Intensive agricultural production generates large volumes of lignocellulosic residues and contributes to heavy metal pollution, particularly copper (Cu). The valorization of these by-products as low-cost adsorbents offers a promising strategy for circular economy implementation and environmental remediation. In this study, lignin–silica nanocomposites were synthesized via a sol–gel process from two abundantly available agricultural wastes in Cuba: rice husk and coffee parchment. The nanocomposites were characterized by FT-IR, TEM and TGA methods. The nanocomposites showed a spherical shape and a diameter between 50 and 60 nm and their silica composition depended on the composition of the starting material. The nanocomposite obtained from rice husk had a silica ratio of 52 % while in the one prepared from coffee parchment it was 11 %. Adsorption capacities and adsorption behaviors with Cu(II) in water of the nanocomposites were studied. The adsorbents reached equilibrium within 10 minutes and the estimated maximum sorption capacities were 15 mg/g using rice husk as the starting material and 12 mg/g for the one prepared from coffee parchment. Nanocomposite synthesis is a promising route for lignocellulosic biomass revalorization as heavy metal adsorbents for environmental sanitation.