Green synthesis, characterization, and adsorption of Co(II) and Cu(II) ions from aqueous solution by mesoporous silica MCM-41

Rice husk (RH) is regarded as one of the most common agricultural residues worldwide. MCM-41 (Mobil Composition of Matter No. 41) is prepared from RH. RH can itself be transformed to sodium silicate through a reaction with NaOH solution. This study includes three steps, the first of which involves extraction of silica from RH using a leaching process in the presence of HNO3; the second and third involve generation of RH-SiO2 and MCM-41 from the extracted silica. Characterization of the synthesized compounds can be successfully achieved, via the use of various techniques including FT-IR, FESEM-EDX, TEM, N2-adsorption-desorption, XRD, and thermogravimetric analysis represented by TGA/DSC. The XRD and TEM investigation demonstrated that MCM-41 with an extremely ordered hexagonal arrangement was generated. The findings of the N2-adsorption-desorption analysis revealed that the average pore diameter, total pore volume, and MCM-41 specific surface area were 6.80 nm, 126.12 cm3 g-1 and 548.92 m2 g-1, respectively. Thermogravimetric analysis (TGA/DSC) of silica materials represented by both RH-SiO2 and MCM-41 revealed two mass reduction steps, where the initial step involved elimination of water adsorbed in physical/chemical processes on the silica surface, and the second involving the breakdown of Si-OH groups. The RH-SiO2 and MCM-41 were utilized for the adsorption of heavy pollutants like Cu(II) and Co(II) ions from aqueous solution.