EDTA-nSiO2纳米颗粒对Cd2+的吸附

nSiO_2纳米颗粒是一种广泛应用的工程纳米材料,为增加其对水溶液中Cd~(2+)的吸附性能,采用接枝改性的方法制备出乙二胺四乙酸(EDTA)改性nSiO_2纳米颗粒(EDTA-nSiO_2),并用透射电镜、氮气吸附-解吸、红外光谱和差热分析等手段对其进行了结构表征,同时以其为吸附剂,通过批处理实验法探讨了体系pH、吸附时间、温度、离子强度等因素对Cd~(2+)吸附的影响,并结合X射线能谱(XPS)分析对其吸附机制进行了分析.结果表明,以EDTA为改性剂,可以成功制备出稳定性良好的EDTA-nSiO_2纳米颗粒,其对Cd~(2+)的吸附受体系p H控制;nSiO_2对Cd~(2+)的吸附量较小,EDTA改性可增加nSiO_2对Cd~(2+)的吸附作用,随着p H的升高,Cd~(2+)的吸附效果逐渐增强,在p H大于4.0后逐渐趋于稳定.EDTA-nSiO_2对Cd~(2+)的吸附速率较快,可在1 h内达到吸附平衡.EDTA-nSiO_2对Cd~(2+)的吸附为吸热的自发过程,吸附等温线可用Langmuir模型描述.NaCl浓度增加会导致Cd~(2+)的吸附量下降,当体系Na Cl浓度从0增加到100 mmol·L~(-1),Cd~(2+)的最大吸附量从0.433 mmol·g-1降低至0.294mmol·g-1.0.1 mol·L~(-1)HCl是较为合适的吸附剂再生液,Cd~(2+)洗脱率约94.36%.结合pH、温度、离子强度、再生和XPS分析结果,可以推测出EDTA-nSiO_2对Cd~(2+)的吸附是包含有简单的物理吸附和离子交换过程,并以化学络合为主的吸附过程.EDTA-nSiO_2是一种对水体Cd~(2+)具有较好吸附能力的工程纳米材料吸附剂.

Adsorption Cd2+ from Solution by EDTA-modified Silicate Nanoparticles

Silicate nanoparticles(nSiO₂) are a kind of widely used engineering material. In order to improve the Cd²⁺ adsorption ability, the EDTA-modified nSiO₂ nanoparticles were prepared by grafting method and characterized by TEM, N₂ adsorption-desorption, FTIR, and TGA. The effects of solution pH, contact time, temperature and ionic strength were examined. The adsorption mechanism was further investigated by XPS. The results showed that the EDTA-nSiO₂ nanoparticles possessed excellent stability, and were successfully prepared. Cd²⁺ adsorption was mainly controlled by solution pH. The raw nSiO₂ had limited Cd²⁺ adsorption ability, while the EDTA-modified nSiO₂ particles had significantly improved adsorption performance. At high pH, the Cd²⁺ adsorption rate increased and kept balance above pH 4.0. The Cd²⁺ adsorption was an endothermic spontaneous process which could be finished within 1 h. Langmuir model could be used to describe the adsorption isotherm. The temperature ranged from 293-313 K during the process, while the maximum adsorption was observed at higher temperature. Higher ionic strength could inhibit the Cd²⁺ adsorption. The Cd²⁺ adsorption decreased from 0.433 to 0.294 mmol·g^-1, when NaCl concentration varied from 0 to 100 mmol·L^-1. The desorption of Cd²⁺ from the EDTA-nSiO₂ nanoparticles was carried out with distilled water, 0.1 mol·L^-1 NaCl and 0.1 mol·L^-1 HCl. The maximum Cd²⁺ desorption of 94.36% was obtained at 0.1 mol·L^-1 HCl. Based on the results of thermodynamics, pH, ionic strength, and XPS analysis, it could be concluded that Cd²⁺ adsorption was a multiple process dominated by chemical chelating reaction, physical adsorption and ion exchange. This study indicated that the EDTA-nSiO₂ is an effective engineering nanomaterial that could be used in Cd²⁺ adsorption.