**2.1 Preparation of Cu/TiO2 film**

The combination of sol–gel and dip-coating process was used for preparing TiO2 film. TiO2 sol solution was made by mixing [(CH3)2CHO]4Ti (purity of 95 wt%, Nacalai Tesque Co.) of 0.3 mol, anhydrous C2H5OH (purity of 99.5 wt%, Nacalai Tesque Co.) of 2.4 mol, distilled water of 0.3 mol, and HCl (purity of 35 wt%, Nacalai Tesque Co.) of 0.1 mol. Netlike glass fiber was cut like a disc, and its diameter and thickness were 50 mm and 1 mm, respectively. The netlike glass fiber disc was dipped into TiO2 sol solution at the speed of 1.5 mm/s and pulled up at the fixed speed of 0.2 mm/s. Then, it was dried out and fired under the controlled firing temperature (*FT*) and firing duration time (*FD*), resulting that TiO2 film was fastened on the netlike glass fiber. *FT* and *FD* were set at 623 K and 180 s, respectively. Cu was loaded on TiO2 film by pulse arc plasma method. The pulse arc plasma gun device (ULVAC, Inc., ARL-300) having Cu electrode whose diameter was 10 mm was applied for Cu loading. After the netlike glass fiber coated with TiO2 was set in chamber of the pulse arc plasma gun device which was vacuumed, the nanosized Cu particles were emitted from Cu electrode with applying the electrical potential difference of 200 V. The pulse arc plasma gun can evaporate Cu particle over the target in the circle area whose diameter is 100 mm when the distance between Cu electrode and the target is 160 mm. Since the difference between Cu electrode and TiO2 film was 150 nm in the present study, Cu particle can be evaporated over TiO2 film uniformly. The amount of loaded Cu was controlled by the pulse number. In the present study, the pulse number was set at 100. Since the netlike glass fiber is transparent, the light can pass through the netlike glass fiber. The present study has also investigated if two layers of two Cu/TiO2 coated on netlike glass fiber put on the top of the other (with certain distance, i.e., overlapping), what impact/improvement would be on the CO2 reduction performance. The overlapping two layers of Cu/TiO2 coated on netlike glass fiber is expected to utilize the light effectively as well as to increase the amount of photocatalyst used for CO2 reduction.
