Room-temperature preparation of highly efficient NH2-MIL-101(Fe) catalyst: The important role of -NH2 in accelerating Fe(III)/Fe(II) cycling

Band gap regulation of MIL-101(Fe) via pyrazine-based ligands substitution for enhanced visible-light adsorption and its photo-Fenton-like application

Regulating the photo-response region of iron metal-organic frameworks (Fe-MOFs) is a viable strategy for enhancing their practical application in the visible-light driven photo-Fenton-like process. This study developed a novel pyrazine-based Fe-MOFs (MIL-101(Fe)-Pz) by substituting the 1,4-dicarboxybenzene acid ligands in typical MIL-101(Fe) with 2,5-pyrazinedicarboxylic acid (PzDC), in which sodium acetate was used as coordinative modulator to control the crystal size (2-3 µm). The incorporation of Fe-pyridine N coordination structures originated from PzDC ligands gave MIL-101(Fe)-Pz narrowed band gap (1.45 eV) than MIL-101(Fe) (2.54 eV) resulting in improved visible-light adsorption capacity (λ > 420 nm), and also increased the proportion of Fe(II) in the Fe-clusters. Thus MIL-101(Fe)-Pz exhibited a synergistic enhanced photo-Fenton-like catalytic performance under visible-light irradiation. The MIL-101(Fe)-Pz/H2O2/Vis system could degrade 99% of sulfamethoxazole within 30 min, which was 10-fold faster than that of the pristine MIL-101(Fe), it also effectively removed other organic micropollutants with high durability and stability. Mechanistic analysis revealed that the PzDC ligands substitution decreased the band gap of MIL-101(Fe), giving MIL-101(Fe)-Pz appropriate band structure (-0.40∼1.05 V vs. NHE) which can cover several light-driven process for the generation of reactive oxygen species, including Fe(III) reduction and H2O2 activation for accelerating •OH generation, as well as oxygen reduction reaction for generating H2O2, O2•- and 1O2. This study highlights the role of pyridine-N containing ligands in regulating the band structure of Fe-MOFs, providing valuable guidance for the design of Fe-MOFs photocatalysts.

Colorimetric/fluorescent dual-mode biosensor based on metalloporphyrin covalently modified NH2-MIL-101(Fe) with highly efficient peroxidase-like activity for the detection of tetracycline in honey samples

Accurate detection of tetracycline residue is of great significance for ensuring product quality and protecting human health. Here, a colorimetric/fluorescent dual-mode biosensor was developed for the detection of tetracycline in honey by using metalloporphyrin [TCPP(Fe)] covalently modified NH2-MIL-101(Fe) [named NH2-MIL-101(Fe)@TCPP(Fe)]. The morphology, chemical structure and peroxidas-like activity of this hybrid nanozyme were comprehensively studied. Based on excellent catalytic activity and intrinsic fluorescence of NH2-MIL-101(Fe)@TCPP(Fe), a colorimetric/fluorescent dual-mode biosensor was developed for the detection of tetracycline. The primary mechanism for this dual mode biosensor was the inhibitory effect of tetracycline on on NH2-MIL-101(Fe)@TCPP(Fe) catalyzed chromatic reaction between H2O2 and 3,3',5,5'-tetramethylbenzidine (TMB)/o-phenylenediamine (OPD), which was ascribed to the consumption of ·OH by tetracycline and the adsorption of tetracycline on the surface of NH2-MIL-101(Fe)@TCPP(Fe). After effective validation, this colorimetric/fluorescent dual mode method was applied to detect tetracycline residues in three actual honey samples.

Amino-functionalized MIL-101(Fe)-NH2 as efficient peracetic acid activator for selective contaminant degradation: Unraveling the role of electron-donating ligands in Fe(IV) generation

Peracetic acid-based advanced oxidation processes (PAA-AOPs), which generate various reactive radicals, have garnered substantial attention for degradation emerging contaminants (ECs). However, nonselective radical-based PAA-AOPs often suffer from interference by water matrix components, causing low contaminants removal efficiency. This study explores the use of amino-(NH2)-functionalized metal-organic frameworks (MIL-101(Fe)-NH2) as heterogeneous catalysts for PAA activation, enabling the generation of high-valent iron- (Fe)-oxo species (Fe(IV)) capable of efficiently degrading ECs (80 -100 %, within 30 min). The Fe(II) clusters in MIL-101(Fe)-NH2, modulated by electron-donating -NH2 groups, play a pivotal role in Fe(IV) generation. Scavenger and probe experiments confirmed Fe(IV) as the primary reactive species responsible for ECs degradation. Density functional theory calculations demonstrated that the four-electron transfer to generate Fe(IV) has lower free energy than the two-electron transfer to generate organic radicals (e.g., CH3COO• and CH3C(O)OO•). Furthermore, thermodynamically unfavorable CH3COO• desorption further promotes Fe(IV) generation. The PAA/MIL-101(Fe)-NH2 system efficiently degraded SMX (kapp= 121.2 -287.2 M-1s-1) and other ECs (kapp= 40 -432 M-1s-1) with minimal interference from water matrix components and excellent reusability. This study demonstrates that MIL-101(Fe)-NH2 is a robust catalyst for PAA activation and provides a novel approach for selectively generating Fe(IV) for ECs degradation.

Amino-functionalized Fe/Co bimetallic MOFs for accelerated Fe (III)/Fe (II) cycling and efficient degradation of sulfamethoxazole in Fenton-like system

Metal-organic frameworks (MOFs) are recognized as important Fenton-like materials for environmental remediation. However, their applications are often hindered by slow cycling between Fe (III) and Fe (II). This study aimed to address the slow Fe (III)/Fe (II) cycling limitation of Fe-MOFs through dual modification strategy: bimetallic modification and amino functionalization. A series of NH2-MOF(Fe, Co) catalysts with varying Fe/Co ratios were synthesized via a hydrothermal method and evaluated for sulfamethoxazole (SMX) degradation. The optimized NH2-MOF(Fe, Co) catalyst (Fe/Co ratio = 7:3) exhibited substantially enhanced catalytic performance, with SMX removal rate and rate constant in the H2O2 system being 3.2 and 43.5 times higher than those of the Fe-MOF/H2O2 system, respectively. The catalyst demonstrated robust performance across a wide pH range (3.05-7.00), addressing a common limitation of Fenton-like systems. Physicochemical characterization revealed that the enhanced performance was attributed to two key factors: the synergistic effect between Co and Fe in the bimetallic active center, and improved electron transfer to the central metal due to -NH2 functionalization. These modifications effectively addressed the Fe (III)/Fe (II) redox cycling limitation. The proposed reaction mechanism provides insights into SMX degradation pathways in the NH2-MOF(Fe, Co)/H2O2 system. This study presents an efficient and stable MOF-based Fenton-like catalyst with potential applications in wastewater treatment and environmental remediation.

Efficient photocatalytic hydrogen production by employing a graphdiyne/NH2-MIL-88B(Fe) composite

The electron transfer rate in photocatalysts is one of the factors determining their hydrogen production activity. In this work, NH2-MIL-88B(Fe) (NFM) was synthesized using a one-step hydrothermal synthesis method and NFM/GDY-25 (NFMG-25) was successfully synthesized by loading graphdiyne (GDY) onto the surface of NFM. The hydrogen production performance and the mechanism of the prepared photocatalysts were systematically investigated using XRD, SEM, FT-IR, XPS, UV-Vis, PL and photoelectrochemical tests. The results showed that the hydrogen production of NFMG-25 reached 61.7 μmol in 5 hours. Photoelectrochemical and Mott-Schottky tests demonstrated that the composite catalyst exhibited high photogenerated carrier separation efficiency and single catalysts were n-type semiconductors. The conduction bands of NFM and GDY were -0.36 V and -0.56 V, respectively, while the valence bands were 1.90 V and 1.12 V. NFM acted as an electron acceptor and donor, which accelerated the transfer of the electrons, and enhanced the photocatalytic hydrogen production efficiency of the composite system. This study provides an effective method for using NFM in photocatalytic hydrogen production.

Nanocellulose encapsulated nZVI@UiO-66-NH2 aerogel for high-efficiency p-chloronitrobenzene removal with selective reduction

A poriferous nZVI aerogel (nZVI@UiO-66-NH2/TCNF) was elaborately constructed by in-situ deposition of nZVI on UiO-66-NH2 and coupling with a bio-based TEMPO oxidized cellulose nanofiber (TCNF) substrate, followed by freeze-drying process for p-chloronitrobenzene (p-CNB) degradation. With degradation efficiency of above 85 % within 3 h under a wide pH range of 3-9, the nZVI@UiO-66-NH2/TCNF aerogel presented better p-CNB removal performance than other developed aerogels. Extended to 24 h, superior p-CNB removal performance (99.83 %) and 4-chloroaniline (p-CAN) selectivity (98.84 %) were successfully achieved. This could be attributed to 1) the facilitated mass transfer via concentration-gradient driving force with buffering and drag-reducing hydrated shear layer from porous channels of hydrophilic TCNF; 2) the enhanced adhesion of p-CNB onto UiO-66-NH2 and accelerated electron transfer by Fe-O-Zr bonds, synergistically improving the nitro- reduction of p-CNB using nZVI. This work pioneered a unique paradigm, providing nZVI with both solid bio-based moldability and highly-selective removal for the treatment of chloronitrobenzene containing wastewater.

Engineering cellulose aerogel composites for mercury ion sequestration and aquatic real time monitoring based on the immobilization of metal-organic frameworks

Industrial wastewater effluents containing elevated levels of mercury are a significant menace to both the ecosystem and human health. Despite the advent of metal-organic frameworks (MOFs) as promising adsorbents, their application in treatment of industrial wastewater has been impeded by the challenges associated with handling their powdered form. In this work, we introduce a straightforward method for fabricating MOF composite cellulose aerogels (5MM-101@CA). The resulting adsorbent showed a high adsorption capacity of 409.84 mg/g for Hg (II), with over 75 % removal efficiency maintained after five consecutive adsorption-desorption cycles. Furthermore, the material exhibited high sensitivity for the real-time detection of Hg (II), with a detection limit as low as 6.89×10-8 M. The adsorbent also showed remarkable fluorescence stability for up to a week, indicative of its excellent optical performance. Dynamic adsorption demonstrated the adsorbent's ability to sustain continuous and stable system operation without compromising adsorption efficiency. These findings underscore the effectiveness of post-synthetic modification (PSM) technology in enhancing the performance of MOFs, while highlighting the utility of low-cost cellulose as an effective carrier. Thus, the composite material developed in this work is promising as it not only maximizes the adsorption capabilities of MOFs but also circumvents the risk of secondary pollution.

Interfacial and electronic dual regulation of metal organic frameworks for enhanced catalytic oxidation of peroxymonosulfate into dyes

In heterogeneous advanced oxidation processes, it is important to improve the catalytic performance, which can be achieved by increasing the mass transfer of catalysts and utilization efficiency of reactive oxygen species (ROSs). Herein, the functional groups, amino group (NH2) and hydroxyl group (OH), were introduced onto the surface of metal organic frameworks (MOFs), FeBDC (Iron terephthalate) by ligand exchange. The synthesized MOFs were used as catalysts to activate peroxymonosulfate (PMS) for the efficient removal of dye from wastewater. The NH2/-OH groups accumulated at the surface of MOFs to significantly enhanced their hydrophilicity, which favored dye adsorption efficiency on the surface of MOFs from aqueous solution. This dye enrichment was benefited to the high utilization of ROSs due to the shorter transfer distance in solution. Additionally, the introduction of NH2/OH favored the reduction in electrochemical resistance both within the bulk and at the interface of the MOFs, thereby facilitating the electron transfer from the MOFs to PMS. The efficient utilization of ROSs (the radicals (SO4- and O2-) and non-radical (1O2)) generated by PMS removed nearly all RB171 (96.2-98.5 %) by oxidation reaction. The azo bonds and aromatic rings of dye molecules were susceptible to the attack by these ROSs. At the utilization of 5 cycles, iron leaching from MOFs/PMS was very low, satisfying the value of discharge standards. This work demonstrates that the functional groups presented in MOFs effectively facilitate the dual regulation of dye enrichment and catalytic activity in heterogeneous advanced oxidation processes.

Pt-N catalytic centres concisely enhance interfacial charge transfer in amines functionalized Pt@MOFs for selective conversion of CO2 to CH4

Improving ligand-to-active metal charge transfer (LAMCT) by finely tuning the organic ligand is a decisive strategy to enhance charge transfer in metal organic frameworks (MOFs)-based catalysts. However, in most MOFs loaded with active metal catalysts, electron transmission encounters massive obstacle at the interface between the two constituents owing to poor LAMCT. Herein, amines (-NH2) functionalized MOFs (NH2-MIL-101(Cr)) encapsulated active metal Pt nanoclusters (NCs) catalysts are synthesized by the polyol reduction method and utilized for the photoreduction of CO2. Surprisingly, the introduction of -NH2 (electron donating) groups within the matrix of MIL-101(Cr) improved the electron migration through the LAMCT process, fostering a synergistic interaction with Pt. The combined experimental analysis exposed the high number of metallic Pt (Pt0) in Pt@NH2-MIL-101(Cr) catalyst through seamless electron shuttling from N of -NH2 group to excited Pt generating versatile hybrid Pt-N catalytic centres. Consequently, these versatile hybrid catalytic centres act as electro-nucleophilic centres, which enable the efficient and selective conversion of CO bond in CO2 to harvest CH4 (131.0 µmol.g-1) and maintain excellent stability and selectivity for consecutive five rounds, superior to Pt@MIL-101(Cr) and most reported catalysts. Our study verified that the precise tuning of organic ligands in MOFs immensely improves the surface-active centres, electron migration, and catalytic selectivity of the excited Pt NCs catalysts encaged inside MOFs through an improved LAMCT pathway.

Efficient CO2 Conversion through a Novel Dual-Fiber Reactor System

Carbon dioxide (CO2) can be converted to valuable organic chemicals using light irradiation and photocatalysis. Today, light-energy loss, poor conversion efficiency, and low quantum efficiency (QE) hamper the application of photocatalytic CO2 reduction. To overcome these drawbacks, we developed an efficient photocatalytic reactor platform for producing formic acid (HCOOH) by coating an iron-based metal-organic framework (Fe-MOF) onto side-emitting polymeric optical fibers (POFs) and using hollow-fiber membranes (HFMs) to deliver bubble-free CO2. The photocatalyst, Fe-MOF with amine-group (-NH2) decoration, provided exceptional dissolved inorganic carbon (DIC) absorption. The dual-fiber system gave a CO2-to-HCOOH conversion rate of 116 ± 1.2 mM h-1 g-1, which is ≥18-fold higher than the rates in photocatalytic slurry systems. The 12% QE obtained using the POF was 18-fold greater than the QE obtained by a photocatalytic slurry. The conversion efficiency and product selectivity of CO2-to-HCOOH were up to 22 and 99%, respectively. Due to the dual efficiencies of bubble-free CO2 delivery and the high QE achieved using the POF platform, the dual-fiber system had energy consumption of only 0.60 ± 0.05 kWh mol-1, 3000-fold better than photocatalysis using slurry-based systems. This innovative dual-fiber design enables efficient CO2 valorization without the use of platinum group metals or rare earth elements.

Performance and Mechanism of the Modified Group Regulated the MIL-101(Fe) Type Fenton-like Catalysts

In order to avoid the disadvantages of the Fenton process in wastewater treatment and reduce the cost of wastewater treatment, a series of MIL-101(Fe)-X (X = -OH, -NH2, -NO2, -H) solid Fenton catalysts were successfully prepared. The performance of these Fenton-like catalysts was studied with the Fenton experiment as a reference and methylene blue (MB) as an organic pollutant. The effects of the H2O2 concentration, catalyst dosage, and reaction pH on catalytic performance were systematically studied. The research had shown that the optimal concentration of H2O2 for catalytic reactions was 0.10 mmol/L and the pH was 3. At this point, their catalytic degradation MB performance was superior to the Fenton reaction and photocatalytic reaction. When the H2O2 participated in the reaction, the performance of MIL-101(Fe)-X (X = -OH, -NH2, -NO2, -H) in catalyzing the degradation of MB followed the rule of -OH > -NH2 > -NO2 > -H. This was due to the synergistic effect of Fenton-like catalysis and photocatalytic degradation in the catalytic degradation of MB. In addition, the electron paramagnetic resonance and electrospray ionization mass spectrometry showed that the hydroxyl radical (·OH) generated during the catalytic process first underwent a redox reaction with the highly electronegative functional groups in the MB molecule, and finally oxidized it to CO2 and H2O. This study successfully prepared commercially applicable Fenton-like catalysts and explored their optimal reaction conditions. This provides a technical reference for wastewater treatment.

Developing a magnetic SERS nanosensor utilizing aminated Fe-Based MOF for ultrasensitive trace detection of organophosphorus pesticides in apple juice

The unreasonable use of organophosphorus pesticides leads to excessive pesticide residues in food, seriously threatening public health, and the potential of surface-enhanced Raman spectroscopy (SERS) technology, incorporating a metal-organic framework, is substantial for the rapid detection of trace pesticide residues. Here, a novel Fe3O4@NH2-MIL-101(Fe)@Ag (FNMA) SERS nanosensor was developed. Results indicated that the FNMA had a high enhancement factor of 1.53 × 108, a low limit of detection (LOD) of 4.55 × 10-12 M, and a relative standard deviation of 7.73 % for 4-nitrothiophenol, demonstrating its good SERS sensitivity and uniformity, and also possessed good storage stability for one month. In quantifying fenthion and methyl parathion in standard solutions and apple juice in the range of 0.05/0.02-20 mg/L, it showed LODs of 3.02 × 10-3 mg/L and 1.43 × 10-3 mg/L, and 0.0407 and 0.0075 mg/L, respectively, demonstrating potentials in ultrasensitive trace detection of pesticides in food.

Pyrazine-based iron metal organic frameworks (Fe-MOFs) with modulated O-Fe-N coordination for enhanced hydroxyl radical generation in Fenton-like process

Rational design of coordination environment of Fe-based metal-organic frameworks (Fe-MOFs) is still a challenge in achieving enhanced catalytic activity for Fenten-like advanced oxidation process. Here in, novel porous Fe-MOFs with modulated O-Fe-N coordination was developed by configurating amino terephthalic acid (H2ATA) and pyrazine-dicarboxylic acid (PzDC) (Fe-ATA/PzDC-7:3). PzDC ligands introduce pyridine-N sites to form O-Fe-N coordination with lower binding energy, which affect the local electronic environment of Fe-clusters in Fe-ATA, thus decreased its interfacial H2O2 activation barrier. O-Fe-N coordination also accelerate Fe(II)/Fe(III) cycling of Fe-clusters by triggering the reactive oxidant species mediated Fe(III) reduction. As such, Fe-ATA/PzDC-7:3/H2O2 system exhibited excellent degradation performance for typical antibiotic sulfamethoxazole (SMX), in which the steady-state concentration of hydroxyl radical (OH) was 1.6 times higher than that of unregulated Fe-ATA. Overall, this study highlights the role of O-Fe-N coordination and the electronic environment of Fe-clusters on regulating Fenton-like catalytic performance, and provides a platform for precise engineering of Fe-MOFs.

Facile synthesis of lignin-based Fe-MOF for fast adsorption of methyl orange

To rapidly remove dyes from wastewater, iron-based metal-organic frameworks modified with phenolated lignin (NH2-MIL@L) were prepared by a one-step hydrothermal method. Analyses of the chemical structure and adsorption mechanism of the NH2-MIL@L proved the successful introduction of lignin and the enhancement of its adsorption sites. Compared with NH2-MIL-101-Fe without phenolated lignin, the modification with lignin increased the methyl orange (MO) adsorption rate of NH2-MIL@L. For the best adsorbent, NH2-MIL@L4, the MO adsorption efficiency in MO solution reached 95.09% within 5 min. NH2-MIL@L4 reached adsorption equilibrium within 90 min, exhibiting an MO adsorption capacity of 195.31 mg/g. The process followed pseudo-second-order kinetics and the Dubinin-Radushkevich model. MO adsorption efficiency of NH2-MIL@L4 was maintained at 89.87% after six adsorption-desorption cycles. In mixed solutions of MO and methylene blue (MB), NH2-MIL@L4 achieved an MO adsorption of 94.02% at 5 min and reached MO adsorption equilibrium within 15 min with an MO adsorption capacity of 438.6 mg/g, while the MB adsorption equilibrium was established at 90 min with an MB adsorption rate and capacity of 95.60% and 481.34 mg/g, respectively. NH2-MIL@L4 sustained its excellent adsorption efficiency after six adsorption-desorption cycles (91.2% for MO and 93.4% for MB). The process of MO adsorption by NH2-MIL@L4 followed the Temkin model and pseudo-second-order kinetics, while MB adsorption followed the Dubinin-Radushkevich model and pseudo-second-order kinetics. Electrostatic interactions, π-π interactions, hydrogen bonding, and synergistic interactions affected the MO adsorption process of NH2-MIL@L4.

Enhanced sorption and fluorescent detection of bisphenol A by using sodium alginate/cellulose nanofibrils/ZIF-8 composite hydrogel

To address the issue of bisphenol A (BPA) contamination in wastewater, a novel hydrogel, sodium alginate/cellulose nanofibrils/ZIF-8 composite hydrogel (SCZC), was synthesized for efficient BPA removal. The SCZC exhibited an exceptional adsorption capacity of 1696 mg/g, aligning well with both Langmuir and pseudo-second-order models. Furthermore, it exhibited remarkable regeneration properties, maintaining 89.1 % of its adsorption capacity even after undergoing five adsorption-desorption cycles. The synthesized SCZC also acted as a fluorescent sensor for detecting BPA, employing dynamic quenching and offering linear detection ranges of 10-100 mg/L and 0.2-1.0 μg/L, with a low detection limit of 0.06 μg/L. Analysis of adsorption and detection mechanisms revealed that SCZC's exceptional performance could be attributed to the three-dimensional (3D) porous structure formed by sodium alginate and cellulose nanofibrils. Economic analysis indicated that SCZC, in comparison to commercially activated carbon, was relatively inexpensive. This study introduces a novel approach for designing and preparing a sodium alginate-based hydrogel incorporating metal-organic frameworks, offering simultaneous BPA detection and removal capabilities.

Construction of 3D-graphene/NH2-MIL-125 nanohybrids via amino-ionic liquid dual-mode bonding for advanced acetaldehyde photodegradation under high humidity

The development of metal organic framework (MOF)-based π-π conjugated structures capable of effectively transforming H2O from humid air to •OH radicals for VOCs photodegradation is a significant but difficult task. Herein, an amino-ionic liquid (NH2-IL) based dual-mode bridging strategy was proposed to connect 3D-graphene with NH2-MIL-125 forming IL-3DGr/NM(Ti) nanohybrids for advanced acetaldehyde photodegradation. The rational integration of these components was responsible for: (1) maintaining π-π conjugated electron transport system; (2) generating abundant coordinatively unsaturated sites and oxygen vacancies; (3) increasing surface area of the nanohybrids. With these attributes, IL-3DGr/NM(Ti) demonstrated enhanced charge separation and transportation electrochemical impedance spectroscopy (EIS): 7-times), acetaldehyde adsorption (22 %), light absorption (bandgap: 1.51 eV). The rapid H2O adsorption and photoconversion to •OH radicals by IL-3DGr/NM(Ti) enabled it to demonstrate superior CH3CHO photodegradation rate under high humidity, surpassing many state-of-the-art photocatalysts by 9 to 187 times under static air conditions and with nearly similar catalyst dosages* (photocatalyst weight and initial acetaldehyde concentration (mg ppm-1) ratio). Interestingly, the IL-3DGr/NM(Ti) photocatalytic activity was enhanced by increasing RH% up-to 80 %. Besides, the nanohybrids demonstrated tremendous stability, with only a 3.9 % decline observed after 5 consecutive-cycles. This strategy provides new prospects to improve the compatibility of graphene/MOF materials for futuristic photoelectrical applications under high humidity.

Degradation of Orange G Using PMS Triggered by NH2-MIL-101(Fe): An Amino-Functionalized Metal-Organic Framework

As an azo dye, OG has toxic and harmful effects on ecosystems. Therefore, there is an urgent need to develop a green, environmentally friendly, and efficient catalyst to activate peroxymonosulfate (PMS) for the degradation of OG. In this study, the catalysts MIL-101(Fe) and NH2-MIL-101(Fe) were prepared using a solvothermal method to carry out degradation experiments. They were characterized by means of XRD, SEM, XPS, and FT-IR, and the results showed that the catalysts were successfully prepared. Then, a catalyst/PMS system was constructed, and the effects of different reaction systems, initial pH, temperature, catalyst dosing, PMS concentration, and the anion effect on the degradation of OG were investigated. Under specific conditions (100 mL OG solution with a concentration of 50 mg/L, pH = 7.3, temperature = 25 °C, 1 mL PMS solution with a concentration of 100 mmol/L, and a catalyst dosage of 0.02 g), the degradation of OG with MIL-101(Fe) was only 36.6% within 60 min; as a comparison, NH2-MIL-101(Fe) could reach up to 97.9%, with a reaction constant k value of 0.07245 min-1. The NH2-MIL-101 (Fe)/PMS reaction system was able to achieve efficient degradation of OG at different pH values (pH = 3~9). The degradation mechanism was analyzed using free-radical quenching tests. The free-radical quenching tests showed that SO4•-, •OH, and 1O2 were the main active species during the degradation of OG.

Asymmetric Fe-O2-Ti structures accelerate reduced-layer-FeII "electron" conversion: Facilitating photocatalytic nitrogen fixation

As a green and sustainable method for ammonia production, solar photocatalytic nitrogen fixation (PNRR) provides a new approach to slowing down the consumption of non-renewable energy resources. Given the extremely huge energy required to activate inert nitrogen, a rational design of efficient nitrogen fixation catalytic materials is essential. This study constructs defective Ti3+-Ti3C2Ox to regulate the NH2-MIL-101(Fe) reduced layer-FeII 'electron' transition; meanwhile, the heterojunction interface electronic structure formed by coupling promotes catalytic charges' transfer/separation, while the interface-asymmetric Fe-O2-Ti structure accelerates the response with nitrogen. It is shown that the heterojunction NM-101(FeII/FeIII)-1.5 exhibits a 75.1 % FeII enrichment (FeII:FeIII), which successfully impedes the fouling relationship between the two (FeII/FeIII). Mössbauer spectroscopy analysis demonstrates that the presence of D1-high spin state FeIII and D2-low/medium spin state FeII structures in the heterojunction boosts the PNRR activity. Furthermore, it is found that the defective state Ti3+-Ti3C2Ox modulation enhances the reduced nitrogen fixation capacity of the heterojunction (CB = -0.84 eV) and decreases the interfacial charge transfer resistance, yielding 450 umol·g-1·h-1 ammonia. Furthermore, this study modulates the charge ration of the catalyst reduction layer by constructing a charge-asymmetric structure with Ti3+-deficient carriers; this method provides a potential opportunity for enhancing photocatalytic nitrogen fixation in the future.

Mechanisms of interaction between metal-organic framework-based material and persulfate in degradation of organic contaminants (OCs): Activation, reactive oxygen generation, conversion, and oxidation

Metal-organic frameworks (MOFs)-based materials have been of great public interest in persulfate (PS)-based catalytic oxidation for wastewater purification, because of their excellent performance and selectiveness in organic contaminants (OCs) removal in complex water environments. The formation, fountainhead and reaction mechanism of reactive oxygen species (ROSs) in PS-based catalytic oxidation are crucial for understanding the principles of PS activation and the degradation mechanism of OCs. In the paper, we presented the quantitative structure-activity relationship (QSAR) of MOFs-based materials for PS activation, including the relationship of structure and removal efficiency, active sites and ROSs as well as OCs. In various MOFs-based materials, there are many factors will affect their performances. We discussed how various surface modification projects affected the characteristics of MOFs-based materials used in PS activation. Moreover, we revealed the process of ROSs generation by active sites and the oxidation of OCs by ROSs from the micro level. At the end of this review, we putted forward an outlook on the development trends and faced challenges of MOFs for PS-based catalytic oxidation. Generally, this review aims to clarify the formation mechanisms of ROSs via the active sites on the MOFs and the reaction mechanism between ROSs and OCs, which is helpful for reader to better understand the QSAR in various MOFs/PS systems.

Empowering Adsorption and Photocatalytic Degradation of Ciprofloxacin on BiOI Composites: A Material-by-Design Investigation

Binary and ternary composites of BiOI with NH2-MIL-101(Fe) and a functionalized biochar were synthesized through an in situ approach, aimed at spurring the activity of the semiconductor as a photocatalyst for the removal of ciprofloxacin (CIP) from water. Experimental outcomes showed a drastic enhancement of the adsorption and the equilibrium (which increased from 39.31 mg g-1 of bare BiOI to 76.39 mg g-1 of the best ternary composite in 2 h time), while the kinetics of the process was not significantly changed. The photocatalytic performance was also significantly enhanced, and the complete removal of 10 ppm of CIP in 3 h reaction time was recorded under simulated solar light irradiation for the best catalyst of the investigated batch. Catalytic reactions supported by different materials obeyed different reaction orders, indicating the existence of different mechanisms. The use of scavengers for superoxide anion radicals, holes, and hydroxyl radicals showed that although all these species are involved in CIP photodegradation, the latter play the most crucial role, as also confirmed by carrying out the reaction at increasing pH conditions. A clear correlation between the reduction of BiOI crystallite sizes in the composites, as compared to the bare material, and the material performance as both adsorbers and photocatalyst was identified.

Ultrafast and Scalable Fabrication of Coordination Polymer Films on Network Substrates via Thermal Current-Induced Dewetting

Coordination polymers are among the most favored active materials by researchers due to their broad application prospects. However, most of them are usually difficult to directly process into applicable devices because of their unsatisfied processability. One process of great concern for researchers is the in situ preparation of the coordination polymer on the applicable substrate, especially for the favored network substrates with good mechanical properties and 3D porous structure, which could provide obvious convenience and facilitation in the application process. Herein, we present an ultrafast and scalable thermal current-induced dewetting strategy to obtain uniform coordination polymer film in situ on network substrates, which could enable unprecedented convenience to obtain directly usable coordination polymer composites such as practical catalytic electrodes with excellent electrocatalytic performance. The proposed thermal current-induced dewetting method provides a highly adaptable and efficient practical production approach to integrate coordination polymer materials with network substrates and also provides new inspiration for understanding and applying the dewetting process on complex 3D network substrates.

Optimizing the performance of Fe-based metal-organic frameworks in photo-Fenton processes: Mechanisms, strategies and prospects

Contaminants in water pose a significant challenge as they are harmful and difficult to treat using conventional methods. Therefore, various new methods have been proposed to degrade organic pollutants in water, among which the photo-Fenton process is considered promising. In recent years, Fe-based metal-organic frameworks (Fe-MOFs) have gained attention and found applications in different fields due to their cost-effectiveness, non-toxic nature, and unique porous structure. Many researchers have applied Fe-MOFs to the photo-Fenton process in recent years and achieved good results. This review focuses on describing different strategies for enhancing the performance of Fe-MOFs in the photo-Fenton process. Also, the mechanism of MOF in the photo-Fenton process is described in detail. Finally, prospects for the application of Fe-MOFs in photo-Fenton systems for the treatment of organic pollutants in water are presented. This study provides information and ideas for researchers to use Fe-MOFs to remove organic pollutants from water by photo-Fenton process.

Simple ultrasonic integration of shapeable, rebuildable, and multifunctional MIL-53(Fe)@cellulose composite for remediation of aqueous contaminants

Metal-organic frames (MOFs) have been recognized as one of the best candidates in the remediation of aqueous contaminants, while the fragile powder shape restricts the practical implementation. In this work, a shapeable, rebuildable, and multifunctional MOF composite (MIL-53@CF) was prepared from MIL-53 (Fe) and cellulose fiber (CF) using a simple ultrasonic method for adsorption and photocatalytic degradation of organic pollutants in wastewater. The results showed MIL-53(Fe) crystals were uniformly growth on CF surfaces and bonded with surface nanofibrils of CF through physical crosslinking and hydrogen bonding. Because of the high bonding strength, the MIL-53@CF composite exhibited an excellent compressive strength (3.53 MPa). More importantly, the MIL-53@CF composite was rebuildable through mechanical destruction followed by re-ultrasonication, suggesting the excellent reusability of MIL-53@CF for water remediation. The MIL-53@CF composite also had high adsorption capacities for methyl orange (884.6 mg·g-1), methylene blue (198.3 mg·g-1), and tetracycline (106.4 mg·g-1). MIL-53@CF composite could degrade TC through photocatalysis. The photocatalytic degradation mechanism was attributed to the Fe(II)/Fe(III) transform cycle reaction of MIL-53 crystal located on MIL-53@CF. Furthermore, the mechanical property and remoldability of MIL-53@CF composite increased its practicability. Comprehensively, MIL-53@CF composite provided a possible strategy to practically apply MOF in the remediation of aqueous contaminants.

A novel molecularly imprinting polypyrrole electrochemiluminescence sensor based on MIL-101-g-C3N4 for supersensitive determination of ciprofloxacin

Ciprofloxacin (CIP), a quinolone antibiotic, was rapidly and sensitively detected by integrating the molecularly imprinted polymer (MIP) with an ultra-sensitive electrochemiluminescence (ECL) method. g-C3N4, a typical polymer semiconductor, exhibited outstanding ECL efficiency and excellent ECL stability after combining with an iron-based metal-organic framework (MIL-101). Subsequently, the molecularly imprinted polypyrrole was electropolymerized on the composites of MIL-101-g-C3N4 modified glassy carbon electrode (GCE). The specific sites that could target rebinding the CIP molecules were formed on the surface of MIP after extracting the CIP templates. The determination of specific concentrations of CIP could be realized according to the difference in ECL intensity (△ECL) between the eluting and rebinding of the CIP. Under optimal conditions, a good linear response of △ECL and the logarithm of CIP concentrations was obtained in the range 1.0 × 10-9 ~ 1.0 × 10-5 mol/L, with a detection limit of 4.5 × 10-10 mol/L (S/N = 3) (the working potential was -1.8 ~ 0 V). The RSD of all points in the calibration plot was less than 5.0% and the real samples recovery was between 98.0 and 104%. This paper displays satisfactory selectivity and sensitivity, providing a rapid, convenient, and cheap method for the determination of CIP in real samples.

Effects and Mechanisms of Cu Species in Fe-MOFs on Fenton-Like Catalytic Activity and Stability

Fe-based MOFs (Fe-MOFs) are deemed promising Fenton-like catalysts due to their well-developed pores and accessible active sites. However, their inferior catalytic activity, iron leaching, and low H₂O₂ utilization always hinder their application as Fe-based MOF catalysts. In this work, we manipulated the structure of Fe-oxo nodes in MIL-88B(Fe) via a Cu^I species substitution method, affording a mixed-valence (Cu-incorporated Fe-MOFs) with highly improved Fenton-like performance. It is found that the Cu^I serves as a shuttle to promote transfer between Fe^II/Fe^III, inducing the formation of a larger amount of stable Fe^II sites, which was proven by experimental and DFT calculation results. A linear relationship was observed for the Fenton-like performance and the amount of Cu^I species for the catalysts. The corresponding value of the ^•OH formation is 2.17 eV for Cu-incorporated MIL-88B(Fe), which is significantly lower than that of MIL-88B(Fe) (2.69 eV). Meanwhile, the enriched Cu^I species suppress Fe species leaching during the catalytic reaction. The Fe-ion leakage of 0.4Cu@MIL-88B is very tiny (0.01-0.03 mg/L), significantly less than that of MIL-88B (2.00-3.02 mg/L). At the same time, H₂O₂ utilization for 0.4Cu@ MIL-88B(Fe) is 88%, which is almost 4.4 times that of pure MIL-88B(Fe). This work provides insights into the rational design of Fe-MOFs as promising Fenton-like catalysts for wastewater treatment.

Preparation of TiO2/Fe-MOF n‒n heterojunction photocatalysts for visible-light degradation of tetracycline hydrochloride

Visible-light-assisted photocatalysis has been recognized as an effective solution to the degradation of various pollutants including antibiotics, pesticides, herbicides, microplastics, and organic dyes. Herein, an n-n heterojunction TiO₂/Fe-MOF photocatalyst is reported, designed via hydrothermal synthesis route. TiO₂/Fe-MOF photocatalyst was characterized by XPS, BET, EIS, EDS, DRS, PL, FTIR, XRD, TEM, SEM and HRTEM techniques. Inspired by XRD, FTIR, XPS, EDS, TEM, SEM, and HRTEM analyses, the successful synthesis of n-n heterojunction TiO₂/Fe-MOF photocatalysts was proved. The migration efficiency of the light-induced electron-hole pairs was confirmed by the PL and EIS tests. TiO₂/Fe-MOF exhibited a significant performance for tetracycline hydrochloride (TC) removal under visible light irradiation. TC removal efficiency for TiO₂/Fe-MOF (15%) nanocomposite reached 97% within 240 min, ca. 11 times higher than pure TiO₂. The photocatalytic enhancement of TiO₂/Fe-MOF could be attributed to the broadening the light response range, forming an n-n junction between Fe-MOF and TiO₂ components, suppressing charge recombination. Based on recycling experiments, TiO₂/Fe-MOF had a good potential to be used in consecutive TC degradation tests.

Synthesis of MRGO@ZIF-7-Based Molecular Imprinted Polymer by Surface Polymerization for the Fast and Selective Removal of Phenolic Endocrine-Disrupting Chemicals from Aqueous Environments

In this study, Zn(NO3)2·6H2O was selected as the metal source, and ZIF-7-modified magnetic graphene-based matrix materials (MRGO@ZIF-7) were prepared by in situ growth. ZIF-7 modified magnetic graphene-based molecular imprinting complexes (MRGO@ZIF7-MIP) were successfully synthesized by a surface molecular imprinting technique using bisphenol A (BPA) as the template molecule. The obtained experimental materials were characterized by X-ray diffraction (XRD), Brunner–Emmet–Teller (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS). The proper adsorption and selective recognition ability of the MRGO@ZIF7-MIP were studied by an equilibrium adsorption method. The obtained MRGO@ZIF7-MIP showed significant molecular recognition of bisphenol A (BPA) and good selectivity and reproducibility for BPA in different aqueous environments such as drinking water, river water, and lake water. These properties make this material potentially applicable for the efficient removal of phenolic endocrine disruptors in real water environments.

Rapidly and ultra-sensitive colorimetric detection of H2O2 and glucose based on ferrous-metal organic framework with enhanced peroxidase-mimicking activity

In this article, a novel metal-organic framework, namely MIL-101(Fe^II), was firstly synthesized via a facile method. In the presence of H₂O₂, MIL-101(Fe^II) possesses excellent peroxidase-like activity toward the classical chromogenic substrate, N,N-Diethyl-p-phenylenediamine sulfate salt (DPD). The substitution of Fe²⁺ enhances the construction of Fe(II)-oxo nodes and accelerates electrons transfer between DPD and H₂O₂, thereby improving the peroxidase-mimicking catalytic activity of MIL-101(Fe^II) nanoenzyme. Additionally, DPD molecules could be adsorbed readily onto the surface of the nanoparticles due to the π-π interaction. The study of Michaelis constant indicates that the MIL-101(Fe^II) exhibits a higher affinity towards DPD (0.16 mM) in contrast to horseradish peroxidase (0.78 mM). In view of the impressive catalytic performance of MIL-101(Fe^II), two reliable monitoring platforms for the rapid detection of H₂O₂ and glucose were established with extremely low detection limits of 18.04 nM and 0.87 μM in the ranges of 40-5000 nM and 1.2-300 μM, respectively. The study of the catalytic mechanism indicates that DPD oxidation is attributed to the hydroxyl radical (·OH) produced from the decomposition of H₂O₂ catalyzed by MIL-101(Fe^II). Furthermore, the developed sensor indicates high selectivity and stability and can be effectively appropriate for the detection of H₂O₂ and glucose in real samples. This work not only provides a novel nanozyme with superior catalytic performance for biological analysis, but also broadens the application field of MIL-101(Fe^II) material.

Phenol degradation in iron-based advanced oxidation processes through ferric reduction assisted by molybdenum disulfide

In the iron-based advanced oxidation processes (AOPs), direct use of Fe^III can be more convenient than Fe^II but the reduction of Fe^III to Fe^II is a rate-limiting step. Introducing co-catalysts with abundant reducing sites to Fe-based AOPs can be an efficient way to accelerate the Fe redox process. Herein, molybdenum disulfide (MoS₂) was used to enhance the catalytic performance of Fe³⁺/persulfate (PS) for phenol removal. In the Fe³⁺/MoS₂/PS system, 99.6 ± 0.1% of phenol was removed in 60 min, comparable to that of the Fe²⁺/PS/MoS₂ system (99.1 ± 0.3%). With the help of MoS₂, 99.3 ± 4.2% of Fe³⁺ was transformed to Fe²⁺ in 10 min, and the Fe²⁺/Fe ratio was able to be maintained at 70.0 ± 1.4% after 60 min. The rapid and complete reduction of Fe³⁺ with MoS₂ made it possible to replace Fe²⁺ by Fe³⁺, which is easier to store, transport, and use. The decrease in XPS peak area percentage of Mo(IV) and the lower valent S after reaction revealed that MoS₂ acted as an electron provider in the Fe redox cycle. Quenching experiment results indicated that the phenol removal was highly depended on the surface-bound radicals, including both SO₄^•- and ^•OH. Those results have demonstrated that ferric salts can be directly used in the Fe-based AOPs and the redox cycle could be sustained with the assistance of MoS₂.

CoNi alloy anchored onto N-doped porous carbon for the removal of sulfamethoxazole: Catalyst, mechanism, toxicity analysis, and application

Developing highly efficient, stable, recyclable, and application value heterogeneous catalysts in advanced oxidation processes has essential application value in the degradation of refractory pollutants. In this paper, the CoNi alloy anchored onto N-doped porous carbon (CoNi-600@NC) catalyst was prepared using bimetallic doped metal-organic frameworks as precursors. The magnetic CoNi-600@NC can activate peroxymonosulfate (PMS) to degrade sulfamethoxazole (SMX). Therefore, SMX can be removed 100% within 25 min. CoNi-600@NC/PMS has a broad pH (3-9) application range, good applicability, and repeatability. Radical quenching, quantitative and electrochemical experiments proved that the degradation of SMX was dominated by free radical (Superoxide anions) and non-free radical pathways (surface-bound radicals). Mechanistic analysis showed that the interaction between Co-N_x/pyridine N-sites and graphitized carbon with PMS induced the formation of surface-bound active species. Moreover, CoNi nanoparticles promoted the redox cycle of metals. The synergistic catalytic mechanisms between the CoNi alloy and the abundant functional groups gave CoNi-600@NC excellent catalytic properties and applicability. Using density functional theory predicted the reaction sites of SMX and proposed four degradation pathways. The toxicity of intermediates was comprehensively evaluated. In addition, a CoNi-600@NC continuous flow reactor was constructed with a daily treatment capacity of 45 L and 100% SMX removal. This study expands the application of persulfate advanced oxidation technology by synthesizing recyclable magnetic catalysts and provides new synergistic degradation mechanisms for removing refractory organics.

A highly stable bimetallic organic framework for enhanced electrical performance of cellulose nanofiber-based triboelectric nanogenerators

Triboelectric nanogenerators (TENGs) have garnered considerable attention as an emerging energy harvesting technology. To improve the electrical properties of the triboelectric materials in TENGs, various micro- and nanomaterials with strong charge-trapping capabilities are introduced as filler materials. However, the fillers generally perform a single function and lack long-term operational durability. Hence, further research is required to achieve stable and efficient TENGs. In this study, NH₂ metal-organic frameworks (NH₂-MOFs) were combined with a cellulose nanofiber (CNF) to prepare a composite film. NH₂-MOFs have an aminated bimetallic organic backbone with strong charge-induction and charge-trapping capabilities. Thus, their addition significantly improved the stability, positive triboelectric properties and charge-trapping performance of the composite film. The optimized composite film and a fluorinated ethylene propylene film were used as triboelectric pairs to assemble a TENG. The electrical performance of the TENG was approximately 230% greater than that of a TENG with a pure CNF film and remained very stable for at least 90 days. These results demonstrate that NH₂-MOFs are promising fillers for improving the performance of TENGs and expanding the range of materials used in TENG construction.