## 3 Results and Discussion
### Adsorption and Catalytic Oxidation Performance of CoPc@s-BC
The typical optical image changes in reactive red X-3B solution during the decoloration process are shown in Figure 8. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Slope** & **Correlation Ratio** \\ \hline BC & 0.0563 & 0.9668 \\ CoPc@BC & 0.1723 & 0.9946 \\ CoPc@DT-BC & 0.2453 & 0.9921 \\ CoPc@TT-BC & 0.3466 & 0.9955 \\ CoPc@TP-BC & 0.3852 & 0.9942 \\ CoPc@PH-BC & 0.2240 & 0.9985 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Slope and correlation ratios regressed from the adsorbed dye-adsorption time curves. Figure 6: Adsorption of reactive red X-3B wastewater (initial concentration 100 \(\upmu\)M, pH = 2, T = 50 \({}^{\circ}\)C) with CoPc@s-BC (1 mg). For CoPc@BC, the decoloration rate was ca. 27 \(\upmu\)mol\(\cdot\)min\({}^{-1}\cdot\)g\({}^{-1}\). With the incorporation of the spacer, enhanced catalytic activity of CoPc catalyst was observed. Under the same reaction conditions, the decoloration rate of CoPc@DT-BC was ca. 8% higher than that of CoPc@BC. Much higher catalytic activity of CoPc was obtained with the incorporation of a longer spacer length. The decoloration rates of CoPc@TT-BC and CoPc@TP-BC were ca. 33 \(\upmu\)mol\(\cdot\)min\({}^{-1}\cdot\)g\({}^{-1}\) and 41 \(\upmu\)mol\(\cdot\)min\({}^{-1}\cdot\)g\({}^{-1}\), which were more than 20% and 50% higher than that of CoPc@BC, respectively. This result is in good accordance with our principle idea--that the incorporation of a flexible spacer is able to keep the CoPc catalyst at a preferred distance from the solid substrate, which, to some extent, mitigates the adverse effects of diffusion limitation and steric hindrance, increases the reaction homogeneity and enhances the accessibility and mobility of the CoPc catalyst. These effects are more likely to occur with longer spacer lengths. However, when the spacer is too long, it is possible that the CoPc molecules covalently immobilize through multiple-bonding, which restricts the free movement of the CoPc and thus, decreases its catalytic activity to some extent. The decoloration rate for CoPc@PH-BC was ca. 33 \(\upmu\)mol\(\cdot\)min\({}^{-1}\cdot\)g\({}^{-1}\), which was higher than CoPc@BC but lower than CoPc@TP-BC. To sum up, the most preferable spacer length to achieve the maximum decoloration efficiency of CoPc@s-BC was derived from the TP spacer. Under optimum immobilization conditions, 2 mmol/g of attached TP together with 495 \(\upmu\)mol/g of immobilized CoPc were obtained, and the decoloration  
Figure 8: Typical optical image changes of reactive red X-3B (initial concentration 100 \(\upmu\)M, pH = 2, T = 50 \({}^{\circ}\)C) with CoPc@s-BC (1 mg) and H\({}_{2}\)O\({}_{2}\) (8 mM). Figure 7: Catalytic oxidation of reactive red X-3B (initial concentration 100 \(\upmu\)M, pH = 2, T = 50 \({}^{\circ}\)C) with CoPc@s-BC (1 mg) and H\({}_{2}\)O\({}_{2}\) (8 mM). Inset: effect of the spacer length on the decoloration rate of reactive red X-3B. rate for the resulting CoPc@TP-BC reached 41 umol-min\({}^{-1}\).g\({}^{-1}\). These results are comparable with related literature. Firstly, flexible spacer-attached BCs were employed to support the CoPc catalyst, which permitted a much higher amount of immobilized CoPc than other materials [44; 45]. Secondly, the incorporation of the spacers increased both the adsorption rate and the adsorption capacity of the nanocomposites [46]. Moreover, the incorporation of the spacers (especially for TP) effectively increased the accessibility and reaction homogeneity of the CoPc catalyst, and thus, its catalytic activity was greatly improved compared to that without the spacer [23]. The EPR spin-trapping technique is a powerful tool for the detection of short-lived, active species. Herein, the 5,5-dimethyl-1-pyrroline-N-oxide (DMPO)-trapped EPR spectra were employed to demonstrate the formation of radicals during the catalytic oxidation of reactive red X-3B with the CoPc@s-BC (CoPc@BC)/H\({}_{2}\)O\({}_{2}\) reaction system (Figure 9). Without the existence of H\({}_{2}\)O\({}_{2}\), no obvious EPR signal was detected.