Fig. 2: The functional groups of extracted electron shuttles.
From: Electron shuttling promotes denitrification and mitigates nitrous oxide emissions in lakes

a, b X-ray photoelectron spectroscopy (XPS) measured C 1s spectrum and atomic% of humic acid (a) and fulvic acid (b) in representative L-MPD, M-MPD, and H-MPD samples. DX_1, LX_3, and LX_1 were randomly selected as representative L-MPD, M-MPD, and H-MPD samples, respectively (Supplementary Table S1). MPD, maximum power density.