Critical Impact of Nitrogen Vacancies in Nonradical Carbocatalysis on Nitrogen-Doped Graphitic Biochar

Abstract

Nitrogen-doped graphitic biochar (NBC) has boosted the development of nonradical peroxymonosulfate (PMS) activation in environmental remediation. However, the specific role of nitrogen species played in NBC-based nonradical carbocatalysis remains vaguely interpreted. To pinpoint the critical nitrogen speciation, a sophisticated thermo-mechanochemical manipulation was exploited to prepare a series of NBCs with similar dimensional structures and oxygen levels but different nitrogen species (i.e., dopants and vacancies). Different from conventional perspectives, nonradical NBC-based carbocatalysis was found to be preferably determined by the nitrogen vacancies more than their parent nitrogen dopants. Raman depth analysis evidenced that a complete transformation of nitrogen dopants into nitrogen vacancies could be achieved at 800 °C, where an excellent nonradical abatement of 4-chlorophenol (4-CH, 90.9% removal) was found for the NBC800 with a low PMS consumption (1.24 mM). According to PMS adsorption experiments, nitrogen vacancies exhibited the highest affinity toward the PMS molecules compared to nitrogen dopants, which accounted for the superior carbocatalysis. Electron paramagnetic resonance and Raman spectroscopic analyses indicated that the original PMS molecules were bound to positively charged nitrogen vacancies, and a robust metastable complex (*HSO5 –) evolved subsequently via hydrogen abstraction by adjacent persistent free radicals. In situ Raman techniques could be adopted to estimate the level of nitrogen vacancies associated with the polarization of electron distribution. The flexible feature and practical prospects of nitrogen vacancy-based carbocatalysis were also observed in the remediation of simulated phenolic industrial wastewater. Overall, this study unravels the dilemma in the current NBC-based nonradical carbocatalysis and advances our understanding of nitrogen doping technology for next-generation biochar design.

Technologies and perspectives for achieving carbon neutrality

“…Owing to its controllable and tailorable electrical conductivity and inherent functional groups, biochar could be easily designed to have photonic, electronic, acoustic, and bio/redox interactions with other reactive substances, making it a viable alternative to replace unsustainable solid C-based catalysts. 250 , 251 , 252 , 253 , 254 In addition, the possible use of biochar in the manufacturing of value-added construction materials has been explored. 255 , 256 For instance, in a study, Das et al.…”

Application of Biochar as Functional Material for Remediation of Organic Pollutants in Water: An Overview

“…On the other hand, PS can also be activated through a nonradical pathway, in which free moving radicals are not involved in organics mineralization. In the biochar/PS system, a nonradical pathway can proceed through surface-bound radicals [40,82], surface-confined complexes [83], electron mediation mechanism, and 1 O 2 generation. Similar to H 2 O 2 activation, surface-bound radicals such as SO 4…”

Sulfur vacancies on MoS2 enhanced the activation of peroxymonosulfate through the co-existence of radical and non-radical pathways to degrade organic pollutants in wastewater

“…The activation of PMS by heterogeneous catalysts containing defect sites has attracted much attention in the past few years. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] Among them, the oxygen vacancies are the most studied, 16,[18][19][20][21][22][23][24][25] which oen appear in various catalysts containing oxygen, including pure metal oxides such as Co 3 O 4 16 and ZnO, 19 perovskite 20 and composited compounds. [21][22][23] For example, Zhao et al 16 reported the role of oxygen vacancies in different Co 3 O 4 crystal planes for the activation of PMS by the formation of 1 O 2 ; Gao et al 20 demonstrated the correlation between oxygen-decient sites in the perovskite and the formation of 1 O 2 in activated PMS.…”

“…Nitrogen defect sites are the other type of vacancy used for activating PMS. 24,25 It oen appeared the cases with nitrogen-doped carbon materials. For instance, Wan et al 24 reported the degradation of 4-chlorophenol by N-doped biological carbon-activated PMS.…”