Three-dimensional hierarchical flower-like Mg–Al-layered double hydroxides: highly efficient adsorbents for As(V) and Cr(VI) removal

Research Center for Biomimetic Functional Materials and Sensing Devices, Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei, Anhui 230031, People's Republic of China.
Nanoscale (Impact Factor: 7.39). 04/2012; 4(11):3466-74. DOI: 10.1039/c2nr30457k
Source: PubMed


3D hierarchical flower-like Mg-Al-layered double hydroxides (Mg-Al-LDHs) were synthesized by a simple solvothermal method in a mixed solution of ethylene glycol (EG) and water. The formation mechanism of the flower-like Mg-Al-LDHs was proposed. After calcination, the flower-like morphology could be completely preserved. With relatively high specific surface areas, Mg-Al-LDHs and calcined Mg-Al-LDHs with 3D hierarchical nanostructures were tested for their application in water purification. When tested as adsorbents in As(V) and Cr(VI) removal, the as-prepared calcined Mg-Al-LDHs showed excellent performance, and the adsorption capacities of calcined Mg-Al-LDHs for As(V) and Cr(VI) were better than those of Mg-Al-LDHs. The adsorption isotherms, kinetics and mechanisms for As(V) and Cr(VI) onto calcined Mg-Al-LDHs were also investigated. The high uptake capability of the as-prepared novel 3D hierarchical calcined Mg-Al-LDHs make it a potentially attractive adsorbent in water purification. Also, this facile strategy may be extended to synthesize other LDHs with 3D hierarchical nanostructures, which may find many other applications due to their novel structural features.

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    • "The removal of Cr(VI) from aqueous solution has been previously examined using a number of different LDHs, including Mg–Al LDH, Ni–Al LDH, Zn–Cr LDH, Zn–Al LDH, Ca–Al LDH, Mg–Fe LDH, and Ni–Fe LDH. In addition, more complex systems, such as calcined graphene/Mg–Al LDH [6] or a 3D hierarchical Mg–Al LDH with a flower-like morphology [7], have been examined for enhanced Cr(VI) removal. We have previously shown that Fe 2+ -doped Mg–Al LDH is superior to Mg–Al LDH for Cr(VI) removal [8]. "
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    ABSTRACT: Ni–Al layered double hydroxide (Ni–Al LDH) and Co–Al LDH were prepared using a coprecipitation method. Ni–Al LDH and Co–Al LDH were found to remove Cr(VI) from aqueous solution through anion exchange of Cr2O72− with Cl− intercalated in the interlayer of the LDHs. Ni–Al LDH and Co–Al LDH were both found to be superior to Mg–Al LDH for removal of Cr(VI). This excellent behavior is attributed to the buffering effect of Ni–Al LDH and Co–Al LDH that results in a lower amount of OH− in solution and allows Cr2O72− to be more easily intercalated in the LDH interlayer. The Cr(VI) removal process was consistent with a Langmuir-type adsorption, indicating that the removal of Cr(VI) proceeded via chemical adsorption involving the anion exchange of Cr2O72− with intercalated Cl−. The maximum adsorption and equilibrium adsorption constant values were 2.0 mmol g−1 and 2.4, respectively, for Ni–Al LDH, and 1.9 mmol g−1 and 1.5, respectively, for Co–Al LDH. The kinetics of Cr(VI) removal by Ni–Al LDH and Co–Al LDH were consistent with a pseudo-second-order reaction, and the rate-determining step for Cr(VI) removal was found to be the anion exchange. The apparent rate constants at 10, 30, and 60 °C for Ni–Al LDH were 2.2 × 10−3, 2.4 × 10−3, and 3.2 × 10−3 g mmol−1 min−1, respectively. The apparent rate constants at 10, 30, and 60 °C for Co–Al LDH were 1.2 × 10−3, 1.6 × 10−3, and 1.9 × 10−3 g mmol−1 min−1, respectively. The Arrhenius plot of the rate constants yielded apparent activation energies of 6.1 and 6.6 kJ mol−1 for Ni–Al LDH and Co–Al LDH, respectively.
    Preview · Article · Dec 2014 · Journal of Water Process Engineering
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    • ", Sendai 980-8579, Japan e-mail: brilliant orange X-GN, arsenate, arsenite, fluoride, bromate, bromide, selenate, borate, nitrate, and chromate (Chubar 2011; Wu et al. 2011; Lv et al. 2012; Halajnia et al. 2012; Yu et al. 2012). As expressed in Eq. 2, the rehydration and subsequent combination of Mg-Al oxide with anions in solution is accompanied by the release of OH -. "
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    ABSTRACT: Mg−Al oxide, obtained by the thermal decomposition of a CO3 2−-intercalated Mg−Al layered double hydroxide (CO3·Mg−Al LDH), simultaneously absorbed Cl− and SO4 2− from seawater and generated a Mg−Al LDH intercalated with Cl− and SO4 2−. The Mg−Al oxide with a molar ratio Mg/Al = 4 was more superior than the oxide with Mg/Al = 2 for Cl− removal, whereas a reverse phenomenon was observed for SO4 2− removal. The removal of Cl− and SO4 2− by the Mg−Al oxide with Mg/Al = 4 could be represented by first-order and pseudo second-order reactions, respectively. The removal of both Cl− and SO4 2− by the Mg−Al oxide with Mg/Al = 2 could be represented by a pseudo second-order reaction. The removal of both Cl− and SO4 2− by the Mg−Al oxides with Mg/Al = 4 and 2 was proceeded under chemical reaction control. The adsorption isotherms for Cl− and SO4 2− adsorbed by the Mg−Al oxides could be expressed by Langmuir-type adsorption. These reactions were derived from monolayer adsorption, indicating the intercalation of Cl− and SO4 2− in the interlayer space of Mg−Al LDH. The uptake of Cl− and SO4 2− from seawater by Mg−Al oxide was proceeded spontaneously.
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    • "adsorbents, it was confirmed that both adsorbents exhibited a flower-like nano-architecture composed of nano-sized flakes. This is in good agreement with the previous reports describing formation of flower-like structure in nano-porous MgO and layered double hydroxide [38] [39] [40]. "
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    ABSTRACT: Nano-structured MgO–Al2O3 aerogel adsorbents (denoted as MgAl-AE-X) with different Mg/Al molar ratio (X) were prepared by a single-step epoxide-driven sol–gel method and a subsequent CO2 supercritical drying method. The effect of Mg/Al molar ratio of nano-structured MgO–Al2O3 aerogel adsorbents on their physicochemical properties and CO2 adsorptive performance at elevated temperature (200 °C) was investigated. Successful formation of flower-like nano-structured MgAl-AE-X adsorbents was confirmed by N2 adsorption–desorption isotherms and SEM analyses. The crystalline structure of MgAl-AE-X adsorbents was transformed in the sequence of Al2O3 → MgAl2O4 → MgO-MgAl2O4 with increasing Mg/Al molar ratio from 0 to 3. All the MgAl-AE-X adsorbents were found to possess weak base site and medium base site except for strong base site. In the dynamic CO2 adsorption, both the total CO2 capacity and the 90% breakthrough CO2 capacity showed volcano-shaped curves with respect to Mg/Al molar ratio, and they were decreased in the order of MgAl-AE-0.5 > MgAl-AE-1.0 > MgAl-AE-2.0 > MgAl-AE-3.0 > MgAl-AE-0. It was found that the 90% breakthrough CO2 capacity increased with increasing medium basicity of the adsorbents. Among the adsorbents tested, MgAl-AE-0.5 (Mg/Al = 0.5) adsorbent with the highest medium basicity showed the best CO2 adsorptive performance. Thus, medium basicity of nano-structured MgO–Al2O3 aerogel adsorbents served as a crucial factor in determining CO2 adsorptive performance at elevated flue gas temperature (200 °C).
    Full-text · Article · Apr 2014 · The Chemical Engineering Journal
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