Synthesis of hollow mesoporous manganese dioxide nanoadsorbents with strong negative charge and their ultra-efficient adsorption for cationic dyes

The efficient removal of organic dyes has important practical significance for environmental protection and human health. Chemical modification and composite materials are the main design strategies for high-performance nanoadsorbents. In this work, taking unmodified hollow mesoporous manganese dioxide (H-MnO2) as an example, its adsorption performance for organic dyes was explored through the morphological design of common adsorbents. Unmodified H-MnO2 with strong negative charge which has good stability under acidic conditions was directly used as nanoadsorbent for the removal of cationic dyes in aqueous solutions. The adsorption capacity of H-MnO2 for crystal violet (CV) reached 3707.3 mg g−1, and such a high adsorption capacity has not been reported. Its adsorption capacity for methylene blue (MB) was 1274.9 mg g−1, which is also at the current high level. In addition, the removal rate of low concentration CV and MB by H-MnO2 can reach 95% (CV with the concentration of 450 mg L-1, MB with the concentration of 200 mg L-1). Through the structural design of common manganese dioxide adsorption material, its dye adsorption performance has been greatly improved. This will provide new insights for the subsequent design and preparation of nanoadsorbents.