Recycling of natural and waste materials as supports for green silver nanoparticles as efficient catalysts in photodegradation of organic pollutants

The use of a sustainable technology to synthesize green silver nanoparticles (AgNP) from renewable resources is very appealing. Here, a green protocol for the production AgNP/composites is introduced, via in situ reduction of Ag+ ions on sustainable materials (clays and waste materials) using eucalyptus leaves extract (ELE) as a reducing and stabilizing agent, without the addition of any harmful or expensive organic solvent, surfactant or dangerous compounds. The synthesized AgNP/composites were evaluated as photocatalysts to degrade Indigo Carmine (IC) dye as a model pollutant under visible light. Kaolin and pistachio shells showed to be promising supports for green AgNP, with decolorization efficiency of 85.3(±1.8)% and 48.3(±4.1)%, respectively, after 120 min of irradiation. The best catalytic results were obtained with kaolin as support and so the influence of different synthesis parameters of AgNP/kaolin nanocomposite was evaluated. The catalytic results indicated that increasing the amount of AgNO3 and ELE in the nanocomposites, increased their photocatalytic performance. Nanocomposites synthesized at room temperature showed smaller amount of AgNP and higher decolorization efficiency, compared to those biosynthesized at 50 °C. The evaluation of active species responsible for the photodegradation of IC showed that O2•- and H+ radicals are species involved in the reaction. The AgNP/kaolin showed also to be efficient to degrade both atrazine and sulfamethoxazole after 120 min of irradiation.