Strategies for Improving the Performance and Application of MOFs Photocatalysts

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.

A Bifunctional Three-Dimensional Zn(II) Metal-Organic Framework with Strong Luminescence and Adsorption Cr(VI) Properties

The mixed ligand 3-amino-1,2,4-triazole (Hatz) and terephthalic acid (H2pta) reacted with Zn(NO3)2·6H2O to synthesize a three-dimensional binuclear Zn(II) metal-organic framework: {[Zn2·(atz)2·(pta)]·3H2O}n (3D-Zn-MOF). This 3D-Zn-MOF has two different types of pores (4.5 × 4.5 Å2, 5.7 × 5.7 Å2). The crystalline 3D-Zn-MOF could be prepared into nanomaterials (3D-N-Zn-MOF) with particles of approximately 100 nm by a cell fragmentation apparatus. Compared with the solid-state luminescence of Hatz and H2pta, it was found that 3D-N-Zn-MOF exhibited strong luminescence performance and significant red-shift phenomenon. Due to the decrease in electronegativity and rigidity of ligands, as well as the effect of ligand metal charge transfer (LMCT), the fluorescence lifetime and quantum yield of 3D-ZN-N-MOF were 2.7241 ns and 3.02%, respectively. The maximum experimental adsorption capacity of 3D-N-Zn-MOF could reach 125.52 mg/g, which was superior to the majority of MOF adsorbents under the optimal adsorption conditions (25 °C, pH = 7, and the adsorbent concentration is 0.2000 g/L). The thermodynamic analysis of adsorption showed that the adsorption of Cr(VI) by 3D-N-Zn-MOF was a spontaneous (△G < 0) and exothermic (△H < 0) process. It could be found that 3D-N-Zn-MOF was a bifunctional material with potential applications by comprehensive analysis of the fluorescence and adsorption Cr(VI) performance.

Porphyrin-Based Metal-Organic Framework Materials: Design, Construction, and Application in the Field of Photocatalysis

Metal-organic frameworks (MOFs) are a novel category of porous crystalline materials with an exceptionally high surface area and adjustable pore structure. They possess a designable composition and can be easily functionalized with different units. Porphyrins with conjugated tetrapyrrole macrocyclic structures can absorb light from ultraviolet to visible light regions, and their structures and properties can be facilely regulated by altering their peripheral groups or central metal ions. Porphyrin-based MOFs constructed from porphyrin ligands and metal nodes combine the unique features of porphyrins and MOFs as well as overcoming their respective limitations. This paper reviewed the design and construction, light absorption and charge transfer pathways, and strategy for improving the photocatalytic performance of porphyrin-based MOFs, and highlighted the recent progress in the field of CO2 reduction, hydrogen evolution, organic synthesis, organic pollutant removal, and nitrogen fixation. The intrinsic relationships between the structure and the property of porphyrin-based MOFs received special attention, especially the relationships between the arrangements of porphyrin ligands and metal nods and the charge transfer mechanism. We attempted to provide more valuable information for the design and construction of advanced photocatalysts in the future. Finally, the challenges and future perspectives of the porphyrin-based MOFs are also discussed.

Synergetic enhancement effect of two-dimensional MoS2 nanosheets and metal organic framework-derived porous ZnO nanorods for photodegradation performance

Two-dimensional transition metal dichalcogenides and semiconductor metal oxides have shown great potential in photocatalysis. However, their stability and efficiency need to be further improved. In this paper, porous ZnO nanorods with high specific surface area were prepared from metal-organic framework ZIF-8 by a simple hydrothermal method. A MoS2/ZnO composite was constructed by loading MoS2 onto the surface of porous ZnO nanorods. Compared with ZnO materials prepared by other methods, MoS2/ZnO prepared in this paper exhibits superior photocatalytic performance. The enhanced photocatalytic activity of the MoS2/ZnO composite can be attributed to the formation of heterojunctions and strong interaction between them, which greatly facilitate the separation of electrons and holes at the contact interface. In addition, due to the wide absorption region of the visible spectrum, MoS2 can greatly broaden the light absorption range of the material after the formation of the composite material, increase the utilization rate of visible light, and reduce the combination of electrons and holes. This study provides a new way to prepare cheap and efficient photocatalysts.

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.

High-Efficiency Adsorption of Cr(VI) and Mn(VII) from Wastewater by a Two-Dimensional Copper-Based Metal-Organic Framework

Cr(VI) and Mn(VII) in industrial wastewater have certain toxicity, and they pose a threat to the environment and human health and safety. Metal-organic frameworks (MOFs) usually have rich adsorption sites and a large specific surface area. They can effectively adsorb Cr(VI) and Mn(VII) from wastewater. In this paper, a two-dimensional copper-based metal-organic framework, {[Cu·(4,4'-bpy)2·(H2O)]·2(NO3)·6(H2O)·(CH3OH)}n (1), is synthesized by hydrothermal synthesis. The structure of 1 is characterized by Fourier transform infrared (IR) spectroscopy, single-crystal X-ray diffraction, element analysis, and X-ray photoelectron spectroscopy (XPS). The results showed that 1 had a two-dimensional network structure, and the specific surface area of the nanostructure was 67.63 m2/g. The nanostructure of 1 could efficiently adsorb Cr(VI) and Mn(VII) from wastewater. The adsorption properties of Cr(VI) and Mn (VII) of 1 showed that the optimal concentration of both adsorbents was 0.2 g/L. It has good adsorption performance in the pH range 4-8. The adsorption performance is the best when pH is 7, which can reach 145 and 83 mg/g, respectively.

A 3D tetrathiafulvalene-based metal-organic framework with intramolecular charge transfer for efficient near-infrared photothermal conversion

The selection of metal centers can endow donor-metal-accepter (D-M-A) type MOFs with progressive framework dimensions. 3D Cd-based MOFs with intramolecular charge transfer caused by D-M-A exhibit a satisfactory photothermal conversion efficiency of 35.7%, with the temperature rapidly rising from 25 °C to 201 °C in 7 s under 808 nm laser irradiation.

Regulation and photocatalytic degradation mechanism of a hydroxyl modified UiO-66 type metal organic framework

Photocatalytic performance can be effectively improved by modifying the functional groups on the organic ligands of metal organic frameworks (MOFs). Herein, the hydroxyl-modified UiO-66 type MOF: UIO-66-2OH(2,3), was successfully synthesized by the method of ligand exchange by the 2,3-dihydroxyterephthalic acid and UIO-66 as raw materials. The mechanism of photocatalytic degradation of methylene blue (MB) by UIO-66-2OH(2,3) shows that the hydroxyl functional group on the organic ligand regulates its electronegativity and expands its light absorption range. The decomposition of MB is carried out in multiple steps under the oxidation of the hydroxyl radical (˙OH). This research result shows the direction for guiding the synthesis of efficient photocatalysts and clarifying the light absorption of MOFs regulated by hydroxyl functional groups.

Metal-Organic Frameworks as Photocatalysts for Solar-Driven Overall Water Splitting

Metal-organic frameworks (MOFs) have been frequently used as photocatalysts for the hydrogen evolution reaction (HER) using sacrificial agents with UV-vis or visible light irradiation. The aim of the present review is to summarize the use of MOFs as solar-driven photocatalysts targeting to overcome the current efficiency limitations in overall water splitting (OWS). Initially, the fundamentals of the photocatalytic OWS under solar irradiation are presented. Then, the different strategies that can be implemented on MOFs to adapt them for solar photocatalysis for OWS are discussed in detail. Later, the most active MOFs reported until now for the solar-driven HER and/or oxygen evolution reaction (OER) are critically commented. These studies are taken as precedents for the discussion of the existing studies on the use of MOFs as photocatalysts for the OWS under visible or sunlight irradiation. The requirements to be met to use MOFs at large scale for the solar-driven OWS are also discussed. The last section of this review provides a summary of the current state of the field and comments on future prospects that could bring MOFs closer to commercial application.

Spindle-like MIL101(Fe) decorated with Bi2O3 nanoparticles for enhanced degradation of chlortetracycline under visible-light irradiation

Improving the photocatalytic performance of metal-organic frameworks (MOFs) is an important way to expand its potential applications. In this work, zero-dimensional (0D) Bi₂O₃ nanoparticles were anchored to the surface of tridimensional (3D) MIL101(Fe) by a facile solvothermal method to obtain a novel 0D/3D heterojunction Bi₂O₃/MIL101(Fe) (BOM). The morphology and optical properties of the as-prepared Bi₂O₃/MIL101(Fe) composite were characterized. The photocatalytic activity of the synthesized samples was evaluated by degrading chlortetracycline (CTC) under visible-light irradiation. The obtained BOM-20 composite (20 wt % Bi₂O₃/MIL101(Fe)) exhibits the highest photocatalytic activity with CTC degradation efficiency of 88.2% within 120 min. The degradation rate constant of BOM-20 toward CTC is 0.01348 min^-1, which is 5.9 and 4.3 times higher than that of pristine Bi₂O₃ and MIL101(Fe), respectively. The enhanced photocatalytic activity is attributed to the formation of a Z-scheme heterojunction between Bi₂O₃ and MIL101(Fe), which is conducive to the rapid separation of photogenerated carriers and the enhancement of photogenerated electron and hole redox capacity. The intermediate products were analyzed by liquid chromatography-mass spectrometry (LC-MS), and a possible photocatalytic degradation path of CTC was proposed. This work provides a new perspective for the preparation of efficient MOF-based photocatalysts.

In Situ Synthesis Mechanism and Photocatalytic Performance of Cyano-Bridged Cu (I)/Cu (II) Ultrathin Nanosheets

In situ synthesis of cyano-bridged Cu (I)/Cu (II) complexes usually requires organometallic catalysts or is carried out under high-temperature and high-pressure conditions. Herein, the cyano-bridged two-dimensional Cu (I)/Cu (II) photocatalyst, [Cu₂ (Py)₃(CN)₃]_n (1), is synthesized in situ at room temperature. The in situ synthesis mechanism of 1 shows that the partial Cu (II) complex catalyzed the C-C bond cleavage of 1,3-isophthalonitrile (L) to introduce -CN and generate Cu (I)/Cu (II). Its ultrathin nanosheets can be obtained by adding sodium dodecyl benzene sulfonate and performing ultrasonic synthesis in the process of synthesis 1. The ultrathin nanosheets of 1 have a lattice distance of about 0.31 nm, and it can rapidly decompose methylene blue (MB) (K = 0.25 mg L⁻¹ min⁻¹ at pH = 3). This research work is beneficial for in situ synthesis of cyano-bridged Cu (I)/Cu (II) complexes at room temperature and explores their synthesis and photocatalytic mechanism.

Switching on photocatalytic NO oxidation and proton reduction of NH2-MIL-125(Ti) by convenient linker defect engineering

Photocatalysis technology has been widely adopted to abate typical air pollutants. Nevertheless, developing photocatalysts aimed at improving photocatalytic efficiency is a challenge. Herein, the linker-defect NH₂-MIL-125(Ti) photocatalyst was synthesized through a convenient one-step heating-stirring method (just adjusting multiple temperatures) to firstly realize efficient photocatalytic performances of NO removal and hydrogen evolution. The optimal sample (named 65-NMIL) with a linker-defect content of 32.08% exhibited a NO removal ratio of 65.49%, which was 37.57% higher than that of pristine NH₂-MIL-125(Ti), and displayed better H₂-production activity. Through ESR, it was confirmed that 65-NMIL can generate more •O₂^- and •OH under visible light, and the radical trapping experiment further proved that •O₂^- played a more important role in photocatalytic activity. Moreover, the photocatalytic NO oxidation process was also monitored by in situ DRIFTS, it was found that the defective samples could promote the oxidation of NO and intermediates to the final product (NO₃^-). On the basis of the above-mentioned photocatalytic experimental results and characterization, a possible mechanism or pathway was proposed and illustrated. This work can provide a new strategy for the subsequent defect engineering for photocatalytic MOFs materials to further solve environmental and energy crises.

Construction of Au and C60 quantum dots modified materials of Institute Lavoisier-125(Ti) architectures for antibiotic degradation: Performance, toxicity assessment, and mechanistic insight

High-performance and stabilized photocatalytic degradation of antibiotic contaminants still remains a challenge in environmental photocatalysis and has been studied worldwide. In this work, hybrid Au and C60 quantum dots decorated Materials of Institute Lavoisier-125(Ti) (MIL-125(Ti)) composites were successfully fabricated for visible-light photocatalytic tetracycline degradation with pristine MIL-125(Ti) as a comparison. The experimental results revealed that the introduction of C60 quantum dots and Au nanoparticles resulted in highly enhanced visible-light harvesting and charge separation for efficient tetracycline degradation. The optimal Au/C60-MIL-125(Ti)-1.0% sample exhibited the highest visible-light photocatalytic performance, and the corresponding rate constant was approximately 9.19 times of MIL-125(Ti), indicating the significant roles of Au and C60 quantum dots in boosting visible-light absorption and charge separation. Furthermore, the radical species, possible degradation pathways and toxicity assessment, and photocatalytic mechanism were also investigated. Current work indicates a synergistic strategy for enhancing visible-light harvesting and charge separation to fabricate high-performance composite photocatalysts.

THE SYNTHESIS AND PROPERTIES OF A SODIUM SUPRAMOLECULAR CRYSTAL NETWORK CONSTRUCTED WITH FUNCTIONAL PYRAZINE SULFONIC ACID

Sulfonic acid groups with C_3ν symmetry can coordinate with metal ions to produce multidimensional structures due to their flexible coordination modes. They can also penetrate into supramolecular structures through an intriguing bridging pattern and weak interactions. Herein, a novel heterocyclic sodium sulfonate supramolecular structure, namely [Na(Pyr-SO₃)(H₂O)]_n where Pyr-SO₃H is pyrazine sulfonic acid, is synthesized by utilizing NaBF₄ to coordinate with the P–SO₃H ligand through the solvent evaporation method. The single crystal X-ray diffraction (XRD) data indicate that the as-formed structure belongs to the Pbca space group. Additional properties are characterized by powder XRD, thermal analysis, and solid-state fluorescence. In particular, the introduction of a soft alkali metal ion can coordinate with the oxygen atom of the sulfonate ligand and form a Na–O bridging configuration that can not only significantly improve the pyrazine sulfonic acid ligand coordination ability, but also provide a reference for the extended study of functional sulfonate polymers in the future.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

A (4,4)-connected zinc(II) coordination polymer constructed with the flexible 2-carboxy phenoxyacetate ligand: synthesis, conformation alteration and fluorescent properties

A new binary ZnII coordination polymer, [Zn(2-cpa)(H2O)] n (2D-Zn) has been prepared by a 120 °C hydrothermal reaction of zinc(II) sulfate heptahydrate and 2-carboxy phenoxyacetic acid (2-H2cpa) in the presence of potassium hydroxide. Single-crystal X-ray diffraction analysis shows that the ZnII ion is located in a deformed ZnO6 octahedron bonded by one water and three 2-carboxy phenoxyacetate (2-cpa) ligands. The 2-cpa exhibits pentadentate double bridging chelate-μ 3 coordination mode and connects adjacent ZnII ions to generate a corrugated (4,4)-connected layer structure. The structures, conformation of 2-cpa and photoluminescence spectra for 2D-Zn have been carefully analyzed and compared with its two closely related compounds ̶ 1D [Zn(2-cpa)(H2O)] n (1D-Zn) and mononuclear [Zn(2-cpa)(H2O)3] (0D-Zn). The results showed that the conformation of 2-cpa in 2D-Zn has the maximum alteration and the corresponding fluorescence emission peak of 2D-Zn has the largest red-shift of 62 nm compared with that of free 2-H2cpa.

Porous framework-based hybrid materials for solar-to-chemical energy conversion: from powder photocatalysts to photoelectrodes

Porous framework materials such as metal organic frameworks (MOFs) and covalent organic frameworks (COFs) can be considered promising materials for solar-to-chemical energy conversion.

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

Solar radiation is becoming increasingly appreciated because of its influence on living matter and the feasibility of its application for a variety of purposes. It is an available and everlasting natural source of energy, rapidly gaining ground as a supplement and alternative to the nonrenewable energy feedstock. Actually, an increasing interest is involved in the development of efficient materials as the core of photocatalytic and photothermal processes, allowing solar energy harvesting and conversion for many technological applications, including hydrogen production, CO2 reduction, pollutants degradation, as well as organic syntheses. Particularly, photosensitive nanostructured hybrid materials synthesized coupling inorganic semiconductors with organic compounds, and polymers or carbon-based materials are attracting ever-growing research attention since their peculiar properties overcome several limitations of photocatalytic semiconductors through different approaches, including dye or charge transfer complex sensitization and heterostructures formation. The aim of this review was to describe the most promising recent advances in the field of hybrid nanostructured materials for sunlight capture and solar energy exploitation by photocatalytic processes. Beside diverse materials based on metal oxide semiconductors, emerging photoactive systems, such as metal-organic frameworks (MOFs) and hybrid perovskites, were discussed. Finally, future research opportunities and challenges associated with the design and development of highly efficient and cost-effective photosensitive nanomaterials for technological claims were outlined.

In situ coupling of TiO2(B) and ZIF-8 with enhanced photocatalytic activity via effective defect

A composite photocatalyst was obtained by coupling ZIF-8 and TiO₂(B) via a simple method, which showed the enhanced photocatalytic due to the oxygen vacancies/Ti³⁺.