Surfactant-modified three-dimensional layered double hydroxide for the removal of methyl orange and rhodamine B: Extended investigations in binary dye systems

Dyes pollution have raised great attention due to its fatal harm on aquatic ecosystem and human health. Generally, multiple dyes (anionic dyes, cationic dyes) present in real wastewater systems. In this work, methyl orange (MO) as anionic dye and rhodamine B (RhB) as cationic dye were chosen as typical dyes to investigate the removal behavior with surfactant-modified three-dimensional MgAl layered double hydroxide (S3D-LDH) via macroscopic and microscopic analyses. Adsorption isotherms revealed that the maximum adsorption capacity of MO and RhB could reach 380.2 and 49.6 mg-g(-1), respectively. The removal process between S3D-LDH and ionic dyes was identified to be a chemical reaction via adsorption kinetics. XRD and MIR demonstrated a decrease of d-spacing value and a red shift of the stretching vibration of lattice water and hydroxyl group in the MO removal and increased d-spacing and a blue shift of water with hydroxyl group in the RhB removal. X-ray photoelectron spectroscopy (XPS) revealed that the RSO3 peak emerged after MO adsorption and the negative bond shift of unbound sulfur of S 2p after RhB adsorption. All investigations revealed that MO adsorbed by S3D-LDH via anion exchange and hydrogen bonding whereas surface adsorption was deemed as the primary pathway for RhB. Furthermore, the MO and RhB adsorption capacity by S3D-LDH was both enhanced in binary component systems. S3D-LDH was demonstrated as a potential broad-spectrum adsorbent for the treatment of dyes wastewater.