Cadmium and sodium adsorption properties of magnetite nanoparticles synthesized from Hevea brasiliensis Muell. Arg. bark: Relevance in amelioration of metal stress in rice

Highlights: • Heavea bark extract primed magnetite nanoparticles. • Phenolics in the bark extract helped nanoparticle formation. • Magnetite nanoparticle adsorbed Cd more efficiently than Na. • Cadmium adsorption was multilayer but that of Na was monolayer. • Amendment of the nanoparticles enhanced Cd and Na tolerance in rice. -- Abstract: Magnetite nanoparticles use for the remediation of toxic metal ions. Therefore, the scope of green synthesis of magnetite nanoparticles from Hevea bark extract, and application of these particles for the environmental remediation of Cd and Na tested. Mixing of 10.0 mL each bark extract (1.0 g in 25.0 mL H₂O) and iron solution (10.0 mM FeCl₃ and 5.0 mM FeCl₂) resulted formation of semicrystalline magnetite nanoparticles having magnetic saturation at 10⁴ G. The particles characterized with the help of scanning electron microscopy, energy dispersive spectroscopy, Uv–vis spectroscopy, vibrating sample magnetometry, powder X-Ray diffraction, Fourier-transform infrared spectroscopy, and differential thermal analysis coupled with thermogravimetry. The phytochemicals responsible for priming and coating of nanoparticle were phenolics, especially benzoic acid derivatives. Adsorption of metal ions to nanoparticles followed pseudo-second-order model. Maximum Cd and Na adsorption capacity were 37.03 and 3.95 mg g⁻¹ respectively. The difference in Cd and Na adsorption capacity was the result of multilayer and monolayer adsorption processes respectively. Highest metal ion adsorption occurred at temperature 10.0–20.0 °C and pH 6.0. Metal adsorption property of the nanoparticles decreased the accumulation of Cd and Na in rice plants. The plant growth promotion effects of nanoparticles explained regarding biomass, osmolyte content, and oxidative stress tolerance. Therefore, the nanoparticles produced in the study can use as a magnetically separable nano sorbent of metal ions as well as ameliorant of metal stress in rice.