Multiple cobalt active sites evenly embedded in mesoporous carbon nanospheres derived from a polymer-metal-organic framework: efficient removal and photodegradation of malachite green.

Abstract

A series of robust photocatalysts of mesoporous carbon nanospheres embedded with multiple cobalt active sites (Co/Co x O y @mC) have been constructed for efficient removal and photodegradation of malachite green (MG). Here, a cobalt-based polymeric-metal-organic framework (polyMOF(Co)) was constructed by using a polyether ligand containing 1,4-benzenedicarboxylic acid units. Afterward, polyMOF(Co) was calcined into a series of Co/Co x O y @mC hybrids at diverse high temperatures (400, 600, and 800 °C) under a N2 atmosphere. Therefore, Co coordination centers were transformed into various active sites such as Co, CoO, and Co3O4, which were embedded within the mesoporous carbon network derived from the polymeric skeleton. Considering the even distribution of Co-related active species and high porosity inherited from polyMOF(Co), the constructed Co/Co x O y @mC hybrid obtained at 600 °C illustrated higher removal ability (79%) with a maximum adsorption capacity of 314 mg g-1 within 120 min and better photodegradation performance (degradation rate of 95%) toward MG than those of the other photocatalysts obtained at 400 and 800 °C. Moreover, the possible photocatalytic reaction mechanisms, including the transfer behavior of charge carriers, generation of reactive species, and intermediate degradation of products, were provided. The present work showed an alternative strategy for the feasible and efficient preparation of photocatalysts based on MOFs.