Hybrid silica aerogel nanocomposite adsorbents designed for Cd(II) removal from aqueous solution

Hybrid silica aerogel (HSA) nanoparticles were synthesized by sol-gel method and drying at ambient pressure. Also, two magnetic nanocomposites of HSA with Fe3O4 nanoparticles and chitosan (CS) were prepared including HSA-Fe3O4 and HSA-Fe3O4-CS. The morphology, structure, and magnetic properties of the HSA as well as its nanocomposites were analyzed by SEM, XRD, TGA, VSM, and ATR-FTIR techniques. The saturation magnetization (M-s) values for the Fe3O4 NPs, HSA-Fe3O4, and HSA-Fe3O4-CS nanocomposite film were 69.93, 19.04, and 5.77 emu/g, respectively. Furthermore, the abilities of the HSA, HSA-Fe3O4, CS, and HSA-Fe3O4-CS adsorbents were assessed for removal of cadmium(II) heavy metal ions (100 ppm) from aqueous solution. All adsorbents removed/adsorbed the maximum Cd(II) ions in 120 min when adsorbent dosage = 20 mg and pH = 8. Moreover, the highest adsorption capacities were 58.5, 69.4, 65.8, and 71.9 mg/g for the HSA, CS, HSA-Fe3O4, and HSA-Fe3O4-CS, respectively. Kinetic studies using all adsorbents verified that Cd(II) adsorption obeyed the second-order model illustrating the analyte chemisorption was happened on the adsorbent surfaces. All adsorption data were well consistent with the Langmuir isotherms. The reusability experiment confirmed that all of adsorbents could preserve >95% of their initial adsorption capacities even after five series of adsorption/desorption tests. Practitioner points Hybrid silica aerogel (HSA), HSA-Fe3O4, and HSA-Fe3O4-CS adsorbents were produced. Nanocomposites were characterized by XRD, TGA, SEM, VSM, and ATR-FTIR analysis. Adsorption of cadmium(II) ions by adsorbents was examined in aqueous solution. The highest adsorption capacity was obtained for the HSA-Fe3O4-CS (71.9 mg/g). Cd(II) adsorption followed second-order kinetics and Langmuir isotherm model.