Green Synthesis of Nanochitosan/Bentonite/SnO₂–ZnO Bionanocomposite for Removal of Heavy Metal Ions and Photocatalytic Degradation of Organic Dye

Biotreatment of wastewater has attracted considerable attention due to its low cost and eco-friendliness. This study developed a novel bionanocomposite comprised of Nanochitosan (NCS), Bentonite (Bt), and SnO₂–ZnO nanocomposite prepared using Salvia officinalis extract as a reducing/stabilizing agent. The NCS/Bt/SnO₂–ZnO bionanocomposite exhibited a rough surface with porous nature. EDX, XRD, and FTIR results confirmed the formation of the bionanocomposite. TGA indicated high thermal stability of the NCS/Bt/SnO₂–ZnO. DRS results revealed that the bionanocomposite had a band gap of 2.60 eV. The surface area of NCS/Bt/SnO₂–ZnO was found to be 32.54 m² g⁻¹ with a 17.98 nm pore size. Adsorption of Fe(III) and Pb(II) ions and photocatalytic degradation of methylene blue (MB) dye using this bionanocomposite were studied. Under optimal conditions, the highest removal of Fe(III) (99.5%) and Pb(II) (91.5%) was achieved after 5 min and 40 min, respectively. The adsorption data fitted the Langmuir isotherm and indicated the removal capacity of 555.55 and 243.90 mgg⁻¹ for Fe(III) and Pb(II), respectively. Also, the NCS/Bt/SnO₂–ZnO showed the MB dye degradation efficiency of 99% within 30 min. Therefore, the NCS/Bt/SnO₂–ZnO can be used as an environmentally friendly, cost-effective, thermally stable, and high-performance adsorbent/photocatalyst to remove heavy metal ions and dye molecules.