The herbicide glyphosate (GLY) or 2,4-dichlorophenoxyacetic acids (2,4D) was intercalated in the interlayer region of a Zn-Al-layered double hydroxide (LDH) to obtain LDH-GLY or the LDH-2,4D hybrid composite because of its controlled release. Compared to the physically mixed herbicides, the LDH-herbicide hybrid composite displayed slow-release properties in decarbonated distilled water. The release rate of herbicides was found to be dependent on the carbonate and chloride anion concentrations in solution. The time at which 50% of the herbicides were released from the hybrid composite into solution, t , ranged from 6.5 to 18.6 h for LDH-GLY and from 10 to 21.5 h for LDH-2,4D. Our results indicate that the application of LDH-GLY or LDH-2,4D hybrid composite to agricultural areas could reduce the maximum 2,4D or GLY contamination and result in the retardation of herbicides leaching through the soil. This study demonstrates the potential applicability of LDHs as supports for the slow release of acid herbicides.
In this study, the performance of poly(layered double hydroxides) [poly(LDHs)] beads as an adsorbent for arsenate removal from aqueous solution was investigated. The poly(LDHs) beads were prepared by immobilizing LDHs into spherical alginate/polyvinyl alcohol (PVA)-glutaraldehyde beads (spherical polymer beads). Batch adsorption studies were conducted to assess the effect of contact time, solution pH, initial arsenate concentrations and co-existing anions on arsenate removal performance. The potential reuse of these poly(LDHs) beads was also investigated. Approximately 79.1 to 91.2% of arsenic was removed from an arsenate solution (50 mg As L(-1)) by poly(LDHs). The adsorption data were well described by the pseudo-second-order kinetics model and the Langmuir isotherm model, and the adsorption capacities of these poly(LDHs) beads at pH 8 were from 1.64 to 1.73 mg As g(-1), as calculated from the Langmuir adsorption isotherm. The adsorption ability of the poly(LDHs) beads decreased by approximately 5-6% after 5 adsorption-desorption cycles. Phosphates markedly decreased arsenate removal. The effect of co-existing anions on the adsorption capacity declined in the following order: HPO4 (2-) >> HCO3 (-) > SO4 (2-) > Cl(-). A fixed-bed column study was conducted with real-life arsenic-containing water. The breakthrough time was found to be from 7 to 10 h. Under optimized conditions, the poly(LDHs) removed more than 82% of total arsenic. The results obtained in this study will be useful for further extending the adsorbents to the field scale or for designing pilot plants in future studies. From the viewpoint of environmental friendliness, the poly(LDHs) beads are a potential cost-effective adsorbent for arsenate removal in water treatment.
The influence of ammonia on TiO 2 -MgFe 2 O 4 catalysts synthesized via a hydrolysis and co-precipitation, followed by calcination at 500 o C, was studied. Two different catalysts, TiO 2 -MgFe 2 O 4 (Am) and TiO 2 -MgFe 2 O 4 (W), were prepared using Ti-precursors, which were synthesized by the hydrolysis of Ti-butoxide with and without ammonia. The resulting TiO 2 -MgFe 2 O 4 catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area measurements, X-ray diffraction, and UV-vis diffuse reflectance techniques. It was revealed that strong electronic coupling exists between the TiO 2 and MgFe 2 O 4 components within the TiO 2 -MgFe 2 O 4 catalysts. Photocatalytic activity toward Rhodamine B (RhB) was investigated in aqueous solution under visible light irradiation. TiO 2 -MgFe 2 O 4 (W) was found to be an effective catalyst and had several advantages over TiO 2 -MgFe 2 O 4 (Am). These results clearly highlight that ammonia had a significant influence on the photocatalytic activity of the TiO 2 -MgFe 2 O 4 catalysts. Therefore, the results reported herein indicate that TiO 2 -MgFe 2 O 4 is a green, low-cost, and highly efficient photocatalyst for environmental remediation.
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