Synthesis and Modification of LDHs for the Adsorption of Cationic and Anionic Dyes and Phosphates

Abstract

AbstractPhosphates and dyes are two common water pollutants. Excess phosphates discharged cause eutrophication due to the hyper-fertilization of phosphorus, while the dyes discharged render water unsafe for consumption. Thus, it is necessary to adsorb both phosphates and dyes from water bodies. We proposed layered double hydroxides (LDHs) as a solution to this. This study proposes the modification of Zn-Al LDH with sodium dodecyl sulfate (SDS), significantly increasing the adsorption capacity of the LDH for cationic dyes, namely methylene blue. The Zn-Al LDH synthesized by co-precipitation involved NaOH with ZnCl2 and AlCl3 salts in a 2:1 ratio. Subsequently, Zn-Al LDH was reconstructed with SDS solution to intercalate the dodecyl sulfate anions. LDHs synthesized were characterized using XRD. The effects of initial methyl orange, methylene blue, phosphate concentration, and pH on the adsorption by the LDHs were studied. Reusability tests were conducted for methyl orange to evaluate the efficacy of the Zn-Al LDH over continuous cycles. Zn-Al LDH has a maximum adsorption capacity of 1110 mgg−1 and 262 mgg−1 on methyl orange and phosphate, respectively, outperforming several other LDHs. Modifying the Zn-Al LDH with SDS enhances its maximum adsorption capacity on methylene blue, attaining a maximum adsorption capacity of 149 mgg−1, outperforming several other LDHs. The Zn-Al LDH can remove close to 95% of dye over multiple cycles.