Green synthesis and application of ZnO nanoparticles for removing malathion and pyrene from aqueous solutions

This study systematically investigates the green synthesis of ZnO nanoparticles using an Artemisia plant-extract-mediated sol-gel method and evaluates their performance for the simultaneous removal of malathion and Pyrene from aqueous solutions. The synthesized nanoparticles were thoroughly characterized by XRD, SEM, TEM, FTIR, XPS, and BET, revealing a highly crystalline, mesoporous structure with a surface area of 180 m²/g, pore diameters of 4-4.5 nm, and abundant surface hydroxyl groups and oxygen vacancies that facilitate adsorption. Batch experiments optimized pH (~ 7), adsorbent dosage (1 g/L), contact time (180 min), and initial pollutant concentrations. Non-linear kinetic modeling shows that adsorption follows the Pseudo-First-Order model (R² ≥ 0.989, SSE < 10^-4), indicating a physisorption process controlled by boundary layer mass transfer. Isotherm analysis fits the Langmuir model well (R² ≥ 0.9588), giving maximum capacities at 298 K of 14.25 mg g^-1 (malathion) and 26.74 mg g^-1 (Pyrene), while Rₗ (0-1) and 1/n < 1 confirm favourable adsorption. Thermodynamic analysis demonstrated that malathion adsorption is endothermic and entropy-driven (ΔH° =  + 33.4 kJ/mol, ΔS° =  + 112.9 J/mol K), whereas Pyrene adsorption is exothermic and enthalpy-driven (ΔH° =  - 8.0 kJ/mol, ΔS° =  - 22.7 J/mol K), with negative ΔG° values confirming spontaneous adsorption under all studied conditions. The ΔH° values below 40 kJ mol^-1 and ΔG° values in the range 0 to - 20 kJ mol^-1 confirm the physical nature of the binding, and long-term sustainability. These findings indicate highlight the capability of green-synthesized ZnO nanoparticles to simultaneously remove structurally diverse organic pollutants under near-neutral conditions, addressing a key limitation in current adsorption systems. However, this study is limited to laboratory-scale conditions with limited evaluation of adsorbent regeneration and real wastewater applicability. Therefore, future work should focus on regeneration efficiency, long-term stability, and performance in real wastewater.