Synthesis of uniformly distributed magnesium oxide micro-/nanostructured materials with deep eutectic solvent for dye adsorption

A deep eutectic solvent (DES) strategy is developed for scalable synthesis of porous magnesium oxide (MgO). The uniformly distributed hierarchical porous MgO microcubes are first obtained based on DES consisting of MgCl2·6H2O and urea (molar ratio of 1:2) via solvothermal method, followed by calcination. The preparation parameters, including proportion of components in DES and process temperature, affecting the morphology of samples are investigated and discussed systematically. Notably, any solvent or organic additive is not involved during the solvothermal process. The adsorption capacity of the MgO microcubes towards anionic dyes of Congo red (CR), Amaranth (AR) and Indigo carmine (IC) reaches up to 666.7, 43.74 and 54.32 mg g−1 at 25 °C, respectively, not only relate to electrostatic attraction, but also associate with hydrogen bonding. Besides, the hierarchical porous structure of MgO could provide plenty of active sites for pollutant molecules. The adsorption kinetics data are well conformed to pseudo-second-order model and the isotherms are described accurately by the Langmuir model. Particularly, their uniformly distributed micrometer-scale structures make them easier to separate from water, or even natural sedimentation, exhibiting wider application prospect in wastewater treatment.