Obtention of Lignin–Silica Nanocomposites from Rice Husk and Coffee Parchment as Adsorbents of Cu(II) in Water

Intensive agricultural production generates significant lignocellulosic waste while contributing to heavy metal pollution, particularly copper (Cu(II)). Synthesizing low-cost nanocomposites from agricultural by-products offers a sustainable circular-economy strategy for water remediation. Here, lignin–silica nanocomposites (LSNCs) were synthesized via a sol–gel method using two abundant Cuban agro-industrial wastes: rice husk and coffee parchment. Physico-chemical characterization (FT-IR, TEM, and TGA) revealed spherical particles (50–60 nm) whose silica contents reflected their parent materials (52% for rice husk vs. 11% for coffee parchment). Batch adsorption experiments showed rapid Cu(II) uptake, with the dissolved Cu(II) concentration exhibiting an apparent plateau from the first sampling point at 10 min onward. The Sips isotherm model best described the process, yielding model-predicted maximum apparent sorption capacity (qm) of 15 mg/g for rice husk-derived LSNC and 12 mg/g for coffee parchment-derived LSNC. These findings demonstrate that valorizing local agricultural waste into functional nanocomposites provides a low-cost platform for heavy metal adsorption. Coffee parchment and rice husk were successfully used as precursors for lignin/silica nanocomposites that reduced dissolved Cu(II) concentrations in batch aqueous experiments; however, the contribution of adsorption could not be separated from possible precipitation.