Non-radical Process Research Articles

N-doped metal-free biochar activation of peroxymonosulfate for enhancing the degradation of antibiotics sulfadiazine from aquaculture water and its associated bacterial community composition

Synthetic antibiotic sulfadiazine (SDZ) in water streams is an increasing concern for its known adverse effects on ecosystems, therefore effective decontamination strategy is of utmost priority. Herein, nitrogen-doped coconut-shell biochar (NCSBC) was synthesized as a heterogeneous catalyst to activate peroxymonosulfate (PMS) for SDZ degradation in aquaculture water. The dopant precursor consists of 1:1 w/w mixture of urea and coconut-shell. The NCSBC/PMS system achieved a maximum SDZ removal of 94% under optimum operating conditions of SDZ concentration of 0.05 mM, NCSBC dosage of 150 mg/L, and neutral pH. The synergistic effect between functionalized N moieties (combination of pyridinicN, pyrrolicN, and graphiteN) of NCSBC and radical (SO4•−/HO•) and/or nonradical (1O2) processes involving the electron transfer reaction in hybrid NCSBC/PMS system aided in SDZ removal. NCSBC remained highly functioning after five consecutive cycles. Salinity and inorganic ions present in the aquaculture water did not significantly influence SDZ degradation. PCR sequencing analysis showed that Aquimonas, belonging to phylum Proteobacteria, was the most bountiful genus in the NCSBC/PMS treated water. The present study offers an innovative biowaste-to-resource strategy and demonstrates the potential of functional NCSBC in PMS activation toward the removal of SDZ from aquatic environments.

Effects of Lewis acid-base site and oxygen vacancy in MgAl minerals on peroxymonosulfate activation towards sulfamethoxazole degradation via radical and non-radical mechanism

Radicals of SO4•-, OH•, non-radical of 1O2 and even direct oxidation all occurred in peroxymonosulfate (PMS) activation process. Hence, to regulate the above radical or non-radical mechanism is of great significance for the treatment of organic pollutants in practical water. In this work, MgAl-minerals exhibited a satisfied performance in controlling the contribution of radicals (SO4•-, OH•) and non-radical (1O2) towards PMS activation based on results of reactive oxygen species scavenger experiments and electron spin resonance spectra. Compared with MgAl-1(61.8%) and MgAl-2 (61.4%) (Al/Mg = 1, 2), MgAl-3 (Al/Mg = 3) exhibited the highest sulfamethoxazole (SMX) removal efficiency (92.5%). Moreover, the contribution of radical and non-radical to SMX degradation were 56.7% and 30.1%, which was different from that of MgAl-1(7.8% and 39.5%) and MgAl-2 (5.2% and 41.6%). The roles of Lewis acid-base site and oxygen vacancies (OVs) in MgAl-minerals on radical and non-radical processes were detailed investigated. Lewis acid sites and OVs can enrich SMX and PMS at the solid-water interface. Simultaneously, OVs promote electron transfer from SMX to PMS acts as electron media, resulting in more SO4•- and OH• generation. While the basic sites favored the generation of 1O2 via PMS self-decomposition mechanism. Therefore, in PMS activation process over MgAl-minerals, the involved reactive oxygen species can be regulated via controlling the amounts of Lewis acid-base sites and oxygen vacancies. This finding provided new insights into PMS oxidation over non-transition metal-based catalysts and water remediation with complex water characteristics.

Constructing a brand-new advanced oxidation process system composed of MgO2 nanoparticles and MgNCN/MgO nanocomposites for organic pollutant degradation

A novel advanced oxidation process (AOP) system with high adaptability and long-term oxidation ability was firstly constructed for organic pollutant degradation via a non-radical process.

Atomically Fe doped hollow mesoporous carbon spheres for peroxymonosulfate mediated advanced oxidation processes with a dual activation pathway

The introduction of atomically dispersed Fe atoms can modulate the PMS activation pathway; that is, the radical-mediated process of PMS activation accelerated by graphitic N is attenuated, in turn boosting electron-transfer-mediated nonradical processes.

Chrome Shaving-Derived Biochar as Efficient Persulfate Activator: Ti-Induced Charge Distribution Modulation for 1o2 Dominated Nonradical Process

Chrome Shaving-Derived Biochar as Efficient Persulfate Activator: Ti-Induced Charge Distribution Modulation for 1o2 Dominated Nonradical Process

The nitrogen-doped multi-walled carbon nanotubes modified membrane activated peroxymonosulfate for enhanced degradation of organics and membrane fouling mitigation in natural waters treatment

The synthesized catalyst nitrogen-doped multi-walled carbon nanotubes (N-MWCNTs) were introduced into membrane technology for peroxymonosulfate (PMS) activation. The enhanced permeability of the N-MWCNTs-modified membrane might be attributed to the increase in hydrophilicity and membrane porosity. The catalytic degradation and membrane filtration performance for the N-MWCNTs-modified membrane/PMS system in treating different types of natural waters were evaluated. The removal of phenol by the N-MWCNTs-modified membrane was 83.67% in 2 min, which was greater than the phenol removal by the virgin membrane (3.39%) and N-MWCNT powder (41.42%), respectively. Moreover, the resultant membrane coupled with PMS activation exhibited outstanding removal effects on the fluorescent organics in the secondary effluent and Songhua River water. The combination effectively reduced the total membrane fouling caused by the secondary effluent, Songhua River water, and three typical model organics by 28.19–61.98%. Electron paramagnetic resonance and classical quenching tests presented that the active species (SO4·−, ·OH, and 1O2) and other non-radical processes generated by N-MWCNTs activated PMS decreased the foulants deposition on the membrane surface. Meanwhile, the membrane interception accelerated the aggregation of pollutants and PMS towards the membrane surface through applied pressure, facilitating their mass transfer to the N-MWCNTs surface for the catalysis exerted more effectively. This study demonstrated the potential application of the coupling of N-MWCNTs catalytic oxidation and the UF, which offers a promising prospect to improve the permeate quality and simultaneously overcome the membrane fouling barriers.

Lignocellulosic biomass derived N-doped and CoO-loaded carbocatalyst used as highly efficient peroxymonosulfate activator for ciprofloxacin degradation

Burning lignocellulosic biomass wastes in an outdoor atmosphere has placed heavy burden on ecological environment and increased risk on human health. Converting solid agricultural wastes into functional materials is a research hotspot. In this study, N-doped and CoO-loaded carbocatalyst (CoO-N/BC) was successfully synthesized from the cotton stalk biomass via a simple synthesis process of impregnation and carbonization. Compared with cotton stalk biomass derived pristine biochar, the CoO-N/BC possessed a higher specific surface area (466.631 m2 g−1vs 286.684 m2 g−1) as well as a better catalytic performance in the activation of peroxymonosulfate (PMS) for CIP degradation. The superior catalytic efficiency was ascribed to the directional flow of electrons on the well-organized carbon network of CoO-N/BC, which accelerated electron migration and improved electron conduction ability. Based on the results of radical quenching experiment and electron paramagnetic resonance (EPR), both radical and non-radical process conjointly led to the stepwise decomposition of CIP, and singlet oxygen (1O2) mediated non-radical pathway was discovered to play a dominant role. Besides, the carbon-bridge mediated non-radical pathway was proved to accelerate this degradation process through the experiments of prolong the time of adding CIP at different time intervals. Nitrogen doped sites and CoO active sites as well as defects formed in sp2-hybridized carbon network were supposed to be the active sites for PMS. Furthermore, EIS and LSV were employed to confirm the electron transfer mediated non-radical process of reaction system. This work provides a modified strategy for the disposition of lignocellulosic biomass wastes and illuminates the underlying mechanism of heterogeneous catalysis by CoO-N/BC.

Oxidative degradation of aqueous organic contaminants over shape-tunable MnO2 nanomaterials via peroxymonosulfate activation

Cryptomelane-type MnO2 nanomaterials with a-crystalline phase were prepared by heat treatment of the mixture of MnCO3 and potassium oxalate followed by acid treatment. The evolution of the crystalline phase and morphology from MnCO3 to cryptomelane was investigated by XRD, BET, SEM and TEM. Moreover, MnO2 in nanoparticle, nanorod and nanofiber shapes could be controlled by adjusting the reaction time and temperature in the acid-treatment step. MnO2 nanofibers demonstrated promoted catalytic activity and recyclability for the oxidative degradation of various organic dyes, tetracyclines and bisphenol A via peroxymonosulfate (PMS) activation. About 99% of RhB, AO7, MB, red 2 and bisphenol A at a concentration of 20–50 mg/L could be degraded over MnO2 nanofibers within 12 min. Furthermore, antibiotics, like tetracycline, chlortetracycline and oxytetracycline, and bisphenol A could be mineralized efficiently, and 69–81% TOC removal was obtained. Compared to MnO2 nanowires synthesized by the traditional method with KMnO4, MnO2 nanofibers showed enhanced surface area (102 m2/g), more labile lattice oxygen species and higher oxygen vacancy content, which might be responsible for the superior catalytic performances. The radical quenching test and EPR analysis proved that radical (O2−, SO4− and OH) and non-radical (1O2) processes both existed, and the latter dominantly contributed to the degradation. Based on kinetic study, the activation energy of MnO2 nanofibers/PMS for RhB degradation was only 10.55 kJ/mol, which was lower than that of MnO2 nanowires (16.80 kJ/mol). This study not only offered a new, simple and economical protocol for the scaled-up synthesis of nano-scale MnO2 materials, but also demonstrated its potential in water remediation.

Fabrication of nitrogen-doped graphene nanosheets anchored with carbon nanotubes for the degradation of tetracycline in saline water

The treatment of wastewater with high salinity is still a challenge because of the quenching effect of various anions on radical processes. The nonradical process may be a more promising pathway. Herein, a 3D structured nitrogen-doped graphene nanosheet anchored with carbon nanotubes (N-GS-CNTs) was prepared by direct pyrolysis of K3Fe(CN)6. The as-prepared catalyst can effectively activate peroxymonosulfate (PMS) for mineralization of tetracycline (TC) over a wide pH range (from 3 to 11) and even in high saline water (500 mM Cl−, HCO3−, etc.). The degradation mechanism was elucidated by both experimental characterizations and DFT calculations. The high catalytic efficiency was attributed to accelerated electron transfer from donor (TC) to acceptor (PMS) in the presence of the catalyst, which acts as electron shuttle mediators to promote a nonradical process. At the same time, the catalyst also enhances the production of singlet oxygen (1O2), hence further increasing the degradation rate. This study not only provides a simple method for synthesizing N-GS-CNT catalysts but also provides new insights into the electron transfer pathway for the removal of organic pollutants under high salinity conditions.

Biochar co-doped with nitrogen and boron switching the free radical based peroxydisulfate activation into the electron-transfer dominated nonradical process

In this study, N/B co-doped biochars were employed as metal-free activators of peroxydisulfate (PDS) for tetracycline degradation, more importantly, the roles of dopants and the relative contribution of radical vs nonradical oxidations were comprehensively investigated. Integrating with electron paramagnetic resonance and kinetics calculations, we showed that co-doping N and B into biochars not only boosted the catalytic activity but also switched the radical PDS-activated process into the electron transfer-dominated nonradical process. Compared with pristine biochar/PDS systems (22%), the nonradical contribution of N/B co-doped biochar/PDS systems increased to 59%, exhibiting outstanding stability and selectivity. Galvanic oxidation tests and theoretical simulations unveiled that doped biochars as conductive tunnels accelerate the potential difference-driven electron transfer from the highest occupied molecular orbital of pollutants to the lowest unoccupied molecular orbital of PDS due to the lower energy gap. This study provided new insights into the critical role of heteroatom-doped carbocatalysts in PDS nonradical activation.

Panda manure biochar-based green catalyst to remove organic pollutants by activating peroxymonosulfate: Important role of non-free radical pathways

Carbonaceous materials have emerged as promising metal-free catalysts to activate peroxymonosulfate (PMS) for the degradation of organic contaminants. In this study, a low-cost carbonaceous material panda manure biochar (PBC) was prepared by pyrolysis. The panda manure biochar showed excellent performance in the degradation reaction, and the removal efficiency of sulfamethazine (SMT), which was selected as a representative organic pollutant, exceeded 85% in 40 min. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) characterization confirmed that the improved catalytic performance was attributed to the oxygen-containing functional groups on the surface of the biochar. Radical quenching and electron paramagnetic resonance (EPR) experiments qualitatively demonstrated that 1O2 played an important role in the degradation of SMT. Moreover, the non-radical process that dominated in the panda manure biochar/PMS system was proposed by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) measurements. Sulfamethazine (SMT) was direct oxidized by the activated PMS where panda manure biochar acted as the electron transfer shuttle. The panda manure biochar /PMS system exhibited a high anti-interference ability to Cl−, HPO4−, HCO3-, SO42-, NO3−, and humic acid (HA) containing environments. This study provides a novel panda manure reuse process with high practicability, and proposes a reasonable degradation pathway for sulfamethazine (SMT) based on non-radical oxidation.

Highly efficient degradation of sulfamethoxazole (SMX) by activating peroxymonosulfate (PMS) with CoFe2O4 in a wide pH range

The cobalt ferrite materials (CoxFe3−xO4) with different molar ratios of Co:Fe (1:16, 1:8, 1:4, 1:2, and 3:4) were synthesized by simple co-precipitation method, and used for catalyzing activation of peroxymonosulfate (PMS) to degrade sulfamethoxazole (SMX). The effects of catalyst dose, PMS dose, pH value, and inorganic ions on the degradation of SMX were investigated. Particularly, the degradation efficiency of SMX reached 91% within 10 min in CoFe2O4/PMS, and the removal rate of SMX achieved 81% at first 1 min. Meanwhile, the CoFe2O4/PMS reaction system exhibited excellent catalytic performance at a wide pH range from 3.00 to 11.00. The CoFe2O4 catalyst could be easily magnetically separated and exhibited high stability in cycle experiments. EPR and quenching experiments showed that 1O2, SO4−, and OH species were produced in the CoFe2O4/PMS system, especially OH and 1O2 played dominant roles during the degradation of SMX. The catalytic degradation mechanism of SMX in the CoFe2O4/SMX system was proposed, involving radical process and non-radical process. This work will provide a new way for the efficient treatment of wastewater especially those containing SMX compounds.

Hierarchical multi-active component yolk-shell nanoreactors as highly active peroxymonosulfate activator for ciprofloxacin degradation

The reasonable design of the structure and composition of catalysts was essential to improve the catalytic performance of advanced oxidation processes (AOPs). Herein, we reported a simple strategy to synthesize hierarchical Co3O4-C@CoSiOx yolk-shell nanoreactors with multiple active components by using metal–organic frameworks (MOFs). The novel nanoreactors are further used to activate peroxymonosulfate (PMS) for ciprofloxacin (CIP) degradation. The effects of reaction parameters (pH value, co-existing ions, reaction temperature, etc.) on CIP degradation were systematically investigated. Especially, ∼98.2% of CIP was degraded within 17 min under the optimal conditions, together with the low cobalt leaching and excellent reusability. The appreciable catalytic performance improvement might be due to the synergistic effect of the structure and component design: (1) the hierarchical yolk-shell structure endowed the catalyst with high surface area (∼232.47 m2/g) and fully exposed active sites; (2) abundant highly active ≡Co-OH+ were formed on the surface of CoSiOx; (3) the presence of oxygen vacancies and nitrogen-doped carbon promoted the decomposition of PMS through a non-radical process. The results revealed both the radical (SO4∙-, ∙OH and O2∙-) and non-radical (1O2 and direct charge transfer) should be responsible for the CIP degradation. Moreover, the possible degradation pathways of CIP were proposed through the identification of intermediates using LC-MS/MS techniques and density functional theory (DFT) calculation. Our work highlights that multi-component catalysts derived from MOFs with novel structure have broad application prospects in AOPs.

Co/N co-doped carbonized wood sponge with 3D porous framework for efficient peroxymonosulfate activation: Performance and internal mechanism

Renewable wood sponge with lamellar structure, compressibility and three-dimensional porous frameworks exhibits excellent functionalization application potential in various fields. Herein, cobalt and nitrogen (Co/N) co-doped carbonized wood sponge (CoNCWS800) was prepared successfully for peroxymonosulfate (PMS) activation to degrade sulfamethoxazole (SMX). The CoNCWS800 material exhibited admirable catalytic activity in PMS activation to oxidize SMX molecules (99.7% within 60 min). Electron paramagnetic resonance (EPR) analysis, quenching tests and electrochemical experiments confirmed the existence of both radical (SO4·−,·OH and O2·−) and non-radical (1O2 and direct charge transfer) pathways during the SMX degradation process. Co species were verified as major contributors for the generation of multiple radicals via activating PMS. Surface defective structure and ketonic CO groups performed the positive linear correlation with reaction kinetic constants, revealing the critical role of the two active sites in PMS activation via non-radical process. This study provides a unique insight in PMS activation mechanism via both radical and non-radical pathways of wood sponge-based functional materials.

A confinement approach to fabricate hybrid PBAs-derived FeCo@NC yolk-shell nanoreactors for bisphenol A degradation

In this study, a FeCo alloy@N-doped carbon yolk-shell nanoreactors (ANCYNs) was synthesized through the confinement pyrolysis of the polydopamine (PDA)-coated Fe/Co Prussian blue analogs (PBAs). The PDA-derived carbon shell formed preferentially via pyrolysis is of relevance to (i) protecting the framework structure from collapsing, (ii) increasing the specific surface areas and pore volumes, (iii) facilitating the adsorption of pollutants, and (iv) solving the metal leaching problem. The resulting ANCYNs exhibits good peroxomonosulfate (PMS) activation to degrade bisphenol A (BPA) (removing 98% of BPA in 5 mins), which is significantly better in catalytic performance and stability than those of the single-metal@NC or Nano-alloy catalysts. First-principles calculations indicate that the charge density redistribution becomes much more pronounced when adsorbed on nitrogen-doped graphene with the compressive strain, which leads to a higher density of active sites exposed. The radicals and non-radical processes were confirmed to be simultaneously responsible for BPA degradation.

Bioleaching assisted conversion of refractory low-grade ferruginous rhodochrosite to Mn-Fe based catalysts for sulfathiazole degradation

Ferruginous rhodochrosite with high impurity is difficult to be utilized by traditional beneficiation process due to the complex characteristics. Herein, a bioleaching process driven by Acidithiobacillus ferrooxidans was proposed to recover Mn and Fe in ferruginous rhodochrosite with economic and environmental benefits. The biogenic Fe3+, H+ and extracellular polymeric substances produced in bioleaching process significantly promoted the metal recovery and reduced the H2S emission. Optimal metal leaching efficiencies (95.94% of Mn and 97.54% of Fe) were achieved in bioleaching group. Furthermore, the Mn and Fe mixed leaching solutions could be directly adopted to fabricate Mn-Fe oxide based materials (MFO). When applied as catalysts for peroxymonosulfate (PMS) activation, the as-synthesized MFO performed well for sulfathiazole (STZ) degradation with a 98.66% removal efficiency in 40 min. Both radical process and non-radical process occurred in the advanced oxidation process, which induced the generation of abundant active species of ̇OH, SO4 ̇− and 1O2. Meanwhile, charge transfer also contributed to STZ degradation. Favorably, MFO-3 exhibited good reusability in recycle study and showed adaptability towards various natural water matrixes. This research not only provided novel insights into the utilization of recalcitrant ferruginous rhodochrosite resources, but also enriched the strategy of PMS activator design for environmentalremediation.

Facile synthesis of oxygen vacancies enriched α-Fe2O3 for peroxymonosulfate activation: A non-radical process for sulfamethoxazole degradation

Hematite (α-Fe2O3) has been commonly used as an eco-friendly catalyst for peroxymonosulfate (PMS) to generate free radicals (SO4•- and/or •OH). However, the activation efficiency of PMS relies heavily on the conversion of Fe(III) to Fe(II) that is slow and rate-limiting. In this study, oxygen vacancies enriched α-Fe2O3 was prepared from thermally treated goethite (α-FeOOH) and employed as a PMS activator. Systematic characterization demonstrated that α-Fe2O3 with most abundant oxygen vacancies could be obtained by heating α-FeOOH at 300 °C. The as-prepared α-Fe2O3 exhibited excellent catalytic activity in activation of PMS for oxidation of sulfamethoxazole (SMX, k = 0.04 min−1). The SMX degradation rate was found to be positively correlated with the concentration of oxygen vacancies. Quenching experiments, EPR, LC/MS and XPS analysis revealed that singlet oxygen (1O2) was the predominant reactive oxygen species. The effects of pH, PMS dosage, catalyst loading, temperature, and anions on SMX degradation were comprehensively investigated. Moreover, the plausible degradation pathways of SMX in the α-Fe2O3/PMS system were proposed. This work not only provides a valuable insight into the mechanism of PMS activation by α-Fe2O3 but also establishes a new strategy for the design of more efficient and practical iron-based catalyst for PMS activation.

Fe–nitrogen–doped carbon with dual active sites for efficient degradation of aromatic pollutants via peroxymonosulfate activation

Fenton-like catalysis has received much attention as the promising technology for organic pollutant degradation, whereas it suffers from low atomic utilization, poor catalysts durability and difficult after-treatment to hamper the catalytic oxidation activity. Herein, a Fe– and nitrogen-codoped carbon (Fe–N–C) originated from nanocellulose-based hydrochar, nitrogen source, and iron salt precursor was developed for improved PMS activation and identification of exclusive role of each species. The catalyst formed with interconnected bamboo-shaped 3D tubular structures and high Fe-doping level (up to ~9.0 wt%) not only realized excellent efficiencies in oxidative degradation of various aromatic pollutants, but was also endowed with high durability and stability toward PMS activation. Compared with that of the control catalysts only comprising either C–N network or supported Fe nanoparticles (Fe–C) with FeIV–oxo complex sites, the co-existent active sites of Fe–N configuration and atomic Fe cluster in Fe–N–C could simultaneously improve the graphitization degree, and act as a “support” for constructing the stable structure. It is likely that the coordinated Fe–N formed with annealing process is devoted to decompose PMS by radical generation for pollutants degradation via a radical oxidation process; while the enhanced C–N bonded with graphitic N contribute to produce 1O2 through the nonradical processes interacted with PMS. This Fe–N–C/PMS-coupled process provided a designed strategy to construct the highly active and stable metal-nitrogen-codoped hydrothermal carbons, and deepened insights on structure-activity-stability relationship for persulfate-based environmental remediation.

Anchoring CuFe2O4 nanoparticles into N-doped carbon nanosheets for peroxymonosulfate activation: Built-in electric field dominated radical and non-radical process

Radical and non-radical dominated PMS activation has been widely researched, but the driving force of this process is not well understood. Herein, CuFe2O4 nanoparticles anchored on nitrogen-doped carbon nanosheets (CFONC-2) was prepared for investigation. Experimental results and DFT calculations indicate that a built-in electric field (BIEF) is formed between CuFe2O4 and N-doped carbon nanosheets, which is proposed as the driving force to adjust the electron transfer for triggering radical and non-radical pathway. Specifically, Cu+/Cu2+ and Fe2+/Fe3+ redox cycles are regarded to be the dominant catalytic sites for radical generation (SO4•–, HO• and •O2–). Whereas graphitic N, sp2-hybridized structure, as well as C = O functional group are main active sites for non-radical production (1O2 and direct electron transfer process). Under the radical and non-radical processes dominated by BIEF, the CFONC-2/PMS system exhibits excellent removal performance of levofloxacin (LVFX), where 84.87% of LVFX is removed in 90 min. This work offers a feasible strategy for designing metallic oxides-carbon catalyst with strong electric field effect to satisfy the charge transfer in PMS catalytic reaction.

Activation of peroxymonosulfate by single-atom Fe-g-C3N4 catalysts for high efficiency degradation of tetracycline via nonradical pathways: Role of high-valent iron-oxo species and Fe–Nx sites

A Fenton-like catalyst was prepared based on isolated Fe single-atom and Fe clusters anchored onto a g-C3N4 framework. It exhibited high activity and stability in the heterogeneous activation of peroxymonosulfate (PMS) for tetracycline (TC) degradation. Both experimental and density functional theory calculation results demonstrated that the unique N-coordinated single Fe atom (Fe–N4) served as active sites with optimal binding energy for PMS activation. The experimental analysis indicated that the single Fe atoms displayed superior catalytic activity to Fe clusters. Furthermore, both high-valent iron-oxo species and single oxygen-dominated nonradical processes caused TC degradation. Among them, single Fe atoms anchored onto Fe-g-C3N4 served as Fe–N4 reactive sites can directly activate PMS to produce high-valent iron-oxo species, which was the key active nonradical species causing TC degradation.