Usb2000 fiber optic spectrometer

Photocatalytic activities of samples were evaluated by the degradation of methylene blue (MB) solution under simulated sunlight. A 500 W Xe lamp (UXL-16B, Ushio, Tokyo, Japan) was used as a light source, with a maximum intensity of 494 nm. The spectrum of incident light was obtained by USB 2000 fiber optic spectrometer (Ocean Optics, Dunedin, FL, USA). The reactor was set 20 cm away from the output beam. In a typical experiment, 0.1 g of the sample was added into 100 mL of 10 mg·L⁻¹ MB solution.
Prior to photocatalytic testing, the solution was stirred for 30 min in darkness to reach the adsorption-desorption equilibrium of MB to avoid any error from the initial adsorption effect, then irradiated with stirring. At different irradiation time intervals, solutions were taken from the reaction suspension, filtered through a 0.45 µm Millipore filter to remove the particles, and then analyzed for MB content using a UV-Vis-NIR spectrophotometer (V-670, Jasco, Oklahoma City, OK, USA) at 664 nm. The rate of degradation was calculated by assuming pseudo-first-order kinetics and, hence, the rate constant for the degradation, k, was obtained from the first-order plot, according to the following equation: ln(C/C₀) = kt, where C₀ is the initial absorbance of MB, C is the absorbance of MB after a time (t), and k is the first-order rate constant.