## 3 Results and Discussion
### Effects of Thermal Activation  
Breakthrough curves of toluene adsorption on the as-synthesized and activated ZIF-8 samples (in the dry air and N\({}_{2}\) atmospheres) are shown in Figure 2a,b. The breakthrough curve fluctuated slightly, which is due to the dynamics of the process. For air-activation, the process was carried out for 3 h at 300 \({}^{\circ}\)C under constant flow of dry air (labeled as ZIF-8/Air/300 \({}^{\circ}\)C). N\({}_{2}\) activation, however, was performed at 300 \({}^{\circ}\)C or 400 \({}^{\circ}\)C (labeled as ZIF-8/N\({}_{2}\)/300 \({}^{\circ}\)C and ZIF-8/N\({}_{2}\)/400 \({}^{\circ}\)C).  
Figure 1: (**a**) XRD and simulated pattern of the Zeolitic imidazolate framework-8 (ZIF-8); (**b**) fourier transform infrared (FT-IR) spectra of the ZIF-8; (**c**) SEM micrograph of the as-synthesized ZIF-8 at magnification of 2000; and (**d**) distribution histogram of the particle size calculated from the SEM image.  
The flow rate of the influent gas (dry air or N\({}_{2}\)) was controlled at 0.02 L\(\cdot\)min\({}^{-1}\). After the activation process, adsorption performances of, 0.05 g of each ZIF-8 sample was studied at 1000 ppmv of toluene concentration under a carrier gas flow rate of 0.02 L\(\cdot\)min\({}^{-1}\) at the desired temperature (e.g., 300 \({}^{\circ}\)C or 400 \({}^{\circ}\)C).  
The adsorption parameters such as, breakthrough point, time of equilibration, adsorption capacity, and total adsorption percentage of the tested ZIF-8 adsorbents are summarized in Table 1. It can be seen that activation of the synthesized ZIF-8 improved its adsorption efficiency for capturing toluene. The ZIF-8/Air/300 \({}^{\circ}\)C sample showed a significantly higher breakthrough point, equilibration time, adsorption capacity, and total adsorption percent compared to the other samples. [PERSON] et al. investigated toluene adsorption by ZIF-8/graphene oxide (GO) hybrid composite with different proportions of GO. They reported that toluene adsorption capacity of ZIF-8/GO with a GO content of 4 wt % was equal to 116 mg\(\cdot\)g\({}^{-1}\)[47]. [PERSON] et al. studied the breakthrough behaviors of three MOF, MIL-101, MIL-53, and CPM-5 for toluene whose adsorption capacity was equal to 211.5, 73, and 38.8 mg\(\cdot\)g\({}^{-1}\) respectively [24].  
XRD patterns of the ZIF-8 after activation at different conditions are illustrated in Figure 3a. The XRD patterns reveal that ZIF-8 structure remained intact after activation. The difference in peak intensity can be attributed to variations in the scattering intensity of the components of the crystal structure and their arrangement in the lattice. Some of the changes can be related to interference between diffractions.  
FT-IR spectra of the ZIF-8/Air/300, ZIF-8/N\({}_{2}\)/400, and as-synthesized ZIF-8 are shown in Figure 3b. It can be seen that FT-IR bands assigned to the ZIF-8 structure are similar in all samples.  
Previous studies confirmed that thermal stability of ZIF-8 depends on the temperature, atmosphere, and exposure time [31; 36; 37]. It is reported that ZIF-8 was stable under dry air atmosphere up to 300 \({}^{\circ}\)C for 5 h, however it was unstable at the same temperature (i.e., 300 \({}^{\circ}\)C) after 24 h of heat treatment. Furthermore, the ZIF-8 structure collapsed after heat treatment under dry air at 400 \({}^{\circ}\)C for 5 h [37]. Thermal gravimetric analysis (TGA) of ZIF-8 under N\({}_{2}\) atmosphere indicated that the structure could tolerate temperatures as high as 550 \({}^{\circ}\)C [31].