Sorption of an anionic dye by uncalcined and calcined layered double hydroxides: a case study

Layered double hydroxides (LDHs) with a Mg/Al molar ratio of 2:1 were synthesized by using a co-precipitation method and their calcined products (CLDHs) were obtained by heating Mg/Al-LDHs at 500 °C. Sorption of a weak acid dye, Brilliant Blue R (BBR), by LDHs and CLDHs indicated equilibrium time required for BBR sorption by CLDHs was less than 12 h, regardless of initial concentration of BBR, whereas BBR sorption by LDHs was longer than 20 h. Sorption capacity of CLDHs was much larger than that of LDHs. Therefore, CLDHs could be used to remove anionic dyes of relatively high concentrations while LDHs may only be used to remove anionic dyes of low concentrations. Isotherms for BBR sorption by CLDHs and LDHs were well described using the Freundlich and Langmuir equations, respectively. When the initial pH of BBR solutions was lower than 8.0, the final pH of the solution after sorption was enhanced and stabilized at 10.6–10.8. The effect of initial pH (<8.0) on BBR removal was negligible, which would be environmentally important for precipitation/co-precipitation of co-existing metal cations. The effects of both Cl⁻ and SO₄²⁻ on BBR sorption by CLDHs were minimal; but the presence of CO₃²⁻ markedly reduced BBR removal. Thermal regeneration for re-use of LDHs and CLDHs after BBR sorption was feasible only within the first two cycles, after which the regenerated materials suffered from a large loss in their sorption capacities.     

酒石酸柱撑水滑石吸附水中的Ni~(2+)的特性研究

采用离子交换法制得酒石酸插层MgAl水滑石(MgAl-TA LDHs),并进行了XRD、IR、SEM、比表面积及孔径分析表征。考察了MgAl-TA LDHs吸附剂对溶液中Ni 2+的吸附能力,探讨了水滑石吸附剂投加量、Ni 2+溶液浓度、pH值以及吸附温度对Ni 2+吸附率的影响,并进行了动力学和热力学特征的研究。结果表明,适宜的水滑石投加量为2g/L,pH值以中性为宜,对于Ni 2+浓度不超过100 mg/L的溶液室温下Ni 2+吸附率在60%以上,而高温有利于提高Ni 2+吸附率。吸附过程符合二级动力学模型,吸附等温曲线可用R-P模型来描述。吸附过程能够自发进行,为吸热过程,属于化学吸附。     

手性阴离子柱撑水滑石的制备和表征

以水滑石Mg4Al2(OH)12CO3.4H2O为前体,采用返混沉淀方法进行插层组装制备了L-(-)-酒石酸、L-(-)-天冬氨酸、L-(-)-苹果酸柱撑水滑石(LDHs),用X射线衍射、红外光谱及差热分析表征了超分子结构手性层柱材料的结构,结果表明,3种手性酸根阴离子可以插入水滑石的层间完全取代CO32-,得到结晶度高、晶相单一且手性酸根阴离子在层间有序排列的超分子结构手性层柱材料。     

Bromide ion removal from contaminated water by calcined and uncalcined MgAl-CO3 layered double hydroxides

A fundamental investigation on the uptake of bromide ion from contaminated water by calcined and uncalcined MgAl-CO3 layered double hydroxides (LDHs) were conducted in batch mode. The uptake capacity of calcined LDHs (CLDH) is higher than that of uncalcined LDHs, due to their different mechanisms which are confirmed by powder X-ray diffraction, FT-IR spectroscopy and TG-MS measurements. The former mechanism is based on the reconstruction of CLDH to Br-LDHs, whilst the latter is related to the surface adsorption. It has been found that the LDHs calcined at 500 degrees C with Mg/Al molar ratio of 4 represents the highest capacity to remove bromide ion from aqueous solution. The equilibrium isotherms of uptake of bromide by CLDH were well fitted by the Langmuir equation, and thermodynamic parameters such as Delta G0, Delta H0 and Delta S0 were calculated from Langmuir constants. The negative value of Delta H0 confirms the exothermic nature of adsorption. Three kinetics models were used to fit the kinetics experimental data, and it was found that the pseudo-second order kinetics model could be used to describe the uptake process appropriately. The value of Ea was calculated to be 79.9 kJ/mol, which suggests that the process of uptake bromide is controlled by the reaction rate of bromide with the CLDH rather than diffusion.     

Ageing behaviour of unary hydroxides in trivalent metal salt solutions: Formation of layered double hydroxide (LDH)-like phases

The hydroxides of Mg, Ni, Cu and Zn transform into layered double hydroxide (LDH)-like phases on ageing in solutions of Al or Cr salts. This reaction is similar to acid leaching and proceeds by a dissolution-reprecipitation mechanism offering a simple method of LDH synthesis, with implications for the accepted theories of formation of LDH minerals in the earth’s crust.     

ZnAlTi型层状双氢氧化物光催化降解亚甲基蓝的性能研究

利用动态尿素水解法制备了3种不同比例的ZnAlTi型层状双氢氧化物,取部分样品分别在温度为500、600、700和900℃条件下煅烧4h,制得具有光催化性能的材料。研究催化剂不同摩尔比、催化剂用量、煅烧温度等不同因素对光催化降解亚甲基蓝过程的影响。结果表明,紫外光照射下,在反应温度为30℃、催化剂中Ti和Al的摩尔比为2、催化剂投加浓度为1.0g/L、亚甲基蓝初始浓度为10mg/L、煅烧温度为600℃的反应条件下,催化剂对亚甲基蓝的降解效果最好,光照反应12h后亚甲基蓝的降解率为94.4%。     

类水滑石的制备与改性及其在聚丙烯阻燃中的应用

采用共沉淀法制备了镁铝类水滑石（LDHs）前驱体,加入少量聚磷酸铵（APP）制得APP-LDHs,探讨了不同质量分数APP对LDHs晶体生长的影响;当APP在LDHs前驱浆液中添加量为0.8wt%时,将APP-LDHs与季戊四醇（PER）、硅烷偶联剂KH-550进行球磨混合,制备插层包覆改性的LDHs;通过XRD、FTIR、SEM和TG等对改性前后的LDHs进行了表征;采用极限氧指数（LOI）、垂直燃烧测试（UL-94）、缺口冲击和弯曲实验等方法研究了LDHs改性前后LDHs/聚丙烯（PP）复合材料的阻燃性能及力学性能的差异。研究结果表明：APP的加入,未显著影响LDHs的层板生长,但其层板堆叠受到抑制;SEM观察表明,所制备的LDHs为片状,且经插层包覆改性后的LDHs粉体形貌较为规整,颗粒粒径为100~250 nm;改性LDHs在较高温度下的热稳定性显著优于未改性的LDHs;当PP中加入质量分数为20%的LDHs及改性LDHs时,可抑制PP燃烧时产生的熔滴,并促使LDHs/PP复合材料表面形成炭层;改性LDHs/PP复合材料具有更好的阻燃性能,且其冲击强度、弯曲强度等力学性能下降不明显。     

Sorption study of an acid dye from an aqueous solutions using modified clays

The removal of the pollutant Supranol Yellow 4GL (S.Y.4GL) was studied by using different clays: clay exchanged with sodium (BNa+) and hydroxyaluminic polycation pillared clays in the presence or absence of non-ionic surfactant. While decomposing the surfactant at 500 degrees C, the surface of the clay changed significantly. The study of the behaviour of the three clays with respect to coloring solutions, allowed to determine the equilibrium time and the rate-determining step of the dye S.Y.4GL adsorption. Two simplified kinetic models, were tested to investigate the adsorption mechanisms in terms of pseudo-first order and pseudo-second order equations. Besides, the adsorption capacity data were fitted to Langmuir and Freundlich equations as well. A better fixation was obtained with an acidic pH. The effect of temperature on the adsorption of dye has been also studied and the thermodynamic parameters DeltaG degrees , DeltaH degrees and DeltaS degrees were determined.     

Equilibrium studies for the adsorption of acid dye onto modified hectorite

The adsorption of Acid dye, C.I. Acid Red 151 from aqueous solution onto modified hectorite at different concentrations and pH has been studied. Hectorite clay has been modified using two cationic surfactants, cetyldimethylbenzylammonium chloride and cetylpyridinium chloride. Present experimental study shows that acidic pH favours enhanced adsorption. The adsorption isotherms are described by means of Langmuir and Freundlich isotherms. The adsorption capacity has been found to be 208.33 and 169.49 mg g(-1) for the modified cetyldimethylbenzylammonium chloride-hectorite (CDBA-hect) and cetylpyridinium chloride (CP-hect), respectively.     

A comparison of corrosion inhibition of magnesium aluminum and zinc aluminum vanadate intercalated layered double hydroxides on magnesium alloys

The magnesium aluminum and zinc aluminum layered double hydroxides intercalated with NO ₃ ^- (MgAl-NO₃-LDH and ZnAl-NO₃-LDH) were prepared by the coprecipitation method, and the magnesium aluminum and the zinc aluminum layered double hydroxides intercalated with VO _x ^- (MgAl-VO _x -LDH and ZnAl-VO _x -LDH) were prepared by the anion-exchange method. Morphologies, microstructures and chemical compositions of LDHs were investigated by SEM, EDS, XRD, FTIR, Raman and TG analyses. The immersion tests were carried to determine the corrosion inhibition properties of MgAl-VO _x -LDH and ZnAl-VO _x -LDH on AZ31 Mg alloys. The results showed that ZnAl-VO _x -LDH possesses the best anion-exchange and inhibition abilities. The influence of treatment parameters on microstructures of LDHs were discussed. Additionally, an inhibition mechanism for ZnAl-VO _x -LDH on the AZ31 magnesium alloy was proposed and discussed.     

Sorption of radioiodine from aqueous solutions on layered double magnesium aluminum hydroxides at 300 K

Sorption of ¹³¹I^? and ¹³¹IO ₃ ^? from aqueous solutions at 300 K on solid layered double magnesium aluminum hydroxides (Mg-Al-LDH) in the carbonate (Mg-Al-LDH-CO₃) and nitrate (Mg-Al-LDH-NO₃) forms was studied. The distribution coefficients of ¹³¹I^? and ¹³¹IO ₃ ^? between solid Mg-Al-LDH-CO₃ and an aqueous solution after contact of these phases for 60 min are 38 and 34 ml g^?1, respectively. The distribution coefficients of ¹³¹I^? and ¹³¹IO ₃ ^? between solid Mg-Al-LDH-NO₃ and an aqueous solution, measured under the similar conditions, are about 5 ml g^?1. After contact of the solid and liquid phases for 14 h, the distribution coefficients of ¹³¹I^? and ¹³¹IO ₃ ^? between an aqueous phase and solid layered double magnesium aluminum oxides (Mg-Al-LDO) prepared by thermolysis of Mg-Al-LDH are 7999 and 7068 ml g^?1, respectively.     

Equilibrium and kinetic studies on free cyanide adsorption from aqueous solution by activated carbon

Adsorption equilibrium and kinetics of free cyanide onto activated carbon were investigated in the batch tests, and the effects of contact time (1–72 h) and initial cyanide concentrations in the range of 102–532 mg/L were studied. Linear regression was used to determine the best fit of equilibrium and kinetics expressions. The two-parameter models including Freundlich, Dubinin–Radushkevich, Temkin and four different linearized forms of Langmuir and three-parameter models including Redlich–Peterson and Koble–Corrigan were employed for fitting the equilibrium data and it was found that, three-parameter models fitted the data better than the two-parameter models and among the three-parameter models the equilibrium data are best represented by Koble–Corrigan model. A number of kinetic models including fractional power, zero order, first order, pseudo-first order, Elovich, second order, intraparticle diffusion and four different linearized forms of pseudo-second order models were tested to fit the kinetic data. The latter was found to be consistent with the data. Intraparticle diffusion plots show that the adsorption process of free cyanide is a two steps process. In the first step, the adsorption of cyanide is fast while in the second step, cyanide adsorption slows down.     

Nanostructured modified layered double hydroxides (LDHs)-based catalysts: A review on synthesis,characterization, and applications in water remediation by advanced oxidation processes

Layered double hydroxides (LDHs) are emerging catalyst materials with inner layer water molecules and higher anion exchange capacity. They have been extensively used as catalyst materials owing to their high specific surface area, environmental friendliness, lower cost, and non-toxicity. However, the lower surface area and leaching of metal ions from LDHs composites reduce the process efficiency of the catalyst. Modifying the LDHs materials with other materials can improve the surface properties of the composite and enhance the catalytic performance. Herein, this review aims to summarize the recent progress of nanostructured modified LDHs materials, their classification, synthesis, and a detailed discussion on their characterization techniques. Further, this study also discusses the application of nanostructured modified LDHs materials as catalysts in advanced oxidation process (AOPs) for various organic pollutants removal.     

水滑石作为药物载体--萘普生的插层和缓释

水滑石(LDHs)是由带正电荷类水镁石层和层间的可交换阴离子组成的阴离子型粘土化合物,由于它的生物适应性,能够以它为主体,以药物为客体,插层组装成超分子结构复合物.抗炎药萘普生采用共沉淀法一步插层进入LDHs,用X射线衍射、红外光谱及热分析方法表征了超分子结构,表明层间距离扩大了,即萘普生已经插层组装成功,并且以单层、垂直作用在层间.萘普生柱撑水滑石的药物释放度在模拟肠液(pH7.4的缓冲液)条件下测定,结果表明萘普生柱撑水滑石释放速度降低,具有缓释作用,说明药物--无机混合物材料能够用作有效的药物传输系统.     

Studies on sorption of some geomaterials for fluoride removal from aqueous solutions

In the present study the defluoridation capacities of some of the naturally occurring materials like low and high iron containing lateritic ores, overburden from chromite mines of Orissa Mining Corporation (OMC) and Tata Steel have been estimated. The various experimental parameters studied for fluoride sorption from aqueous solutions were: time, pH, initial fluoride concentration, sorbent dose and temperature. The three geomaterials, namely chromite overburden from Orissa Mining Corporation, both low and high iron containing lateritic ores sorbed fluoride effectively. The sorption kinetics for these samples was found to follow first order rate expression and the experimental equilibrium sorption data fitted reasonably well to both Langmuir and Freundlich models. The negative values of ΔG° suggest the sorption of fluoride onto three samples to be spontaneous and the exothermic nature of sorption is confirmed by the −ΔH° values. The negative ΔS° values for these sorbents point towards decreased randomness at the solid/solution interface. The sorption studies were also carried out at natural pH conditions for fluoride removal from ground water samples and the fluoride level could be reduced from 10.25 to <1.0 mg L⁻¹ by multistage adsorption process using OMC and NH samples.     

Synthesis and characterization maleate-alumoxane nanoparticles for removal of reactive yellow 84 dye from aqueous solution

Maleate-alumoxane nanoparticles (Mal-A) were synthesized from boehmite and applied for adsorption of an azo dye (Reactive Yellow 84) from aqueous solution. Its adsorption capacity was compared with three types of carboxylate alumoxane nanoparticles synthesized from boehmite including salicylate alumoxane (Sal-A), para-aminobenzoate alumoxane (Pab-A) and fumarate alumoxane (Fum-A). The characterizations of prepared materials were analyzed using FTIR, SEM, X-ray diffraction and BET measurements. Among utilized alumoxanes at natural pH, the adsorption capacity of Mal-A was 45, 67, 116 and 215% higher than that of Fum-A, Boehmite, Pab-A, Sal-A nanoparticles, respectively. Response surface methodology (RSM) using Box-Behnken design of experiment was employed to investigate the influence of pH, initial concentration of dye and adsorbent dosage on dye removal efficiency of Mal-A. Box-cox transformation was chosen to improve model adequately and a good prediction (R²: 0.998) was achieved. Under optimum condition, i.e., pH: 4.3, dye concentration: 151.5 mg/L and adsorbent dosage: 1.2 g/L, the adsorption capacity and dye removal efficiency were obtained 130.6 mg/g and 99.2%, respectively. The kinetics and equilibrium data were perfectly represented with linear pseudo-second-order and linear Langmuir isotherm models, respectively.     

Sorption of cesium, strontium, and yttrium radionuclides from the aqueous phase on layered double hydroxides

Sorption of ¹³⁷Cs, ^85,90Sr, and ⁹⁰Y from aqueous solutions on the solid phase of layered double hydroxides (LDHs) and layered double oxides (LDOs) of various compositions was studied. On the solid phase of Mg-Al and Cu-Al LDHs and Mg-Al LDO, the Sr and Cs radionuclides are very weakly sorbed from aqueous solutions containing 10^?5 M of the corresponding element (Cs⁺ or Sr²⁺). Introduction of EDTA ions into Mg-Al LDH increases the distribution coefficients K _d of Sr by a factor of more than 40. After 96-h contact of the solid and liquid phases, K _d of radioactive Sr in sorption from aqueous solution on Mg-Al LDH and Mg-Al LDH-EDTA is 2.4 and 100 ml g^?1, respectively. The Sr and Y radionuclides are efficiently sorbed from aqueous solutions containing 10^?5 M Sr²⁺ and Y³⁺ on the Mg-Nd LDH solid phase. After 5-min contact of the solid and liquid phases, K _d of Sr exceeds 10⁵ ml g^?1. For Y, the distribution coefficients equal to 700–800 ml g^?1 are attained after 30-min contact of the solid and liquid phases. Aging of the Mg-Nd LDH precipitate does not affect its sorption properties toward Sr and Y radionuclides. With an increase in the Sr(NO₃)₂ concentration in the solution from 10^?5 to 10^?1 M, the distribution coefficients K _dz of Sr drastically decrease (virtually to zero) and those of Y change insignificantly.     

Sorption of 60Co from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Sorption of ⁶⁰Co from aqueous solutions of various compositions on layered double hydroxides (LDHs) of Mg, Al, and Nd in carbonate and hydroxide forms and on layered double oxides (LDOs) of Mg and Al was studied. ⁶⁰Co is poorly sorbed from aqueous nitrate solutions onto LDH-Mg-Al-OH. The ⁶⁰Co distribution coefficient K _d does not exceed 50 ml g^?1 at a phase contact time of 15 min and V/m = 50 ml g^?1. At the same time, ⁶⁰Co is efficiently sorbed from 10^?3?C10^?5 M aqueous Co(NO₃)₂ solutions onto LDH-Mg-Al and LDH-Mg-Nd with CO ₃ ^2? in the interlayer space. At a phase contact time of 15 min and V/m = 50 ml g^?1, K _d exceeds 2 × 10⁴ ml g^?1 for LDH-Mg-Nd and does not exceed 5 × 10³ ml g^?1 for LDH-Mg-Al. The ⁶⁰Co desorption from LDH-Mg-Nd-CO₃ into 0.05?C0.2 M solutions of Na₂CO₃, NaNO₃, (NH₄)₂C₂O₄, and Na₂H₂EDTA and into distilled water was studied. Na₂H₂EDTA is the most efficient desorbing agent. After 15-min contact of LDHMg(⁶⁰Co)-Nd-CO₃ with 0.1 and 0.05 M Na₂H₂EDTA solutions, the degree of desorption of ⁶⁰Co is ??100 and ??99%, respectively.     

Facile Li-Al layered double hydroxide films on Al alloy for enhanced hydrophobicity,anti-biofouling and anti-corrosion performance

In this work,lithium (Li)-aluminum (Al) layered double hydroxide (LDH) films modified by 4-amino-2-((hydrazine methylene) amino)-4-oxobutanoic acid (denoted as AOA acid) and/or 1H,1H,2H,2H-perfluorooctyltriethoxysilane were prepared on 6N01 Al alloy by a facile,in-situ growth method with enhanced hydrophobicity,anti-biofouling and anti-corrosion performance.The preparation is low energy consumptive and environment friendly,relying on self-assembly at ambient temperature.The structure,molecular weight and functional groups of the synthesized AOA acid were characterized by NMR spectrometer,ESI-MS spectrometer and Fourier transform infrared (FT-IR) spectroscopy.And the compositions,structure and morphology of the films were characterized by Fourier transform infrared(FT-IR) spectroscopy,glancing-angle X-ray diffraction (GA-XRD),X-ray photoelectron spectroscopy (XPS),field emission scanning electron microscopy (FE-SEM) and energy-dispersive x-ray spectrum (EDS).Water contact angle measurements (CA) and atomic force microscopy (AFM) characterization show that the films possess a micro/nanostructure with an improved hydrophobicity.Immersion test,neutral salt tests (NSS) and electrochemical impedance spectroscopy (EIS) conducted in 3.5 wt.％ NaCl solutions demonstrate the improved corrosion resistance of the films over bare Al alloy.Meanwhile,the films also possess an excellent anti-bacterial property to Escherichia coli,Bacillus subtilis and sulfate-reducing bacteria.