Selective Degradation of Organic Pollutants Using an Efficient Metal-Free Catalyst Derived from Carbonized Polypyrrole via Peroxymonosulfate Activation

Abstract

Metal-free carbonaceous materials, including nitrogen-doped graphene and carbon nanotubes, are emerging as alternative catalysts for peroxymonosulfate (PMS) activation to avoid drawbacks of conventional transition metal-containing catalysts, such as the leaching of toxic metal ions. However, these novel carbocatalysts face relatively high cost and complex syntheses, and their activation mechanisms have not been well-understood. Herein, we developed a novel nitrogen-doped carbonaceous nanosphere catalyst by carbonization of polypyrrole, which was prepared through a scalable chemical oxidative polymerization. The defective degree of carbon substrate and amount of nitrogen dopants (i.e., graphitic nitrogen) were modulated by the calcination temperature. The product carbonized at 800 °C (CPPy-F-8) exhibited the best catalytic performance for PMS activation, with 97% phenol degradation efficiency in 120 min. The catalytic system was efficient over a wide pH range (2-9), and the reaction of phenol degradation had a relatively low activation energy (18.4 ± 2.7 kJ mol). The nitrogen-doped carbocatalyst activated PMS through a nonradical pathway. A two-step catalytic mechanism was extrapolated: the catalyst transfers electrons to PMS through active nitrogen species and becomes a metastable state of the catalyst (State I); next, organic substrates are oxidized and degraded by serving as electron donors to reduce State I. The catalytic process was selective toward degradation of various aromatic compounds with different substituents, probably depending on the oxidation state of State I and the ionization potential (IP) of the organics; that is, only those organics with an IP value lower than ca. 9.0 eV can be oxidized in the CPPy-F-8/PMS system.

Adsorption Characteristics and Mechanism of Bisphenol A by Magnetic Biochar

“…The two main peaks at 710.7 eV and 724.3 eV correspond to Fe 2p 3/2 and Fe 2p 1/2 , respectively. The satellite peak at 719.3 eV is the characteristic peak of γ-Fe 2 O 3 [44]. Moreover, the surface of MBC is slightly red.…”

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

“…[26][27][28] The ionization potential (IP) of the organic compounds has been utilized as an indicator to estimate the redox capacity of an oxidative system. 29 In the electron mediation mechanism, an organic compound with an IP beyond 9.0 eV (the threshold) cannot be oxidized in N-graphene/PMS system due to the relatively mild redox potential of the surface confined metastable nonradical ROS. In this work, BA and NB with IP values above the threshold were hardly decomposed (Figure 2b), whereas the organics (PN, BPA, and HBA with lower IP values were vulnerable to be degraded with high 9 reaction rates (Table S1, Figures 2b and S7).…”

N-doped graphene aerogels as efficient heterogeneous catalytic activators for peroxymonosulfate to remove 2-sec-butyl-4,6-dinitrphenol (DNBP) in aqueous solution

“…A low level of GO in NGAs was not benefit for the formation of the interconnected hierarchical pore structure. The graphitic N content of NGAs has important influence on PMS activation because graphitic N has high charge density and asymmetric spin density, which could induce the peroxy-bond breakage to generate reactive radicals [47]. Based on the area integral of the peak corresponding to graphitic N, the relative atomic percentage of graphitic N in NGAs carbocatalysts was determined by XPS.…”