Green synthesis of silver sulfide nanoparticles and Nigella sativa seeds-based nanocomposites for efficient adsorption of Pb(II) ion in wastewater

The pollution of water bodies by hazardous heavy metals, more specifically lead ions, continue to constitute a substantial threat to the environment and human health owing to their toxicity, persistence as well as non-biodegradability. This study presents an ecologically sustainable and cost-effective approach of remove Pb(II) ions from synthetic wastewater. Ag₂S nanoparticles were synthesized through homogeneous precipitation route and subsequently incorporated into activated carbon derived from Nigella sativa (black cumin) seeds to form composite adsorbents. Characterization methods such as FTIR, UV-Vis spectroscopy, XRD, TEM, SEM, and TGA to characterize the materials. TEM of Ag₂S nanoparticles showed spherical shaped particles with an average diameter of 6.982 nm. The seed-derived carbon matrix showed high porosity and a functional surface suitable for nanoparticle anchoring. Batch adsorption experiments were conducted to assess the effects of contact time, temperature, initial concentration and solution pH. Optimal adsorption occurred at pH=5 and equilibrium reached its peak in 120 minutes. Kinetic and isotherm studies indicated that the adsorption process exhibited pseudo-second-order kinetics and matched well with the Langmuir isotherm model, implying monolayer sorption. Thermodynamic data validated the reaction as spontaneous and endothermic. • Ag 2 S nanoparticles were synthesized through homogeneous precipitation method and the Nigella Sativa-Based Nanocomposites were successfully prepared • TEM of Ag₂S nanoparticles showed spherical shaped particles with an average diameter of 6.982 nm • The effects of contact time, temperature, initial Pb(II) concentration and solution pH were studied • Optimum adsorption conditions of were pH 5 • Adsorption was driven by biding sites such as carboxyl biding with complexation, alkenes binding with π bonds, alkanes and amines biding with hydrogen bonds. • AC-Ag 2 S nanocomposites yielded maximum percentage removal of 98.6%. • The equilibrium was reached its peak in 120 minutes