Papers by Keyword: Hydrotalcite

Abstract: Adsorption of gold from a solution in the form of gold nanoparticles (AuNPs) is a challenging approach. In this paper, Mg/Al hydrotalcite (Mg/Al HT) was functionalized with ascorbic acid (Mg/Al HT-AA) and applied to adsorb and reduce Au³⁺ to Au⁰. The anion exchange method was observed as a recommended way to immobilize and intercalate ascorbic acid to Mg/Al HT. Based on the TEM image, the formation of AuNPs was confirmed with the average diameter 16.3 nm. These findings suggest that Mg/Al HT-AA has a good potential as multifunctional adsorbent that can recover gold in solution and simultaneously turn it into gold nanoparticles.

Abstract: Metal oxide electrode materials have relatively high theoretical capacitance. However, structure, morphology and composition of this kind of materials have significant influence on electrochemical performance. Moreover, metal oxide electrode materials have problems of low power density and cyclic stability. In this work, Mo-doped hydroxide zinc carbonate material (Mo-HZC) is synthesized on foam Ni surface by hydrothermal method. This Mo-doping electrode exhibits typical pseudocapacitance. Specific capacitance of Mo-HZC in 1.0 mol L^-1 KOH is 698.9 F g^-1 (1.0 A g^-1), which is 2.5 times that of the undoped sample. The maximum energy density and power density of Mo-HZC electrode are 32.1 WH kg^-1 and 3.16 KW kg^-1, respectively. Assembled Mo-HZC//AC capacitor exhibits a long-term cycling performance with remains 79.5% capacitance retention within 20 000 cycles at 1.0 A g^-1.

Abstract: Growing environmental conservation concerns have led researchers to seek the means to treat and recover wastewater. The textile industry dumps vast quantities of wastewater from textile dyes. By means of clays, dye waste can be separated and reused for other industrial processes. Clay absorption varies depending on the type of dye employed because factors like the reactivity of the dye molecule and its size are very important during the absorption process. The absorption capacity of calcined hydrotalcite at several concentrations was compared in a 0.05 g • L^-1 solution of four distinct dyes: Direct Blue 199, Direct Red 23, Direct Blue 71 and Reactive Yellow. Dyes have different molecular weights because the weight of reactive dyes is considerably lighter than that of direct dyes, which is why the Lambert-Beer lines of each dye are previously considered. We worked with a 5 g • L^-1 clay concentration to introduce the dye into the clay by stirring for 24 h in 100 ml of each dye solution before filtering it and leaving it to dry. In all cases, the dye absorption by nanoclay was nearly absolute and the initial solution was very clean, which are excellent results from the wastewater treatment point of view. Color measurement was performed by a Jasco V-670, double-beam spectrophotometre between 190-2700 nm. Differences in color were calculated and represented in CIE-Lab* color space diagrams. Finally, thermogravimetric (TGA) and X-ray diffraction (XRD) analyses were carried out to ensure both nanoclay-dye interactions and hydrotalcite structure recovery. No large differences were observed under these conditions, which reinforces the idea of using low nanoclay concentrations.

Abstract: Using magnesium nitrate, nickel nitrate and aluminum nitrate as raw materials and urea as precipitant, magnesium nickel aluminum ternary hydrotalcites with large specific surface area were prepared by hydrothermal method. The prepared samples were characterized by SEM、XRD、BET and EDS etc., respectively. The adsorption properties of MgNiAl-LDHs, MgAl-LDHs and their calcined products (MgNiAl-LDOs, MgAl-LDOs) for chloride ions in solution were investigated. The results show that MgNiAl-LDHs are cubic with rod-like structure, with a specific surface area of 197.62 m²/g, which is much larger than that of MgAl-LDHs (102.82 m²/g). Under the same adsorption conditions, the saturated adsorption capacities of MgNiAl-LDHs and MgAl-LDHs for chloride ions are 130.06mg/g and 110.02 mg/g respectively. MgNiAl-LDOs showed better adsorption ability for chloride ions. By simulating the adsorption data, the results show that the adsorption kinetics and the adsorption isotherm are in accordance with the quasi-second-order kinetic model and the Langmuir isotherm model, respectively.

Abstract: Hydrotalcite are anionic clay material presenting LDH arrangement and high porosity and specific areas, which make it a good adsorbent for pollutant species in water. Besides that, that material type can be used as catalyst or catalyst support in several industrial processes. The most common compositions is based on metallic mix hydroxide with high content of magnesium, but their adsorptive properties arise from aluminum replacement in layer structure. The present work presents the synthesis of carbonated magnesium-aluminum hydrotalcite through the precipitation method in order to investigate the co-insertion of iron (III) in aluminum site. It was found the iron (III) co-inserted samples obtained at 100 and 200 oC for 4 hours present no substantial harming in relation to the common magnesium-aluminum composition. All of the samples presented high porosity and specific area, becoming an alternative anionic adsorptive.

Abstract: Magnesium-aluminum hydrotalcites can be co-substituted with others trivalent cations, such as iron III in aluminum site, which can be a promising way to modify the properties of that synthetic adsorptive material. In the present work, hydrotalcite containing 5 mol% iron III in co-substitution to the aluminum was prepared by precipitation process and compared with no co-substituted sample along the temperature of calcination at 100 and 500 oC for 4 hours. The calcined samples were characterized by simultaneous TG/DTA, X-ray Diffraction and nitrogen adsorption-desorption techniques. The iron (III) insertion showed positive results in order to provide more stable structure against high temperatures of calcination, which was observed by lesser structural decomposition of rhombohedral hydrotalcite and a more mesoporous structure.

Abstract: Etiology of halitosis is often concerned with gram-negative anaerobic bacteria, which produce the malodorous compounds such as volatile sulfur compounds (VSC), hydrogen sulfide and methyl mercaptan. The absorbents for the malodorous compounds are expected to prevent the teeth from decaying and peiodontics disease. The VSC adsorption capabilities of layered double hydroxides, of which composition is A_1-xB_x(OH)₂C_x/n·mH₂O, where A and B are Mg and Fe ions, and C are carbonate (CO₃^2- : MgFe LDH CO₃) and fluorine (F ^- : MgFe LDH F) ions in aqueous medium was studied by GC/FPD. The concentration of H₂S rapidly decreased for first 1 hours of soaking in H₂S water and fell to 0% in 4-5 h when MgFe LDH CO₃ was applied. MgFe LDH F was used, then the H₂S concentration was quickly decreased the same as MgFe LDH CO₃, and 8 mg/l of fluorine was released at a time. The iron ion was not detected in the H₂S water after soaking for 18 hours. The MgFe LDHF are expected to be likely adsorbent for the fast removal of VSC from the mouth and fluorine releasing agent.

Abstract: Mg/Al hydrotalcite-like materials containing ceria were synthesized as catalysts precursors for the reaction of dry methane reforming. The nickel species were introduced into the catalytic systems via adsorption from aqueous solution of [Ni (EDTA)]^2- complexes for 4 and 24h and the effect of adsorption time on the catalytic properties of obtained materials was evaluated. The mixed nanooxides were obtained by thermal decomposition of hydrotalcite-like materials at 550°C for 4h and the catalysts were subsequently characterized by XRD, elemental analysis, H₂-TPR and low temperature N₂ sorption techniques. The adsorption duration of [Ni (EDTA)]^2- influenced the properties of the prepared materials, such as textural properties, nickel crystallite size, and thus their catalytic activity in the reaction of dry reforming of methane. The sample which underwent adsorption for 24h turned out to be the most active in DRM reaction. However, over this catalyst RWGS reaction was well developed, which caused the excess of CO in the products of the reaction and faster deactivation of the catalyst.

Abstract: Several compounds are being investigated for CO₂ capture, besides alkolamines, including solid materials as activated charcoal, zeolites, metal organic frameworks, metal oxides and hydrotalcites. Hydrotalcites, also called layered double hydroxides (LDHs), present some characteristics that are very interesting for CO₂ capture, including their speed to achieve equilibrium and their high regeneration. These compounds can be represented by the general formula [M_1-x²⁺M_x³⁺(OH)₂]^x+ [(A^n-)_x/n.yH₂O]^x, where M²⁺ and M³⁺ are divalent metals and trivalent cations, respectively, and A^n- is an anion of valency n which occupies the interlayer region, and maintains electrical neutrality of these materials. In the present work, we have synthesized specific LDHs, thermally modified for CO₂ sorption. LDH’s were synthesized intercalated with carbonate anions employing the heterogeneous precipitation method, also known as co precipitation method. After LDH's calcination at different temperatures, the formation of oxides was observed with different surface areas and therefore a varied adsorption capacity. The products were characterized by X-ray diffraction, infrared absorption spectroscopy and thermo gravimetric analysis. The maximum efficiency of CO₂ adsorption was observed at reduced pressure with the calcined sample of LDH-CO_3, Mg₂Al which indicates that the material maintained stable and with a high crystallinity. These properties presented for LDH-CO_3, Mg₂Al synthesized in this work indicate that these materials can be good and also cheap candidates for CO₂ capture.

Abstract: Most etiology of bad breath is often concerned with gram-negative anaerobic bacteri, and pharmacotherpy using pharmaceutical drugs should be effective but limited, because bacteria at deep periodontal pocket may be sterilized but cannot be washed out and the malodorous compounds remain. The absorbents for the malodorous compound such as volatile sulfur compounds (VSC), hydrogen sulfide (H₂S), are expected to prevent the teeth from decaying and peiodontics disease. The VSC adsorption capabilities of layered double hydroxides, of which composition is A_1-xB_x(OH)₂C_x/n·mH₂O, where A and B are Mg and Fe ions, and C are carbonate (CO₃^2- : MgFe HTCO₃) and chlorine (Cl ^- : MgFe HTCl) ions in aqueous medium was studied by GC/FPD. The concentration of H₂S rapidly decrease to less than 15% for first 1 hours of soaking in H2S water and fell to 0% in 4-5 h when the MgFe HTCO₃ and MgFe HTCl were used. The iron ion was not detected in the H₂S water after soaking for 18 hours.The MgFe HTCO₃ and MgFe HTCl are expected to be likely adsorbent for the fast removal of VSC from the mouth.