# Low-Cost Nanocarbon-Based Peroxidases from Graphite and Carbon Fibers
## 2 Results and Discussion  
### Synthesis and Characterization of Carbon Nanomaterials  
Three carbon nanomaterials, Carbon nanomaterials-1 (prepared from polypropylene carbon fibers), Carbon nanomaterials-2 (prepared from graphite), and Carbon nanomaterials-3 (nitrogen doped GQDs from GO) were prepared according to the the detail process in the Method section. All carbon nanomaterials were fully characterized by TEM (JEM-2010 UHR microscopy, JEOL, Tokyo, Japan), XPS spectroscopy (ESCALAB250 Xi, Thermo Fisher Scientific, Beijing, China), FT-IR (VERTEX 70, Bruker, Bremen, Germany), Zeta potential measurements (Zetasizer Nano-ZS ZEN3600 Malvern, Worcestershire, UK) and Raman spectra (INVIA plus Laser Raman Spectrometer, Renishaw, New Mills, UK). First, the morphology and size of Carbon nanomaterials-1, Carbon nanomaterials-2 and Carbon nanomaterials-3 were characterized by TEM. The size distribution of Carbon nanomaterials-1, Carbon nanomaterials-2 and Carbon nanomaterials-3 is in the range of 2-5 nm, 3-8 nm and 1-3 nm respectively (Figure 1). X-ray photoelectron spectroscopy (XPS) was then used to characterize these carbon nanomaterials. As shown in Figure 2, the dominant graphitic C 1s peak at 284.8 eV and 0 1s peak at 532 eV were observed for three carbon nanomaterials, and N 1s peak around 400 eV could be detected for Carbon nanomaterials-3. According to the deconvoluted XPS spectra of C 1s in Figure 3, there were C\(-\)C, C\(-\)O and \(-\)COOH on Carbon nanomaterials-1 surface, and C\(=\)O on Carbon nanomaterials-2 and Carbon nanomaterials-3 surface. The carbonyl group can act as substrate binding sites [30], which are beneficial to peroxidase like catalytic reaction. This can prove that the catalytic activity of Carbon nanomaterials-2 and Carbon nanomaterials-3 is better than that of Carbon nanomaterials-1. The nitrogen element in Carbon nanomaterials-3 belongs to pyridine type nitrogen, and exists in the form of amino, amide or others (Figure 3). Therefore, all carbon nanomaterials with many hydrophilic functional groups, showed good solubility (up to 1 mg\(\cdot\)mL\({}^{-1}\)) in water, and the solution could keep stable for several months at room temperature. Figure 1: Typical transmission electron microscopy (TEM) images of synthesized carbon nanomaterials in this work: (**a**) Carbon nanomaterials-1; (**b**) Carbon nanomaterials-2; (**c**) Carbon nanomaterials-3; and diameter distribution of carbon nanomaterials; (**d**) Carbon nanomaterials-1; (**e**) Carbon nanomaterials-2; (**f**) Carbon nanomaterials-3. FT-IR spectroscopy (Figure S1) reveals the existence of O-H in different carbon nanomaterials, which can be seen from the obvious peak at 3650 cm\({}^{-1}\). The peak at 3000 cm\({}^{-1}\) corresponds to the carboxyl group, and the peak at 1724 cm\({}^{-1}\) in the spectrum of Carbon nanomaterials-2 is from the  
Figure 3: High-resolution XPS spectra of as-synthesized carbon nanomaterials in this work: (**a**) Carbon nanomaterials-1; (**b**) Carbon nanomaterials-2; (**c**,**d**) Carbon nanomaterials-3. Figure 2: X-ray photoelectron spectroscopy (XPS) survey spectra of the as-synthesized carbon nanomaterials in this work: (**a**) Carbon nanomaterials-1; (**b**) Carbon nanomaterials-2; (**c**) Carbon nanomaterials-3. carbonyl group. The Raman spectra illustrate the existence of 1350 cm\({}^{-1}\) (D) and 1570 cm\({}^{-1}\) (G) peaks in different carbon nanomaterials. The G peak means the sp\({}^{2}\) hybrid carbon atom and the D peak means the sp\({}^{3}\) hybrid carbon atom. The value of \(I_{D}/I_{G}\) represents the defect layer in the surface and the edge of the carbon material. To be specific, when the value of \(I_{D}/I_{G}\) is less than 1, some functional groups may be introduced into the carbon nanomaterials, thus endowing the nanomaterials with special properties (Figure S2). Among three kinds of carbon nanomaterials, Carbon nanomaterials-3 shows the highest \(I_{D}/I_{G}\) value owing to the introduction of nitrogen atoms.