa provides carbohydrates for L. plantarum in return. The N-CDs, which have active surface functional groups, a graphitized carbon core and electron-rich nitrogen doping, enhance light absorption, photoelectron transfer and electron conduction. Consequently, the C. pyrenoidosa–L. plantarum–CD system achieved a bioH₂ production rate as high as 0.63 μmol_H2 mg⁻¹ h⁻¹ (4.21 μmol_H2 mg_chlorophyll⁻¹ h⁻¹). This work provides a spontaneous, solar-driven new method for bioH₂ production, which has great potential in sustainable green energy.