Sustainable synthesis of modulated Fe-MOFs with enhanced catalyst performance for persulfate to degrade organic pollutants

Advances and challenges in the removal of organic pollutants via sulfate radical-based advanced oxidation processes by Fe-based metal-organic frameworks: A review

Organic contaminants, notorious for their complexity and resistance to degradation, are prevalent in aquatic environments, posing severe threats to ecosystems. Sulfate radical-based advanced oxidation processes (SR-AOPs), known for their stability and high effectiveness, have become a common choice for treating organic wastewater. Metal-organic framework materials (MOFs) have garnered substantial attention due to their facile chemical manipulation, unique structural configurations, and other favorable properties. Therefore, this article critically reviews recent advances in research involving the utilization of Fe-based MOFs (Fe-MOFs) and their derivatives in SR-AOPs. Specifically, it highlights the manipulation of influencing factors within the system to enhance the degradation of organic pollutants. The mechanisms and applications underlying the degradation of organic pollutants in the SR-AOPs system are also elucidated.

FeCu bimetallic metal organic frameworks photo-Fenton synergy efficiently degrades organic pollutants: Structure, properties, and mechanism insight

The high ion leaching, low photogenerated charge separation efficiency, and slow metal valence cycling of Fe-based metal organic frameworks (MOFs) have limited their application in the deep treatment of organic pollutants. Herein, FeCu bimetallic MOFs (FeCuBDC) were synthesized using a modified solvothermal method, and a coupled photo-Fenton degradation system was successfully constructed. Degradation performance tests showed that FeCuBDC could efficiently degrade 99.3% ± 0.1% of 50 mg/L phenol within 40 min. The reaction rate constants of the photo-Fenton system were 11.0 and 64.7 times higher than those of the single Fenton reaction and photocatalysis, respectively. FeCuBDC also exhibits good cycling stability, degradation generalization, and excellent photoelectric catalytic properties. Such a considerable enhancement in the overall performance pertains to the following. First, the introduction of Cu into Fe-MOFs not only improves the crystallinity and stability, but also reduces the band gap value, increases the absorption capacity of visible light, and promotes the generation of photogenerated carriers. Second, the FeCu in MOFs are all mixed valence. Initially, the high-valence FeCu captures photogenerated electrons and promotes photogenerated charge separation and transfer. Then, the low-valence FeCu adsorbs and decomposes H2O2, accelerating the valence cycling of the bimetallic sites. The core of the reaction mechanism is that FeCuBDC effectively promotes the photo-Fenton synergy.

MXene-supported MIL-88A(Fe) as persulfate activator for removal of tetracycline

The poor conductivity, poor stability, and agglomeration of iron-based metal organic framework MIL-88A(Fe) limit its application as persulfate (PS) activator in water purification. Herein, MXene-supported MIL-88A(Fe) composites (M88A/MX) were synthesized to enhance its adsorption and catalytic capability for tetracycline (TC) removal. Scanning electron microscope (SEM), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FT-IR), and X-ray photoelectron spectroscopy (XPS) were used to characterize prepared materials, confirming the successful attachment of MIL-88A(Fe) to the surface of MXene. M88A/MX-0.2 composites, prepared with 0.2 g MXene addition, exhibit optimal degradation efficiency, reaching 98% under conditions of 0.2 g/L M88A/MX-0.2, 1.0 mM PS, 20 ppm TC, and pH 5. The degradation rate constants of M88A/MX-0.2 were 0.03217 min-1, which was much higher than that of MIL-88A(Fe) (0.00159 min-1) and MXene (0.00626 min-1). The removal effects of reaction parameters, such as dosage of M88A/MX-0.2 and PS; initial solution pH; and the presence of the common co-existing constituents (humic acid and the inorganic anions) were investigated in detail. Additionally, the reuse of M88A/MX-0.2 showed that the composites had good cycling stability by recurrent experiments. The results of electron paramagnetic resonance (EPR) and quenching experiments indicated that ·OH, ·SO4-, and ·O2- were involved in the M88A/MX-0.2/PS system where persulfate oxidation process was activated with prepared M88A/MX-0.2. In addition, the intermediates of photocatalytic degradation were determined by HPLC-MS, and the possible degradation pathways of the target molecules were inferred. This study offered a new avenue for sulfate-based degradation of Fe-based metal organic framework.

Facile synthesis of bimetallic ACF/CC@FeOCl-Cu composite cathode for efficient degradation of sulfamethoxazole at neutral pH by a flow-through heterogeneous electro-Fenton process

Flow-through heterogeneous electro-Fenton (FHEF) process shows a broad prospect for refractory organic pollutants removal. However, maintaining a long-term service life of higher catalytic cathode is crucial for the development of cathode materials, especially for iron-functionalized cathode operated under harsh conditions. In this study, a novel bimetallic CC@FeOCl-Cu composite was synthesized through one-step calcination, coupled with a series of microstructure characterization methodology, including XRD, SEM-EDS, XPS, and FTIR. The superior catalytic activity of CC@FeOCl-Cu could be ascribed to Fe-Cu synergy and better dispersion of FeOCl nanosheets. With the optimal Cu:Fe ratio of 1:60, the bifunctional ACF/CC@FeOCl-Cu cathode was employed in FHEF process, exhibiting an outstanding performance for sulfamethoxazole (SMX) removal over a wide pH range (3.0-9.0). Comparison of experimental results indicated that the ACF/CC@FeOCl-Cu-FHEF process showed higher performance than ACF/CC@FeOCl-FHEF and homogeneous EF processes. The average SMX removal efficiency was 98% and TOC removal efficiency was more than 57% even after 10 cycles. Radical quenching experiments and electron spin resonance test confirmed that •OH was the primary active species. More •OH was generated in the ACF/CC@FeOCl-Cu-FHEF process because the doping of Cu could enhance catalytic activity of cathode. In addition, the satisfactory performance could be observed in the ACF/CC@FeOCl-Cu-FHEF process for the treatment of real landfill leachate, indicating its potential for practical application in wastewater treatment.

Application of Fe-MOFs in Photodegradation and Removal of Air and Water Pollutants: A Review

Photocatalytic technology has received increasing attention in recent years. A pivotal facet of photocatalytic technology lies in the development of photocatalysts. Porous metal-organic framework (MOF) materials, distinguished by their unique properties and structural characteristics, have emerged as a focal point of research in the field, finding widespread application in the photo-treatment and conversion of various substances. Fe-based MOFs have attained particular prominence. This review explores recent advances in the photocatalytic degradation of aqueous and gaseous substances. Furthermore, it delves into the interaction between the active sites of Fe-MOFs and pollutants, offering deeper insights into their mechanism of action. Fe-MOFs, as photocatalysts, predominantly facilitate pollutant removal through redox processes, interaction with acid sites, the formation of complexes with composite metal elements, binding to unsaturated metal ligands (CUSs), and hydrogen bonding to modulate their respiratory behavior. This review also highlights the focal points of future research, elucidating the challenges and opportunities that lie ahead in harnessing the characteristics and advantages of Fe-MOF composite catalysts. In essence, this review provides a comprehensive summary of research progress on Fe-MOF-based catalysts, aiming to serve as a guiding reference for other catalytic processes.

Oxygen Vacancies in Piezoelectric ZnO Twin-Mesocrystal to Improve Peroxymonosulfate Utilization Efficiency via Piezo-Activation for Antibiotic Ornidazole Removal

Piezoelectric mesocrystals as defective materials have been demonstrated to possess adsorptive and catalytic properties in redox reactions. However, there is still a lack of research on the quantitative relationship between the defect concentration and the piezocatalytic performance in piezoelectric mesocrystals. Herein, twin-hierarchical structure ZnO piezoelectric mesocrystals are taken with different oxygen-vacancies (OVs) concentrations to quantitatively investigate the effect of defect content on the peroxymonosulfate (PMS) piezo-activation in water purification. The ZnO piezoelectric mesocrystal with moderate OVs concentration exhibits a rapid antibiotic ornidazole (ORZ) pollutants degradation rate (0.034 min^-1 ) and achieves a high PMS utilization efficiency (0.162) that exceeds the most state-of-the-art catalytic processes, while excessive OVs suppressed the piezocatalytic performance. Through calculations of electron property and reactants affinity, a quantitative relationship between OVs concentration and piezocatalytic properties is established. The ZnO mesocrystal with moderate OVs concentration realized increased electron delocalization, reduced charge transfer barrier, and enhanced reactants affinity, thus accelerating the kinetics of PMS activation. This work provides theoretical guidance for the application of defect engineering in mesocrystal to realize enhanced piezocatalytic performance.

Revealing the synergistic mechanism of the generation, migration and nearby utilization of reactive oxygen species in FeOCl-MOF yolk-shell reactors

Fenton-like reactions is attractive for environmental pollutant control, but there is an urgent need to improve the utilisation of hydroxyl radicals (·OH) in practical applications. Here, for the first time, FeOCl is encapsulated within a Metal Organic Framework (MOF) (Materials of Institut Lavoisier-101 (MIL-101(Fe))) as a yolk-shell reactor (FeOCl-MOF) by in situ growth. The interaction between FeOCl and the MOF not only increases the electron density of FeOCl, but also shifts down the d-band centre. The increase of electron density could promote the efficient conversion of H₂O₂ to ·OH catalysed by FeOCl. And the shift of the d-band centre to the lower energy level facilitates the desorption of ·OH. Experimental and theoretical calculations showed that the high catalytic performance was attributed to the unique yolk-shell structure that concentrates the catalytic and adsorption sites in a confinement space, as well as the improved electron density and d-band centre for efficient generation, rapid desorption and utilized nearby of ·OH. Which is utilized nearby by the organic pollutants adsorbed by the surface MOF, thus greatly improving the effective conversion of H₂O₂ and the ·OH utilisation (from 25.5% (Fe²⁺/H₂O₂) to 77.1% (FeOCl-MOF/H₂O₂)). In addition, a catalytic reactor was constructed to achieve continuous efficient treatment of organic pollutants. This work provides a Fenton-like microreactor for efficient generation, rapid desorption, and nearby utilization of ·OH to improve future technologies for deep water purification in complex environments.

Recent advances in application of metal-organic frameworks (MOFs) as adsorbent and catalyst in removal of persistent organic pollutants (POPs)

The presence of persistent organic pollutants (POPs) in the aquatic environment is causing widespread concern due to their bioaccumulation, toxicity, and possible environmental risk. These contaminants are produced daily in large quantities and released into water bodies. Traditional wastewater treatment plants are ineffective at degrading these pollutants. As a result, the development of long-term and effective POP removal techniques is critical. In water, adsorption removal and photocatalytic degradation of POPs have been identified as energy and cost-efficient solutions. Both technologies have received a lot of attention for their efforts to treat the world's wastewater. Photocatalytic removal of POPs is a promising, effective, and long-lasting method, while adsorption removal of persistent POPs represents a simple, practical method, particularly in decentralized systems and isolated areas. It is critical to develop new adsorbents/photocatalysts with the desired structure, tunable chemistry, and maximum adsorption sites for highly efficient removal of POPs. As a class of recently created multifunctional porous materials, Metal-organic frameworks (MOFs) offer tremendous prospects in adsorptive removal and photocatalytic degradation of POPs for water remediation. This review defines POPs and discusses current research on adsorptive and photocatalytic POP removal using emerging MOFs for each type of POPs.

Development of MOF Based Recyclable Photocatalyst for the Removal of Different Organic Dye Pollutants

The preparation of metal organic frameworks (MOFs) has come to the forefront in recent years because of their outstanding physical and chemical properties. Many MOFs such as Zn, Co, Ni, Fe, and Ag, etc., have been successfully synthesized. In this work, we followed the solvothermal assisted route to synthesize Ag-MOF (abbreviated as AMOF) nanosheets and then applied them as a photocatalyst to remove different organic pollutants, namely methyl orange (MO), crystal violet (CV), and methylene blue (MB). Chemical composition, optical properties, morphology, and microstructural analysis were analyzed using XPS, UV-visible spectrophotometer, FESEM, TEM, and EDS, respectively. The structural properties of AMOF nanosheets were studied by X-ray diffraction (XRD). Nitrogen adsorption and desorption isotherm analysis were utilized to evaluate the specific surface area and pore size of the AMOF nanosheets. Further, AMOF nanosheets showed notable photocatalytic performance for various dye pollutants degradation. The results confirmed 74.5, 85.5, and 90.7% of MO, CV, and MB dye pollutants removal after 120 min of irradiation with the rate constants (k) of 0.0123, 0.0153, and 0.0158 min^-1, respectively. The effect of superoxide radicals (O₂^-) and photogenerated holes (h⁺) on the organic dye pollutants removal was investigated using radical scavenger trapping studies. Moreover, the stability study also confirmed the recyclability of the photocatalyst. Therefore, the findings of this research present a realizable method to grow AMOF photocatalyst for successful degradation of various dye pollutants.

A novel polydopamine-modified metal organic frameworks catalyst with enhanced catalytic performance for efficient degradation of sulfamethoxazole in wastewater

In this study, a novel polydopamine (PDA)-modified metal organic frameworks (MOFs) catalyst (MIL/PDA) was successfully fabricated to activate persulfate (PS) for the degradation of sulfamethoxazole (SMX) in wastewater. The experimental results indicated that PDA-modified catalyst exhibited superior catalytic performance and enhanced the degradation of SMX (91.5%) compared to pure MOFs. The physical-chemical properties of the MIL/PDA catalyst were comprehensively characterized, and the applications in the catalytic degradation of SMX were evaluated. It was found that the modification of PDA enhanced the electron transfer, while promoting the redox cycle of Fe(III)/Fe(II), which in turn boosted the production of active oxygen species. Furthermore, MIL/PDA showed high stability and reusable performance over multiple cycles. Both radical and non-radical pathways were jointly involved in the activation process of PS were confirmed by quenching experiments combined with electron paramagnetic resonance (EPR). Based on this, the possible mechanism of the catalytic reaction was investigated. Finally, five degradation pathways of SMX degradation were proposed according to the results of liquid chromatography-mass spectrometry (LC-MS). This work provided a new insight into the design of novel and efficient heterogeneous catalysts for advanced wastewater treatment.

Biphase Co@C core-shell catalysts for efficient Fenton-like catalysis

Despite the vital roles of Co nanoparticles catalytic oxidation in the Fenton-like system for eliminating pollutants, contributions of Co phases are typically overlooked. Herein, a biphase Co@C core-shell catalyst was synthesized by the electrochemical co-reduction of CaCO₃ and Co₃O₄ in molten carbonate. Unlike the traditional pyrolysis method that is performed over 700 °C, the electrolysis was deployed at 450 °C, at which biphase structures, i.e., face-centered cubic (FCC) and hexagonal close-packed (HCP) structures, can be obtained. The biphase Co@C shows excellent catalytic oxidation performance of diethyl phthalate (DEP) with a high turnover frequency value (TOF, 28.14 min^-1) and low catalyst dosage (4 mg L^-1). Furthermore, density functional theory (DFT) calculations confirm that the synergistic catalytic effect of biphase Co@C is the enhancement for the breaking of the peroxide O-O bond and the charge transfer from catalysts to PMS molecule for the activation. Moreover, the results of radicals quenching experiments and electron paramagnetic resonance (EPR) tests confirm that SO₄^•-, •OH, O₂^•-, and ¹O₂ co-degrade DEP. Remarkably, 100% removals of three model contaminants, including DEP, sulfamethoxazole (SMX) and 2,4-dichlorophen (2,4-DCP), were achieved, either in pure water or actual river water. This paper provides an electrochemical pathway to leverage the phase of catalysts and thereby mediate their catalytic capability for remediating refractory organic contaminants.

S-doped MIL-53 as efficient heterogeneous electro-Fenton catalyst for degradation of sulfamethazine at circumneutral pH

The reduced S-modified MIL-53(Fe) was prepared by sulfurizing MIL-53(Fe) at low temperature, which was an efficient electro-Fenton catalyst at wide pH range (3-9) for sulfamethazine (SMT) degradation. The best temperature and MIL-53(Fe)/S ratio were 350 °C and 1:2, at which the BET surface area was much enlarged. The MIL-53(Fe) surface was etched by S to many 2D nanosheets with the thickness of ~50 nm, while S_2-2 replaced OH^- to coordinate with Fe²⁺ and increased the Fe²⁺ content, which improved the catalytic performance. Even at initial pH of 7.0, the SMT removal was 95.8%, and the rate constant (k) in the Hetero-EF process was 16-folds of that in the Homo-EF process. The turnover frequency (TOF_d) value of MIL-53(Fe)/S(1:2)-350 was 0.48 L g^-1 min^-1, which was 6.8 times that of commercial FeS₂. The S_2-2in catalyst adjusted the pH superfast, and promoted the generation of Fe²⁺ and thus efficiently activating H₂O₂ to form surface ^·OH, which was verified to be the main radical by EPR and radical scavenger experiments. This catalyst showed promising prospect for environmental application and could be regenerated by sulfidation method. S-doped MIL-53(Fe) was an excellent pH regulator, thus promoting promising application in Hetero-EF processes.

A Robust PVDF-Assisted Composite Membrane for Tetracycline Degradation in Emulsion and Oil-Water Separation

Tetracycline (TC) contamination in water has progressively exacerbated the environmental crisis. It is urgent to develop a feasible method to solve this pollution in water. However, polluted water often contains oil. This paper reported a glass fiber (FG)-assisted polyvinylidene fluoride (PVDF) hybrid membrane with dual functions: high TC degradation efficiency in emulsion and oil-water separation. It can meet the catalytic degradation of tetracycline in complex water. This membrane was decorated by coating the glass fiber with PVDF solution containing hydrophilic graphene oxide hybridized NH2-MIL-101(Fe) particles. Moreover, due to its strong mechanical strength enhanced by the glass fiber, it can be reused as TC degradation catalysts for dozens of times without cracking. Thanks to the hydrophobicity of PVDF and the surface pore size of MOFs, the prepared membrane showed a good oil-water separation performance. Besides, the hydrophilic graphene oxide (GO) and NH2-MIL-101(Fe) improved the membrane's anti-fouling performance, allowing it to be reused as the separation membrane. Therefore, the outstanding stability and recoverability of the membrane make it as a fantastic candidate material for large-scale removal of TC as well as oil-water separation application.

Highly Sensitive Detection of Trace Tetracycline in Water Using a Metal-Organic Framework-Enabled Sensor

Due to the abuse application of antibiotics in the recent decades, a high level of antibiotics has been let out and remains in our environment. Electrochemical sensing is a useful method to sensitively detect antibiotics, and the key factor for a successful electrochemical sensor is the active electrode materials. In this study, a sensitive electrochemical sensing platform based on a metal-organic framework (MOF) of MIL-53 (Fe) was facilely fabricated. It shows highly selective and sensitive detection performance for trace tetracycline. Differential pulse voltammetry (DPV) was applied to analyze the detection of tetracycline. The linear range of tetracycline detection was 0.0643 μmol/L-1.53 μmol/L, and the limit of detection (LOD) is 0.0260 μmol/L. Furthermore, the MOF-enabled sensor can be effectively used in actual water bodies. The results indicate that the electrochemical sensor is a high potential sensing platform for tetracycline.

Application of Magnetic Composites in Removal of Tetracycline through Adsorption and Advanced Oxidation Processes (AOPs): A Review

Water pollution induced by the tetracycline (TC) has caused global increasing attention owing to its extensive use, environmental persistence, and potential harm for human health. Adsorption and advanced oxidation processes (AOPs) have been promising techniques for TC removal due to ideal effectiveness and efficiency. Magnetic composites (MCs) which exploit the combined advantages of nano scale, alternative sources, easy preparation, and separation from wastewater are widely used for catalysis and adsorption. Herein, we intensively reviewed the available literature in order to provide comprehensive insight into the applications and mechanisms of MCs for removal of TC by adsorption and AOPs. The synthesis methods of MCs, the TC adsorption, and removal mechanisms are fully discussed. MCs serve as efficient adsorbents and photocatalysts with superior performance of photocatalytic performance in TC degradation. In addition, the TC can be effectively decomposed by the Fenton-based and SO4•− mediated oxidation under catalysis of the reported MCs with excellent catalytic performance. Based on the existing literature, we further discuss the challenge and future perspectives in MCs-based adsorption and AOPs in removing TC.

Preparation of porous silicate supported micro-nano zero-valent iron from copper slag and used as persulfate activator for removing organic contaminants

Porous silicate supported micro-nano zero-valent iron (PSi@ZVI) was prepared from copper slag (CS) through carbothermal reduction technology, and used as a persulfate (PS) activator for removing organic contaminants. Results showed that the properties of the activator were greatly affected by the preparation conditions. Calcination for 20 min at 1100 °C with 20% anthracite was considered the optimum preparation condition for degradation of orange G (OG). The removal rate of OG was improved by increasing the dosages of PSi@ZVI or PS and raising the reaction temperature. Moreover, PSi@ZVI exhibited excellent PS activator ability in a wide range of initial pH, good degradation capability for eosin Y, methyl orange, acid fuchsine, and methylene blue. The reusability and safety of PSi@ZVI were verified. Electron paramagnetic resonance and radical quenching tests indicated that sulfate radical (SO₄^-) was the main active species in the PSi@ZVI/PS system. The X-ray diffraction results indicated that a high calcination temperature (1100 °C) was beneficial to the reduction of iron-bearing minerals to ZVI. Scanning electron microscopy and energy-dispersive spectroscopy results revealed that the formation of porous structure of PSi@ZVI and the generation of nano to micro-sized ZVI particles on the surface of the silicate holes. The X-ray photoelectron spectra showed that ZVI was first convert into Fe(II), which mainly activated PS and generated Fe(III) in the PSi@ZVI/PS system. Furthermore, the intermediates of OG were detected using gas chromatography-mass spectrometry, and the possible degradation pathway of OG was proposed. This study provides a novel approach for reuse of CS as a heterogeneous activator to effectively activate PS.

A Critical Review on Metal-Organic Frameworks and Their Composites as Advanced Materials for Adsorption and Photocatalytic Degradation of Emerging Organic Pollutants from Wastewater

Water-borne emerging pollutants are among the greatest concern of our modern society. Many of these pollutants are categorized as endocrine disruptors due to their environmental toxicities. They are harmful to humans, aquatic animals, and plants, to the larger extent, destroying the ecosystem. Thus, effective environmental remediations of these pollutants became necessary. Among the various remediation techniques, adsorption and photocatalytic degradation have been single out as the most promising. This review is devoted to the compilations and analysis of the role of metal-organic frameworks (MOFs) and their composites as potential materials for such applications. Emerging organic pollutants, like dyes, herbicides, pesticides, pharmaceutical products, phenols, polycyclic aromatic hydrocarbons, and perfluorinated alkyl substances, have been extensively studied. Important parameters that affect these processes, such as surface area, bandgap, percentage removal, equilibrium time, adsorption capacity, and recyclability, are documented. Finally, we paint the current scenario and challenges that need to be addressed for MOFs and their composites to be exploited for commercial applications.

Activation of peroxymonosulfate using drinking water treatment residuals modified by hydrothermal treatment for imidacloprid degradation

In this study, water treatment residuals (WTRs), a safe and valuable by-product containing iron, was used as a precursor for preparing effective activator (HWTRs) of peroxymonosulfate (PMS) for imidacloprid (IMD) degradation by hydrothermal treatment. Several affecting parameters on IMD degradation including PMS concentration, HWTRs dosage, initial pH and water matrix were discussed. The results of degradation experiments demonstrated that within the reaction time of 4 h, 97.64% of IMD could be removed with 0.5 g L^-1 HWTRs and 1.5 mM PMS, and the acidic conditions were favorable for IMD degradation. Both sulfate radicals (SO₄^•-) and hydroxyl radicals (·OH) were generated to attack the target pollutant IMD, and ·OH was the dominating radical in the HWTRs/PMS system, which was confirmed by the results of radicals scavenging experiments, electron spin-resonance spectroscopy (ESR) tests and quantitative analysis. What's more, X-ray photoelectron (XPS) spectroscopy was used to further verify the activation mechanism. Consequently, the activation by Fe(II) on the surface of HWTRs might dominate the reaction was confirmed. In addition, the possible degradation pathways of IMD were proposed on the basis of the degradation intermediates identified by LC-MS. This study offers an innovative idea for modifying raw WTRs to prepare efficient catalysts to activate PMS under relatively mild conditions.

Facile preparation of iron oxide doped Fe-MOFs-MW as robust peroxydisulfate catalyst for emerging pollutants degradation

A novel catalyst (Fe-MOFs-MW) was facilely synthesized under microwave-assisted with NaOH as modulator for activating peroxydisulfate (PDS). The accelerated nucleation process was confirmed by Johnson-Mehl-Avrami (JMA) model. There were abundant reactive sites on prepared Fe-MOFs-MW while maintaining high Space-Time-Yield value up to 2300 kg/m³·d. Degradation performance of Fe-MOFs-MW as PDS catalyst on sulfamethoxazole (SMX) removal was evaluated. Results indicated that Fe-MOFs-MW with more Fe element anchored (10%) exhibited excellent catalytic capacity for PDS. Besides, the fantastic stability and reusability were confirmed through recycle experiment. After recycled for 4 times, the removal efficiency of SMX and TOC was 88% and 31.3% compared to 98% and 38% without recycling, respectively. An accurate prediction model on the degradation effect with water matrices coexisted was established by response surface methodology (RSM) method. Moreover, SO₄^·-, O₂^·- and ·OH were confirmed as the main reactive species through chemical quenching and EPR tests. The mechanism of Fe-MOFs-MW/PDS process mainly based on electron circulation theory was proposed. As the robust PDS catalyst, facile prepared Fe-MOFs-MW was promising in the treatment of emerging pollutants.

Enhanced catalytic activity of MIL-101(Fe) with coordinatively unsaturated sites for activating persulfate to degrade organic pollutants

In this work, four novel defective MIL-101(Fe) catalysts with coordinatively unsaturated sites were successfully prepared via a facile synthesis strategy by employing benzoic acid, acetic acid, oxalic acid, or citric acid as a modulator. The modified catalysts were demonstrated the existence of defects in the parent framework by a series of characterizations. As compared to the initial MIL-101(Fe), the electronic structure of defective MIL-101(Fe) catalyst was effectively adjusted; meanwhile, the coordinatively unsaturated Fe sites were efficiently generated and the pore sizes were enlarged. Besides, the defective MIL-101(Fe) catalysts exhibited excellent catalytic performance for rhodamine B degradation by persulfate activation. To be specific, the degradation rates of rhodamine B increased from 58.70 to 94.05%, 86.11%, 78.70%, and 82.62%, respectively. The defective MIL-101(Fe) with coordinatively unsaturated sites showed good reusability and stability, and the probable catalytic mechanism was also investigated.