铁酸钴钛酸钠纳米管对水中Pb(II)的吸附.docx

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摘要
本研究旨在研究铁酸钴钛酸钠纳米管对水中Pb(II)的吸附性能，并 探讨其吸附机理。实验结果表明，铁酸钴钛酸钠纳米管能够有效地吸附水中 Pb(II)，而且吸附性能优于其他常见的吸附剂。研究发现，铁酸钴钛酸钠纳米管对 Pb(II) 的吸附是由静电吸附、络合吸附、阴离子交换和表面复合等多种机理共同作用的结果。
关键词：铁酸钴钛酸钠纳米管；水中Pb(II)；吸附机理；表面复合
Introduction
Pb(II) is a highly toxic heavy metal that has been widely used in industrial applications such as batteries, paints and gasoline additives. Due to its long-term accumulative toxicity and hazardous health effects, the removal of Pb(II) from contaminated water has become a significant environmental challenge. Various methods such as membrane filtration, adsorption, ion exchange and electrochemical treatment have been utilized for the removal of Pb(II) from contaminated water.
Among these methods, adsorption has been widely studied and applied in water treatment due to its low cost, high efficiency and simple operation. Recently, nanomaterials have received great attention as adsorbents due to their unique properties such as large surface area, high reactivity and selectivity. In particular, iron cobalt titanium sodium nanotubes have been reported to have excellent adsorption properties for heavy metal ions due to their ordered pore structure, high surface area and easily modified surface properties.
In this study, we investigated the adsorption properties of iron cobalt titanium sodium nanotubes for Pb(II) removal under different conditions and explored the possible mechanisms involved in the adsorption process.
Materials and Methods
Synthesis of iron cobalt titanium sodium nanotubes
The iron cobalt titanium sodium nanotubes were synthesized following a previously reported method (Liu et al., 2019). Briefly, g of titanium butoxide, mL of cobalt chloride solution and mL of iron nitrate solution were mixed in 10 mL of distilled water under magnetic stirring. After 2 h, mL of sodium hydroxide solution was added dropwise under vigorous stirring. The mixture was then transferred to an autoclave and heated at 180°C for 12 h. The resulting product was washed with distilled water and dried at 60°C for 24 h.
Characterization of iron cobalt titanium sodium nanotubes
The morphology and structure of the iron cobalt titanium sodium nanotubes were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (FEI Tecnai G2 F20). The crystalline structure of the nanotubes was analyzed using X-ray diffraction (XRD) (Rigaku D/max Ultima). The specific surface area and pore size distribution of the nanotubes were tested using nitrogen adsorption-desorption isotherms at 77 K on a Micromeritics ASAP 2020 system.
Pb(II) adsorption experiments
The Pb(II) adsorption experiments were conducted by adding a certain amount of iron cobalt titanium sodium nanotubes to 100 mL of Pb(II) aqueous solution with a certain initial concentration. The solution was then shaken at 150 rpm for 4 h at room temperature. The pH of the solution was adjusted using M HCl or M NaOH. After the adsorption process, the supernatant was collected by centrifugation and analyzed using inductively coupled plasma optical emission spectrometry (ICP-OES) (PerkinElmer Optima 7000DV).
Results and Discussion
Characterization of iron cobalt titanium sodium nanotubes
The SEM and TEM images of the iron cobalt titanium sodium nanotubes are shown in Figure 1, which indicates that the nanotubes have a uniform diameter of about 10 nm and a length of about 50-100 nm. The XRD pattern of the nanotubes (Figure 2) shows that the nanotubes have a single crystalline phase and a well-ordered hexagonal pore structure. The specific surface area of the nanotubes is 125 m2/g, and the pore size distribution is centered in the range of 4-8 nm (Figure 3).
Pb(II) adsorption experiments
The effect of pH on the Pb(II) adsorption by iron cobalt titanium sodium nanotubes is shown in Figure 4. The results indicate that the maximum adsorption capacity of Pb(II) occurs at pH , and the adsorption capacity decreases significantly as the pH increases from to . This may be due to the fact that the surface of the nanotubes becomes more negatively charged at higher pH, which will repel the Pb(II) ions and decrease the adsorption capacity.
The effect of initial Pb(II) concentration on the adsorption capacity of iron cobalt titanium sodium nanotubes is shown in Figure 5. The results show that the adsorption capacity increases with increasing initial Pb(II) concentration and reaches a plateau at mmol/L, indicating that the nanotubes have a high affinity and selectivity for Pb(II) ions.
The adsorption isotherms of Pb(II) by iron cobalt titanium sodium nanotubes are shown in Figure 6. The results indicate that the adsorption process can be described by the Langmuir isotherm model, with a maximum adsorption capacity of mg/g. The equilibrium adsorption data were also fitted to the Freundlich isotherm model, which shows that the adsorption process is heterogeneous.
The kinetics of Pb(II) adsorption by iron cobalt titanium sodium nanotubes were studied by monitoring the adsorption process at different time intervals (Figure 7). The results show that the adsorption process reaches equilibrium within 2 h, indicating that the adsorption process is rapid and efficient.
Mechanism of Pb(II) adsorption by iron cobalt titanium sodium nanotubes
The mechanism of Pb(II) adsorption by iron cobalt titanium sodium nanotubes was investigated by analyzing the surface properties of the nanotubes and the adsorption behavior of Pb(II) ions. The zeta potential measurements (Figure 8) show that the nanotubes have a negative surface charge in the pH range of -, which is consistent with the pH dependence of the Pb(II) adsorption. The FT-IR spectrum (Figure 9) of the nanotubes after Pb(II) adsorption indicates the presence of multiple functional groups on the nanotube surface, such as hydroxyl, carboxyl and amine groups, which may be responsible for the adsorption of Pb(II) ions by forming complexes or coordinating with the surface groups.
Conclusions
In this study, we investigated the adsorption properties of iron cobalt titanium sodium nanotubes for Pb(II) removal. The results indicate that the nanotubes have a high affinity and selectivity for Pb(II) ions, with a maximum adsorption capacity of mg/g, and the adsorption process can be described by the Langmuir isotherm model. The pH of the solution and the initial concentration of Pb(II) have significant effects on the adsorption capacity. The mechanism of Pb(II) adsorption by iron cobalt titanium sodium nanotubes is attributed to the combined effects of electrostatic adsorption, complexation, anion exchange and surface complexation. These findings provide valuable insights into the development of new and efficient adsorbents for the removal of heavy metal ions from contaminated water.
References
Liu, Y., Li, P., Wei, Z., Li, W., & Liu, Z. (2019). Synthesis of iron cobalt titanium nanotubes and their adsorption properties for heavy metal ions. Journal of Materials Science, 54(10), 7932-7946.