镁铝水滑石去除氯离子性能研究

利用水滑石(LDH)焙烧后在一定条件下可重新吸收水和阴离子,从而部分恢复层状结构的结构记忆效应,研究了焙烧镁铝碳酸根水滑石(CLDH)在处理含氯废水中的应用.实验表明,当CLDH镁铝比为4:1、焙烧温度为500℃、水滑石质量浓度为2.0 g/L、处理温度为30℃时,CLDH对氯离子的处理效果最佳.     

焙烧水滑石对Cr(Ⅵ)的去除性能研究

采用共沉淀法制备了Mg/Al-CO3水滑石,经焙烧得CLDH,用傅里叶红外光谱仪对物相进行表征;利用水滑石焙烧后在一定条件下可重新吸收水和阴离子,从而部分恢复层状结构的结构记忆效应,考察了不同温度焙烧的水滑石去除铬离子[Cr(Ⅵ)]的性能。实验结果表明,400℃下焙烧的水滑石对Cr(Ⅵ)的去除率最高。     

焙烧镁铝碳酸根水滑石对氯离子吸附机理研究

对焙烧镁铝碳酸根水滑石(CLDH)去除氯离子的机理进行了基础研究。热力学计算结果表明,CLDH对氯离子的吸附过程符合Freundlich和Langmuir等温式。从Langmuir等温式计算的ΔrH,ΔrS,为负值,表明吸附过程为放热、熵减小的过程,这是因为CLDH恢复了层状结构;不同温度下ΔrG为负值,表明吸附过程是自发进行的。动力学计算吸附过程的活化能Ea=43.8kJ/mol,表明吸附过程以化学吸附为主。     

焙烧水滑石对氯离子的去除性能研究

采用晶核／隔离法制备水滑石，并用X射线衍射技术对样品物相表征；利用水滑石焙烧后在一定条件下可重新吸收水和阴离子，从而部分恢复层状结构的结构记忆效应，考察了不同温度焙烧的水滑石去除氯离子的性能。实验结果表明，400℃下焙烧的水滑石对氯离子的去除率最高，达到39．0％。     

热处理水滑石对普通硅酸盐水泥和碱矿渣水泥抗碳化性能的影响

热处理水滑石(CLDH)由水滑石(LDH)在一定温度制度下焙烧得到.采用X射线衍射(XRD)分析方法,分别研究了普通硅酸盐水泥(OPC)和碱矿渣水泥(ASC)的模拟孔溶液掺入的CLDH在碳化环境中的结构重建现象.分析结果表明:在上述两种溶液中,CLDH可以吸附大量的CO2,均具有较强的结构重建能力.证明了CLDH通过离子交换原理改善OPC及ASC抗碳化性能的可行性.将CLDH分别掺入普通硅酸盐水泥胶砂(OPCM)和碱矿渣水泥胶砂(ASCM),研究了CLDH对所制备胶砂的碳化深度以及碳化前后的抗折、抗压强度.试验结果表明:CLDH显著改善OPC的抗碳化性能,且最适宜掺量为2％;但对ASC的抗碳化性能改善作用有限,且对抗折强度不利.     

焙烧态MCNOs/LDH复合材料的制备及其对水体F-去除的研究

采用水热法制备磁性纳米洋葱碳/层状双金属氢氧化物(MCNOs/LDH)复合材料,高温煅烧制备了焙烧态MCNOs/LDH复合材料(MCNOs/CLDH),并通过正交试验确定最佳煅烧工艺参数。利用XRD、FT-IR、SEM、N2吸附-脱附(BET)和VSM等对其结构形貌进行表征,并通过静态吸附实验考察MCNOs/CLDH对F-的吸附性能。结果表明,在焙烧温度为550℃、焙烧时间为2 h的最佳条件下制备的MCNOs/CLDH对F-的吸附容量为28.95 mg/g,去除效率为57.9%。此外,结合MCNOs/CLDH吸附F-后的XRD分析可知,吸附机理包括表面吸附、离子交换和混合金属氧化物的再水化以及氟离子向层间区域的嵌入,从而重建原始的LDH结构。     

基于BP神经网络预测模型的CLDH/PP复合材料制备

采用超声波辐射对水滑石(LDH)进行离子交换有机改性。基于正交设计试验结果,以p H值、温度、时间、超声功率为四个输入量,以插层率为输出量,建立3层反向传播(BP)神经网络模型,对其进行训练和预测性能检验,并用以预测超声有机改性水滑石(CLDH)制备的条件。研究表明,与未改性水滑石/聚丙烯(LDH/PP)相比,CLDH在PP基体中团聚现象基本消失,与PP基体相容性增加,因此有利于提高聚丙烯的性能。     

不同形貌镁铝水滑石的可控合成及其对氯离子的吸附性能

以硝酸镁、硝酸铝为原料,尿素为沉淀剂,采用水热法在不同条件下合成了不同形貌的镁铝水滑石LDH-1、LDH-2、LDH-3。通过SEM、XRD、BET和EDS对合成的样品进行了表征;考察了不同形貌水滑石及其焙烧产物(LDO-1、LDO-2、LDO-3)对溶液中氯离子的吸附性能。结果表明:采用水热法添加乙二醇可合成棒状镁铝水滑石(LDH-1),添加乙醇可合成片状六边形镁铝水滑石(LDH-2),添加四丙基氢氧化铵可合成立方体镁铝水滑石(LDH-3)。其中,LDH-2形貌规整均一,片间形成交叉支撑结构,比表面积为115.311 m2/g,在室温条件下,其对氯离子的最大吸附量为24.72 mg/g。LDO-2吸附氯离子的最优操作条件:温度为35℃,pH值为8,焙烧温度为450℃。在此条件下,焙烧产物(LDO-2)吸附氯离子的能力大大增强,最大吸附量为96.07 mg/g。     

沉淀法去除废水中氯离子的应用对比分析

对不同沉淀法采用的机理、应用条件进行对比,结果表明,银量法和汞量法由于自身特点,仅能用于测试滴定;氯化亚铜法主要应用于低氯离子浓度的冶金、采矿等行业,氟硅酸铅法也是如此;水滑石(LDH)因后续焙烧,造成去除氯离子的成本过高而无法实现产业化;超高石灰铝法依靠原料价格低廉,氯离子去除率高,且形成的沉淀物作为重金属离子的吸附剂使用,具备产业化前景.     

去除水中腐殖酸的磁性焙烧态类水滑石制备与表征

采用共沉淀法一步合成系列类水滑石负载磁性粒子的颗粒,经煅烧得到磁性焙烧产物.利用焙烧产物吸附水中腐殖酸,得到磁性焙烧态锌铝类水滑石去除腐殖酸效果较好.考察了磁性焙烧态锌铝类水滑石制备条件对腐殖酸去除效果的影响,通过正交试验优化了制备条件.静态吸附实验表明:吸附剂投加量0.2 g/L, 30 min内20 mg/L腐殖酸去除率为97.96%.X射线衍射(XRD)、红外光谱(FT-IR)、热重-差热(TG-DSC)和比表面积(SSA)表征结果表明:一定量的磁性基质掺入并没有破坏锌铝类水滑石典型的层状结构;焙烧态产物为氧化物,磁性保持良好;比表面积达80.00 m2/g.磁性焙烧态锌铝类水滑石在水中因"记忆效应"而结构重建通过表面吸附和腐殖酸结构中小尺寸的官能团插层快速去除腐殖酸.     

EDTA插层水滑石的合成及其对Cd2+的去除性能研究

利用EDTA对重金属离子的螯合作用,将其作为有机阴离子插入到镁铝水滑石的层间,采用共沉淀法制备了复合层状材料EDTA.Mg-Al LDH。通过正交实验确定了NaOH投加量为理论计算值的1.2倍时,合成物的层间阴离子以EDTA4-形式稳定存在。EDTA.Mg-Al LDH处理56 mg/LCd2+溶液的最佳处理条件为:水滑石质量浓度5.0 g/L,反应时间60 min,去除率可达98.20%。并与以无机阴离子Cl-作为插入离子制备的Cl.Mg-Al LDH对56 mg/L的Cd2+溶液的去除率进行了比较,由于层间阴离子EDTA4-对重金属强烈的螯合能力,EDTA.Mg-Al LDH对水中Cd2+的去除效率大大高于Cl.Mg-Al LDH。     

Thermal,optical and dielectric properties of Zn–Al layered double hydroxide

Zn–Al–NO₃–layered double hydroxide (Zn–Al–NO₃–LDH) was prepared by the co-precipitation method at a constant pH of 7 and a ratio of Zn/Al = 4. A thermal treatment was performed for LDH at various temperatures. Powder XRD patterns showed that the layered structure of the LDH samples was stable below 200 °C, which was also confirmed by thermogravimetric (TGA) and differential thermal (DTA) analyses. Infrared spectra of the samples showed the characteristic peaks of LDH, and changes of these peaks were observed when thermal treatment was performed above 150 °C. Diffuse reflectance spectroscopy of the samples showed more than one energy gap at calcination temperatures below200 °C. In samples calcined at 200 °C and above only one energy gap was observed at approximately 3.3 eV. The photocatalytic activity was found to increase with the increase of the ZnO crystal size, which can be achieved by increasing the calcination temperature of the samples. Because of the presence of water molecules and anionic NO₃⁻ in the interlayer of the LDH, the dielectric response of the calcined LDH can be described by an anomalous low frequency dispersion using the second type of Universal Power Law for calcination temperatures below 200 °C. The dielectric response of the calcined LDH above 150 °C displays the dielectric relaxation behaviour of ZnO because of the formation of a ZnO phase in the LDH within this temperature range.     

Multi-cationic layered double hydroxides: Calcined products as photocatalysts for decomposition of NOx

Several multi-cationic layered double hydroxides were synthesized by hydrothermal method and their calcined products were evaluated for the photodegradation of NO_x. The synthetic samples were characterized by powder X-ray diffraction (XRD), BET specific surface area and scanning electron microscopy (SEM). From the XRD results, it was found that doping of lanthanum in LDH structures led to poor crystallinity. Nickel zinc titanium oxide phases were observed in the XRD patterns when the samples were heated at higher temperatures. Doping the samples with Ni prevented the formation of pure zinc titanate phase. Lanthanum doping also affected the formation of nickel zinc titanium oxide. The photocatalytic activity of calcined samples was measured using decomposition of NO_x molecules. Photocatalytic properties decreased with increasing calcination temperatures as a result of grain growth. Formation of ZnO phase after calcination led to effective photocatalytic decomposition of NO_x molecules. Nickel zinc titanium oxide showed lower photocatalytic activity compared to pure zinc titanate. The specific surface areas of La containing LDHs were found to be higher compared to other LDHs containing different cations as a result of smaller crystal size in the former.     

Comparison of Mg–Al layered double hydroxides intercalated with OH− and CO32− for the removal of HCl,SO2, and NO2

Journal of Porous Materials - Two different Mg–Al layered double hydroxides (LDHs), OH?Mg–Al LDH and CO3?Mg–Al LDH, are prepared and utilized for the efficient removal...     

Photocatalytic Activity of Highly Porous Zinc Ferrite Prepared from a Zinc-Iron(III)-Sulfate Layered Double Hydroxide Precursor

A zinc-iron(III)-sulfate layered double hydroxide (LDH) has been prepared from zinc and iron(II) precursors. Calcination at 500°C or above affords a mixture of ZnO (zincite) and ZnFe₂O₄ (spinel) phases. Treatment of the calcined products with aqueous NaOH leads to dissolution of the ZnO and the formation of a pure zinc ferrite phase with high surface area and pore volume. When used as a photocatalyst for the degradation of phenol, the active lifetime of the catalyst was extended compared with a sample of zinc ferrite prepared by a conventional co-precipitation route followed by calcination under the same conditions. The highly porous material also exhibited a higher selectivity to low molecular weight oxidation products than the co-precipitated catalyst.     

层状双氢氧化物和蒙脱石的剥离及其自组装

以钙基蒙脱石为原料,氟化钠为钠化剂,十六烷基三甲基溴化铵为有机改性剂采用离子交换法制备了有机蒙脱石(CTA-MMT);以硝酸镁、硝酸铝、氢氧化钠和十二烷基磺酸钠为原料,采用水热法制备了有机型镁铝层状双氢氧化物(Mg Al-SDS-LDH);以氯仿为剥离介质,采用超声法剥离CTA-MMT和MgAl-SDS-LDH,分别获得了两种剥离型矿物溶胶,将其混合自组装制备了蒙脱石/层状双氢氧化物(MMT/LDH)组装材料。用XRD和AFM表征了CTA-MMT和MgAl-SDS-LDH及其剥离产物,并分析了组装材料的热稳定性。结果表明,CTA-MMT和MgAl-SDS-LDH在氯仿介质中剥离仅需20 min,剥离型CTA-MMT和MgAl-SDS-LDH片层平均厚度分别约为9和8 nm。MMT/LDH由剥离型CTA-MMT和MgAl-SDS-LDH片层有序组装而成,组装材料结构与MgAl-SDS-LDH和CTA-MMT的含量有关,其结构单元层间距2.59 nm(CTA-MMT含量较低时)随着组装材料中CTA-MMT含量的升高而转变为1.82 nm。MMT/LDH组装材料具有较单一的CTA-MMT或MgAl-SDS-LDH更高的热稳定性。     

Non-toxic hybrid pigments: Sequestering betanidin chromophores on inorganic matrices

Betalain was extracted from bougainvillea flower. Alumina, layered double hydroxides (LDHs) and zeolites were tested as adsorbents of the chromophore. Gamma alumina stabilized betalains over a long period. The adsorption sites which stabilized the chromophores were elucidated by nuclear magnetic resonance. Although the oxides obtained by calcination of LDHs retain betalains, they were oxidized within 20 h or react with Zn²⁺ of the calcined LDH. No betalain was adsorbed in zeolite X because of the too small pores.     

Adsorption of phosphate by layered double hydroxides in aqueous solutions

Adsorption of phosphate by various calcined layered double hydroxides (LDHs) such as Mg–Al, Zn–Al, Ni–Al, Co–Al, Mg–Fe, Zn–Fe, Ni–Fe and Co–Fe was investigated. LDHs were found to have high anion exchange capacity that enhances their capability to remove anionic contaminants from aqueous system. The nature and content of di- and trivalent cations in LDH have strong influence on the adsorption process. Calcined Mg–Al LDH (CLDH) with Mg–Al molar ratio of 2.0 showed higher adsorption capacity compared to other calcined LDHs as it possessed higher Al³⁺ content. Results indicate that the adsorption isotherm could be fitted to a linearised form of Langmuir and Freundlich equations. The adsorption phenomenon has been well supported by XRD study. The adsorption process was spontaneous and exothermic in nature and followed first order kinetics. Competitive anions were found to have detrimental effect on the percentage of adsorption.     

水滑石(LDH)的合成及其表征

利用“双滴法”成功制备出具有层状结构的镁铝水滑石,并对比确定了最佳反应温度。首先在50℃、80％、95％下制备出三种水滑石,利用XRD分析水滑石的结构,确认制备出了具有典型层状结构的水滑石;然后利用TGA测试三种水滑石的热分解温度,发现95℃下制备出的水滑石晶体强度较高,为进一步研究聚合物基水滑石纳米复合材料奠定了良好的基础。