Ligand modification of UiO-66 with an unusual visible light photocatalytic behavior for RhB degradation

Functionalized UiO-66 induces shallow electron traps in heterojunctions with InN for enhanced photocathodic water splitting

Indium nitride (InN) exhibited significant potential as a photoelectrode material for photoelectrochemical (PEC) water splitting, attributed to its superior light absorption, high electron mobility, and direct bandgap. However, its practical application was constrained by rapid carrier recombination occurring within the bulk and at the surface. To address these limitations, researchers developed InN/UiO-66 heterojunction photoelectrodes, which markedly enhanced PEC water splitting for hydrogen production. Functionalization of the UiO-66 metal-organic framework (MOF) with hydroxyl (-OH) groups optimized the bandgap and improved light absorption, facilitating efficient charge separation and transfer processes. The functionalization also mitigated surface defect states in the InN nanorods (NRs), which were a major source of photogenerated carrier recombination, thereby enhancing overall photocatalytic activity. Compared to pristine InN NRs, the optimized InN/UiO-66-(OH)2 electrode achieved a photocurrent density of -0.42 mA cm-2 and an applied bias photon-to-current efficiency (ABPE) of 0.47 % at -0.5 V vs. reversible hydrogen electrode (RHE). Furthermore, the InN/Ag/UiO-66-(OH)2 system demonstrated a hydrogen production rate of 1.82 μmol min-1 under AM 1.5G illumination, with excellent long-term stability. This study provided critical insights into the design of efficient and durable PEC photoelectrodes, achieved the highest hydrogen yield reported for indium-based photocathodes to date, and underscored the promise of InN-based materials for solar-driven hydrogen production in the context of clean energy applications.

Development of a hydrophilic-lipophilic-balanced copolymer@zirconium-based metal-organic framework-based solid-phase microextraction probe for the trace determination of organophosphorus pesticides in tea infusions

Organophosphorus pesticides (OPPs) present in tea infusions pose a serious threat to human health. In this study, a sensitive method for the determination of OPPs was developed based on a direct-immersion solid-phase microextraction (DI-SPME) probe. By fine adjustment of the ratio and one-step polymerization of dihydroxy-functionalized zirconium-based metal-organic framework UiO-66-(OH)2 and divinylbenzene-N-vinyl pyrrolidone (DVB-NVP) microspheres, the DVB-NVP@ UiO-66-(OH)2 (D-N@U) composite with an optimal hydrophilic-lipophilic balance (HLB) was achieved. Furthermore, D-N@U was adhesively bonded to stainless-steel wires to fabricate a DI-SPME probe. OPPs, especially those with nonpolar properties characterized by a high octanol-water partition coefficient (log KOW), were selectively and efficiently enriched on the D-N@U-coated DI-SPME probe from tea infusions. Coupled with a gas chromatography-flame photometric detector, the as-fabricated D-N@U-coated DI-SPME probe achieved good performance for OPPs analysis with a wide linear dynamic range of 0.10-500.00 μg/L and low detection limits of 1.96-6.69 ng/L. Moreover, in spiked samples, the recoveries and relative standard deviations were in the ranges of 73.12%-101.20 % and 1.03%-6.56 %, respectively. Owing to its simple operation, high extraction efficiency, and high sensitivity, this approach has great potential for the rapid determination of multiple pesticide trace-level residues in food.

A Novel Composite Material UiO-66-Br@MBC for Mercury Removal from Flue Gas: Preparation and Mechanism

To reduce the mercury content in flue gas from coal-fired power plants and to obtain high-performance, low-cost mercury adsorbents, a novel composite material was prepared by structural design through the in situ growth method. Functionalization treatments such as the modification of functional groups and multilayer loading of polymetallic were conducted. These materials include the MOF material UiO-66 and modified biochar doped with Fe/Ce polymetallic, both of which contain unsaturated metal centrals and oxygen-containing functional groups. On the basis of obtaining the effects of adsorption temperature and composite ratio on the Hg0 removal characteristics, coupling and synergistic mechanisms between the various types of active centers included were investigated by using a variety of characterization and analysis tools. The active adsorption sites and oxidation sites were identified during this process, and the constitutive relationship between the physicochemical properties and the performance of Hg0 removal was established. The temperature-programmed desorption technique, Grand Canonical Monte Carlo simulation, and adsorption kinetic model were employed to reveal the mechanism of Hg0 removal. The results showed that the UiO-66-Br@MBC composite adsorbent possessed an excellent Hg0 removal performance at adsorption temperatures ranging from 50 to 250 °C, and targeted construction of adsorption and oxidation sites while maintaining thermal stability. The Hg0 removal by the composites is the result of both adsorption and oxidation. The micropores and small pore mesopores in the samples provide physical adsorption sites. The modified biochar acts as a carrier to facilitate the full exposure of the central metal zirconium ions, the formation of more active sites, and the process of electron transfer. The doping modification of the Br element can enhance the overall redox ability of the sample, and the introduced Fe and Ce polymetallic ions can work in concert to promote the oxidation process of Hg0. The excellent regulation of the ratio between adsorption and oxidation sites on the surface of the composite material finally led to a significant boost in the samples' capacity to remove Hg0.

Derivatives of Br-doped metal-organic framework for improved acetaldehyde adsorption-photocatalytic oxidation

Different Br-doped metal-organic frameworks (MOFs) derived (Brx@UiO-66) have been prepared by heat treatment using UiO-66 as the precursor. The experimental results showed that Br0.2@UiO-66 exhibited the best photocatalytic oxidation and adsorption performances toward acetaldehyde. In the dynamic system, the acetaldehyde removal rate and adsorption capacity of Br0.2@UiO-66 were 93.2 % and 230.59 mg/g, respectively. The improvement of the photocatalytic performance can be attributed to the presence of Br ions and CBr bonds, which facilitated the rapid separation of electrons and holes and the production of •O2-. In addition, Br0.2@UiO-66 had a better adsorption performance than 300UiO-66, mainly because of the increased Lewis acidity of the metal active sites due to Br doping. Radical capture experiments indicated that •O2- and e- were the primary active substances in acetaldehyde oxidation, and allowed establishing the possible mechanism of acetaldehyde oxidation. This work shows that MOFs can have high catalytic oxidation performances toward volatile organic compounds (VOCs) while retaining their adsorption capacity, and can be used for practical applications in the adsorption-catalytic integrated degradation of VOCs.

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.

Fabrication of UiO-66/GCN, a Hybrid Photocatalyst, for Effective Degradation of Ciprofloxacin, Toxicity Estimation, and Its Antibacterial Activity

Fabrication of a metal-organic framework-based photocatalyst has been gaining much interest due to its higher surface area and reasonable band gap, enhancing its photocatalytic activity. This study attempted a facile synthesis of the hybrid photocatalyst UiO-66 doped with graphitic carbon nitride (GCN) by a simple solvothermal method. This composite minimized the drawback related to photogenerated charge transfer and recombination and helped the absorption of visible light. The material was investigated by using various instrumental techniques. In this work, ciprofloxacin (CIP), a fluoroquinolone drug, was chosen as a target micropollutant, and a photodegradation experiment was carried out by using UiO-66, GCN, and UiO-66/GCN under a visible light source, which exhibited 81.85, 69.48, and 93.60% of degradation, respectively. Finally, liquid chromatography mass spectrometry analysis and theoretical computation were carried out to identify the CIP degradation mechanism, and T.E.S.T. software was used to investigate the toxicity of the intermediate products. Apart from photocatalytic activity, the prepared material was also tested for its antibacterial properties against Staphylococcus aureus and Escherichia coli.

MOF-Based Photocatalytic Membrane for Water Purification: A Review

Photocatalytic membranes can effectively integrate membrane separation and photocatalytic degradation processes to provide an eco-friendly solution for efficient water purification. It is of great significance to develop highly efficient photocatalytic membranes driven by visible light to ensure the long-term stability of membrane separation systems and the maximum utilization of solar energy. Metal-organic framework (MOF) is an emerging photocatalyst with a well-defined structure and tunable chemical properties, showing a broad application prospect in the construction of high-performance photocatalytic membranes. Herein, this work provides a comprehensive review of recent advancements in MOF-based photocatalytic membranes. Initially, this work outlines the main tailoring strategies that facilitate the enhancement of the photocatalytic activity of MOF-based photocatalysts. Next, this work introduces commonly used methods for fabricating MOF-based photocatalytic membranes. Subsequently, this work discusses the application and mechanisms of MOF-based photocatalytic membranes toward organic pollutant degradation, metal ion removal, and membrane fouling mitigation. Finally, challenges in developing MOF-based photocatalytic membranes and their practical applications are presented, while also pointing out future research directions toward overcoming these existing limitations.

Effect of ligand substitution in UiO-66 metal-organic frameworks on the photocatalytic oxidation of acetaldehyde

A series of functionalized X-UiO-66 (X = NH2, H, Br and NO2) materials were prepared using a hydrothermal method and modified with various ligands. Their photocatalytic activity was evaluated by the oxidation of acetaldehyde. Experimental results show that the introduction of different ligands significantly influences the physicochemical properties of UiO-66. Br-UiO-66 exhibited the highest photocatalytic activity and CO2 selectivity of 85.6% and 85.7%, respectively. Photochemical properties reveal that -Br functional group facilitate the separation of photogenerated electrons and holes, significantly improving their transfer and oxygen reduction. As a result, an increased number of hydroxyl and superoxide radicals can form, improving the efficiency of the photocatalytic reaction. Br-UiO-66 accumulates fewer intermediates on its surface and still shows excellent photocatalytic activity and structural stability after 24 h of dynamic reaction. This work demonstrates the excellent adsorption and catalytic oxidation performance of Br-UiO-66 towards acetaldehyde and may provide new ideas for researching catalysts in the photocatalytic degradation of pollutants.

Boosting the catalysis of cesium phosphomolybdate encapsulated in hierarchical porous UiO-66 by microenvironment modulation for epoxidation of alkenes

The chemical microenvironment of polyoxometalates (POMs) encapsulated in metal-organic frameworks (MOFs) presents a significant influence on their catalytic performance, which can be easily regulated by the linker functional group alteration or metal substitution in MOFs. Herein, a series of cesium phosphomolybdate (CsPM) encapsulated in hierarchical porous UiO-66-X composites (CsPM@HP-UiO-66-X, X = H, 2CH3, or 2OH, where X represents the alterable group grafted onto the linker benzene ring) were successfully synthesized through a one pot modulated solvothermal method. The catalytic performances of the obtained materials were explored in alkene epoxidation reaction with tert-butyl hydroperoxide (t-BuOOH). CsPM@HP-UiO-66-2CH3 showed relatively high catalytic activity, stability, and epoxidation selectivity in cyclooctene epoxidation among the CsPM@HP-UiO-66-X composites. Moreover, CsPM@HP-UiO-66-2CH3 was effective in the epoxidation of numerous alkenes, especially cyclic alkenes. The superior catalytic activity of CsPM@HP-UiO-66-2CH3 is mainly attributed to the modulation of the microenvironment surrounding CsPM active sites by introducing a hydrophobic methyl group. Meanwhile, the size-matched effect, the introduction of cesium cations, and the strong metal-support interactions (SMSIs) between CsPM and HP-UiO-66-2CH3 play a crucial role in the stability of CsPM@HP-UiO-66-2CH3.

Metal-organic frameworks as photocatalysts in energetic and environmental applications

Metal-organic frameworks (MOFs) are an exciting new class of porous materials with great potential for photocatalytic applications in the environmental and energy sectors. MOFs provide significant advantages over more traditional materials when used as photocatalysts due to their high surface area, adaptable topologies, and functional ability. In this article, we summarize current developments in the use of MOFs as photocatalysts for a variety of applications, such as CO2 reduction, water splitting, pollutant degradation, and hydrogen production. We discuss the fundamental properties of MOFs that make them ideal for photocatalytic applications, as well as strategies for improving their performance. The opportunities and challenges presented by this rapidly expanding field are also highlighted.

Photo-Induced Active Lewis Acid-Base Pairs in a Metal-Organic Framework for H2 Activation

The establishment of active sites as the frustrated Lewis pair (FLP) has recently attracted much attention ranging from homogeneous to heterogeneous systems in the field of catalysis. Their unquenched reactivity of Lewis acid and base pairs in close proximity that are unable to form stable adducts has been shown to activate small molecules such as dihydrogen heterolytically. Herein, we show that grafted Ru metal-organic framework-based catalysts prepared via N-containing linkers are rather catalytically inactive for H2 activation despite the application of elevated temperatures. However, upon light illumination, charge polarization of the anchored Ru bipyridine complex can form a transient Lewis acid-base pair, Ru+-N- via metal-to-ligand charge transfer, as confirmed by time-dependent density functional theory (TDDFT) calculations to carry out effective H2-D2 exchange. FTIR and 2-D NMR endorse the formation of such reactive intermediate(s) upon light irradiation.

Synthesis of Ag3PO4/Ag/g-C3N4 Composite for Enhanced Photocatalytic Degradation of Methyl Orange

In this study, we have successfully constructed Ag3PO4/Ag/g-C3N4 heterojunctions via the hydrothermal method, which displays a wide photo-absorption range. The higher photocurrent intensity of Ag3PO4/Ag/g-C3N4 indicates that the separation efficiency of the photogenerated electron-hole pairs is higher than that of both Ag3PO4 and Ag/g-C3N4 pure substances. It is confirmed that the efficient separation of photogenerated electron-hole pairs is attributed to the heterojunction of the material. Under visible light irradiation, Ag3PO4/Ag/g-C3N4-1.6 can remove MO (~90%) at a higher rate than Ag3PO4 or Ag/g-C3N4. Its degradation rate is 0.04126 min-1, which is 4.23 and 6.53 times that of Ag/g-C3N4 and Ag3PO4, respectively. After five cycles of testing, the Ag3PO4/Ag/g-C3N4 photocatalyst still maintained high photocatalytic activity. The excellent photocatalysis of Ag3PO4/Ag/g-C3N4-1.6 under ultraviolet-visible light is due to the efficient separation of photogenerated carriers brought about by the construction of the Ag3PO4/Ag/g-C3N4 heterostructure. Additionally, Ag3PO4/Ag/g-C3N4 specimens can be easily recycled with high stability. The effects of hydroxyl and superoxide radicals on the degradation process of organic compounds were studied using electron paramagnetic resonance spectroscopy and radical quenching experiments. Therefore, the Ag3PO4/Ag/g-C3N4 composite can be used as an efficient and recyclable UV-vis spectrum-driven photocatalyst for the purification of organic pollutants.

Rapid synthesis of cerium-UiO-66 MOF nanoparticles for photocatalytic dye degradation

An unprecedented synthesis method is used to form a series of Ce-UiO-66-X (X = NH2, OH, H, NO2, COOH) metal-organic frameworks by precipitation from mixed solvents, with instantaneous crystallisation on combining separate solutions of ligands and metal precursors. This allows the first direct synthesis of Ce-UiO-66-OH. Powder X-ray diffraction (PXRD) shows that all materials are pure phase with a broadened profile that indicates nano-scale crystallite domain size. The effect of different functional groups on the benzene-1,4-dicarboxylate linker within the UiO-66 structure has been investigated on degradation of two cationic (methylene blue and rhodamine B) and two anionic (Congo red, and Alizarin red S) dyes under UV and visible light irradiation at room temperature. Analysis of the dye adsorption in the absence of light is accounted for using pseudo-first order kinetics, and the Ce-UiO-66-NH2, Ce-UiO-66-OH, and Ce-UiO-66-H materials display a considerable photocatalytic activity to degrade Alizarin red S and Congo red rapidly between 1 and 3 minutes. The materials show excellent photostability and recyclability under UV and visible light, with no loss of crystallinity seen by PXRD and activity maintained over 5 cycles, with 16 hours photostability for Ce-UiO-66-NH2.

One-pot solvothermal synthesis of In-doped amino-functionalized UiO-66 Zr-MOFs with enhanced ligand-to-metal charge transfer for efficient visible-light-driven CO2 reduction

Metal organic frameworks (MOFs) with high porosity and highly tunable physical/chemical properties can serve as heterogeneous catalysts for CO₂ photoreduction, but the application is hindered by the large band gap (E_g) and insufficient ligand-to-metal charge transfer (LMCT). In this study, a simple one-pot solvothermal strategy is proposed to prepare an amino-functionalized MOF (aU(Zr/In)) featuring an amino-functionalizing ligand linker and In-doped Zr-oxo clusters, which enables efficient CO₂ reduction driven with visible light. The amino functionalization leads to a significant reduction of E_g as well as a charge redistribution of the framework, allowing the absorption of visible light and the efficient separation of photogenerated carriers. Furthermore, the incorporation of In not only promotes the LMCT process by creating oxygen vacancies in Zr-oxo clusters, but also greatly lowers the energy barrier of the intermediates for CO₂-to-CO conversion. With the synergistic effects of the amino groups and the In dopants, the optimized aU(Zr/In) exhibits a CO production rate of 37.58 ± 1.06 μmol g^-1 h^-1, outperforming the isostructural University of Oslo-66- and Material of Institute Lavoisier-125-based photocatalysts. Our work demonstrates the potential of modifying MOFs with ligands and heteroatom dopants in metal-oxo clusters for solar energy conversion.

Methylthio-functionalized UiO-66 to promote the electron-hole separation of ZnIn2S4 for boosting hydrogen evolution under visible light illumination

Solar-driven water splitting offers a leading-edge approach to storing abundant and intermittent solar energy and producing hydrogen as a clean and sustainable energy carrier. More importantly, constructing well-designed photocatalysts is a promising approach to develop clean hydrogen energy. In this paper, flower spherical UiO-66-(SCH₃)₂/ZnIn₂S₄ (UiOSC/ZIS) photocatalysts are successfully synthesized by a simple two-step hydrothermal method, and they exhibit high hydrogen production activity in light-driven water splitting. The optimized 30-UiOSC/ZIS (the content of UiOSC was 30 mg) composite exhibits optimal hydrogen production activity with a hydrogen production of 3433 μmol g^-1 h^-1, which is 5 and 235 times higher than that of pure ZIS and UiOSC, respectively. In addition, a long-cycling stability test has shown that the UiOSC/ZIS composite has good stability and recyclability. Experimental and characterization results show the formation of a type-II heterojunction between UiOSC and ZIS. This effectively suppresses the recombination of electrons-holes and promotes the carrier transfer, thus significantly improving the hydrogen production performance. This research further promotes the application of UiO-66-(SCH₃)₂ in the field of photocatalytic hydrogen production and provides a reference for the rational design of UiO-66-based composite photocatalysts.

Facile synthesis of direct Z-scheme UiO-66-NH2/PhC2Cu heterojunction with ultrahigh redox potential for enhanced photocatalytic Cr(VI) reduction and NOR degradation

Z-scheme heterojunction-based photocatalysts typically have robust removal efficiencies for water contaminants. Herein, we employed p-type PhC₂Cu and n-type UiO-66-NH₂ to develop a direct Z-scheme UiO-66-NH₂/PhC₂Cu photocatalyst with an ultrahigh redox potential for Cr(VI) photoreduction and norfloxacin (NOR) photodegradation. Moreover, UV-vis diffuse reflectance, photoelectrochemical measurements, photoluminescence (PL) spectra and electron spin resonance (ESR) technique revealed that the UiO-66-NH₂/PhC₂Cu composite boosted light capturing capacities to promote photocatalytic efficiencies. Strikingly, the optimized UiO-66-NH₂/PhC₂Cu50 wt% rapidly reduced Cr(VI) (96.2%, 15 min) and degraded NOR (97.9%, 60 min) under low-power blue LED light. In addition, the UiO-66-NH₂/PhC₂Cu photocatalyst also exhibited favorable mineralization capacity (78.4%, 120 min). Benefitting from the enhanced interfacial electron transfer and ultrahigh redox potential of the Z-scheme heterojunction, the UiO-66-NH₂/PhC₂Cu photocatalyst greatly enhanced the separation efficacies of photogenerated carriers. This resulting abundance of active species (e.g., e^-, h⁺, O₂^•-, and •OH) were generated to photo-reduce Cr(VI) and photo-oxidize NOR. Base on the identified intermediates, four degradation pathways of NOR were proposed. Finally, the Z-scheme mechanism were systematically confirmed through X-ray photoelectron spectroscopy (XPS), ESR, cyclic voltammetry (CV) tests, and photodeposition techniques.

Advances in Titanium Carbide (Ti3C2T x ) MXenes and Their Metal-Organic Framework (MOF)-Based Nanotextures for Solar Energy Applications: A Review

Introducing new materials with low cost and superior solar harvesting efficiency requires urgent attention to solve energy and environmental challenges. Titanium carbide (Ti3C2T x ) MXene, a 2D layered material, is a promising solution to solve the issues of existing materials due to their promising conductivity with low cost to function as a cocatalyst/support. On the other hand, metal-organic frameworks (MOFs) are emerging materials due to their high surface area and semiconducting characteristics. Therefore, coupling them would be promising to form composites with higher solar harvesting efficiency. Thus, the main objective of this work to disclose recent development in Ti3C2T x -based MOF nanocomposites for energy conversion applications to produce renewable fuels. MOFs can generate photoinduced electron/hole pairs, followed by transfer of electrons to MXenes through Schottky junctions for photoredox reactions. Currently, the principles, fundamentals, and mechanism of photocatalytic systems with construction of Schottky junctions are critically discussed. Then the basics of MOFs are discussed thoroughly in terms of their physical properties, morphologies, optical properties, and derivatives. The synthesis of Ti3C2T x MXenes and their composites with the formation of surface functionals is systematically illustrated. Next, critical discussions are conducted on design considerations and strategies to engineer the morphology of Ti3C2T x MXenes and MOFs. The interfacial/heterojunction modification strategies of Ti3C2T x MXenes and MOFs are then deeply discussed to understand the roles of both materials. Following that, the applications of MXene-mediated MOF nanotextures in view of CO2 reduction and water splitting for solar fuel production are critically analyzed. Finally, the challenges and a perspective toward the future research of MXene-based MOF composites are disclosed.

Fabrication of ternary UiO-66(Ce)/Ag/BiOBr heterojunction for enhanced photocatalytic degradation of ketoprofen via effective electron transfer process: Pathways, DFT calculation and mechanism

Photocatalytic oxidation technique is considered as one of the most prospective approaches to solve the problem of environmental pollution. Herein, the novel ternary nanocomposite UiO-66(Ce)/Ag/BiOBr was fabricated via simple synthetic strategy. The obtained UiO-66(Ce)/Ag/BiOBr exhibited an excellent performance and photocatalytic efficiency of ketoprofen reached 93.5% after 180 min illumination. The ·OH and ·O₂^- were main active species and play an important role during the photocatalytic reaction. Furthermore, intermediate products and degradation pathways of ketoprofen were analyzed based on the 3D-EEM, DFT calculation and LC-MS. The possible reaction mechanism was proposed as follows: (1) the successful construction of heterojunction broadened the light absorption range to the visible light region; (2) the design of Ce-based MOFs provided more chances for electron transfer due to the Ce⁴⁺/Ce³⁺ cycling; (3) the combination of plasmon resonance effect, Schottky junction and effect of Ag bridge was an important strategy to accelerate charge transfer and improve photocatalytic efficiency.

Towards the Sustainable Production of Ultra-Low-Sulfur Fuels through Photocatalytic Oxidation

Nowadays, the sulfur-containing compounds are removed from motor fuels through the traditional hydrodesulfurization technology, which takes place under harsh reaction conditions (temperature of 350–450 °C and pressure of 30–60 atm) in the presence of catalysts based on alumina with impregnated cobalt and molybdenum. According to the principles of green chemistry, energy requirements should be recognized for their environmental and economic impacts and should be minimized, i.e., the chemical processes should be carried out at ambient temperature and atmospheric pressure. This approach could be implemented using photocatalysts that are sensitive to visible light. The creation of highly active photocatalytic systems for the deep purification of fuels from sulfur compounds becomes an important task of modern catalysis science. The present critical review reports recent progress over the last 5 years in heterogeneous photocatalytic desulfurization under visible light irradiation. Specific attention is paid to the methods for boosting the photocatalytic activity of materials, with a focus on the creation of heterojunctions as the most promising approach. This review also discusses the influence of operating parameters (nature of oxidant, molar ratio of oxidant/sulfur-containing compounds, photocatalyst loading, etc.) on the reaction efficiency. Some perspectives and future research directions on photocatalytic desulfurization are also provided.

Ni2P NPs loaded on methylthio-functionalized UiO-66 for boosting visible-light-driven photocatalytic H2 production

The UiO-66 family shows promising photocatalytic prospects in water splitting for hydrogen evolution under visible light irradiation due to its suitable band gap and adequate active sites. In this work, novel Ni₂P/UiO-66-(SCH₃)₂ composites were prepared by a simple solvothermal method. These as-synthesized samples were fully characterized by XRD, SEM, TEM, HRTEM, EDS, and XPS methods. The effectiveness of visible light driven photocatalytic water-splitting to produce hydrogen was investigated in the presence of sacrificial agents. The results showed that the optimal hydrogen yield of 5 wt% Ni₂P/UiO-66-(SCH₃)₂ is 3724.22 μmol g^-1 h^-1, reaching almost 187 times that of pristine UiO-66-(SCH₃)₂ (19.93 μmol g^-1 h^-1). Meanwhile, long term cycling stability tests also showed that Ni₂P/UiO-66-(SCH₃)₂ composites present an excellent photocatalytic H₂ production stability. Photoelectrochemical performance analysis revealed that the high catalytic activity of the composite materials could be associated with the synergistic effect of UiO-66-(SCH₃)₂ and Ni₂P. Light stimulates UiO-66-(SCH₃)₂ to generate electrons and holes, and Ni₂P as a cocatalyst could effectively transmit electrons and boost photogenerated charge separation. This work provides a reference for exploring UiO-66 family catalysts with good catalytic activity.

Visible-Light-Driven Zr-MOF/BiOBr Heterojunction for the Efficient Synchronous Removal of Hexavalent Chromium and Rhodamine B from Wastewater

With the rapid industrial development, the coexistence of multiple pollutants in wastewater has become a common phenomenon. Thus, developing highly efficient decontamination methods is imperative. In this work, a string of UiO-66-NH₂/BiOBr heterojunctions with varying ratios of BiOBr were prepared and applied to remove hexavalent chromium Cr(VI) and rhodamine B (RhB). The possible growth process of BiOBr nanosheets on UiO-66-NH₂, removal activity of contaminants, and photocatalysis mechanism were investigated. When the mass ratio of UiO-66-NH₂ to BiOBr reaches 1:0.75, the heterojunction (NB-75) shows optimal photocatalytic activity. After 30 min of adsorption, the total removal rates of Cr(VI) (50 mg/L) and RhB (10 mg/L) over NB-75 (0.25 g/L) reaches 96.7% within 120 min of illumination and 98.9% within 80 min of illumination, respectively. For the removal process, there are two factors. The first is the high adsorption capacity for RhB and Cr(VI) owing to the high porosity of UiO-66-NH₂ and interlayer surface positive charge of BiOBr. The second is the improved visible-light photocatalytic performance of the UiO-66-NH₂/BiOBr heterojunction via rapid separation of photoinduced carriers. In addition, the active species capture study reveals that the electrons (e^-) and the superoxide radicals (^•O₂ ^-) play key roles in Cr(VI) reduction, while the holes (h⁺) are major reactive groups participating in the degradation of RhB. This work demonstrated a kind of promising MOF-based photocatalysis material for eliminating Cr(VI) and RhB simultaneously.

Metal organic framework-based antibacterial agents and their underlying mechanisms

Bacteria, as the most abundant living organisms, have always been a threat to human life until the development of antibiotics. However, with the wide use of antibiotics over a long time, bacteria have gradually gained tolerance to antibiotics, further aggravating threat to human beings and environmental safety significantly. In recent decades, new bacteria-killing methods based on metal ions, hyperthermia, free radicals, physical pricks, and the coordination of several multi-mechanisms have attracted increasing attention. Consequently, multiple types of new antibacterial agents have been developed. Among them, metal organic frameworks (MOFs) appear to play an increasingly important role. The unique characteristics of MOFs make them suitable multiple-functional platforms. By selecting the appropriate metastable coordination bonds, MOFs can act as reservoirs and release antibacterial metal ions or organic linkers; by constructing a porous structure, MOFs can act as carriers for multiple types of agents and achieve slow and sustained release; and by designing their composition and the pore structure precisely, MOFs can be endowed with properties to produce heat and free radicals under stimulation. Importantly, in combination with other materials, MOFs can act as a platform to kill bacteria effectively through the synergistic effect of multiple types of mechanisms. In this review, we focus on the recent development of MOF-based antibacterial agents, which are classified according to their antibacterial mechanisms.

Synthesis, characterization, and application of MOF@clay composite as a visible light-driven photocatalyst for Rhodamine B degradation

Metal Organic Frameworks (MOFs) with natural clay materials is a relatively new research avenue that appears to reduce high production costs and address the instability issues of pure MOFs. A novel MOF and natural clay composites of MOF@Sp_n (n = 1-4) were fabricated by the in situ precipitation of stable MOF, Zr₆O₄(OH)₄ (ABDC)₆ (where ABDC = 2-aminobenzene-1,4-dicarboxylic acid), over natural sepiolite (Sp) clay and used as a photocatalysts for elimination of organic dyes in aqueous media. The formation of MOF@Sp_n due to its strong electrostatic interactions between the positively charged MOF and the negatively charged sepiolite. Optimizing the Sp content in the composite strongly influenced the dispersibility, crystallinity of MOFs, resulting in progressively functional hybrid materials with an excellent optoelectronic properties. The composites lessened the shortcomings of the individual components and made them suitable as a visible light-active, highly efficient, standalone photocatalyst material that can degrade RhB.

Visible-light-driven Z-scheme protonated g-C3N4/wood flour biochar/BiVO4 photocatalyst with biochar as charge-transfer channel for enhanced RhB degradation and Cr(VI) reduction

For the simultaneous photocatalytic reduction of hexavalent chromium (Cr(VI)) and the degradation of rhodamine B (RhB), directional charge-transfer channels and efficient separation of photogenerated holes and electrons are important. Herein, a Z-scheme heterojunction photocatalyst, protonated g-C₃N₄/BiVO₄ decorated with wood flour biochar (pCN/WFB/BiVO₄), was prepared through a hydrothermal reaction and electrostatic self-assembly for Cr(VI) photoreduction and RhB photodegradation. The morphological features, crystalline structure, chemical composition, optical properties, specific surface area, and photoelectrochemical properties of the prepared samples were investigated. The pCN/WFB/BiVO₄ photocatalyst exhibited superior removal performance when used to remove Cr(VI) and RhB separately or RhB-Cr(VI) system. The biochar bridge served as a charge-transfer channel between two semiconductors, and the electrons in protonated g-C₃N₄ (pCN) and BiVO₄ achieved a charge balance. This led to the formation of a Z-scheme heterojunction, fast photogenerated charge separation, and a powerful redox ability. The pCN/WFB/BiVO₄ photocatalyst provides new insight into the mechanisms responsible for boosting multicomponent photocatalytic reactions, while constituting a promising candidate for wastewater treatment.

Construction of direct Z-scheme Bi5O7I/UiO-66-NH2 heterojunction photocatalysts for enhanced degradation of ciprofloxacin: Mechanism insight, pathway analysis and toxicity evaluation

Direct Z-scheme Bi₅O₇I/UiO-66-NH₂ (denoted as BU-x) heterojunction photocatalysts were successfully constructed through ball-milling method. Photocatalytic activities of the as-prepared BU-x samples were determined by using a typical fluoroquinolone antibiotic, ciprofloxacin (CIP). All BU-x heterojunctions exhibited better CIP removal performances than that of pristine Bi₅O₇I and UiO-66-NH₂ upon exposure to white light irradiation. In comparison, the heterojunction with UiO-66-NH₂ content of 50 wt% (BU-5) showed excellent structural stability and the optimal adsorption-photodegradation efficiency for the CIP removal. The removal efficiency of CIP (10 mg/L) over BU-5 (0.75 g/L) achieved 96.1% within 120 min illumination. Meanwhile, the effect of photocatalyst dosage, pH and inorganic anions were systemically explored. Reactive species trapping experiments, electron spin resonance (ESR) signals, Mott-Schottky measurements and density functional theory (DFT) simulation revealed that the photo-generated holes (h⁺), hydroxyl radical (·OH) and superoxide radical (·O₂^-) played crucial roles in CIP degradation. This result can be ascribed to that the unique Z-scheme charge transfer configuration retained the excellent redox capacities of Bi₅O₇I and UiO-66-NH₂. Meanwhile, the CIP degradation pathways and the toxicity of various intermediates were subsequently analyzed. This work provided a feasible idea for removing antibiotics by bismuth-rich bismuth oxyhalide/MOF-based heterostructured photocatalysts.

Facile Strategy for Efficient Charge Separation and High Photoactivity of Mixed-Linker MOFs

Two new sets of UiO-Zr metal-organic framework (MOF) bearing mixed linkers BDC-(SCH₃)₂ and BDC-(SOCH₃)₂ that have different band gaps and edges were prepared through post oxidation and direct methods, namely, UiO-66-(SCH₃)₂-xh (x = 4, 9, 12 oxidation hours) and UiO-66-(SOCH₃)_x(SCH₃)_2-x (x = 0, 0.4, 0.6, 2), respectively. These composites with stoichiometric components were fully characterized via proton nuclear magnetic resonance (¹H NMR) spectroscopy, powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectra, Brunauer-Emmett-Teller (BET), photo electrochemical measurements, and femtosecond transient absorption (fs-TA) spectroscopy. The structure, electronic property, and photoresponsive and catalytic ability as the functions of the molar ratio of linkers and the synthetic protocol were first investigated. The mixed-linker UiO-66-(SCH₃)₂-xh and UiO-66-(SOCH₃)_x(SCH₃)_2-x exhibited improved performances as compared to the UiO-66-(SCH₃)₂ and UiO-66-(SOCH₃)₂ possessing neat linkers only. Their photo response and catalytic activity varied with different linker ratios. For UiO-66-(SCH₃)₂-xh, the performance increased with the increasing linker BDC-(SOCH₃)₂ ratio upon oxidation but reached the highest as the BDC-(SOCH₃)₂ being of 24.4% in UiO-66-(SCH₃)₂-9h. In comparison, the best photocurrent (80.74 uA/cm^-2) and the highest H₂ generation rate (2018.8 μmol g^-1 h^-1) (λ > 400 nm) in UiO-66-(SCH₃)₂-9h are about twice those of UiO-66-(SOCH₃)_0.4(SCH₃)_1.6 obtained by direct synthesis, although the linker BDC-(SOCH₃)₂ ratio of those two composites is almost the same (24.4% vs 23.9%). Recorded shorter lifetime and higher charge separation efficiency of the former than those of the latter suggest the postsynthetic protocol as the efficient method for achieving the mixed-liner-MOF-based photocatalyst with high performance. A new type-II tailored homojunction is proposed in these mixed-linker MOFs for their efficient charge separation and improved activity.

Application of sand particles modified with NH2-MIL-101(Fe) as an efficient visible-light photocatalyst for Cr(VI) reduction

This study presented chemical immobilization of an iron(III)-based metal-organic framework [NH₂-MIL-101(Fe)] on the surface of sand particles and its application for Cr(VI) photocatalytic reduction using visible light. The surface of sand particles was functionalized with (3-chloropropyl)trimethoxy silane to provide the active sites for bond formation with MOF particles. Using a heat treatment step, MOF particles were bonded on the surface of sand particles, thereby providing a photocatalyst more applicable in real environments. The presence of amino-functional groups in MOF was influential in bond formation. Furthermore, they are effective in the activation of the photocatalyst under visible-light irradiation. The photocatalyst properties were investigated by FESEM, FTIR, XPS, EDS, and DRS analysis. The impact of various parameters, such as light power, irradiation and contact time, TDS impact, and pH, was examined. The composite produced by immobilization of NH₂-101(Fe) on the surface of sand-Cl showed the high Cr(VI) removal efficiency (80% at 20 mg L^-1) as a result of the strong chemical bond formation through the suitable functional groups incorporated in materials. Under the optimum conditions, the reduction rate reached more than 99% using irradiation by 1000 W visible light for 30 min.

Advanced applications of Zr-based MOFs in the removal of water pollutants

The global water pollution is caused by the increase of industrial and agricultural activities, which have produced various toxic pollutants. Pollutants in water generally consist of metal ions, pharmaceuticals and personal care products (PPCPs), oil spills, organic dyes, and other organic pollutants. Amongst the adsorbents that have been developed to deal with pollutants in water, Zr-based metal-organic frameworks (MOFs) have drawn scientists' great attention due to their excellent stability and adjustable functionalization. Herein, the present review article introduces the synthetic methods of functionalized Zr-based MOFs and summarizes their applications in water pollution treatment. It also clarifies the interactions and removal mechanisms between pollutants and Zr-based MOFs. The use of these MOFs with eminent adsorption ability and recycling performance have been discussed in detail. Zr-based MOFs also face some challenges such as high cost, lack of real water environment applications, selective removal of pollutants, and low ability to remove composite pollutants. Future research should focus on addressing these issues. Although there is still a blank of the practical utility of Zr-based MOFs on a commercial scale, the research reported to date clearly shows that they are very promising materials for the water treatment.

De Novo synthesis of platinum-nanoparticle-encapsulated UiO-66-NH2 for photocatalytic thin film fabrication with enhanced performance of phenol degradation

The structural and chemical stability of UiO-66-NH₂ and its simulated solar irradiation responsive characteristic make it a suitable metal-organic framework (MOF) candidate as photocatalytic material. Platinum nanoparticles (Pt NPs) are typically immobilized in MOF to enhance the photocatalytic efficiency. However, introducing high metal content in MOF with high dispersion is still challenging using conventional methods. In this paper, we present de novo synthesis of Pt@UiO-66-NH₂, which can reach a highest metal content of 16 wt% with an average nanoparticle size of around 2 nm as confirmed by ICP-MS analysis and TEM images. The presence of benzoic acid plays multiple important roles in Pt@UiO-66-NH₂ formation, including binding formation with Zr clusters, facilitating Pt dispersion, and being a modulator in MOF construction. In addition, the Pt@UiO-66-NH₂ is fabricated on the α-Al₂O₃ substrate as a photocatalytic membrane reactor (PMR) for phenol degradation, which shows over 70 % removal efficiency under light irradiation and H₂O₂ addition. The recycle test shows that the PMR can maintain high catalytic efficiency. The facile de novo synthesis method proposed in this study enables effective immobilization of high metal content in MOF, and construction of membrane-based photocatalyst for scale-up application.

Improved photocatalytic degradation of ketoprofen by Pt/MIL-125(Ti)/Ag with synergetic effect of Pt-MOF and MOF-Ag double interfaces: Mechanism and degradation pathway

It is a central issue to improve the separation efficiency of photogenerated charge carriers and the utilization of visible light in the field of photocatalysis. Herein, taking MIL-125(Ti) as a host material, the Pt/MIL-125(Ti) was first prepared by solvothermal method to build the interface of Schottky junction. Ag was then introduced onto the surface of Pt/MIL-125(Ti) to form the interface with the surface plasmon resonance effect. These double interfaces in the composite play a synergistic role on the photodagradation. The morphology, crystallinity and photochemical properties of the material were tested. By comparison, Pt/MIL-125(Ti)/Ag (4 wt% Ag) exhibited the best performance in the photodegradation of ketoprofen (KP, 10 mg/L) and the degradation process conformed to the pseudo-first-order kinetics. The photodegradation rate is 0.0253 min^-1, which was higher than MIL-125(Ti) (0.0009 min^-1). The TOC removal efficiency of KP reached approximately 51.5%. The electron paramagnetic resonance (EPR) and free radical capture tests verified that h⁺ and ·OH played the prominent roles during the reaction system. The degradation process, possible pathways and reaction mechanism were proposed. The design of the double interfaces between semiconductor and noble metals is a novel strategy to enhance the photocatalytic performance.

Electronic Structure Modeling of Metal-Organic Frameworks

Owing to their molecular building blocks, yet highly crystalline nature, metal-organic frameworks (MOFs) sit at the interface between molecule and material. Their diverse structures and compositions enable them to be useful materials as catalysts in heterogeneous reactions, electrical conductors in energy storage and transfer applications, chromophores in photoenabled chemical transformations, and beyond. In all cases, density functional theory (DFT) and higher-level methods for electronic structure determination provide valuable quantitative information about the electronic properties that underpin the functions of these frameworks. However, there are only two general modeling approaches in conventional electronic structure software packages: those that treat materials as extended, periodic solids, and those that treat materials as discrete molecules. Each approach has features and benefits; both have been widely employed to understand the emergent chemistry that arises from the formation of the metal-organic interface. This Review canvases these approaches to date, with emphasis placed on the application of electronic structure theory to explore reactivity and electron transfer using periodic, molecular, and embedded models. This includes (i) computational chemistry considerations such as how functional, k-grid, and other model variables are selected to enable insights into MOF properties, (ii) extended solid models that treat MOFs as materials rather than molecules, (iii) the mechanics of cluster extraction and subsequent chemistry enabled by these molecular models, (iv) catalytic studies using both solids and clusters thereof, and (v) embedded, mixed-method approaches, which simulate a fraction of the material using one level of theory and the remainder of the material using another dissimilar theoretical implementation.

Modified Nano-TiO2 Based Composites for Environmental Photocatalytic Applications

TiO2 probably plays the most important role in photocatalysis due to its excellent chemical and physical properties. However, the band gap of TiO2 corresponds to the Ultraviolet (UV) region, which is inactive under visible irradiation. At present, TiO2 has become activated in the visible light region by metal and nonmetal doping and the fabrication of composites. Recently, nano-TiO2 has attracted much attention due to its characteristics of larger specific surface area and more exposed surface active sites. nano-TiO2 has been obtained in many morphologies such as ultrathin nanosheets, nanotubes, and hollow nanospheres. This work focuses on the application of nano-TiO2 in efficient environmental photocatalysis such as hydrogen production, dye degradation, CO2 degradation, and nitrogen fixation, and discusses the methods to improve the activity of nano-TiO2 in the future.