Solid base catalysts derived from Ca-M-Al(M = Mg, La, Ce, Y) layered double hydroxides for dimethyl carbonate synthesis by transesterification of methanol with propylene carbonate

Composite solid base catalysts derived from Ca‐M‐Al(M=Mg,La,Ce,Y)layered double hydroxides(LDH)were synthesized,characterized and applied to the transesterification of methanol with propylene carbonate.X‐ray diffraction analyses of the catalysts show that all of the catalysts were in the form of composite oxides.Compared with the Ca‐Al LDH catalyst,the specific surface areas and pore volumes of the catalysts were increased with the introduction of Mg,La or Ce.The catalytic performance of these catalysts increases in the order of Ca‐Y‐Al<Ca‐Al<Ca‐Ce‐Al<Ca‐La‐Al<Ca‐Mg‐Al,which is consistent with the total surface basic amounts of these materials and the formation of especially strong basic sites following modification with Mg and La.The Ca‐Mg‐Al catalyst shows the highest(Ca+Mg):Al atomic ratio,indicating that it likely contains more unsaturated O2?ions,providing it with the highest concentration of very strong basic sites.The recyclability of these catalysts is improved following the addition of Mg,La,Ce or Y,with the Ca‐Mg‐Al maintaining a high level of activity after ten recycling trials.X‐ray diffraction analyses of fresh and used Ca‐Mg‐Al demonstrate that this catalyst is exceptionally stable,which could be of value in practical applications related to heterogeneous catalysis.

3D Hierarchical Co–Al Layered Double Hydroxides with Long-Term Stabilities and High Rate Performances in Supercapacitors

Three-dimensional(3D) flower-like Co–Al layered double hydroxide(Co–Al-LDH) architectures composed of atomically thin nanosheets were successfully synthesized via a hydrothermal method in a mixed solvent of water and butyl alcohol. Owing to the unique hierarchical structure and modification by butyl alcohol, the electrochemical stability and the charge/mass transport of the Co–Al-LDHs was improved. When used in supercapacitors, the obtained Co–Al-LDHs deliver a high specific capacitance of 838 Fg^(-1) at a current density of 1 Ag^(-1)and excellent rate performance(753 Fg^(-1) at 30 Ag^(-1) and 677 Fg^(-1) at 100 Ag^(-1)), as well as excellent cycling stability with 95% retention of the initial capacitance even after 20,000 cycles at a current density of 5 Ag^(-1). This work provides a promising alternative strategy to enhance the electrochemical properties of supercapacitors.

Self-assembling organomodified Co/Al based layered double hydroxides (LDH) via one-step route

The preparation of self-assembling organomodified Co/Al-layered double hydroxide(LDH)via one-step route was studied. A common surfactant,sodium dodecylbenzenesulfonate(DBS),was employed as an organic modifier.The behavior and structure of self-assembled intercalated organic Co/Al-LDH were investigated by FTIR,SEM,WAXS,element analysis and TGA.Based upon the WAXS results and calculation by Bragg equation,the interlayer distance(d value)for organic Co/Al-LDH is enlarged from 0.75 nm to 3.10 nm,showing that the self-assembling behavior has been carried out successfully.Considering the observation from SEM, the product shows the morphology of organic Co/Al-LDH of a layered structure.In addition,FTIR,element analysis and TGA analysis show that the modifier is intercalated into the gallery of the Co/Al-LDH.Since organic modification for nanofiller is deemed to be necessary before applying it into polymer,the successful preparation of organomodified Co/Al-LDH will be significantly beneficial to the preparation and investigation of novel polymer/LDH nanocomposite.

In-situ layered double hydroxides on Mg−Ca alloy:Role of calcium in magnesium alloy

Mg−Al layered double hydroxides(LDHs),produced on cast Mg−xCa(x=0.5,0.8,2.0,wt.%)alloys by an in-situ growth method,showed good corrosion resistance compared to the bare magnesium substrate.The influence mechanism of the second phase(Mg_(2)Ca)on LDHs production was investigated.Increasing Ca content increased the amount of Mg_(2)Ca,decreasing the grain size and the corrosion rate of the alloys.The increased amount of the second phase particles and the grain refinement promoted the growth of LDHs,and thus led to the decreasing of corrosion rate of the Mg−xCa alloys with LDHs.A higher Mg_(2)Ca amount resulted in forming fluffy LDHs.Due to the dual effects of the second phase(Mg_(2)Ca)for LDHs growth and microgalvanic corrosion,LDHs/Mg−0.8Ca showed the lowest corrosion rate.

Thermodynamic and Kinetic Studies of Effective Adsorption of 2,4,6-trichlorophenol onto Calcine Mg/Al-CO_3 Layered Double Hydroxide

Adsorption of 2, 4, 6-trichlorophenol（TCP） onto the calcined Mg/Al-CO_3 layered double hydroxide（CLDH） was investigated. The prepared Mg/Al-CO_3 layered double hydroxide（LDH） and CLDH were characterized by powder X-ray diffraction（XRD） and thermo gravimetric analyzer-differential scanning calorimeters（TG-DSC）. Moreover, 2,4,6-trichlorophenol（TCP） was removed effectively（94.7% of removal percentage in 9h） under the optimized experimental conditions. The adsorption kinetics data fitted the pseudosecond-order model well. The Freundlich, Langmuir, and Tempkin adsorption models were applied to the experimental equilibrium adsorption data at different temperatures of solution. The adsorption data fitted the Freundlieh adsorption isotherm with good values of the correlation coefficient. A mechanism of the adsorption process is proposed according to the intraparticle diffusion model, which indicates that the overall rate of adsorption can be described as three steps.

微弧氧化后Mg-8Li合金表面MgLiAlY-LDHs@GO膜层的生长及耐蚀性能

目的提高Mg-8Li合金的耐蚀性能。方法首先在Mg-8Li合金表面制备微弧氧化膜(MAO),然后使用原位水热法在微弧氧化膜表面原位生长掺杂氧化石墨烯(GO)的四元(MgLiAlY)层状双羟基金属氧化物(LDHs)智能自修复膜层。采用SEM、XRD、FT-IR、EDS、ICP等手段研究MgLiAlY-LDHs@GO膜层的形貌、结构以及成分。通过EIS、Tafel以及浸泡试验等研究膜层的耐蚀性能,分析膜层的腐蚀行为,阐释其耐蚀机理。结果GO的掺杂可以促使LDHs纳米片生长得更加致密,主体层板中具有缓蚀作用的Y3+可以提高涂层的耐蚀性,四元LDHs的生长所需要的Mg^(2+)、Li^(+)、Al^(3+)等离子来源于镁锂合金基体以及微弧氧化膜的溶解,其中Li+也可以促进LDHs纳米片生长得更为均匀细密。膜层的腐蚀电流密度为6.03×10^(–7)A/cm^(2),比MAO膜层降低了1个数量级,提高了镁锂合金的耐蚀性能。结论GO的负载使LDHs的耐蚀性能和膜层稳定性均有一定程度的提升,引入稀土元素Y会改变LDHs的骨架,造成晶格畸变,使得LDHs微观形貌呈现褶皱状,剩下部分以Y(OH)3形式存在于涂层表面,可进一步提高膜层的耐蚀性能和稳定性。

Li-Al LDH固态电解质及其Cs^(+)掺杂研究

固态电池因其所具有的高能量密度和高安全性而极具发展前景,而开发离子电导率高的固态电解质是固态电池发展的一大关键问题。通过水热法制备了一种锂铝水滑石材料(Li-Al LDH),并对其结构与形貌、热稳定性、电化学性能进行了表征。从XRD和SEM分析可以看出,Li-Al LDH在180℃条件下仍然保持稳定,EIS测试结果表明Li-Al LDH的离子电导率为8.25×10^(-5) S/cm。进一步对Li-Al LDH进行了Cs^(+)掺杂研究,结果表明,对Li-Al LDH成功实现了Cs+掺杂,且所制得的Li-Al LDH(Cs0.1)样品,其离子电导率约为5.2×10^(-4) S/cm,达到了现有氧化物固态电解质离子电导率水平。研究表明Cs+掺杂的Li-Al LDH作为锂电池固态电解质具有潜在的应用前景。

类水滑石Ti/Li/Al-LDHs的制备及其CO_2吸附性能

采用共沉淀法制备了一系列新型的类水滑石Ti/Li/Al-LDHs材料,通过原子吸收光谱(AAS)、X射线衍射(XRD)、扫描电镜(SEM)、热重分析(TG)和傅里叶变换红外光谱(FT-IR)等技术对其进行了表征,研究了不同金属元素比例和焙烧温度对该Ti/Li/Al-LDHs材料的结构、形貌及其CO_2吸附性能的影响。结果表明,当Ti/Li/Al比为1∶3∶4时,水滑石Ti/Li/AlLDHs的结晶度最好,形貌最规整,而Ti/Li/Al比为1∶3∶2、300℃下焙烧后得到的Ti_1Li_3Al_2-LDHs_(300)的CO_2吸附性能最好。Ti_1Li_3Al_2-LDHs_(300)上CO_2吸附量可达53.5 mg/g,10次循环吸附后,CO_2吸附量仅下降了2.4%。

Zn-Mg-Al LDO的制备及其除氟性能研究

半导体、电镀、冶金和陶瓷行业排放高浓度含氟废水,因此天然水中的氟化物污染已成为一个全球性问题,而Zn-Mg-Al LDO是很好的吸附材料。在n(Zn^(2+))/n(Mg^(2+))/n(Al^(3+))、反应温度不同的条件下,采用共沉淀法合成Zn-Mg-Al LDH,并将Zn-Mg-Al LDH在不同温度下焙烧制得Zn-Mg-Al LDO;利用X射线衍射(XRD)、扫描电子显微镜(SEM)、傅里叶变换红外光谱(FT-IR)、BET比表面积测试法等方法,探究了Zn-Mg-Al LDO的结构和性质;对50 mL质量浓度为20.0 mg/L的NaF溶液进行吸附实验,考察了Zn-Mg-Al LDO吸附去除氟离子的性能。结果表明,在n(Zn^(2+))/n(Mg^(2+))/n(Al^(3+))=2∶1∶1、反应温度为75℃、焙烧温度为400℃的条件下制备的Zn-MgAl LDO吸附去除氟离子的性能最好,氟离子的吸附去除率达到85.39%;Zn-Mg-Al LDO具有水滑石特征峰,晶型良好,呈层状结构;Zn-Mg-Al LDO为介孔材料,其比表面积为103.15 m2/g。此外,还研究了吸附过程的动力学和吸附机理。结果表明,吸附过程符合Langmuir吸附等温线和准二级动力学方程。

Synthesis of layered cathode materials Li[Co_x Ni_y Mn_(1-x-y)]O_2 from layered double hydroxide precursors

Cathode materials Li[CoxNiyMn1-x-y]O2 for lithium secondary batteries have been prepared by a new route using layered double hydroxides （LDHs） as a precursor. The resulting layered phase with the α- NaFe02 structure crystallizes in the rhombohedral system, with space group R-3m having an interlayer spacing close to 0.47 nm. X-ray photoelectron spectroscopy （XPS） was used to measure the oxidation states of Co, Ni and Mn. The effects of varying the Co[Ni[Mn ratio on both the structure and electrochemical properties of Li[CoxNiyMn1-x-y]O2 have been investigated by X-ray diffraction and electrochemical tests. The products demonstrated a rather stable cycling behavior, with a reversible capacity of 118 mAh/g for the layered material with Co/Ni/Mn = 1/1/1.

Ca(ALG)_2-LiCl·2Al(OH)_3·nH_2O的合成研究

聚氯乙烯常被用于吸附剂造粒,由于聚氯乙烯水溶性差,所以吸附时间比较长。本文首次采用沉淀法合成了LiCl·2Al(OH)_3·nH_2O,以海藻酸钙为载体制备了Ca(ALG)_2-LiCl·2Al(OH)_3·nH_2O微球。通过单因素实验确定了LiCl·2Al(OH)_3·nH_2O最佳的合成条件。实验结果表明:反应温度80℃、Al^(3+)/Li^+=1.5、OH^-/Al^(3+)=2.5、吸附剂∶载体=2∶1为前躯体最佳的合成条件,吸附量可达15.02 mg/g。吸附剂微球透水性能好,可以实现快速达到吸附饱和的目的,且吸附剂对水体不造成危害。

ZnAl-LDH/Al(OH)_(3)复合材料的制备及其对废水中Pb^(2+)的去除性能

利用共沉淀法,以Zn(NO_(3))_(2)和Al(NO_(3))_(3)为原料成功制备了锌铝复合材料ZnAl-LDH/Al(OH)_(3)(标记为ZAL/AH),采用SEM表征了ZAL/AH的形貌,利用FTIR、XPS和XRD分析了样品的结构及组成。结果表明,所制备的ZAL/AH为片状结构,相组成受投料比的影响。其中,ZAL/AH-1具有高的比表面积,达到82.7 m^(2)·g^(-1)。同时,利用所制备的复合材料ZAL/AH对水中的Pb^(2+)离子进行了吸附实验,ZAL/AH-1对Pb^(2+)的去除率能够达到95%。对吸附结果进行了吸附动力学、Freundlich和Langmuir模型拟合,Langmuir拟合计算得到的最大吸附量为143.3 mg·g^(-1)。

Synthesis of Mg-Al-carbonate layered double hydroxide by an atom-economic reaction

A clean method for preparing layered double hydroxides （LDHs） has been developed, featured by using the hydroxides of two different metals as starting materials by atom-economic reactions. The reactions were carried out under hydrothermal conditions in either a high pressure autoclave or a microwave digester. The compositions, structural parameters and thermal behavior of the resulting LDHs are very similar to those of materials produced by using the separate nucleation and aging steps （SNAS） method. The major advantage of the new method is that no by-product is produced, so that filtration and washing processes are unnecessary. The consequent reduction in water consumption is beneficial to the environment.

Density functional theory study on the influence of cation ratio on the host layer structure of Zn/Al double hydroxides

A density functional theory （DFT） study has been carried out for [Zn-1AI（OH2）n＋6（OH）2n-2]^3＋ （n=3-6） and [Znn-1AI（OH2）2n-2（OH）2n-2]^3＋ （n = 7） clusters, which include the basic structural information of the brucite-like lattice structure of Zn/Al layered double hydroxides （LDHs） with Zn/AI molar ratio （R） in the range 2-6, in order to understand the effect of the Zn/Al ratio on the structure and stability of binary Zn/Al LDHs. Based on systematic calculations of the geometric parameters and formation energies of the cluster models, it was found that it is possible for Zn^2＋ and Al^3＋ cations to replace Mg^2＋ isomorphously in the brucite-like structure with different R values, resulting in differences in microstructure of the clusters and unit cell parameter a of the Zn/Al LDHs. Analysis of the geometry and bonding around the trivalent Al^3＋ or divalent Zn^2＋ cations reveals that Al^3＋ plays a more significant role than Zn^2＋ in determining the microstructure properties, formation and bonding stability of the corresponding ZnRAl clusters when R〈5, while the influence of Zn^2＋ becomes the dominant factor in the case of R〉 5. These findings are in good agreement with experiments. This work provides a detailed electronic-level understanding of how the composition of cations affects the microstructure and stability of Zn-containing binary LDH layers.

锂铝层状双金属氢氧化物的制备及其锂脱嵌过程

锂铝层状双金属氢氧化物(Li/Al-LDHs)是一种适用于高镁锂比卤水中提锂的吸附剂,但其存在吸附容量偏低、吸附机理与适用条件不够清晰等问题。本工作以铝粉、氢氧化锂为原料制备Li/Al-LDHs,考察了适用条件下溶液中阴阳离子对吸附过程的影响并进行了不同溶液组成下的提锂性能测试,结合红外光谱测试和X射线光电子能谱等表征明晰了锂脱嵌机理。结果表明,Li/Al-LDHs在卤水中的最大吸附容量为8.350mg/g,阳离子选择性顺序为Li^(+)>Na^(+)>Mg^(2+)>Ca^(2+)>K^(+)。Li/Al-LDHs对Li^(+)的吸附符合Langmuir等温吸附模型和准二级吸附动力学模型,吸附过程主要是基于尺寸筛分效应进行的,Li^(+)进入吸附剂层间的空位后需要等量的阴离子(Cl^(-)、SO_(4)^(2-)等)进行电荷平衡,其吸锂容量随溶液体系总离子浓度的增加而变大,因此更适用于从高含盐量卤水中提锂。研究结果可为后续废旧金属铝制取Li/Al-LDHs用于盐湖卤水提锂提供技术参考。

Ni离子掺杂对CoAl双氢氧化物电化学电容的影响

CoAl LDHs with different molar ratio of Ni have been prepared by chemical co -precipitation method.XRD results show that these materials have layered struc tures.Electrochemical tests show that Co(Ni)Al LDHs as electrode material hav e typical capacit ive properties in a wide voltage range of0.0to0.6V;Co(Ni)Al LDH(Ni∶Co =4∶6)as an electrode material has the highest capacitance of960F · g -1 and good cycling performance.But the poor capacitive properties of NiAl LDH electrode are showed in a narrow voltage range of0.3to0.55V.

Mg-Al水滑石的水热合成及晶面选择性生长

以MgO、Al(OH)3为镁源和铝源,采用一步水热法合成了镁铝水滑石(Mg-AlLDHs),考察了水热时间及水热温度对水滑石晶粒度和晶面选择性生长的影响规律。用XRD、SEM等对合成产物进行了表征。结果发现水热时间不变,升高水热温度,或水热温度不变,延长水热时间,LDHs的晶体结构均趋于完整,径厚比呈增大趋势;并且晶体沿a轴方向的生长速率比沿c轴方向的生长速率大,即[110]晶面的生长速率比[003]晶面的生长速率快。

Ni/Al-LDH/MCNTs原位复合材料的制备与电化学性能

以Ni(NO3)2·6H2O、Al(NO3)3·9H2O、尿素和MCNTs为原料,采用原位均相沉淀法制备了MCNTs含量(质量分数)分别为1%、3%和5%的Ni/Al-LDH/MCNTs复合电极活性材料。采用X射线衍射(XRD)、傅里叶变换红外光谱(FTIR)和场发射扫描电子显微镜(FESEM)表征了材料的微观结构和形貌;采用循环伏安(CV)、电化学交流阻抗(EIS)和充放电测试研究了该复合材料作为镍氢电池正极材料的电化学性能。结果表明,在Ni/Al-LDH中复合MCNTs能够提高材料的电化学活性,降低电化学反应电阻,显著改善材料的大电流充放电性能。其中MCNTs含量为3%的Ni/Al-LDH/MCNTs复合材料具有最佳的电化学性能,在200、500、1000和2000mA·g-1电流密度下的放电比容量分别为330、321、307和288 mA·h·g-1,而未复合MCNTs的Ni/Al-LDH在2000 mA·g-1电流密度下放电比容量仅为205 mA·h·g-1。

Mn0．8Zn0．2Fe2O4／MgAl-LDHs复合材料的磁性能和磁热效应

采用共沉淀法将纳米锰锌铁氧体粒子(Mn_(0.8)Zn_(0.2)Fe_2O_4)与镁铝双金属氢氧化物(MgAl-LDHs)进行组装合成了磁性纳米镁铝双金属氢氧化物,并通过TEM、FTIR、DTA、XRD、VSM等方法对其进行表征.样品的结构分析结果表明,复合材料具有典型的核壳结构,镁铝双金属氢氧化物被赋予磁性后并没有改变其层状结构的典型特征.样品的磁学性能和磁热性能测试结果表明,铁氧体的含量对复合材料的磁性能和磁热效应起着决定性作用;MgAl-LDHs对铁氧体粒子没有显著的磁屏蔽效应,复合材料的饱和磁化强度与铁氧体的含量呈正线性相关,而复合材料的矫顽力随MgAl-LDHs含量的增加呈现先减小后增大的趋势,但整体变化幅度很小,同时MgAl-LDHs对铁氧体粒子磁热效应的影响也极小.

Zn-Al-CO_3 LDHs催化碳酸二苯酯与1,4-丁二醇酯交换合成聚碳酸酯二醇

采用共沉淀法制备了不同n(Zn)/n(Al)比的锌铝类水滑石(Zn-Al-CO3 LDHs),并用XRD、FT-IR和TG-DTA等方法对它们进行了表征。研究了不同n(Zn)/n(Al)比的Zn-Al-CO3 LDHs对碳酸二苯酯(DPC)与1,4-丁二醇(1,4-BD)酯交换反应合成聚碳酸酯二醇(PCDL)的催化活性,并与镁铝水滑石(Mg-Al-CO3 LDHs)、乙醇钠和三乙烯二胺等催化剂进行了比较。在酯交换过程中,以苯酚的收率表征催化剂的活性;在缩聚过程中,以产品的数均分子量Mn、羟基值表征催化剂的活性。结果显示,n(Zn)/n(Al)比为2.0的Zn-Al-CO3 LDH的催化活性较好。在优化反应条件下,获得了分子量分布较窄的PCDL,其数均分子量为1610,羟基值为69.7 mg KOH.g.1。