Kinetics and mechanism of carbamazepine degradation by a modified Fenton-like reaction with ferric-nitrilotriacetate complexes

Organic cocatalysts improved Fenton and Fenton-like processes for water pollution control: A review

In recent times, organic compounds have been extensively utilized to mitigate the limitations associated with Fe(Ⅲ) reduction and the narrow pH range in Fenton and Fenton-like processes, which have garnered considerable attention in relevant studies. This review presents the latest advancements in the comprehensive analysis and applications of organic agents as assistant/cocatalysts during Fenton/Fenton-like reactions for water pollution control. The primary focus includes the following: Firstly, the mechanism of organic co-catalytic reactions is introduced, encompassing both complexation and reduction aspects. Secondly, these organic compounds are classified into distinct categories based on their functional group structures and applications, namely polycarboxylates, aminopolycarboxylic acids, quinones, phenolic acids, humic substances, and sulfhydryl compounds, and their co-catalytic functions and mechanisms of each category are discussed in meticulous detail. Thirdly, a comprehensive comparison is conducted among various types of organic cocatalysts, considering their relative merits, cost implications, toxicity, and other pertinent factors. Finally, the review concludes by addressing the universal challenges and development prospects associated with organic co-catalytic systems. The overarching objective of this review is to provide insights into potential avenues for the future advancement of organic co-catalytic Fenton/Fenton-like reactions in the context of water purification.

Removal of pharmaceutically active compounds (PhACs) by zero-valent iron: quantification of removal mechanisms consisting of degradation, adsorption and co-precipitation

The removal mechanisms of carbamazepine (CBZ), which is one of pharmaceutically active compounds, using zero-valent iron (ZVI) were quantified by defining three fractions, namely "degradation", "adsorption", and "co-precipitation". The maximum total organic carbon (TOC) removal was obtained at pH 4. The results demonstrate that the adsorption on the ZVI surface is dominant in the TOC removal of CBZ for 4 ≤ pH ≤ 6 while the degradation by oxidative and reductive reactions is efficient exclusively for pH ≤ 3. TOC removal was not obtained for pH ≥ 8. The most dominant mechanism in the removal of CBZ by ZVI is the adsorption onto the iron oxides/hydroxides layer formed on ZVI surface rather than the degradation by oxidative and reductive reactions including Fenton and Fenton-like reactions for pH ≥ 4. A novel kinetic model for removal of CBZ by ZVI was developed to simulate the dynamic concentration profiles of CBZ, TOC, total Fe ions, and dissolved oxygen linked closely with each other and the contributions of degradation, adsorption, and co-precipitation in TOC removal of CBZ. Reasonable agreement between experimental data and model predictions suggests the applicability of the proposed kinetic model to quantitatively analyze the mechanisms of CBZ removal by ZVI.

Iron boride boosted Fenton oxidation: Boron species induced sustainable FeIII/FeII redox couple

The regeneration of Fe(II) is the rate-limiting step in the Fenton/Fenton-like chain reactions that seriously hinder their scientific progress towards practical application. In this study, we proposed iron boride (FeB) for the first time as a new material to sustainably decompose H₂O₂ to generate hydroxyl radicals, which can non-selectively degrade a wide array of refractory organic pollutants. Fe(II) can be steadily released by the stepwise oxidation of FeB to stimulate Fenton reaction, meanwhile, B-B bonds as electron donors on the surface of FeB effectively promote the regeneration of Fe(II) from Fe(III) species and significantly accelerate the production of hydroxyl radicals. The low generation of toxic by-products and the high utilization rate of iron species validly avoid the secondary organic/metal pollution in the FeB/H₂O₂ system. Therefore, FeB mediated Fenton oxidation provides a novel strategy to realize a green and long-lasting environmental remediation.

Water disinfection by the UVA/electro-Fenton process under near neutral conditions: Performance and mechanisms

An efficient and thorough water disinfection is critical for human health. In this study, UVA-LEDs, nitrilotriacetic acid (NTA) and a boron-doped diamond anode were respectively used as the UVA source, the iron chelator and the anode for the UVA/electro-Fenton (E-Fenton) reaction to treat wastewater. The disinfection performance of the UVA/E-Fenton had been investigated. The mechanisms of the E. coli inactivation had been clarified. The results showed that complete disinfection (about 5.6-log removal) could be achieved within 50 min at a certain condition due to the synergistic effort of the UVA, anodic oxidation and the electro-Fenton. The quenching experiments and the electron paramagnetic resonance (EPR) detection indicated that •OH, •O₂^- and ¹O₂ play important roles for inactivating E. coli. The results of SEM images and genomic DNA electrophoresis suggested that both the cell structure and the DNA had been thoroughly destroyed during the UVA/E-Fenton process. Increasing the UVA irradiation, oxygen bubbling could improve the disinfection rate, while it also would increase the energy consumption. The appropriate Fe and NTA ratio was 1:2 to realize an efficient Fenton reaction under near neutral condition. Complete disinfection was also achieved within 50 min when it used for treating real wastewater. Thus, the UVA/E-Fenton process is a satisfied way for water disinfection.

H2O2 activation by two-dimensional metal-organic frameworks with different metal nodes for micropollutants degradation: Metal dependence of boosting reactive oxygen species generation

The existence of organic micropollutants (OPMs) in water poses a considerable threat to the environment. A centralized approach towards pollutants abatement has dominated over the recent decades wherein heterogeneous Fenton-like based advanced oxidation processes can be a promising technology. The application of engineered nanomaterials offers more opportunities to enhance their catalyst properties. This study synthesizes a series of ultrathin two-dimensional (2D) Metal-organic frameworks (MOFs) nanosheets with tunable metal clusters. The formation of reactive oxygen species (^•OH and ¹O₂) can be significantly boosted via transferring the adsorbed H₂O₂ onto the solid-liquid interface by systematically tuning the metal species. The Co-MOF nanosheets exhibited an ultrafast degradation kinetic for BPA with a rate of 2.23 min^-1 (4.98 times higher than that of the bulk MOF) and TOF (turnover frequency) value of 9.99 min^-1, which are observably greater than that of the existing materials reported to date. Density functional theory simulation and experimental results unravel the mechanism for ROS formation, which is strongly metal-depend. We further loaded the powder onto a flow-through poly (vinylidene fluoride) (PVDF) microfiltration membrane and observed that the representative OPMs could be rapidly degraded, indicating promising properties for practical application.

Synergistic effect of nitrate on UV-chlorine photochemical degradation of carbamazepine

We investigated the use of UV-chlorine advanced oxidation process for the removal and transformation of carbamazepine (CBZ), and its photochemical synergy with NO₃^- for the production of ^.OH towards enhancing CBZ removal in aqueous solution. Production of ^.OH by UV-chlorine system with/without NO₃^- was studied under different conditions, by using salicylic acid (SA) as the chemical probe for ^.OH. Initial concentration of 30 mg/L SA, 5 and 10 mg/L chlorine, and 0-10 mg/L NO₃^- under irradiation at 254 nm (3.026 W/L) in a photochemical reactor was used. Aqueous solutions containing 10 mg/L chlorine and spiked with 4 mg/L NO₃^- gave the highest reproducible generation of ^.OH. Using initial concentrations of 10 mg/L CBZ and 10 mg/L chlorine, 60 % CBZ was removed after 10 min of irradiation without NO₃^-, while 72 % CBZ was removed with 4 mg/L NO₃^- added. There was no noticeable CBZ removal after 10 min of irradiation in the presence of NO₃^- without chlorine. Corresponding dark reactions were also conducted, with no noticeable degradation of CBZ. Samples were analyzed via UHPLC, LC-MS, and TOC (total organic carbon) analyzer for CBZ and TOC concentrations respectively. Although, there was significant reduction in CBZ concentration during both photochemical degradation processes, the was low TOC removal (~10%) in each case. The two photochemical degradation processes also seem to generate similar degradation products indicating that the addition NO₃^- of the UV-chlorine process might not have changed the degradation mechanism. The results indicate that NO₃^- could act synergistically in a UV-chlorine system to increase CBZ removal and reduce the quantity of free chlorine required to achieve a target removal efficiency. This could facilitate reduction in the potential production of chlorinated byproducts in the system.

Elimination of recalcitrant micropollutants by medium pressure UV-catalyzed bioelectrochemical advanced oxidation process: Influencing factors, transformation pathway and toxicity assessment

Bio-electro-Fenton (BEF) processes have been widely studied in recent years to remove recalcitrant micropollutants from wastewater. Though promising, it still faces the critical challenge of residual iron and iron sludge in the treated effluent. Thus, an innovative medium-pressure ultraviolet-catalyzed bio-electrochemical system (MUBEC), in which medium-pressure ultraviolet was employed as an alternative to iron for in-situ H₂O₂ activation, was developed for the removal of recalcitrant micropollutants. The influence of operating parameters, including initial catholyte pH, cathodic aeration rate, and input voltage, on the system performance, was explored. Results indicated that complete reduction of 10 mg L^-1 of model micro-pollutants ibuprofen (IBU) and carbamazepine (CBZ) was achieved at pH 3, with an aeration rate of 1 mL min^-1 and a voltage of 0.3 V, following pseudo-first-order kinetics. Moreover, potential transformation pathways and the associated intermediates during the degradation were deduced and detected, respectively. Thus, the MUBEC system shows the potential for the efficient and cost-effective degradation of recalcitrant micropollutants from wastewater.

Degradation of Rhodamine B in Wastewater by Iron-Loaded Attapulgite Particle Heterogeneous Fenton Catalyst

The water pollution caused by industry emissions makes effluent treatment a serious matter that needs to be settled. Heterogeneous Fenton oxidation has been recognized as an effective means to degrade pollutants in water. Attapulgite can be used as a catalyst carrier because of its distinctive spatial crystal structure and surface ion exchange. In this study, iron ions were transported on attapulgite particles to generate an iron-supporting attapulgite particles catalyst. BET, EDS, SEM and XRD characterized the catalysts. The particle was used as a heterogeneous catalyst to degrade rhodamine B (RhB) dye in wastewater. The effects of H2O2 concentration, initial pH value, catalyst dosage and temperature on the degradation of dyes were studied. The results showed that the decolorization efficiency was consistently maintained after consecutive use of a granular catalyst five times, and the removal rate was more than 98%. The degradation and mineralization effect of cationic dyes by granular catalyst was better than that of anionic dyes. Hydroxyl radicals play a dominant role in RhB catalytic degradation. The dynamic change and mechanism of granular catalysts in catalytic degradation of RhB were analyzed. In this study, the application range of attapulgite was widened. The prepared granular catalyst was cheap, stable and efficient, and could be used to treat refractory organic wastewater.

Highly efficient activation of peracetic acid by nano-CuO for carbamazepine degradation in wastewater: The significant role of H2O2 and evidence of acetylperoxy radical contribution

Peracetic acid (PAA)-based advanced oxidation processes (AOPs) has attracted increasing attentions towards contaminant degradation in the wastewater treatment. Herein, we report the efficient activation of PAA by nano-CuO (nCuO/PAA) to degrade carbamazepine (CBZ) for the first time. Rapid degradation of CBZ was observed in the nCuO/PAA system at neutral initial pH. A new scavenging experiment with Mn²⁺ as a specific scavenger was developed to distinguish the dominant role of CH₃C(O)OO^● for CBZ degradation in the nCuO/PAA process. The oxidation of CBZ by CH₃C(O)OO^● was verified to proceed via the electrons transfer, and the acute and chronic toxicity of the transformation products was significantly reduced. The efficient activation of PAA by nCuO was found to be realized through continuous conversion of Cu(II) to Cu(I), which was significantly boosted by co-existing H₂O₂. The nCuO/PAA process was slightly affected by the water matrices, and maintained high efficiency in real water samples. The findings obtained in this study provide new insights into the catalytic formation of CH₃C(O)OO^● from PAA and facilitate the development and application of PAA-based AOPs in wastewater treatment.

Ultraviolet-Light-emitting-diode activated monochloramine for the degradation of carbamazepine: Kinetics, mechanisms, by-product formation, and toxicity

Monochloramine (NH₂Cl) oxidant combined with a Ultraviolet (UV)-Light-emitting-diode (LED) light source forms a new advanced oxidation process (AOP), which can achieve high-efficiency degradation of carbamazepine (CBZ). The degradation of CBZ displayed pseudo-first-order reaction kinetics (R² > 0.98, k_CBZ = 0.0043 cm² mJ^-1 at pH 7). The degradation of CBZ was dependent on UV-LED wavelength, with maximum degradation efficiency observed at 265 nm since it was the lowest wavelength studied among UV-LEDs. Variation in pH across the range, which might be expected under normal environmental conditions (pH 6-8), and the presence of Cl^- had no significant effect on the degradation efficiency of CBZ, while the presence of HCO₃^- and natural organic matter (NOM) inhibited degradation. Electron paramagnetic resonance (EPR) experiments detected OH in the system. Probe compounds were used to distinguish the contribution of reactive chlorine species (RCS). It was proved that OH and Cl played major roles and OH was responsible for around 50% of the observed degradation of CBZ. Eight transformative products (TPs) in the degradation process of CBZ were identified, with a generally decreasing toxicity. The concentration of disinfection by-products (DBPs) formed during CBZ degradation was all within limits of WHO and China standard for drinking water. Although the concentration of nitrogen-containing DBPs (N-DBPs) was the lowest, N-DBPs were the main contributors to toxicity, and these would require more attention in practical applications. UV-LED/NH₂Cl AOP was identified as an effective way to degrade pharmaceutically active compounds.

A novel diagnostic method for distinguishing between Fe(IV) and •OH by using atrazine as a probe: Clarifying the nature of reactive intermediates formed by nitrilotriacetic acid assisted Fenton-like reaction

In this work, we found that the distribution of two specific atrazine (ATZ) oxidation products (desethyl-atrazine (DEA) and desisopropyl-atrazine (DIA)) was different in oxidation processes involving aqueous ferryl ion (Fe(IV)) species and ^•OH. Specifically, the molar ratio of produced DEA to DIA (i.e., [DEA]/[DIA]) increased from 7.5 to 13 with increasing pH from 3 to 6 when ATZ was oxidized by Fe(IV), while the treatment of ATZ by ^•OH led to the [DEA]/[DIA] value of 2 which was independent of pH. Moreover, ATZ showed high reactivity towards Fe(IV) over a wide pH range, especially at near-neutral pH, at which ATZ oxidation in Fe(II)/peroxydisulfate system was even much faster than another well-defined Fe(IV) scavenger, the sulfoxides. By using this approach, it was obtained that the [DEA]/[DIA] value remained at 2 during ATZ transformation by the nitrilotriacetic acid (NTA) assisted Fenton-like (Fe(III)/H₂O₂) system, which was independent of solution pH and reactants dosage. This result clarified that ^•OH was the primary reactive intermediate formed in the NTA assisted Fe(III)/H₂O₂ system. This study not only developed a novel sensitive diagnostic tool for distinguishing Fe(IV) from ^•OH, but also provided more credible evidence to the nature of reactive intermediate in a commonly controversial system.

Oxygen functionalized g-C3N4 strengthen Fe(III)/H2O2 system by accelerating Fe(III)/Fe(II) cycles under natural solar light: A mutual-promoting configuration

In response to the inherent restriction of low Fe(II) regeneration in the Fenton process, this study demonstrated a mutual-promoting configuration, where oxygen functionalized g-C₃N₄ (OCN) was applied in Fe(III)/H₂O₂ system to utilize mild natural solar light (SL) for persistent Fe(II) generation. The constructed OCN/Fe(III)/H₂O₂/SL system exhibited strong adaptability to various pollutants, and it well outperformed the g-C₃N₄ (GCN) modified system and the traditional Fenton system in pollutants degradation efficiency. Compared with GCN, OCN could significantly promote the Fe(II) generation under solar light (SL), leading to more efficient H₂O₂ activation. The characterization analyses revealed the larger surface area and enhanced charge separation of OCN, which were considered to take main responsibility for its enhanced photoactivity. The complexation of Fe(III) with the carboxyl groups of OCN also benefited the Fe(II) generation. ·OH was detected as the dominant radical responsible for metronidazole (MNZ) degradation, and its production in the OCN modified system was about twice that in the GCN modified system and the Fenton system. Moreover, the precipitation of FeO_x on the OCN surface benefited the charge separation of the OCN, so that the improved OCN enabled a slight enhancement of MNZ degradation in the reuse experiments. The intermediates of MNZ degradation were analyzed based on the results of LC-MS, which provided insight into MNZ degradation pathways. This work highlighted the concept of self-improving photocatalyst, the ingenious combination of photocatalysis and Fenton-like system formed a mutual-promoting situation where the OCN and the Fenton-like system could both be improved, which endowed the configuration great potential for green and economical oxidation in environmental remediation.

Application of Chelating Agents to Enhance Fenton Process in Soil Remediation: A Review

Persistent organic contaminants affecting soil and groundwater pose a significant threat to ecosystems and human health. Fenton oxidation is an efficient treatment for removing these pollutants in the aqueous phase at acidic pH. However, the in-situ application of this technology for soil remediation (where pHs around neutrality are required) presents important limitations, such as catalyst (iron) availability and oxidant (H2O2) stability. The addition of chelating agents (CAs), forming complexes with Fe and enabling Fenton reactions under these conditions, so-called chelate-modified Fenton process (MF), tries to overcome the challenges identified in conventional Fenton. Despite the growing interest in this technology, there is not yet a critical review compiling the information needed for its real application. The advantages and drawbacks of MF must be clarified, and the recent achievements should be shared with the scientific community. This review provides a general overview of the application of CAs to enhance the Fenton process for the remediation of soils polluted with the most common organic contaminants, especially for a deep understanding of the activation mechanisms and influential factors. The existing shortcomings and research needs have been highlighted. Finally, future research perspectives on the use of CAs in MF and recommendations have been provided.

New insights into the mechanisms of tartaric acid enhancing homogeneous and heterogeneous copper-catalyzed Fenton-like systems

The specific roles of tartaric acid (TA), as an eco-friendly ligand, in homogeneous and heterogeneous copper-catalyzed systems were systematically revealed and new mechanisms of TA enhancing the three Fenton-like processes were proposed to provide a theoretical significance in overcoming the deficiency of conventional Fenton processes. The results identified hydroxyl radical (•OH) as the main species responsible for the simultaneous decomposition of TA and metronidazole (MNZ) according to TOC removal. The ESR technique was used to detect superoxide radicals (•O₂^-), carbon-centered radical (•R) and hydrogen radical (•H) in the Cu²⁺/TA/H₂O₂ system, which contributed to the acceleration of the Cu²⁺/Cu⁺ redox cycle. The enhancing effect of TA on the homogeneous process was ascribed to the formation of a soluble complex with Cu²⁺, which favored the pH range extension, Cu⁺ oxidation, and radical generation. Moreover, the adsorption of TA on the catalysts surface promoted the consumption of H₂O₂, inducing •OH generation. The formed surface complex (≡Cu²⁺-TA) also accelerated the regeneration of ≡Cu⁺, which was confirmed by density functional theory (DFT) calculation and surface characterization analysis (SEM, XRD, and XPS). The possible degradation pathways of MNZ in TA-modified Fenton-like system were also clarified.

Efficient removal of bisphenol A with activation of peroxydisulfate via electrochemically assisted Fe(III)-nitrilotriacetic acid system under neutral condition

In this work, an innovative electrochemically assisted Fe(III)-nitrilotriacetic acid system for the activation of peroxydisulfate (electro/Fe(III)-NTA/PDS) was proposed for the removal of bisphenol A (BPA) at neutral pH with commercial graphite electrodes. The efficient BPA decay was mainly originated from the continuous activation of PDS by Fe(II) reduced from Fe(III)-NTA complexes at the cathode. Scavenger experiments and electron paramagnetic resonance (EPR) measurements confirmed that the removal of BPA occurred through graphite adsorption, direct electron transfer (DET) and radical oxidation. Sulfate and hydroxyl radicals were primarily responsible for the oxidation of BPA while graphite adsorption and DET played a minor role in BPA removal. The influence of Fe(III) concentration, PDS dosage, input current, NTA to Fe(III) molar ratio as well as coexisting inorganic anions (Cl^-, NO₃^-, H₂PO₄^- and HCO₃^-) on BPA elimination was explored. The BPA removal efficiency reached 93.5 % after 60 min reaction in the electro/Fe(III)-NTA/PDS system under the conditions of initial pH 7.0, 0.30 mM Fe(III), 0.15 mM NTA, 5 mM PDS and 5 mA constant current. Overall, this research provided a novel perspective and potential for remediation of organic wastewater using NTA in combination with electrochemistry in the homogeneous Fe(III)/persulfate system.

Effective degradation of aqueous carbamazepine on a novel blue-colored TiO2 nanotube arrays membrane filter anode

The effective electrochemical oxidation of aqueous carbamazepine (CBZ) using a novel blue-colored TiO₂ nanotube arrays (BC-TiO₂NTA) membrane filter anode was studied. The BC-TiO₂NTA was characterized using SEM, TEM, BET, mercury intrusion porosimetry, XPS, XRD, CV, and LSV. The BC-TiO₂NTA had reserved pore structure, formed mesopores, specific and electroactive surface areas of 2.01 m² g^-1 and 9.32 cm² cm^-2, respectively. The oxygen evolution potential was 2.61 V vs. SCE. CBZ could be degraded by OH, SO₄^- and O₂^- on BC-TiO₂NTA in accordance to pseudo-first-order kinetic, which was greatly enhanced in flow-through mode. The optimal kinetic rate constant of CBZ degradation of 0.403 min^-1 was achieved at 3 mA cm^-2, while energy consumption per order was 0.086 kW h m^-3. The mineralization efficiency and mineralization current efficiency were 50.8 % and 9.5 % at 180 min, respectively. The presence of Cl^- (0.3-3 mM) accelerated electrochemical degradation of CBZ, while NO₃^- (0.1-2 mM) inhibited the reaction. Based on density functional theory calculation and UPLC-Orbitrap-MS/MS measurement, we found that electrochemical degradation of CBZ was initialized by cleavage of -CONH₂ group and attack of OH on the olefinic double bond of the central heterocyclic ring.

Degradation of carbamazepine by MWCNTs-promoted generation of high-valent iron-oxo species in a mild system with O-bridged iron perfluorophthalocyanine dimers

Metal phthalocyanine has been extensively studied as a catalyst for degradation of carbamazepine (CBZ). However, metal phthalocyanine tends to undergo their own dimerization or polymerization, thereby reducing their activity points and affecting their catalytic properties. In this study, a catalytic system consisting of O-bridged iron perfluorophthalocyanine dimers (FePcF₁₆-O-FePcF₁₆), multi-walled carbon nanotubes (MWCNTs) and H₂O₂ was proposed. The results showed MWCNTs loaded with FePcF₁₆-O-FePcF₁₆ can achieve excellent degradation of CBZ with smaller dosages of FePcF₁₆-O-FePcF₁₆ and H₂O₂, and milder reaction temperatures. In addition, the results of experiments revealed the reaction mechanism of non-hydroxyl radicals. The highly oxidized high-valent iron-oxo (Fe(IV)=O) species was the main reactive species in the FePcF₁₆-O-FePcF₁₆/MWCNTs/H₂O₂ system. It is noteworthy that MWCNTs can improve the dispersion of FePcF₁₆-O-FePcF₁₆, contributing to the production of highly oxidized Fe(IV)=O. Then, the pathway of CBZ oxidative degradation was speculated, and the study results also provide new ideas for metal phthalocyanine-loaded carbon materials to degrade emerging pollutants.

TBAOH assisted synthesis of ultrathin BiOCl nanosheets with enhanced charge separation efficiency for superior photocatalytic activity in carbamazepine degradation

Ultrathin nanosheets show great promise in photocatalytic technology, due to short path for electron transfer and large surface for reactant adsorption. However, there is no report that ultrathin nanosheets photocatalyst has been used to degrade carbamazepine (CBZ) in aquatic environment. This paper aimed at fabricating ultrathin BiOCl nanosheets to improve the photocatalytic degradation efficiency of CBZ. Herein, tetrabutylammonium hydroxide (TBAOH) was firstly applied to synthesize ultrathin BiOCl nanosheets (BiOCl-T) by a simple hydrolysis route in water at ambient conditions. TBAOH could act as a structure-directing agent, determining the structure and property of BiOCl-T. Assisted by TBAOH, BiOCl-T exhibited ultrathin nanosheets structure with preferential exposed (1 1 0) face. PL, photocurrent density, and EIS Nyquist plots demonstrated the enhanced charge separation efficiency in BiOCl-T. Furthermore, BiOCl-T displayed large pore size and specific surface area. Thus, BiOCl-T showed high photocatalytic activity toward CBZ degradation under simulated sunlight. Upon 30 min irradiation, the degradation efficiency of CBZ was 91.1% with fast degradation kinetics, which is 2.46 times higher than ordinary BiOCl. Active species of h⁺, O₂^-, and OH contributed to CBZ degradation reaction. The obtained result provides a novel viewpoint to fabricate ultrathin nanosheets and broadening their application in the degradation of recalcitrant pharmaceuticals.

A highly efficient flow-through electro-Fenton system enhanced with nitrilotriacetic acid for phenol removal at neutral pH

Low pH requirement is one of the biggest limitations of the application of traditional Fenton and electro-Fenton (EF) process because Fe^II/Fe^III would precipitate at high pH. In this study, a flow-through EF system operated in batch recirculation mode was constructed. Nitrilotriacetic acid (NTA) was used as a chelating agent in the EF system (NTA/EF) to keep iron soluble at high pH values, producing OH by reaction of H₂O₂ generated in situ with Fe^IINTA that obtained by the reduction of Fe^IIINTA at the cathode. This flow-through NTA/EF system accelerated the mass transfer of target molecules to the electrode surface and showed high efficiency for phenol removal at pH 5-8 with rate constants (k) at around 0.26 min^-1, higher than that of the batch test (k = 0.15 min^-1) and EF process without NTA (k = 0.16 min^-1). The influences of aeration rate, current, flow rate, Fe dose, the ratio of NTA to Fe, pH, and initial phenol concentration on the phenol removal were investigated. The system could be used for at least 3 times for phenol removal without obvious efficiency decline. The flow-through NTA/EF system is promising for the removal of organic contaminants in a wide pH range.

Efficient degradation of pharmaceutical micropollutants in water and wastewater by FeIII-NTA-catalyzed neutral photo-Fenton process

Ferric-nitrilotriacetate complex (Fe^III-NTA) has been adopted to catalyze the photo-Fenton degradation of emerging pharmaceutical micropollutants in water and wastewater at neutral pH. The generation of hydroxyl radicals (HO) in UVA/Fe^III-NTA/H₂O₂ was identified by using electron spin resonance (ESR) trapping technique. The effects of critical parameters (e.g., NTA:Fe^III molar ratio, Fe^III-NTA and H₂O₂ dosages) on the steady-state HO concentrations were studied in terms of the degradation of carbamazepine (CBZ, as a model compound) in Milli-Q water. In addition, the degradation of pharmaceuticals mixtures (including CBZ, crotamiton (CRMT) and ibuprofen (IBP)) in wastewater effluents from a biological aerated filter (BAF) by UVA/Fe^III-NTA/H₂O₂ was studied in continuous-flow mode. The results showed that the efficacies of Fe^III-NTA in catalyzing photo-Fenton degradation of pharmaceuticals in wastewater effluents were comparable to those obtained by Fe^III-ethylenediamine-N,N'-disuccinic acid (Fe^III-EDDS), and far exceeded other Fe^III-L complex (e.g., citric acid, malonic acid, oxalic acid and tartaric acid). More than 92% degradation efficiencies of CBZ, CRMT and IBP were obtained in continuous-flow mode under the given conditions of 0.178 mM Fe^III-NTA (1:1), 4.54 mM H₂O₂, UVA intensity 4.05 mW cm^-2, hydraulic retention time (HRT) 2 h, influent pH 7.6 (±0.2) and temperature 20 °C. The results presented herein suggest that Fe^III-NTA-catalyzed neutral photo-Fenton reaction can be an alternative tertiary process for the treatment of pharmaceutical micropollutants in secondary wastewater effluents.

Insight into the generation of toxic products during chloramination of carbamazepine: Kinetics, transformation pathway and toxicity

As a widely used antiepileptic drug, carbamazepine (CBZ) has been frequently detected in aquatic environments, even in drinking water. Chloramine is a widely used alternative disinfectant due to its low-level formation of regulated disinfection byproducts (DBPs). However, there is previous evidence linking product mixtures of chloraminated CBZ to stronger DNA damage effects than those caused by CBZ itself. The present study further investigated the reaction rate, transformation mechanism and multi-endpoint toxicity of transformation products (TPs) of CBZ treated with NH₂Cl under different pH conditions. The results showed that the reaction between CBZ and NH₂Cl at pH 8.5, where NH₂Cl is stable, is a second-order reaction with a rate of 4.2 M^-1 h^-1. Compared to both alkaline and acidic conditions, CBZ was quickly degraded at pH 7. This indicated that HOCl produced from NH₂Cl hydrolysis is more effective in degrading CBZ than NH₂Cl and NHCl₂. Furthermore, the concentration variation of four TPs formed during the chloramination of CBZ under different pH conditions was investigate by quantitative analysis, and the transformation pathway from CBZ to 9(10H)-acridone was confirmed. Three of the detected TPs showed cytotoxicity, DNA damage effects or chromosome damage effects. Acridine and 9(10H)-acridone, which accumulated with increasing time, showed higher cytotoxic or genotoxic effects than CBZ itself. In addition, a similar transformation mechanism was observed in real ambient water during simulated chloramination with a low level of CBZ. These results suggested that despite the chloramination of CBZ being slower than chlorination, TPs with higher cytotoxicity or genotoxicity may lead to greater toxic risks.

A critical review of the application of chelating agents to enable Fenton and Fenton-like reactions at high pH values

To overcome the drawback of low pH requirement of the classical Fenton reaction, researchers have applied chelating agents to form complexes with Fe and enable Fenton reaction at high pHs, which is reviewed in this article. The chelating agents reviewed include humic substances, polycarboxylates, aminopolycarboxylic acids, and polyoxometalates. Ligands affect the reactivity of Fe-complexes by changing their redox potentials, promoting their reaction with H₂O₂, and competing with target contaminants for the oxidative species. Fe(III)-complexes are reduced to Fe(II)-complexes by O₂^- not H₂O₂, as indicated by their redox potentials. The stability constants of Fe-complexes increase with increasing pK_a values of the corresponding ligands and also with increasing charge density of the metal ions. A higher stability constant of Fe(III)-complex indicates higher reaction rate of corresponding Fe(II)-complex with H₂O₂ and lower reduction rate of Fe(III)-complex to Fe(II)-complex. OH, O₂^-, and ferryl species were reported to be the reactive species on the contaminant removal in the chelate-modified Fenton process. The generation of these species depends on the chelating agents and reaction conditions. The process is very efficient in degrading contaminants, indicating a potential treatment approach for the pollution remediation at natural pH.

The first-line antiepileptic drug carbamazepine: Reaction with biologically relevant free radicals

Carbamazepine (CBZ) is one of the most widely used antiepileptic drugs by both adults and children. Despite its widespread use, CBZ is associated with central nervous system toxicity and severe hypersensitivity reactions, which raise concerns about its chronic use. While the precise mechanisms of CBZ-induced adverse events are still unclear, metabolic activation to the epoxide (CBZ-EP) has been thought to play a significant role. This work reports first-hand evidence that CBZ reacts readily with biologically relevant thiyl radicals with no need for bioactivation. Using liquid chromatography coupled with high resolution mass spectrometry, multiple products from direct reaction of CBZ with glutathione (GSH) and N-acetyl-L-cysteine (NAC) were unequivocally identified, including the same product obtained upon ring-opening of CBZ-EP. The product profile is complex and consistent with radical-mediated mechanisms. Importantly, side products and adducts compatible with this non-enzymatic pathway were identified in liver extracts from CBZ-treated Wistar rats. The reaction of CBZ with GSH and NAC is more extensive in the presence of oxygen. Taking into consideration that GSH conjugation is, in general, a detoxification pathway, these results suggest that under hyperoxia/oxidative stress conditions the bioavailability of the parent drug may be compromised. Additionally, this non-enzymatic process can be anticipated to play, at least in part, a role in the onset of CBZ-induced adverse reactions due to the concomitant generation of reactive oxygen species. Therefore, the search for causal relationships between the formation of non-enzymatically-driven CBZ products and the occurrence of CBZ-induced adverse events in human patients merits further research, aiming the translation of basic mechanistic findings into a clinical context that may ultimately lead to a safer CBZ prescription.

Degradation and Mineralization of Carbamazepine Using an Electro-Fenton Reaction Catalyzed by Magnetite Nanoparticles Fixed on an Electrocatalytic Carbon Fiber Textile Cathode

Pharmaceutical wastes are considered to be important pollutants even at low concentrations. In this regard, carbamazepine has received significant attention due to its negative effect on both ecosystem and human health. However, the need for acidic conditions severely hinders the use of conventional Fenton reagent reactions for the control and elimination of carbamazepine in wastewater effluents and drinking water influents. Herein, we report of the synthesis and use of flexible bifunctional nanoelectrocatalytic textile materials, Fe₃O₄-NP@CNF, for the effective degradation and complete mineralization of carbamazepine in water. The nonwoven porous structure of the composite binder-free Fe₃O₄-NP@CNF textile is used to generate H₂O₂ on the carbon nanofiber (CNF) substrate by O₂ reduction. In addition, ·OH radical is generated on the surface of the bonded Fe₃O₄ nanoparticles (NPs) at low applied potentials (-0.345 V). The Fe₃O₄-NPs are covalently bonded to the CNF textile support with a high degree of dispersion throughout the fiber matrix. The dispersion of the nanosized catalysts results in a higher catalytic reactivity than existing electro-Fenton systems. For example, the newly synthesized Fe₃O₄-NPs system uses an Fe loading that is 2 orders of magnitude less than existing electro-Fenton systems, coupled with a current efficiency that is higher than electrolysis using a boron-doped diamond electrode. Our test results show that this process can remove carbamazepine with high pseudo-first-order rate constants (e.g., 6.85 h^-1) and minimal energy consumption (0.239 kW·h/g carbamazepine). This combination leads to an efficient and sustainable electro-Fenton process.

Degradation mechanisms of carbamazepine by δ-MnO2: Role of protonation of degradation intermediates

Carbamazepine (CBZ), a widely used antiepileptic drug, is refractory to biological wastewater treatment. Rapid removal of CBZ is possible using synthetic manganese oxide (δ-MnO₂) but the removal mechanisms require further investigation. In this study, CBZ degradation by δ-MnO₂ was carried out at different pH to further explore the degradation mechanisms. Results show that CBZ degradation by δ-MnO₂ was highly pH dependent, and rapid degradation occurred when pH <2.8. Based on the density functional theory calculations, increasing [H⁺] not only increased the reactivity of δ-MnO₂, but also enhanced the secondary reactions of the intermediates. During the degradation process, protonation of CBZ degradation intermediates, instead of CBZ, played an important role. The overall kinetics of CBZ degradation was then described by the retarded first-order model. The initial rate (r_init) in the model between pH 2.0 and 6.2 was determined to be r_init = (2.41 ± 0.51) × 10^-3[CBZ]^1.21[MnO₂]^1.07[H⁺]^1.41. This is the first report revealing that protonation of intermediates from CBZ degradation can improve the CBZ oxidation by δ-MnO2. The pathways of CBZ degradation by δ-MnO₂ were also proposed. The results of this study provide a new insight into the processing mechanism.

Improved biodegradability of hardly-decomposable wastewaters from petrochemical industry through photo-Fenton method and determination of optimum operational conditions by response surface methodology

BACKGROUND

Petrochemical wastewaters are highly polluting due to having various destructive materials such as aromatic hydrocarbons and heavy metal ions. Therefore, they need to be treated before disposal to the environment. However, due to low biodegradability, applying common treatment methods such as activated sludge is not feasible for these wastewaters.

METHODS

Photo-Fenton is an advanced oxidation process which was applied to promote the biodegradability of hardly-decomposable petrochemical wastewaters. The wastewater samples were provided by Maroon and Karoon petrochemical plants, located in Mahshahr, Iran. To design the experiments and analyze the experimental results, response surface method with four variables (input COD and TDS concentrations and injected a dosage of H2O2 and Fe2+) and four fixed parameters (temperature, pH, retention time, and UV power) were used.

RESULTS

The ranges of input COD, H2O2, Fe2+ and TDS were 1000 to 2500 mg L- 1, 1000 to 4000 mg L- 1, 500 to 3000 mg L- 1, and 4500 to 11,500 mg L- 1, respectively. Average input BOD5/COD ratio was 0.09. These ranges and values were determined according to the quality of the raw wastewater and experimental design. Output BOD5/COD ratio was varying between 0.3 and 0.6, which declined with an increase of input COD. The results showed that the biodegradability of the industrial wastewater was promoted upon application of higher H2O2 and Fe2+ concentrations. Meanwhile, TDS concentration had no significant effect on biodegradability of this wastewater. The following optimum conditions were resulted by evaluating the maximum efficiency of the reactor in enhancing the biodegradability of the wastewater: 1000 mg L- 1 input COD, 2668 mg L- 1 H2O2, 1655 mg L- 1 Fe2+, 8000 mg L- 1 TDS, 0.6 output BOD5/COD, 852 mg L- 1 output BOD5 and 939 mg L- 1 output COD.

CONCLUSION

Photo-Fenton method is highly efficient for increasing the biodegradability of petrochemical wastewaters before applying biological wastewater treatment.

Enhanced Fe(III)-mediated Fenton oxidation of atrazine in the presence of functionalized multi-walled carbon nanotubes

In this study we reported that the presence of functionalized multi-walled carbon nanotubes (FCNT-H) would greatly enhance the degradation of atrazine (ATZ), a model contaminant, in the Fe(III)-mediated Fenton-like system. Efficient ATZ degradation (>90%) was achieved within 30 min in the presence of 20 mg.L^-1 FCNT-H, 2.0 mg.L^-1 Fe(III), and 170 mg.L^-1 H₂O₂, whereas negligible ATZ degradation occurred in FCNT-H free system. The structure and surface chemistry of FCNT-H and other CNTs were well characterized. The formed active species were determined based on ESR analysis, and the mass balance of Fe species during the reaction was monitored. In particular, a new method based on ferrozine complexation was proposed to track the formed Fe(II). The results indicated that ATZ was mainly degraded by the generated hydroxyl radical (HO·), and Fe(III)/Fe(II) cycling was still the rate-limiting step. Besides a small fraction of Fe(III) reduced by FCNT-H, a new pathway was revealed for fast reduction of most Fe(III), i.e., reaction of FCNT-H-Fe(III) complexes with H₂O₂. Comparison of different CNTs-mediated Fe(III)/H₂O₂ systems indicated that such enhanced effect of CNTs mainly resulted from the surface carboxyl group instead of hydroxyl and carbonyl group. Combined with X-ray photoelectron spectroscopy (XPS) analysis, the electron density migration from Fe(III) to FCNT-H possibly resulted in the fast reduction of FCNT-H-Fe(III) complexes by H₂O₂. This study enables better understanding the enhanced Fe(III)-mediated Fenton-like reaction in the presence of MWCNTs and thus, will shed new light on how to develop more efficient similar Fenton systems via Fe(III) complexation.

TCE degradation in groundwater by chelators-assisted Fenton-like reaction of magnetite: Sand columns demonstration

Trichloroethylene (TCE) degradation in sand columns has been investigated to evaluate the potential of chelates-enhanced Fenton-like reaction with magnetite as iron source for in situ treatment of TCE-contaminated groundwater. The results showed that successful degradation of TCE in sand columns was obtained by nitrilotriacetic acid (NTA)-assisted Fenton-like reaction of magnetite. Addition of ethylenediaminedisuccinic acid (EDDS) resulted in an inhibitory effect on TCE degradation in sand columns. Similar to EDDS, addition of ethylenediaminetetraacetic acid (EDTA) also led to an inhibition of TCE degradation in sand column with small content of magnetite (0.5 w.t.%), but enhanced TCE degradation in sand column with high content of magnetite (7.0 w.t.%). Additionally, the presence of NTA, EDDS and EDTA greatly decreased H₂O₂ uptake in sand columns due to the competition between chelates and H₂O₂ for surface sites on magnetite (and sand). Furthermore, the presented results show that magnetite in sand columns remained stable in a long period operation of 230 days without significant loss of performance in terms of TCE degradation and H₂O₂ uptake. Moreover, it was found that TCE was degraded mainly to formic acid and chloride ion, and the formation of chlorinated organic intermediates was minimal by this process.

Aquatic photochemistry of sulfamethazine: multivariate effects of main water constituents and mechanisms

The ubiquity of sulfonamides (SAs) in natural waters requires insight into their environmental fate for ecological risk assessment. Extensive studies focused on the effect of univariate water constituents on the photochemical fate of SAs, yet the multivariate effects of water constituents in environmentally relevant concentrations on SA photodegradation are poorly understood. Here, response surface methodology was employed to explore the integrative effects of main water constituents (dissolved organic matter (DOM), NO₃^-, HCO₃^-, Cu²⁺) on the photodegradation of a representative SA (sulfamethazine). Results showed that besides single factors, interaction of factors also significantly impacted the photodegradation. Radical scavenging experiments indicated that triplet-excited DOM (³DOM*) was responsible for the enhancing effect of DOM on the photodegradation. Additionally, DOM may also quench the ³DOM*-mediated oxidation intermediate of sulfamethazine causing the inhibiting effect of DOM-DOM interaction. We also found that HCO₃^- was oxidized by triplet-excited sulfamethazine producing CO₃˙^-, and the high reactivity of CO₃˙^- with sulfamethazine (second-order rate constant 2.2 × 10⁸ M^-1 s^-1) determined by laser flash photolysis revealed the enhancing photodegradation mechanism of HCO₃^-. This study is among the first attempts to probe the photodegradation of SAs considering the integrative effects of water constituents, which is important in accurate ecological risk assessment of organic pollutants in the aquatic environment.

Application of RuO2/Ni foam electrodes for remediation of ibuprofen in soil matrix-the effect of electrokinetic parameters

Pharmaceuticals and personal care products (PPCPs) are an extraordinary and diverse group of chemicals used in veterinary medicine, agriculture, and for human health and cosmetics care. They are considered emerging contaminants and have raised great concern in recent years. Among the PPCPs, ibuprofen (IBP) is one of the most known non-steroidal anti-inflammatory drugs, which has been found at a high concentration in irrigation water in the USA and showed harmful effect for organisms. This study examined IBP degradation performance by an electrokinetic process coupled with 24-96 cm² of RuO₂/Ni foam (RN) electrodes applied 1-3 V cm^-1 potential gradient for 5-9 days. The electroosmosis permeabilities (k _e) and the treatment efficiency of IBP increased from 1.5 × 10^-4 to 1.8 × 10^-4 cm² V^-1 s^-1 and from 65.4 to 78.4%, respectively, as the potential gradient increased from 1 to 3 V cm^-1. The k _e values also increased with electrode area, but it was much less insignificant than that of the potential gradient. Prolonging the treatment time and increasing the electrode area only enhanced the IBP remediation efficiency by a trivial amount. The degradation mechanism was more critical for IBP remediation than was the electrokinetic (EK) removal mechanism. A cost analysis revealed that processing fluid accounted for 84.1-87.6% of the operation cost. The electrode characteristics and the treatment mechanism are also discussed. This study confirmed that the IBP-contaminated soil was successfully remediated by electrokinetic process coupled with RN electrodes.

CTAB and SDS assisted facile fabrication of SnO2 nanoparticles for effective degradation of carbamazepine from aqueous phase: A systematic and comparative study of their degradation performance

In the present study, SnO₂ nanoparticles were successfully synthesized by chemical precipitation method using anhydrous aspartic acid and surfactant at two annealing temperatures, 300 °C and 600 °C. The effect of surfactants cationic CTAB and anionic SDS on the synthesized SnO₂ nanoparticles (NPs) were studied elaborately. In this article, for the first time, SnO₂ NPs were employed as an excellent photocatalyst in the degradation of carbamazepine (CBZ), a popular antiepileptic drug which is most commonly detected pharmaceutically active compounds (PhACs) in municipal wastewater under UV-C light irradiation. Comparative studies between the photocatalytic activity of SnO₂ NPs synthesized with CTAB (SC1) and SDS (SS1) on the degradation of the CBZ drug were investigated. Parameters like the effect of catalytic loading, initial concentration, pH and contact time were also studied for optimization. The results indicate that SC1 is a better photocatalyst with rate constant 6.66 × 10^-2 min^-1 than SS1 with rate 5.7 × 10^-2 min^-1. To determine the transformation product formed on the photodegradation LCMS (ESI) analysis was done. The synthesized SnO₂ NPs can be recycled up to 8th cycles without any notable alteration in its photocatalytic activity.

Chlorination, chloramination and ozonation of carbamazepine enhance cytotoxicity and genotoxicity: Multi-endpoint evaluation and identification of its genotoxic transformation products

Investigations have focused on the removal and transformation of pharmaceuticals during drinking water and wastewater treatment. In the present study, we investigated for the first time the changes of the cytotoxicity and genotoxicity based on different modes of action (MoAs) during chlorination, chloramination and ozonation processes of the anti-epileptic drug carbamazepine (CBZ). The results illustrated that ozonation enhanced the cytotoxicity and the chromosome damage effects on CHO-K1 cells detected by cytokinesis-block micronucleus (CBMN) assay based on high-content screening technique, though ozonation showed the highest removal efficiency for CBZ. Non-target chemical analysis followed by quantitative structure-activity relationship (QSAR) analysis for the transformation products (TPs) suggested that the chromosomal damage effects could probably be attributed to 1-(2-benzaldehyde)-4-hydro-(1H,3H)-quinazoline-2-one (BQM) and 1-(2-benzaldehyde)-(1H,3H)-quinazoline-2,4-dione (BQD). In contrast to CBZ itself and the ozonated sample, the chlorinated and chloraminated samples caused DNA damage effects in SOS/umu test. Acridine, 9 (10) H-acridone, chlorinated 9 (10) H-acridone and TP-237, which were first identified in the chlorination or chloramination processes, were predicted to be the DNA damaging agents. These genotoxic TPs were primarily generated from the oxidation of seven-membered N-heterocyclic in CBZ. This study highlighted the potential adverse effects generated in ozonation process and the oxidation of N-heterocyclic containing pollutants.

Rapid degradation, mineralization and detoxification of pharmaceutically active compounds in aqueous solution during pulsed corona discharge treatment

In the present study, plasma generated by pulsed corona discharge was used for the degradation of diclofenac, carbamazepine and ciprofloxacin. Pollutants in aqueous solution were plasma treated under two categories: single and mixed pollutant condition. Mixed pollutant condition showed an antagonistic behaviour and thus the degradation time was higher for mixed condition compared to the single condition. At different voltage and frequencies, degradation efficiency followed the trend, diclofenac>carbamazepine>ciprofloxacin. Acidic pH slightly favoured the degradation process whereas in presence of radical scavengers (HCO₃^-, CO₃^2- and humic acid) the degradation yield was significantly decreased. With an input power of 101.5 W, complete degradation was achieved within 4-16 min of plasma treatment for pharmaceutical's concentrations of 1-10 mg/L. As the pollutant concentration increased from 1 to 10 mg/L, the pseudo first order rate constant decreased, while yield increased. Complete degradation pathway of diclofenac, carbamazepine and ciprofloxacin in plasma treatment process are proposed by identifying the intermediates using LC-MS analysis. TOC analysis confirmed 80% mineralization within 10 min of plasma treatment for higher pharmaceutical's concentrations of 10 mg/L. The microalgae ecotoxicity study and disc diffusion test confirmed the complete detoxification of PACs that took place after 6 min of plasma treatment.

Monitoring pharmaceuticals and personal care products in reservoir water used for drinking water supply

In this work, the presence of selected emerging contaminants has been investigated in two reservoirs, La Fe (LF) and Rio Grande (RG), which supply water to two drinking water treatment plants (DWTPs) of Medellin, one of the most populated cities of Colombia. An analytical method based on solid-phase extraction (SPE) of the sample followed by measurement by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) was developed and validated for this purpose. Five monitoring campaigns were performed in each reservoir, collecting samples from 7 sites (LF) and 10 sites (RG) at 3 different depths of the water column. In addition, water samples entering in the DWTPs and treated water samples from these plans were also analysed for the selected compounds. Data from this work showed that parabens, UV filters and the pharmaceutical ibuprofen were commonly present in most of the reservoir samples. Thus, methyl paraben was detected in around 90% of the samples collected, while ibuprofen was found in around 60% of the samples. Water samples feeding the DWTPs also contained these two compounds, as well as benzophenone at low concentrations, which was in general agreement with the results from the reservoir samples. After treatment in the DWTPs, these three compounds were still present in the samples although at low concentrations (<40 ng/L), which evidenced that they were not completely removed after the conventional treatment applied. The potential effects of the presence of these compounds at the ppt levels in drinking water are still unknown. Further research is needed to evaluate the effect of chronic exposure to these compounds via consumption of drinking water.

Magnetic cobalt ferrite composite as an efficient catalyst for photocatalytic oxidation of carbamazepine

A magnetic spinel cobalt ferrite nanoparticle composite (CFO) was prepared via an ultrasonication-assisted co-precipitation method. The morphological structure and surface composition of CFO before and after reaction were investigated by using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray, and Fourier transform infrared spectroscopy, indicating the consumption of iron oxide during photodegradation. X-ray photoelectron spectroscopy and vibrating sample magnetometry confirm the preparation of the ferrite nanoparticle composite and its magnetic properties. The prepared CFO was then used for the photocatalytic degradation of carbamazepine (CBZ) as an example of pharmaceuticals and personal care products (PPCPs) from aqueous solution. The effects of the nanocomposite dosage, contact time, and solution pH on the photodegradation process were investigated. More than 96% of the CBZ was degraded within 100 min at 0.2 g·L^-1 CFO in the presence of UV light. The reactive species for CBZ degradation in the CFO/UV system was identified as hydroxyl radicals by the methanol scavenging method. Combined with the detection of leached iron ions during the process, the CBZ degradation mechanism can be presumed to be heterogeneous and homogeneous photocatalytic degradation in the CFO/UV system. Furthermore, iminostilbene and acridine were detected as intermediate products by GC-MS.

Self-floating graphitic carbon nitride/zinc phthalocyanine nanofibers for photocatalytic degradation of contaminants

The effective elimination of micropollutants by an environmentally friendly method has received extensive attention recently. In this study, a photocatalyst based on polyacrylonitrile (PAN)-supported graphitic carbon nitride coupled with zinc phthalocyanine nanofibers (g-C3N4/ZnTcPc/PAN nanofibers) was successfully prepared, where g-C3N4/ZnTcPc was introduced as the catalytic entity and the PAN nanofibers were employed as support to overcome the defects of easy aggregation and difficult recycling. Herein, rhodamine B (RhB), 4-chlorophenol and carbamazepine (CBZ) were selected as the model pollutants. Compared with the typical hydroxyl radical-dominated catalytic system, g-C3N4/ZnTcPc/PAN nanofibers displayed the targeted adsorption and degradation of contaminants under visible light or solar irradiation in the presence of high additive concentrations. According to the results of the radical scavenging techniques and the electron paramagnetic resonance technology, the degradation of target substrates was achieved by the attack of active species, including photogenerated hole, singlet oxygen, superoxide radicals and hydroxyl radicals. Based on the results of ultra-performance liquid chromatography and mass spectrometry, the role of free radicals on the photocatalytic degradation intermediates was identified and the final photocatalytic degradation products of both RhB and CBZ were some biodegradable small molecules.

Mn(2+)-mediated homogeneous Fenton-like reaction of Fe(III)-NTA complex for efficient degradation of organic contaminants under neutral conditions

In this work, we report a novel Mn(2+)-mediated Fenton-like process based on Fe(III)-NTA complex that is super-efficient at circumneutral pH range. Kinetics experiments showed that the presence of Mn(2+) significantly enhanced the effectiveness of Fe(III)-NTA complex catalyzed Fenton-like reaction. The degradation rate constant of crotamiton (CRMT), a model compound, by the Fe(III)- NTA_Mn(2+) Fenton-like process was at least 1.6 orders of magnitude larger than that in the absence of Mn(2+). Other metal ions such as Ca(2+), Mg(2+), Co(2+) and Cu(2+) had no impacts or little inhibitory effect on the Fe(III)-NTA complex catalyzed Fenton-like reaction. The generation of hydroxyl radical (HO) and superoxide radical anion (O2(-)) in the Fe(III)-NTA_Mn(2+) Fenton-like process were suggested by radicals scavenging experiments. The degradation efficiency of CRMT was inhibited significantly (approximately 92%) by the addition of HO scavenger 2-propanol, while the addition of O2(-) scavenger chloroform resulted in 68% inhibition. Moreover, the results showed that other chelating agents such as EDTA- and s,s-EDDS-Fe(III) catalyzed Fenton-like reactions were also enhanced significantly by the presence of Mn(2+). The mechanism involves an enhanced generation of O2(-) from the reactions of Mn(2+)-chelates with H2O2, indirectly promoting the generation of HO by accelerating the reduction rate of Fe(III)-chelates to Fe(II)- chelates.

Synergistic effect between UV and chlorine (UV/chlorine) on the degradation of carbamazepine: Influence factors and radical species

For successful wastewater reclamation, advanced oxidation processes have attracted attention for elimination of emerging contaminants. In this study, the synergistic treatment with UV irradiation and chlorine (UV/chlorine) was used to degrade carbamazepine (CBZ). Neither UV irradiation alone nor chlorination alone could efficiently degraded CBZ. UV/chlorine oxidation showed a significant synergistic effect on CBZ degradation through generation of radical species (OH and Cl), and this process could be well depicted by pseudo first order kinetic. The degradation rate constants (kobs,CBZ) of CBZ increased linearly with increasing UV irradiance and chlorine dosage. The degradation of CBZ by UV/chlorine in acidic solutions was more efficient than that in basic solutions mainly due to the effect of pH on the dissociation of HOCl and OCl(-) and then on the quantum yields and radical species quenching of UV/chlorine. When pH was increased from 5.5 to 9.5, the rate constants of degradation of CBZ by OH decreased from 0.65 to 0.14 min(-1) and that by Cl decreased from 0.40 to 0.11 min(-1). The rate constant for the reaction between Cl and CBZ was 5.6 ± 1.6 × 10(10) M(-1) s(-1). Anions of HCO3(-) (1-50 mM) showed moderate inhibition of CBZ degradation by UV/chlorine, while Cl(-) did not. UV/chlorine could efficiently degrade CBZ in wastewater treatment plant effluent, although the degradation was inhibited by about 30% compared with that in ultrapure water with chlorine dosage of 0.14-0.56 mM. Nine main oxidation products of the CBZ degradation by UV/chlorine were identified using the HPLC-QToF MS/MS. Initial oxidation products arose from hydroxylation, carboxylation and hydrogen atom abstraction of CBZ by OH and Cl, and were then further oxidized to generate acylamino cleavage and decarboxylation products of acridine and acridione.

Enhanced degradation of trichloroethene by calcium peroxide activated with Fe(III) in the presence of citric acid

Trichloroethene (TCE) degradation by Fe(III)-activated calcium peroxide (CP) in the presence of citric acid (CA) in aqueous solution was investigated. The results demonstrated that the presence of CA enhanced TCE degradation significantly by increasing the concentration of soluble Fe(III) and promoting H₂O₂ generation. The generation of HO• and O₂^-• in both the CP/Fe(III) and CP/Fe(III)/CA systems was confirmed with chemical probes. The results of radical scavenging tests showed that TCE degradation was due predominantly o direct oxidation by HO•, while O₂^-• strengthened the generation of HO• by promoting Fe(III) transformation in the CP/Fe(III)/CA system. Acidic pH conditions were favorable for TCE degradation, and the TCE degradation rate decreased with increasing pH. The presence of Cl^-, HCO₃^-, and humic acid (HA) inhibited TCE degradation to different extents for the CP/Fe(III)/CA system. Analysis of Cl^- production suggested that TCE degradation in the CP/Fe(III)/CA system occurred through a dechlorination process. In summary, this study provided detailed information for the application of CA-enhanced Fe(III)-activated calcium peroxide for treating TCE contaminated groundwater.