High-specific-surface-area magnetic porous carbon microspheres (MPCMSs) were fabricated by annealing Fe(2+)-treated porous polystyrene (PS) microspheres, which were prepared using a two-step seed emulsion polymerization process. The resulting porous microspheres were then sulfonated, and Fe(2+) was loaded by ion exchange, followed by annealing at 250 °C for 1 h under an ambient atmosphere to obtain the PS-250 composite. The MPCMS-500 and MPCMS-800 composites were obtained by annealing PS-250 at 500 and 800 °C for 1 h, respectively. The iron oxide in MPCMS-500 mainly existed in the form of Fe3O4, which was concluded by characterization. The MPCMS-500 carbon microspheres were used as catalysts in heterogeneous Fenton reactions to remove methylene blue (MB) from wastewater with the help of H2O2 and NH2OH. The results indicated that this catalytic system has a good performance in terms of removal of MB; it could remove 40 mg L(-1) of MB within 40 min. After the reaction, the catalyst was conveniently separated from the media within several seconds using an external magnetic field, and the catalytic activity was still viable even after 10 removal cycles. The good catalytic performance of the composites could be attributed to synergy between the functions of the porous carbon support and the Fe3O4 nanoparticles embedded in the carrier. This work indicates that porous carbon spheres provide good support for the development of a highly efficient heterogeneous Fenton catalyst useful for environmental pollution cleanup.

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Electrochemical in situ hydrogen peroxide (H2O2) generation from a two-electron water oxidation reaction (2e-WOR) is a challenge, not only on catalyst selection but also on electrode making. Herein, the H2O2 electrocatalyst CaSnO3 nanoparticles were prepared by low-cost glucose as an agent and characterized by X-ray diffraction (XRD), thermogravimetric and differential scanning calorimetry (TG-DSC), Fourier transform infrared spectra (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The active sites for the OH– adsorption on the surface CaSnO3 (121) was identified by density functional theory (DFT) calculation, and the corresponding reaction mechanism of H2O2 formation was proposed. The CaSnO3 nanoparticles can be formed from 650 to 850 °C, and the particle sizes are in the range of 27.2–37.3 nm. The mechanism of catalyst formation is that species of Ca and Sn reacted with oxygen to generate CaO and SnO2 during low-temperature calcination and CaSnO3 generated during high-temperature calcination. The active sites are the coordination-unsaturated Sn ions, which easily adsorb the negative-charge OH– from the solution, forming an OH* intermediate, and two adsorbed OH* can combine to generate a neutral H2O2 molecule. The H2O2 generation rate over CaSnO3 was calcinated at 850 °C is 347.7 μmol·min–1·g–1 at 2.6 V versus Ag/AgCl under dark conditions. The work opens an in situ H2O2 generation route, direct water oxidation, with wide application prospects.

Nitrobenzene (NB) is considered a toxic and potential carcinogen. Continuous contamination has resulted in an urgent need for remediation. Fenton reagent provides an advanced oxidation process that is capable of remediating recalcitrant nitroaromatic compounds, such as NB. However, one drawback of Fenton chemistry is that the reaction requires acidic pH to prevent precipitation of iron. Our studies have investigated Fenton conversion of NB at near-neutral pH with several organic additives: β-cyclodextrin (β-CD), hydroxypropyl-β-cyclodextrin (HPCD), carboxymethyl-β-cyclodextrin (CMCD), and polyethylene glycol (molecular weight (MW) = 200, 400, and 600) for developing a process for treating NB-contaminated waters. The main factors influencing NB conversion, such as iron concentration, hydroxyl radicals (·OH) scavengers, and kinds or concentration of organic additives, were examined. Meanwhile, the reactive mechanisms and kinetics were investigated for Fenton conversion of NB. The results show that organic additives for Fenton process should be a good alternative for the advanced treatment of NB at near-neutral pH.