α-Fe2O3/SiO2纳米颗粒混合体系表面的酸碱性质及其对重金属离子的吸附行为

以Fe(NO₃)₃·9H₂O和正硅酸乙酯(TEOS)为原料, 通过溶胶-凝胶法和辅助模板法分别制备了纳米α-Fe₂O₃和SiO₂, 并对所合成样品进行了粉末X射线衍射(XRD)和BET表征. 使用自动电位滴定仪测定了α-Fe₂O₃/SiO₂纳米颗粒混合体系的表面酸碱性质. 研究了在不同pH下α-Fe₂O₃/SiO₂混合体系对Cu²⁺、Pb²⁺、Zn²⁺离子的吸附行为. 基于上述实验数据, 用WinSGW软件计算了α-Fe₂O₃/SiO₂混合体系表面酸碱配位常数, 并得出结论: α-Fe₂O₃/SiO₂混合体系表面反应为单一脱质子反应≡XOH ⇔ ≡XO^-+ H⁺(lg K = -8.19±0.15), 明显区别于同时具有加质子和脱质子反应的α-Fe₂O₃/SiO₂/γ-Al₂O₃, α-Fe₂O₃/γ-Al₂O₃和SiO₂/γ-Al₂O₃等纳米颗粒混合体系. 在此基础上拟合得到α-Fe₂O₃/SiO₂混合体系吸附重金属离子Cu²⁺、Pb²⁺、Zn²⁺的表面络合反应平衡常数分别为:
≡XOH + M²⁺ ⇔ ≡XOM⁺+ H⁺ [lg K = -3.1, -3.6, -3.8 (M = Cu, Pb, Zn)].
≡XOH＋M²⁺＋H₂O ⇔≡XOMOH＋2H⁺[lg K = -8.8, -8.0, -10.5 (M = Cu, Pb, Zn)]

Acid-Base Properties and Adsorption Behaviors of Heavy Metal Ions at the Surface of α-Fe2O3/SiO2Nano-Mixed System

α-Fe₂O₃and SiO₂were prepared from ferric nitrate and TEOS by sol-gel method in combination with using templates. The synthetic samples were characterized by powder X-ray diffraction (XRD) and N₂adsorption/desorption methods. We determined the surface acid-base properties of α-Fe₂O₃/SiO₂nano-mixed system by potentiometric titration technique, and studied the adsorption behaviors of heavy metal ions on the solid surface of α-Fe₂O₃/SiO₂nano-mixed system at different pH values. According to the above experimental data, we calculated the surface acid-base reaction equilibrium constants of the nano-mixed system using WinSGW software to be ≡XOH ⇔ ≡XO^-+ H⁺(lg K = -8.19±0.15). The calculated result reveals that the single deprotonation surface of α-Fe₂O₃/SiO₂nano-mixed system is obviously different from the surfaces of α-Fe₂O₃/SiO₂/γ-Al₂O₃, α-Fe₂O₃/γ-Al₂O₃ and SiO₂/γ-Al₂O₃nano-mixed system with surface protonation as well as deprotonation at the same time. Based on the above result, the surface complexation constants of Cu²⁺, Pb²⁺, Zn²⁺on the surface of α-Fe₂O₃/SiO₂mixed systems were simulated respectively as follows:
≡XOH + M²⁺ ⇔ ≡XOM⁺+ H⁺ [lg K =-3.1, -3.6, -3.8 (M = Cu, Pb, Zn)].