Peroxymonosulfate (PMS)-based advanced oxidation processes (PMS-AOPs) as an efficient strategy for organic degradation are highly dependent on catalyst design and structured active sites. However, the identification of the active sites and their relationship with reaction mechanisms for organic degradation are not fully understood for a composite catalyst due to the complex structure. Herein, we developed a family of Co encapsulated in N-doped carbons (Co-PCN) with tailored types and contents of active sites via manipulated pyrolysis for PMS activation and ciprofloxacin (CIP) degradation, focusing on the correlation of active sites to generated reactive species and degradation routes of organics. The structure-function relationships between the different active sites in Co-PCN catalysts and reactive oxygen species (ROS), as well as bond breaking position of CIP, were revealed through regression analysis and density functional theory calculation. Co-Nx, O-C═O, C═O, graphitic N, and defects in Co-PCN stimulate the generation of 1O2 for oxidizing the C-C bond in the piperazine ring of CIP into C═O. The substitution of F by OH and hydroxylation of the piperazine ring might be induced by SO4•- and •OH, whose formation was affected by C-O, Co(0), Co-Nx, graphitic N, and defects. The findings provided new insights into reaction mechanisms in PMS-AOP systems and rational design of catalysts for ROS-oriented degradation of pollutants.

Correlation of Active Sites to Generated Reactive Species and Degradation Routes of Organics in Peroxymonosulfate Activation by Co-Loaded Carbon.

Nitrogen was usually doped into carbon matrix to boost its catalytic activity owing to its electronic adjusting activity toward the topological carbon structure. Herein, an overlooked role of nitrogen dopant was unraveled. The nitrogen dopant was firstly incorporated into the carbon matrix and then partially evaporated, leaving the newly generated topological intrinsic defects under high temperature. It was confirmed that peroxymonosulfate (PMS) could be activated by topological defects-rich carbon catalysts. Surface-activated PMS complex was found to be the dominant reactive oxidation species for organic degradation through electron-transfer mechanism. The distinct current density attenuation revealed that N-rich carbon catalysts possessed more effective stoichiometric reaction between the surface-activated PMS and adsorbed organic than topological defects-rich carbon. Findings from this work confirmed the roles of topological defects and extrinsic defects in PMS activation and provided new insight into the synthesis of defects-rich carbon catalysts.

Overlooked role of nitrogen dopant in carbon catalysts for peroxymonosulfate activation: Intrinsic defects or extrinsic defects?

Designing Fe-carbon catalyst with multiple active sites for persulfate (PS) activation to water purification is challenging. Herein, nitrogen-doped biochar (NBC) loaded with ferrous sulfide (FeS) was synthesized via two-step ball milling. In FeS@NBC BM /PS system, both electron transfer process and reactive oxygen species (ROSs) including SO 4 ⋅ − , O ⋅ H , O 2 • − and 1 O 2 contributed to phenol degradation. Surface-bound S(II) not only interacted with PS for generating SO 4 • − , but also accelerated Fe(III)/Fe(II) circulation by reducing Fe(III). NBC was favorable for phenol adsorption and exposure of oxygen-containing groups, graphitic and pyridinic N active sites, which mediated electron transfer or ROSs formation. Owing to multiple active sites, this system fast achieved almost complete phenol degradation with excellent adaptability to wide pH range of 3–9, high anti-interference capacity to coexisting substances, and was efficient to various water matrices. Furthermore, phenol degradation pathways were elucidated by DFT calculations with intermediate products showing lower toxicity, demonstrating great potentials of proposed system. • Ball-milled N-doped biochar-supported FeS is synthesized for persulfate activation. • FeS@NBC BM shows 27.7 and 9.88-fold catalytic activity compared to NBC BM and FeS@BC. • Surface-bound S(II) participates in SO 4 • − formation and promotes Fe(III)/Fe(II) cycle. • Graphitic/pyridinic N mediate electron transfer or nucleophilic addition of PS. • Both radical and non-radical pathways are involved in phenol degradation process. 

Ball milling-assisted preparation of N-doped biochar loaded with ferrous sulfide as persulfate activator for phenol degradation: Multiple active sites-triggered radical/non-radical mechanism

Rational design to manganese and oxygen co-doped polymeric carbon nitride for efficient nonradical activation of peroxymonosulfate and the mechanism insight

CuBi2O4/BiOBr composites promoted PMS activation for the degradation of tetracycline: S-scheme mechanism boosted Cu2+/Cu+ cycle

N-doped carbonaceous materials are promising efficient catalysts for peroxymonosulfate (PMS) activation In this study, the high-efficient N-doped carbon materials were prepared by direct carbonization of polyaniline (PANI) at 700 °C–1000 °C It was optimized that the CPANI-9 (carbonized polyaniline prepared at 900 °C) exhibited excellent catalytic performance to activate PMS for phenol degradation, which was efficient over a wide pH range (pH 35∼9) In the CPANI-9/PMS system, the PMS adsorption/activation was identified as the key step determining the reaction rate The quenching experiments and electron paramagnetic resonance demonstrated that the non-radical pathway was dominant in phenol degradation and singlet oxygen (1O2) was the main active specie Graphitic N, pyridinic N, defects and ketonic groups (C O) were identified as catalytic sites Interestingly, only the presence of PO43− greatly decreased the phenol degradation rate and PMS decomposition The CPANI-9/PMS system could also degrade effectively various organic pollutants, indicating that it had potential practical application

Fei Huang

Papers

Carbonized polyaniline activated peroxymonosulfate (PMS) for phenol degradation: Role of PMS adsorption and singlet oxygen generation