# Low-Cost Nanocarbon-Based Peroxidases from Graphite and Carbon Fibers
## 1 Introduction  
Artificial enzymes as highly stable and low-cost alternatives to natural enzymes hold a great potential and widespread application in biosensor and biomedicine [1]. Metal complexes, supramolecules and biomolecules have been extensively explored to mimic various intrinsic properties of natural enzymes [2]. Recently, nanoparticles (NPs) have attracted increasing attention because of their unique physicochemical properties, such as their comparable size to natural enzymes, high surface area to volume ratio, the presence of a large number of catalytically active sites on their surface and the availability of multifunctional reactive groups for modification and further functionalization [3; 4]. In 2007, [PERSON] et al. provided the first evidence that inert ferromagnetic nanoparticles have intrinsic peroxidase-like activity [5]. So far, it has been reported over 50 kinds of nanomaterials, which possess intrinsic activity similar to enzymes, such as magnetic nanoparticles, gold nanoparticles, platinum nanoparticles, cerium oxide nanoparticles and carbon nanomaterials [2; 3; 4; 5; 6; 7; 8].  
Compared with nanomaterials of metals and their oxides, carbon nanomaterials have the advantages of diverse sources, low cost and less toxic in vivo [8; 9; 10]. It is also known that carbon nanomaterials can be used as nanotemplates for being functionalized with a wide range of(bio)molecules, make it possible their application in different analytical areas or can be implemented in fields of nanomedicine, catalysis, electrocatalysis, electronics, optoelectronics and photovoltaics [11; 12; 13; 14; 15]. In 2010, [PERSON] et al. reported the peroxidase-like activity of graphene oxide (GO) and its application to glucose detection [16]. Subsequently, [PERSON]'s and other several groups expanded GO to graphene nanocomposites [17], carbon nanotubes (CNTs) [18; 19], carbon dots (CDs) [20; 21; 22] and graphene quantum dots (GQDs) [23; 24; 25] as peroxidase-like catalysts and further prepared GQD-band-aid for wound disinfection [26]. Recently, [PERSON] et al. utilized dopamine as nitrogen source and GO as carbon source to prepare \(N\)-doped GQDs (\(N\)-GQDs) and found \(N\)-GQDs exhibited the enhanced peroxidase catalytic activity [27].  
Although graphene quantum dots (GQDs) and doped GQDs have gained great attention owing to intrinsic peroxidase-like activity for colorimetric and UV-vis absorption detection, GQDs is typically prepared from expensive graphene oxide (GO, the price of 100 mg GO is about $15.6) with energy consumed microwave reaction of 12 h [26; 27]. Very recently, we developed a one-pot solvothermal method to prepare carbon dots decorated graphite felt (CDs/GF) electrode, which exhibited excellent wettability and greatly enhanced activity towards vanadium redox couples [28; 29]. Herein, we demonstrated the use of low-cost graphite (the price of 100 mg graphite is about $0.0056) and polypropylene carbon fibers (the price of 100 mg polypropylene carbon fibers is about $1.37) as carbon source for mixed acid preparation of carbon nanomaterials, and also prepared \(N\)-doped GQDs with cheap urea as nitrogen source and GO as carbon source. Three carbon nanomaterials were defined as Carbon nanomaterials-1 (prepared from carbon fibers), Carbon nanomaterials-2 (prepared from graphite), and Carbon nanomaterials-3 (prepared from nitrogen doped graphene oxide) in this manuscript. They were fully characterized by transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), Zeta potential measurements and Raman spectra. Subsequently, the peroxidase catalytic activities of these carbon nanomaterials were investigated and the catalytic mechanism was discussed. These carbon nanomaterials with peroxidase-like catalytic activity, taking Carbon nanomaterials-2 (prepared from graphite) as an example, were further applied to remove phenolic compounds, the pollutant in water.