# Synthesis of Mesoporous MWCNT/HKUST-1 Composite for Wastewater Treatment
## 3 Results and Discussion
### \(N_{2}\) Adsorption/Desorption Isotherms  
The nitrogen adsorption and desorption isotherms of the samples are shown in Figure 7a. The isotherm for the as-received MWCNTs, HKUST-1, and FMWCNT/HKUST-1 composites exhibited hysteresis loops, which are associated with mesopores. It can be observed that the hysteresis loops of the MWCNTs were of type H1, while those of HKUST-1 and the FMWCNT/HKUST-1 composites belonged to type H4. According to [PERSON] [42], the characteristic features of the type H4 hysteresis loop is its narrow slit-like shape over a range of high relative pressure (_P/Po_). A small hysteresis loop was observed at a high relative pressure in the HKUST-1 sample. It is worth noting that the addition of functionalized MWCNTs resulted in a broader hysteresis loop of virgin HKUST-1 MOFs. Table 2 summarizes the textural properties of as-received MWCNT, functionalized MWCNT, HKUST-1 and FMWCNT/HKUST-1 composite calculated from the isotherms. The HKUST-1 MOF had the highest surface area, 1177 m\({}^{2}\)/g.  
However, the value of HKUST-1 produced in this study is small compared to the 1615 m\({}^{2}\)/g reported by [PERSON] et al. [34]. This could have been because of the insufficient removal of solvent [9]. It was observed that the MWCNT/HKUST-1 composites showed a slight reduction in surface area relative to the virgin sample. However, the pore size and pore volume were higher than those of the HKUST-1 sample. This could have possibly been due to the MWCNTs, which helped in the removal of unreactive Cu species that blocked the pores. [PERSON] et al. [43] found that the addition of MWCNTs helped to enhance both the pore size and pore volume of MOF-5 by removing the unreacted species during pore activation. It is important to note that despite the incorporation of 0.5 g of functionalized MWCNTs during synthesis, the surface area of FMWCNT/HKUST-1 was relatively close to that of the virgin HKUST-1 sample. The results of the average pore size of HKUST-1 and/FMWCNT/ HKUST-1 suggested that the samples synthesized in this work were mesoporous. Figure 7b,c shows the pore size distribution (PSD) of HKUST-1 and FMWCNT/HKUST-1 calculated using the Barrett-Joyner-Halenda (BJH) method.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \begin{tabular}{c} **BET Surface** \\ **Area (m\({}^{2}\) g\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **BJH Description Average** \\ **Pore Diameter (nm)** \\ \end{tabular} &
\begin{tabular}{c} **BJH Desorption Cumulative** \\ **Pore Volume (cm\({}^{3}\) g\({}^{-1}\))** \\ \end{tabular} \\ \hline As-received MWCNTs & 277.18 & 12.88 & 0.89 \\ FMWCNTs & 1131.20 & 3.43 & 0.09 \\ HKUST-1 & 1176.66 & 2.57 & 0.76 \\ FMWCNT/HKUST-1 & 1108.85 & 6.97 & 1.93 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Textural properties of HKUST-1 and the composites synthesized in this study using the hydrothermal method.  
The pore sizes of HKUST-1 were distributed along the range of 3.2-4.5 nm, while the pore sizes of the composites were distributed along the narrow range of 3.2-4.1 nm. It can be observed that the addition of MWCNTs increased the virgin HKUST-1 cumulative pore volume. The large surface area and relatively high pore size and pore volume obtained in this work suggest that the material would be a good adsorbent by providing multiple channels for contaminants and increasing their immigration into the pores [14].  
Figure 7: (**a**) N\({}_{2}\) adsorption/desorption isotherms of (**l**) as-received MWCNTs, (**l**) HKUST-1, and (**l**) FMWCNT/HKUST-1, and BjH pore size distributions of MOF and HKUST-1 composite samples; (**b**) cumulative pore volume; (**c**) incremental pore volume.