Photocatalytic Degradation of Organic Dyes

The photocatalytic activity of M-HW was evaluated through the photocatalytic degradation of the organic pollutants. Precisely, 1 mg of M-HW composites (photocatalyst) was added to 40 mL of MO (20 mg/L, target dye). The mixture was stirred continuously in the dark for 30 min to obtain a homogenized mixture and achieve adsorption–desorption equilibrium. Then, the mixture was transferred to the photocatalytic reaction system and irradiated under light at a specific time, and aliquots of 4 mL of the solution were collected in 7 mL Eppendorf (Ep) tubes every 20 min, and the supernatant was removed twice using high-speed centrifugation at 9500 rpm for 10 min. The absorbance value of MO at the maximum absorption wavelength (464 nm) was measured using a visible spectrophotometer (Shanghai Prism Technology 722SP). Different target dyes, such as rhodamine B (1 × 10⁻⁵ M, λ_max = 554 nm) and eosin B (5 × 10⁻⁵ M, λ_max = 518 nm), were changed in the same condition to record the maximum absorption value. The photocatalytic activities of M-HW on different dyes were studied using the photocatalytic degradation curve.
The photocatalytic degradation curve of organic dyes can be fitted using the first-order kinetic Equation (1) as follows: $$\mathrm{In}\frac{{\mathrm{C}}_0}{\mathrm{C}}=\mathrm{kt}$$
where C₀ (mg/mL) and C (mg/mL) represent the initial organic dye concentration and the dye concentration after irradiation, respectively; k represents the apparent rate constants, and t represents the reaction time (min) [44 (link)]. Thus, k was used to evaluate the photocatalytic activity in this work.