MgO and MgO/char nanocomposites as efficient catalysts for the removal of thiophene and malachite green from aqueous systems

MgO nanoparticles were synthesized by precipitation-calcination: 0.1 M Mg(NO₃)₂·6H₂O was precipitated with 0.5 M NaOH to pH 10–11, aged for 2 h, washed, dried at 100 °C, and calcined at 450 °C for 3 h. The MgO/char nanocomposite was fabricated by ultrasonically dispersing biomass-derived activated carbon (0.5 g in 100 mL water for 30 min), adding pre-synthesized MgO nanoparticles, stirring, aging for 2 h, washing, and drying at 100 °C. Analytical-grade chemicals and deionized water were used. Materials were characterized by UV–Vis (band-edge absorption at ~307 nm), FTIR, XRD (cubic periclase MgO; crystallite sizes 9.71 ± 1.39 nm for pure MgO and 19.95 ± 1.60 nm for composite), XPS (O 1 s: 530.10 eV in MgO vs. 531.58 eV in composite; Mg 2p: 51.08 eV vs. 52.30 eV), SEM (reduced aggregation in composite), and EDX (confirmed Mg, O, and C presence). Photocatalytic tests under simulated sunlight (0.05 g catalyst in 100 mL pollutant solution) showed thiophene degradation of 99.24% (MgO) and 100% (composite) in 90 min. Malachite green degradation reached 99.91% (MgO) but only 88.92% (composite) in 140 min, reflecting adsorption dominance in the composite. Experiments were triplicated with mean ± standard deviation reported.