2.3. Rhodamine B (RhB) dye adsorption
Firstly, RhB aqueous solutions with different concentrations (1–10 mg/L) were prepared. The adsorption experiments were carried out at room temperature with magnetic stirring. For adsorption isotherm investigations, 100 mL RhB aqueous solutions with different concentrations were mixed with 10 mg BiOBr-PVP or BiOBr samples under magnetic stirring for 60 min. Then, the powders were separated by centrifugation to measure the remaining concentrations of RhB in the solution. The concentrations of RhB were determined by measuring the absorbance at 554 nm by using AT 1015 UV–Vis spectrophotometer (UV 7502PCS). And the UV–Vis absorbance of RhB dye solution at 554 nm and the concentrations exhibit a linear relationship in the range of 1–10 mg/L as shown in Fig. S1.
2.4. Photocatalytic experiments
To compare the photocatalytic performances of BiOBr-PVP hybrids and BiOBr samples, photocatalytic degradations of RhB and phenol were also carried out. 20 mg as-prepared BiOBr-PVP or BiOBr samples were dispersed in 100 mL RhB aqueous solutions (20 mg/L) and stirred in dark for 30 min to establish an adsorption–desorption equilibrium. Then, the above suspensions were exposed to light irradiation. A 4 mL solution was taken every 2 min, and centrifuged to remove the catalysts. The solution was analyzed by a UV–Vis spectrophotometer (UV 7502PCS). The percentage of degradation is reported as C/C0, where C is the absorption of the dye solutions taken at each time interval at the maximum absorption peak, and C0 is the absorption of the initial concentration of the dye solution. The photocatalytic degradation experiments of phenol is similar as the case of RhB except for the interval times, which is taken every 30 min.