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.

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.

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.

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 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.

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。

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。

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.

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。

一步水热合成Eu^3＋掺杂Mg-Al水滑石及其发光性能研究

采用一步水热合成了稀土Eu掺杂的镁铝水滑石层状化合物(MgAlEuCO3-LDHs)。探讨了水热温度和水热时间对水滑石晶体结构的影响。利用XRD、SEM、FT-IR和荧光光谱对样品的组成和性质进行表征。XRD、FT-IR结果表明:当n(Mg2+):n(Al3+):n(Eu3+)=2:1:0.15时120℃、4h水热处理后即可得到结晶完好的层状MgAlEuCO3-LDHs,Eu3+成功地插层组装进入LDHs层板。荧光光谱测试发现掺杂稀土Eu3+离子的MgAlEuCO3-LDHs具有Eu3+的5D0→7FJ特征光谱。

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-Al水滑石晶粒生长特性研究

以水镁石和Al(NO3)3.9H2O为镁源和铝源,采用液相共沉淀法合成Mg-Al水滑石,重点考察了溶液中Mg2+浓度、晶化时间和晶化温度对Mg-Al水滑石晶体结构、晶粒尺寸及晶面选择性生长的影响规律,并通过XRD,SEM等对合成产物进行了表征。结果表明:提高Mg2+浓度,Mg-Al水滑石晶体结构规整性降低,对水滑石层板和层板叠合方向的发育和生长不利,晶粒尺寸减小;在Mg2+浓度不变的情况下,固定晶化温度而延长晶化时间,或固定晶化时间而提高晶化温度,Mg-Al水滑石的晶体结构均趋于完整,晶粒尺寸显著增大,其沿a轴方向的生长速率比沿c轴方向的生长速率快,即[110]晶面的生长速率比[003]晶面的生长速率快。在Mg2+浓度为0.12mol/L,晶化时间为8 h,晶化温度为80℃的条件下,制得了粒度达到纳米级的Mg-Al水滑石。

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。

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LDH中间层的纳滤膜及其镁锂分离性能

实现盐湖卤水中镁锂的分离成为盐湖提锂过程中面临的巨大挑战,开发具有高镁锂分离性能的纳滤膜成为亟待解决的关键问题。通过化学刻蚀法获得了多孔层状双金属氢氧化物(layered double hydroxide,LDH)纳米片,然后将其沉积在聚丙烯腈多孔膜表面作为中间层,在该中间层上通过聚乙烯亚胺与均苯三甲酰氯界面聚合形成聚酰胺分离层,最终获得表面荷正电的LDH/聚酰胺纳滤膜。LDH中间层不仅增强了膜表面的荷正电性,且诱导聚酰胺层形成咖啡环结构,提高了膜表面的粗糙度,因此同步提高了膜的选择性和渗透性。当分离镁锂比为20的混合溶液时,LDH/聚酰胺纳滤膜的镁锂分离因子为17,渗透性为1.15×10^(-4)L/(m^(2)·h·Pa),且在实验时间(100 h)范围内性能稳定,展现出良好的镁锂分离应用前景。

SO42-对MgAl-LDHs吸附Cl-和阻锈性能的影响

通过共沉积法制备Mg Al 层状双金属氢氧化合物(MgAl LDHs),以碱性溶液模拟混凝土孔溶液通过等温吸附试验、自腐蚀电位(E )、电化学阻抗谱(EIS)研究了SO2-和Cl^-共存环境下corr 4MgAl LDHs的吸附性能及对混凝土中钢筋腐蚀的阻锈性能.此外,通过X射线衍射(XRD)和傅里叶变换红外光谱( FTIR)对LDHs微结构进行观测揭示其作用机理.结果表明:MgAl LDHs对Cl^-和 SO4^2-离子的吸附过程符合 Langmuir 等温吸附模型,最大吸附量分别为 2. 853、1. 587 mmol/ g,SO4^2-的存在会抑制MgAl LDHs对于Cl^-的吸附;MgAl LDHs对钢筋具有明显的缓蚀效果,且随着SO4^2-含量的增加钢筋腐蚀先缓解后加剧;MgAl LDHs对Cl^-吸附是其缓蚀的主要原因.而随着 SO4^2-含量的增加,反应生成石膏在钢筋表面吸附是钢筋腐蚀先缓解的原因,但 MgAl LDHs会优先吸附SO4^2-导致残余的Cl^-增加,钢筋腐蚀加剧.

多羟基醇类共溶剂对Mg/Al水滑石水热制备的影响

以Mg(NO3)2.6H2O为镁源、Al(NO3)3.9H2O为铝源,采用水热法制备Mg/Al水滑石。鉴于水滑石中广泛存在的氢键相互作用,以多羟基醇为共溶剂,对比分析了水、水/乙醇、水/乙二醇、水/丙三醇及水/季戊四醇等5种溶剂条件下水热合成得到的Mg/Al水滑石的结构和热性质。利用XRD、SEM、IR、DSC等的分析结果表明,随着共溶剂中醇羟基数目的增多,所得水滑石中结晶水的水合程度提高。共溶剂与水滑石之间水滑石,晶粒形貌类似于纯水得到的水滑石。而以水/丙三醇及水/季戊四醇为溶剂得到的水滑石,晶形变的不规则,且伴随着粒径尺寸变小和晶粒团聚现象。同时,随着共溶剂中醇羟基数目的增多,层间结合水的释放温度提高,而层间CO2脱除和基本层上的羟基脱水温度则相应降低。