Oxidation Of Micropollutants Research Articles

Percarbonate-periodate system: A novel and efficient “oxidant-oxidant” strategy for selective oxidation of micropollutants in water

The development of effective and selective oxidation technology in complex water matrices is crucial for water ecological security. This study reports for the first time the synergistic use of “oxidant-oxidant” about sodium percarbonate (SPC) and periodate (PI) to selectively degrade organic micropollutants. The SPC/PI system showed degradation rates of 0.0946–0.2978 min−1 for various pollutants, which was 3.7–1787 times higher than those in the PI alone and SPC alone systems and can achieve the effect of H2O2/PI systems. Additionally, SPC/PI was a safe water treatment technology without generating reactive iodine species (e.g., HOI). The slightly reduced removal rate of bisphenol F under different ionic species and strengths is indicative of the good anti-interference of the SPC/PI system. Scavenging, probe, and electron spin resonance experiments showed that ▪OH and CO3▪- played a major role in this process, rather than O2▪- and 1O2. Finally, the oxidized products and the possible transformation pathways of three different micropollutants in the SPC/PI and H2O2/PI systems were characterized and clarified, and the toxicity of the degradation products was predicted. Generally, the study proposed a new selective oxidation strategy of SPC/PI that can effectively eliminate micropollutants in water treatment and clarified the interaction mechanisms between PI and SPC.

Crucial role of nitrogen vacancies in carbon activated persulfate toward nonradical abatement of micropollutants from secondary effluent

Biomass-derived carbonaceous materials exhibit fascinating potentials in nonradical oxidation of micropollutants (MPs) by activating persulfate and their performances mainly rest on graphitic N. However, the simultaneously derived N vacancy received little attention. Herein, a graphene-like material rich in N vacancy was synthesized from coffee residues. It showed excellent removal efficiency (95 %) and degradation kinetics (0.21 min−1) in abating tetracycline antibiotics from secondary effluent and significant biotoxicity was diminished. Solid nonradical oxidation consisting of electron transfer (89 %) and singlet oxygen (1O2) oxidation (11 %) was determined. By tracking 1O2 source and electron flow, ketone group appeared at N vacancy was found as the critical site to grab electrons from peroxydisulfate (PDS) with production of 1O2. Then the electrons were transferred to graphitic N driven by the microelectric field between them. This work notices the function of vacancies in biomass resources for high-efficient removal of MPs from real water matrix.

Overlooked role of boron precursors in tuning engineered zero-valent iron to activate peracetic acid for sustainable micropollutant oxidation

This work comprehensively investigated how the characteristics of boron (B) precursors affect the catalytic activity of microscale zero-valent iron (mZVI) towards peracetic acid (PAA) activation for micropollutant degradation. Three boron precursors were introduced into mZVI by ball milling with their physical-chemical properties carefully characterized, and their ability to activate PAA comprehensively evaluated via sulfamethoxazole (SMX) oxidation efficiency. It’s found that B2O3-ZVI demonstrated the highest capability to activate PAA for SMX degradation, with kobs 2 ∼ 3 times higher than Na2B4O7-ZVI and H3BO3-ZVI. Specially, B precursors regulate the ability of mZVI to activate PAA via the following two aspects: (1) affecting the formation and content of FeB to accelerate Fe(II) regeneration; (2) increasing the hydrophilicity of the iron particles and the affinity of B-ZVI for binding PAA to different extent. This study highlights the important role of boron precursors in tuning engineered mZVI to initiate Fenton-like process for water purification.

Oxidation of antibiotic micropollutants in various water resources through integration of Bi2WO6 and g-C3N4.

Recently, the hazardous effects of antibiotic micropollutants on the environment and human health have become a major concern. To address this challenge, semiconductor-based photocatalysis has emerged as a promising solution for environmental remediation. Our study has developed Bi2WO6/g-C3N4 (BWCN) photocatalyst with unique characteristics such as reactive surface sites, enhanced charge transfer efficiency, and accelerated separation of photogenerated electron-hole pairs. BWCN was utilized for the oxidation of tetracycline antibiotic (TCA) in differentwater sources. It displayed remarkable TCA removal efficiencies in the following order: surface water (99.8%) > sewage water (88.2%) > hospital water (80.7%). Further, reusability tests demonstrated sustained performance of BWCN after three cycles with removal efficiencies of 87.3, 71.2 and 65.9% in surface water, sewage, and hospital water, respectively. A proposed photocatalytic mechanism was delineated, focusing on the interaction between reactive radicals and TCA molecules. Besides, the transformation products generated during the photodegradation of TCA were determined, along with the discussion on the potential risk assessment of antibiotic pollutants. This study introduces an approach for utilizing BWCN photocatalyst, with promising applications in the treatment of TCA from various wastewater sources.

Peroxysulfur species-mediated enhanced oxidation of micropollutants by ferrate(VI): Peroxymonosulfate versus peroxydisulfate

Many studies have shown that Peroxymonosulfate (PMS) works synergistically with ferrate (Fe(VI)) to remove refractory organic compounds in a few minutes. However, little has been reported on the combined effects of peroxydisulfate (PDS) and Fe(VI). Since PDS is stable and cost effective, it is of practical significance to study the reaction mechanism and conditions of the PDS/Fe(VI) system. The results of the study indicate that the intermediate Fe(II) is formed during the decomposition of Fe(VI), which is then rapidly oxidized. Due to the asymmetry of the PMS molecular structure, PMS can rapidly trap Fe(II) (kPMS/Fe(II)= 3 × 104 M−1∙s−1), whereas PDS cannot (kPDS/Fe(II)= 26 M−1∙s−1). Hydroxylamine hydrochloride (HA) can reduce Fe(VI) and Fe(III) to Fe(II) to excite PDS to produce SO4•−. Acetate helps to detect Fe(II), but does not help PDS to trap Fe(II). Active species such as SO4•−, •OH, 1O2, and Fe(IV), Fe(V) are present in both systems, but in different amounts. In the PMS/Fe(Ⅵ) system, all these active species react with ibuprofen (IBP) and degrade IBP within several minutes. The effects of the initial pH, PMS or Fe(VI) dosage, and different amounts of IBP on the removal rate of IBP were investigated. According to the intermediates detected by the GC-MS, the degradation process of IBP includes hydroxylation, demethylation and single bond breakage. The degradation pathways of IBP were proposed. The degradation of IBP in tap water and Songhua River was also investigated. In actual water treatment, the dosage needs to be increased to achieve the same results. This study provides a basis and theoretical support for the application of PMS/Fe(Ⅵ) and PDS/Fe(VI) system in water treatment.

Exploring the potential of CoMoO4-modified graphitic carbon nitride to boost oxidation of amoxicillin micropollutants in hospital wastewater.

This study investigates the removal of amoxicillin micropollutants (AM) from hospital wastewater using CoMoO4-modified graphitic carbon nitride (CMO/gCN). Consequently, CMO/gCN exhibits notable improvements in visible light absorption and electron-hole separation rates compared to unmodified gCN. Besides, CMO/gCN significantly enhances the removal efficiency of AM, attaining an impressive 96.5%, far surpassing the performance of gCN at 48.6%. Moreover, CMO/gCN showcases outstanding reusability, with AM degradation performance exceeding 70% even after undergoing six cycles of reuse. The removal mechanism of AM employing CMO/gCN involves various photoreactions of radicals (•OH, •O2-) and amoxicillin molecules under light assistance. Furthermore, CMO/gCN demonstrates a noteworthy photodegradation efficiency of AM from hospital wastewater, reaching 92.8%, with a near-complete reduction in total organic carbon levels. Detailed discussions on the practical applications of the CMO/gCN photocatalyst for removal of micropollutants from hospital wastewater are provided. These findings underline the considerable potential of CMO/gCN for effectively removing various pollutants in environmental remediation strategies.

Insights into atomic arrangement in CuMnO2 with tailored exposed crystal facets for effectively micropollutant oxidation via peroxymonosulfate activation

Crystal facet engineering of bimetallic ABO2 oxides is regarded as decisive strategy for regulation of catalytic activity, whereas precisely identifying the intrinsic mechanism of facet-dependent activity are still significant challenging. Herein, crednerite CuMnO2 nanoflake material with tailored crystal facets were synthesized and identified as efficient peroxymonosulfate (PMS) activators, in which CuMnO2-160 catalyst with exposed (201) facet exhibited more superior catalytic efficiency compared to CuMnO2-80 with (020) facet towards p-hydroxybenzoic acid (HBA) oxidation. Notably, CuMnO2-160 demonstrated substantial activity across a wide pH range even under high concentration inorganic anions and humic acid (HA). Quenching experiments and EPR spectra elucidated the crucial reactive species of •OH and SO4•-, with 1O2 playing an auxiliary role in HBA degradation. Computational analysis and characterization results collectively revealed that PMS molecules adopted two distinct adsorption modes on different CuMnO2 facets, and the PMS adsorption-activation behavior was significantly altered by detailed atom arrangement of CuMnO2 in tailored exposed facets, thereby lowering the charge transfer energy barrier to favor PMS bonding interaction on (201) facet. This study systematically underscores the catalyst microstructure and crystal facet dominated PMS activation behavior and oxidation mechanism, providing valuable and novel insights for further understanding of crystal facets and the morphology control relied catalytic mechanism.

Rapid detection of hypobromous acid by a tetraphenylethylene-based turn-on fluorescent AIE probe and its applications

BackgroundSimilar to hypochlorous acid (HClO), hypobromous acid (HBrO) is one of the most notable reactive oxygen species (ROS). Overexpression of HBrO is linked to various diseases causing organ and tissue loss. Due to HBrO's role in the oxidation of micropollutants, real-time monitoring of HBrO in water-based systems is essential. Tetraphenylethylene (TPE)-based organic aggregation-induced emission luminophores (AIEgens) are an emerging category of fluorescent probe materials that have attracted considerable attentions. However, AIE probes are rarely applied to detect HBrO. Developing faster, more precise, and more sensitive AIE probes is thus crucial for detecting biological and environmental HBrO. ResultsA small molecule fluorescent probe 4-(1,2,2-triphenylvinyl)benzamidoxime (SWJT-21) was synthesized for the sensitive and selective detection of hypobromous acid (HBrO) based on aggregation-induced emission (AIE). The amidoxime unit of SWJT-21 would undergo an oxidation reaction with HBrO, leading to a structure differentiation between the probe and the product, and therefore the turn-on fluorescence by the AIE effect. The probe could recognize hypobromous acid rapidly (less than 3 s) in high aqueous phase (99 % water) with a turn-on fluorescence response. It was determined that the limit of detection for HBrO was 5.47 nM. Moreover, SWJT-21 demonstrates potential as a test strip for the detection of HBrO. SWJT-21 was also successfully used for the monitoring of HBrO in water samples and for the detection of endogenous/exogenous HBrO in living cells and zebrafish. SignificanceA special AIE fluorescence turn-on probe SWJT-21 based on tetraphenylethylene was designed for detecting HBrO in the environmental and biological systems. This probe has an extremely low detection limit of 5.47 nM and is able to detect HBrO in 99 % aqueous phase in less than 3 s.

Insights into the enhanced oxidation of organic micropollutants by single-atom Cu catalyst activated peroxydisulfate: Valence-dominated nonradical pathway

Herein, we anchored Cu atoms with four N atoms into waste adsorbent-based biochar (SACu30@NC) containing both Cu(I) and Cu(II) to explore the role of different Cu valences for PDS activation mechanism. The atomic Cu was identified as the active site, and Cu(III) and electron shuttle process dominated organics degradation in SACu30@NC/PDS system. Therein, Cu(I) preferred to activate the adsorbed PDS to produce Cu(III) (Cu(I)N4-PDS→Cu(II)N4-SO4•-→Cu(III)N4-SO42-), whereas PDS adsorbed on Cu(II) surface was more likely to extract electrons from organic pollutants directly. Benefiting from non-radical process, SACu30@NC exhibited selective and anti-interference performance for organic pollutants in complex matrixes. The promising catalytic activity of SACu30@NC (BPA=50 mg/L, 100% within 180 min) with low Cu leaching (<0.1 mg/L) in continuous-flow experiments further revealed the potential of SACu30@NC for practical applications. This work provides new insights into the PDS activation mechanism by single-atom Cu catalysts and develops an efficient approach for practical wastewater purification.

Mechanically treated Mn2O3 triggers peracetic acid activation for superior non-radical oxidation of micropollutants: Identification of reactive complexes

This study used a simple mechanical ball milling strategy to significantly improve the ability of Mn2O3 to activate peracetic acid (PAA) for sustainable and efficient degradation of organic micropollutant (like bisphenol A, BPA). BPA was successfully removed and detoxified via PAA activation by the bm-Mn2O3 within 30 min under neutral environment, with the BPA degradation kinetic rate improved by 3.4 times. Satisfactory BPA removal efficiency can still be achieved over a wide pH range, in actual water and after reuse of bm-Mn2O3 for four cycles. The change in hydrophilicity of Mn2O3 after ball milling evidently elevated the affinity of Mn2O3 for binding to PAA, while the reduction in particle size exposed more active sites contributing partially to catalytic oxidation. Further analysis revealed that BPA oxidation in the ball mill-treated Mn2O3 (bm-Mn2O3)/PAA process mainly depends on the bm-Mn2O3-PAA complex (i.e., Mn(III)−OO(O)CCH3) mediated non-radical pathway rather than R-O• and Mn(IV). Especially, the existence of the Mn(III)-PAA complex was definitely verified by in situ Raman spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Simultaneously, density functional theory calculations determined that PAA adsorbs readily on manganese sites thereby favoring the formation of Mn(III)−OO(O)CCH3 complexes. This study advances an in-depth understanding of the underlying mechanisms involved in the manganese oxide-catalyzed activation of PAA for superior non-radical oxidation of micropollutants.

Prussian blue analogue nanospheres immobilized on self-floating biochar for micropollutant degradation via photo-Fenton process

Fe-Co Prussian blue analogue (PBA) nanospheres were immobilized on biochar (PBA-on-biochar) to remove contaminants via photo-Fenton process. The loading weight of FeCo PBA on biochar increased with increasing PBA aging temperature and time. The PBA exhibited efficient chloroquine phosphate (CQ) degradation under both LED light and sunlight, where OH and 1O2 dominated the oxidation. The CQ degradation was slightly affected by pH value (3.5–9.5) and co-existing anions like SO42−, Cl− and NO3–. The application potential of the PBA-on-biochar was evaluated in a continuous reaction device. Theoretical calculation revealed the dominant role of Fe sites in PBA for H2O2 activation. The degradation pathway was proposed based on nine intermediate products. Also, the excellent photo-Fenton activity and good floatability enable PBA-on-biochar to be efficient in inhibiting the activity of Microcystis aeruginosa under sunlight. The results implied that PBA-on-biochar is applicable for fast micropollutant oxidation from water.

Ferrate(VI)/percarbonate for the oxidation of micropollutants: Interactive activation and release of low-concentration hydrogen peroxide for efficient electron utilization

A novel "ferrate/percarbonate (Fe(VI)/SPC) co-oxidation process" was used to treat ciprofloxacin (CIP) and various micropollutants (MPs), which owned better performance than mixture of Fe(VI), Na2CO3 and H2O2. The mechanism investigation found that the low-concentration H2O2 (1–2 µM) released by SPC can promote the high-valent iron intermediates (Fe(IV)/Fe(V)) of Fe(VI) to the MP oxidation, and Fe(VI) products can also activate SPC to produce hydroxyl radical (·OH). The interactive activation of Fe(VI) and SPC was realized, which retained the high selectivity of Fe(VI) to electron-rich pollutants, and also made up the oxidation of electron-deficient pollutants through •OH, improving the degradation effect of various MPs by 20–30%, and the rate constant was increased by 1 to 3 times. Moreover, non-purgeable organic carbon (NPOC) determination confirmed that •OH participation reduced the NPOC value of CIP from 5.43 mg/L to 4.37 mg/L. The transformation pathway of CIP showed that Fe(VI)/SPC resulted in more hydroxylation intermediates of CIP than Fe(VI) alone. Acute toxicity assays found that the photoinhibition rate of CIP treated with Fe(VI) alone was 14.5%, while the sample treated with Fe(VI)/SPC showed no significant photoinhibition effect, which proved that the new process had good detoxification properties for CIP.

How Should We Activate Ferrate(VI)? Fe(IV) and Fe(V) Tell Different Stories about Fluoroquinolone Transformation and Toxicity Changes.

Many studies have investigated activation of ferrate (Fe(VI)) to produce reactive high-valent iron intermediates to enhance the oxidation of micropollutants. However, the differences in the risk of pollutant transformation caused by Fe(IV) and Fe(V) have not been taken seriously. In this study, Fe(VI)-alone, Fe3+/Fe(VI), and NaHCO3/Fe(VI) processes were used to oxidize fluoroquinolone antibiotics to explore the different effects of Fe(IV) and Fe(V) on product accumulation and toxicity changes. The contribution of Fe(IV) to levofloxacin degradation was 99.9% in the Fe3+/Fe(VI) process, and that of Fe(V) was 89.4% in the NaHCO3/Fe(VI) process. The cytotoxicity equivalents of levofloxacin decreased by 1.9 mg phenol/L in the Fe(IV)-dominant process while they significantly (p < 0.05) increased by 4.7 mg phenol/L in the Fe(V)-dominant process. The acute toxicity toward luminescent bacteria and the results for other fluoroquinolone antibiotics also showed that Fe(IV) reduced the toxicity and Fe(V) increased the toxicity. Density functional theory calculations showed that Fe(V) induced quinolone ring opening, which would increase the toxicity. Fe(IV) tended to oxidize the piperazine group, which reduced the toxicity. These results show the different-pollutant transformation caused by Fe(IV) and Fe(V). In future, the different risk outcomes during Fe(VI) activation should be taken seriously.

Interlayer single-atomic Fe−N4 sites on carbon-rich graphitic carbon nitride for notably enhanced photo-Fenton-like catalytic oxidation processes towards recalcitrant organic micropollutants

Glucose-assisted supramolecule self-assembly of melamine and cyanuric acid in the presence of Fe(NO3)3 combined with thermal polymerization is designed to fabricate C-rich g-C3N4-embedded interlayer single-atomic Fe−N4 sites catalyst (Fe1/C-CN). Fe1/C-CN exhibits outstanding photo-Fenton-like catalytic oxidation activity towards typical recalcitrant organic micropollutants. For example, the pseudo-first-order kinetic constant of Fe1/C-CN photo-Fenton-like system is 7.5 and 21.1 times higher than Fe1/C-CN photocatalysis and Fenton-like systems in degradation of p-nitrophenol, and TOC removal efficiency reaches up to 100% after reaction proceeds for 4 h. Mechanism studies reveal that synergy of maximum Fe atom utilization efficiency and boosted photoexcited charge separation dynamics accelerates regeneration of ≡Fe(II) and efficient H2O2 activation of Fe1/C-CN, leading to plentiful active oxygen species for deep oxidation of organic micropollutants. Fe1/C-CN also shows a robust reusability in long-term remediation of organic micropollutants, attributing to interlayer Fe−N coordination interactions for preventing single Fe atoms from agglomeration and leaching to reaction media.

A bioinspired iron-peroxy species of feroxyhyte for micropollutants oxidation with ultrahigh peroxymonosulfate utilization efficiency

Efficient purification of water is essential to remove organic micropollutants for human and environmental health. The development of catalysts with high activity and peroxymonosulfate (PMS) utilization efficiency for removal of organic micropollutants remains challenging. Inspired by natural enzymes, we designed δ-FeOOH nanosheets with abundant 5-coordinated iron sites, which are responsible for the formation of iron-peroxy (FeIII-O-O-FeIII) species with PMS. The iron-peroxy species can directly oxidize and degrade electron-rich micropollutants (e.g. BPA) with an ultra-high PMS utilization efficiency of 78.4%. A laminar membrane constructed from a stack of δ-FeOOH nanosheets, replete with an abundance of 5-coordinated iron sites. The laminar membrane can degrade multiple micropollutants by almost 100% due to nonlinear transport between the δ-FeOOH nanolayers, compared with the dispersed catalyst. This work would motivate the community to focus more on the diversified behavior of the coordination number of active centers in the design of efficient catalysts for water purification.

Iodate(V) activated ferrate(VI) for enhanced oxidation of micropollutants from water and sediment media

In this study, a new Fe(VI)/I(V) system was developed to efficiently strengthen utilization efficiency of generated Fe(IV)/Fe(V). This system could effectively degrade sulfamethoxazole, carbamazepine, bisphenol A and tetracycline within 4 min with k1 values of 0.60648 min−1, 1.39726 min−1, 0.65921 min−1 and 0.93298 min−1, which were 21–66 times higher than the sum of k1 values of I(V) alone and Fe(VI) alone systems, and also much better than H2O2, peroxydisulfate, and peroxymonosulfate strengthened Fe(VI) systems. In addition, Fe(VI)/I(V) exhibited favorable anti-interference, that high-salinity and high organic showed negligible inhibition on pollutant degradation. More importantly, I(V), as an excellent catalyst, hardly decayed during treatment process, which broadens the application field of Fe(VI)/I(V) in different contaminated environmental media and provides a distinguished efficiency for recycling use in contaminated sediment with only consumed Fe(VI) supplement. Fe(VI) consumption in Fe(VI)/I(V) system was not enhanced compared with Fe(VI) alone system, and thus saving agent costs is another significant advantage of Fe(VI)/I(V) system. Above multiple superiorities are still obvious even compared with the systems of other oxidants enhancing Fe(VI) developed in recent years. The main active species was identified as Fe(IV)/Fe(V). The mechanisms of I(V) strengthening Fe(VI) were determined as Fe(IV)/Fe(V) oxidation enhancement, rather than Fe(VI) decay enhancement. Utilization efficiency of Fe(IV)/Fe(V) was improved by oxidation reactivity modulation with I(V) complexes formation, thereby strengthening decontamination significantly. This study proposed a strategy for decontamination in different mediums with high treatment efficiency, high selectivity, satisfactory reusability, and low consumption of agents.

Valorization of olive mill solid waste-derived biochar: An efficient approach for simultaneous adsorption and oxidation of micropollutant in surface water

This study explores the utilization of olive mill solid waste (OMSW) as a source of biochar (BC) for effective removal of micropollutants during surface water treatment. The conversion of OMSW into BC was accomplished via pyrolysis conducted at varying temperatures ranging from 400 to 600 °C. To improve its performance, BC was subjected to activation through either physical-thermal or chemical techniques. BC samples were characterized by SEM microscopy revealing a porous structure, surface area analysis showed an increase in surface area for biochar samples subjected to physical-thermal activation (BC-T) (20 m2/g) and chemical activation using potassium hydroxide (BC-KOH) (70 m2/g) or zinc/iron (BC-Zn/Fe) (456 m2/g). The zero point of charge range from <3 to 4.2 for the different BC samples whereas FTIR measurements showed that physical activation at 900 °C favors a graphitic structure in BC.The catalytic properties of the biochar samples were investigated in the activation of sodium persulfate (PSF) for the oxidation of micropollutants (MPS), including ciprofloxacin (CPX), sulfamethoxazole (SMZ), and paracetamol (PCM), in natural Lake Kinneret water. BC-KOH exhibited the highest removal efficiency, and the removal of MPS increased with higher dosages of BC and PSF. Under optimized conditions ([biochar]: 500 mg/L and [PSF]: 200 mg/L), significant removal efficiencies were achieved for PCM (88.2 % ± 0.7), CPX (80.8 % ± 1.9), and SMZ (64.1 % ± 3.2) after a 5-hour treatment. Finally, MPS adsorbed on BC experienced significant surface oxidation, resulting in removal efficiencies for PCM (97.9 %), CPX (92 %), and SMZ (77.9 %). This oxidation process is expected to enhance the treatment effectiveness prior to regeneration.

Efficient charge carrier separation over carbon-rich graphitic carbon nitride for remarkably improved photocatalytic performance in emerging organic micropollutant degradation and H2 production

Graphitic carbon nitride (g-C3N4) shows great potentials in visible-light-driven catalytic oxidation of organic micropollutants to harmless products and reduction of water to H2 but suffers from drawback of sluggish charge carrier separation and transfer dynamics. To overcome this drawback, here a novel point defect engineering strategy, by a nicotinic acid or barbituric acid-assisted supramolecule self-assembly of dicyandiamide followed by thermal polymerization, is designed to prepare pyridine unit-incorporated g-C3N4 (CPyr-CNx) and carbon atom self-doped g-C3N4 (C-CNx). The strategy leads to well-regulated chemical structures of CPyr-CNx and C-CNx and thus the precisely controlled electronic structures. The CPyr-CNx and C-CNx both exhibit remarkably improved visible-light photocatalytic activity in degradation of emerging organic micropollutants (methylparaben, acetaminophen and bisphenol A) and water-splitting to H2 production in comparison of bulk g-C3N4 and carbon-rich g-C3N4 prepared by a direct thermal copolymerization of nicotinic acid or barbituric acid with dicyandiamide, and their photocatalytic redox activity depends on carbon doping level. Experimental results combined with theoretical simulations reveal that the superior photocatalytic redox performance of CPyr-CNx and C-CNx is mainly dominated by the significantly boosted charge carrier separation and transfer dynamics driven by carbon doping induced-local electric field and -midgap states, which finally generates abundant reactive oxidation species including •O2− anion radicals, •OH radicals and 1O2 for the deep oxidation of target organic micropollutants to significantly reduce their ecotoxicity; additionally, such efficient charge carrier separation and transfer also favors high mobility for free electron-involved photocatalytic H2 evolution reaction.

Packed OV-SnO2-Sb bead-electrodes for enhanced electrocatalytic oxidation of micropollutants in water

Electrocatalytic oxidation is an appealing treatment option for emerging micropollutants in wastewater, however, the limited reactive surface area and short service lifetime of planar electrodes hinder their industrial applications. This study introduces an innovative electrochemical wastewater treatment technology that employs packed bead-electrodes (PBE) as a dynamic electrocatalytic filter on a dimensionally stable anode (DSA) acting as a current collector. By using PBE, the electroactive volume is expanded beyond the vicinity of the common planar anode to the thick porous media of PBE with a vast electrocatalytic surface area. This greatly enhances the efficiency of electrochemical degradation of micropollutants. The OV-SnO2-Sb PBE filter achieved a nearly 100 % degradation of moxifloxacin (MOX) in under 2 min of single-pass filtration, with a degradation rate over an order of magnitude higher than the conventional electrochemical oxidation processes. The generation of abundant radical species (•OH) and non-radical species (1O2 and O3), along with the enhanced direct oxidation, led to the outstanding performance of the charged PBE system in MOX degradation. The OV-SnO2-Sb PBE was remarkably stable, and the separation between the electroactive PBE layer and the base Ti anode allows for easy renewal of the bead-electrode materials and scaling up of the system for practical applications. Overall, our study presents a dynamic electroactive PBE that advances the electrocatalytic oxidation technology for effective control of emerging pollutants in the water environment. This technology has the potential to revolutionize electrochemical wastewater treatment and contribute to a more sustainable future environment.

Enhanced oxidation of micropollutants by ozone/ferrate(VI) process: Performance, mechanism, and toxicity assessment

A novel advanced oxidation technology of ozone and ferrate (ozone/Fe (VI)) was investigated and used to degrade micropollutants (e.g., sulfamethoxazole (SMX), diclofenac sodium (DCF)) in this study. The results demonstrated that the ozone/Fe(VI) process can rapidly and efficiently degrade SMX and DCF. The SMX and DCF degradation was substantially accelerated by increasing the Fe(VI) dosage (5 to 25 μM) or ozone concentration (10 to 52 μM), up to 77.0 % and 82.7 % of SMX and DCF were obtained, respectively. The removal efficiencies of SMX and DCF was higher in acidic conditions, and decreased from 98.4 % to 44.7 % and from 94.3 % to 62.9 %, respectively, at pH 5–9 in the presence of buffer. Besides, CO32−, Cl−, and HA had a little negative effect on SMX and DCF removal, and the ozone/Fe(VI) process still obtained high degradation efficiency (>64.5 %) for SMX and DCF in real water. On the basis of the finding of scavenging and probe experiments, ozone, Fe(VI), OH, and Fe(IV)/Fe(V) species were identified as the predominant oxidants for SMX and DCF degradation. Sixteen and eighteen transformation products (TPs) of SMX and DCF in ozone/Fe(VI) process were detected by UPLC-QTOF-MS. Then, the reaction pathways of SMX and DCF were proposed by Fukui function analysis and TPs identification. Using the ECOSAR software, the ecotoxicity of SMX, DCF, and their TPs were evaluated. These findings might provide useful information and a theoretical foundation for the application of ozone/Fe(VI) process in water treatment.