Hierarchical mesoporous MoO2 hollow microspheres: Synthesis, mechanism and application in removing Cr (VI) from wastewater

• Hierarchical MoO2 hollow microspheres were prepared through a convenient hydrothermal reductive route.
• MoO2 hollow microspheres have mesoporous shell with pore size of 5–20 nm.
• Center-hollowing evolution process induced by Ostwald ripening was proposed.
• MoO2 hollow microspheres exhibited higher adsorption capacity for Cr (VI) compared to activated carbon.

Hierarchical MoO2 hollow microspheres have been successfully fabricated on a large scale through a convenient hydrothermal reductive process. MoO2 hollow microspheres are composed of subunits (nanospheres or nanoplates), which are actually self-aggregated by hundreds of tiny primary nanoparticles. BET nitrogen adsorption reveals that the MoO2 hollow microspheres have mesoporous shell with pore size of 5–20 nm. Reaction parameters, such as mole ratio of reactant, reaction temperature and time, were discussed in detail. Center-hollowing evolution process induced by Ostwald ripening was proposed to explain the formation mechanism of hierarchical MoO2 hollow microspheres. The adsorption ability of MoO2 hollow microspheres was evaluated by adsorbing Cr (VI) at room temperature. The experimental results indicated that MoO2 absorbent displayed higher adsorption capacity compared to activated carbon, which would be potential application in wastewater treatment.

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