# Adsorption Separation of Various Polar Dyes in Water by Oil Sludge-Based Porous Carbon
## 5 Conclusions  
In this study, low-oil-content sludge served as the starting material, and ZnCl\({}_{2}\) was employed as the activating agent. The OSC was prepared through the thermal decomposition of light and heavy organic constituents in the oily sludge at elevated temperatures, followed by carbon deposition processes.  
The as-prepared OSC was thoroughly characterized, and its absorption properties were investigated. The results revealed that the C network framework can be effectively formed in OS by using ZnCl\({}_{2}\) as an activator and carbonizing at 700 \({}^{\circ}\)C for 1 h. The theoretical monolayer saturation adsorption capacities of OSC700 for MG, MB, and CV were determined to be 33.41 mg/g, 16.41 mg/g, and 13.56 mg/g, respectively. Under  
Figure 9: Infrared spectra of OSC700 before and after adsorption of MG, MB and CV.  
optimal adsorption conditions, the removal efficiencies achieved were 95.74%, 64.97% and 24.14%, respectively. The adsorption of MG, MB, and CV by OSC700 was found to follow the pseudo-second-order kinetic model, suggesting a combined mechanism of physical and chemical adsorption, with chemical adsorption being the predominant mode. The adsorption process was spontaneous, exothermic, and entropy-increasing. Quantum functional theory calculations revealed that the dipole moments of MG, MB, and CV follow the polarity order of MG < MB < CV. Notably, the adsorption of MG, MB, and CV by OSC700 showed an inverse correlation between polarity and adsorption performance, with weaker polarity leading to better adsorption effects and higher theoretical and actual saturation adsorption capacities in oily sludge-based porous carbon. The adsorption of low-polarity materials by porous carbon derived from oily sludge is primarily driven by the presence of aromatic functional groups, hydrophily, \(\pi\)-\(\pi\) FDA interactions, and the formation of hydrogen bonds on the surface of the porous carbon. For dyes with higher polarity, electrostatic interactions and hydrophobic effects play a dominant role, with electrostatic adsorption being the primary adsorption mechanism. Notably, the formation of hydrogen bonds is negligible during the adsorption process. In summary, this study provides an effective approach and theoretical guidance for the removal of organic dyes, particularly those with lower polarity, from wastewater, providing valuable insights for the development of efficient wastewater treatment strategies.  
Conceptualization, H.C. and L.P.; methodology, H.C. and F.H.; software, H.C. and F.H.; validation, H.C., L.P., B.Z., J.L. and J.Y.; formal analysis, H.C., L.P., B.Z. and J.Y.; investigation, H.C., B.Z. and J.Y.; resources, L.P. and B.Z.; data curation, H.C. and C.M.; writing--original draft preparation, H.C.; writing--review and editing, C.M., J.L. and B.Z.; visualization, H.C. and F.H.; supervision, L.P.; project administration, L.P.; funding acquisition, L.P. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Qinchuangyuan \"Scientist + Engineer\" Team Development Program of the Shaanxi Provincial Department of Science and Technology, grant number 2024 QCY-KXJ-053 and the National Natural Science Foundation of China, grant number 52102144.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
Thanks to [PERSON] for his important technical help and for providing experimental equipment and related materials.  
The authors declare no conflicts of interest.  
The following abbreviations are used in this manuscript:  
OS  Oily Sludge  
OSC  Oily Sludge-based porous Carbon  
NOSC  Oily Sludge-based porous carbon without the addition of a zinc chloride activator  
MG  Malachite Green  
MB  Methylene Blue  
CV  Crystal Violet  
PFO  Pseudo-first-orderequation  
PSO  Pseudo-second-orderequation  
EDA  electron-donor-acceptor