Interface coupling to improve O2 adsorption and accelerate charge separation for boosting photocatalytic performance of ZnO/ZnIn2S4 composite in H2O2 production and environmental remediation.

The key to heterogeneous photo-Fenton technology lies in the efficient generation of hydrogen peroxide (H2O2). Herein, a newly-designed ZnO/ZnIn2S4 composite with heterostructure is synthesized. Benefiting from the formation of built-in electric field, the recombination of photoinduced electrons and holes is suppressed and interfacial charge transfer resistance is reduced. Importantly, the embedding of ZnO in ZnIn2S4 can improve the hydrophobicity and create microscopic three-phase interface, thereby boosting the capture capability for O2 and providing the convenience for the occurrence of O2 reduction reaction. More interestingly, the existence of ZnIn2S4 in the ZnO/ZnIn2S4 composite can reduce the Gibbs free energy (ΔG) of key intermediate (OOH*) formation, which will accelerate the generation of H2O2. As a result, the ZnO/ZnIn2S4 composite displays excellent performance in photocatalytic H2O2 production, and the highest yield was about 897.6 µmol/g/h within 60 min under visible light irradiation. The transfer of photoinduced carriers follows the S-scheme type mechanism. The photogenerated holes can be captured by drug residues (i.e., diclofenac sodium) to accelerate H2O2 production, while generated H2O2 can combine with Fe2+ to construct photo-Fenton system for achieving the advanced degradation of diclofenac sodium, which was mainly related to the formation of OH•. Furthermore, generated H2O2 can be applied for performing the inactivation of pathogenic bacteria. In short, current work will provide a valuable reference for future research.

Light Emission from Fe2+-EGTA-H2O2 System Depends on the pH of the Reaction Milieu within the Range That May Occur in Cells of the Human Body.

A Fe2+-EGTA(ethylene glycol-bis (ß-aminoethyl ether)-N,N,N',N'-tetraacetic acid)-H2O2 system emits photons, and quenching this chemiluminescence can be used for determination of anti-hydroxyl radical (•OH) activity of various compounds. The generation of •OH and light emission due to oxidative damage to EGTA may depend on the buffer and pH of the reaction milieu. In this study, we evaluated the effect of pH from 6.0 to 7.4 (that may occur in human cells) stabilized with 10 mM phosphate buffer (main intracellular buffer) on a chemiluminescence signal and the ratio of this signal to noise (light emission from medium alone). The highest signal (4698 ± 583 RLU) and signal-to-noise ratio (9.7 ± 1.5) were noted for pH 6.6. Lower and higher pH caused suppression of these variables to 2696 ± 292 RLU, 4.0 ± 0.8 at pH 6.2 and to 3946 ± 558 RLU, 5.0 ± 1.5 at pH 7.4, respectively. The following processes may explain these observations: enhancement and inhibition of •OH production in lower and higher pH; formation of insoluble Fe(OH)3 at neutral and alkaline environments; augmentation of •OH production by phosphates at weakly acidic and neutral environments; and decreased regeneration of Fe2+-EGTA in an acidic environment. Fe2+-EGTA-H2O2 system in 10 mM phosphate buffer pH 6.6 seems optimal for the determination of anti-•OH activity.

Triggering Dual Two-electron Pathway for H2 O2 Generation by Multiple [Bi-O]n Interlayers in Ultrathin Bi12 O17 Cl2 towards Efficient Piezo-self-Fenton Catalysis.

Piezo-self-Fenton system (PESF) has been emerging as a promising water treatment technology but suffering from unsatisfied H2 O2 production efficiency. Herein, we rationally design a Bi12 O17 Cl2 piezo-catalyst with multiple [Bi-O]n interlayers towards highly efficient H2 O2 production. The introduction of [Bi3 O4.25 ] layers initiates dual two-electron pathway for H2 O2 generation by altering the interlayer properties. It is found that the additional [Bi3 O4.25 ] layers not only enhance the polarization electric field but also serve as active sites for triggering dual pathways of two-electron O2 reduction and H2 O oxidation reaction for H2 O2 production. Therefore, the Bi12 O17 Cl2 exhibits an ultrahigh rate of H2 O2 generation (7.76 mM h-1 g-1 ) in pure water. Based on the adequate H2 O2 yield, a PESF was constructed for acetaminophen (ACE) degradation with an apparent rate constant of 0.023 min-1 . This work not only presents a potential strategy of tuning the activity of bismuth based piezo-catalysts but also provides a good example on the construction of highly efficient PESF for environmental remediation by using natural mechanical energy.

Photocatalytic Self-Fenton System of g-C3N4-Based for Degradation of Emerging Contaminants: A Review of Advances and Prospects.

The discharge of emerging pollutants in the industrial process poses a severe threat to the ecological environment and human health. Photocatalytic self-Fenton technology combines the advantages of photocatalysis and Fenton oxidation technology through the in situ generation of hydrogen peroxide (H2O2) and interaction with iron (Fe) ions to generate a large number of strong reactive oxygen species (ROS) to effectively degrade pollutants in the environment. Graphite carbon nitride (g-C3N4) is considered as the most potential photocatalytic oxygen reduction reaction (ORR) photocatalyst for H2O2 production due to its excellent chemical/thermal stability, unique electronic structure, easy manufacturing, and moderate band gap (2.70 eV). Hence, in this review, we briefly introduce the advantages of the photocatalytic self-Fenton and its degradation mechanisms. In addition, the modification strategy of the g-C3N4-based photocatalytic self-Fenton system and related applications in environmental remediation are fully discussed and summarized in detail. Finally, the prospects and challenges of the g-C3N4-based photocatalytic self-Fenton system are discussed. We believe that this review can promote the construction of novel and efficient photocatalytic self-Fenton systems as well as further application in environmental remediation and other research fields.

Degradation of the mixed nuclear-grade cationic and anionic exchange resins using Fe2+/H+ homogeneous Fenton oxidation.

To further improve the treatment capacity of actual wastes, H+ was introduced into the homogeneous Fenton system as a co-catalyst for dissolution and degradation of the mixed nuclear-grade cationic and anionic exchange resins. The effects of acid type and concentration, catalyst type and concentration, H2O2 dosage, initial temperature, antifoaming agent and resin ratio were studied. The concentration of inorganic acid, type and concentration of catalyst had significant influence on the decomposition of mixed resins. The experimental results showed that when the mixing ratio of resins was 1:1, the initial temperature was 96 ± 1 °C, the amount of H2O2 was 200 mL, and the concentration of H+/Fe2+ was 1 M/0.1 M, complete dissolution and 79% weight reduction of mixed resins were obtained. Combined with density functional theory (DFT) calculations, cationic exchange resin and anionic exchange resin showed different reactivity in the experiment. Hydroxyl radicals (•OH) tended to attack -SO3- groups with more negative charges, and the barrier energy of -SO3- ion dissociation was 8.2 kcal/mol, which caused the cationic exchange resin to be easily destroyed. According to the characterization results, the characteristic intermediates were determined, indicating that desulfonation, valence change of nitrogen atom, and cleavage of long-chain carbon skeleton existed during the reaction, but incomplete oxidation still remained.

Concentration Dependence of Anti- and Pro-Oxidant Activity of Polyphenols as Evaluated with a Light-Emitting Fe2+-Egta-H2O2 System.

Hydroxyl radical (•OH) scavenging and the regeneration of Fe2+ may inhibit or enhance peroxidative damage induced by a Fenton system, respectively. Plant polyphenols reveal the afore-mentioned activities, and their cumulative net effect may determine anti- or pro-oxidant actions. We investigated the influence of 17 phenolics on ultra-weak photon emission (UPE) from a modified Fenton system (92.6 µmol/L Fe2+, 185.2 µmol/L EGTA (ethylene glycol-bis(ß-aminoethyl-ether)-N,N,N',N,-tetraacetic acid) and 2.6 mmol/L H2O2 pH = 7.4). A total of 8 compounds inhibited (antioxidant effect), and 5 enhanced (pro-oxidant effect) UPE at all studied concentrations (5 to 50 µmol/L). A total of 4 compounds altered their activity from pro- to antioxidant (or vice versa) along with increasing concentrations. A total of 3 the most active of those (ferulic acid, chlorogenic acid and cyanidin 3-O-glucoside; mean UPE enhancement by 63%, 5% and 445% at 5 µmol/L; mean UPE inhibition by 28%, 94% and 24% at 50 µmol/L, respectively) contained catechol or methoxyphenol structures that are associated with effective •OH scavenging and Fe2+ regeneration. Most likely, these structures can determine the bidirectional, concentration-dependent activity of some phenolics under stable in vitro conditions. This is because the concentrations of the studied compounds are close to those occurring in human fluids, and this phenomenon should be considered in the case of dietary supplementation with isolated phenolics.

Construction of novel in-situ photo-Fenton system based on modified g-C3N4 composite photocatalyst.

In this study, a reduced g-C3N4/PDI/Fe (R-gCPF) photocatalyst was synthesized by loading Fe ion onto a reduced g-C3N4/PDI (R-gCP), which was obtained by reducing g-C3N4/PDI with NaBH4. The synthesized R-gCPF photocatalyst was used to construct a novel in-situ photo-Fenton system under visible light for pollutants removal. The R-gCPF2 (0.7% mass ratio of Fe/R-gCP) exhibited the optimal degradation efficiency toward benzoic acid (BA) and the photocatalytic degradation was much better than that of the unmodified g-C3N4/PDI (gCP). The X-ray photoelectron spectroscopy (XPS) characterization indicated that Fe was successfully loaded and bounded to the R-gCP material in the form of Fe2O3. The quenching experiments and the electron paramagnetic resonance (EPR) spectroscopic analysis revealed that the photo-Fenton system was built up, and water was oxidized to OH in the system. Further, the Mott-Schottky and UV-vis diffuse reflectance spectrometry (UV-vis DRS) measurements confirmed the ability of valence band on R-gCPF to oxidize water. Photoluminescence spectral (PL) analysis indicated that loaded Fe could promote the separation of photogenerated electrons and holes, and consequently improved the photocatalytic efficiency of materials. The effect of initial pH, different ions and dissolved organic matter (DOM) on BA degradation was also studied. The stability of the photocatalyst was confirmed by recycle and the leaching experiments.

Effect of Physiological Concentrations of Vitamin C on the Inhibitation of Hydroxyl Radical Induced Light Emission from Fe2+-EGTA-H2O2 and Fe3+-EGTA-H2O2 Systems In Vitro.

Ascorbic acid (AA) has antioxidant properties. However, in the presence of Fe2+/Fe3+ ions and H2O2, it may behave as a pro-oxidant by accelerating and enhancing the formation of hydroxyl radicals (•OH). Therefore, in this study we evaluated the effect of AA at concentrations of 1 to 200 µmol/L on •OH-induced light emission (at a pH of 7.4 and temperature of 37 °C) from 92.6 µmol/L Fe2+-185.2 µmol/L EGTA (ethylene glycol-bis (ß-aminoethyl ether)-N,N,N',N'-tetraacetic acid)-2.6 mmol/L H2O2, and 92.6 µmol/L Fe3+-185.2 µmol/L EGTA-2.6 mmol/L H2O2 systems. Dehydroascorbic acid (DHAA) at the same range of concentrations served as the reference compound. Light emission was measured with multitube luminometer (AutoLumat Plus LB 953) for 120 s after automatic injection of H2O2. AA at concentrations of 1 to 50 µmol/L and of 1 to 75 µmol/L completely inhibited light emission from Fe2+-EGTA-H2O2 and Fe3+-EGTA-H2O2, respectively. Concentrations of 100 and 200 µmol/L did not affect chemiluminescence of Fe3+-EGTA-H2O2 but tended to increase light emission from Fe2+-EGTA-H2O2. DHAA at concentrations of 1 to 100 µmol/L had no effect on chemiluminescence of both systems. These results indicate that AA at physiological concentrations exhibits strong antioxidant activity in the presence of chelated iron and H2O2.

Detecting and Quantifying Polyhaloaromatic Environmental Pollutants by Chemiluminescence-Based Analytical Method.

Polyhaloaromatic compounds (XAr) are ubiquitous and recalcitrant in the environment. They are potentially carcinogenic to organisms and may induce serious risks to the ecosystem, raising increasing public concern. Therefore, it is important to detect and quantify these ubiquitous XAr in the environment, and to monitor their degradation kinetics during the treatment of these recalcitrant pollutants. We have previously found that unprecedented intrinsic chemiluminescence (CL) can be produced by a haloquinones/H2O2 system, a newly-found ●OH-generating system different from the classic Fenton system. Recently, we found that the degradation of priority pollutant pentachlorophenol by the classic Fe(II)-Fenton system could produce intrinsic CL, which was mainly dependent on the generation of chloroquinone intermediates. Analogous effects were observed for all nineteen chlorophenols, other halophenols and several classes of XAr, and a novel, rapid and sensitive CL-based analytical method was developed to detect these XAr and monitor their degradation kinetics. Interestingly, for those XAr with halohydroxyl quinoid structure, a Co(II)-mediated Fenton-like system could induce a stronger CL emission and higher degradation, probably due to site-specific generation of highly-effective ●OH. These findings may have broad chemical and environmental implications for future studies, which would be helpful for developing new analytical methods and technologies to investigate those ubiquitous XAr.

Antioxidant Properties of a Nanostructured Clathrate Complex Selenopyran with ß-Cyclodextrin in Model Systems of Oxidative Stress.

We studied the effect of nanostructured clathrate complex 9-phenyl-symm-octahydoselenoxanthene (selenopyran) with ß-cyclodextrin on the generation of ОН· radicals in the Fenton system and parameters of oxidative stress in rat liver cells incubated at 37°Ð¡ for 1 h. The complex inhibits the development of free-radical oxidative processes induced by ROS and the most toxic ОН· radicals, reduces the increased level of ROS induced by prooxidants, and exhibits antioxidant activity.

Insight into CaO2-based Fenton and Fenton-like systems: strategy for CaO2-based oxidation of organic contaminants.

This study conducted a comparison of the CaO2-based Fenton (CaO2/Fe(II)) and Fenton-like (CaO2/Fe(III)) systems on their benzene degradation performance. The H2O2, Fe(II), Fe(III), and HO● variations were investigated during the benzene degradation. Although benzene has been totally removed in the two systems, the variation patterns of the investigated parameters were different, leading to the different benzene degradation patterns. In terms of the Fe(II)/Fe(III) conversion, the CaO2/Fe(II) and CaO2/Fe(III) systems were actually inseparable and had the inherent mechanism relationships. For the CaO2/Fe(III) system, the initial Fe(III) must be converted to Fe(II), and then the consequent Fenton reaction could be later developed with the regenerated Fe(II). Moreover, some benzene degradation intermediates could have the ability to facilitate the transformation of the Fe(III) to Fe(II) without the classic H2O2-associated propagation reactions. By varying the Fe(II) dosing method, an effective degradation strategy has been developed to take advantage of the two CaO2-based oxidation systems. The proposed strategy was further successfully tested in TCE degradation, therefore extending the potential for the application of this technique.

Light emission from the Fe2+ -EDTA-ascorbic acid-H2 O2 system strongly enhanced by plant phenolic acids.

Oxidative reactions can result in the formation of electronically excited species that undergo radiative decay depending on electronic transition from the excited state to the ground state with subsequent ultra-weak photon emission (UPE). We investigated the UPE from the Fe2+ -EDTA (ethylenediaminetetraacetic acid)-AA (ascorbic acid)-H2 O2 (hydrogen peroxide) system with a multitube luminometer (Peltier-cooled photon counter, spectral range 380-630 nm). The UPE, of 92.6 µmol/L Fe2+ , 185.2 µmol/L EDTA, 472 µmol/L AA, 2.6 mmol/L H2 O2 , reached 1217 ± 118 relative light units during 2 min measurement and was about two times higher (P < 0.001) than the UPE of incomplete systems (Fe2+ -AA-H2 O2 , Fe2+ -EDTA-H2 O2 , AA-H2 O2 ) and medium alone. Substitution of Fe2+ with Cr2+ , Co2+ , Mn2+ or Cu2+ as well as of EDTA with EGTA (ethylene glycol-bis(ß-aminoethyl ether)-N,N,N',N'-tetraacetic acid) or citrate powerfully inhibited UPE. Experiments with scavengers of reactive oxygen species (dimethyl sulfoxide, mannitol, sodium azide, superoxide dismutase) revealed the dependence of UPE only on hydroxyl radicals. Dimethyl sulfoxide at the concentration of 0.74 mmol/L inhibited UPE by 79 ± 4%. Plant phenolics (ferulic, chlorogenic and caffec acids) at the concentration of 870 µmol/L strongly enhanced UPE by 5-, 13.9- and 46.8-times (P < 0.001), respectively. It is suggested that augmentation of UPE from Fe2+ -EDTA-AA-H2 O2 system can be applied for detection of these phytochemicals.

Light Emission from the Fe2+-EGTA-H2O2 System: Possible Application for the Determination of Antioxidant Activity of Plant Phenolics.

Oxidative reactions can result in the formation of electronically excited species that undergo radiative decay depending on electronic transition from the excited state to the ground state with subsequent ultra-weak photon emission (UPE). We investigated the UPE from the Fe2+-EGTA (ethylene glycol-bis(ß-aminoethyl ether)-N,N,N',N'-tetraacetic acid)-H2O2 system with a multitube luminometer (Peltier-cooled photon counter, spectral range 380 to 630 nm). The UPE of 92.6 µmol/L Fe2+-185.2 µmol/L EGTA-2.6 mmol/L H2O2 reached 4319 ± 755 relative light units during 2 min measurement and was about seven times higher (p < 0.001) than the UPE of incomplete systems (Fe2+-H2O2, EGTA-H2O2) and medium alone. Substitution of Fe2+ with Cr2+, Co2+, Mn2+ or Cu2+ as well as of EGTA with EDTA (ethylenediaminetetraacetic acid) or citrate completely abolished UPE. Experiments with ROS scavengers revealed the dependence of UPE on hydroxyl radicals suggesting occurrence of oxidative attack and cleavage of the ether bond in EGTA backbone structure and formation of triplet excited carbonyl groups with subsequent light emission. Plant phenolics (ferulic, chlorogenic and caffec acids) at concentration 87 µmol/L and ascorbate at 0.46 mmol/L inhibited UPE by 90 ± 4%, 90 ± 5%, 97 ± 2% and 92 ± 1%, respectively. Quenching of UPE from Fe2+-EGTA-H2O2 system can be used for evaluation of antioxidant activity of phytochemicals.

Dye degradation by green heterogeneous Fenton catalysts prepared in presence of Camellia sinensis.

This work describes the synthesis and characterization of supported green iron catalysts, prepared with Camellia sinensis tea extract, and their application in heterogeneous Fenton degradation of pollutant dyes. The influence of the catalyst synthesis conditions in the iron and organic content were investigated by X-ray fluorescence and thermogravimetric analyses. Irregular, chain-like nanoparticles, in the size range of 20-100 nm, capped by polyphenolic natural compounds, were visualized by TEM micrographs. TEM-EDS revealed a high iron content in the nanoparticles as well as a high carbon content all over the catalyst surface, indicating the coverage by the polyphenolic compounds of the tea. X-ray powder diffraction revealed the amorphous nature of the nanoparticles, tentatively ascribed to iron(II)/(III) oxides and oxohydroxides composites. The Fenton degradation of different dyes was successfully accomplished, leading to complete decolourization in less than 3 h of reaction. Influence of hydrogen peroxide concentration, catalyst dosage, pH, temperature and catalyst support, were investigated. The catalysts prepared with black tea over silica furnished the higher iron contents and were the most actives for dye degradation.

Effect of Selected Plant Phenolics on Fe2+-EDTA-H2O2 System Mediated Deoxyribose Oxidation: Molecular Structure-Derived Relationships of Anti- and Pro-Oxidant Actions.

In the presence of transition metal ions and peroxides, polyphenols, well-known dietary antioxidants, can act as pro-oxidants. We investigated the effect of 13 polyphenols and their metabolites on oxidative degradation of deoxyribose by an •OH generating Fenton system (Fe2+-ethylenediaminetetraacetic acid (EDTA)-H2O2). The relationship between phenolics pro-oxidant/anti-oxidant effects and their molecular structure was analyzed using multivariate analysis with multiple linear regression and a backward stepwise technique. Four phenolics revealed a significant inhibitory effect on OH-induced deoxyribose degradation, ranging from 54.4% ± 28.6% (3,4-dihydroxycinnamic acid) to 38.5% ± 10.4% (catechin) (n = 6), correlating with the number of -OH substitutions (r = 0.58). Seven phenolics augmented the oxidative degradation of deoxyribose with the highest enhancement at 95.0% ± 21.3% (quercetin) and 60.6% ± 12.2% (phloridzin). The pro-oxidant effect correlated (p < 0.05) with the number of -OH groups (r = 0.59), and aliphatic substitutes (r = -0.22) and weakly correlated with the occurrence of a catechol structure within the compound molecule (r = 0.17). Selective dietary supplementation with phenolics exhibiting pro-oxidant activity may increase the possibility of systemic oxidative stress in patients treated with medications containing chelating properties or those with high plasma concentrations of H2O2 and non-transferrin bound iron.

Construction of stable photo-Fenton system with efficient removal capability of ciprofloxacin by accelerating in-situ photoreduction of Fe3+ in MIL-100(Fe).

Well-dispersed MIL-100(Fe) nanoparticles were synthesized under mild conditions and used to construct a photo-Fenton system (VMH system) with the assistance of visible-light irradiation and hydrogen peroxide. In such a VMH system, the MIL-100(Fe) has a high specific surface area and provides numerous Fe3+ active sites, thus accelerating the reaction of Fe3+ with photo-generated electrons under visible-light irradiation and generates Fe2+, and then the acquired Fe2+ can activate H2O2 to generate ⋅OH, accompanying with the oxidation of Fe2+ to Fe3+. Hence, the in-situ recycling of Fe2+/Fe3+ promotes the generation of ·OH, thus making the VMH system exhibits promising photocatalytic activity. The removal rate of ciprofloxacin in the VMH system is as high as 95.2% within 120 min photo-Fenton reaction, which is about 26 times higher than that of the Visible light/MIL-100(Fe) system. Moreover, the VMH system also exhibits strong degradation ability to other typical antibiotics, such as tetracycline, norfloxacin and cephalexin, and maintains high cyclic stability, revealing great practical application potential in the purification of antibiotic wastewater.

Nanoscale zero-valent iron/biochar composites containing persistent free radicals (PFRs) for degradation of p-nitrophenol.

Despite the vital roles of Fe0/biochar composites in the Fenton-like systems for eliminating pollutants that have been recognized, the contributions of persistent free radicals (PFRs) of carbon-based materials are typically overlooked. In this study, the high-PFR-containing biochar nanoiron composites were prepared (nZVI/500), and the in situ generation of hydroxyl radicals (·OH) and degradation of p-nitrophenol (PNP) were investigated. The results showed that nZVI/500 could effectively remove PNP in solution within the pH range of 3-8. Quantitative experiments of ·OH presented that, compared with low PFRs-containing composites, nZVI/500 could generate 64.6 µM ·OH in 60 min without any extra energy consumption. Mechanistic studies revealed that (1) both PFRs and Fe0 are able to utilize dissolved oxygen to generate H2O2 in situ; (2) PFRs can promote the cycling of Fe3+/Fe2+ in the system due to their strong electron exchange ability; and (3) PFRs directly transfer electrons to H2O2; therefore, the presence of PFRs accelerates the generation of ·OH in the system and facilitates the removal of PNP. This study provides an important theoretical basis and technical reference for expanding the application of PFR-rich carbon-based materials to remove environmental pollutants.

The application of ferrous and graphitic N modified graphene-based composite cathode material in the bio-electro-Fenton system driven by sediment microbial fuel cells to degrade methyl orange.

In this work, the ferrous (Fe2+) and graphitic N modified graphene-based composite cathode materials (N-rGO/Fe3O4) were developed through an in-situ reduction method, aiming to facilitate the two-electron pathway in the oxidation-reduction process. This approach generated a specific concentration of H2O2, enabling the construction of a sediment bio-electro-Fenton system using Fe2+ released from the cathode materials. Notably, this system operates without the need for proton exchange membranes. During the cathode material preparation, the utilization of Fe2+ as a reduction agent for graphene oxide (GO), triggered ammonia water to form graphitic N in graphene sheets. This addition enhanced the two-electron pathway, resulting in increased H2O2 production. Specifically, when the Fe2+ concentration was maintained at 0.1 mol/L, precise preparation of N-rGO/Fe3O4 occurred, leading to a maximum output voltage of 0.528 V and a maximum power density of 178.17 mW/m2. The degradation of methyl orange (MO) reached 68.91% within a 25-h period, a phenomenon contributed to the presence of graphitic N in the graphene sheets. H2O2, a byproduct of the two-electron pathway in cathode oxidation reduction reaction, played a crucial role in constructing the bio-electro-Fenton system. This system, in conjunction with Fe2+ released from N-rGO/Fe3O4, facilitated the complete degradation process of MO.

Efficient photocatalytic in-situ Fenton degradation of 2,4-dichlorophenol via anthraquinone-modified carbon nitride for 2e- oxygen reduction.

Constructing a photocatalytic in-situ Fenton system (PISFs) is a promising strategy to address the need for continuous hydrogen peroxide (H2O2) addition and the low efficiency of H2O2 activation for hydroxyl radical generation in the traditional Fenton reaction. In this study, we constructed a photocatalytic in-situ Fenton system using anthraquinone-modified carbon nitride (AQ-C3N4) for efficient pollutant degradation. The resultant AQ-C3N4 not only enhanced the production of H2O2 but also increased the generation of hydroxyl radical (·OH). Experimental results demonstrated that, the apparent rate constant for the degradation of 2,4-Dichlorophenol (2,4-DCP) by AQ-C3N4-PISFs was 0.145 min-1, which is 2.74 times higher than that of C3N4 under visible light. Density functional theory (DFT) calculations indicate that AQ modification promotes electron-hole separation while increasing the adsorption energy of O2. Independent gradient model (IGM) analysis based on Hirshfeld Partition revealed that van der Waals interactions between AQ-C3N4 and 2,4-DCP promoted the degradation process. This work provides new ideas to overcome the problems of continuous addition of H2O2 and low utilization of ·OH that exist in conventional Fenton system.

In-situ production and activation of H2O2 over hydroxyapatite modified CuFeO2 for self-sufficient heterogeneous photo-Fenton degradation of doxycycline hydrochloride.

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.