Controlled synthesis of porous Zn/Fe based layered double hydroxides: Synthesis mechanism, and ciprofloxacin adsorption

Present work include the designing of a novel porous Zn/Fe layered double hydroxide (LDH) based adsorbent using a combination of three methods, namely, co-precipitation, hydrothermal, and thermal treatment. The Zn/Fe LDH was synthesized by co-precipitation followed by hydrothermal method. The LDH was then intercalated with H₂O₂ and its decomposition under the thermal treatment created oxygen bubbles that pierce holes in the layered structure of the LDH by local pressure build-up. Major techniques used for assessing the morphology and surface area characteristics of the LDH and porous LDH were Scanning electron microscope (SEM) and Brunauer-Emmet-Teller (BET). The intercalation of H₂O₂ and its later decomposition triggered by thermal treatment lead to the introduction of pores in the LDH layers that increased the surface area from 108.863 m²/g to 168.923 m²/g. The synthesized adsorbent was utilized for the removal of an antibiotic; ciprofloxacin (CIP) from the aqueous solution. The porous Zn/Fe LDH adsorbent was featured with an admirable CIP adsorption capacity of 344.83 mg/g at pH 6.5 and temperature 298 K. The adsorption of CIP onto porous Zn/Fe LDH adsorbent followed the Freundlich isotherm model and pseudo-second-order kinetic model. The temperature increase negatively affected the adsorption rate. The adsorption mechanism of CIP onto porous Zn/Fe LDH was also projected and established, and Cπ- metal interactions, hydrogen bonding, and electrostatic interactions, were found to be the major interactive forces. The thermodynamic study revealed the exothermic and spontaneous nature of the adsorption experiments. Overall, the synthesized adsorbent is sustainable in terms of its usability and non-toxic nature.