Photocatalytic degradation of Alizarin by CdS quantum dot modified SBA-15 nanocomposites

Photocatalytic degradation of pollutants based on semiconductor quantum dots (QDs), which utilize the solar energy can be used for wastewater purification methods. But, application of free QDs was associated with some difficulties, such as oxidation and agglomeration of QDs and difficulties in separation. As a solution for these problems, we have studied the production and application of CdS quantum dots modified mesoporous SBA-15 nanocomposites for photocatalytic degradation of Alizarin.Mesoporous SBA-15 was hydrothermally synthesized using pure SiO2 powder extracted from rice husk ash [1] and copolymer p123 as the template [2]. Then, about 300 mg of synthesized SBA-15 was added to 50 mL of aqueous solution containing 500 mg CdCl2 under magnetic stirring for 24 h. finally, 10 ml of aqueous solution containing 500 mg Na2S was droplet added to the previous solution. After 6 h, the obtaining mesoporous nanocomposites were filtrated, washed with distilled water, and dried.To examine the photocatalytic activity of prepared catalysts, 250 mg of desired catalyst dispersed in 24 mL double distilled water and then 6 mL of alizarin aqueous solution (250 ppm) was added and stirred in dark place for 60 min to attain an adsorption/desorption equilibrium. Afterwards, the suspension was irradiated by sunlight under moderate stirring. The temperature of the solution was fixed by a water bath to prevent any heating effect on results. At specified time intervals, the concentration of dye in the supernatant was determined by UV–vis absorption spectroscopy at the λmax=435 nm [3]. The photocatalytic degradation kinetics was studied and a detailed mechanism was proposed. The proposed mechanism based on reactive species was also studied by free radicals trapping experiments; which results demonstrated that the °O2- radicals have active role in the photodegradation mechanism. In total, results were shown that, the proposed method is an attractive process for photocatalytic degradation of dyes in wastewaters.