Mechanical analysis of double-layered circular graphene sheets as building material embedded in an elastic medium

Possessing the unique and highly valuable properties, graphene sheets(GSs) have attracted increasing attention including that from the building engineer due to the fact that Graphene can be utilized to reinforce concrete and other building materials. In this work, the nonlocal elastic theory and classical plate theory(CLPT) are used to derive the governing equations. The element-free framework for analyzing the buckling behaviors of double layer circular graphene sheets(DLCGSs) relying on an elastic medium is proposed. Pasternak-type model is adopted to describe the elastic medium. Accordingly, the influences of boundary conditions, size of GSs and nonlocal parameters on the buckling behavior of DLCGSs are investigated. The results show that the OP buckling modes are only sensible to the van der Waals forces.

Advances in preparation methods and mechanism analysis of layered double hydroxide for lithium-ion batteries and lithium-sulfur batteries

Lithium-ion(Li-ion) battery and lithium-sulfur(Li-S) battery have attracted significant attention as promising components for large-scale energy storage because of high theoretical capacity of Li,excellent energy density or environmental friendness for two kinds of batteries.However,there still exist some respective obstacles for commercial applications,such as limited theoretical capacity,high cost and low conductivity of Li-ion cells or shuttle effect of lithium polysulfides of Li-S cells.As typical twodimensional materials,layered double hydroxides(LDHs) exhibit excellent potential in the field of energy storage due to facile tunability of composition,structure and morphology as well as convenient composite and strong catalytic properties.Consequently,various LDHs toward novel separators or interlayers,cathodes,anodes,and interesting catalytic templates are researched to resolve these challenges.In this review,the recent progress for LDHs applied in Li-ion batteries and Li-S batteries including the synthesis methods,designs and applications is presented and reviewed.Meanwhile,the existing challenges and future perspectives associated with material designs and practical applications of LDHs for these two classes of cells are discussed.WeWe hope that the review can attract more attention and inspire more profound researches toward the LDH-based electrochemical materials for energy storage.

Preparation of PO_4^(3-),P_2O_7^(4-) Anion-Pillared Nanocrystalline Mg-Al and Zn-Al Layered Double Hydroxides in Microwave Fields

Using nanocrystalline [Mg-Al-CO3] and [Zn-Al-CO3] as precursors, [Mg-Al-PO4], [Zn-Al-PO4], [Mg-Al-P2O7] and [Zn-Al-P2O7] have been successfully synthesized by a direct reaction with the free PO43- or P2O74- using the microwave techniques and the anion-exchange method. And the samples thus obtained were characterized by TEM, FT-IR and XRD. The results show that the initial interlayer carbonate ions can be completely replaced by the free PO43- or P2O74-under controlled microwave conditions employed for a short time.

Desorption of Cl^(-) from Mg-Al layered double hydroxide intercalated with Cl^(-) using CO_(2) gas and water

Mg-Al layered double hydroxide intercalated with CO_(3)^(2-)(CO_(3)·Mg-Al LDH) is effective for treating HCl exhaust gas.HCl reacts with CO_(3)^(2-) in CO_(3)·Mg-Al LDH, resulting in the formation of Cl·Mg-Al LDH.We propose that CO_(2) can be used for the desorption of Cl^(-)from Cl·Mg-Al LDH to regenerate CO_(3)·Mg-Al LDH.Herein,we studied the desorption of a from CI-Mg-Al LDH by adding water to Cl·Mg-Al LDH and blowing CO_(2) into it.We also analyzed the effects of temperature and water addition speed on the desorption of CI^(-)from Cl·Mg-Al LDH.Our results show that the added water adhered to CI·Mg-Al LDH and that CO_(2) in the gaseous phase was dissolved in this adhered water,thus generating CO_(3)^(2-).Therefore,anion exchange occurred between CO_(3)^(2-) and Cl^(-)in the Cl·Mg-Al LDH,thus desorbing Cl^(-).

Pt_(1)/Ni_(6)Co_(1)layered double hydroxides/N-doped graphene for electrochemical non-enzymatic glucose sensing by synergistic enhancement of single atoms and doping

The development of novel single-atom catalysts is important for highly efficient electrochemical catalysis and sensing.In this work,a novel Pt single atoms(SAs)supported on Ni_(6)Co_(1)layered double hydroxides/nitrogen-doped graphene(Pt_(1)/Ni_(6)Co_(1)LDHs/NG)was constructed for electrochemical enzyme-free catalysis and sensing towards glucose.The loading of Pt single atoms increases with doping of Co atoms that generate more anchoring sites for Pt SAs.The resulting Pt_(1)/Ni_(6)Co_(1)LDHs/NG exhibits low oxidative potential of 0.440 V with high sensitivity of 273.78μA·mM^(−1)·cm^(−2)toward glucose,which are 85 mV lower and 15 times higher than those of Ni(OH)_(2),respectively.Pt_(1)/Ni_(6)Co_(1)LDHs/NG also shows excellent selectivity and great stability during 5-week testing.Theoretical and experimental results show that the boosted performance of Pt_(1)/Ni_(6)Co_(1)LDHs/NG originates from its stronger binding energy with glucose and the synergistic effect of Pt SAs,Co doping,and NG.This work provides a general strategy of designing highly active SACs for extending their application in electrochemical sensing.

Spacing graphene and Ni-Co layered double hydroxides with polypyrrole for high-performance supercapacitors

The urgent need of high-performance of energy storage devices triggers us to design newly class of materials.Generally,the materials feature with high conductivity,abundant pore s and excellent stability.Here,a sandwiched hybrid composite containing reduced graphene oxide,polypyrrole and Ni-Co layered double hydroxides(RGO/PPy/NiCo-LDH) was prepared in a facile way.The polypyrrole was incorporated in the two dimensional(2D) nanosheets,which not only serve as the spacer to increase the surface area,but also enhance the conductivity of the nanocomposite.The obtained architecture was employed as an advanced electrode in a supercapacitor.The electrode shows an ultrahigh specific capacitance(2534 F g^-1 at 1 A g^-1) and good cycling efficiency(78 % after 5000 cycles).Moreover,an asymmetric cell based RGO/PPy/NiCo-LDH composite demonstrates excellent electrochemical properties and good prospect of practical use.

Layered double hydroxide- and graphene-based hierarchical nanocomposites： Synthetic strategies and promising applications in energy conversion and conservation

The persistent need for a sustainable energy economy has led researchers to focus on novel energy conversion and storage technologies, inspiring the discovery of smart material designs such as hierarchical nanocomposites~ These nanocomposites have proven effective in the advancement of energy-based technologies. The synergistic properties of hierarchical nanocomposites composed of two types of two-dimensional layered materials, layered double hydroxides and graphene, have resulted in improved electrochemical as well as photocatalytic performance. Synthetic strategies and their effect on the electrochemical and photocatalytic performance of these nanocomposites as high-performance supercapacitors and water oxidation catalysts are discussed in detail in this review.

Development of metal-organic framework(MOF) decorated graphene oxide/Mg Al-layered double hydroxide coating via microstructural optimization for anti-corrosion micro-arc oxidation coatings of magnesium alloy

An efcient and simple in-situ growth strategy has been discovered for the preparation of highly reproducible and continuous symbiotic ZIF-8-based anticorrosion coating by using graphene oxide(GO)/Mg AlNO3layered double hydroxides(G/LDHs) buffer layer as a new type of connecting carrier based on micro-arc oxide(MAO) coating of AZ31 magnesium alloy. The components of ZIF-8 were adsorbed and bounded to the surface of the G/LDHs buffer layer-modified substrates to promote the nucleation of ZIF-8,thus growing a phase-pure, uniform, and good symbiosis ZIF-8 membrane. ZIF-8 particles with different growth times compensate for the grain boundary defects of the G/LDHs coating precursor buffer layer to different degrees. The prepared ZIF-8-based coating has excellent stability and corrosion resistance. The results demonstrate that the G/LDHs buffer layer provides a new channel for the MOF-modified MAO substrate of AZ31 magnesium alloy. It also proves that it is feasible to build high-performance anticorrosive coatings with MOF materials.

Nonlocal Galerkin Strip Transfer Function Method for Vibration of Double-Layered Graphene Mass Sensor

Double-layered graphene sheets （DLGSs） can be applied to the development of a new generation of nanomechanical sensors due to their unique physical properties. A rectangular DLGS with a nanoparticle randomly located in the upper sheet is modeled as two nonlocal Kirchhoff plates connected by van der Waals forces. The Galerkin strip transfer function method which is a semi-analytical method is developed to compute the natural frequencies of the mass- plate vibrating system. It can give exact closed-form solutions along the longitudinal direction of the strip. The results obtained from the semi-analytical method are compared with the previous ones, and the differences between the single-layered graphene sheet （SLGS） and the DLGS mass sensors are also investigated. The results demonstrate the similarity of the in-phase mode between the SLGS and DLGS mass sensors. The sensitivity of the DLGS mass sensor can be increased by decreasing the nonlocal parameter, moving the attached nanoparticle closer to the DLGS center and making the DLGS smaller. These conclusions are helpful for the design and application of graphene-sheet-based resonators as nano-mass sensors.

A superior catalyst for ozone decomposition: NiFe layered double hydroxide

Ground-level ozone is harmful to human beings and ecosystems,while room-temperature catalytic decomposition is the most effective technology for ozone abatement.However,solving the deactivation of existing metal oxide catalysts was caused by oxygen-containing intermediates is challenging.Here,we successfully prepared a two-dimensional NiFe layered double hydroxide (NiFe-LDH) catalyst via a facile co-precipitation method,which exhibited stable and highly efficient performance of ozone decomposition under harsh operating conditions (high space velocity and humidity).The NiFe-LDH catalyst with Ni/Fe=3and crystallization time over 5 hr (named Ni3Fe-5) exhibited the best catalytic performance,which was well beyond that of most existing manganese-based oxide catalysts.Specifically,under relative humidity of 65%and space velocity of 840 L/(g·hr),Ni3Fe-5 showed ozone conversion of 89%and 76%for 40 ppmV of O3within 6 and 168 hr at room-temperature,respectively.We demonstrated that the layered structure of NiFe-LDH played a decisive role in its outstanding catalytic performance in terms of both activity and water resistance.The LDH catalysts fundamentally avoids the deactivation caused by the occupancy of oxygen vacancies by oxygen-containing species (H2O,O-,and O2-) in manganese-based oxide.This study indicated the promising application potential of LDHs than manganese-based oxide catalysts in removal of gaseous ozone.

Ultrathin layered double hydroxide nanosheets prepared by original precursor method for photoelectrochemical photodetectors

Layered double hydroxides(LDHs)are widely used owing to their unique alternating anionic and cationic layered twodimensional(2D)structures.However,studies on the preparation of 2D LDH nanosheets with uniform thickness and their photodetectors are limited.In this study,two novel ultrathin LDH(Ca-In and Ca-Al LDH)nanosheets are peeled off from precursor bimetallic phosphides through the original precursor method.Both Ca-In and Ca-Al LDH nanosheets demonstrate a uniform thickness distribution with an average thickness of 3–4 nm,micron-level lateral sizes,and moderate bandgap.Owing to its broad light absorption range,hydrophilicity,and stability,Ca-In and Ca-Al LDH nanosheets are applied for the first time in photoelectrochemical photodetectors,realizing a wide range of light detection from ultraviolet(365 nm)to visible light(635 nm).Moreover,the fabricated photodetectors exhibit excellent cycle stability,and the average photocurrent density shows no reduction after 70 days.Therefore,this study provides an effective method to prepare 2D Ca-In and Ca-Al LDH nanosheets with uniform thickness and photoelectric application prospects.

Tribological behavior of layered double hydroxides with various chemical compositions and morphologies as grease additives

The layered double hydroxide(LDH)is a kind of natural mineral,which can also be manually prepared.It has been practically applied in various fields due to its unique crystal structure and diversity of composition,size,and morphology.In this work,LDHs with different chemical compositions(Co^(2+),Mg^(2+),Zn^(2+),and Ni^(2+))and topographical features(flower‐like,spherical,and plate‐like)were successfully prepared by controlling the reaction conditions.Then,they were mechanically dispersed into base grease and their tribological properties were evaluated by a ball‐on‐disk tester under a contact pressure of 2.47 GPa.It was found that the variation of morphology,instead of chemical composition,had great influence on the tribological performance.The“flower‐like”LDH sample with high specific surface area(139 m^(2)/g)was demonstrated to show the best performance.With 1 wt%additive,the wear volume was only about 0.2%of that lubricated by base grease.The tribofilm with unique microscopic structure and uniform composition was derived from tribochemical reaction between LDH additives and sliding solid surfaces,effectively improving tribological properties of the lubrication system.This work provided the guidance for optimizing lubricant additives and held great potential in future applications.

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.

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。

添加Al(NO_(3))_(3)对镁合金表面水滑石蒸汽涂层耐蚀性能的影响

目的研究原位蒸汽法制备层状双金属氢氧化物(LDH)的反应机理,以及添加Al(NO_(3))_(3)对AZ91D镁合金表面水滑石蒸汽涂层耐蚀性的影响和耐蚀机理。方法在蒸汽源中添加不同浓度的Al(NO_(3))_(3),以提供Al3+,采用原位蒸汽法在150℃下进行5 h水热反应,在AZ91D镁合金表面制备水滑石蒸汽涂层。使用XRD、FT-IR、SEM、EDS等测试手段对水滑石蒸汽涂层进行表征,通过动电位极化、电化学阻抗和盐雾试验,研究水滑石蒸汽涂层的生长机理及腐蚀机理。结果基于不同浓度梯度的Al(NO_(3))_(3),在AZ91D镁合金表面成功制备了水滑石蒸汽涂层,涂层的主要组成物相为Mg(OH)_(2)、Mg-Al-NO_(3)LDH、Mg-Al-CO_(2)LDH。Al(NO_(3))_(3)/LDH相较于未添加Al(NO_(3))_(3)得到的LDH,其生长均匀、结构致密,耐腐蚀性能由大到小的顺序为LDH-100、LDH-200、LDH-50、LDH-20、LDH、AZ91D镁合金。水滑石蒸汽涂层的腐蚀产物主要为Mg(OH)_(2)、MgCO_(3)。结论在添加100 mmol/L的Al(NO_(3))_(3)作为蒸汽源时,充足的Al^(3+)保证了合成结构致密水滑石的需要,副产物最少,且耐蚀性最好。最后,讨论了水滑石蒸汽涂层的生长机理和腐蚀机理。

钴镍双金属氢氧化物/石墨烯电控分离膜排异性回收废水中低浓度磷酸盐

采用滴涂结合电化学沉积两步法制备了一种具有优良电活性的三维花状钴镍双金属氢氧化物/石墨烯(CoNi-LDH/G)杂化膜,用于电控离子交换过程(electrically switched ion exchange,ESIX)吸附水溶液中低浓度的磷酸根(PO_(4)^(3-))离子。结合X射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等对CoNi-LDH/G杂化膜进行形貌、组成及结构表征。采用电化学方法考察了该杂化膜在不同吸附电压、不同初始浓度、共存离子及不同pH值条件下对PO_(4)^(3-)吸附性能的影响。实验结果表明:通过调节氧化还原电位,即使在低浓度下,杂化膜对PO_(4)^(3-)也具有良好的吸附性能,且可以在较宽的pH值(4~10)范围内使用,同时受共存离子及其浓度变化影响甚小。此外,G对PO_(4)^(3-)的吸附容量为1.10 mg·g^(-1),CoNi-LDH对PO_(4)^(3-)的吸附容量为11.74 mg·g^(-1),二者吸附容量之和小于CoNi-LDH/G对PO_(4)^(3-)的吸附容量(16.25 mg·g^(-1))。同时,结合O1s的XPS数据分析发现,CoNi-LDH/G杂化膜对PO_(4)^(3-)的吸附过程除了层间阴离子交换、PO_(4)^(3-)与层板金属离子配位的配体交换外,还存在G与CoNi-LDH之间的协同效应。

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.

Zn-Al-Zr LDH/氧化石墨烯对水中草甘膦的去除研究

采用氯化锌、六水合氯化铝、八水合氧氯化锆和氧化石墨烯为原料,氢氧化钠和一水合碳酸钠为碱溶液,通过共沉淀法合成Zn-Al-Zr LDH/GO纳米复合材料(LDH/GO)。XRD、SEM、BET和UV-Vis分光光度计,分别用于表征Zn-Al-Zr LDH/GO复合材料的物相组成、微观形貌、孔隙结构和吸附过程。结果表明:GO的掺入可以改善LDH的形貌结构,当温度在303 K,pH=7,投料量为0.5g/L,LDH/GO对草甘膦的吸附容量可达10.707 mg/g;其吸附过程符合准二级动力学和Freundlich等温吸附模型,LDH/GO对草甘膦的去除机理为静电吸引和表面络合;其草甘膦吸附性能优于当前商业磷吸附产品Phoslock。因此,Zn-Al-Zr LDH/GO可作为一种有前景的草甘膦去除剂。

层状双金属氢氧化物活化过硫酸盐在水处理中的应用

基于硫酸根自由基的高级氧化技术(SR-AOPs)具有宽pH耐受性、强氧化性以及方便操作性等优势而受到关注。层状双金属氢氧化物(LDHs)因其独特的层状结构优势、层板组成可调控性、结构记忆效应和阴离子可交换性等特性,在活化过硫酸盐方面表现出良好的活性和催化优势。本论文重点综述了LDHs及其复合材料作为非均相催化剂活化过硫酸盐在水污染处理领域的应用现状,最后,对LDHs催化体系持续改进以及未来研究方向进行了展望。

不同合成方法的类水滑石对磷吸附特性研究

不同合成方法制备的类水滑石其结晶度、比表面积和孔容孔径存在差异,进而影响其吸附性能。该文采用水热法和共沉淀法制备了镁铝类水滑石(LDH-H和LDH-C),研究了初始pH、吸附时间、初始浓度和共存离子等对吸附磷酸根的影响,拟合了吸附动力学和吸附等温模型。结果表明:LDH-H在pH为3~6时性能更为稳定;LDH-H和LDH-C对磷酸根的吸附更符合拟二级动力学方程和Langmuir吸附等温模型,属于单层化学吸附;LDH-H的吸附速率是LDH-C的7.2倍,两者对应的最大吸附容量分别为41.003 mg/g和22.179 mg/g;低浓度的共存离子(Cl^(-)、NO_(3)^(-)、CO_(3)^(2-)和SO_(4)^(2-))对LDH-H和LDH-C吸附磷酸根的影响较弱。结合X射线衍射、傅里叶变换红外能谱对吸附前后的材料表征结果,LDH-H吸附性能优于LDH-C的原因在于其层间离子交换作用更强。该研究可为缓解水体的富营养化和开发高效除磷吸附剂提供技术支持。