The optical absorption property of the samples is investigated
via Uv-vis diffuse reflectance spectrum (UV-vis DRS) (Fig. S5 in Supporting information) [
25]. The Bi
2WO
6/HRP-2 sample displays a slight red-shift of absorption edge and produces the obvious absorption in excess of 450 nm, which is in favor of the solar harvest and utilization. In addition, the band gap energy of Bi
2WO
6 decreases from 2.63 eV to 2.53 eV after immobilizing HRP, which suggests electrons are more easily excited from valence band (VB) to conduction band (CB) to enhance the photocatalytic activity. Meanwhile, the VB values of Bi
2WO
6 before and after immobilizing HRP can be calculated to be 3.02 eV and 2.97 eV, while corresponding CB values are 0.39 eV and 0.44 eV, respectively. Moreover, it is reported that photocurrent and electrochemical impedance spectroscopy (EIS) reflect the migration and separation ability of photogenerated electron-hole pairs [
26-
28]. As shown in
Fig. 3a, the photocurrent intensity of the Bi
2WO
6/HRP-2 electrode is far higher than that of Bi
2WO
6, which indicates that the incorporation of HRP distinctly improves the interfacial charge separation efficiency and mobility. The Nyquist curve radius of the Bi
2WO
6/HRP-2 electrode is clearly smaller than that of Bi
2WO
6 (
Fig. 3b), suggesting that the former possesses the lower charge migration resistance in interfacial electrolyte solution, in favor of enhancing photocatalytic degradation activity. Furthermore, as polarization curves shown in
Fig. 3c, the overpotential of Bi
2WO
6/HRP-2 electrode (−0.54 V) at 10 mA/cm
2 is distinctly smaller than that of Bi
2WO
6 (−0.63 V), which demonstrates that the incorporation of HRP effectively decreases the overpotential and thus fundamentally improves the photocatalytic degradation activity [
29,
30]. Moreover, based on the time-resolved photoluminescence (TR-PL) decay plots (
Fig. 3d), the fitted fluorescence lifetime (1.89 ns) of Bi
2WO
6/HRP-2 sample is obviously shorter than that of Bi
2WO
6 (3.45ns), which implies that the probable new nonradioactive decay way is produced to suppress recombination of photogenerated electrons and holes [
31,
32]. These results indicate that the immobilization HRP on Bi
2WO
6 microsphere has a positive effect to improve the photocatalytic activity. Besides, the similar pore structure and specific surface areas of the Bi
2WO
6 and Bi
2WO
6/HRP-2 samples (Fig. S6 in Supporting information) imply that they have insignificant effect on the photocatalytic activity, indirectly attesting that the enhanced degradation activity mainly originates from the photoenzyme synergic catalytic effect produced on the Bi
2WO
6/HRP-2 sample.