Atomistic Approach toward Selective Photocatalytic Oxidation of a Mustard-Gas Simulant: A Case Study with Heavy-Chalcogen-Containing PCN-57 Analogues

Crystal-Defect-Induced Longer Lifetime of Excited States in a Metal-Organic Framework Photocatalyst to Enhance Visible-Light-Mediated CO2 Reduction

We report the structural defects in Zr-metal-organic framework (MOFs) for achieving highly efficient CO2 reduction under visible light irradiation. A series of defective Zr-MOF-X (X = 160, 240, 320, or 400) are synthesized by acid-regulated defect engineering. Compared to pristine defect-free Zr-MOF (NNU-28), N2 uptake increases for Zr-MOF-X synthesized with the HAc modulator, producing a larger pore space and Brunauer-Emmett-Teller surface area. The pore size distribution demonstrates that defective Zr-MOF-X exhibits mesoporous structures. Electrochemistry tests show that defective Zr-MOF-X possesses a more negative reduction potential and a higher photocurrent responsive signal than that of pristine NNU-28. Consequently, the defective samples exhibit a significantly higher efficiency in the photoreduction of CO2 to formate. Transient absorption spectroscopies manifest that structural defects modulate the excited-state behivior of Zr-MOF-X and improve the photogenerated charge separation of Zr-MOF-X. Furthermore, electron paramagnetic resonance and in-suit X-ray photoelectron spectroscopy provide additional evidence of the high photocatalytic performance exhibited by defective Zr-MOF-X. Results demonstrate that structural defects in Zr-MOF-X also improve the charge transfer, producing abundant Zr(III) catalytically active sites, exhibiting a slower decay process than defect-free Zr-MOF. The long-lifetime Zr(III) species in defective Zr-MOF-X are fully exposed to a high-concentration CO2 atmosphere, thereby enhancing the photocatalytic efficiency of CO2 reduction.

Interface-regulated S-type core-shell PCN-224@TiO2 heterojunction for visible-light-driven generation of singlet oxygen for selective photooxidation of 2-chloroethyl ethyl sulfide

Selective oxidation of sulfur mustard gas (HD) to non-toxic sulfoxide by the visible-light-catalyzed generation of singlet oxygen (1O2) is a promising degradation strategy. Although PCN-224 can absorb visible light, it suffers from rapid electron-hole recombination and low redox capacity, which limits the performance of HD degradation. Titanium dioxide (TiO2) is an excellent photocatalyst but it lacks visible-light-activity in degrading HD. In this study, PCN-224@TiO2 heterojunction with S-type core-shell structure was synthesized by in-situ growth method to prolong the visible light absorption capacity of TiO2 and inhibit the rapid recombination of PCN-224. The interface formation and internal electric field were optimized by adjusting the Zr/Ti ratio to enhance the charge transfer, redox capacity, electron-hole separation, and visible light absorption. In this study, the formation of heterojunction composites based on Zr-O-Ti linkages is demonstrated by a series of characterization methods. It is demonstrated by experiments and theoretical calculations that PCN-224@TiO2 can generate nearly 100 % 1O2 under visible light conditions without a sacrificial agent, resulting in efficient and selective oxidation of 2-chloroethyl ethyl sulfide (CEES), a simulant of HD, to non-toxic sulfoxide form.

Linker Engineering toward Tunable Emission Behavior of Porous Interpenetrated Zr-Organic Frameworks

Conjugated molecules with donor-acceptor-donor (D-A-D) moieties have garnered significant attention for their ability to form luminescent metal-organic frameworks (LMOFs). D-A-D molecules feature tunable bandgaps, which can be varied systematically to control the fluorescence wavelength of LMOFs. In this study, we prepared and characterized the fluorescence properties of two porous interpenetrated Zr-organic frameworks (PIZOFs) constructed using 4,4'-(benzo[c][1,2,5]selenadiazole-4,7-diylbis(ethyne-2,1-diyl))dibenzoic acid (L-Se) or 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(ethyne-2,1-diyl))dibenzoic acid (L-S) as linkers. The corresponding MOFs are denoted as PIZOF-Se and PIZOF-S, respectively. Through our investigation, we explored the correlation between the structure of the frameworks and their respective optical properties. Our findings revealed that there are distinct differences in the fluorescence properties of the two PIZOFs. Specifically, the fluorescence of PIZOF-S is red-shifted from that characteristic of the corresponding linker, L-S. By contrast, the fluorescence of PIZOF-Se is substantially blue-shifted from that of linker L-Se. The emission of mixed-linker MOFs is explored by combining L-S or L-Se with structurally analogous, but nonfluorescent linker, 4,4'-((perfluoro-1,4-phenylene)bis(ethyne-2,1-diyl))dibenzoic acid (L-F). Based on steady-state and time-resolved photoluminescence experiments, as well as confocal fluorescence microscopy combined with fluorescence lifetime imaging (FILM), we demonstrated that linker engineering is an effective method to tune the emission behavior of LMOFs.

Single-Chain Conjugated Polymer Guests Confined inside Metal-Organic Frameworks (MOFs): Boosting the Detection and Degradation of a Sulfur Mustard Simulant

Real-time detection and effective degradation of toxic gases have attracted considerable attention in environmental monitoring and human health. Here, we demonstrate a solvent-assisted dynamic assembly strategy to strongly enhance the detection and degradation performance for 2-chloroethyl ethyl sulfide (CEES, as a sulfur mustard simulant) via confinement of a conjugated polymer in metal-organic frameworks (MOFs). The conjugated polymer poly(9,9-di-n-octylfluorene-altbenzothiadiazole) (F8BT) is infiltrated into one-dimensional nanochannels of the Zr-based topological MOF NU-1000 in a single-chain manner, which is caused by the nanoconfinement effect and the steric hindrance between 9,9-dioctylfluorene units and benzothiadiazole units. The obtained F8BT⊂NU-1000 composites provide a high specific surface area and abundant active sites. Based on the cooperative effect of F8BT and NU-1000, rapid and sensitive detection of CEES has been achieved. Moreover, the F8BT⊂NU-1000 composites can selectively oxidize CEES into 2-chloroethyl ethyl sulfoxide (CEESO) under mild photooxidation conditions. Overall, this study opens a new avenue for the fabrication of conjugated polymer/MOF hybrid materials that show great potential for the sensitive detection and effective removal of hazardous chemicals.

Reticular framework materials for photocatalytic organic reactions

Photocatalytic organic reactions, harvesting solar energy to produce high value-added organic chemicals, have attracted increasing attention as a sustainable approach to address the global energy crisis and environmental issues. Reticular framework materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are widely considered as promising candidates for photocatalysis owing to their high crystallinity, tailorable pore environment and extensive structural diversity. Although the design and synthesis of MOFs and COFs have been intensively developed in the last 20 years, their applications in photocatalytic organic transformations are still in the preliminary stage, making their systematic summary necessary. Thus, this review aims to provide a comprehensive understanding and useful guidelines for the exploration of suitable MOF and COF photocatalysts towards appropriate photocatalytic organic reactions. The commonly used reactions are categorized to facilitate the identification of suitable reaction types. From a practical viewpoint, the fundamentals of experimental design, including active species, performance evaluation and external reaction conditions, are discussed in detail for easy experimentation. Furthermore, the latest advances in photocatalytic organic reactions of MOFs and COFs, including their composites, are comprehensively summarized according to the actual active sites, together with the discussion of their structure-property relationship. We believe that this study will be helpful for researchers to design novel reticular framework photocatalysts for various organic synthetic applications.

Size- and Emission-Controlled Synthesis of Full-Color Luminescent Metal-Organic Frameworks for Tryptophan Detection

The development of nanoscaled luminescent metal-organic frameworks (nano-LMOFs) with organic linker-based emission to explore their applications in sensing, bioimaging and photocatalysis is of great interest as material size and emission wavelength both have remarkable influence on their performances. However, there is lack of platforms that can systematically tune the emission and size of nano-LMOFs with customized linker design. Herein two series of fcu- and csq-type nano-LMOFs, with precise size control in a broad range and emission colors from blue to near-infrared, were prepared using 2,1,3-benzothiadiazole and its derivative based ditopic- and tetratopic carboxylic acids as the emission sources. The modification of tetratopic carboxylic acids using OH and NH2 as the substituent groups not only induces significant emission bathochromic shift of the resultant MOFs, but also endows interesting features for their potential applications. As one example, we show that the non-substituted and NH2 -substituted nano-LMOFs exhibit turn-off and turn-on responses for highly selective and sensitive detection of tryptophan over other nineteen natural amino acids. This work sheds light on the rational construction of nano-LMOFs with specific emission behaviours and sizes, which will undoubtedly facilitate their applications in related areas.

Advances in Metal-Organic Frameworks for the Removal of Chemical Warfare Agents: Insights into Hydrolysis and Oxidation Reaction Mechanisms

The destruction of chemical warfare agents (CWAs) is a crucial area of research due to the ongoing evolution of toxic chemicals. Metal-organic frameworks (MOFs), a class of porous crystalline solids, have emerged as promising materials for this purpose. Their remarkable porosity and large surface areas enable superior adsorption, reactivity, and catalytic abilities, making them ideal for capturing and decomposing target species. Moreover, the tunable networks of MOFs allow customization of their chemical functionalities, making them practicable in personal protective equipment and adjustable to dynamic environments. This review paper focuses on experimental and computational studies investigating the removal of CWAs by MOFs, specifically emphasizing the removal of nerve agents (GB, GD, and VX) via hydrolysis and sulfur mustard (HD) via selective photooxidation. Among the different MOFs, zirconium-based MOFs exhibit extraordinary structural stability and reusability, rendering them the most promising materials for the hydrolytic and photooxidative degradation of CWAs. Accordingly, this work primarily concentrates on exploring the intrinsic catalytic reaction mechanisms in Zr-MOFs through first-principles approximations, as well as the design of efficient degradation strategies in the aqueous and solid phases through the establishment of Zr-MOF structure-property relationships. Recent progress in the tuning and functionalization of MOFs is also examined, aiming to enhance practical CWA removal under realistic battlefield conditions. By providing a comprehensive overview of experimental findings and computational insights, this review paper contributes to the advancement of MOF-based strategies for the destruction of CWAs and highlights the potential of these materials to address the challenges associated with chemical warfare.

Porphyrin-Moiety-Functionalized Metal-Organic Layers Exhibiting Catalytic Capabilities for Detoxifying Nerve Agent and Blister Agent Simulants

The development of very efficient bifunctional catalysts for the simultaneous detoxification of two kinds of the deadliest chemical warfare agents (CWAs), nerve agent and blister agent, is highly desirable. In this study, two porphyrin-based ligands [tetrakis(4-carboxyphenyl) porphyrin (TCPP) and protoporphyrin IX (PPIX)] are introduced into 2D Zr-1,3,5-tris(4-carboxyphenyl)benzene (BTB) metal-organic layers (MOLs), composed of six-connected Zr₆ nodes and the tritopic carboxylate ligand BTB, by a solvent-assisted ligand incorporation method. The loads of TCPP and PPIX are 6.4 and 10.9 wt %, respectively. The detoxification of simulants of the nerve agent and the blister agent was conducted to investigate the catalytic activity of porphyrin-moiety-functionalized MOLs. The reaction half-life of optimal TCPP-functionalized MOL catalyzing the hydrolysis of a nerve agent simulant is only 2.8 min, meanwhile, the half-life of the selective catalytic oxidation of a blister agent simulant is only 1.2 min under LED illumination. More importantly, such a degradation half-life is only about 4 min under natural sunlight (∼60 mW/cm²). To our knowledge, TCPP-functionalized MOL is by far the most efficient catalyst for blister agent simulant degradation under solar light. Therefore, 2D ultrathin MOLs on demand appear to be a promising and efficient material platform for the development of bifunctional catalysts for CWA protection.

4,7-Diarylbenzo[c][1,2,5]thiadiazoles as fluorophores and visible light organophotocatalysts

A library of 26 electron donor-acceptor organophotocatalysts based on the benzo[c][1,2,5]thiadiazole (BTZ) group has been developed. These visible light organophotocatalysts were then used in a Minisci-type alkylation of heteroarenes under both batch and continuous flow conditions.

Vapor phase catalytic photooxidation of sulfides to sulfoxides: application to the neutralization of sulfur mustard simulants

A visible-light photocatalytic approach was developped for the aerobic oxidation of sulfides into the corresponding sulfoxides, including sulfur mustard simulants. The heterogeneous catalytic system is selective, operates in the gas...

Building a Pyrazole-Benzothiadiazole-Pyrazole Photosensitizer into Metal-Organic Frameworks for Photocatalytic Aerobic Oxidation

Charge separation plays a crucial role in regulating photochemical properties and therefore warrants consideration in designing photocatalysts. Metal-organic frameworks (MOFs) are emerging as promising candidates for heterogeneous photocatalysis due to their structural designability and tunability of photon absorption. Herein, we report the design of a pyrazole-benzothiadiazole-pyrazole organic molecule bearing a donor-acceptor-donor conjugated π-system for fast charge separation. Further attempts to integrate such a photosensitizer into MOFs afford a more effective heterogeneous photocatalyst (JNU-204). Under visible-light irradiation, three aerobic oxidation reactions involving different oxygenation pathways were achieved on JNU-204. Recycling experiments were conducted to demonstrate the stability and reusability of JNU-204 as a robust heterogeneous photocatalyst. Furthermore, we illustrate its applications in the facile synthesis of pyrrolo[2,1-a]isoquinoline-containing heterocycles, core skeletons of a family of marine natural products. JNU-204 is an exemplary MOF platform with good photon absorption, suitable band gap, fast charge separation, and extraordinary chemical stability for proceeding with aerobic oxidation reactions under visible-light irradiation.

Z-Scheme In2 S3 /NU-1000 Heterojunction for Boosting Photo-Oxidation of Sulfide into Sulfoxide under Ambient Conditions

Photocatalytic oxidation of sulfide into sulfoxide has attracted extensive attention as an environmentally friendly strategy for chemical transformations or toxic chemicals degradation. Herein, we construct a series of In₂ S₃ /NU-1000 heterojunction photocatalysts, which can efficiently catalyze the oxidation of sulfides to form sulfoxides as the sole product under LED lamp (full-spectrum) illumination in air at room temperature. Especially, the sulfur mustard simulant, 2-chloroethyl ethyl sulfide (CEES), can also be photocatalytically oxidized with In₂ S₃ /NU-1000 to afford nontoxic 2-chloroethyl ethyl sulfoxide (CEESO) selectively and effectively. In contrast, individual NU-1000 and In₂ S₃ show very low catalytic activity on this reaction. The significantly improved photocatalytic activity is ascribed to the constructing of an efficient Z-scheme photocatalysts In₂ S₃ /NU-1000, which exhibits the enhancement of light harvesting, the promotion of photogenerated electron-hole separation, and the retention of high porosity of the parent MOF. Moreover, mechanism studies in photocatalytic oxidation reveal that the superoxide radical (^. O₂ ^- ) and singlet oxygen (¹ O₂ ) are the main oxidative species in the oxidation system. This work exploits the opportunities for the construction of porous Z-scheme photocatalysts based on the photoactive MOFs materials and inorganic semiconductors for promoting catalytic organic transformations. More importantly, it provides a route to the rational design of efficient photocatalysts for the detoxification of mustard gas.

Interrogating Light-initiated Dynamics in Metal-Organic Frameworks with Time-resolved Spectroscopy

Time-resolved spectroscopy is an essential part of both fundamental and applied chemical research. Such techniques access light-initiated dynamics on time scales ranging from femtosecond to microsecond. Many techniques falling under this description have been applied to gain significant insight into metal-organic frameworks (MOFs), a diverse class of porous coordination polymers. MOFs are highly tunable, both compositionally and structurally, and unique challenges are encountered in applying time-resolved spectroscopy to interrogate their light-initiated properties. These properties involve various excited state mechanisms such as crystallographically defined energy transfer, charge transfer, and localization within the framework, photoconductivity, and structural dynamics. The field of time-resolved MOF spectroscopic studies is quite nascent; each original report cited in this review was published within the past decade. As such, this review is a timely and comprehensive summary of the most significant contributions in this emerging field, with focuses on the overarching spectroscopic concepts applied and on identifying key challenges and future outlooks moving forward.

Metal-organic frameworks for chemical sensing devices

Metal-organic frameworks (MOFs) are exceptionally large surface area materials with organized porous cages that have been investigated for nearly three decades. Due to the flexibility in their design and predisposition toward functionalization, they have shown promise in many areas of application, including chemical sensing. Consequently, they are identified as advanced materials with potential for deployment in analytical devices for chemical and biochemical sensing applications, where high sensitivity is desirable, for example, in environmental monitoring and to advance personal diagnostics. To keep abreast of new research, which signposts the future directions in the development of MOF-based chemical sensors, this review examines studies since 2015 that focus on the applications of MOF films and devices in chemical sensing. Various examples that use MOF films in solid-state sensing applications were drawn from recent studies based on electronic, electrochemical, electromechanical and optical sensing methods. These examples underscore the readiness of MOFs to be integrated in optical and electronic analytical devices. Also, preliminary demonstrations of future sensors are indicated in the performances of MOF-based wearables and smartphone sensors. This review will inspire collaborative efforts between scientists and engineers working within the field of MOFs, leading to greater innovations and accelerating the development of MOF-based analytical devices for chemical and biochemical sensing applications.

Superoxide Ion and Singlet Oxygen Photogenerated by Metalloporphyrin-Based Metal-Organic Frameworks for Highly Efficient and Selective Photooxidation of a Sulfur Mustard Simulant

The exploration of highly efficient materials for the degradation of chemical warfare agents has been a longstanding task for preventing human exposure. Herein, we report a series of metal-organic frameworks (MOFs) M-TCPP-La based on metallo-tetra(4-carboxyphenyl)porphyrin and La^III, which were applied to selectively oxidize 2-chloroethyl ethyl sulfide (CEES, a sulfur mustard simulant) as heterogeneous photocatalysts. After irradiation from a commercial blue light-emitting diode (LED), both superoxide ion and singlet oxygen were generated by M-TCPP-La and involved in selective oxidization of CEES to 2-chloroethyl ethyl sulfoxide (CEESO). Notably, a very short half lifetime (2.5 min) was achieved using Fe-TCPP-La as the photocatalyst. In comparison to currently utilizing singlet oxygen and hydrogen peroxide as oxidizing agents, this work employing both singlet oxygen and superoxide ion represents a new and effective strategy of detoxification of mustard gas.

Effective degradation of sulfur mustard simulant using novel sulfur-doped mesoporous zinc oxide under ambient conditions

Sulfur doped metal oxides were synthesized using a two-step precipitation method. When reacted against neat 2-CEES (2-chloroethyl-ethyl sulfide, a mustard gas simulant) under ambient conditions, sulfur doped mesoporous zinc oxide (MS-Zn) showed higher catalytic activity than the other metal oxides with 92.7% overall conversion in 24 h for a 2.5 μL neat 2-CEES droplet added on top of 2 × 2 cm large 400 mg catalyst layer. The reaction proceeded mainly by hydrolysis and further solvolysis reaction also occurred depending on the extracting solvents. Cyclic sulfonium ion intermediate reaction was thought to be involved in this reaction, and metal oxide surfaces were thought to facilitate the formation of sulfonium ions from adsorbed 2-CEES. All other by-products were also found to form via sulfonium ions, reconfirming the well-known importance of this intermediate species for the degradation reaction to proceed. The sulfur content for MS-Zn was varied and tested for degradation of neat 2-CEES. This modification showed that there is an optimal amount of sulfur content for the peak catalytic activity of MS-Zn for 2-CEES degradation. Adsorption energy of a 2-CEES molecule was calculated on model sulfur doped and non doped zinc oxide surfaces and the different adsorption energy levels were correlated with the catalytic activity of sulfur doped zinc oxide.

Directional Exciton Migration in Benzoimidazole-Based Metal-Organic Frameworks

Highly luminescent metal-organic frameworks (MOFs) have recently received great attention due to their potential applications as sensors and light-emitting devices. In these MOFs, the highly ordered fluorescent organic linkers positioning prevents excited-state self-quenching and rotational motion, enhancing their light-harvesting properties. Here, the exciton migration between the organic linkers with the same chemical structure but different protonation degrees in Zr-based MOFs was explored and deciphered using ultrafast laser spectroscopy and density functional theory calculations. First, we clearly demonstrate how hydrogen-bonding interactions between free linkers and solvents affect the twisting changes, internal conversion processes, and luminescent behavior of a benzoimidazole-based linker. Second, we provide clear evidence of an ultrafast energy transfer between well-aligned adjacent linkers with different protonation states inside the MOF. These findings provide a new fundamental photophysical insight into the exciton migration dynamics between linkers with different protonation states coexisting at different locations in MOFs and serve as a benchmark for improving light-harvesting MOF architectures.

Metal-Organic Frameworks: Synthetic Methods and Potential Applications

Metal-organic frameworks represent a porous class of materials that are build up from metal ions or oligonuclear metallic complexes and organic ligands. They can be considered as sub-class of coordination polymers and can be extended into one-dimension, two-dimensions, and three-dimensions. Depending on the size of the pores, MOFs are divided into nanoporous, mesoporous, and macroporous items. The latter two are usually amorphous. MOFs display high porosity, a large specific surface area, and high thermal stability due to the presence of coordination bonds. The pores can incorporate neutral molecules, such as solvent molecules, anions, and cations, depending on the overall charge of the MOF, gas molecules, and biomolecules. The structural diversity of the framework and the multifunctionality of the pores render this class of materials as candidates for a plethora of environmental and biomedical applications and also as catalysts, sensors, piezo/ferroelectric, thermoelectric, and magnetic materials. In the present review, the synthetic methods reported in the literature for preparing MOFs and their derived materials, and their potential applications in environment, energy, and biomedicine are discussed.

Multimodal Characterization of Materials and Decontamination Processes for Chemical Warfare Protection

This Review summarizes the recent progress made in the field of chemical threat reduction by utilizing new in situ analytical techniques and combinations thereof to study multifunctional materials designed for capture and decomposition of nerve gases and their simulants. The emphasis is on the use of in situ experiments that simulate realistic operating conditions (solid-gas interface, ambient pressures and temperatures, time-resolved measurements) and advanced synchrotron methods, such as in situ X-ray absorption and scattering methods, a combination thereof with other complementary measurements (e.g., XPS, Raman, DRIFTS, NMR), and theoretical modeling. The examples presented in this Review range from studies of the adsorption and decomposition of nerve agents and their simulants on Zr-based metal organic frameworks to Nb and Zr-based polyoxometalates and metal (hydro)oxide materials. The approaches employed in these studies ultimately demonstrate how advanced synchrotron-based in situ X-ray absorption spectroscopy and diffraction can be exploited to develop an atomic- level understanding of interfacial binding and reaction of chemical warfare agents, which impacts the development of novel filtration media and other protective materials.

The role of photoinduced charge transfer for photocatalysis, photoelectrocatalysis and luminescence sensing in metal–organic frameworks

Understanding PCT taking place within MOFs is crucial for designing porous photo/electrocatalysts and luminescent sensors. Unique features of PCT in MOFs and recent progress along with state-of-the-art characterization methods are discussed in the context of its applications.

Conjugated Microporous Polymers as Heterogeneous Photocatalysts for Efficient Degradation of a Mustard-Gas Simulant

Compared with traditional metal-based photosensitizers, heterogeneous and organic photocatalysts with visible-light activity are more environmentally friendly and sustainable. The simultaneous introduction of electron-rich and electron-deficient units in donor-acceptor typed conjugated microporous polymer (CMP) photocatalysts can significantly enhance their visible-light harvesting and separation efficiency of photogenerated carriers. Here, two carbazole-based CMPs (CzBSe-CMP and CzBQn-CMP) were successfully constructed through a cost-effective process. They show inherent porosity with large Brunauer-Emmett-Teller surface area and excellent thermal and chemical stability. Their photoelectric properties, energy levels, optical band gaps, transient photocurrent response, and photocatalytic activity could be conveniently tailored through tuning the electron-deficient moiety in polymer networks. More importantly, CzBSe-CMP was found to be a superior solid photocatalyst for selective photo-oxidation of mustard gas simulant 2-chloroethyl ethyl sulfide into a nontoxic product by using molecular oxygen as a sustainable oxygen source under visible-light illumination. In addition, the obtained CMP-based photocatalysts also showed excellent recyclability and could be reutilized through adding more simulants or a simple separation procedure. The current contribution provides great application prospects for CMPs as metal-free, solid photocatalysts in organic transformation and environmental protection.

Polyoxometalate-Supported Aminocatalyst for the Photocatalytic Direct Synthesis of Imines from Alkenes and Amines

Developing efficient photocatalysts for direct oxidative coupling of alkenes and amines with O₂ under mild conditions is very significant. Herein, ZnW-PYI is well-designed by assembling a [PZnW₁₁O₃₉(H₂O)]^5- photooxidation catalyst and chiral aminocatalyst pyrrolidine-2-ylimidazole (PYI) via a coordination model. ZnW-PYI efficiently catalyzed the synthesis of imines from alkenes and amines using O₂ as the oxidant through nucleophilic catalysis by employing pyrrolidine as an organocatalyst. Combining a polyoxometalate and PYI within one single framework is an effective approach not only for stabilization and heterogenization of the redox-active catalyst and aminocatalyst but also for realization of compatibility between the reaction intermediates and synergy of multiple catalytic cycles.

Metal Organic Frameworks as Robust Host of Palladium Nanoparticles in Heterogeneous Catalysis: Synthesis, Application, and Prospect

Metal organic frameworks (MOFs) are one set of the most excellent supports for Pd nanoparticles (NPs). MOFs as the host mainly have the following advantages: (i) they provide size limits for highly dispersed Pd NPs; (ii) fixing Pd NPs is beneficial for separation and reuse, avoiding the loss of expensive metals; (iii) the MOFs skeleton is diversified and functionalized, which is beneficial to enhancing the interaction with Pd NPs and prolonging the service life of the catalyst. This review discusses the synthesis strategy of Pd@MOF, which provides guidance for the synthesis of similar materials. After that, the research advance of Pd@MOF in heterogeneous catalysis is comprehensively summarized, including C-C coupling reaction, benzyl alcohol oxidation reaction, simple olefin hydrogenation reaction, nitroaromatic compound reduction, tandem reaction, and the photocatalysis, with the emphasis in providing a comparison with the performance of other alternative Pd-containing catalysts. In the final section, this review presents the current challenges and which are the next goals in this field.

Selective Photooxidation of Amines and Sulfides Triggered by a Superoxide Radical Using a Novel Visible-Light-Responsive Metal-Organic Framework

Photocatalysis is an efficient and sustainable approach to convert solar energy into chemical energy, simultaneously supplying valuable chemicals. In this study, a novel metal-organic framework (MOF) compound is constructed from anthracene-based organic linkers, which shows visible-light absorption and efficient photoinduced charge generation property. It was applied for triggering photooxidation of benzylamines and sulfides in the presence of environmental benign oxidants of molecular oxygen or hydrogen peroxide. Results show that it is a highly selective photocatalyst for oxidation reactions to produce valuable imines or sulfoxides. We further investigate the underlying mechanism for these photocatalytic reactions by recognizing reactive oxygen species in the reactions. It has been demonstrated that the superoxide radical (O₂^•-), generated by electron transfer from a photoexcited MOF to oxidants, serves as the main active species for the oxidations. The work demonstrates the great potential of photoactive MOFs for the transformation of organic chemicals into valuable complexes.

Rapid Capture and Hydrolysis of a Sulfur Mustard Gas in Silver-Ion-Exchanged Zeolite Y

Sulfur mustard gas, also called HD, is one of the main chemical warfare agents and has claimed thousands of lives and left many more contaminated. The development of functional materials to promptly capture and detoxify sulfur mustard within a few minutes is extremely important to save the lives of the affected people. This has motivated us to explore excellent detoxification systems that can be deployed in the field to rapidly capture and hydrolyze mustard gas in a short time. To that end, we present a silver-ion-exchanged zeolite Y [(Ag⁺) _n@Y, n = 5, 13, 21, 32, 43, and 55] that can rapidly capture mustard gas and its simulant (2-chloroethyl ethyl sulfide, CEES) in ambient conditions to enable the prompt hydrolysis of the CEES captured in its nanopores. The capture and hydrolysis ability of Ag⁺@Y positively correlated with its number of Ag⁺ ions. In addition, 70% of CEES (2.5 μL in 1 mL) was captured by (Ag⁺)₅₅@Y within 20 min at 25 °C in ambient conditions. Moreover, 100% CEES (2.5 μL in 1 mL aqueous ethanol cosolvent) was hydrolyzed in 1 min at 25 °C. The efficiency of Ag⁺@Y in capturing and hydrolyzing CEES as well as mustard gas is thus a system with high detoxification efficiency for this dangerous chemical warfare agent.

Improving the Efficiency of Mustard Gas Simulant Detoxification by Tuning the Singlet Oxygen Quantum Yield in Metal-Organic Frameworks and Their Corresponding Thin Films

The photocatalytically driven partial oxidation of a mustard gas simulant, 2-chloroethyl ethyl sulfide (CEES), was studied using the perylene-based metal-organic framework (MOF) UMCM-313 and compared to the activities of the Zr-based MOFs: PCN-222/MOF-545 and NU-1000. The rates of CEES oxidation positively correlated with the singlet oxygen quantum yield of the MOF linkers, porphyrin (PCN-222/MOF-545) < pyrene (NU-1000) < perylene (UMCM-313). Subsequently, thin films of UMCM-313 and NU-1000 were solvothermally grown on a conductive glass substrate to minimize catalyst loading and prevent light scattering by suspended MOF particles. Using a conductive glass support, the initial turnover frequencies of the MOFs in the photocatalytic reaction improved by 10-fold.

Ratiometric Luminescent Detection of Organic Amines Due to the Induced Lactam-Lactim Tautomerization of Organic Linker in a Metal-Organic Framework

Here we demonstrate that a fluorescent benzothiadiazole (BTD)-conjugated terphenyldicarboxylate (TPDC) linker (denoted as H₂-ostpdc) has been hybridized by a quinoxaline-2,3-(1H,4H)-dione (QD) moiety possessing lactam-lactim tautomerism, which was further integrated into a robust and porous UiO-68 type zirconium metal-organic framework (MOF UiO-68-osdm) by utilizing the mixed two dicarboxylate struts with the same ligand lengths. The resultant MOF UiO-68-osdm can work as a ratiometric luminescent sensor for visual and selective detection of alkyl amines. Furthermore, it can discriminate secondary alkylamines from other type amine species.