Comparative investigation on the adsorption behavior of bromate in aqueous solutions using Zn/Ni/Al-LDH and Ni/Al-LDH: optimization, equilibrium analysis, and mechanistic insights

The presence of bromate in water poses a significant health risk. In order to effectively eliminate bromate from water, this study synthesized a series of ternary Zn-Ni-Al layered double hydroxides with varying Zn/Ni/Al atomic ratios using a co-precipitation method. The adsorbents were characterized using various techniques including XRD, Fourier transform infrared spectroscopy, and N₂ adsorption-desorption isotherms. Among them, ZnNiAl-2 exhibited the highest crystallinity and largest specific surface area (316.1 m² g⁻¹), which was compared to the binary hydrotalcite NiAl-LDH for its ability to adsorb bromate from water. Results demonstrated that the adsorption isotherm of bromate on ZnNiAl-2 followed the Langmuir model, with a maximum adsorption capacity of 120.5 mg g⁻¹, significantly higher than that of NiAl at 75.5 mg g⁻¹, indicating strong adsorption capability and reusability performance. The adsorption kinetics were also found to be in accordance with the pseudo-second-order kinetic model. The mechanism involved both surface adsorption and anion exchange.