Preparation and Characterization of Sulfhydryl Modified Palygorskite and Their Application for Cadmium Adsorption
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摘要: 为明确巯基改性坡缕石(MPAL)作为修复材料对Cd的吸附机制以及其在修复Cd污染土壤中的应用潜力，以坡缕石(PAL)为原料，通过高速剪切凝胶法制备MPAL作为钝化剂开展吸附试验与土壤钝化试验，研究MPAL对Cd的吸附效果. 通过X射线衍射(XRD)、BET孔结构分析、傅里叶红外光谱(FTIR)、扫描电子显微镜(SEM)以及X射线光电子能谱(XPS)对吸附前后的样品进行表征，探讨其吸附机制. 结果表明：PAL和MPAL均能有效吸附水溶液中的Cd2+，MPAL吸附效果优于PAL. 拟二级动力学模型更适合描述Cd2+在PAL和MPAL上吸附量的动态变化过程，MPAL约90 min达到吸附平衡，相比于PAL能更加迅速达到吸附平衡. Freundlich等温吸附模型能够更好地描述吸附数据特征，在试验条件下，MPAL的饱和吸附容量为44.41 mg/g，明显高于PAL的饱和吸附容量(33.65 mg/g). MPAL在投加量为0.1%~0.3%时可使土壤DTPA提取态Cd含量降低53.45%~78.43%. XRD衍射峰分析、FTIR官能团振动模式分析以及XPS关键元素结合能分析结果显示，PAL主要通过表面羟基与Cd2+形成表面络合来吸附Cd，而MPAL还提供了大量巯基官能团作为吸附位点，通过表面的羟基和巯基与Cd2+发生络合反应形成络合沉淀. 研究显示，MPAL对Cd的吸附能力更强，是一种在Cd污染农田土壤上具有良好应用潜力的高效钝化剂.Abstract: In order to understand the adsorption mechanism of Cd by sulfhydryl modified palygorskite (MPAL) as a remediation material and its application potential in the remediation of Cd-contaminated soil, MPAL was prepared by high speed shear gel method using palygorskite (PAL) as raw material to carry out adsorption experiments and soil passivation experiments, and the adsorption effect of MPAL on Cd was studied. X-ray diffraction (XRD), BET pore structure analysis, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the samples before and after adsorption, and to explore the adsorption mechanism. The results showed that both PAL and MPAL could effectively adsorb Cd2+ in aqueous solution, and the adsorption effect of MPAL was better than PAL. The pseudo second order kinetics model is more suitable to describe the dynamic change process of Cd2+ adsorption on PAL and MPAL. MPAL reaches the adsorption equilibrium in about 90 minutes, which is faster than PAL. Freundlich isotherm absorption can describe the adsorption data better. Under the experimental conditions, the saturated adsorption capacity of MPAL is 44.41 mg/g, which is significantly higher than that of PAL (33.65 mg/g). The DTPA extractable Cd concentrations in soil can be reduced by 53.45%-78.43% when the dosage of sulfhydryl modified palygorskite is 0.1%-0.3%. X-ray diffraction peak analysis, FTIR functional group vibration mode analysis and binding energy analysis of key elements of XPS showed that PAL adsorbed Cd through the formation of surface complexation between the surface hydroxyl group and Cd2+, while MPAL also provided a large number of sulfhydryl functional groups as adsorption sites, and formed complexation precipitation through the complexation reaction between the surface hydroxyl group and the sulfhydryl group and Cd2+. The study showed that MPAL has stronger adsorption capacity for Cd, and it is an efficient passivating agent with good application potential in Cd polluted farmland soil.
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Key words:
- palygorskite /
- cadmium /
- adsorption /
- hydroxyl group /
- sulfhydryl group
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图 2 Cd2+在PAL和MPAL上的等温吸附模型拟合线
Figure 2. Adsorption isotherms of Cd2+ adsorption on PAL and MPAL
图 3 不同处理土壤中DTPA提取态Cd含量的变化
Figure 3. Soil DTPA extractable Cd concentrations after different treatments
图 6 PAL和MPAL及其吸附Cd后的FTIR图谱
Figure 6. FTIR spectra of PAL, MPAL and adsorption products
图 9 Cd2+在PAL和MPAL上的吸附机理示意
Figure 9. Schematic of sorption mechanisms of Cd2+ on PAL and MPAL
表 1 Cd2+在PAL和MPAL上的吸附动力学参数
Table 1. Adsorption kinetic parameters of Cd2+ adsorption on PAL and MPAL
钝化材料 拟一级动力学模型 拟二级动力学模型 qm1/(mg/g) k1/min−1 R2 qm2/(mg/g) k2/[g/(mg·min)] R2 PAL 6.87±0.16 0.331±0.074 2 0.947 32 7.08±0.13 0.095±0.026 4 0.97244 MPAL 8.25±0.13 0.31±0.045 0.974 85 8.47±0.08 0.081±0.011 3 0.99306 
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表 2 Cd2+在PAL和MPAL上的等温吸附模型拟合参数
Table 2. Isotherm parameters of Cd2+ adsorption on PAL and MPAL
钝化材料 Langmuir等温吸附模型 Freundlich等温吸附模型 Qm/(mg/g) k/(L/mg) R2 KF/(L/g) n R2 PAL 33.65±2.30 0.07±0.02 0.966 89 5.80±0.61 2.74±0.19 0.986 92 MPAL 44.41±5.33 0.06±0.03 0.938 31 12.01±1.12 3.96±0.38 0.979 57
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表 4 PAL和MPAL及其吸附产物的XRD参数
Table 4. XRD indexes of PAL, MPAL and adsorption products
hkl PAL MPAL PAL-Cd MPAL-Cd 2θ/(°) d(Å) 2θ/(°) d(Å) 2θ/(°) d(Å) 2θ/(°) d(Å) (110) 8.49 10.395 9 8.42 10.482 6 8.38 10.531 8 8.39 10.524 4 (040) 19.69 4.504 3 19.71 4.498 5 19.75 4.490 6 19.63 4.517 9 (121) 20.90 4.246 6 20.79 4.268 0 20.84 4.257 1 20.86 4.253 9 (221) 24.03 3.699 0 24.02 3.701 7 24.07 3.693 7 23.98 3.707 6 (231) 26.61 3.346 4 26.59 3.348 5 26.65 3.341 1 26.59 3.348 5 (331) 30.91 2.890 5 30.87 2.893 6 30.93 2.888 0 30.88 2.892 7 a1) — 12.830 4 — 12.854 7 — 12.782 5 — 12.843 4 b1) — 17.886 3 — 17.962 4 — 17.936 2 — 17.951 7 c1) — 5.209 4 — 5.199 4 — 5.206 7 — 5.198 1 注：1)晶格常数a、b和c由Jade 6.5根据峰值位置和米勒指数计算得到.
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表 5 PAL和MPAL的N2吸附-脱附分析结果
Table 5. Analysis results of N2 adsorption-desorption of PAL and MPAL
钝化材料 BET表面积/(m2/g) 总孔体积/(cm3/g) 平均孔径/nm 微孔体积/(cm3/g) 微孔面积/(m2/g) 外表面积/(m2/g) PAL 111.84 0.16 7.98 0.012 709 28.673 8 83.165 4 MPAL 88.70 0.14 11.32 0.004 881 10.041 8 78.659 5
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表 6 PAL和MPAL及其吸附产物的XPS参数
Table 6. XPS indexes of PAL, MPAL and adsorption products
材料 Al2p Si2p O1s S2p Cd3d3/2 结合能/eV 原子比/% 结合能/eV 原子比/% 结合能/eV 原子比/% 结合能/eV 原子比/% 结合能/eV 原子比/% PAL 74.77 5.19 102.88 16.13 532.03 53.35 — — — — PAL-Cd 74.45 6.48 102.89 19.14 532.01 58.81 — — 413.39 0.26 MPAL 74.82 4.74 102.98 14.71 532.15 47.04 163.81 2.30 — — MPAL-Cd 74.96 5.00 103.11 16.31 532.26 50.88 164.01 1.70 412.78 0.46
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