# Adsorption Separation of Various Polar Dyes in Water by Oil Sludge-Based Porous Carbon
## 3 Results  
### Microstructure Analysis  
1.1 Thermogravimetry-Differential Scanning Calorimetry, X-ray Diffraction and Fourier-Transform Infrared Spectroscopy Analysis  
The pyrolysis TG and DTG curves of OS are shown in Figure 1a, demonstrating a four-stage thermal activation process. Stage 1 (117 \({}^{\circ}\)C to 385.7 \({}^{\circ}\)C) is attributed to water evaporation, characterized by a significant mass loss peak of 3.5%. Stage 2 (385.7 \({}^{\circ}\)C to 603 \({}^{\circ}\)C) and Stage 3 (603 \({}^{\circ}\)C to 818 \({}^{\circ}\)C) represent the primary pyrolysis reactions, where light organic components are initially vaporized, followed by the cracking of heavy organic components into low molecular weight gases and oil products, resulting in a cumulative mass loss of 8.2%. Finally, Stage 4 (818 \({}^{\circ}\)C to 1000 \({}^{\circ}\)C) involves the condensation reactions of coke residue and the decomposition of inorganic minerals within the matrix. Figure 1b displays the XRD patterns of OS, NOSC (OSC without activation), and OSC700. The XRD analysis reveals that the OS is composed of SiO\({}_{2}\), calcite (CaCO\({}_{3}\)), and albite (Na\({}_{2}\)O-Al\({}_{2}\)O\({}_{3}\)-6 SiO\({}_{2}\)), as reported in previous studies [38,39]. Notably, the SiO\({}_{2}\) phase remains present in NOSC even after heat treatment at 700 \({}^{\circ}\)C for 2 h, as seen in the XRD patterns of NOSC and OSC700. Particularly in the case of the OSC activated with ZnCl\({}_{2}\), the XRD peak at 26.6\({}^{\circ}\) is broadened, indicating that the activated C exists in an amorphous form with a disordered layer structure. It has been reported that ZnCl\({}_{2}\) acts as a strong dehydrating agent, promoting the decomposition of organic matter in OS at high temperatures and the formation of porous structures during carbonization [40]. Furthermore, the dehydration caused by ZnCl\({}_{2}\) also increases the amount of amorphous C, leading to a broader XRD peak. The FTIR absorption spectra of OS and OSC700 are presented in Figure 1c. As shown by the OS spectrum (red line), a broad absorption peak at 3420 cm\({}^{-1}\) is observed, attributable to O-H stretching vibration absorption in OS. Additionally, peaks at 1430 cm\({}^{-1}\) and 1640 cm\({}^{-1}\) correspond to aliphatic C-H and aromatic C=C vibrations, respectively [14,18]. The peak at 1440 cm\({}^{-1}\) is attributed to the asymmetric deformation vibration of methyl carbon. A strong peak at 1020 cm\({}^{-1}\) is assigned to Si-O and Si-O-Si stretching vibrations, which arises from the overlapping absorption bands of minerals such as quartz, calcite, and albite [41]. The peak at 776 cm\({}^{-1}\) is attributed to the out-of-plane deformation vibration of C-H in a benzene ring substituted with five adjacent H atoms [14]. Furthermore, the absorption peaks in the range of 872 cm\({}^{-1}\) to 471 cm\({}^{-1}\) indicate the presence of silica and silicates [41]. In contrast, the FTIR absorption spectrum of OSC700 (purple line in Figure 1c) shows a significant enhancement in the intensity of aliphatic C-H vibrations (-3420 cm\({}^{-1}\)). The reason can be attributed to the formation of numerous hydrocarbon substances, such as alcohols and phenolic hydroxyl groups, during the high-temperature pyrolysis process of light and heavy organic materials. Meanwhile, the aromatic C=C skeletal vibration peak, observed at 1640 cm\({}^{-1}\), is also intensified. This enhancement is attributed to the formation of a C network structure on the surface, which occurs during the calcination and pyrolysis process of both light and heavy organic matter present in the sludge. The formation of the C network structure leads to an increase in C=C content, resulting in an intensification of the C=C skeletal vibration peak [42]. This finding is consistent with the XRD pattern. Notably, new absorption peaks emerge at 465 cm\({}^{-1}\), 618 cm\({}^{-1}\), 990 cm\({}^{-1}\), and 1075 cm\({}^{-1}\), respectively. Specifically, the peak at 465 cm\({}^{-1}\) is characteristic of ZnO in OSC [43].