# Surfactant-Modified Construction Waste Bricks for the Removal of Diclofenac from Aqueous Solutions
## 3 Results and Discussion  
### Characteristics of Waste Bricks  
The microstructures of the PRBPs and CCBPs were characterized via SEM. As shown in Figure 1a, the PRBP surface was relatively irregular, with different sizes of micropores before the incorporation of CTAB. However, as shown in Figure 1b, the CCBP surface was much rougher and more uneven while maintaining the main structure of the bricks. Furthermore, compared to PRBP, there were some different microsopres on the CCBP surface, indicating that CTAB had successfully assembled on the surfaces of the waste bricks.  
Figure 2 shows the N2 adsorption-desorption isotherms and BJH pore size distributions of both the PRBPs and CCBPs. As shown in Figure 2a, the PRBPs and CCBPs have narrow pore size distributions. The adsorption-desorption isotherms of both adsorbents, as shown in Figure 2b, indicate the existence of a porous structure on their surfaces, as evidenced by their type IV with hysteresis loops [32; 33]. The pore structural properties of the PRBPs and CCBPs are illustrated in Table 2. Following the addition of CTAB, the surface area of the waste bricks reduced from 10.42 m\({}^{2}\)/g to 4.33 m\({}^{2}\)/g, whereas the pore volume and size increased from 0.0059 to 0.0068 cm\({}^{3}\)/g and 4.51 to 5.16 nm, respectively. These results are the same as those of clay organo-modified with CTAB [31].  
To investigate the characteristics of the waste bricks further, XRD analyses of the PRBPs and CCBPs were conducted, and the results are shown in Figure 3. Significant peaks were observed at 20-26\({}^{\circ}\), which were attributed to the SiO\({}_{2}\), consistent with previous studies [34]. After functionalization with CTAB, the main diffraction patterns of the bricks remained virtually unchanged, indicating that the primary structure and composition of the waste red bricks were largely unaltered. The increasing intensity of CCBP suggested that the amount of CTAB incorporated into the samples' framework was limited and did not lead to significant structural changes.  
The zeta potentials of the PRBPs and CCBPs are shown in Figure 4. As the pH values of the solution were increased from 2.0 to 12.0, the zeta potentials of the PRBPs remained negative, indicating that the surface charges of the PRBPs were predominantly negative. On the other hand, for CCBP, the zeta potential increased initially with the increase in pH values, followed by a decrease, and the isoelectric point was observed at approximately pH 7.0. This result suggested that CCBPs mainly demonstrated electropositivity with  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**A adsorbents**} & **BET Surface Area** & **BJH Pore Volume** & **BJH Pore Size (nm)** \\  & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **BJH Pore Size (nm)** \\ \hline PRBP & 10.42 & 0.0059 & 4.51 \\ CCBP & 4.33 & 0.0068 & 5.16 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Pore structural properties of samples.  
Figure 1: The scanning electron micrograph images of PRBP (**a**) and CCBP (**b**).  
Figure 2: The pore size distribution (**a**) and N\({}_{2}\) adsorption–desorption isotherms (**b**) of PRBP and CCBP.  
the solution at a pH \(\leq\) 7.0, while they showed electronegativity with the solution at a pH \(\geq\) 7.0. These results could be attributed to the characteristics of CTAB, which showed good coordination with anionic nonionic amphoteric surfactants [31]. The cation exchange between CTAB and the PRBPs could change the surface characteristics and electrical property of the adsorbent, which would be beneficial for the removal of negatively charged contaminants from aqueous solutions.