Ea 2400 2

The organic element content was determined using elemental analysis (EA) (EA 2400 II, PerkinElmer, USA). Because the nitrogen content of various proteins was 16%, the amount of protein in the samples was obtained by multiplying the percentage of nitrogen element by 6.25 [36 (link)]. The morphology, structure, and elemental maps of the samples were determined by scanning electron microscopy (SEM) (Sigma 300, Zeiss, German) with energy dispersive X-ray spectroscopy (EDS). A fluorescence microscope (IX73P2F, Olympus, Japan) was used to collect optical and fluorescence microscopy images. Other characteristics were determined using Fourier transform infrared spectroscopy (FT-IR) (Vertex 70, Bruker, USA), X-ray photoelectron spectroscopy (XPS) (PHI-5000 Versaprobe III, ULVAC-PHI, Japan), X-ray diffraction (XRD) (SmartLab, Rigaku, Japan), and flow cytometry (FCM) (MoFlo Astrios EQ, Beckman Coulter, USA).

Use a modified thermal analysis method [19 (link),77 ] to analyze fixed carbon (FC) and ash content of biochar samples. In brief, each char sample contained in a ceramic crucible was dried for 24 h at 105 °C, heated for 1 h at 450 °C, and then heated for another 6 h at 750 °C, recording the weight loss between the three. Ash content was the weight of the residue after the third heating, while FC content was the difference between the initial weight and the three weight losses. Using the elemental analyzer (EA 2400 II, PerkinElmer, Waltham, MA, USA) to determine the contents of C, N, and H, while the O content was determined using the elemental analyzer (Varia ELIII, Elementa, Frankfurt, Germany) by combusting the samples at 1150 °C, both of which were carried out simultaneously on the same batch of samples.