To estimate the porous TiO
2 nanowires activity as the photocatalyst, the mixture was treated by UV light irradiation for a period of time. The intensity of absorption peak of the solution was measured to calculate photodagradation rate. When porous TiO
2 nanowires act as catalyst, during the process of irradiation, the absorbance spectra of RhB solution was shown in Fig. 4(a). It can be clearly observed that at 665 nm, the maximum absorbance decreases rapidly with increasing the irradiation time. After the mixture was irradiated by UV light for 7 min, the photodagradation rate reaches approximate 25.6%. After irradiation for 49 min, no obvious absorption peak was observed. The degradation ratio of RhB can be calculated using 1−
Ct/
C0, where
Ct is the concentration of dyes and
C0 is the initial concentration. The plots of irradiation time vs degradation ratio shows the degradation ratio of RhB can reaches up to 98.76%. Since no obvious absorption peak can be observed, the RhB in mixture can be considered to be almost totally decomposed. Figure 4(a) (inset) also exhibits photodagradation of RhB solution without any catalyst when the solution was exposed at different duration time under the same experiment condition. It’s clearly found that after 49 min irradiation, there was almost no degradation in RhB solution, indicating that the as-synthesized porous TiO
2 nanowires are promising to act as excellent photocatalyst to remove RhB in water. Meanwhile, the plots of irradiation time vs degradation ratio were also achieved without catalyst, see Fig. 4(a) (inset). The result suggests that after the same duration time, no obvious degradation of RhB solution happened. Figure 4(b) shows characteristic absorption peak of MB solution with the catalyst. It clearly shows that the porous TiO
2 nanowires can serve as excellent catalyst for degradation of MB. Figure 4(b) (inset) demonstrates that the degradation ratio of MB solution reaches up to 97.98% after irradiation for 56 min. The photocatalytic performances of TiO
2 materials with different morphologies are listed in Table 1. The degradation ratio of the porous TiO
2 nanowires is higher than the previous reported values obtained under UV light irradiation with commercial TiO
2 powders (P25) [
14], porous TiO
2 nanospheres [
14], anatase nano-TiO
2 [
21], and hierarchical TiO
2 nanoflowers [
22]. Therefore, the as-prepared porous TiO
2 nanowires have great potential application in wastewater treatment. It is widely acknowledged that the catalytic process is primarily associated with the adsorption and desorption of molecules that usually occur on the surface of the catalyst. The possible reasons of the high performance TiO
2 nanowires may be ascribed to three aspects. First, the small size of nanocrystallites in the porous TiO
2 nanowires can effectively promote the transportation of carrier and greatly decrease the recombination rate between photoelectrons and holes, thus enhancing photocatalytic activities. Secondly, the porous structure of the TiO
2 nanowires facilitates the transportation of the pollutant molecules onto the surface of TiO
2 nanocrystallites and stores more molecules. Finally, the porous TiO
2 nanowires have the highest specific surface area than other catalysts, reaching up to 86.4 m
2·g
−1 (as shown in Table 1), which means it can produce more unsaturated surface coordination sites exposed to the solution, provide much more active reaction sites on the surface of material, and effectively promote the separation of electron–hole pairs, resulting in the high photocatalytic activities.