Magnetic biochar supported α-MnO2 nanorod for adsorption enhanced degradation of 4-chlorophenol via activation of peroxydisulfate

Abstract

A novel magnetic catalytic composite (MBM) was developed by compositing α-MnO2 with a magnetic biochar containing Fe3O4. XRD and EDS confirmed the crystalline structure and the chemical composition of MBM, while the one-dimensional α-MnO2 nanorods were observed on MBM by SEM. 4-chlorophenol as a typical toxic chlorinated organic compound was selected as the model pollutant. Even the MBM composite (MnO2 content: 0.2 g/L) needed the same time (120 min) as the pure α-MnO2 nanorods (0.2 g/L) to completely remove the 4-chlorophenol (10 mg/L) with overdosed peroxydisulfate (PDS), MBM indicated faster pollutant removal rate than the pure α-MnO2 nanorods in the first 100 min. It is possible that the adsorption of 4-chlorophenol by biochar might shorten the migration pathway of the generated active species to the pollutants, resulting the boosted removal rate. MBM was stable in the neutral environment which was desirable for the efficient pollutant removal. Both the radical quenching tests and the EPR spectra identified the main active specie generated by activation of PDS through MBM was singlet oxygen possibly generated by recombination of superoxide ions from the metastable manganese intermediates at neutral pH. TOC data of the effluent ensured 63.5% of the pollutant molecules were completely mineralized after the degradation. The applied magnetic field could recover MBM easily for reuse. This work shed lights on the preparation of highly efficient and environmentally friendly catalytic composites for PDS activation in persistent pollutant removal.