photo-Fenton Process Research Articles

Cu single atoms anchored on hydrangea-like carbon nitride for facilitating photo-Fenton: Role of Cu2+/Cu+ cycle

Single-atom photo-Fenton (PF) reaction is widely employed for the degradation of antibiotics and water disinfection. However, the key fundamental issues of the valence state cycling of single-atom metals and the activation of hydrogen peroxide (H2O2) in the PF process remain indistinct. Herein, we developed a catalyst donated as Cu single atoms anchored hydrangea-like carbon nitride (Cu-SA/CNH) with Cu−N4 coordination for PF reaction. Compared to pristine CNH, the Cu-SA/CNH exhibited a 2.42-fold increase in PF kinetics. The Cu-SA/CNH/PF system achieved 98.1% degradation efficiency of tetracycline and effectively inactivated Escherichia coli within 30 min. Density functional theory calculations demonstrated that the formation of Cu−N4 effectively improved the energy of the Cu d orbitals, leading to the generation of intermediate states that facilitated the Cu2+/Cu+ cycle. The adsorption capacity of Cu dxz orbitals on H2O2 increased nearly 10 times. This work provides valuable insights for enhancing single-atom PF activity to address environmental pollution.

Improving water security and sanitation in rural areas: comparative evaluation of TiO2 and photo-Fenton processes for rural wastewater treatment and reuse

Improving water security and sanitation in rural areas: comparative evaluation of TiO2 and photo-Fenton processes for rural wastewater treatment and reuse

Acids from fruits generate photoactive Fe-complexes, enhancing solar disinfection of water (SODIS): A systematic study of the novel “fruto-Fenton” process, effective over a wide pH range (4 – 9).

This study aimed to enhance solar disinfection (SODIS) by the photo-Fenton process, operated at natural pH, through the re-utilization of fruit wastes. For this purpose, pure organic acids present in fruits and alimentary wastes were tested and compared with synthetic complexing agents. Owing to solar light, complexes between iron and artificial or natural chelators can be regenerated through ligand-to-metal charge transfer (LMCT) during disinfection. The target complexes were photoactive under solar light, and the Fe:Ligand ratios for ex situ prepared iron complexes were assessed, achieving a balance between iron solubilization and competition with bacteria as a target for oxidizing species. In addition, waste extracts containing natural acidic ligands were an excellent raw material for our disinfection enhancement purposes. Indeed, lemon and orange juice or their peel infusions turned out to be more efficient than commercially available organic acids, leading to complete inactivation in less than 1 h by this novel "fruto-Fenton" process, i.e. in the presence of a fruit-derived ligand, Fe(II) and H2O2. Finally, its application in Lake Leman water and in situ complex generation led to effective bacterial inactivation, even in mildly alkaline surface waters. This work proposes interesting SODIS and fruit-mediated photo-Fenton enhancements for bacterial inactivation in resource-poor contexts and/or under the prism of circular economy.

468 https://doi.org/10.31881/TLR.2024.010 Decolourization of Synthetic Wastewater Related to the Textile Industry Using Photo-Fenton

The artisanal textile industry plays a vital role in the economy by providing a wide variety of products. However, this sector generates large quantities of wastewater containing a diversity of organic compounds, including dyes that, when released into the environment, contribute significantly to water pollution. In this research, samples of synthetic wastewater containing green aniline were subjected to decolourization using the photo-Fenton process. Synthetic textile wastewater was prepared at a concentration of 40 mg/L, and a calibration curve was established. During the treatment, ferrous sulfate (at concentrations of 50 and 150 mg/L) and H2O2 (at concentrations of 0.5 and 1.0 g/L) were added to 1 L of the synthetic effluent in a stirring medium (at 1000 rpm) and exposed to solar radiation for 1, 2, or 3 hours, while maintaining a pH of 3. To quantify the degree of decolourization, absorbance was measured at the beginning and end of the treatment using a colourimeter. The optimal conditions for Fe2+ concentration, H2O2 concentration, and treatment time, with an initial concentration of 40 mg/L, were found to be 150 mg/L, 1.0 g/L, and 3 hours, respectively. Under these conditions, the percentage of decolourization reached 97.546%. The study demonstrated that the concentration of Fe2+ and treatment time, as well as the interaction between Fe2+ concentration, H2O2 concentration, and treatment time, significantly influenced the degree of decolourization. Conversely, the concentration of H2O2 and other interactions did not exhibit significant influence.

Insight into heterogeneous photo-Fenton degradation of naphthol by natural magnetite: Redundancy analysis and toxicity assessment

Magnetite is a ubiquitous iron mineral in nature and its iron ions are usually isomorphically substituted by Ti and V cations, which shows a high ability for degradation of organic contaminants via the photo-Fenton process. However, numerous reports pay more attention to the activity of synthetic magnetite rather than natural magnetite. Here, three types of natural magnetite (HG01, HG02, and GCL01) with different Ti and V contents were investigated from the perspective of the difference in structural property, catalytic activity, H2O2 decomposition, and reactive oxygen species generation. Structural characterization exhibited that the purity of natural magnetite obeyed the order: GCL01 > HG02 > HG01. HG01 contained the highest Ti content in the form of ilmenite, followed by HG02 and GCL01. Moreover, HG01 yielded the highest photo-Fenton catalytic activity with 99.5 % of naphthol degradation and 96.0 % of H2O2 decomposition after 60 min reaction. The superior activity of HG01 was attributed to the relatively high Ti and V content as demonstrated by redundancy analysis. Mechanistic investigation implied that the Ti and V in the octahedral sites of the magnetite surface can accelerate the electron transfer from Fe(III) to Fe(II), resulting in higher Fenton activity. Besides, ilmenite in HG01 enhanced naphthol degradation because H2O2 accelerated the separation of photoelectron-holes pairs to promote O2− production. Furthermore, as revealed by gas chromatography-mass spectrometry and the toxicity of identified products predicted by the ECOSAR model, the toxicity of naphthol can effectively reduce accompanied by the harmless products generated. The high reusability, low iron ions residual in water, harmless end products, and easily recycled with magnetic separation suggest that natural magnetite has a promising application prospect for wastewater purification.

Microcontaminants degradation in tertiary effluent by modified solar photo-Fenton process at neutral pH using organic iron complexes: Influence of the peroxide source and matrix composition

Peroxymonosulfate (HSO5–) and persulfate (S2O82–), both sources of sulfate radicals (SO4*–), were evaluated for the first time in modified solar photo-Fenton using Fe-chelating agents (nitriloacetic acid (NTA), ethylene diaminetetraacetic acid (EDTA), ethylenediamine-N,N′-disuccinic acid (EDDS) and citrate (Cit)) in comparison with hydrogen peroxide (H2O2) to degrade benzophenone-3 (BP-3), fipronil (FIP) and propylparaben (PPB) (100 µg L–1 each) in municipal tertiary effluent. Increasing HSO5– concentrations from 1.5 to 5.9 mmol L–1 reached ≥ 96 % removal for all iron complexes, while treatment efficiencies for all tested S2O82– concentrations (1.5–5.9 mmol L–1) were limited to 20 % to 55 %. This difference can be attributed to a pH decrease in the HSO5– system. The influence of pH and matrix composition upon treatment performance were also assessed in the FeNTA/S2O82– system, which was more efficient at pH < 7.0 due to higher availability of soluble iron, and partial removal of bicarbonate and humic acids caused by acidification. Matrix composition significantly influenced the process as higher degradation rates were achieved after isolated or combined removals of chloride, bicarbonate and sulfate. The comparison between naproxen (a high electron density compound) degradation and that of BP-3, FIP, and PPB by SO4*– - based advanced oxidation processes (SR-AOPs) was used to evaluate the influence of target compound structures upon treatment performance. S2O82− and HSO5– were ineffective for treatment at pH 7.0. Thus, H2O2 was the best peroxide source for target compounds degradation at neutral pH as this is the natural pH of municipal tertiary effluent and results indicated that the assessment and choice for SR-AOPs should consider the chemical structure of target compounds.

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

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

Interface engineering of 1D/2D FeVO4/MoS2 hetero-structured nanocomposite with effective interfacial charge transfer: Facile synthesis and antibiotic drug degradation

The rapid accumulation of organic contaminants in wastewater is a considerable environmental concern. We are investigating nanoscale FeVO4 and MoS2 structures for enhanced removal of organic pollutants to overcome this challenge. The FeVO4/MoS2 nanocomposite was synthesized via a hydrothermal technique. This study looks at how the FeVO4/MoS2 nanocomposite could be explored as a good catalyst for the degradation of ciprofloxacin drug through Photo-Fenton process. The synergy between FeVO4 and MoS2 and hydroxyl radicals leads to accelerated degradation. Our findings imply that FeVO4/MoS2 nanocomposites could remove pharmaceutical pollutants from wastewater sources, contributing to water treatment technology.

Investigating the Efficiency of Photo-Fenton (UV/H2O2/Fe2+) in Removing the Indomethacin Antibiotic From Aqueous Solutions

Water pollution caused by antibiotics is one of the major challenges in the world today. The current research aims to investigate the effect of the Photo-Fenton process in removing indomethacin antibiotics from aqueous solutions. This experiment-based study was conducted on a laboratory scale and discontinuous manner. The influential variables affecting the removal efficiency of indomethacin include initial antibiotic concentration, pH, time, hydrogen peroxide concentration, and iron ion. The study was conducted base on standard methods (APHA, AWWA, CFWP, 2005). The Design Expert software was used to analyze the effect of independent variables on the removal efficiency of indomethacin antibiotics in the Photo-Fenton process (UV/H2O2/Fe2+) using response surface methodology (RSM) and central composite design (CCD). To ensure the repeatability of the results, each experiment was repeated three times and the reported the average. The results showed that the optimal removal conditions for indomethacin antibiotics were pH = 4, H2O2 oxidant concentration = 50 ppm, Fe2+catalyst concentration = 50 ppm, time = 75 minutes, and initial antibiotic concentration = 20 ppm, with a removal efficiency of 91.03% . The variables of initial antibiotic concentration, H2O2 concentration, and pH had the greatest impact on the removal efficiency of indomethacin. The results of this study indicate that under optimal conditions, more than 90% of indomethacin antibiotics can be removed from aqueous solutions using the Photo-Fenton process, which is a significant result for removing this pharmaceutical pollutant from aquatic environments.

Tyrosol removal by photo–Fenton–like process using CaAlFe mixed oxides synthesized via hydrocalumite from aluminum salt cake

Solids with potential application in tyrosol (Ty) removal by photo–Fenton processes have been synthesized using aluminum salt cake as a source. Two series of hydrocalumite layered double hydroxides (LDH) were synthesized: one containing structural Fe3+ (occupying octahedral positions in the LDH) and another containing surface impregnated Fe3+; all solids were calcined in air at 750 °C. The solids were characterized by powder X–ray diffraction, FT–infrared spectroscopy, thermal analysis, N2 adsorption–desorption isotherms at –196 °C, particle size distribution and electron microscopy. One of the main differences between the two series was that Fe3+ impregnation by the incipient wetness method and subsequent calcination at 750 °C did not lead to the formation of CaAlFe mixed oxides. The calcined solids were evaluated as photocatalysts in the photo–Fenton process for Ty removal (a typical compound found in olive oil mill wastewater), the samples containing surface Fe3+ showing better results. The solid prepared by impregnation of hydrocalumite with 20% iron and subsequently calcined at 750°C, under the optimum reaction conditions (catalyst dose = 0.5 g/L, [H2O2] = 0.468 g/L and [Ty]0 = 100 mg/L, in the presence of UV light), reached complete Ty removal with contaminant mineralization of 95% after only 60 min reaction. The cyclic study showed that this sample maintained its stability after 3 cycles of reuse without iron leaching, and a better performance than other materials reported in the literature.

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.

Performance and oxidation mechanism of VUV photo–Fenton in simultaneous removal of Ni-EDTA and hypophosphite: decomplexation, low-valent phosphorous oxidation and DFT calculation

The photo–Fenton process offers a promising alternative for the oxidation of complex heavy metals. However, the potential influence of coexisting substrates may be overlooked. The •OH radicals generated in the photo–Fenton process ensure superior oxidation ability. In this study, we used a vacuum ultraviolet (VUV) light-assisted photo–Fenton (VPF) process to explore its performance in the synergistic oxidation of Ni-ethylenediaminetetraacetic acid (EDTA) and coexisting hypophosphite, typical pollutants in electroless nickel plating (ENP) wastewater. Based on electron spin resonance (ESR) and DMSO-probing results, •OH was the predominant reactive oxygen species, and VPF possessed the highest •OH concentration compared to other photochemical processes under identical conditions (pH, Fe, H2O2). Enhanced •OH generation in VPF was attributed to various photochemical reactions, including photo–Fenton, UV/H2O2, and VUV/H2O. Consequently, VPF exhibited efficient Ni-EDTA decomplexation and hypophosphite oxidation. Notably, the evolution and rate-limiting steps during hypophosphite oxidation were demonstrated by experimental results and density functional theory calculations. Hypophosphite was initially oxidized to phosphite, which subsequently oxidized to phosphate. The oxidation of phosphite could be considered the rate-limiting step as it exhibits higher energy barriers than hypophosphite oxidation. Adequate •OH generation in the VPF process could overcome this energy barrier, indicating its potential for application in pollutant removal and resource recovery from ENP wastewater.

Degradation of antibiotic sulphamethoxazole by application of modified photo-Fenton processes: kinetics, degradation pathways and toxicity

ABSTRACT Degradation of antibiotic sulphamethoxazole (SMX) was studied by applying modified photo-Fenton reactions (MPF) with the novel choice of using sodium tripolyphosphate (STP) and sodium hexametaphosphate (SHP) complexing agents. STP and SHP have a strong ability as complexing agents because they can sequester and complex with different ions. Process optimisation was performed using Doehlert design at pH = 6. This study presented higher performance for MPF using STP and SHP complexing agents than conventional photo-Fenton and H2O2 + UV process. The best yields were associated with the formation of a smaller number of intermediates with high degradation efficiency and low oxidative stress, environment-friendly and promising processes.

Photocatalytic Degradation of Crystal Violet Dye Using Iron Oxide Nanoparticles

Increased industrial population causes water pollution. The release of toxic waste products from various industries become a major environmental issue. There are several methods for water decontamination and the advanced oxidation process (AOP) is one of them. The AOP’s rate can be increased using a variety of nanoparticles as a catalyst to degrade contaminants dyes like Crystal violet (CV). Magnetic nanoparticles (MNPs) are one of the most suitable materials to deal with this environmental issue because of their easy reusability along with high reactive surface area and easy to synthesize. Considering this, using the co-precipitation method iron oxide nanoparticles (IONPs) were synthesised in the present work. The as-prepared nanoparticles are then systematically characterized by various analytical tools. The XRD and FTIR suggest the crystalline structure and surface functional groups of the IONPs. The zeta potential study depicts the surface charge of nanoparticles within the colloidal solution. Additionally, the catalytic activity of IONPs was studied by the photo-Fenton process. The utilization of various catalytic parameters like pH (3–7), catalyst dosage (100–400 mg), dye concentration (0.025–0.1 mM) and H2O2 concentration (2–8 mM) has enhanced the effectiveness of the photo-Fenton process for the efficient removal of organic pollutant. Degradation efficiency was observed to be 94% after 90 minutes in the treatment of 5 mg nanoparticles with 0.05 mM dye solution. This magnetically recyclable catalyst will facilitate the advancement of water treatment in an environmentally sustainable and cost-effective manner, with notable potential.

PPS/TA-PEI/β-FeOOH membranes with powerful photo-Fenton self-cleaning capability for efficient oil–water emulsion separation

Polyphenylene sulfide (PPS) microporous membranes have garnered extensive research enthusiasm concerning their outstanding permeation performance and separation accuracy in treating oily wastewater. Nevertheless, the inherent hydrophobic chemical structure, along with the noticeable concentration polarization effect, predisposes them to severe membrane contamination during the separation process. Accordingly, it is desirable to design a PPS self-cleaning membrane with superior anti-fouling capability, fast transport, and remarkable flux recovery. This study marks the first combination of PPS membrane materials with the photo-Fenton process. In detail, the polyphenol (tannic acid, TA)-polycation (polyethyleneimine, PEI)-metal ion (Fe3+) double cross-linking coatings were first assembled on the PPS substrate surface. Subsequently, β-FeOOH photocatalysts were synthesized through in-situ mineralization to further strengthen the hydrophilicity of the membranes. The obtained PPS/TA-PEI/β-FeOOH composite membrane achieved exceptional separation of diverse oil-in-water (O/W) emulsions. The PPS/TA-PEI/β-FeOOH membranes exhibited in-air superhydrophilic and under-water superoleophobicity, exhibiting under-water oil contact angles greater than 151° for diverse oil agents. The fabricated composite membranes displayed high permeability (a flux of the petroleum ether-in-water (P/W) emulsion reached 3400.5 L m−2h−1 bar−1 driven by a pressure of 0.05 MPa) along with ideal oil rejection (98.6 %). Significantly, the PPS/TA-PEI/β-FeOOH membrane possessed powerful photo-Fenton self-cleaning capability, and its flux recoveries of the contaminated membrane exceeded 90.3 % for varied O/W emulsions after being cleaned by visible light for 10 min. We believe that our research presents a novel approach for the exploitation of PPS-based photo-Fenton self-cleaning membranes, which also exhibit great applicative potential in oily wastewater treatment.

Evaluation of Fenton, Photo-Fenton and Fenton-like Processes in Degradation of PE, PP, and PVC Microplastics

The global problem of microplastics in the environment is “inspiring” scientists to find environmentally friendly and economically viable methods to remove these pollutants from the environment. Advanced oxidation processes are among the most promising methods. In this work, the potential of Fenton, photo-Fenton, and Fenton-like processes for the degradation of microplastics from low-density polyethylene (LDPE), polypropylene (PP), and poly(vinyl chloride) (PVC) in water suspensions was investigated. The influence of three parameters on the efficiency of the degradation process was tested: the pH of the medium (3–7), the mass of added iron (10–50 times less than the mass of microplastics), and the mass of added H2O2 (5–25 times more than the mass of added iron). The effectiveness of the treatment was monitored by FTIR-ATR spectroscopy. After 60-min treatments, the PP microparticles were found to be insensitive. In the Fenton treatment of PVC and the photo-Fenton treatment of LDPE and PVC, changes in the FTIR spectra related to the degradation of the microplastics were observed. In these three cases, the treatment parameters were optimized. It was found that a low pH (3) and a high iron mass (optimal values were 1/12 and 1/10 of the mass of the microplastics for LDPE and PVC, respectively) favored all three. The degradation of LDPE by the photo-Fenton treatment was favored by high H2O2 concentrations (25 times higher than the mass of iron), while these concentrations were significantly lower for PVC (11 and 15 times for the Fenton and photo-Fenton treatment, respectively), suggesting that scavenging activity occurs.

Effect of different salt precursors on zinc ferrite synthesis and their photo-Fenton activity

Polycrystalline and mesocrystalline zinc ferrite were successfully fabricated via a solvo-thermal method using different salt precursors. This study found that when iron sulfate salt was used as a precursor, polycrystalline zinc ferrite was formed. Polycrystalline zinc ferrite is a well-dispersed 400-nm sphere solid particle. Primary nano-crystals have highly preferred orientations; however, defects exist among the particles. When iron chloride salt was used as a substitute as a prime material, mesocrystalline zinc ferrite was synthesised. The products are shaped as hollow-spheres with an average size of approximately 500 nm and are composed of nano-crystal sub-units aligned in a highly oriented crystallographic structure. Zinc ferrite mesocrystalline samples have many voids, and the inter-spaces of their structure indicate the high porosity hollow-sphere architecture of zinc ferrite. The experimental results show that specific adsorption of Cl− and SO42− ions on the surface plays a crucial role during the growth process of products with different morphologies and crystallographic structures. Cl− adsorption on the surface may promote the formation of mesocrystal hollow-sphere particles; whereas, SO42− gives rise to polycrystalline solid spheres. The use of the as-prepared products as catalysts for the photo-Fenton degradation of Rhodamine B (RhB) with an H2O2 oxidant under visible-light irradiation and the effects of reaction conditions, including pH, catalyst amount and H2O2 contratentation on the removal of RhB, were investigated. The reuse of the catalysts and a possible catalytic mechanism were also proposed. These results indicate that mesocrystalline hollow-sphere zinc ferrite is a favourable catalyst for dye degradation photo-Fenton processes.

HOFs structured CN template enables the dual regulation of Cu–O and Cu–N active sites in porous Cu-g-CN for synergistic photo-Fenton process

Photo-Fenton catalysis with strong oxidation potential and cyclic stability represents a promising technique for addressing the escalating environmental challenges. However, the photo-Fenton activity using Fe/Cu doped graphitic carbon nitride (g-CN) catalysts is significantly hindered by the limited reaction interface and non-tunable surface-active sites. Herein, we present a novel CN polymer type hydrogen bonded organic framework (CN-HOFs) template derived Cu-g-CN (Cu/CH-g-CN) based hybriding catalyst (CN-HOFs/Cu/CH-g-CN), which process greatly optimized surface features for high-performance photo-Fenton reaction with exceptional durability in a broad pH range of 3–11. Importantly, the distinctive porous structure of CN-HOFs template offers not only high specific surface area, but also the possibility to regulate Cu active sites. The coexistence of Cu–O and Cu–N active sites is identified by XPS, which facilitates the separation and migration of photogenerated charges, expediting the redox cycle. The synergistic photo-Fenton reaction boosted by the porous CN-HOFs structure and the dual Cu active sites (Cu–O and Cu–N) was verified by degradation activity of tetracycline. Under visible light irradiation at a concentration of 20 mg/L, the degradation efficiency reaches nearly 100% within 20 min, with exceptional cycling stability. Further investigations have revealed that the Cu–O active site is conducive to the adsorption of organic pollutants, while the Cu–N active site promotes electron transfer, accelerates the cyclic conversion of Cu+ and Cu2+. The dual copper active site is beneficial for the generation of hydroxyl radicals and the stable operation of the catalyst, resulting in significant photo-Fenton activity. This work underscores the importance of regulating the nanoscale morphology and electronic structure of photofunctional catalysts, not only to increase the active sites for photo-Fenton reactions but also to facilitate charge transfer and the cycling of active metal ions, thereby improving the sustainability of heterogeneous photo-Fenton process.

Directional and rapid electron transfer in perylene diimide modified iron-manganese bimetallic metal-organic frameworks for enhanced photo-Fenton process

Bimetallic metal-organic frameworks (MOFs) with iron and another transition metal in the inorganic nodes, as newly developed photo-Fenton catalysts, have gained an ample attention because of the synergistic effect and enhanced properties compared to the monometallic counterparts. However, the photo-Fenton application of bimetallic MOFs still faces the obstacle of unsatisfactory photogenerated electrons transfer due to the fast recombination of photogenerated electron-hole pairs. In this work, perylene diimide (PDI) was modified upon bimetallic NH2-MIL-88B(Fe, Mn) (FM88B) via the ammonolysis process to construct PDI/FM88B heterojunction structure. The constructed heterostructure mediated the directional transfer of photogenerated electrons from PDI (electron donor) to FM88 (electron acceptor). The built-in electric field (BIEF) between PDI and FM88B promoted the separation and directional transfer of photogenerated electron-hole pairs. The interfacial amide bond as the high-speed electronic transmission channel reduced the transfer distance and energy barrier of photogenerated electrons from PDI to FM88B, accelerating the photogenerated electrons delivery. As a result, both Fe(III)/Fe(II) and Mn(III)/Mn(II) redox couples were continuously and rapidly cycled, ultimately boosting the performance of FM88B for H2O2 activation. Compared with FM88B, the optimal 6%PDI/FM88B exhibited excellent degradation performance against tetracycline (TC) (degradation efficiency and apparent rate constant, as 89% and 0.067 min−1) and notable synergy between photocatalysis and Fenton-like process (synergistic factor of 77.61%). DFT calculation and HPLC-MS analysis were used to verify the possible degradation pathways of TC. Meanwhile, the corresponding toxicity changes during TC degradation were studied in detail. This work paves the way for improving the heterogeneous photo-Fenton performance of the bimetallic MOFs in environmental remediation.

Insight on the degradation of P-chlorophenol based on the Co-g-C3N4/diatomite composite photo-Fenton process

The non-metallic photocatalyst g-C3N4 is characterized by non-toxicity and straightforward preparation. Still, the drawbacks of low specific surface area and fast carrier complexation rate limit its practical application in photocatalysis. In this work, Co-doped g-C3N4 was prepared on the surface of diatomite (DE) through a simple one-step calcination method and used to degrade 4-chlorophenol (4-CP). Photocatalytic experiments showed that Co-g-C3N4/DE removed up to 98.7% of 4-CP. The doping of Co could capture the photogenerated electrons, thereby reducing the recombination of photocarriers and accelerating the oxidation–reduction reaction of Co3+/Co2+ and H2O2, promoting the generation of OH. Introducing DE improved the aggregation of g-C3N4 and expanded its surface area. Moreover, the Co-g-C3N4/DE composite material exhibited a low metal leaching rate and good reusability throughout the experiments. In addition, based on DFT calculations, the ROS attack mechanism of 4-CP degradation was speculated and calculated. The final product of 4-CP was found to pose a more minor environmental threat, according to the T.E.S.T. In short, the prepared Co-g-C3N4/DE composite realized the capture of photogenerated electrons and the acceleration of photocatalytic reactions, which are expected to solve the challenges in wastewater treatment.