High-efficient removal of organic dyes from model wastewater using Mg(OH)2-MnO2 nanocomposite: synergistic effects of adsorption, precipitation, and photodegradation

Abstract Hierarchical Mg(OH)2-MnO2 nanocomposite (MMNC) was successfully synthesized by a facile water-bath method, and further applied to Congo red (CR) and methyl orange (MO) removal. Batch experiments revealed that the maximum removal capacity of the nanocomposite to CR and MO reached 17100 and 7300 mg g-1, respectively. The CR removal mechanism was systemically investigated by FESEM, XRD, EDX and XPS techniques. The results showed that the CR removal proceed mainly through chemisorption on MMNC at low concentration. However, at high concentration, Mg2+ will release from the nanocomposite and react with CR to form a precipitate (Mg-CR), leading to a huge removal capacity. Moreover, MMNC also exhibits excellent performance for photodegradation of CR under visible light irradiation. The active species trapping experiments revealed holes in MMNC and superoxide radical anions as the major active species responsible for photodegradation of CR. The synergistic effects of adsorption, precipitation, and photodegradation enable higher CR removal efficiency, making Mg(OH)2-MnO2 nanocomposite an ideal material for dyes removal from water samples in both low concentration and scabrous high concentration dye-containing wastewater scenarios.