## 3 Results and Discussion
### Influence of Loading Value and Reaction Temperature on Hg\({}^{0}\) Removal Performance  
Figure 4 shows the experimental results of Set I testing. The Hg\({}^{0}\) removal efficiency of the raw CNFs was only 16.02%. Therefore, the effect of residual Ni in the raw CNFs on their Hg\({}^{0}\) removal efficiency could be ignored. The Hg\({}^{0}\) removal efficiency of CNFs(OX) slightly increased to 18.73%. The increase in the Hg\({}^{0}\) removal efficiency of CNFs(OX) was probably owing to the increase of the specific surface area and the content of surface oxygen-containing functional groups, which enhanced the physicochemical adsorption of Hg\({}^{0}\). Meanwhile, the Hg\({}^{0}\) removal efficiency increased consistently as the loading value increased from 6% to 15%; however, the efficiency of 18%MnO\({}_{\rm x}\)-18% CeO\({}_{\rm 2}\)/CNFs(OX) slightly decreased. This suggested that the optimal loading value for the MnO\({}_{\rm x}\)-CeO\({}_{\rm 2}\)/CNFs(OX) sorbent was 15%. This is consistent with the XRD results. The decrease in Hg0 removal efficiency for 18%MnO\({}_{\rm x}\)-18% CeO\({}_{\rm 2}\)/CNFs(OX) was ascribed to the agglomeration of excessive MnO\({}_{\rm 2}\), which resulted in insufficient use of Mn active components. The Hg\({}^{0}\) removal efficiencies of individual Mn or Ce supported on CNFs(OX) were also tested. As shown in Figure 4, the Hg\({}^{0}\) removal efficiency of 30%Mn/CNFs(OX) was 80.64%, while it was 64.69% for 30%Ce/CNFs(OX). Both of these results were lower than that of 15%MnO\({}_{\rm x}\)-15% CeO\({}_{\rm 2}\)/CNFs(OX). The results further demonstrated that Mn and Ce have synergistic effects, consistent with a previous  
Figure 3: Micromorphology of the **(a)** CNFs and **(b)** 15%MnO\({}_{\rm x}\)–15%CeO\({}_{\rm 2}\)/CNFs(OX), and the EDS mapping of the elements of 15%MnO\({}_{\rm x}\)–15%CeO\({}_{\rm 2}\)/CNFs(OX). \begin{table}
\begin{tabular}{c c} \hline \(\alpha\) & **Capacity (ug\(\cdot\)g\({}^{-1}\))** \\ \hline
12\% & 74.8 \(\pm\) 1.7 \\
15\% & 118.4 \(\pm\) 2.3 \\
18\% & 54.1 \(\pm\) 1.2 \\ \hline \end{tabular}
\end{table} 
Table 3: Mercury capacity of the sorbents (Q/M = 300,000 mL\(\cdot\)h\({}^{-1}\cdot\)g\({}^{-1}\)). study [16; 19; 22]. Meanwhile, the Hg\({}^{0}\) removal performance of the oxidized-activated-carbon-supported Mn and Ce sorbent (15%MnOx-15%CeO\({}_{2}\)/AC(OX)) was also investigated. It was apparent that CNFs(OX) was a better support of MnOX-CeO\({}_{2}\) for Hg\({}^{0}\) removal. The mercury capacities of the sorbents (\(\alpha\) = 12%, 15% and 18%) are listed in Table 3. In the present study, the Hg\({}^{0}\) capacity was defined as the amount of Hg\({}^{0}\) adsorbed per mass of sorbent when Hg\({}^{0}\) breakthrough reached only 1%. Therefore, subsequent studies were carried out with 15%MnOX-15%CeO\({}_{2}\)/CNFs(OX). As shown in Figure 5, the influence of reaction temperature on the Hg\({}^{0}\) removal performance was investigated. The observation indicated that the optimal reaction temperature for 15%MnOX-15%CeO\({}_{2}\)/CNFs(OX) sorbent was 120 \({}^{\circ}\)C. It should be noted that over 90% of the Hg\({}^{0}\) was removed by 15%MnOX-15%CeO\({}_{2}\)/CNFs(OX) sorbent in the relatively broad temperature window of 120-220 \({}^{\circ}\)C.  
In order to evaluate the performance of our sorbents, it was compared with other Mn-based or Ce-based sorbents in some of the published literature [16; 19; 22; 23]. All the results were selected under similar experimental conditions and tested under a N\({}_{2}\) + O\({}_{2}\) atmosphere. The ratios of total gas flow rate to sorbent mass in different studies were converted into Q/M. As seen from a general view in Table S2, under similar N\({}_{2}\) + O\({}_{2}\) atmosphere and Q/M experimental conditions, the sorbent in the present study exhibited relatively superior activity.