Advances in Mg-Al-layered double hydroxide steam coatings on Mg alloys:A review

Layered double hydroxide(LDH)coatings on magnesium(Mg)alloys shine brightly in the field of corrosion protection because of their special ion-exchange function.State-of-the-art steam coating as a type of LDH film preparation technique has emerged in recent years because only pure water is required as the steam source and its environmentally friendly LDH coating fits the current need for green development.Moreover,this coating can effectively inhibit the corrosion of the Mg alloy substrate due to the chemical bonding between the coating and the Mg alloy substrate.This review systematically explains cutting-edge advancements in the growth mechanism and corrosion behavior of LDH steam coatings,and analyzes the advantages and limitations of the steam-coating method.The influencing factors including pressure,CO_(2)/CO_(3)^(2-),aluminum content of the substrate alloy,solution type,and acid-pickling pretreatment,as well as the post-treatment of steam-coating defects,are comprehensively elucidated,providing new insights into the development of the in situ steam-coating technique.Finally,existing issues and future prospects are discussed to further accelerate the widespread application of Mg alloys.

Layered double hydroxide-like Mg_3Al_(1–x)Fe_x materials as supports for Ir catalysts: Promotional effects of Fe doping in selective hydrogenation of cinnamaldehyde

Supported Ir catalysts were prepared using layered double hydrotalcite‐like materials,such as Mg3Al1-xFex,containing Fe and Al species in varying amounts as supports.These Ir catalysts were applied for the selective hydrogenation of cinnamaldehyde(CAL).When x was changed from 0(Ir/Mg3Al)to 1(Ir/Mg3Fe),the rate of CAL hydrogenation reached a maximum at approximately x=0.25,while the selectivity to unsaturated alcohol,i.e.,cinnamyl alcohol,monotonously increased from 44.9%to 80.3%.Meanwhile,the size of the supported Ir particles did not change significantly with x,remaining at 1.7-0.2 nm,as determined by transmission electron microscopy.The chemical state of Ir and Fe species in the Ir/Mg3Al1-xFex catalysts was examined by temperature programmed reduction by H2 and X‐ray photoelectron spectroscopy.The surface of the supported Ir particles was also examined through the in‐situ diffuse reflectance infrared Fourier‐transform of a probe molecule of CO.On the basis of these characterization results,the effects of Fe doping to Mg3Al on the structural and catalytic properties of Ir particles in selective CAL hydrogenation were discussed.The significant factors are the electron transfer from Fe2+in the Mg3Al1–xFex support to the dispersed Ir particles and the surface geometry.

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.

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.

Preparation and Characterization of a New Layered Double Hydroxide,Mg–Fe–Ce

1 Introduction In the present paper,MgCl2·6H2O,FeCl3·6H2O,and CeCl3·6H2O were used as raw materials in the precipitationhydrothermal method to synthesize MgF eC e hydrotalcite.The effects of the Fe:Ce molar ratio on the composition,crystal structure,and thermal stability of hydrotalcite are examined.Energy-dispersive X-ray spectroscopy(EDS),X-

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。

Development of anti-corrosive coating on AZ31 Mg alloy modified by MOF/LDH/PEO hybrids

The self-assembly of hybrid inorganic-organic materials on stationary platforms plays a critical role in improving their structural stability and wide usability.In this work,a novel two-step hydrothermal approach is proposed for synthesizing stable and advanced hybrid coatings on metal-oxide platforms through the surface modification of layered double hydroxide(LDH)films using novel metal-organic frameworks(MOFs).Initially,Mg-Al LDH nanocontainers,grown on a magnesium oxide layer produced through plasma electrolytic oxidation(PEO)of AZ31 Mg alloy substrate,were intercalated with cobalt via an oxidation route,providing the metallic coordination center for the MOF formation.In the subsequent step,a pioneering technique is introduced,utilizing tryptophan as the organic linker for the first time at a pH of 10.The self-assembly of cobalt-tryptophan complex,driven by the strong bonding between electrophilic sites of monomers and nucleophilic sites,facilitated the formation of a MOF network having a cloud-like structure on the surface of MgAl LDH's film.The resulting MOF-LDH encapsulation containers demonstrate exceptional electrochemical stability when exposed to a 3.5 wt.%NaCl solution,surpassing the performance of PEO and pure LDH coatings.This enhanced stability is attributed to the development of a dense top layer and a stable composition within the self-assembled MOF,effectively sealing flaws and preventing the infiltration of corrosive ions into the underlying metallic substrate.The formation mechanism of MOFs on LDH galleries is investigated using density functional theory calculations.

Mg/Fe水滑石吸附水中磷的动力学及热力学研究

以MgCl2和FeCl3为原料通过共沉淀法制备了Mg/Fe水滑石,并对其进行焙烧得到了焙烧态Mg/Fe水滑石。采用X射线衍射（XRD）和傅里叶红外光谱（FTIR）对所得产物进行了结构表征。利用焙烧前后的水滑石作吸附剂吸附处理含磷废水,比较了两者对磷的吸附能力,并在不同温度和pH条件下进行了吸附动力学实验。结果表明,焙烧前后的水滑石对磷都具有很好的吸附能力,但300℃焙烧后水滑石的吸附能力提高了约5%。动力学实验表明,水滑石对磷的吸附可很好地用准二级动力学方程进行描述,其线性相关系数达0.999以上。在15∽35℃下进行了等温吸附实验,结果发现水滑石对磷的吸附更符合Langmuir方程。经热力学研究发现,标准吸附焓变（ΔH0）〉0J/mol、标准吸附自由能（ΔG0）〈0J/mol和标准吸附熵变（ΔS0）〉0J/（mol·K）,说明水滑石对磷的吸附反应是自发的吸热反应,且是一个熵增加的过程。

Bimetallic Ni-Fe catalysts derived from layered double hydroxides for CO methanation from syngas

Carbon deposition and sintering of active components such as nano particles are great challenges for Ni-based catalysts for CO methanation to generate synthetic natural gas from syngas. Facing the challenges, bimetallic catalysts with different Fe content derived from layered double hydroxide containing Ni, Fe, Mg, A1 elements were prepared by co-precipitation method. Nanoparticles of Ni-Fe alloy were supported on mixed oxides of aluminium and magnesium after calcination and reduction. The catalysts were characterized by Brunner- Emmett-Teller （BET）, X-ray diffraction, hydrogen tem- perature programmed reduction, inductively coupled plasma, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric techniques, and their catalytic activity for CO methanation was investigated. The results show that the Ni-Fe alloy catalysts exhibit better catalytic performance than mono- metallic catalysts except for the Ni4Fe-red catalyst. The Ni2Fe-red catalyst shows the highest CO conversion （100% at 260-350 ~C）, as well as the highest CH4 selectivity （over 95% at 280-350 ~C）, owing to the formation of Ni-Fe alloy. In stability test, the Ni2Fe-red catalyst exhibits great improvement in both anti-sintering and resistance to carbon formation compared with the Ni0Fe-red catalyst. The strong interaction between Ni and Fe element in alloy and surface distribution of Fe element not only inhibits the sintering ofnanoparticles but restrains the formation of Ni clusters.

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.

Mg-Fe/LDH的合成及其对废水酸性黑10B脱色研究

采用共沉淀法制备了Mg-Fe双金属氢氧化物材料(Mg-Fe/LDH),用于处理偶氮类染料酸性黑10B,通过改变吸附时间、pH和酸性黑10B废水含量及掺加共存无机阴离子等因素探讨了材料对酸性黑10B的脱色效果。结果表明,处理10mL酸性黑10B,当材料用量20.0mg、处理时间1h、pH在2～11时,酸性黑10B的脱色率可达91.3%以上,且水中共存阴离子对其干扰小。材料对酸性黑10B的吸附过程符合Freundlich等温吸附模式,对酸性黑10B的最大饱和吸附量为95mg·g-1。Mg-Fe/LDH对酸性黑10B有较好的吸附脱色性能,可望在印染废水的脱色方面有较好的应用前景。

Mg/Fe-LDHO/PES复合膜吸附材料的制备与除氟性能

以层状氢氧化镁铁的焙烧产物(Mg/Fe-LDHO)和聚醚砜(PES)为原料,采用共混法制备了Mg/Fe-LDHO/PES复合膜吸附材料,并研究了其对水中氟离子的吸附性能,考察了初始pH值、初始F-浓度、吸附温度、吸附时间以及共存阴离子等因素对吸附效果的影响。结果表明:在25℃条件下,该复合膜饱和吸附容量为12.34mg/g,能在pH=4~10范围内保持稳定的吸附性能,吸附速率较高,前5min内即可达到平衡吸附容量的75%;低温有利于提高复合膜的吸附性能,吸附过程符合准二级动力学模型。通过傅里叶变换红外光谱仪(FT-IR)和扫描电子显微镜(SEM)对复合膜的形貌及结构进行了表征,采用电位滴定法测得复合膜的零电位点pH值(pHpzc)为9.4。

基于MgAl-8-HQ LDH复合粒子选择性检测Fe^(3+)的荧光传感器

为实现对Fe^(3+)高选择和简便检测,基于镁铝层状双氢氧化物(MgAl LDH)层板的Al^(3+)的可调控性及易与8-羟基喹啉(8-HQ)发生配位作用,设计制备了8-HQ插层配位的高荧光性8-羟基喹啉镁铝层状双氢氧化物(Mg_xAl-8-HQ LDH),同时采用IR,XRD,UV-Vis及分子荧光光谱仪表征其结构和性能。IR分析表明8-HQ与铝离子生成C-O-Al和C-N-Al配位键;XRD揭示8-HQ插入MgAl LDH的层板间,致(003)衍射峰向2θ低角度方向移动,衍射峰强度随Mg与Al摩尔比增加而增强;因MgAl LDH层间的8-HQ与Al^(3+)配位,致8-HQ在314 nm处的吸收峰消失,同时在376 nm处出现了金属离子与配体之间的跃迁吸收峰;荧光分析表明:Mg_xAl-8-HQ LDH的荧光强度随Al^(3+)含量降低而增强,当镁铝离子物质的量之比为4∶1时,荧光强度显著强于8-羟基喹啉铝。通过研究金属离子对Mg_4Al-8-HQ LDH粒子荧光光谱的影响,发现该粒子对金属离子表现出显著的选择和差异性,尤其对Fe^(3+)具有高选择性。进一步研究[Fe^(3+)]对Mg_4Al-8-HQ LDH粒子的溶液颜色及荧光强度的影响表明:在10^(-6)~10^(-2)mol·L^(-1)内随[Fe^(3+)]增加,Mg_4Al-8-HQ LDH粒子溶液的颜色由浅黄色变成墨绿色,故可实现上述浓度范围内Fe^(3+)的比色传感;同时其荧光强度显著降低,当[Fe^(3+)]为10^(-3)mol·L^(-1)可完全猝灭其荧光,当-log[Fe^(3+)]为3~6时,-log[Fe^(3+)]与溶液荧光强度呈负相关函数关系,可实现对Fe^(3+)的高选择和灵敏性荧光传感检测,据此本实验成功建立了Mg_A Al-8-HQ LDH粒子荧光和比色双重传感检测Fe^(3+)的新方法。

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。

Ca-Mg-Al-Fe层状金属氢氧化物材料的制备及应用

以镁渣酸浸液为原料,采用共沉淀法制备Ca-Mg-Al-Fe层状金属氢氧化物(LDHs),探究pH值、晶化温度和时间对制备Ca-Mg-Al-Fe层状金属氢氧化物及其吸附性能的影响。结果表明,pH值为11.9,晶化温度和时间分别为150℃和16 h时,制得试样结晶度较高,且具有层状金属氢氧化物的特定结构。LDHs试样用量为0.02 g,对100 mL 100 mg/L甲基橙溶液的吸附量为268.815 mg/g。本研究拓展了层状金属氢氧化物在有机染料废水处理领域的应用价值,为镁渣的综合利用奠定了基础。

MgFe类水滑石法强化混凝深度处理猪场尾水及混凝污泥特性研究

为了深度处理经二级生化处理后的猪场尾水,采用Mg Fe类水滑石法强化混凝猪场尾水。考察了不同pH值、Mg与Fe摩尔配比[n(Mg∶Fe)]等混凝条件对猪场尾水常规指标以及其中微量重金属[Zn^(2+)、Cu^(2+)、Cr(Ⅵ)]和兽用抗生素(磺胺甲基异恶脞,SMX)等去除效果的影响,并利用X射线衍射(XRD)、扫描电镜(SEM)和傅立叶转换红外(FTIR)等技术对混凝污泥特性进行分析,制备了催化材料,进行了混凝污泥资源化利用初探。结果表明:当猪场尾水初始pH>6.5时,TP、浊度和Cr(Ⅵ)去除率分别在95%、80%和35%以上。当初始pH值进一步调节至大于8.0时,MgFe类水滑石对Zn^(2+)和Cu^(2+)去除率可达85%以上,对SMX去除率在75%以上;Mg与Fe摩尔配比对各水质指标去除效果影响不大。混凝污泥主要形成的矿物相有类水滑石与磷酸铁矿物。通过煅烧混凝污泥制备高级氧化催化剂,发现在相同过硫酸氢钾(PMS)投加量的条件下,700℃限氧热解混凝污泥制得的催化剂比同条件下利用人工合成MgFe类水滑石制得的催化剂具有更高的催化活性。研究结果可为养猪处理废水与混凝污泥资源化利用研究提供支持。

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.

Enabling high-efficiency ethanol oxidation on NiFe-LDH via deprotonation promotion and absorption inhibition

Nucleophile oxidation reaction(NOR), represented by ethanol oxidation reaction(EOR), is a promising pathway to replace oxygen evolution reaction(OER). EOR can effectively reduce the driving voltage of hydrogen production in direct water splitting. In this work, large current and high efficiency of EOR on a Ni, Fe layered double hydroxide(NiFe-LDH) catalyst were simultaneously achieved by a facile fluorination strategy. F in NiFe-LDH can reduce the activation energy of the dehydrogenation reaction, thus promoting the deprotonation process of NiFe-LDH to achieve a lower EOR onset potential. It also weakens the absorption of OH-and nucleophile electrooxidation products on the surface of NiFe-LDH at a higher potential, achieving a high current density and EOR selectivity, according to density functional theory calculations. Based on our experiment results, the optimized fluorinated NiFe-LDH catalyst achieves a low potential of 1.386 V to deliver a 10 mA cm^(-2)EOR. Moreover, the Faraday efficiency is greater than 95%, with a current density ranging from 10 to 250 mA cm^(-2). This work provides a promising pathway for an efficient and cost-effective NOR catalyst design for economic hydrogen production.

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。

AB24在MgAl-LDO上的吸附性能及机理研究

本文探讨了nMg/nAl=3的水滑石焙烧产物（MgAl-LDO）对染料酸性黑24（AB24）的吸附性能及其机理。考察了不同因素对MgAl-LDO吸附AB24性能的影响，并研究了吸附过程的热力学和动力学机理。实验结果表明：MgAl-LDO对AB24具有优异的吸附性能，在298 K，pH=10条件下，1.0 g·L^-1 MgAl-LDO对1 000 mg·L^-1 AB24溶液的吸附容量和去除率分别达到998.31 mg·g^-1和99.83%。动力学和热力学研究表明：MgAl-LDO对AB24的吸附过程同时符合Langmuir和Freundlich等温吸附方程，并且是个放热、自发的过程。计算所得的吉布斯自由能绝对值在10-15 kJ·mol^-1，这主要是由染料分子与水滑石层板的氢键作用产生，结合Materials Studio 5.5软件模拟AB24染料分子在MgAl-LDHs上的排列分布，推测MgAl-LDO对AB24的吸附机理是表面吸附（占优势）与层间插层的协同作用。同时，该吸附过程符合准二级反应动力学模型。