Structure-Function Correlations of Carbonaceous Materials for Persulfate-Based Advanced Oxidation

Fe-N co-doped biochar derived from biomass waste triggers peracetic acid activation for efficient water decontamination

In this study, the porous carbon material (FeN-BC) with ultra-high catalytic activity was obtained from waste biomass through Fe-N co-doping. The prominent degradation rate (> 96.8%) of naproxen (NAP) was achieved over a wide pH range (pH 3.0-9.0) in FeN-BC/PAA system. Unlike previously reported iron-based peracetic acid (PAA) systems with •OH or RO• as the dominated reactive species, the degradation of contaminants was attributed to singlet oxygen (1O2) produced by organic radicals (RO•) decomposition, which was proved to be thermodynamically feasible and favorable by theoretical calculations. Combining the theoretical calculations, characteristic and experimental analysis, the synergistic effects of Fe and N were proposed and summarized as follows: i) promoted the formation of extensive defects and Fe0 species that facilitated electron transfer between FeN-BC and PAA and continuous Fe(II) generation; ii) modified the specific surface area (SSA) and the isoelectric point of FeN-BC in favor of PAA adsorption on the catalyst surface. This study provides a strategy for waste biomass reuse to construct a heterogeneous catalyst/PAA system for efficient water purification and reveals the synergistic effects of typical metal-heteroatom for PAA activation.

Degradation and mechanism of PFOA by peroxymonosulfate activated by nitrogen-doped carbon foam-anchored nZVI in aqueous solutions

Perfluorooctanoic acid (PFOA) is an emerging pollutant that is non-biodegradable and presents severe environmental and human health risks. In this study, we present an effective and mild approach for PFOA degradation that involves the use of nitrogen-doped carbon foam anchored with nanoscale zero-valent iron (nZVI@NCF) to activate low concentration peroxymonosulfate (PMS) for the treatment. The nZVI@NCF/PMS system efficiently removed 84.4% of PFOA (2.4 μM). The active sites of nZVI@NCF including Fe0 (110) and graphitic nitrogen played crucial roles in the degradation. Electrochemical analyses and density functional theory calculations revealed that nZVI@NCF acted as an electronic donor, transferring electrons to both PMS and PFOA during the reaction. By further analyzing the electron paramagnetic resonance and byproducts, it was determined that electron transfer and singlet oxygen were responsible for PFOA degradation. Three degradation pathways involving decarboxylation and surface reduction of PFOA in the nZVI@NCF/PMS system were determined. Finding from this study indicate that nZVI@NCF/PMS systems are effective in degrading PFOA and thus present a promising persulfate-advanced oxidation process technology for PFAS treatment.

Unveiling the mechanisms of peracetic acid activation by iron-rich sludge biochar for sulfamethoxazole degradation with wide adaptability

Advanced oxidation processes (AOPs) based on peracetic acid (PAA) has been extensively concerned for the degradation of organic pollutants. In this study, metallic iron-modified sludge biochar (Fe-SBC) was employed to activate PAA for the removal of sulfamethoxazole (SMX). The characterization results indicated that FeO and Fe2O3 were successfully loaded on the surface of the sludge biochar (SBC). Fe-SBC/PAA system achieved 92% SMX removal after 30 min. The pseudo-first-order kinetic reaction constant of the Fe-SBC/PAA system was 7.34 × 10-2 min-1, which was 2.4 times higher than the SBC/PAA system. The degradation of SMX was enhanced with increasing the Fe-SBC dosage and PAA concentration. Apart from Cl-, NO3- and SO42- had a negligible influence on the degradation of SMX. Quenching experiments and electron paramagnetic resonance (EPR) techniques identified the existence of reactive species, of which CH3C(O)OO•, 1O2, and O2•- were dominant reactive species in Fe-SBC/PAA system. The effect of different water matrices on the removal of SMX was investigated. The removal of SMX in tap water and lake water were 79% and 69%, respectively. Four possible pathways for the decay of SMX were presented according to the identification of oxidation products. In addition, following the ecological structure-activity relationship model (ECOSAR) procedure and the germination experiments with lettuce seeds to predict the toxicity of the intermediates. The acute and chronic ecotoxicity of SMX solution was dramatically diminished by processing with Fe-SBC/PAA system. In general, this study offered a prospective strategy for the degradation of organic pollutants.

Polar electric field-modulated peroxymonosulfate selective activation for removal of organic contaminants via non-radical electron transfer process

Nonradical electron transfer process (ETP) in peroxomonosulfate (PMS) based advanced oxidation processes (AOPs) is regarded promising for selective degradation of organic contaminants in water, however, the subjective modulation strategy and the definitive mechanistic elucidation of ETP are still lacking. Herein, we proposed a heretofore unreported yet efficient ETP indution approach by construction of polar electrical field on biochar via nonmetallic elements co-doping. Physicochemical characterizations and density functional theory (DFT) calculations verified the electronegativity difference among boron, nitrogen, and sulfur elements bestowed robust local electric fields on biochar surface (BC-BNS), which effectively enhanced the adsorption complexation and charge transfer between biochar and PMS. Compared to the other single-doped or co-doped biochar, BC-BNS exhibited superior catalytic performance of PMS activation for degradation of atrazine (ATZ) (kobs=0.036 min-1), as well as various kinds of electron-rich organics. The remarkable catalytic degradation capacity was further verified in various aqueous matrices and background factors, representing the excellent selectivity. Analysis of contribution from reactive oxygen species and electrochemical testing together substantiated the role of polar electric fields in facilitating the modulation from singlet oxygen (1O2) to ETP as a prevailing mechanism. DFT calculations and apparent interactions revealed the dissociation of S-O bond was thermodynamically favored within this potent localized electric field, which further induced the cleavage of OO bond and ultimately promoted the dual electron transfer between ATZ and PMS. The superiority of BC-BNS/PMS system was further validated with the low ecotoxicity caused by enhanced dechlorination, the low energy consumption, and the long-term effectiveness. The novel modulation principle and atomic-level mechanism exploration gave suggestions for advancing ETP-dominated AOP to remove recalcitrant contaminants during water treatment and restoration.

Assisted wet deposition targeted synthesis of Co-N coordination single-atom catalysts for efficient Fenton-like catalytic degradation of micropollutants

Assisted wet deposition methods to localize the active phase metal on the carrier surface and prevent atomic aggregation during conventional heat treatment are strongly preferred. Herein, single-atom cobalt catalysts (SA-Co-PCN) with different metal-central content were target-prepared using a combination of impregnation and secondary annealing on polymerized carbon nitride (PCN) through reticular confinement. Fitting the coordination configuration of the Co-N pathway within the first coordination shell according to quantitative EXAFS indicated that the ligancy of Co-N was 4. The removal efficiency of representative micropollutants in the SA-Co-PCN/PMS system achieved 100% within 15 min. The outstanding degradation properties of micropollutants were ascribed to the SA-Co-PCN boosts PMS to a 1O2-dominated system. Moreover, the effects of substituents on the degradation behavior and ecotoxicology of sulfonamides (SAs) in PMS-activated systems were investigated in depth. The combination of DFT theoretical calculations and LC-MS further confirmed that the similar electron-rich sites on the SAs molecules allowed for commonality in the degradation pathway. Both S-N bond and C-S bond fragments became the initial attack and cleavage sites in the series of SAs. Ecotoxicity predictions indicated that most intermediates of SAs exhibited lower acute and chronic toxicity, especially acute toxicity, than the parent compounds. ENVIRONMENTAL IMPLICATION: Assisted wet deposition to localize the active phase metal on the carrier surface allows easy target formation of single-atom cobalt catalysts (SA-Co-PCN), which could boost PMS to a 1O2-dominated system for efficient oxidation of typical micropollutants. The degradation behavior and ecotoxicology of sulfonamides in the SA-Co-PCN/PMS system were investigated in depth, revealing that most intermediates of sulfonamides exhibited lower acute and chronic toxicity, especially acute toxicity, than the parent compounds. This work provides a strategy for the development of facilely prepared single-atom catalysts and contributes to the development and application potential of PMS advanced oxidation technology for water pollution control.

Rational regulation of peroxymonosulfate activation over porous Co3O4 with carbon coating to boost utilization efficiency of peroxymonosulfate and achieve rapid removal of pollutants

It is of great significance to regulate rationally the activation mechanism of persulfate for promoting the development of sulfate radical-based advanced oxidation processes in wastewater treatment. Herein, carbon coated porous Co₃O₄ with hollow structure was synthesized. Notably, the formation of porous hollow structure improved specific surface area of Co₃O₄ and offered more redox couples of Co²⁺/Co³⁺, thereby reducing electron transfer resistance. Thus, the generation of reactive oxygen species and the role of high-valent transition metal complexes (namely Co₃O₄Co⁴⁺) were improved. The formation of carbon layer on the Co₃O₄ surface can avoid the release of Co ion during reaction process. Benefiting from the role of carbon layer in electron transport, catalyst-mediated the direct electron transfer from pollutant to PMS was boosted. Radical and nonradical pathways worked in coordination each other and realized the rapid removal of various organic pollutants in the presence of a little PMS. In short, current work revealed that modulating rationally the microstructure of catalyst was an efficient strategy for achieving controllable regulation of PMS activation process. More significantly, whether the direct electron transfer process can occur or not depended on both catalyst structure and electronic density of pollutants.

Dual S-scheme ZnO–g-C3N4–CuO heterosystem: a potential photocatalyst for H2 evolution and wastewater treatment

A ZnO–g-C3N4–CuO catalyst prepared by an ecofriendly solution combustion process is used for H2 evolution. The mechanism of H2 evolution over ZnO–g-C3N4–CuO is described under visible light illumination.

Development of Z-scheme bimetallic tungstate-supported nitrogen deficient g-C3N4 heterojunction for the treatment of refractory pharmaceutical pollutants

The binary BMT/ND-GCN-based heterostructure photocatalyst for pharmaceutical industry wastewater treatment.

Efficient Activation of Peroxymonosulfate by V-Doped Graphitic Carbon Nitride for Organic Contamination Remediation

Advanced oxidation processes (AOPs) based on peroxymonosulfate (PMS) activation have been developed as an ideal pathway for completely eradication of recalcitrant organic pollutants from water environment. Herein, the V-doped graphitic carbon nitride (g-C₃N₄) is rationally fabricated by one-step thermal polymerization method to activate PMS for contamination decontamination. The results demonstrate the V atoms are successfully integrated into the framework of g-C₃N₄, which can effectively improve light absorption intensity and enhance charge separation. The V-doped g-C₃N₄ displays superior catalytic performance for PMS activation. Moreover, the doping content has a great influence on the activation performances. The radical quenching experiments confirm •O₂^-, SO₄^•-, and h⁺ are the significant species in the catalytic reaction. This work would provide a feasible strategy to exploit efficient g-C₃N₄-based material for PMS activation.

Efficient activation of peracetic acid by mixed sludge derived biochar: Critical role of persistent free radicals

Peracetic acid (PAA)-based advanced oxidation processes (AOPs) were increasingly identified as the alternative scheme in wastewater treatment. Cost-effective and easily available catalyst for activation of PAA was in urgent demand for promoting engineering application process. In this study, a new type of biochar catalyst derived from pyrolysis of mixture of primary sludge (PSD) and secondary sludge (SSD) was prepared and showed effective PAA activation ability. The degradation of p-chlorophenol (4-CP) improved with PAA activation by mixed sludge derived biochar (PS-SDBC) than secondary sludge derived biochar (S-SDBC) and primary sludge derived biochar (P-SDBC), and the highest removal efficiency achieved by PS-SDBC with the PSD/SSD ratio of 5/5 (k_obs=0.057 1/(M·min), pH 9). Correlation analysis firstly indicated that persistent free radicals (PFRs) rather than chemical composition and material structure dominated PAA activation and organic radicals (RO•) was proved to be the major reactive species through electron paramagnetic resonance (EPR) detection. The mixture of PSD and SSD caused the synergy of inorganic metals and organic matters through pyrolysis processes, resulting in larger specific surface area (SSA) (110.71 m²/g), more abundant electron-donating groups (e.g., C = O, -OH) and massive defects (I_D/I_G = 1.519) of PS-SDBC than P-SDBC and S-SDBC, which eventually promoted PFRs formation. A fascinating phenomenon was observed in PS-SDBC/PAA system that the active sites of PFRs could be regenerated by RO• attacking onto PS-SDBC, which contributed to the wide pH applicability and continuous stability of PS-SDBC/PAA system in practical wastewater treatment. This study not only significantly deepened the understanding of the reaction mechanism between PAA and biochar, but also provided a potential PAA-based AOPs for micropollutants removal in wastewater.

Discovery of Electronic Structure and Interfacial Interaction Features in Catalytic Activity

The selective transformation of inert bonds (C-H, C-O, C-C, C-F, etc.) via various catalysts is one of the most challenging areas, with applications in organic synthesis, materials science, and biological and pharmaceutical chemistry. The catalytic performance of homogeneous and heterogeneous catalysts can be rationally controlled in two ways: (i) electronic structure modulation of the active site, such as the metal center, ligands, and coordination modes, to improve the catalytic activity and stability and (ii) tuning intermolecular or interfacial interactions to promoting the reaction kinetics by accelerating the transmission of electrons between the catalyst and solvents or support. The rational design of catalysts based on adjustable features, such as metal (monometallic or bimetallic) active sites, crystal phase, ligands, solvents, and supports for inert bond activation under mild conditions remains a challenge. This Perspective summarizes the features of electronic structures, interfacial interactions, and their effects on molecular catalysis, metal-organic frameworks (MOFs), and natural mineral catalysis. The discovery of efficient catalysts could be promoted using machine-learning methods with high-performance descriptors. More attention should be paid to high-throughput quantum-chemical computations and experiments, automatic searches of chemical reaction pathways, and efficient machine-learning or deep-learning methods to accelerate catalyst design and synthesis in the future.

Exfoliation-induced O-doped g-C3N4 Nanosheets with improved photoreactivity towards RhB degradation and H2 evolution

Graphitic carbon nitride (g-C3N4) nanosheets exfoliated from bulk-sized counterparts are limited by quantum size effect-induced widened bandgap. In this work, a (NH4)2S2O8 (APS) induced thermal exfoliation approach is introduced to...