Chiang Mai Journal of Science

     Spherical porous SiO₂ was synthesized via TEOS hydrolysis combined with NaOH etching, and its application in removing heavy metal Cu²⁺ from wastewater was investigated. The morphology, specific surface area, pore structure, and phase of pre- and post-etching SiO₂ were characterized using transmission electron microscopy (TEM), N₂ adsorption analyzer, and X-ray diffraction (XRD), respectively. Additionally, detailed studies were conducted on the adsorption kinetics, isotherms, and thermodynamics, as well as the effects of adsorbent dosage, ionic strength, and pH on Cu²⁺ removal. The results showed that the post-etching SiO₂ (denoted as ESP-SiO₂) presented a porous nanospherical morphology, with significantly larger specific surface area and pore volume compared to the pre-etching sample. Furthermore, the SiO₂ underwent a transformation from an amorphous to a crystalline phase. The adsorption kinetics of Cu²⁺ onto ESP-SiO₂ was well fitted by the pseudo-second-order model, and the adsorption isotherm conformed to the Langmuir model, with a maximum adsorption capacity of 172.41 mg/g. Thermodynamic analysis revealed that the adsorption process was spontaneous, exothermic, and accompanied by an increase in entropy. For a 50 mg/L Cu²⁺ solution, a removal efficiency of 86.5% was achieved when the dosage of ESP-SiO₂ was 0.05 g. Moreover, the material exhibited strong resistance to interference from ionic strength (up to 0.1 mol/L), and the optimal pH for adsorption was 5.5. Given its advantages of low cost, simple preparation, and high removal efficiency, ESP-SiO₂ holds great application potential in the treatment of heavy metal-containing wastewater.