Adsorption Performance of Spherical Porous SiO2 on Heavy Metal Cu2+ in Wastewater

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.