Facile Synthesis of Sodium Iron Silicate/Sodium Iron Oxide Silicate Nanostructures from Canned Beans and Rice Husk Wastes for Efficient Removal of Cd(II) Ions from Aqueous Media

Waste materials are often available without cost, making them economically viable sources for the production of nanoadsorbents. This can significantly reduce the overall cost of manufacturing and contribute to cost-effective waste management strategies. Hence, in this study, canned beans and rice husk wastes were employed as sources of iron and silicon, respectively, for facile and low-cost hydrothermal synthesis of novel sodium iron silicate/sodium iron oxide silicate nanostructures. The nanostructures, which were produced after 6, 12, 18, and 24 hrs, were abbreviated as N6, N12, N18, and N24, respectively. The average crystal size of the N6, N12, N18, and N24 nanostructures is 15.23, 25.64, 40.21, and 42.87 nm, respectively. Additionally, the BET surface area of the N6, N12, N18, and N24 nanostructures is 71.57, 48.25, 32.92, and 32.19 m(2)/g, respectively. The produced nanostructures were utilized for the efficient removal of Cd(II) ions from aqueous media. The maximum adsorption capacity of the N6, N12, N18, and N24 samples towards Cd(II) ions is 248.76, 207.47, 182.82, and 173.61 mg/g, respectively. The removal efficiency of Cd(II) ions from 100 mL of a 150 mg/L solution using 0.05 g of nanostructures increased with raising pH from 2.5 to 6.5. The removal efficiency of Cd(II) ions by the N6, N12, N18, and N24 samples at pH 6.5 is 80.96, 66.99, 58.49, and 55.72 %, respectively. Also, the removal efficiency of Cd(II) ions from 100 mL of a 150 mg/L solution using 0.05 g of nanostructures increased with raising the contact time from 5 to 30 min due to the availability of adsorption sites. The removal efficiency of Cd(II) ions by the N6, N12, N18, and N24 samples after 30 min is 80.45, 66.32, 57.68, and 55.08 %, respectively. The removal efficiency of Cd(II) ions from 100 mL of a 150 mg/L solution using 0.05 g of nanostructures decreased with raising the solution temperature from 298 to 328 K. Besides, the removal efficiency of Cd(II) ions decreased with raising the concentration from 50 to 250 mg/L. The pseudo-second-order kinetic model and Langmuir isotherm are the best equations for describing the adsorption of Cd(II) ions by the synthesized nanostructures. The adsorption of Cd(II) ions by the synthesized nanostructures is spontaneous, exothermic, and chemical. The synthesized nanostructures were renewed and used multiple times to remove Cd(II) ions without losing their efficiency.