Efficient removal of heavy metal ions from wastewater and fixation of heavy metals in soil by manganese dioxide nanosorbents with tailored hollow mesoporous structure

Heavy metals in wastewater and soil pose serious threats to the ecological environment and human health. Chemical modification and composite design are the main design strategies for high-performance heavy metal adsorbents. However, in this study, a unique way was adopted to improve the adsorption performance of MnO2 by tailoring its hollow mesoporous structure (HMN). Unmodified HMN which has good stability under acidic conditions was directly used for adsorption and fixation of heavy metals in wastewater and soil. The adsorption capacity of HMN has been greatly improved compared with other MnO2 adsorbents, and its adsorption capacities for Pb2+, Cu2+ and Cd2+ reached 897.0, 437.5 and 354.3 mg g−1, respectively. Such high adsorption performance is rarely seen in manganese-based adsorbents. Purification results of laboratory wastewater and industrial wastewater showed that it has good application prospect for actual environmental water samples. The adsorption mechanism mainly includes physical adsorption, electrostatic adsorption, surface complexation (oxygen sites and hydroxyl groups) and ion exchange between Na+ and heavy metal ions. In addition, HMN can effectively passivate heavy metals in contaminated soil and reduce their leaching concentration to improve soil safety. This improvement in the performance of adsorbents by tailoring their structures is instructive and provides insight and approach for the design and preparation of advanced adsorbents.