## 3 Results and Discussion
### Photocatalytic Activities of Metal Oxide Nanofibers
The process is as follows:  
\[\text{TiO}_{2}+h\upsilon\rightarrow\text{h}^{+}+\text{e}^{-} \tag{3}\]  
\[\text{h}^{+}+\text{OH}^{-}\rightarrow\cdot\text{OH} \tag{4}\]  
\[\text{h}^{+}+\text{H}_{2}\text{O}\rightarrow\cdot\text{OH}+\text{H}^{+} \tag{5}\]  
\[\text{e}^{-}+\text{O}_{2}\rightarrow\cdot\text{O}_{2}\text{}^{-} \tag{6}\]  
\[\text{H}_{2}\text{O}+\cdot\text{O}_{2}\text{}^{-}\rightarrow\text{HO}_{2} \text{}\cdot+\text{OH}^{-} \tag{7}\]  
\[\text{HO}_{2}\cdot+\text{H}_{2}\text{O}\rightarrow\text{H}_{2}\text{O}_{2}+ \cdot\text{OH} \tag{8}\]  
\[\text{H}_{2}\text{O}_{2}+\text{e}^{-}\rightarrow\cdot\text{OH}+\text{OH}^{-} \tag{9}\]  
\[\text{H}_{2}\text{O}_{2}+\cdot\text{O}_{2}\text{}^{-}\rightarrow\cdot\text{OH }+\text{OH}^{-}+\text{O}_{2} \tag{10}\]  
\[\cdot\text{OH}+\text{MB}\rightarrow\text{ intermediates}\rightarrow\text{CO}_{2}+ \text{H}_{2}\text{O} \tag{11}\] \begin{table}
\begin{tabular}{l l l l l l l} \hline \hline \multicolumn{1}{c}{\multirow{2}{*}{**Photocatalysts**}} & \multicolumn{2}{c}{**Raw Materials**} & \multicolumn{1}{c}{\multirow{2}{*}{**Dye**}} & \multicolumn{1}{c}{\multirow{2}{*}{**Light Source**}} & \multicolumn{1}{c}{\multirow{2}{*}{**Degradation (\%)**}} & \multicolumn{1}{c}{\multirow{2}{*}{**Time**}} & \multirow{2}{*}{**Ref.**} \\  & \multicolumn{1}{c}{**(Concentration)**} & & & & & \\ \hline TiO\({}_{2}\) nanofiber & Ti rods & Malachite green (10\({}^{-5}\) M) & Ultraviolet lamp & 93\% & 240 & [48] \\ TiO\({}_{2}\) nanofiber & Titanium & Methylene blue (20 mg/L) & Visible light, 150 W & 25\% & 80 & [49] \\ TiO\({}_{2}\)@CNFs nanofiber & TiO\({}_{2}\)/polyacrylamideonitrile (PAN) & Rhodamine (10 mg/L) & Ultraviolet lamp, 250 W & 98.2\% & 60 & [50] \\ ZnO nanofiber & Zn(CH\({}_{3}\)COO)\({}_{2}\)\(\cdot\)2H\({}_{2}\)O/ & Methylene blue (10 mg/L) & Mercury lamp, 50 W & 50\% & 360 & [51] \\ ZnO nanofiber & Zn rods & Malachite green (10\({}^{-5}\) M) & Ultraviolet lamp & 91\% & 240 & [48] \\ ZnO nanofiber & ZnCl\({}_{2}\)/PVP & Methylene blue (10 mg/L) & Ultraviolet lamp, 500 W & 98.6\% & 100 & [43] \\ NiO nanofiber & Ni(CH\({}_{3}\)COO)\({}_{2}\)\(\cdot\)4H\({}_{2}\)O/ & Methyl orange (10 mg/L) & Ultraviolet lamp, 12 W & 40\% & 150 & [52] \\ NiO nanofiber & Ni(CH\({}_{3}\)COO)\({}_{2}\)\(\cdot\)4H\({}_{2}\)O/PAN & Rhodamine B (10 mg/L) & Ultraviolet lamp, 50 W & 46.2\% & 50 & [53] \\ NiO nanofiber & Ni(CH\({}_{3}\)COO)\({}_{2}\)/PVP & Methylene blue (10 mg/L) & Ultraviolet lamp, 300 W & 47.3\% & 80 & [54] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of commonly employed TiO\({}_{2}\), ZnO and NiO nanofibers for photocatalysis. Furthermore, it should be pointed out that the photocatalytic degradation is actually a free radical reaction. The photodegradation efficiency is mainly due to electron-hole pair recombination inhibition by charge transfer processes. In the previous study, the particle sizes of Co\({}_{3}\)O\({}_{4}\) and Mn\({}_{2}\)O\({}_{3}\) were relatively large. When Co\({}_{3}\)O\({}_{4}\) and Mn\({}_{2}\)O\({}_{3}\) are excited by UV light, electrons (e\({}^{-}\)) are easily recombined with holes (h\({}^{+}\)) in the process of reaching the conduction band and starting to move toward the surface of the particles, which are emitted in the form of heat [59]. Therefore, OH and \(\cdot\)O\({}_{2}\)\({}^{-}\) cannot be formed in this process, so methyl blue cannot be degraded by Co\({}_{3}\)O\({}_{4}\) and Mn\({}_{2}\)O\({}_{3}\) nanofibers.