Enhanced degradation of enoxacin using ferrihydrite-catalyzed heterogeneous photo-Fenton process

The ferrihydrite-catalyzed heterogeneous photo-Fenton reaction shows great potential for environmental remediation of fluoroquinolone (FQs) antibiotics. The degradation of enoxacin, a model of FQ antibiotics, was studied by a batch experiment and theoretical calculation. The results revealed that the degradation efficiency of enoxacin reached 89.7% at pH 3. The hydroxyl radical (∙OH) had a significant impact on the degradation process, with a cumulative concentration of 43.9 μmol L-1 at pH 3. Photogenerated holes and electrons participated in the generation of ∙OH. Eleven degradation products of enoxacin were identified, with the main degradation pathways being defluorination, quinolone ring and piperazine ring cleavage and oxidation. These findings indicate that the ferrihydrite-catalyzed photo-Fenton process is a valid way for treating water contaminated with FQ antibiotics.

Z-scheme Fe@Fe2O3/BiOBr heterojunction with efficient carrier separation for enhanced heterogeneous photo-Fenton activity of tetracycline degradation: Fe2+ regeneration, mechanism insight and toxicity evaluation

The recombination of photogenerated carrier leads to inefficient Fe2+ regeneration, which limits the extensive application of heterogeneous photo-Fenton. Here, a novel Fe@Fe2O3/BiOBr catalyst with Z-scheme heterojunction structure is designed, and the establishment of the Z-scheme heterojunction facilitates the separation and transfer of photogenerated carrier and maintains the superior redox capability of the system. As-prepared Fe@Fe2O3/BiOBr catalyst exhibits outstanding catalytic performance and stability, especially for the optimum composite FFB-3, its degradation efficiency of tetracycline (TC) achieves 98.22% and the mineralization degree reaches 59.48% within 90 min under natural pH. The preeminent catalytic efficiency benefited from the synergistic of heterogeneous photo-Fenton and Z-scheme carriers transfer mechanism, where Fe2+ regeneration was achieved by photogenerated electrons, and increased hydroxyl radicals were produced with the participation of H2O2 in-situ generated. The results of free-radical scavenging experiment and ESR illustrated that •OH, •O2-, 1O2 and h+ were active species participating in TC degradation. Furthermore, the TC degradation paths were proposed according to LC-MS, and the toxicity evaluation result showed that the toxicity of TC solutions was markedly decreased after degradation. This study provides an innovative strategy for heterogeneous photo-Fenton degradation of antibiotic contaminations by constructing Z-scheme heterojunctions.

Synergistic photogeneration of reactive oxygen species by Fe species self-deposited on resorcinol-formaldehyde towards the degradation of phenols under visible light

In this study, a heterogeneous photo-Fenton catalyst of Fe species/resorcinol-formaldehyde (Fe/RF) was synthesized in the degradation process of phenols under visible light in a homogeneous photo-Fenton system. The in situ generated H2O2 by bare RF in the medium and the follow-added Fe2+ can construct homogeneous photo-Fenton system, and Fe/RF heterogeneous photo-Fenton catalyst was formed after the reaction through Fe species self-deposition. Due to the addition of Fe2+, more hydroxyl radical (·OH) generated in the homogeneous Fenton system, which lead to the higher degradation efficiency of phenols that achieved 90.5 % with 150 min. Fe/RF was subsequently formed and more C=O functional group in the structure appeared, which was beneficial to the production of H2O2. The above-mentioned results can be proved by the involved calculation and experimental results. Fe species, including Fe2+ and Fe3+, were beneficial to the conversion of reactive oxygen species (ROSs), and further improved the degradation efficiency of Phenols. Since the existence of photo-generated electrons, Fe2+ concentration in the solution can maintain a stable level. Interestingly, the degradation efficiency of Phenols was higher when Fe3+ was used instead of Fe2+ as the additive, which may be caused by the promotive effect of Fe3+ on singlet oxygen (1O2) generation. In addition, the degradation efficiency of Phenols under alkaline conditions was higher than that under acid conditions, which broke the limit of traditional Fenton process that works mostly in acidic medium. This study shows promising results in terms of synergistic photocatalytic/photo-Fenton processes for the degradation of organic pollutants in water.

Heterogeneous photo-Fenton catalyst α-Fe2O3@g-C3N4@NH2-MIL-101(Fe) with dual Z-Scheme heterojunction for degradation of tetracycline

A novel photo-Fenton catalyst α-Fe2O3@g-C3N4@NH2-MIL-101(Fe) (FGN) with dual Z-scheme heterojunction was successfully prepared by hydrothermal method to degrade tetracycline (TC). The preparation conditions were optimized by orthogonal test, and the successful synthesis was confirmed by characterization analyses. The prepared FGN showed better light absorption performance, higher photoelectrons-holes separation efficiency, lower photoelectrons transfer resistance, and higher specific surface area and pore capacity compared with α-Fe2O3@g-C3N4 and α-Fe2O3. The effects of experimental conditions on the catalytic degradation of TC were investigated. The degradation rate of 10 mg/L TC could reach 98.33% within 2 h when the dosage of FGN was 200 mg/L, and the degradation rate could remain 92.27% after 5 times of reuse. Furthermore, the XRD spectra and XPS spectra of FGN before and after reuse were compared to explore the structural stability and catalytic active sites of FGN, respectively. According to the identification of oxidation intermediates, three degradation pathways of TC were proposed. Through H2O2 consumption experiment, radical-scavenging experiments, EPR results, the mechanism of the dual Z-scheme heterojunction was proved. The improved performance of FGN was attributed to the dual Z-Scheme heterojunction effectively promoting the separation of photogenerated electrons from the holes and accelerating the electrons transfer, and the increase of the specific surface area.

Synergistic improving photo-Fenton and photo-catalytic degradation of carbamazepine over FeS2/Fe2O3/organic acid with H2O2in-situ generation

Herein, a heterogeneous photo-Fenton and photo-catalytic system was constructed using oxide pyrite (FeS₂/Fe₂O₃) mineral and organic acids including tartaric acid (TA), ascorbic acid (AA), and citric acid (CA). In the proposed system, FeS₂/Fe₂O₃ can be successfully activated through irradiation to generate photogenerated carriers, which generated H₂O₂in-situ through the reduction reactions between e^- and O₂. The addition of organic acids enhanced the dissolution of iron from FeS₂/Fe₂O₃. Based on the iron and in-situ generated H₂O₂, •OH was produced through a photo-Fenton reaction. Furthermore, h⁺, e^-, and •O₂^-, which were generated through the photo-catalytic activation of FeS₂/Fe₂O₃, also played a certain role in the degradation of carbamazepine (CBZ). Therefore, the synergistic photo-Fenton and photo-catalytic reaction improved the degradation of CBZ, with the degradation efficiencies of 86%, 62%, and 68% in FeS₂/Fe₂O₃/TA, FeS₂/Fe₂O₃/AA, and FeS₂/Fe₂O₃/CA systems, respectively. This investigation provides an innovative strategy for the removal of organic pollutants using natural minerals.

Oxygen vacancies and interfacial iron sites in hierarchical BiOCl nanosheet microflowers cooperatively promoting photo-Fenton

Controllable active site construction, crystal structure regulation and efficient charge separation are core issues in heterogeneous photo-Fenton. Herein, abundant oxygen vacancies and well-dispersed interfacial iron sites are simultaneously constructed in hierarchical nanosheet-assembled BiOCl microflowers. The composites exhibit superior performance in photo-Fenton oxidation of carbamazepine (10 mg L^-1) with a low H₂O₂ concentration (1.3 mM). The high performance highly depends on the synergistic effects between oxygen vacancies and iron species. Rather than modulating the valence band, the involvements of oxygen vacancies and iron species could modify the conduction band of BiOCl. The presence of oxygen vacancies promotes the migration of photo-generated electrons and accelerates the redox cycling of ≡Fe(III)/≡Fe(II) to boost the activation of H₂O₂ to generate hydroxyl radicals, and oxygen vacancies can be well preserved after cyclic use. This work provides understanding on efficient utilization of oxygen vacancies and interfacial iron sites to assist photo-Fenton and the underlying electron transfer mechanism.

Enhanced catalytic performance of Cu-doped MnFe2O4 magnetic ferrites: Tetracycline hydrochloride attacked by superoxide radicals efficiently in a strong alkaline environment

It is important to develop a catalyst that can maintain good activity in alkaline environment for Fenton or Fenton-like reactions. In order to achieve stable Fenton catalytic degradation in a wide pH range, this study reports Cu-doped MnFe₂O₄ heterogeneous catalysts still has excellent effect when the pH is extended to 11 for removing organic pollutants, such as tetracycline hydrochloride (TC-HCl). The synergistic effect among Fe, Mn and Cu ions has been proved to enhanced the catalytic activity in this work. When the molar ratio of Cu/Mn = 4:1, the porous Cu_0·8Mn_0·2Fe₂O₄ materials had the highest photo-Fenton catalytic activity compared with pure MnFe₂O₄, CuFe₂O₄ and other Cu_xMn_1-xFe₂O₄. The XPS showed that Cu_0·8Mn_0·2Fe₂O₄ formed oxygen vacancies, which exposed more active sites to attract more H₂O₂ for TC-HCl degradation. Results indicated 94.3% of TC-HCl was efficiently degraded by 0.1 g/L Cu_0·8Mn_0·2Fe₂O₄ with 50 mM H₂O₂ at pH = 11 under 30 min visible light irradiation, and the corresponding apparent rate constant was 0.08286 min^-1. With free radicals quenching experiment, O₂^- was responsible for the high catalytic degradation and OH was participated in the photo-Fenton reaction. To sum up, Cu_0·8Mn_0·2Fe₂O₄ exhibited high activity, great stability and easily recyclable, which eliminated the pH limitation of the Fenton reaction and provided practical application performance for water purification.

Amorphous iron oxides anchored on BiOCl nanoplates as robust catalysts for high-performance photo-Fenton oxidation

Semiconductor supported iron oxides are highly promising catalysts to remove organic pollutants in photo-Fenton. Development of robust composite catalysts with both high activity and stability is essential. In this work, amorphous iron oxide layers are uniformly and tightly anchored on two-dimensional (2D) BiOCl nanoplates through post precipitation-deposition and subsequent low-temperature thermal treatment at 150-350 °C. A low iron loading amount (1-2 wt.%) is sufficient to make the resulted composite (BiOCl-Fe) catalysts superior in photo-Fenton oxidation of phenol (10 mg/L) with high mineralization efficiency (up to about 80% in 60 min). The low-temperature thermal treatment can significantly enhance the stability of catalysts with much less iron leached and high photo-Fenton performance maintained. The intimate contact between the amorphous iron oxide layers and the 2D BiOCl nanoplates could guarantee the fluent electron transfer and efficient activation of H₂O₂ at interfaces. Compared with the pristine BiOCl, the BiOCl-Fe catalysts possess faster separation of the charge carriers. The predominant active species turns from O₂^•- in photocatalysis to HO^• in the photo-Fenton catalysis. This research could provide enhanced understanding on the synthesis of robust catalysts and the structure optimization of BiOCl supported iron oxides for photo-Fenton.

Amino-functionalized MIL-88B as heterogeneous photo-Fenton catalysts for enhancing tris-(2-chloroisopropyl) phosphate (TCPP) degradation: Dual excitation pathways accelerate the conversion of FeIII to FeII under visible light irradiation

In this work, the amino-functionalized metal-organic frameworks (MIL-88B-NH₂) was synthesized, characterized and used as heterogeneous photo-Fenton catalyst for tris-(2-chloroisopropyl) phosphate (TCPP) degradation. The photo-Fenton activity of MIL-88B-NH₂ was investigated on the basis of influence factors, such as initial pH and TCPP concentration, and coexisting impurities. The results revealed that MIL-88B-NH₂+H₂O₂+Vis system exhibited a satisfactory degradation efficiency of TCPP (almost 100%) within 60 min accompanied by a good reusability. Noticeably, the degradation kinetics constant of TCPP by MIL-88B-NH₂+H₂O₂+Vis system was 0.086 min^-1, which was visibly higher than that of MIL-88B+H₂O₂+Vis system (0.021 min^-1) since the addition of amino-functionalized organic linker inhibiting the recombination rate of the photo-generated electron-hole pairs and improving the visible light response. Combined with the characterization, the conversion of Fe^III to Fe^II could be accelerated by the photo-generated electron from the excitation of Fe-O clusters and NH₂ functionalities, which strengthened the decomposition of H₂O₂ and formed plenty •OH. Simultaneously, six steady products were validated and potential degradation pathways of TCPP were proposed. It was anticipated that MIL-88B-NH₂ could be considered as a desirable and alternative candidate in the application of heterogeneous photo-Fenton reaction to control the environmental risks caused by organophosphate flame retardants (OPFRs).

The degradation of BPA on enhanced heterogeneous photo-Fenton system using EDDS and different nanosized hematite

Photo-Fenton processes have been widely studied in wastewater treatment. In this research, the degradation of bisphenol A (BPA) was carried out in a new heterogeneous photo-Fenton process. The ethylenediamine-N,N'-disuccinic acid (EDDS) was used as chelating agent in this system with two different kinds of commercially available nanosized hematite (30 nm and 80 nm) addition. The results showed that the present of EDDS could enhance the degradation efficiency. And can be concluded that the degradation efficiency is better in the system with 30 nm hematite. The TEM, XRD, and specific surface area were conducted to understand the different characteristics of the two size hematite. The adsorption experiments of BPA and EDDS on hematite proved that there was little adsorption of BPA while the EDDS was adsorbed much more on hematite, which has confirmed Fe(III) and EDDS can form Fe(III)-EDDS complex. The effects of different parameters including hematite loading, H₂O₂, and EDDS concentrations on the degradation process were investigated. According to the results, the optimum condition for BPA degradation using 30 nm (0.8 g L^-1 hematite, 0.1 mmol L^-1 H₂O₂, and 1.2 mmol L^-1 EDDS) and 80 nm (0.6 g L^-1 hematite, 0.05 mmol L^-1 H₂O₂, and 1.2 mmol L^-1 EDDS) hematite were selected. It was confirmed that the ·OH plays an important role in the oxidation process through attacking the BPA molecule and produce hydroxyl addition derivative. In addition, O₂ can react with electron (e^-) and holes (h⁺) produced by iron oxide under UV irradiation to create ¹O₂, which could work as potential reactive species to oxidize BPA.

Application of heterogeneous photo-Fenton process for the mineralization of imidacloprid containing wastewater

The imidacloprid was mineralized by heterogeneous photo-Fenton process in a three-phase fluidized bed reactor using waste iron oxide as catalyst. The effects of catalyst loading, dosage of H₂O₂ and pH were investigated to determine the optimal experiments conditions. The results revealed that TOC removal efficiency increases with an increase in H₂O₂ dosage of up to 105.0 mM, an increase in catalyst dosage from 1.0 to 5.0 g L^-1, and a decrease in pH from 5.0 to 3.5. Under the optimal conditions, 97.7% TOC removal was achieved in 6 h under 254-nm UV irradiation. Moreover, recycling experiments indicated that the waste iron oxide had a good stability and the TOC removal of pesticide yielded more than 80% under the fourth recycles.

Heterogeneous photo-Fenton process using iron-modified regional clays as catalysts: photonic and quantum efficiencies

A regional raw clay was used as the starting material to prepare iron-pillared clays with different iron contents. The catalytic activity of these materials was tested in the heterogeneous photo-Fenton process, applied to the degradation of 2-chlorophenol chosen as the model pollutant. Different catalyst loads between 0.2 and 1.0 g L^-1 and pH values between 3.0 and 7.0 were studied. The local volumetric rate of photon absorption (LVRPA) in the reactor was evaluated solving the radiative transfer equation applying the discrete ordinate method and using the optical properties of the catalyst suspensions. The photonic and quantum efficiencies of the 2-chlorophenol degradation depend on both the catalyst load and the iron content of the catalyst. The higher values for these parameters, 0.080 mol Einstein^-1 and 0.152 mol Einstein^-1, respectively, were obtained with 1.0 g L^-1 of the catalyst with the higher iron content (17.6%). For the mineralization process, photonic and quantum efficiencies depend mainly on the catalyst load. Therefore, it was possible to employ a natural and cheap resource from the region to obtain pillared clay-based catalysts to degrade organic pollutants in water.

Novel RGO/α-FeOOH supported catalyst for Fenton oxidation of phenol at a wide pH range using solar-light-driven irradiation

A novel solar-light-driven (SLD) Fenton catalyst was developed by reducing the ferrous-ion onto graphene oxide (GO) and forming reduced graphene oxide/α-FeOOH composites (RF) via in-situ induced self-assembly process. The RF was supported on several mesoporous supports (i.e., Al-MCM-41, MCM-41 and γ-Al₂O₃). The activity, stability and energy use for phenol oxidation were systematically studied for a wide pH range. Furthermore, the catalytic mechanism at acid and alkaline aqueous conditions was also elucidated. The results showed that Fe(II) was reduced onto GO nanosheets and α-FeOOH crystals were formed during the self-assembly process. Compared with Fenton reaction without SLD irradiation, the visible light irradiation not only dramatically accelerated the rate of Fenton-based reactions, but also extended the operating pH for the Fenton reaction (from 4.0 to 8.0). The phenol oxidation on RF supported catalysts was fitting well with the pseudo-first-order kinetics, and needed low initiating energy, insensitive to the reacting temperature changes (273-318K). The Al-MCM-41 supported RF was a more highly energy-efficient catalyst with the prominent catalytic activity at wide operating pHs. During the reaction, OH radicals were generated by the SLD irradiation from H₂O₂ reduction and H₂O oxidation in the Fe^Ⅱ/Fe^Ⅲ and Fe^Ⅲ/Fe^Ⅳ cycling processes.

Enhanced heterogeneous photo-Fenton process modified by magnetite and EDDS: BPA degradation

In this research, magnetite and ethylenediamine-N,N'-disuccinic acid (EDDS) are used in a heterogeneous photo-Fenton system in order to find a new way to remove organic contaminants from water. Influence of different parameters including magnetite dosage, EDDS concentration, H₂O₂ concentration, and pH value were evaluated. The effect of different radical species including HO^· and HO₂^·/O₂^·- was investigated by addition of different scavengers into the system. The addition of EDDS improved the heterogeneous photo-Fenton degradation of bisphenol A (BPA) through the formation of photochemically efficient Fe-EDDS complex. This effect is dependent on the H₂O₂ and EDDS concentrations and pH value. The high performance observed at pH 6.2 could be explained by the ability of O₂^·- to generate Fe(II) from Fe(III) species reduction. GC-MS analysis suggested that the cleavage of the two benzene rings is the first degradation step followed by oxidation leading to the formation of the benzene derivatives. Then, the benzene ring was opened due to the attack of HO^· radicals producing short-chain organic compounds of low molecular weight like glycerol and ethylene glycol. These findings regarding the capability of EDDS/magnetite system to promote heterogeneous photo-Fenton oxidation have important practical implications for water treatment technologies.

Determination of phthalate esters in airborne particulates by heterogeneous photo-Fenton catalyzed aromatic hydroxylation fluorimetry

The environmental contaminants phthalic acid esters (PAEs) were determined by aromatic hydroxylation fluorimetry combined with heterogeneous photo-Fenton process in the presence of vermiculite supported BiFeO₃ (VMT-BiFeO₃). In strong alkaline solution, PAEs were hydrolyzed into phthalates with no fluorescence, which then reacted with hydroxyl free radicals produced in photo-Fenton process catalyzed by VMT-BiFeO₃ to form the fluorescent hydroxyl phthalates. The fluorescence intensity was proportional to the concentration of PAEs with the maximum excitation and emission wavelength of 300nm and 417nm, respectively. A good linear relationship can be obtained in the range of 3.8×10^-7 to 4.8×10^-5molL^-1 for DEP with correlation coefficient of 0.9997, and the sensitivity of the method was high with detection limit of 5.43×10^-8molL^-1. The method has been successfully applied to determine total PAEs in airborne particulates with satisfactory results.

Heterogeneous photo-Fenton decolorization of Orange II over Al-pillared Fe-smectite: response surface approach, degradation pathway, and toxicity evaluation

A ferric smectite clay material was synthesized and further intercalated with Al2O3 pillars for the first time with the aim of evaluating its ability to be used as heterogeneous catalyst for the photo-Fenton decolorization of azo dye Orange II. UV irradiation was found to enhance the activity of the catalyst in the heterogeneous photo-Fenton process. Catalyst loading of 0.5g/L and hydrogen peroxide concentration of 13.5mM yielded a remarkable color removal, accompanied by excellent catalyst stability. The decolorization of Orange II followed the pseudo-first-order kinetics for initial dye concentrations from 20 to 160mg/L. The central composite design (CCD) based on the response surface methodology (RSM) was applied to evaluate the effects of several operating parameters, namely initial pH, catalyst loading and hydrogen peroxide concentration, on the decolorization efficiency. The RSM model was derived and the response surface plots were developed based on the results. Moreover, the main intermediate products were separated and identified using gas chromatography-mass spectrometry (GC-MS) and a possible degradation pathway was proposed accordingly. The acute toxicity experiments illustrated that the Daphniamagna immobilization rate continuously decreased during 150min reaction, indicating that the effluent was suitable for sequential biological treatment.