Defect-Induced Nanoporous MgO Derived from Metal–Organic Frameworks for Rapid and Efficient Removal of Dye

Efficient removal of refractory organic dyes from water presents a significant challenge in environmental remediation. Traditional magnesium oxide (MgO) adsorbents are often hindered by low specific surface area, insufficient active sites, and sluggish adsorption kinetics. In this study, we developed a defect-regulated strategy based on metal–organic frameworks (MOFs) to construct a defect-rich nanoporous MgO adsorbent. During the synthesis of the Mg-MOF-74 precursor, PVP served as a soft template, while NH 3 ·H 2 O acted as a regulator, effectively modulating nucleation and crystal growth. This process resulted in a precursor with a reduced particle size and altered crystallization behavior. Subsequent calcination transformed the precursor into a defect-rich nanoporous MgO-N with high specific surface area (150.3 m 2 /g), well-developed mesoporosity of pore sizes (4–8 nm), and abundant oxygen-vacancy-related defects. These structural advantages endow MgO-N with an exceptional adsorption capacity for Congo red (3882.7 mg/g) and rapid adsorption kinetics, surpassing both the control sample and most previously reported adsorbents. The enhanced adsorption performance is attributed to the synergistic effects of electrostatic attraction, coordination interactions, hydrogen bonding, and pore filling. Furthermore, the material demonstrates an excellent cycling stability and structural integrity. This defect strategy offers an effective approach to overcoming the performance limitations of MgO adsorbents and showcases broad application potential in the advanced treatment of organic dye-containing wastewater.