Figure 7.

UV–vis absorption spectra and plots of absorbance versus absorption and irridiation time. (A,C) Absorption and photodegradation spectrum of a solution of methyl orange (A) and congo red (C) in the presence of the hollow octahedral Cu₂O sample shown in Figure1c. (B,D) Plots of absorbance versus absorption time (0 to 120 min) and irradiation time (20 min, 40 min, 60 min) for methyl orange (B) and congo red (D) in the presence of different Cu₂O samples: (a), solid octahedral Cu₂O shown in Figure 3a; (b), hollow sphere Cu₂O shown in Figure 1a; (c), hollow octahedral Cu₂O (SI1-D3 in Additional file 1); (d), hollow octahedral Cu₂O shown in Figure 3b; (e), hollow octahedral Cu₂O shown in Figure.  1b; (f), hollow sphere Cu₂O shown in Figure 4d. Analytical grade TiO₂ reagent (100 nm, anatase phase).