Biogenic silver nanoparticles on carbonaceous material from sewage sludge for degradation of methylene blue in aqueous solution

Silver nanoparticles (Ag NPs) were synthesized in situ, using a one-step green methodology with Camellia sinensis (green tea) aqueous extract as reducing agent, and supported on a carbonaceous material (Ag-CM), originated from the pyrolysis of sewage sludge. UV–Vis spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Brunauer–Emmet–Teller were used to characterize the nanocomposite. Ag-CM composite exhibited very good catalytic activity in the degradation process of methylene blue (MB) dye in aqueous solution without using sunlight or UV radiation. Batch kinetic and isothermal experiments, using 30 mg/L MB solution, showed that Ag-CM composite removed near to 91 % of MB in 9 h, whereas the carbonaceous material alone removed only 60 % in 30 h. Experimental data were adjusted to different kinetic and isotherms models, where both materials fit the second-order and Langmuir–Freundlich models, respectively; therefore, a chemisorption mechanism probably occurs in these heterogeneous materials.