Efficient selective removal of indole by Mg/Al-LDH@MOF: mechanistic insights and adsorption behavior

Due to the high toxicity and carcinogenicity of indole, wastewater should be treated to remove indole before discharge. In this study, a novel composite material, Mg/Al-LDH@MIL-101(Fe), was developed by integrating MIL-101(Fe), a high-porosity metal-organic framework (MOF), with Mg/Al-layered double hydroxide (LDH) nanosheets. This composite was designed for the efficient adsorption and removal of indole. The crystal structure, surface morphology, and chemical composition of the composite were analyzed using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and other characterization techniques. The results indicate that the composite exhibits a higher specific surface area and a greater number of active adsorption sites compared to Mg/Al-LDH and MIL-101(Fe). The adsorption of indole can be effectively removed by electrostatic adsorption on the surface of the material, and π-π stacking. The experimental results demonstrated that the indole removal rate could reach 93.14% under the following conditions: pH = 7, adsorbent dosage of 0.1 g L^-1, adsorption time of 2 hours, and indole concentration of 20 mg L^-1. With excellent recyclability (>82% efficiency after 5 cycles) and anti-interference capability (>86% efficiency under coexisting species), this work advances the potential for scalable coking wastewater treatment.