Persulfate Activation on Crystallographic Manganese Oxides: Mechanism of Singlet Oxygen Evolution for Nonradical Selective Degradation of Aqueous Contaminants

Abstract

Minerals and transitional metal oxides of earth-abundant elements are desirable catalysts for in situ chemical oxidation in environmental remediation. However, catalytic activation of peroxydisulfate (PDS) by manganese oxides was barely investigated. In this study, one-dimension manganese dioxides (α-and β-MnO2) were discovered as effective PDS activators among the diverse manganese oxides for selective degradation of organic contaminants. Compared with other chemical states and crystallographic structures of manganese oxide, β-MnO2 nanorods exhibited the highest phenol degradation rate (0.044 min-1 , 180 min) by activating PDS. A comprehensive study was conducted utilizing electron paramagnetic resonance, chemical probes, radical scavengers, and different solvents to identity the reactive oxygen species (ROS). Singlet oxygen (1 O2) was unveiled to be the primary ROS, which was generated by direct oxidation or recombination of superoxide ions and radicals from a metastable manganese intermediate at neutral pH. The study dedicates to the first mechanistic study into PDS activation over manganese oxides and provides a novel catalytic system for selective removal of organic contaminants in wastewater.

Tuning of Persulfate Activation from a Free Radical to a Nonradical Pathway through the Incorporation of Non-Redox Magnesium Oxide

“…This conclusion was further supported by the nonlinear relationship between the degradation rate constants k and F factor calculated from Eq. 10, 26 ( Figure S47), which also suggested the that the decrease of 4-CP degradation at high pH was resulted from the surface electrostatic repulsion.…”

“…The first order degradation rate constant of FFA, calculated at 0.1 mM was 0.3085 min -1 , which was far higher than that of 4-CP (0.16 min -1 ). Moreover, the calculated amount of 1 O 2 from the degradation of FFA, using the equation of [ 1 O 2 ]= k obs /FFA, was 1.848 × 10 −4 M (at 10.0 mM FFA) ( Figure S20), which was much higher than MnO 2 /PDS system (1.65 × 10 −11 M at 0.3 mM FFA) 26 and typical 1 O 2 -mediated RB light irradiated system (0.05 × 10 −11 M at 0.27 mM FFA). 35 To further confirmed the presence of 1 O 2 as dominant reactive species, the degradation of 4-CP was conducted in D 2 O.…”

“…24,[59][60] Therefore, the influence of inorganic anions on the efficiency loss of the CuOMgO/Fe 3 O 4 +PMS system was also investigated. Figure 3D depicts that the Cl − , NO 3 − , SO 26 Additionally, humic acid (HA, a typical NOM), which is excessively found in wastewater and is considered to be another free radical scavenger. 7 The analysis showed that HA decreased the degradation of 4-CP in the initial 20 minutes.…”

Manganese oxide integrated catalytic ceramic membrane for degradation of organic pollutants using sulfate radicals

“…Zhu et al studied the mechanism of β-MnO2/PS system and found that the sulfate and hydroxyl radicals were not produced. The singlet oxygen was generated and accounted for the phenol oxidation (Zhu et al 2019). Zhou et al analysed the radical generation in α-MnO2/PMS and δ-MnO2/PMS systems.…”

Synthesis of Hollow Flower-Like Fe3O4/MnO2/Mn3O4 Magnetically Separable Microspheres with Valence Heterostructure for Dye Degradation

“…Manganese dioxide (MnO 2 ) has already been used as catalyst due to its abundant sources, low cost, good redox, and environmental friendliness [15][16][17][18][19][20][21][22]. The degradation of organic pollutants by active metal oxides strongly depends on the specific surface area of the catalyst.…”