磁性水滑石的制备、表征及其吸附刚果红的应用研究

The preparation and characterization of Fe_3O_4-layered double hydroxide composite and its application for the removal of Congo red

[目的]采用水热法制备磁性水滑石材料(MNP-LDH),并以该材料作为吸附剂来吸附水体中的刚果红染料,探究其脱附和循环利用性,同时制备磁纳米四氧化三铁(MNP)和水滑石(LDH)作为对照。[方法]采用扫描电子显微镜、透射电子显微镜、红外光谱、比表面积测定仪以及X射线衍射仪对上述材料进行表征;采用静态吸附的方法,以紫外可见分光光度计为检测手段,考察了pH、吸附时间和初始浓度等对材料吸附性能的影响;采用Langmuir吸附等温模型和准二级动力学吸附模型对上述材料进行了热力学和动力学模拟研究;以氢氧化钠为洗脱剂,对MNP-LDH进行了脱附和循环利用性研究。[结果]1)由电子显微镜图谱可以看出:MNP-LDH与MNP均呈规则的球型结构,粒径同为100 nm左右,MNP-LDH形成的孔径较裸露的MNP更小;MNP-LDH与LDH的红外光谱图中400~600 cm^(-1)的吸收峰代表Fe—O、Al—O及Mg—O的伸缩振动和弯曲振动,1 300 cm^(-1)附近的吸收峰对应C—O的伸缩振动,3 400 cm^(-1)左右的峰归属于O—H伸缩振动。X射线衍射光谱图显示:MNP-LDH以及MNP都为Fe_3O_4晶型,且出现了MNP-LDH的特征峰;MNP-LDH的单点BET比表面积远大于LDH的单点BET比表面积。2)当pH值从2增至4时,材料对水中刚果红的吸附能力随之明显降低,当pH值达到4以后,吸附容量基本保持平衡,且MNP-LDH的吸附容量大于MNP和LDH的吸附容量。3)随着刚果红初始质量浓度增大,MNP-LDH和MNP对刚果红的吸附容量也不断增大,当质量浓度达到100 mg·L^(-1)后,材料达到吸附饱和。4)随着超声时间延长,MNP-LDH的吸附容量不断增加,10 min以后,材料对不同初始质量浓度刚果红的吸附都达到平衡。5)MNP-LDH和MNP对刚果红的吸附符合Langmuir等温吸附模型和准二级动力学吸附模型。6)0.1 mol·L^(-1)的氢氧化钠可以定量洗脱刚果红,且材料可循环使用4次而脱附率基本没有变化。7)将本材料应用于某工业废水中刚果红的去除分析,待测物的回收率为113%,说明本材料可有效去除实际水样中的刚果红。[结论]在pH2.5,刚果红初始质量浓度为150 mg·L^(-1),超声时间为15 min的条件下,MNP-LDH可以达到最大吸附容量265.96 mg·g^(-1);MNP-LDH具有良好的再生性。

[Objectives]In this paper,a new kind of Fe3O4-layered double hydroxide composite（MNP-LDH） was prepared by hydrothermal method and it was used as adsorbent to remove Congo red in the aqueous solution.For comparison,the magnetic Fe3O4 nanoparticles（MNP） and Mg-Al hydrotalcite（LDH） were prepared in the same time.[Methods]The absorbents were characterized by scanning electron microscope（SEM）,transmission electron microscope（TEM）,fourier transform infraredspectroscopy（FT-IR）,BET surface analyzer and X ray diffraction spectroscopy（XRD）.The effects of pH,the initial concentration of Congo red and ultrasonic time on the adsorption rate of Congo red using static adsorption method were investigated in this study.The Congo red concentrations were determined using spectrophotometry.The Langmuir isotherm model was used for the isotherm study and the pseudo-second-order kinetic model was used to study the sorption kinetics.The desorption and regeneration of MNP-LDH was also evaluated.[Results]1） From SEM and TEM,MNP-LDH and MNP were regular spherical structure and these particle sizes were both about 100 nm.The pore size of MNP-LDH was smaller than that of MNP.The peaks at 400-600 cm^-1 observed in infrared spectrums were related to Fe—O,Al—O and Mg—O,the peak at 1 300 cm^-1 was related to C—O and the peak at 3 400 cm^-1 was ascribed to O—H.The X-ray diffraction spectrum results showed that both materials had Fe3 O4 crystal and the characteristic peak of MNP-LDH was showed.The single point specific surface area of LDH was smaller than that of MNP-LDH.2） The adsorption capacity of Congo red decreasedrapidly with the enhancing pH from 2 to 4 for MNP-LDH,MNP and LDH and then remained constant.The adsorption capacity of MNP-LDH was higher than that of MNP and LDH.3） The adsorption capacity of MNP-LDH and MNP increased with the increasing of the initial concentration of Congo red.After the initial concentration reached 100 mg·L^-1,the materials reached adsorption saturation.4） The adsorption capacity of MNP-LDH increased with the increasing of the reaction time.After the reaction time reached 10 min,MNP-LDH reached adsorption equilibrium.5） The experimental data fited well with the Langmuir adsorption isotherm and the pseudo-second-order kinetic model.6） The effect of Na OH on desorption of Congo red was studied in this experiment.The spent MNP-LDH could be refreshed by 0.1 mol·L^-1 Na OH and it could be reused for four times without any decrease of desorption rate.7） The prepared material was applied for the removal of Congo red and the recovery for the spiked industrial waste water sample was 113%,which indicated that the material in this work could remove Congo red from the water sample effectively.[Conclusions]The maximum adsorption capacity of MNP-LDH can be 265.96 mg·g^-1 when pH value is 2.5,reaction time is 15 min and the initial concentration of Congo red is 150 mg·L^-1.Moreover,MNP-LDH has good reuse property,which displays that it is an excellent adsorption material.