2D N-Doped Porous Carbon Derived from Polydopamine-Coated Graphitic Carbon Nitride for Efficient Nonradical Activation of Peroxymonosulfate

Abstract

Nitrogen-doped carbon materials attract broad interest as catalysts for peroxymonosulfate (PMS) activation toward an efficient, nonradical advanced oxidation process. However, synthesis of N-rich carbocatalysts is challenging because of the thermal instability of desirable nitrogenous species (pyrrolic, pyridinic, and graphitic N). Furthermore, the relative importance of different nitrogenous configurations (and associated activation mechanisms) are unclear. Herein, we report a “coating-pyrolysis” method to synthesize porous 2D N-rich nanocarbon materials (PCN-x) derived from dopamine and g-C3N4 in different weight proportions. PCN-0.5 calcined at 800 °C had the highest surface area (759 m2/g) and unprecedentedly high N content (18.5 at%), and displayed the highest efficiency for 4-chlorophenol (4-CP) degradation via PMS activation. A positive correlation was observed between 4-CP oxidation rates and the total pyridinic and pyrrolic N content. These N dopants serve as Lewis basic sites to facilitate 4-CP adsorption on the PCN surface and subsequent electron-transfer from 4-CP to PMS, mediated by surface-bound complexes (PMS–PCN-0.5). The main degradation products were chlorinated oligomers (mostly dimeric biphenolic compounds), which adsorbed to and deteriorated the carbocatalyst. Overall, this study offers new insights for rational design of nitrogen-enriched carbocatalysts, and advances mechanistic understanding of the critical role of N species during nonradical PMS activation.

Atomically Dispersed Cobalt Sites on Graphene as Efficient Periodate Activators for Selective Organic Pollutant Degradation

“…The current at both activatorcovered electrodes showed conspicuous drops after injecting the IO 4 − species, which were attributed to interactions between the activators and IO 4 − (i.e., electron-transfer processes), indicating the formation of activator−periodate* complexes. 38 Both activator-modified GCEs subsequently exhibited significant current jumps after 4-CP was added. The observed current increases were attributed to the electron-transportation processes from the electron donor (i.e., the injected 4-CP) to the acceptor (i.e., activator−periodate* complexes).…”

“…Nevertheless, the role of N should not be ignored since N-doping promoted the water dispersity of rGO (Supporting Information, Figure S7) and the subsequent adsorption of electrophilic contaminants (e.g., 4-CP). 38 The effect of the solution's initial pH (pH 0 ) on the efficiency of 4-CP removal in the N-rGO-CoSA/IO 4 − system was investigated by setting the pH 0 parameter at 3.2, 5.1, 7.0, and 8.9. Higher pH conditions were not studied to avoid the alkali-mediated activation of IO 4 − .…”

Rapid pollutant degradation by peroxymonosulfate via an unusual mediated-electron transfer pathway under spatial-confinement

“…The case here is contrary to the known mediated electron transfer process in carbon and noble metal catalyzed reactions wherein the addition of the pollutant accelerates PMS decomposition. 10,58,[60][61][62] The sharp contrast herein indicates that the spatial-connement of Co nanocrystals may alters the electron transfer process from pollutants to PMS.…”

Insights into the relationship of reactive oxygen species and anions in persulfate-based advanced oxidation processes for saline organic wastewater treatment

“…1 O 2 -Dominated oxidation processes were frequently reported, and metal oxides and carbon materials including porous carbon, graphenes, and carbon nanotubes were the catalysts. 74,154,155 As mentioned above, the degradation processes are largely dependent on the properties of ROS. Zhu and co-authors reported the 1 O 2 -dominated degradation process in the PDS/β-MnO 2 catalytic system that showed excellent degradation performance at pH of 5.…”