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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.

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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.

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The self-sufficient heterogeneous photo-Fenton (SH-PF) system was constructed for doxycycline hydrochloride (DOH) degradation with hydroxyapatite (Hap) modified CuFeO2 (Hap/CuFeO2) composites through H2O2 in-situ production. The modification of Hap could improve the specific surface area, visible-light response, light conversion efficiency, photoelectron lifetime and oxygen vacancies (OVs) of CuFeO2, which was conducive to H2O2 production and DOH degradation in SH-PF system. Notably, Hap/CuFeO2 fabricated with 0.5 g Hap (Hap/CuFeO2-0.5) displayed more superior performance for DOH degradation compared to other synthesized catalysts. The Hap/CuFeO2-0.5 load and initial solution pH for DOH degradation in SH-PF system were optimized, and the Hap/CuFeO2-0.5 had good reusability and stability. The •OH was the main active species for DOH degradation, and the facilitation effect of •O2- and photoelectrons on DOH degradation was associated with the H2O2 production in the present work. In addition, the capture of photogenerated holes suppressed the recombination of photogenerated carriers, elevating the production of photoelectrons and thereby enhancing H2O2 production and DOH degradation. The degradation pathways for DOH were proposed and the comprehensive toxicities of DOH were relieved after degradation in SH-PF system.

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The heterogeneous photo-Fenton system using Fe-Co/γ-Al2O3 as a catalyst was applied in the study of sulfamethoxazole(SMX) degradation. The morphology, structure, elemental composition and metal valence distribution of Fe-Co/γ-Al2O3 were found to be relatively stable before and after the reaction. The highest SMX degradation efficiency and mineralization (The ratio of organic matter being oxidized to carbon dioxide and water) were obtained under the conditions of 15% Fe-Co loading rate, 1:1 mass ratio of Fe and Co, 1 g/L catalyst dosage, 1.5 mL 30% H2O2 dosage, 18 W UV lamp power and 60 min reaction time, which were 98% and 66%, respectively. Radical quenching experiments and electronic paramagnetic resonance (EPR) characterization revealed that ·OH played an important role in the degradation and mineralization SMX in the Fe-Co/γ-Al2O3 heterogeneous photo-Fenton system. Combined with the analysis of N, S and intermediate products, there may be three degradation pathways of SMX in the heterogeneous photo-Fenton system. This work provides a technical reference for realizing the efficient degradation and mineralization of SMX in a heterogeneous photo-Fenton reaction system.

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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.

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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.

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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.

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The increasing organic and microbiological pollutions in fresh water caused by human activities and industrial development have become a global concern nowadays. In this study, three-dimensional (3D) hierarchical FeS2/TiO2 structures with nanotube geometries were grown on a Ti mesh (M-TNTAs-FeS2). Benefitting from the abundant available reactive sites on the open 3D micro/nanoporous structures, excellent photocatalytic activity of FeS2/TiO2 heterostructure in solar light, and satisfactory Fenton activity of FeS2, the obtained M-TNTAs-FeS2 exhibits outstanding performance as an all-day-active catalyst. Importantly, flexible meshes can be easily tailored and enveloped into fluorinated ethylene propylene (FEP) pockets in a series as a flow-through belt for large-capacitance applications (998 L m-2 at a flow rate of 417 L m-2 h-1 for a four-pockets belt), as indicated by the degradation of azo dyes, antibiotics, pesticides, and pathogens. This study may inspire a new tailorable catalyst design for a promising point-of-use purification device.

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The co-occurrence of various chemical and biological contaminants of emerging concerns has hindered the application of water recycling. This study aims to develop a heterogeneous photo-Fenton treatment by fabricating nano pyrite (FeS2) on graphene oxide (FeS2@GO) to simultaneously remove antibiotic resistant bacteria (ARB), antibiotic resistance genes (ARGs), and micropollutants (MPs). A facile and solvothermal process was used to synthesize new pyrite-based composites. The GO coated layer forms a strong chemical bond with nano pyrite, which enables to prevent the oxidation and photocorrosion of pyrite and promote the transfer of charge carriers. Low reagent doses of FeS2@GO catalyst (0.25 mg/L) and H2O2 (1.0 mM) were found to be efficient for removing 6-log of ARB and 7-log of extracellular ARG (e-ARG) after 30 and 7.5 min treatment, respectively, in synthetic wastewater. Bacterial regrowth was not observed even after a two-day incubation. Moreover, four recalcitrant MPs (sulfamethoxazole, carbamazepine, diclofenac, and mecoprop at an environmentally relevant concentration of 10 µg/L each) were completely removed after 10 min of treatment. The stable and recyclable composite generated more reactive species, including hydroxyl radicals (HO•), superoxide radicals (O2• -), singlet oxygen (1O2). These findings highlight that the synthesized FeS2@GO catalyst is a promising heterogeneous photo-Fenton catalyst for the removal of emerging contaminants.

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The immobilized coatings as a kind of promising Fenton-like catalysts with excellent performance and reusability for the efficient degradation of antibiotics and phenol under solar light irradiation is investigated. Herein, the porous γ-Fe2O3/SiO2 immobilized ceramic coating on TC4 titanium alloy as photo-Fenton catalyst was prepared via plasma electrolytic oxidation technology. The as-obtained immobilized coating manifested a remarkable catalytic activity that the removal efficiencies of phenol and various antibiotics could reach more than 92% within 90 min, and presented excellent reusability after six runs in phenol removal. The high activity and excellent reusability of γ-Fe2O3 were attributed to the synergistic effect of multiple pathways to jointly produce abundant •OH, and the combination of γ-Fe2O3 and SiO2 in the coating could effectively reduce iron leaching during the heterogeneous photo-Fenton process, respectively. This work provides a novel strategy for the synthesis of high-performance photo-Fenton catalysts to dispose of wastewater in the future.

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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.

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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 Cu0·8Mn0·2Fe2O4 materials had the highest photo-Fenton catalytic activity compared with pure MnFe2O4, CuFe2O4 and other CuxMn1-xFe2O4. The XPS showed that Cu0·8Mn0·2Fe2O4 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 Cu0·8Mn0·2Fe2O4 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, Cu0·8Mn0·2Fe2O4 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.

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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 FeIII to FeII 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).

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In this study, we investigated the efficiency of photocatalytic degradation and chemical oxygen demand (COD) reduction from woodchips industry wastewater using α-Fe2O3@TiO2@SO3H. A magnetic α-Fe2O3@TiO2@SO3H was prepared as a heterogeneous photo-Fenton catalyst. The Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and elemental mapping (MAP) analyses were performed to determine the structure and morphology of synthesized photocatalysts. The response surface methodology (RSM) was used to optimize the photo-Fenton process based on a Box-Behnken design (BBD). The parameters such as catalyst dosage, H2O2 dosage, pH, and contact time on photocatalytic degradation and the reduction of COD were studied. The maximum photocatalytic degradation of 93.75% and COD reduction of 86.54% were achieved at a dosage of the catalyst of 1 g L-1, H2O2 dosage of 40 mg L-1, and a pH of 3.5 at 45 min. The kinetics of the photo-Fenton process was studied for the woodchips wastewater treatment under optimum conditions. The pseudo-second-order kinetic model for photocatalytic degradation and COD reduction was obtained. The results indicated that a α-Fe2O3@TiO2@SO3H could be used as an effective heterogeneous photocatalyst for the treatment of woodchips industry wastewater. Preparation and application of α-Fe2O3@TiO2@SO3H for photocatalytic degradation and COD reduction of woodchips industry wastewater.

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The visible-light induced heterogeneous photo-Fenton-like (HPF-like) process is regarded as a promising technique for organic pollutants degradation due to its efficient utilization of solar energy and high H2O2 activation activity. This study prepared the CuFeO2/biochar catalysts via hydrothermal technique at no extra reductant and systematically investigated their band structure and photoelectric properties. The dispersed distribution of CuFeO2 particles in CuFeO2/biochar composites narrowed bandgap of CuFeO2 and promoted electron transport of CuFeO2. Compared with CuFeO2, the CuFeO2/biochar containing 1.0 g biochar in the preparation (CuFeO2/biochar-1.0) possessed higher carrier density and longer photoelectron lifetime, which is beneficial to higher catalytic performance. The apparent rate constant for tetracycline as target pollutant degradation by CuFeO2/biochar-1.0 was 2.0 times higher than that by CuFeO2. The acquired optimum conditions for tetracycline degradation were 220 mg L-1 CuFeO2/BC-1.0, 22 mM H2O2 and pH 6.4 using response surface methodology. The quenching experiments and ESR analysis revealed that OH was the predominant active species, and photoelectron and O2- were auxiliary species. The photoelectron could promote in-situ recycling of Cu2+ to Cu+ and Fe3+ to Fe2+, which significantly improved H2O2 activation by CuFeO2. The possible pathway of tetracycline was proposed according to intermediates identified by HPLC/MS. The toxicity analysis demonstrated that the overall toxicity of the identified intermediates was reduced in HPF-like system.

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Titania (TiO2) supported iron oxides (Fe-TiO2) are ideal catalysts to be applied in heterogeneous photo-Fenton oxidation (HPFO) for wastewater treatment because of the capabilities of TiO2 in photocatalysis and iron oxides in interfacial H2O2 activation. It is important to understand the influences of the structural parameters of Fe-TiO2 catalysts and the complicated interplay between TiO2 and iron oxides on the performance of HPFO. In this paper, a series of Fe-TiO2 catalysts are obtained through a facile solid-phase synthesis method. The iron loading content and the calcination temperature are systematically adjusted to tune the crystal phase, size, anatase/rutile ratio and density of oxygen vacancy (OV) site of TiO2, the dispersing state of iron species, and the interfacial structure of the Fe-TiO2 catalysts. Then, the performance of these catalysts in HPFO for degrading methylene blue (MB) are comparatively studied. Correlations between the performance and various structural properties of the catalysts are clarified. The interplay between TiO2 and iron oxides in the HPFO process is elucidated. The insight reaction mechanism is also discussed. Under optimized conditions (an iron loading of 1 wt% and a temperature of 600 °C), Fe-TiO2 catalysts with iron lattice doping, well-dispersed ultrasmall α-Fe2O3 nanoparticles, appropriate anatase/rutile ratios and abundant OV sites can be obtained. The anatase-rutile-Fe2O3 heterojunction, ultrasmall α-Fe2O3 nanoparticles and OV sites in the optimized catalysts work synergistically to improve the charge migration and interfacial activation of H2O2, leading to superior HPFO performance for MB degradation and mineralization.

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Heterogeneous photo-Fenton systems offer efficient solutions for the treatment of wastewaters in the textile industry. This study investigated the fabrication and structural characterization of novel peculiar-shaped CuIIO, FeIII 2O3, and FeIIO nanoparticles (NPs) compared to the properties of the iron(II)-doped copper ferrite CuII 0.4FeII 0.6FeIII 2O4. The photocatalytic efficiencies of these NPs and the composite of the simple oxides (CuIIO/FeIIO/FeIII 2O3) regarding the degradation of methylene blue (MB) and rhodamine B (RhB) as model dyes were also determined. The catalysts were synthesized via simple co-precipitation and calcination technique. X-ray diffractometry (XRD), scanning electron microscopy (SEM), and diffuse reflectance spectroscopy (DRS) were utilized for structural characterization. The structure of CuIIO was bead-like connected into threads, FeIII 2O3 was rod-like, while FeIIO pallet-like, with average crystallite sizes of 18.9, 36.9, and 37.1 nm, respectively. The highest degradation efficiency was achieved by CuIIO for RhB and by CuII 0.4FeII 0.6FeIII 2O4 for MB. The CuIIO/FeIIO/FeIII 2O3 composite proved to be the second-best catalyst in both cases, with excellent reusability. Hence, these NPs can be successfully applied as heterogeneous photo-Fenton catalysts for the removal of hazardous pollutants. Moreover, the simple metal oxides and the iron(II)-doped copper ferrite displayed a sufficient antibacterial activity against Gram-negative Vibrio fischeri.

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Four different catalysts from drinking water treatment residuals (DWTR) were prepared via impregnation in the iron nitrate, calcined at different temperatures ranged from 200°C to 500°C, and tested for the reactive blue 19 oxidation using the heterogeneous photo-Fenton, under UVA light source. XRD and XPS results revealed that iron nature was found under a ferric oxide form (Fe3+ ) similar to the magnetite. Calcination temperature results showed a significant effect on the activity of the catalysts. RB19 and TOC removals were 99% and 79%, respectively, with the best catalyst that calcined at 500°C in optimal conditions as follows: initial pH solution = 3, 10 mM of H2 O2 dosage, 0.5 g/L of catalyst loading, reaction temperature 35°C, and IUVA  = 3.55 MW/cm2 for 50 mg/L of RB19. The reusability of the catalyst after three cycles showed complete removal of RB19 and 65% TOC removal. PRACTITIONER POINTS: Synthetized heterogeneous photo-Fenton catalyst from drinking water treatment residuals for the photo Fenton oxidation. The calcination temperatures plays a crucial role in catalyst photocatalytic activity. Degradation of reactive blue 19 with Fe/DWTR-500 in presence of H2 O2 . The Fe/DWTR-500 catalyst exhibited the best photocatalytic activity. Reusability studies of Fe/DWTR-500 and the kinetics of reactive blue 19 degradation were investigated.

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In this work, the effectiveness of green zero-valent iron nanoparticles (gnZVIs) for the removal of the antibiotic sulfadiazine (SDZ) from water via adsorption and reduction was tested. Additionally, the effectiveness of this material as a catalyst for the Fenton and photo-Fenton processes was also investigated. This represents the first study concerning the use of gnZVIs for the degradation of a sulfonamide antibiotic. The results obtained indicate that gnZVIs were able to remove up to 58% of SDZ via adsorption and up to 69% via adsorption plus reduction using a SDZ/Fe3+ molar ratio of 1:61.6. Furthermore, gnZVIs showed strong effectiveness as a catalyst for the Fenton and photo-Fenton reactions, with complete SDZ removal in 8 h and 5 min, respectively, using a SDZ/Fe3+/H2O2 molar ratio of 1:38.4:38.4. These results demonstrate that the use of gnZVIs constitutes an attractive and potential alternative technology for water remediation, reducing environmental impact and operational costs.

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Present work shows results of a study on heterogeneous Fenton-like degradation of lignin alkaline hydrolysates formed in the process of obtaining a fibrous mass from rice husk. Fe-impregnate biogenic amorphous silica Fe/RH-SiO2 obtained from rice husk was used as a catalyst. Using IR spectroscopy, X-ray diffraction and EDX analysis it was shown that iron(III) oxide in the form of hematite is present on the catalyst surface. Phenol was used for preliminary assessment of catalytic activity of the catalyst Fe/RH-SiO2. The degree of degradation of phenol by the UV/visible radiation/Fe/RH-SiO2/H2O2 system reaches 90%. The catalytic activity of Fe/RH-SiO2 was studied in the reaction of lignin degradation of rice husk alkaline hydrolysates under ultraviolet and visible irradiation in the presence of hydrogen peroxide. The lignin solutions with COD: Н2О2 ratios from 1:2 to 1:16 were exposure under UV irradiation for 15-minute and the subsequent lightening on sunny days between 9 am and 8 pm in April for 7 days in the presence of a catalyst and without it. The catalyst concentration was 1.0 g L-1. After that, it was found the content of phenolic compounds in the presence of a catalyst is 2-20 times lower than without it. The COD with the COD: Н2О2 = 1:16 ratio in the presence of a catalyst decreases 1.5 times as compared with the initial solution, whereas without a catalyst it increases 13 times.

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