Cu-Ca-Al-layered double hydroxide modified by itaconic acid as an adsorbent for anionic dye removal: Kinetic and isotherm study

Here, for the first time, Cu-Ca-Al-based layered double hydroxide (LDH) was prepared using a facile co-precipitation method. Itaconic acid (ITA) was used as a biodegradable and green organic molecule to modify the LDH and then physicochemical properties of the ITA-modified LDH (LDH-ITA) were studied using FTIR, FE-SEM, TEM, XRD, and TGA techniques. Then the synthesized LDH and LDH-ITA were applied as novel adsorbents for the removal of Congo red as a model of an anionic dye from aqueous media. Several parameters such as the solution pH, contact time, adsorbent amount, and initial concentration of the dye on the adsorption process were monitored and kinetic and isotherm studies were conducted to gain a more in-depth insight into the adsorption mechanism in the process. The results demonstrated that the adsorption of Congo red onto both the LDH and LDH-ITA adsorbents followed the pseudo-second-order kinetic model. Also, isotherm investigations revealed that the Freundlich model provided the best fit with the equilibrium data of both adsorbents. Maximum adsorption capacities of 81 and 84 mg g(-1) for Cong red were obtained using Cu-Ca-Al-LDH and LDH-ITA adsorbents, respectively, surpassing those values obtained for most adsorbents reported in the previous studies.