Corrosion resistance of in-situ Mg-Al hydrotalcite conversion film on AZ31 magnesium alloy by one-step formation

In situ growth of nano-sized layered double hydroxides （LDH） conversion film on AZ31 alloy was synthesized by a urea hydrolysis method. The formation mechanism of the film was proposed. Firstly, the dissolved Mg2＋ ions deposited into a precursor film consisted of MgCO3 and Mgs（CO3）4（OH）2·4H2O; secondly, the precursor translated into the crystalline Mg（OH）2 in alkaline conditions; finally, the Mg2＋ ions in Mg（OH）z were replaced by A13＋ ions, Mg（OH）2 translated into the more stable LDH structure, simultaneously, the OH- ions in the interlayer were exchanged by CO32-, thus led to the formation of the LDH （Mg6Alz（OHh6CO3·4H2O） film. The results indicated that the LDH film characterized by interlocking plate-like nanostructures and ion-exchange ability significantly improved the corrosion resistance of the AZ31 Mg alloy.

Effect of solution concentration on sealing treatment of Mg-Al hydrotalcite film on AZ91D Mg alloy

Cerium-based sealing treatment was developed for Mg-Al hydrotalcite film on AZ91D Mg alloy,and the influence of cerium salt solution was investigated to modify the surface integrity and corrosion resistance.Scanning electron microscope(SEM)and X-ray diffraction(XRD)measurements were carried out to analyze the surface morphology and phase composition.The corrosion resistance of Mg-Al hydrotalcite film after sealing treatment was evaluated by the polarization curve and electrochemical impedance spectroscopy(EIS)tests.The results showed that lower concentration of Ce-containing solution was beneficial to seal the micro-cracks on Mg-Al hydrotalcite film,and improve the surface integrity and corrosion resistance;higher concentration of Ce-containing solution could seal fewer micro-cracks,and the corrosion resistance was decreased owing to the disintegration of Mg-Al hydrotalcite film.

Aqueous-phase catalytic hydrogenation of furfural to cyclopentanol over Cu-Mg-Al hydrotalcites derived catalysts:Model reaction for upgrading of bio-oil

A series of Cu-Mg-Al hydrotalcites derived oxides with a(Cu+Mg)/Al mole ratio of 3 and varied Cu/Mg mole ratio(from 0.07 to 0.30) were prepared by co-precipitation and calcination methods, then they were introduced to the hydrogenation of furfural in aqueous-phase. Effects of Cu/Mg mole ratio, reaction temperature, initial hydrogen pressure, reaction time and catalyst amount on the conversion rate of furfural as well as the selectivity toward desired product cyclopentanol were systematically investigated. The conversion of furfural over calcined hydrotalcite catalyst with a Cu/Mg mole ratio of 0.2 was up to 98.5% when the reaction was carried out under 140 ?C and the initial hydrogen pressure of 4 MPa for 10 h, while the selectivity toward cyclopentanol was up to 94.8%. The catalysts were characterized by XRD and SEM. XRD diffraction of all the samples showed characteristic pattern of hydrotalcite with varied peak intensity as a result of different Cu content. The catalytic activity was improved gradually with the increase of Cu component in the hydrotalcite.

Influence of the preparation method on the catalytic activity of Mg-Al hydrotalcites as solid base catalysts

Mg-Al hydrotalcites were synthesized using different preparation methods(a co-precipitation method, a urea method, and a simple one) to analyze their effect on the catalytic activity of these solid base catalysts. The method strongly affected the structure of their layers(e.g., the growth and stacking of the layers, and the type of intercalated anions) and, accordingly, their catalytic activity. The Mg-Al hydrotalcite prepared by co-precipitation showed the best catalytic performance in the isomerization of glucose into fructose, due to the small crystallite size and sand rose morphology enhancing the exposure of surface active sites to reactants.

Efficient Removal of Phosphate from Aqueous Solutions Using Corundum-hollow-spheres Supported Caclined Hydrotalcite Porous Thin Films

Phosphate was removed from aqueous environment by corundum-hollow-spheres supported caclined hydrotalcite (cHT) thin films. Mg-Al-CO3 hydrotalcite (HT) thin films were deposited on corundumhollow-sphere substrates by hydrothermal homogeneous precipitation at 120℃for 30-240 min and cHT thin films were obtained by annealing of the HT thin films at 500℃for 180 min. Their crystal phase, morphology and microstructure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The results show that homogeneous, well-crystallized and hierarchical flower-like thin films were deposited firmly on the surface of the corundum. The mechanism of nucleation and growth of the HT thin films was fitted well with the anion coordination polyhedron growth unit model. To determine the absorption of phosphate by this adsorbent, different bed depth (10-30 cm) and flow rate (1.0-3.0 m L/min) were examined by column experiments. The highest removal efficiency of phosphate amounted to 98.5%under optimum condition (pH=7.2). The adsorption capacity increased as the bed depth increased and decreased as the flow rate increased.

Effect and Mechanism of Rare Earth Hydrotalcite Inhibiting Coal Spontaneous Combustion

A hydrotalcite(layered double hydroxide, LDH) inhibitor which is suitable for the whole process of coal spontaneous combustion and a LDH inhibitor containing rare earth lanthanum elements were prepared. The inhibition effect and mechanism were analyzed by scanning electron microscopy(SEM),X-ray diffraction(XRD), thermal performance analysis, in-situ diffuse reflectance infrared spectroscopy and temperature-programmed experiment. The results have shown that the inhibitor containing lanthanum can play a good inhibitory role in every stage of coal oxidation. During the slow oxidation of coal samples, the inhibitor containing lanthanum ions can slow down the oxidation process of coal and increase the initial temperature of coal spontaneous combustion. At the same time, because the hydroxyl groups in LDHs are connected with-COO-groups on the coal surface through hydrogen bonds, the stability of coal is improved. With the increase of temperature, LDHs can remove interlayer water molecules and reduce the surface temperature of coal. CO release rate of coal samples decreases significantly after adding inhibitor containing lanthanum element, and the maximum inhibition rate of the inhibitor is 58.1%.

Graphene oxide/hydrotalcite modified polyethersulfone nanohybrid membrane for the treatment of lead ion from battery industrial effluent

In the present study, polyethersulfone based nanohybrid membranes were effectively fabricated by incorporating graphene oxide(GO) and hydrotalcite(HT) nanosheets into the membrane structure. HT was prepared to overcome the irreversible agglomeration behavior of GO at a high concentration which affects the performance of the membranes. In particular, the shedding of HT in formamide provides a two-dimensional nanosheet with a higher positive charge density to prevent the restacking of GO nanosheets. Here, exfoliated GO and HT with different combinations(1:1, 1:2 and 1:3) were infused in the membrane matrix to treat lead-acid battery effluent effectively. Finally, the hybrid membranes were characterized for hydrophilicity, mechanical strength and pure water flux. In combination with the superior properties of GO and HT, the prepared hybrid membranes can be used as effectively to improve the separation and permeation performance. The phase inversion process eliminated the leaching of nanoparticles from the membrane matrix. The reusability of the hybrid membrane was achieved using0.1 mol·L^(-1)NaOH solution and reused without significant reduction in lead removal efficiency. The cost analysis of the membrane was also estimated from the lab study. Therefore, the present study suggested the selective and sustainable treatment of lead from a real-life effluent.

Ni-Co/Mg-Al catalyst derived from hydrotalcite-like compound prepared by plasma for dry reforming of methane

Ni-Co bimetallic catalysts with different Ni/Co content were derived from cold plasma jet decomposition and reduction of hydrotalcite-like compounds containing Ni,Co,Mg and Al,and their catalytic performance was investigated with dry reforming of methane.Experimental results showed that the hydrotalcite-like precursors could be completely decomposed and partly reduced by cold plasma jet,and the Nicontained catalysts exhibited much higher activity than the catalyst without Ni.Especially,the catalyst with Ni/Co ratio of 8/2 achieved not only the highest conversions of 80.3%and 69.3%for CH4 and CO2,respectively,but also the best stability in 100 h testing.The catalysts were characterized by XRD,XPS,TEM and N2 adsorption techniques,and the results showed that the better performance of the 8Ni2Co bimetallic catalyst was attributed to its higher metal dispersion,smaller metal particle size,as well as the interaction effect between Ni and Co,which were brought by the special catalyst preparation method.

Mg-Al水滑石的制备及对水中氟离子的吸附效果研究

通过共沉淀法制备了Mg-Al水滑石,研究了镁铝摩尔比对Mg-Al水滑石的晶格结构、微观形貌、光谱性能的影响。以NaF溶液为模拟含氟废水,测试了Mg-Al水滑石对水中氟离子的吸附量和去除率,通过吸附模型研究了相应的吸附过程和机理。结果表明,Mg-Al水滑石外观为片层状结构,片层之间相互交叉堆积,镁铝比增大时,Mg-Al水滑石的层间距增大。水滑石对氟离子的饱和吸附量和去除率随着镁铝比的增大表现出先增大后减小的趋势,在吸附80 min时吸附量接近饱和,3Mg-Al水滑石的饱和吸附量达到最大值43.16 mg/g,去除率在120 min时达到最大值90.5%,经过5次吸附再生循环使用后,3Mg-Al水滑石对氟离子的去除率降至69.4%,保持率达到76.69%,具有良好的可重复利用性能。通过对Mg-Al水滑石吸附氟离子的数据进行拟合,发现Mg-Al水滑石吸附氟离子的过程更符合准二级动力学模型,主要以化学吸附作用为主。

新型Al-C晶粒细化剂的制备及对Mg-Al合金显微组织的影响研究

采用原位反应烧结法制备了新型Al-5C中间合金,利用光学显微镜(OM)、X射线衍射(XRD)和扫描电子显微镜(SEM)等研究了制备工艺对Al-5C中间合金组织以及该中间合金对Mg-Al合金晶粒细化的影响。结果表明,原位反应烧结法改善了Al与C的润湿性,Al-C的反应程度与球磨时间、烧结温度、烧结时间和压块方式有关;延长球磨时间、提高烧结温度或适当延长烧结时间均能促进Al-C反应,生成细小的Al4C3颗粒;Al-5C中间合金能有效地细化Mg-3Al合金的组织,添加量(质量分数)为2%时晶粒细化效果最佳。

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。

Hydrotalcite的合成与应用

介绍了以碱式碳酸镁、铝酸碱金属盐为原料合成Hydrotalcite的方法,并论述了其作为制酸剂和抗胃脘剂、聚烯烃树脂的中和剂、PVC热稳定剂的应用。

Adsorption removal of thiocyanate from aqueous solution by calcined hydrotalcite

A hydrotalcite with Mg/AI molar ratio 2 was prepared by co-precipitation method and was characterized by XRD, TG/DTA, Zeta potential and BET surface area. The hydrotalcite was calcined at 500℃, with the dehydration from interlayer, the dehydroxilation from the brucite-like layer and the decomposition of carbonate successively, transformed into the mixed oxide type. The removal of thiocyanate from aqueous solution by using the original hydrotalcite and calcined hydrotalcite （HTC-500） was investigated. The results showed that the thiocyanate adsorption capacity of calcined hydrotalcite was much higher than that of the original form. Calcined hydrotalcite was particularly effective at removing thiocyanate, and that the effective range of pH for the thiocyanate removal are between 5.5-10.0. The experimental data of thiocyanate removal fit nicely with Langmuir isotherm, and the saturated adsorption uptake was 96.2 mg SCN-/g HTC-500. The adsorption of thiocyanate by calcined hydrotalcite follows first-order kinetics. And the intercalation to the structure recovery for calcined hydrotalcite. But the presence of additional anions could affect the adsorption behavior of thiocyanate.

Effects of hydrotalcite combined with esomeprazole on gastric ulcer healing quality: A clinical observation study

AIM To evaluate the effects of hydrotalcite combined with esomeprazole on gastric ulcer healing quality. METHODS Forty-eight patients diagnosed with gastric ulcer between June 2014 and February 2016 were randomly allocated to the combination therapy group or monotherapy group. The former received hydrotalcite combined with esomeprazole, and the latter received esomeprazole alone, for 8 wk. Twenty-four healthy volunteers were recruited and acted as the healthy control group. Endoscopic ulcer healing was observed using white light endoscopy and narrow band imaging magnifying endoscopy. The composition of collagen fibers, amount of collagen deposition, expression of factor. and TGF-beta 1, and hydroxyproline content were analyzed by Masson staining, immunohistochemistry, immunofluorescent imaging and ELISA. RESULTS Following treatment, changes in the gastric microvascular network were statistically different between the combination therapy group and the monotherapy group (P < 0.05). There were significant differences (P < 0.05) in collagen deposition, expression level of Factor. and TGF-beta 1, and hydroxyproline content in the two treatment groups compared with the healthy control group. These parameters in the combination therapy group were significantly higher than in the monotherapy group (P < 0.05). The ratio of collagen. to collagen. was statistically different among the three groups, and was significantly higher in the combination therapy group than in the monotherapy group (P < 0.05). CONCLUSION Hydrotalcite combined with esomeprazole is superior to esomeprazole alone in improving gastric ulcer healing quality in terms of improving microvascular morphology, degree of structure maturity and function of regenerated mucosa.

Unique catalysis of Ni-Al hydrotalcite derived catalyst in CO_2 methanation: cooperative effect between Ni nanoparticles and a basic support

Ni-Al hydrotalcite derived catalyst （Ni-Al2O3-HT） exhibited a narrow Ni particle-size distribution with an average particle size of 4.0 nm. Methanation of CO2 over this catalyst initiated at 225℃ and reached 82.5% CO2 conversion with 99.5% CH4 selectivity at 350℃, which was much better than its impregnated counterpart. Characterizations by means of CO2 microcalorimetry and 27 Al NMR indicated that large amount of strong basic sites existed on Ni-Al2O3-HT, originated from the formation of Ni-O-Al structure. The existence of strong basic sites facilitated the activation of CO2 and consequently promoted the activity. The combination of highly dispersed Ni with strong basic support led to its unique and high efficiency for this reaction. Keywords

Catalytic depolymerization of calcium lignosulfonate by NiMgFeO_x derived from sub-micron sized NiMgFe hydrotalcite prepared by introducing hydroxyl compounds

A new method for regulating the synthesis of Ni Mg Fe hydrotalcites(NMF LDHs) with the addition of hydroxyl compounds was proposed. A series of NMF LDHs were prepared by the above method, and then were calcined to obtain the Ni Mg FeOx(NMFOx) samples. The NMFOxsamples were characterized by XRD,SEM, TG-DTG, XPS and CO2-TPD, respectively. The catalytic performance of NMFOxfor depolymerizing calcium lignosulfonate(CLS) was evaluated by hydrothermal reaction. The results showed that the addition of hydroxyl compounds favored reducing the particle sizes of NMF LDHs. For the depolymerization of CSL, the yield of liquid product increased from 45% to 75.8% with the addition of NMFOx-ethanol(NMFOxET). The liquid products were mainly phenolics, aromatics, ketones and esters. The total selectivity of oxy-containing compounds was over 90.6%, among them, the phenolics were approximately 35.2%. The valence of Ni and Fe, crystalline phase and basicity almost remained unchanged. The NMFOx-ET samples were recycled for the depolymerization of CLS, moreover, the NMFOx-ET samples had high activity and stability after 4 cycles.

Preparation,Characterization and Application of ZnAlLa-Hydrotalcite-Like Compounds

The preparation of ZnAlLa-hydrotalcite-like compounds [ZnAlLa-HTLcs] wasstudied. ZnAlLa-HTLcs were synthesized by a method of variable pH with the raw materials ofZn(NO_3)_2, Al(NO_3)_3, La(NO_3)_3, and NaOH. The eS'ccts of some factors (i.e. pH values, the moleratio of Al^(3+) to La^(3+), temperature and the period of hydrothermal treatment) on thepreparation of HTLcs were discussed systematically. XRD, TG-DTA, FT-IR spectroscopy, and ICP wereperformed to characterize ZnAlLa-HTLcs samples, and the thermal stability of HTLcs was alsodiscussed. It was shown that unique ZnAlLa-HTLcs with high crystallinity can be prepared, under theconditions of pH = 5.5-6.5, n(Zn^(2+))/n(Al^(3+) + La^(3+))=2 and the atomic ratio of La^(3+) toAl^(3+) ranging from 0.07 to 2, hydrothermal treatment at 120 ℃ for 5 h. When the calcination ofthe HTLcs is performed at temperatures above 200 ℃, ZnO phase is detected with Al_2O_3 and La_2O_3spreading on its top. The complex metal oxides derived from ZnAlLa-HTLcs at 500 ℃ have highercatalytic activity and selectivity than those from ZnAl-HTLcs for the esterification of acetic acidwith n-butanol under the same reaction conditions.

Preparation, Characterization of Hydrotalcites and the Catalytic Properties in Synthesis of o-Phenylphenol over Pt/CHT

Mg/Al mixed oxides with molar ratios of 2_6 of Mg to Al used as supports for platinum catalysts were obtained by the thermal decomposition method. The effect of the composition of the mixed oxides on the physicochemical properties was studied by TPD, nitrogen sorption, XRD and TG-DTA characterization methods. The synthesis of o-phenylphenol(OPP) from a dimer(obtained from cyclohexanone condensation) was investigated over Pt/CHT catalysts and compared with those over Pt/MgO and Pt/Al 2O 3 catalysts. These catalysts show a high activity and selectivity for OPP, with a conversion reaching 93.8% and a selectivity reaching 87.9% in some experiments. For Pt/CHTx catalysts, the calcined hydrotalcites exhibited strong base sites, which were necessary to catalyze the synthesis of OPP.

Preparation and Characterization of Mg/Al/Fe Hydrotalcite with Superb Absorption Capacity toward Congo Red

Mg/Al/Fe layered double hydroxide(MAF-LDH1) was prepared by solvothermal method with the sodium dodecyl sulfate as the template, and the ethanol system was benefit to growth of sample. The nature in the resulting MAF-LDH was investigated by X-ray diffraction, field emission scanning electron microscopy, Fourier transformed infrared spectra, thermogravimetric analysis, and N2 adsorption-desorption.The morphology of MAF-LDH1 is petal-like with the size of 400-500 nm and the thickness about 10-20 nm. The adsorption performance of the samples was evaluated by absorption of the Congo red(CR) solutions. Compared with Mg/Al layered double hydroxide(MA-LDH), the maximum adsorption capacities of the MAF-LDH1 samples were 943.4 mg/g which was greatly enhanced. Furthermore, after seven cycling tests, the adsorption performance was still up to 90%. Theoretical calculation results revealed that the adsorption process was spontaneous and followed the pseudo-second-order kinetic model and Freundlich model. This work provides a promising alternative strategy to enhance the adsorptive properties of hydrotalcite-like materials.

The Adsorption of NO_X on Magnesium Aluminium Hydrotalcite

Magnesium aluminium hydrotalcite (Mg-Al-HT) with molar ratio of Mg-to-Al of 3 to l was prepared and characterized by X-ray diffraction (XRD) and infrared spectra (IR). The performances of Mg-Al-HT for the adsorption and desorption of NOx were studied. The results indicated that the adsorption capacity of the hydrotalcite for NOx was 1398.2 mg/g, and it was higher than the acticarbon's. The adsorption capacities depended on adsorption time and temperature. Mg-Al-HT could be regenerated by thermal decomposition, and the adsorption efficiency had not changed markedly after three cycles.