EDTA-nSiO_2纳米颗粒对Cd^(2+)的吸附

Adsorption Cd^(2+) from Solution by EDTA-modified Silicate Nanoparticles

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.

Silicate nanoparticles（ nSiO2） are a kind of widely used engineering material. In order to improve the Cd^2＋adsorption ability,the EDTA-modified nSiO2 nanoparticles were prepared by grafting method and characterized by TEM,N2adsorption-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. Cd^2＋adsorption was mainly controlled by solution pH. The raw nSiO2 had limited Cd^2＋adsorption ability,while the EDTA-modified nSiO2 particles had significantly improved adsorption performance. At high pH,the Cd^2＋adsorption rate increased and kept balance above pH 4. 0. The Cd^2＋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 Cd^2＋adsorption. The Cd^2＋adsorption decreased from 0. 433 to 0. 294 mmol·g^-1,when Na Cl concentration varied from 0 to 100 mmol·L^-1. The desorption of Cd^2＋from the EDTA-nSiO2 nanoparticles was carried out with distilled water,0. 1 mol·L^-1Na Cl and 0. 1 mol·L^-1 HCl. The maximum Cd^2＋desorption of 94. 36% was obtained at 0. 1 mol·L^-1HCl. Based on the results of thermodynamics,pH,ionic strength,and XPS analysis,it could be concluded that Cd^2＋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 Cd^2＋ adsorption.