Photocatalytic Degradation and Reduction

The photocatalytic behaviour was investigated by the oxidation of methylene blue and reduction of Cr(VI). The photocatalytic performance was evaluated under simulated solar light using a 300 W Xe lamp (a high-pressure 150 W xenon lamp, LOT – QuantumDesign GmbH equipped with the AM1.5G filter). The intensity of the incident light that reaches the surface of the investigated solution was equal to 100 mWcm⁻² (measured using a Coherentâ FieldMate Laser Power Meter). In a typical test, 20 mg of catalyst was placed in a 50 mL aqueous pollutant solution. The concentration of MB and Cr(VI) was 1·10^–5 M. Before irradiation, the suspension was vigorously stirred in the dark for 30 min to reach desorption-adsorption equilibrium. The change in MB and Cr(VI) concentration was monitored by its absorption at 665 nm and 351 nm, respectively, from the UV–Vis (Spektrofotometr UV5100) spectra of the solution, using distilled water as a reference. A total of 0.75 ml of suspension was collected and centrifuged before UV‒Vis measurement. In the case of Cr(VI) photoreduction, the process was conducted in acidified (pH = 3) solutions.
To study the reusability of the prepared photocatalysts, the cycle experiment was repeated 4 times for the photodegradation of methylene blue. After each photodegradation test, the catalyst was collected by centrifugation, dried under natural conditions and used for the next degradation experiment. Moreover, to indicate the role of hydroxyl radicals (·OH), (h +) holes and superoxide radicals (·O2-) in the process of MB degradation, experiments were performed in the presence of appropriate scavengers: t-butanol (TBA), ammonium oxalate (AO) and benzoquinone (BQ). The concentration of each scavenger was equal to 1 mM.