Zn-Al layered double hydroxides for adsorption and photocatalytic removal of с ationic dye

Abstract

The removal of hazardous substances from wastewater is a major problem in the world. The advantages of application of Zn-Al layered double hydroxides (LDHs) and their derivatives for removal of organic contaminants consist in the combination of high adsorption capacity of LDHs and the presence of a photoactive component. Therefore, the present paper focuses on study of the adsorption and photocatalytic capabilities of Zn-Al LDHs to remove cationic dye methylene blue (MB) from aqueous solutions. Zn-Al LDHs with Zn:Al ratio 2 were synthesized by coprecipitation method. Zn-Al LDHs were characterized by XRD, thermogravimetric and spectroscopy analysis. The reconstruction of calcined Zn-Al LDHs in sodium dodecyl sulfate (SDS) solutions in the range of concentrations from 0.012 mol•L-1 to 0.205 mol•L-1 was performed to obtain organo/Zn-Al LDHs. The partial SDS intercalation was clearly evidenced by the appearance of a peak at low 2θ values. SDS-modified LDHs demonstrate the high adsorption capacity to MB. About 90 % of dye was adsorbed with organo/Zn-Al LDHs from 2×10-4 mol•L-1 MB solution. The study on optical properties of calcined and reconstructed Zn-Al LDHs has detected the presence of ZnO that makes possible the using of Zn-Al LDHs as photocatalysts. About 50 % of dye was destructed by irradiation of MB solution in the presence of Zn-Al LDHs from 2×10-5 mol•L-1 MB solution in the presence of calcined at 450 °C Zn-Al LDHs. It has been found that the most complete removal of the dye from highly concentrated solutions is achieved by MB adsorption with organo/Zn-Al LDH. The investigation of the irradiation influence on the optical spectra of MB adsorbed on the surface of organo/Zn-Al LDH is needed to clarify the photocatalytic activity of ZnO-contained organo/Zn-Al LDH. The high adsorption capacity of organo/Zn-Al LDHs and the ease of both synthesis and separation processes rendered this adsorbent to be a promising candidate for environmental remediation.

Structural and Photoprotective Characteristics of Zn-Ti, Zn-Al, and Mg-Al Layered Double Hydroxides—A Comparative Study

“…The photocatalytic properties of the synthesized LDH were analyzed by observing the photodegradation of MB over a period of 4 h. The inherent adsorption of MB on different LDH was measured prior to photocatalytic testing [50][51][52]. Only minimal surface adsorption of MB on LDH was observed in the absence of UV, and the equilibrium concentration were 0.013, 0.004, and 0.029 g/L, respectively, for Zn-Ti, Zn-Al, and Mg-Al LDH.…”

Nanoparticles of zirconium hydrophosphate framed with a weakly-acidic cation-exchange polymer

“…Other types of sorbents include inorganic matrix (silica [5][6][7], zirconia [8] or clay [9]) functionalized with organic fragments. Synthetic (for instance, double hydrated oxides [10]) and natural (clays [11][12][13], zeolites [13]) materials modified with surfactants can be related to intermediate types of sorbents. They are capable to remove not only toxic inorganic ions, but also organic compounds.…”