| With the development of printing and dyeing industry, there is a lot of printing and dyeing wastewater discharged into rivers each year. Because of its complex characteristics, such as a high concentration of organic pollutants, deep chromaticity, low biodegradability and complex ingredients, dyeing wastewater is difficult to treat by conventional wastewater treatment processes. In particular, the dyes are one of the most challenging parts of treating dyeing wastewater because of their complex molecular structures, which make them more stable and difficult to treat. Adsorption is a common method for dye removal because it is effective and economical among the many techniques. The existing adsorbents may perform well for the sorption of a single kind of dye, but fail in the removal of all of the dyes. Therefore, it is essential to find a broad-spectrum adsorbent that can effectively remove various kinds of dyes and has a high sorption capacity.Layered double hydroxides (LDHs) are a promising new class of sorbent that have attracted considerable because of their unique layered structure, electrical properties and ion exchange capacity. They are ineffective for the removal of hydrophobic non-ionic organic contaminants because of the preferential attraction of hydrophilic groups to the LDHs surface, although they are good sorbents for anionic compounds. Consequently, research efforts have been focused on changing the surface properties of LDHs from hydrophilic to hydrophobic characteristics by intercalation of long chain anionic surfactants. It is expected that modified organo-LDHs may be promising adsorbents for a range of organic contaminants including organic dyes from wastewater.In this study, sodium dodecylsulfate (SDS) was intercalated into layered double hydroxides by co-precipitation, and was characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The use of LDHs-SDS as adsorbent to remove acid orange Ⅱ, a model anionic dye, from aqueous solution was investigated in terms of adsorbent dosage, pH, dye concentration, temperature, and contact time. It was found that LDHs-SDS was particularly effective in removing acid orange II in a pH range between3and11. When the dosages of LDHs-SDS were0.2mg/L and0.4mg/L at298K, the maximum removal efficiencies were97.41%and97.13%for the dye concentration of100mg/L and200mg/L, respectively. The adsorption of acid orange II on LDHs-SDS reached equilibrium within2hours. The adsorption isotherm can be well fitted by Langmuir equation. The saturated adsorption capacity of LDHs-SDS for acid orange II was486.44mg/g at298K. The adsorption process was endothermic. The adsorption kinetic of acid orange II onto LDHs-SDS can be best described by pseudo-second-order model. The results showed that LDHs-SDS can be used as a potential and effective adsorbent in treating dye effluent.On the basis of the study on acid orange II, systematic studies were carried on the sorption of anionic dyes (direct blue G-RB (DB), reactive yellow4GL (RY), acid red GR(AR)), cationic dye(basic blue (BB)) and nonionic dye (disperse red3B (DR)) by organo-LDHs. The sorption was found to be independent of pH from5to10. The maximum removal capacities for DB, RY, AR, DR and BB were620.58,307.85,124.32,229.63and138.35mg/g, respectively, at298K. The adsorption isotherm for AR fitted the Freundlich model well, and data for the other dyes fitted the Langmuir model. The sorption kinetics of all five dyes were well described by the pseudo-second-order model. The thermodynamic parameters calculated from Van’t Hoff plots indicated the sorption process is a spontaneous physisorption. After treating actual dye wastewater with LDHs-SDS, the results indicate that this could be a potentially effective adsorbent for treating dye effluent. |
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