A New Photoactive Crystalline Highly Porous Titanium(IV) Dicarboxylate

Mesoporous TiO2 from Metal-Organic Frameworks for Photoluminescence-Based Optical Sensing of Oxygen

Metal−organic frameworks (MOFs) are a class of porous coordination networks extraordinarily varied in physicochemical characteristics such as porosity, morphologies, and compositions. These peculiarities make MOFs widely exploited in a large array of applications, such as catalysis, chemicals and gas sensing, drug delivery, energy storage, and energy conversion. MOFs can also serve as nanostructured precursors of metal oxides with peculiar characteristics and controlled shapes. In this work, starting from MIL125-(Ti), a 1,4-benzenedicarboxylate (BDC)-based MOF with Ti as metallic center, mesoporous TiO2 powders containing both anatase and rutile crystalline phases were produced. A challenging utilization of these porous MOF-derived Ti-based oxides is the optically-based quantitative detection of molecular oxygen (O2) in gaseous and/or aqueous media. In this study, the photoluminescence (PL) intensity changes during O2 exposure of two MOF-derived mixed-phase TiO2 powders were probed by exploiting the opposite response of rutile and anatase in VIS-PL and NIR-PL wavelength intervals. This result highlights promising future possibilities for the realization of MOF-derived doubly-parametric TiO2-based optical sensors.

The Composites of PCL and Tetranuclear Titanium(IV)-oxo Complexes as Materials Exhibiting the Photocatalytic and the Antimicrobial Activity

Excessive misuse of antibiotics and antimicrobials has led to a spread of microorganisms resistant to most currently used agents. The resulting global threats has driven the search for new materials with optimal antimicrobial activity and their application in various areas of our lives. In our research, we focused on the formation of composite materials produced by the dispersion of titanium(IV)-oxo complexes (TOCs) in poly(ε-caprolactone) (PCL) matrix, which exhibit optimal antimicrobial activity. TOCs, of the general formula [Ti₄O₂(OⁱBu)₁₀(O₂CR’)₂] (R’ = PhNH₂ (1), C₁₃H₉ (2)) were synthesized as a result of the direct reaction of titanium(IV) isobutoxide and 4-aminobenzoic acid or 9-fluorenecarboxylic acid. The microcrystalline powders of (1) and (2), whose structures were confirmed by infrared (IR) and Raman spectroscopy, were dispersed in PCL matrixes. In this way, the composites PCL + nTOCs (n = 5 and 20 wt.%) were produced. The structure and physicochemical properties were determined on the basis of Raman microscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), electron paramagnetic resonance spectroscopy (EPR), and UV–Vis diffuse reflectance spectroscopy (DRS). The degree of TOCs distribution in the polymer matrix was monitored by scanning electron microscopy (SEM). The addition of TOCs micro grains into the PCL matrix only slightly changed the thermal and mechanical properties of the composite compared to the pure PCL. Among the investigated PCL + TOCs systems, promising antibacterial properties were confirmed for samples of PCL + n(2) (n = 5, 20 wt.%) composites, which simultaneously revealed the best photocatalytic activity in the visible range.

Improved Capture and Removal Efficiency of Gaseous Acetaldehyde by a Self-Powered Photocatalytic System with an External Electric Field

Using clean and sustainable stochastic energy from the environment to eliminate pollution caused by gaseous aldehydes would be an effective strategy to achieve the sustainable development of energy and preserve the environment. Here, a piston-based triboelectric nanogenerator (P-TENG) was used to enhance gaseous acetaldehyde absorption and photocatalytic degradation. An external electric field could be generated on a conductive substrate by the P-TENG, converting wind energy into electricity. This made it possible to efficiently degrade gaseous acetaldehyde in the photocatalytic system. Driven by a light breeze (3.0 m/s), the acetaldehyde removal rate of the system reached 63% within 30 min. The presence of an external electric field could generate more hydroxyl radicals (^•OH), superoxide radicals (^•O₂^-), and holes (h⁺), which has a positive effect on the photocatalytic degradation of acetaldehyde. The design and concept of this study not only realized the efficient conversion of renewable and sustainable random energy but also could be applied to the efficient removal of gaseous aldehydes, providing an effective way to create a cleaner environment.

Construction of C-C bonds via photoreductive coupling of ketones and aldehydes in the metal-organic-framework MFM-300(Cr)

Construction of C-C bonds via reductive coupling of aldehydes and ketones is hindered by the highly negative reduction potential of these carbonyl substrates, particularly ketones, and this renders the formation of ketyl radicals extremely endergonic. Here, we report the efficient activation of carbonyl compounds by the formation of specific host-guest interactions in a hydroxyl-decorated porous photocatalyst. MFM-300(Cr) exhibits a band gap of 1.75 eV and shows excellent catalytic activity and stability towards the photoreductive coupling of 30 different aldehydes and ketones to the corresponding 1,2-diols at room temperature. Synchrotron X-ray diffraction and electron paramagnetic resonance spectroscopy confirm the generation of ketyl radicals via confinement within MFM-300(Cr). This protocol removes simultaneously the need for a precious metal-based photocatalyst or for amine-based sacrificial agents for the photochemical synthesis.

A Showcase of Green Chemistry: Sustainable Synthetic Approach of Zirconium-Based MOF Materials

Zirconium-based metal-organic framework materials (Zr-MOFs) have more practical usage over most conventional benchmark porous materials and even many other MOFs due to the excellent structural stability, rich coordination forms, and various active sites. However, their mass-production and application are restricted by the high-cost raw materials, complex synthesis procedures, harsh reaction conditions, and unexpected environmental impact. Based on the principles of "Green Chemistry", considerable efforts have been done for breaking through the limitations, and significant progress has been made in the sustainable synthesis of Zr-MOFs over the past decade. In this review, the advancements of green raw materials and green synthesis methods in the synthesis of Zr-MOFs are reviewed, along with the corresponding drawbacks. The challenges and prospects are discussed and outlooked, expecting to provide guidance for the acceleration of the industrialization and commercialization of Zr-MOFs.

Size modulation of MIL-125 nanocrystals to promote the catalytic performance towards oxidative desulfurization

The Ti-based metal-organic framework (Ti-MOF) MIL-125 with tunable crystalline size in the range of ca. 50 nm to 1500 nm was synthesized by the coordination modulation method using trans-cinnamic acid (CA) as a modulator. The coordination modulation also induced hierarchical porosity and structure defects on the nanocrystals. A significant size-dependent catalytic activity towards the oxidative desulfurization (ODS) reaction was observed for these MIL-125 nanocrystals. In particular, the MIL-125 nanocrystals with a mean size of ca. 50 nm exhibit dramatically enhanced catalytic performance for the bulky sulfur compound 4,6-dimethyldibenzothiophene (4,6-DMDBT) compared to the microcrystals. It is demonstrated that the size modulation of MIL-125 is an effective approach to promote its performance for the catalysis of bulky molecules.

Metal-organic framework membranes with single-atomic centers for photocatalytic CO2 and O2 reduction

The demand for sustainable energy has motivated the development of artificial photosynthesis. Yet the catalyst and reaction interface designs for directly fixing permanent gases (e.g. CO₂, O₂, N₂) into liquid fuels are still challenged by slow mass transfer and sluggish catalytic kinetics at the gas-liquid-solid boundary. Here, we report that gas-permeable metal-organic framework (MOF) membranes can modify the electronic structures and catalytic properties of metal single-atoms (SAs) to promote the diffusion, activation, and reduction of gas molecules (e.g. CO_2, O₂) and produce liquid fuels under visible light and mild conditions. With Ir SAs as active centers, the defect-engineered MOF (e.g. activated NH₂-UiO-66) particles can reduce CO₂ to HCOOH with an apparent quantum efficiency (AQE) of 2.51% at 420 nm on the gas-liquid-solid reaction interface. With promoted gas diffusion at the porous gas-solid interfaces, the gas-permeable SA/MOF membranes can directly convert humid CO₂ gas into HCOOH with a near-unity selectivity and a significantly increased AQE of 15.76% at 420 nm. A similar strategy can be applied to the photocatalytic O₂-to-H₂O₂ conversions, suggesting the wide applicability of our catalyst and reaction interface designs.

Photoreduction of permanent gas faces challenges in reactant diffusion and activation at the three-phase interface. Here the authors showed porous metal-organic framework membranes decorated by metal single atoms can boost the photoreduction of CO₂ and O₂ at the high-throughput gas-solid interface.

Photoactive Zr and Ti Metal-Organic-Frameworks for Solid-State Solar Cells

Solid-state photovoltaic cells based on robust metal-organic frameworks (MOFs), MIL-125(Ti), MIL-125(Ti)-NH₂ , UiO-67, Ru(bpy)₂ -UiO-67, (bpy 2,2'-bipyridine) as active components and spiro-MeOTAD (MeOTAD 2,2',7,7'-tetrakis[N,N-di(p-methoxyphenyl)amino]-9,9'-spirobifluorene) as hole transporting layer have been prepared., The photovoltaic response of this material increases in the presence of bathochromic -NH₂ groups on the linker or Ru (II) polypyridyl complexes light harvester. These results show that the strategies typically employed in photocatalysis to enhance the photocatalytic activity of MOFs can also be applied in the field of photovoltaic devices.

Support Effect of Metal-Organic Frameworks on Ethanol Production through Acetic Acid Hydrogenation

We present a systematic study on the support effect of metal-organic frameworks (MOFs), regarding substrate adsorption. A remarkable enhancement of both catalytic activity and selectivity for the ethanol (EtOH) production reaction through acetic acid (AcOH) hydrogenation (AH) was observed on Pt nanoparticles supported on MOFs. The systematic study on catalysis using homogeneously loaded Pt catalysts, in direct contact with seven different MOF supports (MIL-125-NH₂, UiO-66-NH₂, HKUST-1, MIL-101, Zn-MOF-74, Mg-MOF-74, and MIL-121) (abbreviated as Pt/MOFs), found that MOFs having a high affinity for the AcOH substrate (UiO-66-NH₂ and MIL-125-NH₂) showed high catalytic activity for AH. This is the first demonstration indicating that the adsorption ability of MOFs directly accelerates catalytic performance using the direct contact between the metal and the MOF. In addition, Pt/MIL-125-NH₂ showed a remarkably high EtOH yield (31% at 200 °C) in a fixed-bed flow reactor, which was higher by a factor of more than 8 over that observed for Pt/TiO₂, which was the best Pt-based catalyst for this reaction. Infrared spectroscopy and a theoretical study suggested that the MIL-125-NH₂ support plays an important role in high EtOH selectivity by suppressing the formation of the byproduct, ethyl acetate (AcOEt), due to its relatively weak adsorption behavior for EtOH rather than AcOH.

A Tunable Multivariate Metal-Organic Framework as a Platform for Designing Photocatalysts

Catalysts for photochemical reactions underlie many foundations in our lives, from natural light harvesting to modern energy storage and conversion, including processes such as water photolysis by TiO2. Recently, metal-organic frameworks (MOFs) have attracted large interest within the chemical research community, as their structural variety and tunability yield advantages in designing photocatalysts to address energy and environmental challenges. Here, we report a series of novel multivariate metal-organic frameworks (MTV-MOFs), denoted as MTV-MIL-100. They are constructed by linking aromatic carboxylates and AB2OX3 bimetallic clusters, which have ordered atomic arrangements. Synthesized through a solvent-assisted approach, these ordered and multivariate metal clusters offer an opportunity to enhance and fine-tune the electronic structures of the crystalline materials. Moreover, mass transport is improved by taking advantage of the high porosity of the MOF structure. Combining these key advantages, MTV-MIL-100(Ti,Co) exhibits a high photoactivity with a turnover frequency of 113.7 molH2 gcat.-1 min-1, a quantum efficiency of 4.25%, and a space time yield of 4.96 × 10-5 in the photocatalytic hydrolysis of ammonia borane. Bridging the fields of perovskites and MOFs, this work provides a novel platform for the design of highly active photocatalysts.

Threefold Collaborative Stabilization of Ag14 -Nanorods by Hydrophobic Ti16 -Oxo Clusters and Alkynes: Designable Assembly and Solid-State Optical-Limiting Application

Ag nanoclusters have received increasing attention due to their atomically precise and diverse structures and intriguing optical properties. Nevertheless, the inherent instability of Ag nanoclusters has seriously hindered their practical application. In this work, for the first time, Ag clusters are collaboratively protected by hydrophobic Ti-oxo clusters and alkyne ligands. Initially, a pyramidal Ag₅ cluster terminated with ^t BuC≡C^- and CH₃ CN was inserted into the cavity of a Ti₈ -oxo nanoring to form Ag₅ @Ti₈ . To overcome the instability of acetonitrile-terminated silver site, such two Ag₅ @Ti₈ clusters could sandwich an Ag₄ unit to form Ag₁₄ -nanorod@Ti₁₆ -oxo-nanoring (Ag₁₄ @Ti₁₆ ), which is peripherally protected by fluorophenyl groups and alkyne caps. This threefold protected (hydrophobic fluorinated organic layer, Ti-O shell, and terminal alkyne ligands) Ag₁₄ @Ti₁₆ exhibits superhydrophobicity and excellent ambient stability, endowing it with solid-state optical limiting characteristics.

Catalytic Performance of Zr-Based Metal-Organic Frameworks Zr-abtc and MIP-200 in Selective Oxidations with H2 O2

The catalytic performance of Zr-abtc and MIP-200 metal-organic frameworks consisting of 8-connected Zr₆ clusters and tetratopic linkers was investigated in H₂ O₂ -based selective oxidations and compared with that of 12-coordinated UiO-66 and UiO-67. Zr-abtc demonstrated advantages in both substrate conversion and product selectivity for epoxidation of electron-deficient C=C bonds in α,β-unsaturated ketones. The significant predominance of 1,2-epoxide in carvone epoxidation, coupled with high sulfone selectivity in thioether oxidation, points to a nucleophilic oxidation mechanism over Zr-abtc. The superior catalytic performance in the epoxidation of unsaturated ketones correlates with a larger amount of weak basic sites in Zr-abtc. Electrophilic activation of H₂ O₂ can also be realized, as evidenced by the high activity of Zr-abtc in epoxidation of the electron-rich C=C bond in caryophyllene. XRD and FTIR studies confirmed the retention of the Zr-abtc structure after the catalysis. The low activity of MIP-200 in H₂ O₂ -based oxidations is most likely related to its specific hydrophilicity, which disfavors adsorption of organic substrates and H₂ O₂ .

Pancake-Like MOF Solid-State Electrolytes with Fast Ion Migration for High-Performance Sodium Battery

Solid-state electrolyte (SSE) of the sodium-ion battery have attracted tremendous attention in the next generation energy storage materials on account of their wide electrochemical window and thermal stability. However, the high interfacial impedance, low ion transference number and complex preparation process restrict the application of SSE. Herein, inspired by the excellent sieving function and high specific surface area of red blood cells, we obtained a solid-like electrolyte (SLE) based on the combination of the pancake-like metal-organic framework (MOF) with liquid electrolyte, possessing a high ionic conductivity of 6.60 × 10^-4 S cm^-1, and excellent sodium metal compatibility. In addition, we investigated the ion restriction effect of MOF's apertures size and special functional groups, and the ion transference number increased from 0.16 to 0.33. Finally, the assembled Na_0.44MnO₂//SLE//Na full batteries showed no obvious capacity decrease after 160 cycles. This material design of SLE in our work is an important key to obtain fast ion migration SLE for high-performance sodium-ion batteries.

Enhanced Visible-Light-Driven Hydrogen Production through MOF/MOF Heterojunctions

A strategy for enhancing the photocatalytic performance of MOF-based systems (MOF: metal-organic framework) is developed through the construction of MOF/MOF heterojunctions. The combination of MIL-167 with MIL-125-NH₂ leads to the formation of MIL-167/MIL-125-NH₂ heterojunctions with improved optoelectronic properties and efficient charge separation. MIL-167/MIL-125-NH₂ outperforms its single components MIL-167 and MIL-125-NH₂, in terms of photocatalytic H₂ production (455 versus 0.8 and 51.2 μmol h^-1 g^-1, respectively), under visible-light irradiation, without the use of any cocatalysts. This is attributed to the appropriate band alignment of these MOFs, the enhanced visible-light absorption, and long charge separation within MIL-167/MIL-125-NH₂. Our findings contribute to the discovery of novel MOF-based photocatalytic systems that can harvest solar energy and exhibit high catalytic activities in the absence of cocatalysts.

Construction of Core-Shell MOFs@COF Hybrids as a Platform for the Removal of UO22+ and Eu3+ Ions from Solution

The binary nanocomposites of metal/covalent-organic frameworks (NH₂-MIL-125(Ti)@TpPa-1) were constructed by solvothermal method, which was developed as a multifunctional platform with adsorption and photocatalysis for radionuclides removal. The batch experiments and physicochemical property (FT-IR, XRD, SEM, TEM, XPS, etc.) corroborated: (i) core-shell NH₂-MIL-125(Ti)@TpPa-1 had a more stable, multilayer pore structure and abundant active functional groups; (ii) NH₂-MIL-125(Ti)@TpPa-1 had fast a removal rate, as well as a high adsorption capacity of 536.73 mg (UO₂²⁺)/g and 593.97 mg (Eu³⁺)/g; (iii) the pseudo-second-order and Langmuir model provided a more reasonable description, indicating the immobilization process was endothermic, spontaneous chemisorption; (iv) the adsorption mechanism was chelation and electrostatic attraction, ascribed to the nitrogen/oxygen-containing functional groups. These results illustrated that NH₂-MIL-125(Ti)@TpPa-1 was a prospective adsorbent for the remediation polluted by radionuclides. In addition, the research provided the theoretical basis for further investigation on the UO₂²⁺(VI) photoreduction.

Metal-Organic-Framework-Based Materials for Antimicrobial Applications

To address the serious threat of bacterial infection to public health, great efforts have been devoted to the development of antimicrobial agents for inhibiting bacterial growth, preventing biofilm formation, and sterilization. Very recently, metal-organic frameworks (MOFs) have emerged as promising materials for various antimicrobial applications owing to their different functions including the controlled/stimulated decomposition of components with bactericidal activity, strong interactions with bacterial membranes, and formation of photogenerated reactive oxygen species (ROS) as well as high loading and sustained releasing capacities for other antimicrobial materials. This review focuses on recent advances in the design, synthesis, and antimicrobial applications of MOF-based materials, which are classified by their roles as component-releasing (metal ions, ligands, or both), photocatalytic, and chelation antimicrobial agents as well as carriers or/and synergistic antimicrobial agents of other functional materials (antibiotics, enzymes, metals/metal oxides, carbon materials, etc.). The constituents, fundamental antimicrobial mechanisms, and evaluation of antimicrobial activities of these materials are highlighted to present the design principles of efficient MOF-based antimicrobial materials. The prospects and challenges in this research field are proposed.

Metal-Organic Frameworks in Oxidation Catalysis with Hydrogen Peroxide

In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen peroxide. MOFs having outstanding thermal and chemical stability, such as Cr(III)-based MIL-101, Ti(IV)-based MIL-125, Zr(IV)-based UiO-66(67), Zn(II)-based ZIF-8, and some others, will be in the main focus of this work. The effects of the metal nature and MOF structure on catalytic activity and oxidation selectivity are analyzed and the mechanisms of hydrogen peroxide activation are discussed. In some cases, we also make an attempt to analyze relationships between liquid-phase adsorption properties of MOFs and peculiarities of their catalytic performance. Attempts of using MOFs as supports for construction of single-site catalysts through their modification with heterometals will be also addressed in relation to the use of such catalysts for activation of H2O2. Special attention is given to the critical issues of catalyst stability and reusability. The scope and limitations of MOF catalysts in H2O2-based selective oxidation are discussed.

Adsorptive removal of hazardous organics from water and fuel with functionalized metal-organic frameworks: Contribution of functional groups

The purification of contaminated water and fuel is very important for our sustainability. Adsorptive removal has attracted significant attention because of possible applications in industry and the rapid development of metal-organic frameworks (MOFs), which can be competitive adsorbents. In this review, the possible/competitive purification of water (contaminated with organics) and fuel (composed of S- and N-Containing compounds) via adsorption using MOFs, especially those with various functional groups (FGs), will be discussed. The contribution of FGs such as -OH, -COOH, -SO₃H, -NH₂, and -NH₃⁺ to adsorption/purification will be analyzed in detail, not only to understand the plausible adsorption mechanism but also to utilize specific FGs in adsorption. Moreover, methods for introducing FGs onto MOFs will be summarized. Finally, the prospects for both adsorption/removal and emerging fields will be suggested. Studies for practical applications in industry with shaped MOFs from inexpensive route will be important. The solution pH should be considered for the adsorption of aqueous solution. Applications of MOFs in other fields like storage/delivery and enrichment of analytes might be deeply studied.

Metal-organic frameworks derived C/TiO2 for visible light photocatalysis: Simple synthesis and contribution of carbon species

A series of in-situ carbon-doped TiO₂ (C_x/TiO₂) composites with a porous and crystalline structure were successfully synthesized via one-step and low-temperature calcination of titanium metal-organic framework (MOF), MIL-125(Ti). The resultant materials were comprehensively investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), N₂ adsorption-desorption measurements, UV-vis diffuse reflectance spectrum (DRS), photoluminescence (PL) spectra and photoelectrochemical measurements, and their photocatalytic activities for bisphenol A (BPA) degradation were assessed. Compared with the benchmark TiO₂ photocatalyst (P25), the C_x/TiO₂ composite material with high specific surface, lower band gap, and reduced photogenerated electron hole ratio exhibited outstanding photodegradation activity and durability for BPA, which could be attributed to the combined effect of co-doping of multiple carbon species (substituent carbon and carbonate) and porous structure. During BPA degradation, the holes and superoxide radicals were the primary role oxidative species in the reaction process. Therefore, this new efficient photocatalyst is promising candidate for photodegradation of organic pollutants.

Tuning the Optoelectronic Properties of Hybrid Functionalized MIL-125-NH2 for Photocatalytic Hydrogen Evolution

Metal-organic frameworks (MOFs) constructed with mixed ligands have shown great promise in the generation of materials with improved sorption, optical, and electronic properties. With an experimental, spectroscopic, and computational approach, herein, we investigated how the incorporation of different functionalized ligands within the structure of MIL-125-NH₂ affects its performance in photocatalytic water reduction. We found that multiligand incorporation within the MOF structure has an impact on the light absorption spectrum and the electronic structure. These combined modifications improve the photocatalytic performance of MIL-125-NH₂, thereby increasing the rate of hydrogen evolution reaction. Of the four nanoparticle/MOF photocatalytic systems tested, we showed that the Pt/MIL-125-NH₂/(OH)₂ system (Pt nanoparticle plus MIL-125-NH₂ with amino and dihydroxyl functionalized ligands) outperforms its counterpart Pt/MIL-125-NH₂ system, attributed to the enhanced p-π conjugation between the lone pairs of O atoms and their aromatic ligands resulting in a red-shifted absorption spectrum and greater spatial distribution of electron density.

Versatile Nanoscale Metal-Organic Frameworks (nMOFs): An Emerging 3D Nanoplatform for Drug Delivery and Therapeutic Applications

For decades, nanoscale metal-organic frameworks (nMOFs) have attracted extensive interest in biomedicine due to their distinct characteristics, including facile synthesis, porous interior, and tunable biocompatibility. With high porosity, versatile nMOFs allow for the facile encapsulation of various therapeutic agents with exceptionally high payloads. Constructed from metal ions and organic linkers through coordination bonds, nMOFs with plentiful functional groups enable the surface modification for active targeting and enhanced biocompatibility. This review outlines the up-to-date progresses on the exploration of nMOFs in the field of biomedicine. First, the classification and synthesis of nMOFs are discussed, followed by the concrete introduction of drug loading strategies of nMOFs and mechanisms of stimulation-responsive drug release. Second, the smart designs of the nMOFs-based platforms for anticancer and antibacterial treatment are summarized. Finally, the basic challenges faced by nMOFs research and the great potential of biomimetic nMOFs are presented. This review article affords an inspiring insight into the interdisciplinary research of nMOFs and their biomedical applications, which holds great expectation for their further clinical translation.

Effect of Ligand Functionalization on the Rate of Charge Carrier Recombination in Metal-Organic Frameworks: A Case Study of MIL-125

Ligand functionalization is a powerful approach for modifying the electronic structure of metal-organic frameworks when targeting the optimal electronic properties for photocatalysis and photovoltaics. However, its effect on the charge carrier lifetimes and recombination pathways remains unexplored. In this work, first-principles simulations, including nonadiabatic molecular dynamics, are performed for the representative TiO₂-based metal-organic framework systems MIL-125-X to unravel the impact of ligand functionalization on the nonradiative electron-hole recombination process, decoherence rates, and phonon modes giving the largest contribution to the nonradiative decay. Nonradiative recombination rates, simulated using the PBE0 density functional, are in excellent agreement with experiment. The ligand functionalization in MIL-125-X influences the recombination rates, unraveling the trend opposite to the evolution of the band gap and affecting the nonadiabatic coupling coefficients. Ligand modification impacts the phonon modes, which contribute most to the recombination process, altering the distribution between soft phonon modes and vibrational modes associated with specific structural motifs.

Single copper sites dispersed on defective TiO2-x as a synergistic oxygen reduction reaction catalyst

Catalysts containing isolated single atoms have attracted much interest due to their good catalytic behavior, bridging the gap between homogeneous and heterogeneous catalysts. Here, we report an efficient oxygen reduction reaction (ORR) catalyst that consists of atomically dispersed single copper sites confined by defective mixed-phased TiO_2-x. This synergistic catalyst was produced by introducing Cu²⁺ to a metal organic framework (MOF) using the Mannich reaction, occurring between the carbonyl group in Cu(acac)₂ and the amino group on the skeleton of the MOF. The embedding of single copper atoms was confirmed by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy and x-ray absorption fine structure spectroscopy. Electronic structure modulation of the single copper sites coupling with oxygen vacancies was further established by electron paramagnetic resonance spectroscopy and first-principles calculations. Significantly enhanced ORR activity and stability were achieved on this special Cu single site. The promising application of this novel electrocatalyst was demonstrated in a prototype Zn-air battery. This strategy of the stabilization of single-atom active sites by optimization of the atomic and electronic structure on a mixed matrix support sheds light on the development of highly efficient electrocatalysts.

Construction of Titanium-Based Metal-Organic Frameworks Based on the Ti/Cu Heteronuclear Cluster

Presented here are two titanium-based metal-organic frameworks (Ti-MOFs) based on well-defined [Ti₆Cu₆(μ₃-O)₂(μ₂-O)₉(HSO₄)₂(SO₄)₆], which can be easily obtained from a cheap Ti source and CuSO₄ and exhibited interesting magnetic properties. Furthermore, this clusters can be isolated in pure phase. Numerous uncoordinated sites of SO₄ and labile ligands on the Ti and Cu centers of this cluster make it a good candidate as a secondary building unit to construct various Ti-MOFs in the future.

Encapsulating organic guest cations in anionic MOFs that exhibit multi-responsive photochromism and photocontrolled luminescence

Two MOF-based host–guest compounds were prepared by incorporating viologen into an anionic framework, and exhibited photochromism upon irradiation with various light sources. Moreover, their luminescence properties can be switched by irradiation.

Early instability of MIL-125-NH2 in aqueous solution and mediation of the visible photogeneration of an NADH cofactor

MIL-125-NH₂ hydrolysis can be minimized by regulating the pH of the medium, thus defining a stability window where it is possible to use it as a photocatalyst for visible light-driven production of NADH.

Biocompatibility and biodegradability of metal organic frameworks for biomedical applications

Metal organic frameworks (MOFs) are a unique class of smart hybrid materials that have recently attracted significant interest for catalysis, separation and biomedical applications. Different strategies have been developed to overcome the limitations of MOFs for bio-applications in order to produce a system with high biocompatibility and biodegradability. In this review, we outline the chemical and physical factors that dictate the biocompatibility and biodegradability characteristics of MOFs including the nature of the metal ions and organic ligands, size, surface properties and colloidal stability. This review includes the in vitro biodegradation and in vivo biodistribution studies of MOFs to better understand their pharmacokinetics, organ toxicity and immune response. Such studies can guide the design of future bio-friendly systems that bring us closer to safely translating these platforms into the pharmaceutical consumer market.

A review of the research status of CO2 photocatalytic conversion technology based on bibliometrics

In order to clarify the research status, hot spots and development trend in the field of conversion of carbon dioxide, a large amount of literature data set in the scientific network database was analyzed by bibliometrics.

Copper(i) pyrimidine-2-thiolate cluster-based polymers as bifunctional visible-light-photocatalysts for chemoselective transfer hydrogenation of α,β-unsaturated carbonyls

The photoinduced chemoselective transfer hydrogenation of unsaturated carbonyls to allylic alcohols has been accomplished using cluster-based MOFs as bifunctional visible photocatalysts.

Modulation of the Bifunctional CrVI to CrIII Photoreduction and Adsorption Capacity in ZrIV and TiIV Benchmark Metal-Organic Frameworks

The presence of hexavalent chromium water pollution is a growing global concern. Among the currently applied technologies to remove CrVI, its adsorption and photocatalytic reduction to CrIII less mobile and toxic forms are the most appealing because of their simplicity, reusability, and low energy consumption. However, little attention has been paid to bifunctional catalysts, that is, materials that can reduce CrVI to CrIII and retain both hexavalent and trivalent chromium species at the same time. In this work, the dual CrVI adsorption–reduction capacity of two iconic photoactive water-stable zirconium and titanium-based metal–organic frameworks (MOFs) has been investigated: UiO-66-NH2 and MIL-125. The bifunctionality of photoactive MOFs depends on different parameters, such as the particle size in MIL-125 or organic linker functionalization/defective positions in UiO-66 type sorbents. For instance, the presence of organic linker defects in UiO-66 has shown to be detrimental for the chromium photoreduction but beneficial for the retention of the CrIII phototransformed species. Both compounds are able to retain from 90 to 98% of the initial chromium present at acidic solutions as well as immobilize the reduced CrIII species, demonstrating the suitability of the materials for CrVI environmental remediation. In addition, it has been demonstrated that adsorption can be carried out also in a continuous flux mode through a diluted photoactive MOF/sand chromatographic column. The obtained results open the perspective to assess the bifunctional sorption and photoreduction ability of a plethora of MOF materials that have been applied for chromium capture and photoreduction purposes. In parallel, this work opens the perspective to develop specific chemical encoding strategies within MOFs to transfer this bifunctionality to other related water remediation applications.

On the limit of proton-coupled electronic doping in a Ti(iv)-containing MOF

Ti^IV-containing metal–organic frameworks are known to accumulate electrons in their conduction bands, accompanied by protons, when irradiated in the presence of alcohols. The archetypal system, MIL-125, was recently shown to reach a limit of 2e⁻ per Ti₈ octomeric node. However, the origin of this limit and the broader applicability of this unique chemistry relies not only on the presence of Ti^IV, but also access to inorganic inner-sphere Lewis basic anions in the MOF nodes. Here, we study the loading of protons and electrons in MIL-125, and assess the thermodynamic limit of doping these materials. We find that the limit is determined by the reduction potential of protons: in high charging regimes the MOF exceeds the H⁺/H₂ potential. Generally, we offer the design principle that inorganic anions in MOF nodes can host adatomic protons, which may stabilize meta-stable low valent transition metals. This approach highlights the unique chemistry afforded by MOFs built from inorganic clusters, and provides one avenue to developing novel catalytic scaffolds for hydrogen evolution and transfer hydrogenation.

Photo-promoted doping of MIL-125 is limited by the potential of MOF-bound protons exceeding the hydrogen evolution reaction.

Ring-opening copolymerization of ε-caprolactone and δ-valerolactone by a titanium-based metal–organic framework

Copolymerization of ε-caprolactone and δ-valerolactone without any co-catalyst in a solvent-free medium under eco-friendly conditions using earth abundant Ti-metal based MOF, MIL-125.

Single- and mixed-metal–organic framework photocatalysts for carbon dioxide reduction

This review focuses on the important roles of varied metal types over MOF-based photocatalysts. The basic principles, types of MOF photocatalysts and roles of the reaction system to achieve efficient MOFs for CO₂ photoreduction are discussed.

The role of metal–organic porous frameworks in dual catalysis

Metal–organic frameworks (MOFs) are a valuable group of porous crystalline solids with inorganic and organic parts that can be used in dual catalysis.

The state of the field: from inception to commercialization of metal–organic frameworks

We provide a brief overview of the state of the MOF field from their inception to their synthesis, potential applications, and finally, to their commercialization.

Effect of modulator connectivity on promoting defectivity in titanium-organic frameworks

The recognition of defect chemistry as a true synthetic tool for targeted creation of defects and controllable performance remains limited by the pool of frameworks explored. The value of defect engineering in controlling the properties of defective frameworks has been beautifully exemplified and largely demonstrated with UiO-type materials based on Zr(iv) nodes. However, titanium-organic frameworks remain largely unexplored in this context arguably due to the complex chemistry in solution of Ti(iv) and the difficulties in growing crystalline solids. We report a systematic study on the ability of mono- and dicarboxylic modulators (benzoic and isophthalic acid) to promote defect creation in the heterometallic Ti-MOF of the MUV-10 family. Our results indicate that both acids behave as capping modulators at high concentrations, but isophthalic acid is a more efficient defect promoter, yielding defective phases with nearly 40% of missing linkers. Our computational results suggest that this difference cannot be solely ascribed to relative changes in acidity but to the ability of this bidentate linker in compensating the structural distortion and energy penalty imposed by breaking the connectivity of the underlying framework.

Metal-organic frameworks for virus detection

Virus severely endangers human life and health, and the detection of viruses is essential for the prevention and treatment of associated diseases. Metal-organic framework (MOF), a novel hybrid porous material which is bridged by the metal clusters and organic linkers, has become a promising biosensor platform for virus detection due to its outstanding properties including high surface area, adjustable pore size, easy modification, etc. However, the MOF-based sensing platforms for virus detection are rarely summarized. This review systematically divided the detection platforms into nucleic acid and immunological (antigen and antibody) detection, and the underlying sensing mechanisms were interpreted. The nucleic acid sensing was discussed based on the properties of MOF (such as metal ion, functional group, geometry structure, size, porosity, stability, etc.), revealing the relationship between the sensing performance and properties of MOF. Moreover, antibodies sensing based on the fluorescence detection and antigens sensing based on molecular imprinting or electrochemical immunoassay were highlighted. Furthermore, the remaining challenges and future development of MOF for virus detection were further discussed and proposed. This review will provide valuable references for the construction of sophisticated sensing platform for the detection of viruses, especially the 2019 coronavirus.

Plasma-Induced Defects Enhance the Visible-Light Photocatalytic Activity of MIL-125(Ti)-NH2 for Overall Water Splitting

Defect engineering in metal-organic frameworks is commonly performed by using thermal or chemical treatments. Herein we report that oxygen plasma treatment generates structural defects on MIL-125(Ti)-NH₂ , leading to an increase in its photocatalytic activity. Characterization data indicate that plasma-treated materials retain most of their initial crystallinity, while exhibiting somewhat lower surface area and pore volume. XPS and FT-IR spectroscopy reveal that oxygen plasma induces MIL-125(Ti)-NH₂ partial terephthalate decarboxylation and an increase in the Ti-OH population. Thermogravimetric analyses confirm the generation of structural defects by oxygen plasma and allowed an estimation of the resulting experimental formula of the treated MIL-125(Ti)-NH₂ solids. SEM analyses show that oxygen plasma treatment of MIL-125(Ti)-NH₂ gradually decreases its particle size. Importantly, diffuse reflectance UV/Vis spectroscopy and valence band measurements demonstrate that oxygen plasma treatment alters the MIL-125(Ti)-NH₂ band gap and, more significantly, the alignment of highest occupied and lowest unoccupied crystal orbitals. An optimal oxygen plasma treatment to achieve the highest efficiency in water splitting with or without methanol as sacrificial electron donor under UV/Vis or simulated sunlight was determined. The optimized plasma-treated MIL-125(Ti)-NH₂ photocatalyst acts as a truly heterogeneous photocatalyst and retains most of its initial photoactivity and crystallinity upon reuse.