Synthesis of polydopamine modified MgAl-LDH for high efficient Cr(VI) removal from wastewater

A highly efficient absorbent was developed in this study by modifying polydopamine film on Mg–Al layered double hydroxide (PDA/MgAl-LDH) to remove Cr(VI) from wastewater. The characterization results showed that the polydopamine film was successfully coated on the MgAl-LDH surface. The preparation ratio, pH, and adsorbent dosage influencing absorption by PDA/MgAl-LDH were systematically investigated. The absorption capacity of Cr(VI) by PDA/MgAl-LDH was 87 mg/g. The equilibrium adsorption isotherm of PDA/MgAl-LDH was in good agreement with that of the Langmuir model. Therefore, the pseudo-second-order kinetic model is suitable for describing adsorption kinetics. The interaction between PDA and Cr(VI) and Cr(III) was investigated using density generalized function theory (DFT), which demonstrated that the PDA amino group could provide electrons for Cr(VI) reduction. Hydrogen and covalent bonding were dominant during the chemisorption process of PDA absorbing Cr(VI), the nitrogen of 5,6-dihydroxyindole was the primary active site for absorbing Cr(III), and electrostatic attraction was mainly responsible for Cr(III) absorption. Therefore, PDA/MgAl-LDH has the potential to adsorb and remove Cr(VI) from wastewater.