## 3 Results and Discussion
### Textural Properties and Zeta Potential Determination  
The porosity of the solids is investigated through the N\({}_{2}\) adsorption-desorption and their BJH pore size distribution analyses. The samples exhibit a typical type-IV isotherm with H\({}_{4}\) hysteresis loop in the relative pressure range of 0.4-1.0 (Figure 2a). This indicates the presence of characteristic mesoporous materials, as also confirmed in the literature [33].  
The textural properties of the solids are obtained from the N\({}_{2}\) adsorption-desorption and their corresponding BJH pore size distribution analyses (Table 1). Accordingly, the BET surface area of Fe sample is 163 m\({}^{2}\cdot\)g\({}^{-1}\) with a pore volume of ca. 0.23 cm\({}^{3}\cdot\)g\({}^{-1}\).  
The elevated textural properties of the solid are attributed to the abundance of void spaces between the interconnected particles during the hydrothermal treatment procedure.  
Meanwhile, the textural properties behavior of FeC composite (122 m\({}^{2}\cdot\)g\({}^{-1}\)) suggests that the effect of coexisting carbon species i.g. graphitic and amorphous carbon on the Fe\({}_{3}\)O\({}_{4}\) cause a decrease of both surface areas and pore volume comparing with those of Fe sample. Simultaneously, the surface area and pore volume of Fe/FeC are greater (202 m\({}^{2}\cdot\)g\({}^{-1}\) and 0.28 cm\({}^{3}\cdot\)g\({}^{-1}\), respectively) than those of Fe and FeC samples. This can illustrate the creation of an additional porosity to the FeC solid due to the successful incorporation of iron in the structure, as found elsewhere [34]. That is to say, iron is included in the structure rather than deposited on solid surface.  
Furthermore, the micropores areas, expressed herewith as t-plot areas follows similar trends as those of the mesoporous parameters. On the basis of this result, the solid developed micropores because of gases evolution during the heating processes. It can be concluded samples mainly contains mesoporous and microporous within its matrix.  
The pore radius is sharply distributed in a narrow range located at around 27 A (Figure 2b) revealing that the pore structure is not affected by the considerations mentioned above.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **BET Surface Areas** & **Pore Volumes** & **t-Plot Surface** & **Pore Sizes** \\  & **(m\({}^{2}\cdot\)g\({}^{-1}\))** & **(cm\({}^{3}\cdot\)g\({}^{-1}\))** & **Areas (m\({}^{2}\cdot\)g\({}^{-1}\))** & **(Å)** \\ \hline Fe & 163 & 0.23 & 170 & 27 \\ FeC & 122 & 0.17 & 126 & 27 \\ Fe/FeC & 202 & 0.28 & 205 & 28 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Textural properties of the solids obtained from nitrogen adsorption–desorption isotherms.  
Figure 2: (a) Nitrogen adsorption–desorption isotherms and (b) pore size distribution curves of the solids studied.  
The electrostatic potentials on the surface are shown in Table 2 through the zeta potential values.  
For Fe sample, the negative surface charge of \(-5.56\) mV is developed. On the contrary, the Fe-based composites depict a positively charged surface of \(+10.8\) and \(+24.9\) mV, respectively for FeC and Fe/FeC samples.