Fulvic acid anchored layered double hydroxides: A multifunctional composite adsorbent for the removal of anionic dye and toxic metal

A novel multifunctional composite adsorbent which possesses the ability for anion exchange and toxic metal complexation has been synthesized by the hybridization of layered double hydroxides (LDH) and fulvic acid (FA) in this study. The results show that FA with lots of functional groups can be effectively and stably anchored on the surface of LDH through coagulation process without occupying the interlayer of LDH. Therefore, the anion exchange ability remains and the adsorption capacity of Orange II can reach 1.9   mmol/g, which is almost as much as stoichiometric anion exchange capacity of pure LDH. Moreover, the composite adsorbent’s adsorption capacity of Cu 2+ , Pb 2+ , Ni 2+ and Cd 2+ can also get to 2.25   mmol/g, 0.98   mmol/g, 0.99   mmol/g and 0.16   mmol/g respectively with an adsorption preference order of Cu 2+   >   Pb 2+   >   Ni 2+   >   Cd 2+ . In addition, Orange II and toxic metals are able to be simultaneously removed by this composite adsorbent, and the adsorption of toxic metals can be enhanced by the synergetic adsorption of Orange II. Anion exchange with Cl − in LDH matrix accounts for the adsorption of Orange II, while the adsorption of toxic metal is mainly attributed to the complexation of carboxyl functional group derived from FA.