Preparation of fibrous magnetic titania composites and their adsorption behavior for La3+
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摘要: 为富集回收低浓度矿山尾水中稀土资源,采用溶胶-凝胶法和水热法制备了纤维状外壳的磁性二氧化钛复合材料Fe3O4@fTiO2,利用SEM、TEM、XPS、FTIR和XRD对材料进行表征,考察了Fe3O4@fTiO2对稀土La3+的吸附行为。结果表明:Fe3O4@fTiO2是外壳为纤维状的核壳结构磁性复合材料;吸附剂具有良好的超顺磁性,饱和磁化强度高达30.81 emu·g−1;在15℃、pH=5的酸性条件下,Fe3O4@fTiO2对稀土La3+在15 min内达到吸附平衡,且符合伪一级动力学模型;Langmuir等温吸附模型能较好地描述吸附La3+过程,理论吸附容量为142.88 mg·g−1;Fe3O4@fTiO2在NaOH的再生下循环利用5次时的吸附量为110 mg·g−1,是首次吸附容量的73.8%,表现出良好的循环利用性。Abstract: In order to enrich and recover rare earth resources in low-concentration mine tail water, a fibrous shell magnetic titanium dioxide composite Fe3O4@fTiO2 was prepared by using sol-gel method and hydrothermal methods. The material was analyzed by SEM, TEM, XPS, FTIR and XRD. The adsorption behavior of Fe3O4@fTiO2 for rare earth La3+ was investigated. The results show that Fe3O4@fTiO2 is a core-shell magnetic composite with a fibrous shell. The adsorbent has good superparamagnetic properties, and the saturation magnetization is as high as 30.81 emu·g−1. At pH=5 and 15℃, Fe3O4@fTiO2 reaches the adsorption equilibrium for rare earth La3+ within 15 min, and conformes to the pseudo-first-order kinetic model. The Langmuir isotherm adsorption model can describe the adsorption process of La3+ well, with the theoretical adsorption capacity of 142.88 mg·g−1. With NaOH solution as the regeneration reagent, the adsorption capacity of Fe3O4@fTiO2 is 110 mg·g−1 after cyclic adsorption/desorption for 5 times, which is 73.8% of the initial value, showing the good cyclic utilization.
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Key words:
- fibrous /
- magnetic /
- titanium dioxide /
- adsorption /
- rare earth
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图 1 Fe3O4 ((a), (d))、Fe3O4@TiO2 ((b), (e)) 和Fe3O4@fTiO2 ((c), (f)) 的SEM及TEM图像;(g) Fe3O4@fTiO2的HRTEM图像;(h) Fe3O4@fTiO2的EDS图谱
d—Interlayer spacing
Figure 1. SEM and TEM images of Fe3O4 ((a), (d)), Fe3O4@TiO2 ((b), (e)) and Fe3O4@fTiO2 ((c), (f)); (g) HRTEM image of Fe3O4@fTiO2; (h) EDS pattern of Fe3O4@fTiO2
表 1 Fe3O4@fTiO2吸附La3+动力学模型的拟合参数
Table 1. Fitting parameters for kinetic models of La3+ adsorption onto Fe3O4@fTiO2
Model k/min−1 qe/(mg·g−1) R2 Pseudo-first-order 0.3036 104.001 0.957 Pseudo-second-order 0.0036 112.663 0.912 Notes: k—Pseudo-first-order kinetic and Pseudo-second-order kinetic constants; R2—Correlation coefficient. 表 2 Fe3O4@fTiO2吸附La3+颗粒的内扩散模型的拟合参数
Table 2. Intra-particle diffusion model parameters of adsorption La3+ on Fe3O4@fTiO2
Model Parameter kid/(mg·min1/2·g−1) cid/(mg·g−1) R2 Boundary layer
diffusion stage67.12 −49.99 0.980 Intragranular
diffusion stage9.01 67.01 0.962 Equilibrium stage 0.33 101.30 0.870 Notes: kid—Intraparticle diffusion rate constant; cid—Constant related to boundary layer thickness. 表 3 Fe3O4@fTiO2在不同pH下上清液的离子组分
Table 3. Ionic components of supernatants of Fe3O4@fTiO2 at different pH
mg/L pH Fe Ti Na La 2 0.93 1.72 25.40 259.82 4 − 0.12 48.50 181.58 6 − 0.13 44.50 143.58 表 4 Fe3O4@fTiO2吸附La3+等温线模型的拟合参数
Table 4. Fitting parameters for isotherm models of La3+ adsorption onto Fe3O4@fTiO2
Langmuir Freundlich KL/min−1 qm/(mg·g−1) R2 Kf/(mg·g−1) n R2 0.01846 142.88 0.979 18.6652 3.276 0.937 Notes: KL—Langmuir coefficient of distribution of the adsorption; qm—Langmuir adsorption maximum; Kf—Freundlich coefficient of distribution of the adsorption; n—Freundlich constant related to adsorption strength. 表 5 La3+在Fe3O4@fTiO2上吸附的热力学参数
Table 5. Thermodynamic parameters of adsorption of La3+ on Fe3O4@fTiO2
Temperature
T/KKT ΔGθ/
(kJ·mol−1)ΔHθ/
(kJ·mol−1)ΔSθ/
(J·mol−1·K−1)288 1.42×105 −28.41 14.88 149.82 303 1.59×105 −30.18 318 2.57×105 −32.94 Notes: KT—A dimensionless parameter calculated using the Langmuir constant KL according to equation (11); ΔGθ—Gibbs free energy; ΔHθ—Enthalpy; ΔSθ—Entropy. 表 6 Fe3O4@fTiO2吸附La3+前后表面元素的原子分数参数
Table 6. Atomic fraction of elements on the surface of Fe3O4@fTiO2 before and after La3+ adsorption
Element La/at% Ti/at% O/at% C/at% Fe/at% Na/at% Before adsorption 0.00 16.60 41.30 26.04 4.00 12.07 After adsorption 2.79 17.34 44.54 31.84 3.49 0.00 表 7 不同吸附剂对La3+吸附能力的比较
Table 7. Comparison of La3+ adsorption capacity among different adsorbents
Materials qm/(mg·g−1) t/min pH Ref. PAMAM 50.12 240 7 [45] LA-IIP 62.80 30 4 [46] ZnO NPs 58.80 70 5 [47] SnO2-TiO2 NPs 65.60 60 5 [48] Activated carbon 175.40 60 3.5 [49] Fe3O4@fTiO2 142.90 15 5 This work Notes: t—Reaction time; PAMAM—Straw grafted with polyamide amine dendritic macromolecules; LA-IIP—Novel La(III) imprinted polymers; NPs—Nanocomposite. -
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