# Unlocking the Detoxification of Phenanthrene from Water Using Alkali-Activated Slag Mortar
## 3 Results and Discussions
### Phenanthrene Sorption Performance  
#### 3.2.1 Sorption Kinetics  
The effect of contact time on PHE sorption is illustrated in Figure 4a. The results demonstrated a rapid sorption of PHE by AAS, with more than 80% of PHE being removed  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **BET Surface Area** & **Pore Volume** & **Pore Size** \\  & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **(Å)** \\ \hline GGBFS & 0.53 & 0.0065 & 14.128 \\ AAS & 61.59 & 0.15 & 97.4 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Specific surface area and pore volume of the synthesized sorbents.  
Figure 3: (**a**) Nitrogen sorption–desorption isotherms of GGBFS and AAS, (**b**) pore size distribution of AAS.  
Figure 2: Scanning electron microscope images of (**a**) GGBFS and (**b**) AAS mortar. The inset shows energy-dispersive X-ray spectroscopy (EDS) of AAS.  
from the solution within the first 12 h. The rapid sorption phase indicated a high affinity between PHE molecules and the active sites on the AAS surface. As the contact time progressed, the rate of PHE removal gradually decreased, eventually reaching equilibrium after approximately 60 h. This equilibrium point suggests that the sorption sites on AAS became saturated or that a dynamic balance was established between the sorbed and free PHE molecules.  
In contrast, GGBFS displayed a significantly slower sorption process. It required about 120 h to reach sorption equilibrium, which is twice as long as that for AAS. Additionally, GGBFS exhibited a much lower sorption capacity (R, %) compared to AAS. The extended time required for GGBFS to achieve equilibrium indicates a lower rate of PHE uptake and potentially fewer or less accessible active sorption sites compared to AAS. The difference in the sorption performance between AAS and GGBFS can be attributed to several factors. The activation process for AAS likely enhanced the surface area, porosity, and chemical functionality of the GGBFS, making AAS more effective in capturing PHE molecules. Conversely, GGBFS may lack the optimized structural and chemical properties needed for efficient sorption.  
These findings underscore the importance of material activation in enhancing sorption capabilities and highlight AAS as a superior sorbent for PHE removal in terms of both speed and capacity. The rapid and high-efficiency removal of PHE by AAS suggests a promising candidate for practical applications in water treatment, where quick and effective  
Figure 4: (**a**) Sorption kinetics of GGBFS and AAS, with results fitted by (**b**) pseudo-first-order and (**c**) pseudo-second-order kinetic models \(C_{o}^{PHE}\) = 0.9 mg/L, solid/liquid = 0.5 g/L, pH = 5.5, contact time = 12–604 h, T = 23 \(\pm\) 1 \({}^{\circ}\)C. (**d**) sorption isotherms of GGBFS and AAS fitted by the [PERSON] and Freundlich sorption models \(C_{o}^{PHE}\) = 0.05–0.9 mg/L, solid/liquid = 0.1 g/L, pH = 5.5, contact time = 240 h, T = 23 \(\pm\) 1 \({}^{\circ}\)C.  
contaminant removal is crucial. Further investigations into the underlying mechanisms of PHE sorption in AAS could provide deeper insights into optimizing the material for even better performance.  
To explore the rate-controlling step in sorption processes, the kinetic data were analyzed using the pseudo-first-order (PFO) and pseudo-second-order (PSO) models (Equations (1) and (2)). The calculated parameters of both kinetic models are presented in Table 3. The fitting of the PFO model (Figure 4b) was poor, indicating that this model did not accurately describe the PHE sorption kinetics. In contrast, the PSO model exhibited a much higher correlation with the observed PHE uptake behavior, as shown in Figure 4c. The higher r\({}^{2}\) of the PSO model suggested this chemisorption. This is consistent with the findings of previous studies, which also indicated that the PSO model is more appropriate for describing the sorption kinetics of organic pollutants like PHE [20; 31; 32].