3D flower-like CuO@NiAl-LDH microspheres with enhanced removal affinity to organic dyes: mechanistic insights, DFT calculations and toxicity assessment

Abstract

Highly efficient removal of organic dyes in wastewater is attracting more and more attention. Here, a novel 3D flower-like copper(II) oxide hybrid nickel–aluminum layered double hydroxide (CuO@LDH) microsphere with increasing catalytically active sites and specific surface area is fabricated by a hydrothermal method and applied for the degradation and adsorption of organic dyes. The Fenton-like system of CuO@LDH with H₂O₂ exhibits excellent degradation activity for methylene blue (MB). Moreover, nearly 99.0% degradation of MB is achieved within 120 min, and its degradation rate constants (k) are 20 and 93 times higher than that of NiAl-LDH and H₂O₂ alone, respectively. Meanwhile, the effect of catalyst dosage, pH, H₂O₂ dosage, and coexisting ions on MB removal is investigated in detail. CuO@LDH can also effectively adsorb congo red (CR) with a maximum adsorption capacity of 560.3 mg g⁻¹. The degradation mechanism is explored via bursting experiments and electron spin resonance (ESR). The degradation pathway of MB is analyzed based on density functional theory (DFT) calculations and the liquid chromatography-mass spectrometry (LC-MS) technique. The biotoxicity of the intermediates is evaluated using a quantitative structure–activity relationship (QSAR). Therefore, this work is expected to expand the application of LDHs in advanced oxidation processes (AOPs) for wastewater treatment.