# Enhanced Photocatalytic Performance of Bi2O2 CO3 Loaded Activated Carbon for Toluene Removal in Air
## 3 Results and Discussion
### Characterization and Propertiesof BOC/AC Composites
#### 3.2.3 Photocatalytic Properties  
The photocatalytic properties of the degradation of gaseous toluene (50.0 ppm) in air over the BOC/AC composites were investigated under light illumination. As shown in Figure 8a, all samples demonstrated good removal efficiency of more than 90%. Among the BOC/AC composites, BOC/AC_100 shows the optimal efficiency with a removal rate of up to 92.2% in 3 h. The performances are comparable and higher than previously reported typical composite photocatalysts such as N-TiO\({}_{2}\)/zeolite [34] and Fe\({}_{2}\)O\({}_{3}\)/In\({}_{2}\)O\({}_{3}\) composite [35], showing the promising potential application of BOC/AC composite catalysts. In previous works, other methods have been used for the removal of toluene from the air, such as biofililtration [36], post-plasma catalytic technology [37], and corona discharge [38]. Compared with those methods, which are usually expensive and complex, the present BOC/AC composite has the advantages of being green and low-cost. The products of toluene degradation were detected using GC. The results demonstrate that CO\({}_{2}\) is the main product (Figures 8b and S2) with the highest productivity of 82.5 mg/m\({}^{3}\) in 3 h for BOC/AC_100, and another main product should be H\({}_{2}\)O, on the basis that toluene is hydrocarbon. More reactive sites are provided for BOC/AC_100 due to the flower-like Bi\({}_{2}\)O\({}_{2}\)CO\({}_{3}\) on the surface of BOC/AC_50 and BOC/AC_100, which leads to enhanced photocatalytic performance. The photocatalytic process of the optimal sample (BOC/AC_100 composite) was investigated further. As shown in Figures 8c and S3, the toluene was completely removed in 7 h. Furthermore, the concentration of CO\({}_{2}\) increased significantly and reached 105.2 mg/m\({}^{3}\) (Figure 8d), which indicated the continuous degradation of toluene. However, the production rates of CO\({}_{2}\) were merely 38.3 mg/m\({}^{3}\) in 3 h and 55.4 mg/m\({}^{3}\) in 7 h for pristine AC. As we mentioned in the introduction, AC acts mainly as an adsorbent. Moreover, according to previous works, AC can also act as a photocatalyst for the degradation of organic contaminants. However, it is only active under UV irradiation with low catalytic efficiency. These results clearly show that the degradation rate of toluene is enhanced after the in-situ growth of BOC on the surface of the AC. This is attributed to the synergistic effect of the adsorption ability of AC and photocatalytic activity of both BOC and AC, demonstrating the advantage of the composite material. The stability of BOC/AC composites (BOC/AC_100) for photocatalytic removal of toluene was evaluated by performing three experimental cycles under light illumination. As shown in Figure 8e, highly stable photocatalytic efficiency was maintained for BOC/AC_100, reaching as high as 90% for toluene removal after three cycles, which demonstrated the excellent recyclability of BOC/AC for photocatalytic toluene degradation. In addition, we investigated the toluene removal efficiency using different amounts of BOC/AC_100 (1 g, 1.5 g, 2 g, and 3 g). As shown in Figure 8f, the photocatalytic activity was enhanced as the amount of catalyst increased, reaching the highest efficiency when 3 g of BOC/AC_100 was used. A proposed photocatalytic reaction mechanism over the BOC/AC composites for the degradation of gaseous toluene under light irradiation can be explained as follows (Figure 9). First, the honeycomb AC matrices adsorb and capture the toluene molecules. Then, under light illumination, the electrons are excited from the valence band (VB) to the conduction band (CB) in the surface of Bi\({}_{2}\)O\({}_{2}\)CO\({}_{3}\) loaded Activated Carbon, leaving holes in the VB. The AC can function as electron acceptors to reduce the recombination rate of electron-hole pairs. Consequently, the excited electrons on CB in Bi\({}_{2}\)O\({}_{2}\)CO\({}_{3}\) can be easily transferred to the surface of AC, thus promoting the separation and migration of photo-generated charge carriers.