双(羟基)金属复合氧化物的表面改性

水滑石;硬脂酸;湿法表面改性;双(羟基)金属复合氧化物的表面改性     

NMR Crystallography Reveals Carbonate Induced Al-Ordering in ZnAl Layered Double Hydroxide

Layered double hydroxides (LDHs) serve a score of applications in catalysis, drug delivery, and environmental remediation. Smarter crystallography, combining X-ray diffraction and NMR spectroscopy revealed how interplay between carbonate and pH determines the LDH structure and Al ordering in ZnAl LDH. Carbonate intercalated ZnAl LDHs were synthesized at different pH (pH 8.5, pH 10.0, pH 12.5) with a Zn/Al ratio of 2, without subsequent hydrothermal treatment to avoid extensive recrystallisation. In ideal configuration, all Al cations should be part of the LDH and be coordinated with 6 Zn atoms, but NMR revealed two different Al local environments were present in all samples in a ratio dependent on synthesis pH. NMR-crystallography, integrating NMR spectroscopy and X-ray diffraction, succeeded to identify them as Al residing in the highly ordered crystalline phase, next to Al in disordered material. With increasing synthesis pH, crystallinity increased, and the side phase fraction decreased. Using ¹H−¹³C, ¹³C−²⁷Al HETCOR NMR in combination with ²⁷Al MQMAS, ²⁷Al-DQ-SQ measurements and Rietveld refinement on high-resolution PXRD data, the extreme anion exchange selectivity of these LDHs for CO₃²⁻ over HCO₃⁻ was linked to strict Al and CO₃²⁻ordering in the crystalline LDH. Even upon equilibration of the LDH in pure NaHCO₃ solutions, only CO₃²⁻ was adsorbed by the LDH. This reveals the structure directing role of bivalent cations such as CO₃²⁻ during crystallization of [M²⁺₄M³⁺₂(OH)₂]²⁺[A²⁻]₁⋅yH₂O LDH phases.     

Intercalation of Azo Compounds into Layered Aluminium Dihydrogentriphosphate and a Layered Double Hydroxide

The inner surfaces of inorganic layered compounds such as aluminium dihydrogen-triphosphate (ADHP) and layered double hydroxide (LDH) were modified by azo compounds. Upon intercalation of 4-phenylazoaniline and 4,4-azodianiline into ADHP, the interlayer spacing increased from 6.4 to 21.5 Å and 20.6 Å, respectively. The intensity of IR peaks due to P-–OH of ADHP and amino groups of guests decreased by the thermal treatment of the intercalates. The interlayer spacings also decreased to 16.9 Å and 16.7 Å, respectively, indicating a dehydration reaction between P–-OH and amino groups. The LDH inner surface was modified by the reaction with trans-p-phenylazobenzoylchloride (PAB-Cl). Upon surface modification, the interlayer spacing increased from 7.6 Å to about 27 Å. The absorption of this surface-modified LDH near 410 nm increased upon irradiation with UV light and decreased upon irradation with visible light, indicating the occurrence of trans–cis isomerization of PAB-Cl between the layers.     

层状复合金属氢氧化物-聚丙烯酸钠水分散体系的双絮凝现象及机理探讨

研究了聚丙烯酸钠(PAAS)对镁铝型层状复合金属氢氧化物(MgAl-LDH)的胶体水分散体系稳定性的影响. 利用总有机碳(TOC)分析技术测定了PAAS在LDH颗粒上的吸附量, 并利用ζ电位表征了LDH颗粒的电性质. 实验结果表明, 在质量分数为1%的LDH水分散体系中加入0.006~2.400 mmol/L PAAS, 随着PAAS浓度的增加, LDH-PAAS混合体系出现了絮凝-分散-再絮凝变化. 同时, 随着PAAS浓度的增加, PAAS在LDH颗粒上的吸附导致颗粒ζ电位由正减至0, 并进一步负向增加, 颗粒间静电斥力先减小后增加, 因此体系先絮凝再分散. 随着LDH颗粒负电性的进一步增强, 未吸附的PAAS引发颗粒间产生的空缺引力成为体系再次絮凝的主要原因. 对吸附PAAS的LDH颗粒的红外光谱分析表明, PAAS主要通过-COO-与LDH的相互作用而吸附在颗粒上.     

层状双金属氢氧化物/碳纳米管复合物的制备及在有机溶剂中的分散

通过硝酸处理在碳纳米管(CNTs)表面生成了羧基(-COOH)基团, 随后采用尿素法在其水悬浮液中原位合成了层状双金属氢氧化物(LDH), 获得了层状双金属氢氧化物/碳纳米管复合物(LDH/CNTs), 考察了CNTs用量对LDH形貌与结构的影响. 结果表明, CNTs的用量对LDH的产率及结构无显著影响; 但当CNTs用量较低(<0.2 g/L)或过高(>4.0 g/L)时, 会导致LDH的粒径分布变宽. 对LDH/CNTs进行氯化及有机化处理, 获得了十二烷基苯磺酸根离子(DBS)插层的DBS-LDH/CNTs. 对DBS-LDH/CNTs在不同有机溶剂中分散及剥离程度的研究发现, DBS-LDH/CNTs在丁醇、 乙醇及二甲苯中均可良好分散且其悬浮液较稳定, LDH在不同溶剂中的剥离程度为丁醇>乙醇>二甲苯>四氢呋喃.     

MgAl无机-有机杂化材料对Pb~(2+)的吸附

采用共沉淀法合成了结晶度良好、具有纯水滑石相的Mg-Al型层状双金属氢氧化物(LDH)及其乙二胺四乙酸二钠(EDTA)-LDH无机-有机杂化物,并进行了表征。考察了Mg-AlLDH和EDTA-LDH对Pb2+的吸附作用,其均有很好的吸附能力,EDTA在LDH通道中可能以直立平行方式排列成单层。在相同条件下,EDTA-LDH的吸附速率和吸附量均高于Mg-AlLDH。结果表明,EDTA的插入具有协同增效作用,吸附动力学符合准二级吸附速率方程。吸附等温线可分为吸附阶段和表面沉淀阶段,吸附阶段的等温线符合Freundlich吸附等温式。初始pH值对Pb2+的吸附基本无影响。Pb2+在LDH和EDTA-LDH上的吸附机理主要为表面沉淀,并存在化学键合和静电键合作用,EDTA-LDH存在EDTA与Pb2+的络合作用。     

双金属氢氧化物催化析氧反应的协同机制研究

双金属氢氧化物(LDH)是催化析氧反应(OER)活性最佳的一类催化剂,其中揭示双金属位点的协同作用是进一步提升其电催化、光催化性能的关键.本工作采用密度泛函方法,从理论计算角度探究了五种M32+N3+-LDH(M2+=Co2+、Ni2+,N3+=Al3+、Cr3+、Mn3+、Fe3+)在催化OER中的反应机制和双金属位...     

层状双金属氢氧化物的控制合成及其在水处理中的应用

层状双金属氢氧化物(LDH)作为无机层状粒子的典型代表,已在众多应用领域展现出巨大潜力。然而,目前的研究大多从LDH的层板组成、层间阴离子种类以及粒子尺寸的角度入手对其进行功能优化,较少关注形貌结构对LDH性能的影响。本文从简要介绍LDH的基本结构和性质出发,详细总结了常规六方片状以及特殊形貌(球状、多面体状、纳米线状、环状等)LDH的制备方法。结合LDH与其他功能粒子复合以提升其综合性能的需求,深入分析了反应配方、合成条件以及基体表面性质对LDH复合材料形貌的调控规律,并综述LDH及其复合物分别作为吸附、催化和分离材料在水处理中的应用。最后,对当前控制合成LDH所存在的难点及其未来研究方向进行了展望。     

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 structures.Electrochemical tests show that Co(Ni)Al LDHs as electrode material have typical capacitive properties in a wide voltage range of 0.0 to 0.6 V;Co(Ni)Al LDH(Ni∶Co =4∶6)as an electrode material has the highest capacitance of 960F·g^-1 and good cycling performance.But the poor capacitive properties of NiAl LDH electrode are showed in a narrow voltage range of 0.3 to 0.55 V.     

水滑石负载 Au 纳米粒子的制备及其催化醇氧化反应

 采用离子交换法和 NaBH4 还原法制备了 Mg-Al-水滑石 (LDH) 负载的 Au 纳米粒子 (Au/LDH) 催化剂. X 射线衍射和透射电镜结果表明, Au 粒子较均匀地分散在水滑石表面, 载体仍保持层状结构. 在温和的反应条件下, Au/LDH 对一系列醇的氧化反应表现出优异的催化性能, 如在室温常压下进行分子 O2 氧化 1-苯基乙醇的反应, 底物转化率和苯乙酮选择性都接近 100%, 而且催化剂经过多次循环使用后, 其活性未见下降. 可见, Au/LDH 催化剂在醇氧化反应中具有良好的应用前景.     

Heterogeneous Fenton Degradation of Organic Pollutants in Water Enhanced by Combining Iron-type Layered Double Hydroxide and Sulfate

Water pollution derived from organic pollutants is one of the global environmental problems. The Fenton reaction using Fe²⁺ as a homogeneous catalyst has been known as one of clean methods for oxidative degradation of organic pollutants. Here, a layered double hydroxide (Fe²⁺Al³⁺-LDH) containing Fe²⁺ and Al³⁺ in the structure was used to develop a “heterogeneous” Fenton catalyst capable of mineralizing organic pollutants. We found that sulfate ion (SO₄²⁻) immobilized on the Fe²⁺Al³⁺-LDH significantly facilitated oxidative degradation (mineralization) of phenol as a model compound of water pollutants to carbon dioxide (CO₂) in a heterogeneous Fenton process. The phenol conversion and mineralization efficiency to CO₂ reached >99% and ca. 50%, respectively, even with a reaction time of only 60 min.     

Enhancing Electrocatalytic Activity through Liquid-Phase Exfoliation of NiFe Layered Double Hydroxide Intercalated with Metal Phthalocyanines in the Presence of Graphene

Earth-abundant transition-metal-based catalysts are attractive for alkaline water electrolysis. However, their catalytic properties are often limited by their poor electrical conductivity. Here, we present a strategy for enhancing the electrical conductivity of NiFe layered double hydroxide (LDH) in order to further improve its properties as an electrocatalyst for the oxygen evolution reaction (OER) in alkaline media. We show that NiFe LDH containing metal tetrasulfonate phthalocyanine in the interlayers between the NiFe oxide galleries can be coupled with graphene during liquid-phase exfoliation by taking advantage of their π-π stacking capabilities. A substantial enhancement in the electrocatalytic activity of NiFe LDH with respect to the OER was observed. Moreover, the activity and selectivity of the catalyst materials towards the oxygen reduction reaction were investigated, demonstrating that both the metal hydroxide layer and the interlayer species contribute to the electrocatalytic performance of the composite material.     

Calcined Mg-Al Layered Double Hydroxide as a Heterogeneous Catalyst for the Synthesis of Urea Derivatives from Amines and CO2

The calcined Mg‐Al layered double hydroxides (LDHs) with a Mg/Al molar ratio of 3:1 were synthesized and characterized thoroughly by X‐ray diffraction (XRD), temperature‐programmed desorption (TPD) of CO₂, and thermogravimetric analysis (TGA). Thus the calcined Mg‐Al LDHs were used as catalyst for the catalytic synthesis of disubstituted ureas from amines and CO₂. The effects of reaction time, reaction temperature, pressure, solvent and calcined temperature on activity have been investigated. The results indicated that aliphatic amines, cyclohexylamine and benzylamine can be converted to the corresponding ureas selectively over the calcined Mg‐Al LDHs catalysts with N‐methyl‐2‐pyrrolidone (NMP) as solvent without using any dehydrating regent. The catalyst can be recycled several times with only slight loss of activity.     

Synthesis of Ni／Mg／Al Layered Double Hydroxides and Their Use as Catalyst Precursors in the Preparation of Carbon Nanotubes

Ni/Mg/Al layered double hydroxides(LDHs) with different n(Ni) : n(Mg) : n(Al) ratio values were prepared via a coprecipitation reaction. Then Ni/Mg/Al mixed oxides were obtained by calcination of these LDHs precursors. Carbon nanotubes were produced in the catalytic decomposition of propane over the Ni/Mg/Al mixed oxide catalysts. The quality of as-made nanotubes was investigated by SEM and TEM. The nanotubes were multiwall with a high length-diameter ratio and appeared to be flexible. The catalytic activities of these mixed oxides increased with increasing the Ni content. The Ni/Mg/Al mixed oxide with the highest Ni content [ n( Ni)/n( Mg)/n(Al) = 1/1/1 ] showed the highest activity and the carbon nanotubes grown on its surface had the best quality.     

New Models to Predict the Acute and Chronic Toxicities of Representative Species of the Main Trophic Levels of Aquatic Environments

To assess the impact of chemicals on an aquatic environment, toxicological data for three trophic levels are needed to address the chronic and acute toxicities. The use of non-testing methods, such as predictive computational models, was proposed to avoid or reduce the need for animal models and speed up the process when there are many substances to be tested. We developed predictive models for Raphidocelis subcapitata, Daphnia magna, and fish for acute and chronic toxicities. The random forest machine learning approach gave the best results. The models gave good statistical quality for all endpoints. These models are freely available for use as individual models in the VEGA platform and for prioritization in JANUS software.     

Promoted Electrocatalytic Nitrogen Fixation in Fe-Ni Layered Double Hydroxide Arrays Coupled to Carbon Nanofibers: The Role of Phosphorus Doping

The key to bringing the electrocatalytic nitrogen fixation from conception to application lies in the development of high-efficiency, cost-effective electrocatalysts. Layered double hydroxides (LDHs), also known as hydrotalcites, are promising electrocatalysts for water splitting due to multiple metal centers and large surface areas. However, their activities in the electrocatalytic nitrogen fixation are unsatisfactory. Now, a simple and effective way of phosphorus doping is presented to regulate the charge distribution in LDHs, thus promoting the nitrogen adsorption and activation. The P-doped LDHs are further coupled to a self-supported, conductive matrix, that is, a carbon nanofibrous membrane, which prevents their aggregation as well as ensuring rapid charge transfer at the interface. By this strategy, decent ammonia yield (1.72×10⁻¹⁰ mol s⁻¹ cm⁻²) and Faradaic efficiency (23 %) are delivered at −0.5 V vs. RHE in 0.1 m Na₂SO₄.     

Studies of the Catalytic Activity and Deactivation of Calcined Layered Double Hydroxides in the Reaction of Ethanol with Propylene Oxide

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Promoted Electrocatalytic Nitrogen Fixation in Fe‐Ni Layered Double Hydroxide Arrays Coupled to Carbon Nanofibers: The Role of Phosphorus Doping

The key to bringing the electrocatalytic nitrogen fixation from conception to application lies in the development of high‐efficiency, cost‐effective electrocatalysts. Layered double hydroxides (LDHs), also known as hydrotalcites, are promising electrocatalysts for water splitting due to multiple metal centers and large surface areas. However, their activities in the electrocatalytic nitrogen fixation are unsatisfactory. Now, a simple and effective way of phosphorus doping is presented to regulate the charge distribution in LDHs, thus promoting the nitrogen adsorption and activation. The P‐doped LDHs are further coupled to a self‐supported, conductive matrix, that is, a carbon nanofibrous membrane, which prevents their aggregation as well as ensuring rapid charge transfer at the interface. By this strategy, decent ammonia yield (1.72×10^?10 mol s^?1 cm^?2) and Faradaic efficiency (23 %) are delivered at ?0.5 V vs. RHE in 0.1 m Na₂SO₄.     

Zn-Al-[V_(10)O_(28)]~(6-)双层氢氧化物掺杂对LY12铝合金表面溶胶-凝胶涂层性能的影响

采用共沉淀法制备Zn-Al-[V10O28]6-双层氢氧化物(以下简称LDH-V),研究不同添加浓度(0.0、0.25×10-3、0.75×10-3、1.5×10-3、3.0×10-3mol·L-1)的LDH-V对LY12铝合金溶胶-凝胶涂层形貌、耐蚀性的影响.采用扫描电子显微镜(SEM)和傅里叶变换红外(FTIR)光谱研究LDH-V对涂层形貌和结构的影响.运用中性盐雾实验对涂层进行耐蚀性评估.利用电化学方法对涂层在0.05 mol·L-1的NaCl溶液中的腐蚀行为进行研究.探讨加入LDH-V后溶胶-凝胶涂层的耐蚀机理.结果表明,一定量LDH-V的加入不仅可以提高溶胶-凝胶涂层的耐蚀性能,还可对涂层被破坏区域进行自修复,起到延缓铝合金基体腐蚀的作用.然而,当LDH-V的添加溶度超过一定值时,会破坏涂层的完整性并降低涂层的腐蚀防护性能.实验结果表明LDH-V最佳的添加浓度为1.5×10-3mol·L-1.