Effective removal of water-soluble azo dyes by cubic MgO micromotors

As one of the main dyes in the textile industry, azo dyes have a serious impact on the ecological environment and health through their wastewater discharge. It has become crucial to develop effective methods for removing these substances. Currently, research on micro-nano technology is underway to develop new micro-nano systems and materials that can rapidly and effectively remove pollutants and heavy metals from water. This study reported the successful preparation of cubic magnesium oxide (MgO) micromotors dynamic nanomaterials through chemical deposition-hydrothermal-ion sputtering and explored the adsorption performance and mechanism of MgO micromotors on methyl orange (MO) azo dye. The surface morphology, composition and motion trajectory of nanomaterials were analysed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), BET automatic specific surface area and pore size analyser, X-ray diffraction (XRD), upright optical microscopy and NIS-Elements software. The MgO micromotors exhibit a mean square displacement of 4.599 μm² and an average velocity of 3.87 ± 0.54 μm/s in a 6% H₂O₂ solution, demonstrating their self-propulsion ability in static water. Furthermore, the adsorption capacity of MgO micromotors for MO is significantly enhanced with increasing H₂O₂ concentration, reaching a removal rate as high as 97.46% at a 6% H₂O₂ concentration. Fourier transform infrared spectroscopy (FTIR) analysis confirmed that a strong chemical bond (coordinate bond) was formed between the negatively charged anionic azo dye MO and the MgO micromotors which could be hydrolysed to produce easily dissociated magnesium hydroxide (Mg(OH)₂) in aqueous solution, resulting in enhanced adsorption properties.