Uptake of heavy metal ions from aqueous solution using Mg–Al layered double hydroxides intercalated with citrate, malate, and tartrate

Mg–Al layered double hydroxide (Mg–Al LDH) was modified with organic acid anions using a coprecipitation technique, and the uptake of heavy metal ions from aqueous solution by the Mg–Al LDH was studied. Citrate·Mg–Al LDH, malate·Mg–Al LDH, or tartrate·Mg–Al LDH, which had citrate³⁻ (C₆H₅O₇³⁻), malate²⁻ (C₄H₄O₅²⁻), or tartrate²⁻ (C₄H₄O₆²⁻) anions intercalated in the interlayer, was prepared by dropwise addition of a mixed aqueous solution of Mg(NO₃)₂ and Al(NO₃)₃ to a citrate, malate, or tartrate solution at a constant pH of 10.5. These Mg–Al LDHs were found to take up Cu²⁺ and Cd²⁺ rapidly from an aqueous solution at a constant pH of 5.0. This capacity was mainly attributable to the formation of the citrate–metal, malate–metal, and tartrate–metal complexes in the interlayers of the Mg–Al LDHs. The uptake of Cu²⁺ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH < citrate·Mg–Al LDH. The uptake of Cd²⁺ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH = citrate·Mg–Al LDH. These differences in Cu²⁺ and Cd²⁺ uptake were attributable to differences in the stabilities of the citrate–metal, malate–metal, and tartrate–metal complexes. These results indicate that citrate³⁻, malate²⁻, and tartrate²⁻ were adequately active as chelating agents in the interlayers of Mg–Al LDHs.     

Photodegradation of 2,4-dichlorophenoxyacetic acid using ZnAlFe layered double hydroxides as photocatalysts

ZnAlFe layered double hydroxides (LDHs) with different Zn:Al:Fe ratio were obtained by the co-precipitation method and tested as photocatalysts for 2,4-dichlorophenoxyacetic acid (2,4-D) degradation. High specific surface areas (138–70 m²/g) as well as semiconductor properties (band gap values of 2.59–2.00 eV) were obtained in the samples calcined at 673 K. When calcined samples were put in contact with as solution containing 300 ppm of 2,4-D, the reconstruction of the LDHs (memory effect) and an unexpected high capacity of 2,4-D adsorption were observed. The photodegradation in aqueous phase after saturation of the LDHs with 2,4-D showed that the confined (adsorbed) 2,4-D can be successfully degraded with ZnAlFe LDH photocatalysts.     

Preparation and characterization of Mg–Al layered double hydroxides intercalated with benzenesulfonate and benzenedisulfonate

Mg–Al layered double hydroxides (Mg–Al LDHs) intercalated with benzenesulfonate (BS^–) and benzenedisulfonate (BDS^2–) ions were prepared by coprecipitation and characterized by X-ray diffraction, FT-IR spectroscopy, and chemical analyses. The intercalated BS^– and BDS^2– maintained their intrinsic molecular structures within the Mg–Al LDH interlayers. At low intercalation levels, the benzene ring of BS^– in BS · Mg–Al LDH was inclined at 30° relative to the plane of the brucite-like layers of Mg–Al LDH. With increasing BS^– content, the benzene ring adopted an additional configuration perpendicular to the Mg–Al LDH layers. In BDS-intercalated Mg–Al LDH, the benzene ring of BDS^2– was tilted at 26° relative to the plane of the Mg–Al LDH layers. Intercalation levels of BDS^2– were smaller than those of BS^– despite the greater charge density of BDS^2–, which was likely attributable to a greater degree of electrostatic repulsion between intercalated anions.     

Adsorption of fluoride ions by Zn–Al layered double hydroxides

Zn–Al layered double hydroxides (LDHs) with different molar ratios Zn/Al (0, 0.17, 0.34, 0.97, 3.47, ∝) were prepared by the co-precipitation of chlorides, characterized and evaluated for their fluoride adsorption at room temperature from aqueous solutions. The fluoride adsorption of the as-synthesized LDHs was influenced by the chemical composition of the LDHs and ZA-11 (Zn/Al = 0.97) had the highest capacity for fluoride adsorption (1.14–4.16 mg/g). The adsorption increased after calcination of the LDH up to 500 °C. The equilibrium data were fitted to the Freundlich, Langmuir, and Temkin equations. The kinetics of fluoride adsorption followed the pseudo-second order model.     

Adsorption and photocatalytic degradation of phenol and 2,4 dichlorophenoxiacetic acid by Mg–Zn–Al layered double hydroxides

Mg–Zn–Al layered double hydroxides (LDHs) with varying amounts of zinc were prepared by the coprecipitation method. Solids were analyzed by XRD and N₂ physisorption, confirming the formation of pure LDH phase; and the production of mixed oxides with high specific surface areas (182–276 m² g⁻¹) after calcination. Band gap energy was also determined, presenting the expected decreasing tendency on increasing zinc amounts. These mixed oxides were tested both for the adsorption of 2,4 dichlorophenoxiacetic acid (2,4-d) and for the photocatalytic degradation of 2,4-d and phenol. Nearly total (97%) degradation of initial 1.45 mmol L⁻¹ of 2,4-d, with 1 g calcined LDH per liter, was accomplished in 9 h, while phenol half-life was as short as 3.5 h, with the catalyst with lowest zinc amount (5 wt.%). Langmuir adsorption isotherms are presented. Solids were also characterized by XRD and FTIR analysis after photocatalytic and adsorption activity, to determine the presence of 2,4-d. The versatility of LDH decomposition products in the elimination of different contaminants by different mechanisms puts them forward as a viable alternative for environmental remediation.     

Thermal behaviour of Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides and characterization of formed oxides

Thermal behaviour of synthetic Cu–Mg–Mn and Ni–Mg–Mn layered double hydroxides (LDHs) with M^II/Mg/Mn molar ratio of 1:1:1 was studied in the temperature range 200–1100 °C by thermal analysis (TG/DTA/EGA), powder X-ray diffraction (XRD), Raman spectroscopy, and voltammetry of microparticles. Powder XRD patterns of prepared LDHs showed characteristic hydrotalcite-like phases, but further phases were indirectly found as admixtures. The Cu–Mg–Mn precipitate was decomposed at temperatures up to ca. 200 °C to form an XRD-amorphous mixture of oxides. The crystallization of CuO (tenorite) and a spinel type mixed oxide of varying composition Cu_xMg_yMn_zO₄ with Mn⁴⁺ was detected at 300–500 °C. At high temperatures (900–1000 °C), tenorite disappeared and a consecutive crystallization of 2CuO·MgO (gueggonite) was observed. The high-temperature transformation of oxide phases led to a formation of Cu^I oxides accompanied by oxygen evolution. The DTA curve of Ni–Mg–Mn sample exhibited two endothermic effects characteristic for hydrotalcite-like compounds. The first one with minimum at 190 °C can be ascribed to a loss of interlayer water, the second one with minimum at 305 °C to the sample decomposition. Heating of the Ni–Mg–Mn sample at 300 °C led to the onset of crystallization of oxide phases identified as Ni_xMg_yMn_zO₄ spinel, (Ni,Mg)O oxide containing Mn⁴⁺ cations, and easily reducible XRD-amorphous species, probably free Mn^III,IV oxides. At 600 °C (Raman spectroscopy) and 700 °C (XRD), the (Ni,Mg)₆MnO₈ oxide with murdochite structure together with spinel phase were detected. Only spinel and (Ni,Mg)O were found after heating at 900 °C and higher temperatures. Temperature-programmed reduction (TPR) profiles of calcined Cu–Mg–Mn samples exhibited a single reduction peak with maximum around 250 °C. The highest H₂ consumption was observed for the sample calcined at 800 °C. The reduction of Ni–Mg–Mn samples proceeded by a more complex way and the TPR profiles reflected the phase composition changing depending on the calcination temperature.     

Adsorption of 2,4-D on Mg/Al–NO3 layered double hydroxides with varying layer charge density

Layered double hydroxides (LDHs) have high surface area and high anion exchange capacity, so they have been proposed to be an effective scavenger for contaminants. In this study, the adsorption of 2,4-dichlorophenoxyacetate (2,4-D) on Mg/Al–NO₃ LDHs with varying layer charge density was investigated with particular attention on the effect of the orientation of the interlayer nitrate. Three Mg/Al LDHs were synthesized with Al³⁺/(Al³⁺ + Mg²⁺) molar ratios of 3.3 (LDH3), 2.6 (LDH4) and 2.1 (LDH5). The results of adsorption experiments showed that LDH5 exhibited an S-type isotherm with a low 2,4-D adsorption capacity due to the low accessibility of 2,4-D to the interlayer space. The accessibility was restricted by the small basal spacing of LDH5 as a result of the parallel orientation of the interlayer nitrate with respect to the hydroxide sheet. Thus, the 2,4-D adsorption occurred mainly on the external surface of the material. On the contrary, LDH3, which has the highest layer charge density among the samples, contains nitrate with an orientation perpendicular to the hydroxide sheet of LDH3. The interlayer nitrate was readily exchanged by 2,4-D. Thus, in addition to the adsorption on the external surface, the replacement of the interlayer nitrate by 2,4-D contributed to a higher adsorbed amount of 2,4-D; the 2,4-D adsorption of LDH3 exhibited an L-type isotherm. For LDH4 that contained interlayer nitrate with both parallel and perpendicular orientations, the adsorption characteristics were between those of LDH3 and LDH5. This work has demonstrated the dependence of 2,4-D adsorption characteristics on the nitrate orientation in LDHs, as a consequence of changing layer charge density.     

Catalytic synthesis of chalcone and flavanone using Zn–Al hydrotalcite adhere ionic liquid

The Claisen–Schmidt condensation of 2′-hydroxy acetophenone and benzaldehyde to chalcone and flavanone show that calcined Zn–Al (6) hydrotalcite is active for this synthesis. Coating of ionic liquid ‘1-(tri-ethoxy-silyl-propyl)-3-methyl-imidazolium chloride’ on Zn–Al hydrotalcites was accomplished employing incipient wetness process and on NaY, NaX, MK-5 and silica gel employing co-condensation methodology. Impregnated IL on calcined Zn–Al (6) catalysts were characterized by XRD, SEM, BET, ¹³C and ²⁷Al NMR analysis and the activity of these catalysts were investigated for chalcone and flavanone synthesis. ²⁷Al CP MAS NMR technique was used to show that interaction of IL with hydrotalcite modifies the acid–base sites and is responsible for enhancement of catalyst activity. Several aromatic aldehydes were screened to assess the general applicability of the system.     

Alkoxylation reaction catalysed by layered double hydroxides

Layered double hydroxides (LDHs) are extensively studied as precursors for catalysts, following a calcination at high temperatures to yield mixed oxides. However, these materials are less used as layered materials, i.e., without undergoing thermal activation. We have focused in this work on the use of a series of as-synthesised LDHs for the catalytic preparation of glycol ethers, which is a reaction of primary commercial importance. Two main systems are considered, namely the [Cu–Cr] and [Mg–Al] LDHs. The [Cu–Cr–Cl] LDH is obtained by the coprecipitation method, then through the appropriate chimie douce exchange reactions the original chloride anions are replaced by a variety of oxo- and polyoxometallates, (CrO₄)²⁻, (Cr₂O₇)²⁻, (V₂O₇)²⁻, (V₁₀O₂₈)⁶⁻ and (Mo₇O₂₄)⁶⁻. On the other hand, the [Mg–Al] hydrotalcites, intercalated by (V₂O₇)²⁻, (V₁₀O₂₈)⁶⁻ and [Fe^III(CN)₆]³⁻ anions, are obtained by structure regeneration. This was done by rehydration of a commercial calcined material (Kyowa) in aqueous solutions containing the desired anion. The different materials have been fully characterised by conventional analytical techniques to evidence their lamellar properties and chemical nature. They were then tested in the catalytic reaction involving butan-1-ol and one or more units of ethylene oxide to make butyl-monoglycol ether (BMGE), di-glycol ether (BDGE), tri-glycol ether (BTGE), etc. The reactions were carried out between 80 and 120°C, temperature range in which no collapse of the lamellar structure is normally observed. In this paper it is shown that decavanadate exchanged LDHs proved to be very selective catalysts for the preparation of the monoglycol adduct, some samples achieving up to 100% selectivity in the screening tests.     

Mesoporous Cu–Mn Hopcalite catalyst and its performance in low temperature ethylene combustion in a carbon dioxide stream

Complete combustion of trace amounts of ethylene in food grade CO₂ over a Cu–Mn Hopcalite catalyst has been investigated. A mesoporous structure is identified in the catalyst. Low temperature calcined samples are found to be more active than the high temperature calcined ones. The presence of Cu²⁺ and Mn³⁺ is essential for the high activity of the catalyst. The Cu–Mn catalyst without a third component deactivates quickly in the reaction stream. However, doping with Al or Mg individually and with Ni–Al or Mg–Al simultaneously increases the lifetime. In situ DRIFTS measurements provide evidence that hydroxyl groups form and adsorb on Mn species. With the doping of Al, Mg and Ni ions, the amount of hydroxyl groups adsorbed reduces and the stability improves. Doping with Al and Mg simultaneously gives the best stability. A synergetic effect between CuO and amorphous Cu–Mn oxide phases is also confirmed.     

Ni-based supported catalysts from layered double hydroxides: Tunable microstructure and controlled property for the synthesis of carbon nanotubes

The carbon nanotubes (CNTs) with straight and helical nanostructures have been synthesized by catalytic chemical vapor deposition of acetylene over a series of Ni-based supported catalysts, which were formed from Ni–Mg–Al layered double hydroxide precursors (LDHs) synthesized through homogenous decomposition of urea under hydrothermal conditions. The materials were characterized by power X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), temperature-programmed reduction experiments (TPR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The results showed that the introduction of Mg into Ni-based supported catalysts could effectively improve the catalytic activities for the growth of CNTs, mainly proceeding from the inhibition effect of spinel phases formed in calcined LDHs on the agglomeration of metallic Ni particles. Furthermore, it is found interestingly that the addition of Mg also could induce the formation of helical structured CNTs with outer diameters of 20 nm and that the higher Mg content gave rise to the more helical nanotubes. The present work provides a simple and facile way to prepare metal-supported catalysts with a good dispersion of catalytically active metal particles for the growth of straight and helical CNTs.     

Synergistic Effect in Selective Reduction of NO by Alkanes over Mechanically Mixed Oxide Catalysts

The process of selective catalytic reduction of nitrogen oxides by propane in the presence of O₂, as well as in the presence or absence of CO, was studied over series of commercial oxide catalysts used in petrochemical processes. For the first time synergistic effect was observed for catalytic systems consisting of mechanical mixtures of Cu–Zn–Ni–Al (catalyst I) + Fe–Cr (catalyst II) and Cu–Zn–Ni–Al (catalyst I) + Ni–Cr (catalyst III). The activity of these mixtures in nitrogen oxides reduction by propane was greater than that of individual components in each case. The worked-out catalytical systems showed high effectivity in the process of simultaneous removal of several toxic components: NO _x , CO, hydrocarbons – from model gas mixtures, as well as from real exhausts of automotive transport.     

Effect of heat treatment on electroless ternary nickel–cobalt–phosphorus alloy

Ternary Ni–Co–P and binary Ni–P alloy coatings were deposited on mild steel panels from an alkaline bath in the presence and absence of cobalt sulfate using an electroless process. The effects of heat treatment on surface topography and crystal orientation of Ni–Co(11.17%)–P(3.49%) alloy coatings were studied in contrast to that of Ni–P ones. It was found that the as plated Ni–Co–P alloy is a supersaturated solid solution of P and Co dissolved in a microcrystalline Ni matrix with 111 preferred direction. Heat treatment induces structural changes. The formation of Ni₃P phase precipitates and recrystallization of nickel occur when the sample is treated at > 400 °C for one hour. It is observed that the Ni diffraction lines of treated Ni–Co–P alloy at > 400 °C are shifted to lower angles as compared to those of treated Ni–P or as plated Ni–Co–P alloys. The surface topography of Ni–Co–P alloy also changes with heat treatment temperature. The surface topography and crystal orientation were characterized by means of scanning electron microscopy and X-ray diffraction, respectively. The hardness and corrosion resistance, in 5 wt % NaCl solution, of heat treated Ni–Co–P samples were studied.     

High temperature water–gas shift reaction over hollow Ni–Fe–Al oxide nano-composite catalysts prepared by the solution-spray plasma technique

The effect of Fe content in Ni–Fe–Al oxide nano-composites prepared by the solution-spray plasma technique on their catalytic activity for the high temperature water–gas shift reaction was investigated. The composites showed a hollow sphere structure, with highly dispersed Fe–Ni particles supported on the outer surface of the spheres. When the water–gas shift reaction was performed over an Ni–Al oxide composite catalyst without Fe, undesired CO methanation took place predominantly compared to the water–gas shift reaction, and significant amounts of hydrogen were consumed. When appropriate amounts of Fe were added to the Ni–Al oxide composite catalyst during the plasma process, methanation was suppressed remarkably, without serious loss of activity for the water–gas shift reaction. The catalyst was characterized by STEM, XRD and H₂ chemisorption measurements.     

Ni–Zn–P alloy deposition from sulfate bath: inhibitory effect of zinc

Electroless Ni–Zn–P alloy deposition from a sulphate bath, containing sodium hypophosphite as reducer, was investigated. To increase the plating rate, the deposition parameters were optimized. The effect of process parameters (T, pH and [Zn²⁺]) on the plating rate and deposit composition was examined and it was found that the presence of zinc in the bath has an inhibitory effect on the alloy deposition. As a consequence, the percentage of zinc in the electroless Ni–Zn–P alloys never reaches high values. Using cyclic voltammetry the electrodeposition mechanism of Ni–Zn–P alloys was investigated. It was observed that the zinc deposition inhibits the nickel discharge and, as a consequence, its catalytic activity on hypophosphite oxidation. It was also found that increase in temperature or pH leads to the deposition of nickel rich alloys.     

Electrochemical characterization of Ni–P and Ni–Co–P amorphous alloy deposits obtained by electrodeposition

Ni–P and Ni–Co–P amorphous alloy deposits were obtained by electrodeposition at 80 °C on carbon steel substrates. The influence of the electrolyte Co²⁺ concentration and of applied current density was investigated. The corrosion behaviour of amorphous and crystalline deposits was evaluated by polarization curves and electrochemical impedance spectroscopy in NaCl 0.1 M solution at room temperature. Impedances were measured for samples under total immersion (free potential against time) and for polarized samples in predefined regions of the polarization curves. It was found that the alloy deposit composition is highly affected by the composition of the electrolyte but displays no significant dependence on applied current density. The results showed that the presence of Co on Ni–P amorphous alloys improves the deposit performance in the studied corrosive medium. It was also verified that the amorphous structure provides higher corrosion resistance to both Ni–P and Ni–Co–P alloys.     

Synthesis of a magnesium/aluminum/iron layered double hydroxide and its flammability characteristics in halogen‐free,flame‐retardant ethylene/vinyl acetate copolymer composites

Mg–Al–Fe ternary hydrotalcites were synthesized by a coprecipitation method and characterized with powder X‐ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The flame‐retardant effects of Mg/Al–CO₃ layered double hydroxides (LDHs) and Mg/Al/Fe–CO₃ LDHs in an ethylene/vinyl acetate copolymer (EVA) were studied with the limited oxygen index (LOI), the UL‐94 test, and the cone calorimeter test (CCT), and the thermal degradation behavior of the composites was examined by thermogravimetric analysis. The results showed that the LOI values of the EVA/(Mg/Al/Fe–CO₃ LDH) composites were basically higher than those of the EVA/(Mg/Al–CO₃ LDH) composites at the same additive level. In the UL‐94 test, there was no rating for the EVA/(Mg/Al–CO₃ LDH) composite at the 50% additive level, and a dripping phenomenon occurred. However, the EVA/(Mg/Al/Fe–CO₃ LDH) composites at the same loading level of LDHs containing a suitable amount of Fe³⁺ ion reached the V‐0 rating, the dripping phenomenon disappearing. The CCTs indicated that the heat release rate (HRR) of the EVA composites with Mg/Al/Fe–CO₃ LDHs containing a suitable amount of Fe³⁺ decreased greatly in comparison with that of the composites with Mg/Al–CO₃ LDHs. The introduction of a given amount of Fe³⁺ ion into Mg/Al–CO₃ LDHs resulted in an increase in the LOI, a decrease in the HRR, and the achievement of the UL‐94 V‐0 rating. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Inorganic layered double hydroxides as a drug delivery system—intercalation and in vitro release of fenbufen

Layered double hydroxides (LDHs), or so-called anionic clays, consist of cationic brucite-like layers and exchangeable interlayer anions. Because of their biocompatibility, some LDHs, such as Mg/Al, Zn/Al, Fe/Al and Li/Al-LDH, can be used as host materials for drug-LDH host–guest supramolecular structures. The anti-inflammatory drug fenbufen has been intercalated into layered double hydroxides for the first time by co-precipitation under a nitrogen atmosphere. The product has been characterized by powder X-ray diffraction (XRD), FT-IR spectroscopy, elemental analysis and thermogravimetry (TG) and shows an expanded LDH structure, indicating that the drug has been successfully intercalated into LDH. In addition, the dependence of the nature of the fenbufen intercalation process on conditions such as pH value and chemical composition of the host has been systematically investigated. The interlayer distance in the intercalated materials increases with increasing pH value, resulting from a change in the arrangement of interlayer anions from monolayer to interdigitated bilayer. Drug release characteristics of the pillared LDH materials were investigated by a dissolution test in a simulated intestinal fluid (buffer at pH 7.8). The results show that the drug release of supramolecular LDH materials was a slow process, especially in the case of Mg/Al intercalated materials, suggesting that these drug-inorganic hybrid materials can be used as an effective drug delivery system.     

Transition metal-based cathodes for hydrogen evolution in alkaline solution: Electrocatalysis on nickel-based ternary electrolytic codeposits

Nickel-molybdenum-iron, nickel-molybdenum-copper, nickel-molybdenum-zinc, nickel-molybdenum-cobalt, nickel-molybdenum-tungsten and nickel-molybdenum-chromium ternary codeposits, obtained through electrodeposition on mild steel strips have been characterized with the objective of qualitatively comparing and assessing their electrocatalytic activities as hydrogen electrodes in alkaline solution. It has been concluded that their electrocatalytic effects for the hydrogen evolution reaction (h.e.r.) rank in the following order: Ni–Mo–Fe>Ni–Mo–Cu>Ni–Mo–Zn>Ni–Mo–Co Ni–Mo–W>Ni–Mo–Cr>Ni-plated steel. Further investigations on these electrocatalysts have revealed that the cathodic overpotential contribution to the electrolysis voltage can be brought down by 0.3 V when compared with conventional steel cathodes. The best and most stable hydrogen evolving cathode of these, namely Ni–Mo–Fe, exhibited an overpotential of about 0.187 V for over 1500 h of continuous electrolysis in 6 M KOH at 300 mA cm^–2 and 353 K. The salient features of the codeposits, such as physical characteristics, chemical composition, current-potential behaviour and the varying effects of the catalytic activation method were analysed with a view to correlating the micro-structural characteristics of the coatings with the hydrogen adsorption process. The stability under open circuit conditions, the tolerance to electrochemical corrosion and the long term stability of Ni–Mo–Fe codeposit cathodes were very encouraging. An attempt to identify the pathway for the h.e.r. on these codeposit cathodes was made, in view of the electrochemical parameters obtained experimentally.     

热改性层状双氢氧化物吸附除Cr(Ⅵ)性能

通过共沉淀法制备得到镁铝层状双氢氧化物(LDHs), 并在450℃高温下进行热改性处理(即C-LDHs)。系统性比较了上述两种材料除Cr(Ⅵ)的吸附动力学及等温线模型, 并考察温度、pH、Cr(Ⅵ)初始浓度等重要因素对吸附效果的影响。使用XRD、SEM、FT-IR和TG-DTG等对两种吸附材料进行了表面特性表征。结果表明, 热改性后C-LDHs的表面性质发生了巨大变化。但其吸附过程仍符合Langmuir吸附等温式。C-LDHs对Cr(Ⅵ)的最大吸附量为105.26 mg·g^-1, 远大于LDHs的吸附量(20.66 mg·g^-1)。本文结果表明, 对层状双氢氧化物进行经济方便的热改性可大幅度增强其对Cr(Ⅵ)的吸附性能, 对层状双氢氧化物的工业化应用具有重要的参考价值。