A simple and stable dual-emission fluorescent system based on R6G/Eu-MOF for the rapid and sensitive determination of orientin

A stable dual-emission fluorescent system, R6G/Eu-MOF, was obtained by simple mixing Eu-MOF with fluorescent rhodamine 6G (R6G). This system not only achieved robust dual luminescence performance at 430 nm (Eu-MOF) and 555 nm (R6G) under single-wavelength excitation, but also endowed it with significantly improved fluorescence stability. Orientin (OT), a bioactive traditional Chinese medicine (TCM) component, was found to efficiently quench the dual fluorescent emissions via the synergistic effect of dynamic quenching, photo-induced electron transfer and molecular interactions. Therefore, a rapid fluorescent assay for OT was developed based on the variations in fluorescence signals at 430 nm and 555 nm, as well as the alterations in the ratio between these two signals. This method can achieve highly sensitive determination of OT in the linear range of 1.1-220 μM, with a LOD of 0.26 μM at 430 nm and 0.16 μM at 555 nm (3σ/N). The R6G/Eu-MOF hybrid exhibits significantly lower detection limits and a broader linear range for OT than either R6G or Eu-MOF alone. This work presents a simple strategy to improve the water stability of Eu-MOF and also provides a rapid analysis of small molecule drugs using a fluorescence approach based on a dual-emission MOF hybrid system.

A post-modified lanthanide metal-organic frameworks as ratiometric luminescent sensor for the visual detection of 5-hydroxytryptamine

5-Hydroxytryptamine (5-HT), a key neurotransmitter, is an important biomarker for carcinoid syndrome. We herein construct a ratiometric luminescent sensor by covalently coupling fluorescein 5-isothiocyanate (FITC) with lanthanide metal-organic frameworks (Ln-MOFs). In the presence of 5-HT, the emission of FITC increases while the emission of Eu3 + decreases, accompanied by a distinct color change of emission from orange to green. This sensor not only has the advantages of high sensitivity (LOD = 0.04 μM), fast response (30 s), excellent selectivity, and large ΔE*ab value (73), but can also be used for the detection of 5-HT in human serum and allow for instant visual detection with the assistant of smartphone. This ratiometric luminescent sensor offers an alternative avenue for early diagnosis of carcinoid syndrome.

Leap-Type Response of Redox/Photo-Active Lanthanide-Based Metal-Organic Frameworks for Early and Accurate Screening of Prostate Cancer

The development of high-accuracy technologies to distinguish the quite tiny concentration change of tumor markers between negative and positive is of vital significance for early screening and diagnosis of cancers, but is still a great challenge for the conventional biosensors because of their "gradual" detection mode. Herein, a unique "leap-type" responsive lanthanide MOF-based biosensor (designated as Tb-CeMOF-X) with defect-mediated redox-/photo-activities is developed for precisely identifying acid phosphatase (ACP), an early pathological marker of prostate cancer (PCa) in serum. The engineered Tb-CeMOF-X probe achieves a bursting switch-on luminescence at the critical concentration of ACP (9 U ⋅ L-1), while keeping silent below this threshold, undergoing a qualitative signal change from "zero" to "one" between negative and positive indicators and thus significantly improving the identification precision. Significantly, such "leap-type" response performance can be further edited and amplified by rational defect engineering in the crystal structure to improve the accessibility of active centers, consequently maximizing the detection sensitivity toward ACP in the complex biological media. This study proposes the first paradigm for the development of "leap-type" biosensors with ultra-sensitive differentiation capability between negative and positive, and provides a potentially valuable tool for early and accurate screening of PCa.

Nanoscale Metal-Organic Frameworks as a Photoluminescent Platform for Bioimaging and Biosensing Applications

The tracking of nanomedicines in their concentration and location inside living systems has a pivotal effect on the understanding of the biological processes, early-stage diagnosis, and therapeutic monitoring of diseases. Nanoscale metal-organic frameworks (nano MOFs) possess high surface areas, definite structure, regulated optical properties, rich functionalized sites, and good biocompatibility that allow them to excel in a wide range of biomedical applications. Controllable syntheses and functionalization endow nano MOFs with better properties as imaging agents and sensing units for the diagnosis and treatment of diseases. This minireview summarizes the tunable synthesis strategies of nano MOFs with controllable size, shape, and regulated luminescent performance, and pinpoints their recent advanced applications as optical elements in bioimaging and biosensing. The current limitations and future development directions of nano MOF-contained materials in bioimaging and biosensing applications are also discussed, aiming to expand the biological applications of nano MOF-based nanomedicine and facilitate their production or clinical translation.

Utilizing excited-state proton transfer fluorescence quenching mechanism, layered rare earth hydroxides enable ultra-sensitive detection of nitroaromatic

Convenient, rapid, and accurate detection of nitroaromatic organic toxins and harmful substances is of great significance in research. In the present study, two-dimensional layered rare-earth hydroxides (LYH) were used as ion-exchange matrix materials, and the anionic fluorescent dye molecules (HPTS) were successfully introduced into the LYH structures in situ via a simple and effective "plug-and-play" strategy, which gave the compounds ultra-sensitive fluorescence sensing detection of nitrobenzene, p-nitrotoluene and p-nitrophenol (Fluorescence response time < 1 sec, and the LOD for nitrobenzene, p-nitrophenol and p-nitrotoluene reached an impressive 349 ppb, 22 ppb and 98 ppb, respectively). Combined with theoretical calculations, we elucidated in detail the fluorescence quenching response mechanism of the LYH-HPTS towards nitroaromatic. Additionally, we also constructed fluorescent paper sensor, which effectively transformed the LYH-HPTS from theoretical detection to device application. The LYH-HPTS material is not only simple to synthesize, cost-effective and stable, but also has the features of fast response, excellent sensitivity and selectivity, and good reproducibility, which provides a new approach for the rapid and accurate detection of nitroaromatic.

Enhancing Two-Photon Excited Fluorescence of Metal-Organic Framework Single Crystals through Modulation of Inorganic Nodes

Regulation of the two-photon excited fluorescence (TPEF) emission intensity and wavelength of metal-organic framework (MOF) crystals with similar constitutions presents a significant challenge. In this study, two MOFs, Zn-BTPPA and Cd3-BTPPA, were constructed using tetrakis(1,1'-biphenyl-4-carboxylic acid)-1,4-benzenediamine (H4BTPPA) as the organic ligand and mononuclear Zn and trinuclear Cd3 inorganic nodes, respectively. The incorporation of H4BTPPA within the MOF structures enables effective TPEF emission in both Zn-BTPPA and Cd3-BTPPA. The TPEF results show that Zn-BTPPA and Cd3-BTPPA exhibited strong emissions at 523 and 463 nm, respectively, when excited with a 780 nm laser. Moreover, Zn-BTPPA and Cd3-BTPPA exhibited much higher two-photon absorption cross sections, approximately 4.9 and 5.2 times higher than that of the reported dinuclear MOF, Cd2-BTPPA, with a similar composition, respectively. With different inorganic nodes, the stacking of chromophores, π···π interactions, and ligand geometry were found to correlate with the enhanced TPEF in Cd3-BTPPA and the blue-shifted TPEF in Zn-BTPPA. This work serves as an inspiration for designing efficient TPEF MOF materials based on the structure-property relationship.

Recent advances and applications of ionic covalent organic frameworks in food analysis

Ionic covalent organic frameworks with both crystallinity and charged sites have attracted significant attention from the scientific community. The versatile textural structures, precisely defined channels, and abundant charged sites of ionic COFs offer immense potential in various areas such as separation, sample pretreatment, ion conduction mechanisms, sensing applications, catalytic reactions, and energy storage systems. This review presents a comprehensive overview of facile preparation methods for ionic covalent organic frameworks (iCOFs), along with their applications in food sample pretreatment techniques such as solid-phase extraction (SPE), magnetic solid-phase extraction (MSPE), and dispersive solid-phase extraction (DSPE). Furthermore, it highlights the extensive utilization of iCOFs in detecting various food contaminants including pesticides, contaminants from food packaging, veterinary drugs, perfluoroalkyl substances, and poly-fluoroalkyl substances. Specifically, this review critically discusses the limitations, challenges, and future prospects associated with employing iCOF materials to ensure food safety.

Fluorescent Sensors for Tetracycline Detection in Aqueous Medium: A Mini-Review

Tetracycline (TC) is a commonly used antibiotic in human therapy and animal husbandry. Public concerns about TC residues inflated due to their negative impact on the environment, food, and human health concerns. To ensure human health and safety, there is a need for fluorogenic chemosensors that can easily detect TC antibiotics with high selectivity and sensitivity in the aqueous medium. This mini-review discusses the progress and achievements in several fluorometric antibiotic tetracycline detection methods. Fluorogenic chemosensors for tetracycline antibiotics with easy-to-use, high selectivity, and sensitivity have been essentially required to regulate food safety and secure human health and safety. Moreover, we gave more attention to the practical applicability of chemosensors for tetracycline antibiotics in food and water quality assessment. This article starts with a section that constitutes an overview of the problems of antibiotics and the typical features of traditional techniques of antibiotic detection. It then goes on to describe up-to-date optical methods for the selective detection and efficient removal of TC. These methods involve a variety of platforms, like tetraphenylethylene polymers, metal complexes, self-assembled CuNCs, and hydrogel. The article also discusses the practical applicability of chemosensors for tetracycline antibiotics in food and water quality.

Low thermal quenching of metal halide-based metal-organic framework phosphor for light-emitting diodes

Phosphor-converted white light-emitting diodes (PC-WLEDs) have attracted considerable attention in solid-state lighting and display. However, urgent issues of thermal quenching and high cost remain formidable challenges. Herein, a novel metal-organic framework (MOF) phosphor [CdCl2(AD)] was facilely prepared using a mixture of CdCl2 and acridine (AD) under solvothermal conditions. It shows intensive green emission with a long lifetime of 31.88 ns and quantum yield of 65% while maintaining 95% and 84% of its initial emission intensity after remaining immersed in water for 60 days and being heated to 150 °C, respectively. The low thermal quenching of this MOF material is comparable to or can even exceed that of commercial inorganic phosphors. The combination of experiments and theoretical calculations reveals that the alternating arrangement of delocalized AD π-conjugated systems and CdCl2 inorganic chains through strong coordination bonds and π⋯π stacking interactions imparts the MOF phosphor with high thermal stability and optoelectronic performance. The successful fabrication of green and white LED devices by coating [CdCl2(AD)] and/or N630 red phosphor on a 365/460 nm commercial diode chip suggests a promising and potential alternative to commercial phosphors.

Highly Specific Sulfadiazine Detection Using a Two-Dimensional Europium-Organic Coordination Polymer

Sulfadiazine (SFZ) is an inexpensive large-consumption antibiotic used for treat bacterial infections but an excess of residues in food can be harmful. Fast and specific luminescence detection of SFZ is highly challenging because of the interference of structurally similar antibiotics. In this work, we develop a two-dimensional europium-organic coordination polymer with excellent luminescence and water stability for highly specific detection of SFZ in the range of 0-0.2 mM. Structural analysis shows that the high stability of coordination polymer is due to the high coordination number of europium ion and the special chelating coordination structure of ligand. The experiment results revealed that the high selectivity and effectively luminescence quenched behaviour of coordination polymer toward SFZ is caused by highly efficient inner filter effect.

Encapsulation engineering of porous crystalline frameworks for delayed luminescence and circularly polarized luminescence

Delayed luminescence (DF), including phosphorescence and thermally activated delayed fluorescence (TADF), and circularly polarized luminescence (CPL) exhibit common and broad application prospects in optoelectronic displays, biological imaging, and encryption. Thus, the combination of delayed luminescence and circularly polarized luminescence is attracting increasing attention. The encapsulation of guest emitters in various host matrices to form host-guest systems has been demonstrated to be an appealing strategy to further enhance and/or modulate their delayed luminescence and circularly polarized luminescence. Compared with conventional liquid crystals, polymers, and supramolecular matrices, porous crystalline frameworks (PCFs) including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), zeolites and hydrogen-bonded organic frameworks (HOFs) can not only overcome shortcomings such as flexibility and disorder but also achieve the ordered encapsulation of guests and long-term stability of chiral structures, providing new promising host platforms for the development of DF and CPL. In this review, we provide a comprehensive and critical summary of the recent progress in host-guest photochemistry via the encapsulation engineering of guest emitters in PCFs, particularly focusing on delayed luminescence and circularly polarized luminescence. Initially, the general principle of phosphorescence, TADF and CPL, the combination of DF and CPL, and energy transfer processes between host and guests are introduced. Subsequently, we comprehensively discuss the critical factors affecting the encapsulation engineering of guest emitters in PCFs, such as pore structures, the confinement effect, charge and energy transfer between the host and guest, conformational dynamics, and aggregation model of guest emitters. Thereafter, we summarize the effective methods for the preparation of host-guest systems, especially single-crystal-to-single-crystal (SC-SC) transformation and epitaxial growth, which are distinct from conventional methods based on amorphous materials. Then, the recent advancements in host-guest systems based on PCFs for delayed luminescence and circularly polarized luminescence are highlighted. Finally, we present our personal insights into the challenges and future opportunities in this promising field.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Prediction of Metal-Organic Frameworks with Phase Transition via Machine Learning

Metal-organic frameworks (MOFs) possess a virtually unlimited number of potential structures. Although the latter enables an efficient route to control the structure-related functional properties of MOFs, it still complicates the prediction and searching for an optimal structure for specific application. Next to prediction of the MOFs for gas sorption/separation and catalysis via machine learning (ML), we report on ML to find MOFs demonstrating a phase transition (PT). On the basis of an available QMOF database (7463 frameworks), we create and train the autoencoder followed by training the classifier of MOFs from a unique database with experimentally confirmed PT. This makes it possible to identify MOFs with a high potential for PT and evaluate the most likely stimulus for it (guest molecules or temperature/pressure). The formed list of available MOFs for PT allows us to discuss their structural features and opens an opportunity to search for phase change MOFs for diverse physical/chemical application.

Meltable Aluminum Molecular Rings with Fluorescence and Nonlinear Optical Properties

Crystal-liquid-glass, which combines the tunable properties of crystalline compounds with the processability of glasses, has emerged as a new class of materials for fabricating bulk-shapable devices in real applications. Inspired by the characteristics of deep eutectic solvent (DES) mixtures involving significant depressions in melting points compared to their neat constituent components, in this study, we designed and synthesized the first examples of meltable aluminum oxo clusters (AlOCs) via lattice doping with DESs at the molecular level. The abundant and strong hydrogen bonding between the aluminum molecular ring, DES components, and lattice solvents is postulated to be the root that affords melting point depressions and, thus, "melting" clusters. We prepared a transparent bubble-free glass film under autogenous pressure using a hot-press method. These cluster-based films exhibited luminescent and nonlinear optical properties similar to those of pristine crystalline compounds. Our study belongs to the interdisciplinary disciplines of chemistry and physics. It not only breaks the limitations of crystalline glass on metal and ligand types but also acts as a general guide for extending the range of meltable crystalline materials.

Porphyrin-Sensitizers and Anthracene-Annihilators Built in Isostructural Frameworks for Investigating Triplet-Triplet Annihilation Upconversion

In this study, four isostructural pillar-layered frameworks were constructed using a porphyrin layer and an anthracene pillar, which served as the sensitizer and annihilator, respectively, in the triplet-triplet annihilation upconversion (TTA-UC) system. Framework 1 demonstrated the highest upconversion quantum yield of 1.01%. Additionally, 1 and 2 also exhibited down-conversion fluorescence resulting from the porphyrin component. A twist intramolecular charge transfer (TICT) state was observed in the bianthracene chromophore of 2, resulting in transient rotation of two anthracene rings and red-shifted emission. Both computational studies and experiments confirmed the transition from a locally excited state to a TICT state upon the inclusion of polar guest molecules into the framework.

Phosphorus removal from water by the metal-organic frameworks (MOFs)-based adsorbents: A review for structure, mechanism, and current progress

Efficacious phosphate removal is essential for mitigating eutrophication in aquatic ecosystems and complying with increasingly stringent phosphate emission regulations. Chemical adsorption, characterized by simplicity, prominent treatment efficiency, and convenient recovery, is extensively employed for profound phosphorus removal. Metal-organic frameworks (MOFs)-derived metal/carbon composites, surpassing the limitations of separate components, exhibit synergistic effects, rendering them tremendously promising for environmental remediation. This comprehensive review systematically summarizes MOFs-based materials' properties and their structure-property relationships tailored for phosphate adsorption, thereby enhancing specificity towards phosphate. Furthermore, it elucidates the primary mechanisms influencing phosphate adsorption by MOFs-based composites. Additionally, the review introduces strategies for designing and synthesizing efficacious phosphorus capture and regeneration materials. Lastly, it discusses and illuminates future research challenges and prospects in this field. This summary provides novel insights for future research on superlative MOFs-based adsorbents for phosphate removal.

Tuning the mechanical properties of sol-gel monolithic metal-organic frameworks by ligand engineering

The sol-gel monolithic MOFs has come to prominent attention for industrial application owing to the higher powder packing density, enhanced processabilities and mechanical stabilities compared to the powder counterpart. The mechanical properties are particularly important during machine shaping processing because of porous framework structure. We used ligand engineering to design and synthesize monoUiO-66-type materials modified different chemical functional groups (-NH2, -2OH, -2COOH) by sol-gel method, with the aim to assess the impact of different functional groups on the mechanical properties of these monolithic materials based on nanoindentation technology. We observe larger mass and sterically bulky functional groups (-2COOH) can significantly decrease the BET areas and pore volume of monoUiO-66 through N2 adsorption isotherms at 77 K. Hence, the two -COOH groups modified monoUiO-66 tends to exhibit the higher H of 0.589 ± 0.018 GPa and E of 15.471 ± 0.250 GPa compared with monoUiO-66 modified with -NH2 (0.334 ± 0.009 GPa/11.959 ± 0.243 GPa) and -2OH (0.331 ± 0.008 GPa/10.251 ± 0.142 GPa) groups. The creep indentation tests and the jump indentation tests further demonstrate the modification by larger functional groups -COOH on monoUiO-66 could resist irreversible plastic deformation. Furthermore, the monoUiO-66-(COOH)2 has significantly smaller the activation volume of 0.34 ∼ 0.43 nm3, highlighting the introduction of -COOH groups reduced the pore volume and restrict the number of pores involved in one collapse event. Our results demonstrate the larger mass and sterically bulky functional groups have significant influence on the mechanical properties of the monoMOFs materials.

Tetraphenylethylene-Based Hydrogen-Bonded Organic Frameworks (HOFs) with Brilliant Fluorescence

By synergistically employing four key strategies: (I) introducing tetraphenylethylene groups as the central core unit with aggregation-induced emission (AIE) properties, (II) optimizing the π-conjugated length by extending the building block branches, (III) incorporating flexible groups containing ethylenic bonds, and (IV) applying crystal engineering to attain dense stacking mode and highly twisty conformation, we successfully synthesized a series of hydrogen-bonded organic frameworks (HOFs) exhibiting exceptional one/two-photon excited fluorescence. Notably, when utilizing the fluorescently superior building block L2, HOF-LIFM-7 and HOF-LIFM-8 exhibiting high quantum yields (QY) of 82.1 % and 77.1 %, and ultrahigh two-photon absorption (TPA) cross-sections of 148959.5 GM and 123901.1 GM were achieved. These materials were successfully employed in one and two-photon excited lysosome-targeting cellular imaging. It is believed that this strategy, combining building block optimization and crystal engineering, holds significant potential for guiding the development of outstanding fluorescent HOF materials.

A Soluble Porous Coordination Polymer for Fluorescence Sensing of Explosives and Toxic Anions under Homogeneous Environment

In the past decades, porous coordination polymers (PCPs) based fluorescent (FL) sensors have received intense attention due to their promising applications. In this work, a soluble Zn-PCP is presented as a sensitive probe towards explosive molecules, chromate, and dichromate ions. In former reports, PCP sensors were usually ground into fine powders and then dispersed in solvents to form FL emulsion for sensing applications. However, their insoluble characters would cause the sensing accuracy which is prone to interference from environmental effects. While in this work, the as-made PCP could be directly soluble in organic solvents to form a clear solution with bright blue emission, representing the first soluble PCP based fluorescence sensor to probe explosive molecules under a homogeneous environment. Moreover, the FL PCP solution also shows sensitive detection behaviors towards the toxic anions of CrO42- and Cr2O72-, which exhibit a good linear relationship between the fluorescence intensity of Zn-PCP and the concentrations of both analytes. This work provides a reference for designing task-specific PCP sensors utilized under a homogeneous environment.

AIE Ligand-Based Luminescent Ln-MOFs for Rapid and Selective Sensing of Tetracycline

The design of highly stable and dual-emission lanthanide metal-organic frameworks (Ln-MOFs) is promising for practical chemical sensor applications. Rational design and synthesis of photoresponsive organic ligands provide a feasible approach to achieving highly fluorescent dual-emission Ln-MOFs. In this study, a tetraphenylpyrazine-based AIE ligand, H4L, was synthesized and combined with lanthanide ions (including Sm3+, Eu3+, Gd3+, and Tb3+) to fabricate a series of Ln-MOFs named Ln-L. The single-crystal analysis revealed that all Ln-L belonged to the tetragonal space group P4212 and featured a 2-fold interpenetrated 3D structure. Leveraging rational design, Eu-L exhibited a sensitive response to tetracycline, making it a promising fluorescence sensor for tetracycline detection. The experiments demonstrated that Eu-L could rapidly and quantitatively detect tetracycline and its analogs within 30 s. The lowest detection limits for tetracycline, oxytetracycline, and chlortetracycline were 0.43, 0.92, and 0.81 μM, respectively. Additionally, the probe displayed excellent reusability and exceptional selectivity. A plausible sensing mechanism was proposed, supported by both experimental and theoretical analyses. Furthermore, the study discovered that on-site and real-time determination of TCs in aqueous solutions could be achieved by using luminescence test papers and composite films derived from Eu-L.

Self-Calibrating Lanthanide Infinite Coordination Polymer Constructs Fluorescent Probes: A Sensitive Approach for Early Diagnosis of Hepatocellular Carcinoma and Environmental Analysis

The development of a self-calibrating ratio fluorescence probe without the need for additional substrates is a major advancement in biosensing. In this study, at room temperature, a self-calibrating infinite coordination polymer (SSA-Tb-ATP ICPs) has been proposed by self-assembling adenosine triphosphate (ATP) with 5-sulfosalicylic acid (SSA) and Tb3+. Due to the antenna effect, SSA-Tb-ATP ICPs exhibited strong green fluorescence emission of Tb3+ (at 547 nm) and blue fluorescence emission of SSA (at 407 nm). This material offers several advantages over existing detection methods, including simplicity of synthesis and exceptional sensitivity. Our self-calibrating SSA-Tb-ATP ICPs demonstrated excellent performance in detecting alkaline phosphatase (ALP) and phosphate (Pi) in both serum and environmental samples with detection limits of 0.076 U/L and 0.025 μM, respectively. Moreover, we successfully employed the SSA-Tb-ATP ICPs to perform cellular imaging of ALP in both hepatocellular carcinoma cells (HepG2) and normal liver cells (LO2), representing a significant advancement in ALP detection and imaging. The simplicity of the synthesis and high sensitivity make this probe a promising tool for early diagnosis of hepatocellular carcinoma in clinical settings and environment analysis.

HCR/DNAzyme-triggered cascaded feedback cycle amplification for self-powered dual-photoelectrode detection of femtomolar HPV16

For high-performance dual-photoelectrode assay, developing a pair of photoactive materials with well-matched band structure and the design of a powerful sensing strategy are highly desirable. Herein, the Zn-TBAPy pyrene-based MOF and BiVO4/Ti3C2 Schottky junction were employed as photocathode and photoanode to form an efficient dual-photoelectrode system. The integration of the cascaded hybridization chain reaction (HCR)/DNAzyme-assisted feedback amplification with DNA walker-mediated cycle amplification strategy realizes femtomolar HPV16 dual-photoelectrode bioassay. Through the activation of the HCR cascaded with the DNAzyme system in the presence of HPV16, plentiful HPV16 analogs are generated that leads to exponential positive feedback signal amplification. Meanwhile on the Zn-TBAPy photocathode, the NDNA hybridizes with the bipedal DNA walker followed by circular cleavage by Nb.BbvCI NEase, producing a dramatically enhanced PEC readout. The achieved ultralow detection limit of 0.57 fM and a wide linear range of 10-6 nM-103 nM showcase the excellent performance of the developed dual-photoelectrode system.

Molecular hybrids of trivacant lacunary polyoxomolybdate and multidentate organic ligands

Functional molecular inorganic-organic hybrids of lacunary polyoxometalates and organic ligands attract much attention for advanced material applications. However, the inherent instability of lacunary polyoxomolybdates hinders the synthesis of hybrids and their utilization. Herein, we present a viable approach for the synthesis of molecular hybrids of trivacant lacunary Keggin-type polyoxomolybdates and multidentate organic ligands including carboxylates and phosphonates, which is based on the use of a lacunary structure stabilized by removable pyridyl ligands as a starting material.

Dual-Emitting Mixed-Lanthanide Metal-Organic Framework for Ratiometric and Quantitative Visual Detection of 2,6-Pyridine Dicarboxylic Acid

The detection of the major biomarker of Bacillus anthracis, 2,6-dipicolinic acid (DPA), has attracted great interest in recent years. In this work, mixed-lanthanide metal-organic frameworks (M'LnMOFs), TbxEu1-x-cppa (cppa = 5-(5-carboxypyridin-3-yl)isophthalic acid), with different Tb/Eu ratios, were solvothermally synthesized. The results reveal that ratiometric fluorescent probe [Tb0.533Eu0.467-(Hcppa)1.5(H2O)(DMF)]·3H2O is water and acid-base stable and exhibits excellent sensitivity (LOD = 2.286 μM), high selectivity, and fast response (<2 min) for the detection of DPA. Due to the blocked energy transfer from Tb3+ to Eu3+ and the inner filter effect upon the addition of DPA, the fluorescent probe shows a distinct color change from orange-red to green. Furthermore, the visual detection of DPA was realized by identifying the RGB values of MOF-based agarose hydrogel films via a smartphone, highlighting the practical application of the fluorescent probe for DPA detection under aqueous solution conditions.

Porous Metal-Organic Frameworks for Light Hydrocarbon Separation

The separation of light hydrocarbon compounds is an important process in the chemical industry. Currently, its separation methods mainly include distillation, membrane separation, and physical adsorption. However, these traditional methods or materials have some drawbacks and disadvantages, such as expensive equipment costs and high energy consumption, poor selectivity, low separation ratios, and separation efficiencies. Therefore, it is important to develop novel separation materials for light hydrocarbon separation. As a new type of organic-inorganic hybrid crystalline material, metal-organic frameworks (MOFs) are promising materials for light hydrocarbon separation due to their designability of structure and easy modulation of function. This review provides an overview of recent advances in the design, synthesis, and application of MOFs for light hydrocarbon separation in recent years, with a focus on the separation of alkane, alkene, and alkyne. We discuss strategies for improving the adsorption selectivity and capacity of MOFs, including pore size limitation, physical adsorption, and chemisorption. In addition, we discuss the advantages/disadvantages, challenges, and prospects of MOFs in the separation of light hydrocarbon.

Reticular Chemistry for Optical Sensing of Anions

In the last few decades, reticular chemistry has grown significantly as a field of porous crystalline molecular materials. Scientists have attempted to create the ideal platform for analyzing distinct anions based on optical sensing techniques (chromogenic and fluorogenic) by assembling different metal-containing units with suitable organic linking molecules and different organic molecules to produce crystalline porous materials. This study presents novel platforms for anion recognition based on reticular chemistry with high selectivity, sensitivity, electronic tunability, structural recognition, strong emission, and thermal and chemical stability. The key materials for reticular chemistry, Metal-Organic Frameworks (MOFs), Zeolitic Imidazolate Frameworks (ZIFs), and Covalent-Organic Frameworks (COFs), and the pre- and post-synthetic modification of the linkers and the metal oxide clusters for the selective detection of the anions, have been discussed. The mechanisms involved in sensing are also discussed.

CsPbX3 (X = Cl, Br, and I) Nanocrystals in Substrates toward Stable Photoluminescence: Nanoarchitectonics, Properties, and Applications

Cesium lead halide (CsPbX3, X = Cl, Br, and I) perovskite nanocrystals (NCs) possess great potential in light-emitting diode applications because of their high brightness, low cost, tunable luminescence, and facile synthesis nature. However, these NCs are often disadvantaged by their instability in nonsolvent environment that hinders the practical applications of the material. In order to solve these issues, cesium lead halide NCs prepared using a solvent environment can be placed on substrates to retain the high stability and expand the applicability of the material. This Review focuses on the transfer of the all-inorganic cesium lead halide NCs (synthesized in solutions) onto matrix materials and their direct synthesis on these bases, including the inert shell growth (inorganic and organic shell), embedment in matrixes (e.g., metal organic frameworks, porous SiO2, glass, ZrO2, Al2O3, and AlOOH), and direct synthesis in substrates. In particular, the strategies for stability and PL property improvement of the materials are also summarized. The purpose of this Review is to provide inspiration for the encapsulation of cesium lead halide NCs with high brightness and stability in matrixes to expand the applicability of these materials in wide color gamut backlighting (e.g., white-light-emitting devices).

Near-infrared metal agents assisting precision medicine: from strategic design to bioimaging and therapeutic applications

Metal agents have made incredible strides in preclinical research and clinical applications in recent years, but their short emission/absorption wavelengths continue to be a barrier to their distribution, therapeutic action, visual tracking, and efficacy evaluation. Nowadays, the near-infrared window (NIR, 650-1700 nm) provides a more accurate imaging and treatment option. Thus, there has been ongoing research focusing on developing multifunctional NIR metal agents for imaging and therapy that have deeper tissue penetration. The design, characteristics, bioimaging, and therapy of NIR metal agents are covered in this overview of papers and reports published to date. To start with, we focus on describing the structure, design strategies, and photophysical properties of metal agents from the NIR-I (650-1000 nm) to NIR-II (1000-1700 nm) region, in order of molecular metal complexes (MMCs), metal-organic complexes (MOCs), and metal-organic frameworks (MOFs). Next, the biomedical applications brought by these superior photophysical and chemical properties for more accurate imaging and therapy are discussed. Finally, we explore the challenges and prospects of each type of NIR metal agent for future biomedical research and clinical translation.

AIEgen-sensitized lanthanide nanocrystals as luminescent probes for intracellular Fe3+ monitoring

The abnormal Fe³⁺ level is known to cause various diseases, such as heart failure, liver damage and neurodegeneration. In situ probing Fe³⁺ in living cells or organisms is highly desired for both biological research and medical diagnostics. Herein, hybrid nanocomposites NaEuF₄@TCPP were constructed by the assembly of an aggregation-induced emission luminogen (AIEgen) TCPP and NaEuF₄ nanocrystals (NCs). The anchored TCPP on the surface of NaEuF₄ NCs can reduce rotational relaxation of the excited state and efficiently transfer the energy to the Eu³⁺ ions with minimized nonradiative energy loss. Consequently, the prepared NaEuF₄@TCPP nanoparticles (NPs) exhibited an intense red emission with a 103-fold enhancement relative to that in NaEuF₄ NCs under 365 nm excitation. A selectively quenching response to Fe³⁺ ions for the NaEuF₄@TCPP NPs makes them luminescent probes for sensitive detection of Fe³⁺ ions with a low detection limit of 340 nM. Moreover, the luminescence of NaEuF₄@TCPP NPs could be recovered by the addition of iron chelators. Benefiting from their good biocompatibility and stability in living cells, together with the characteristic of the reversible luminescence response, the lipo-coated NaEuF₄@TCPP probes were successfully applied for real-time monitoring of Fe³⁺ ions in living HeLa cells. These results are expected to motivate the exploration of AIE-based lanthanide probes for sensing and biomedical applications.

Highly thermostable mixed lanthanide organic frameworks with high quantum yield for warm white light-emitting diodes

A mixed lanthanide organic framework was prepared via hydrothermal methods using m-phthalic acid (m-H₂BDC), 1,10-phenanthroline (1,10-Phen), and Ln³⁺ ions, formulated as [HNMe₂][Eu_0.095Tb_1.905(m-BDC)₃(phen)₂] (ZTU-6). The structure and stability of ZTU-6 were characterised by X-ray diffraction (XRD) and thermogravimetric analysis (TGA), which revealed a three-dimensional pcu topology with high thermal stability. Fluorescence tests showed that ZTU-6 emitted orange light with a high quantum yield of 79.15%, and it can be effectively encapsulated in a light-emitting diode (LED) device emitting orange light. In addition, ZTU-6 was found to be compatible with BaMgAl₁₀O₁₇:Eu²⁺ (BAM) blue powder and [(Sr,Ba)₂SiO₄:Eu²⁺] silicate yellow and green powder to create a warm white LED with a high colour rendering index (CRI) of 93.4, a correlated colour temperature (CCT) of 3908 K, and CIE coordinates of (0.38, 036).

Terbium-based metal-organic frameworks through energy transfer modulation for visual logical sensing zinc and fluorine ions

Zinc is the second most abundant trace element in the human central nervous system, which is closely related to various physiological activities in the human body. Fluoride ion is one of the most harmful elements in drinking water. Excessive intake of F^- may cause dental fluorosis, renal failure, or DNA damage. Therefore, it is urgent to develop sensors with high sensitivity and selectivity for the detection of Zn²⁺ and F^- ions at the same time. In this work, a series of mixed lanthanide metal-organic frameworks (Ln-MOFs) probes are synthesized using a simple method of in situ doping. The luminous color can be finely modulated by changing the molar ratio of Tb³⁺ and Eu³⁺ during synthesis. Benefiting from the unique energy transfer modulation mechanism, the probe has the continuous detection capability of zinc ions and fluoride ions. The detection of Zn²⁺ and F^- in a real environment shows that the probe has a good practical application prospect. The as-designed sensor at 262 nm excitation can sequentially detect Zn²⁺ concentrations ranging from 10^-8 to 10^-3 M (LOD = 4.2 nM) and F^- levels ranging from 10^-5 to 10^-3 M (LOD = 3.6 μM) with high selectivity. Based on different output signals, a simple Boolean logic gate device is constructed to realize intelligent visualization of Zn²⁺ and F^- monitoring.

Effect of Functional Groups on Low-Concentration Carbon Dioxide Capture in -Type Metal-Organic Frameworks

The selective capture of low-concentration CO₂ from air or confined spaces remains a great challenge. In this study, various functional groups were introduced into UiO-66 to generate functionalized derivatives (UiO-66-R, R = NO₂, NH₂, OH, and CH₃), aiming at significantly enhancing CO₂ adsorption and separation efficiency. More significantly, UiO-66-NO₂ and UiO-66-NH₂ with high polarity exhibit exceptional CO₂ affinity and optimal separation characteristics in mixed CO₂/O₂/N₂ (1:21:78). In addition, the impressive stability of UiO-66-NO₂ and UiO-66-NH₂ endows them with excellent recycling stability. The effective adsorption and separation performances demonstrated by these two functional materials suggest their potential as promising physical adsorbents for capturing low-concentration CO₂.

Chiral metal-organic frameworks for photonics

Recently, there has been significant interest in the use of chiral metal-organic frameworks (MOFs) and coordination polymers (CPs) for photonics applications. The promise of these materials lies in the ability to tune their properties through judicious selection of the metal and ligand components. Additionally, the interaction of guest species with the host framework can be exploited to realise new functionalities. In this review, we outline the methods for synthesising chiral MOFs and CPs, then analyse the recent innovations in their use for various optical and photonics applications. We focus on two emerging directions in the field of MOF chemistry - circularly polarised luminescence (CPL) and chiroptical switching - as well as the latest developments in the use of these materials for second-order nonlinear optics (NLO), particularly second-harmonic generation (SHG). The current challenges encountered so far, their possible solutions, and key directions for further research are also outlined. Overall, given the results demonstrated to date, chiral MOFs and CPs show great promise for use in future technologies such as optical communication and computing, optical displays, and all-optical devices.

Applications of Metal-Organic Frameworks and Their Derivatives in Electrochemical CO2 Reduction

Electrochemically reducing CO2 to more reduced chemical species is a promising way that not only enables the conversion of intermittent energy resources to stable fuels, but also helps to build a closed-loop anthropogenic carbon cycle. Among various electrocatalysts for electrochemical CO2 reduction, multifunctional metal-organic frameworks (MOFs) have been employed as highly efficient and selective heterogeneous electrocatalysts due to their ultrahigh porosity and topologically diverse structures. Up to now, great progress has been achieved in the design and synthesis of highly active and selective MOF-related catalysts for electrochemical CO2 reduction reaction (CO2RR), and their corresponding reaction mechanisms have been thoroughly studied. In this review, we summarize the recent progress of applying MOFs and their derivatives in CO2RR, with a focus on the design strategies for electrocatalysts and electrolyzers. We first discussed the reaction mechanisms for different CO2RR products and introduced the commonly applied electrolyzer configurations in the current CO2RR system. Then, an overview of several categories of products (CO, HCOOH, CH4, CH3OH, and multi-carbon chemicals) generated from MOFs or their derivatives via CO2RR was discussed. Finally, we offer some insights and perspectives for the future development of MOFs and their derivatives in electrochemical CO2 reduction. We aim to provide new insights into this field and further guide future research for large-scale applications.

A Multimodal Ratiometric Luminescent Thermometer Based on a Single-Dysprosium Metal-Organic Framework

The design of high-performance luminescent MOF thermometers with multi-operation modes has been long sought but remains a formidable challenge. In this work, for the first time, we present a multimodal luminescent ratiometric thermometer based on the single-lanthanide metal-organic framework (MOF) DyTPTC-2Me (H₄TPTC-2Me = 2',5'-dimethyl-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid). It not only has the characteristic luminescence of Dy³⁺ in which the atomic transitions from the ⁴I_15/2 and ⁴F_9/2 states (thermally coupled energy levels, TCELs) are included but also emits ligand fluorescence due to the efficient energy back-transfer of Dy³⁺ to the ligand, thus allowing accurate non-invasive determination of temperature by different modes. In particular, the TCEL-based emissions of the Dy³⁺ ions give ideal signals for measuring the temperature in the 303-423 K range. The emissions of the ligand and Dy³⁺ (⁴F_9/2 → ⁶H_13/2) are used for temperature sensing in the range of 423 to 503 K. Both two modes feature promising thermometric performance, including high relative sensitivity, high temperature resolution, and excellent repeatability. Their combination is thus beneficial to achieve more accurate temperature detection over a broad temperature range, which can broaden the application scope of the ratiometric luminescent thermometers.

Ratiometric luminescent sensing of a biomarker for sugar consumption in an aqueous medium using a Cu(II) coordination polymer

An innovative [Cu(Hadp)₂(Bimb)]_n (KA@CP-S3) coordination polymer expands its dimensionality from a 1D chain to a 2D network. The topological analysis reveals that KA@CP-S3 has 2-connected uninodal 2D 2C1 topology. KA@CP-S3 has capable luminescent sensing for volatile organic compounds (VOCs), nitroaromatics, heavy metal ions, anions, disposed antibiotics (nitrofurantoin and tetracycline) and biomarkers. Intriguingly, KA@CP-S3 exhibits outstanding selective quenching of about 90.7% and 90.5% for the 125 mg dl^-1 and 150 mg dl^-1 strengths of sucrose, respectively, in aqueous solution along with other ranges in between. The photocatalytic degradation efficiency of KA@CP-S3 for the potentially harmful organic dye Bromophenol Blue displays 95.4%, which is the highest among the 13 dyes that were evaluated.

A novel spectroscopic technique for studying metal-organic frameworks based on Mie scattering

Metal-organic frameworks (MOFs) are promising candidates for a wide range of applications, and spectroscopic techniques are important tools for analyzing their structures and properties. Here, we propose a novel and general scattering spectroscopic approach to study various MOFs such as zeolitic imidazolate frameworks (ZIF-67 and ZIF-8), HKUST-1, Co-based MOF (Co-MOF), and Ni-based MOF (Ni-MOF) based on their inherent Mie scattering properties. We show that by using a dark-field microscope, the inherent scattering colors and spectra can be obtained, which are mainly from the high-order magnetic and electric resonant modes. The scattering capacities are dependent on the chemical structures for producing polarized charges and internal circular displacement currents. Additionally, all the MOFs are capable of responding to solvent guests due to their high porosity, and the scattering peaks are in a linear correlation with solvent refractive indices, displaying scattering solvatochromic behaviors. Our results open up a powerful and universal avenue for visually studying the host-guest interactions in MOFs.

A Cerium Organic Framework with {Cu2I2} Cluster and {Cu2I2}n Chain Modules: Structure and Fluorescence Sensing Properties

In this work, a copper iodine module bearing a coordination polymer (CP) with a formula of [(Cu₂I₂)₂Ce₂(INA)₆(DMF)₃]·DMF (1, HINA = isonicotinic acid, DMF = N,N'-dimethyl formamide) is presented. The title compound features a three dimensional (3D) structure, in which the {Cu₂I₂} cluster and {Cu₂I₂}_n chain modules are coordinated by N atoms from a pyridine ring in INA^- ligands, while the Ce³⁺ ions are bridged by the carboxylic groups of INA^- ligands. More importantly, compound 1 exhibits an uncommon red fluorescence (FL) with a single emission band maximized at 650 nm belonging to near infrared (NIR) luminescence. The temperature dependent FL measurement was applied to investigate the FL mechanism. Remarkably, 1 could be used as a FL sensor to cysteine and the nitro-bearing explosive molecule of trinitropheno (TNP) with high sensitivity, demonstrating its potential FL sensing applications for biothiol and explosive molecules.

Metal-Organic Framework-Based Colloidal Particle Synthesis, Assembly, and Application

Metal-organic frameworks (MOFs) assembled from metal nodes and organic ligands have received significant attention over the past two decades for their fascinating porous properties and broad applications. Colloidal MOFs (CMOFs) not only inherit the intrinsic properties of MOFs, but can also serve as building blocks for self-assembly to make functional materials. Compared to bulk MOFs, the colloidal size of CMOFs facilitates further manipulation of CMOF particles in a single or collective state in a liquid medium. The resulting crystalline order obtained by self-assembly in position and orientation can effectively improve performance. In this review, we summarize the latest developments of CMOFs in synthesis strategies, self-assembly methods, and related applications. Finally, we discuss future challenges and opportunities of CMOFs in synthesis and assembly, by which we hope that CMOFs can be further developed into new areas for a wider range of applications.

A Zn(II)-Metal-Organic Framework Based on 4-(4-Carboxy phenoxy) Phthalate Acid as Luminescent Sensor for Detection of Acetone and Tetracycline

As hazardous environmental pollutants, residual tetracycline (TC) and acetone are harmful to the ecosystem. Therefore, it is necessary to detect the presence of these pollutants in the environment. In this work, using Zn (II) salt, 4-(4-carboxy phenoxy) phthalic acid (H₃L), and 3,5-bis(1-imidazolyl) pyridine (BMP), a new metal-organic framework (Zn-MOF) known as [Zn₃(BMP)₂L₂(H₂O)₄]·2H₂O was synthesized using a one-pot hydrothermal method. The Zn-MOF has a three-dimensional framework based on the [Zn1N₂O₂] and [Zn2N₂O₄] nodes linked by a tridentate bridge BMP ligand and an L ligand with the μ₁:η¹η⁰/μ₁:η¹η⁰/μ₀:η⁰η⁰ coordination mode. There were two kinds of left- and right-handed helix chains, Zn1-BMP and Zn1-BMP-Zn1-L. The complex was stable in aqueous solutions with pH values of 4-10. The Zn-MOF exhibited a strong emission band centered at 385 nm owing to the π*→π electron transition of the ligand. It showed high luminescence in some common organic solvents as well as in the aqueous solutions of pH 4-10. Interestingly, TC and acetone effectively quenched the luminescence of the Zn-MOF in aqueous solution and enabled the Zn-MOF to be used as a sensor to detect TC and acetone. The detection limits of TC and acetone were observed to be 3.34 µM and 0.1597%, respectively. Even in acidic (pH = 4) and alkaline (pH = 10) conditions, the Zn-MOF showed a stable luminescence sensing capability to detect TC. Luminescence sensing of the Zn-MOF for TC in urine and aquaculture wastewater systems was not affected by the interfering agent. Furthermore, the mechanism of sensing TC was investigated in this study. Fluorescence resonance energy transfer and photoinduced electron transfer were found to be the possible quenching mechanisms via UV-Vis absorption spectra/the excitation spectra measurements and DFT calculations.

Noncentrosymmetric Lanthanide-Based MOF Materials Exhibiting Strong SHG Activity and NIR Luminescence of Er3+: Application in Nonlinear Optical Thermometry

Optically active luminescent materials based on lanthanide ions attract significant attention due to their unique spectroscopic properties, nonlinear optical activity, and the possibility of application as contactless sensors. Lanthanide metal-organic frameworks (Ln-MOFs) that exhibit strong second-harmonic generation (SHG) and are optically active in the NIR region are unexpectedly underrepresented. Moreover, such Ln-MOFs require ligands that are chiral and/or need multistep synthetic procedures. Here, we show that the NIR pulsed laser irradiation of the noncentrosymmetric, isostructural Ln-MOF materials (MOF-Er³⁺ (1) and codoped MOF-Yb³⁺/Er³⁺ (2)) that are constructed from simple, achiral organic substrates in a one-step procedure results in strong and tunable SHG activity. The SHG signals could be easily collected, exciting the materials in a broad NIR spectral range, from ≈800 to 1500 nm, resulting in the intense color of emission, observed in the entire visible spectral region. Moreover, upon excitation in the range of ≈900 to 1025 nm, the materials also exhibit the NIR luminescence of Er³⁺ ions, centered at ≈1550 nm. The use of a 975 nm pulse excitation allows simultaneous observations of the conventional NIR emission of Er³⁺ and the SHG signal, altogether tuned by the composition of the Ln-MOF materials. Taking the benefits of different thermal responses of the mentioned effects, we have developed a nonlinear optical thermometer based on lanthanide-MOF materials. In this system, the SHG signal decreases with temperature, whereas the NIR emission band of Er³⁺ slightly broadens, allowing ratiometric (Er³⁺ NIR 1550 nm/SHG 488 nm) temperature monitoring. Our study provides a groundwork for the rational design of readily available and self-monitoring NLO-active Ln-MOFs with the desired optical and electronic properties.

Metal-Organic Frameworks-Based Optical Nanosensors for Analytical and Bioanalytical Applications

Metal-organic frameworks (MOFs)-based optical nanoprobes for luminescence and surface-enhanced Raman spectroscopy (SERS) applications have been receiving tremendous attention. Every element in the MOF structure, including the metal nodes, the organic linkers, and the guest molecules, can be used as a source to build single/multi-emission signals for the intended analytical purposes. For SERS applications, the MOF can not only be used directly as a SERS substrate, but can also improve the stability and reproducibility of the metal-based substrates. Additionally, the porosity and large specific surface area give MOF a sieving effect and target molecule enrichment ability, both of which are helpful for improving detection selectivity and sensitivity. This mini-review summarizes the advances of MOF-based optical detection methods, including luminescence and SERS, and also provides perspectives on future efforts.

Recent progress on small molecular temperature-sensitive fluorescent probes

Temperature is an important biophysical parameter that is closely related with the metabolic activity in living cells. Therefore, the detection of intracellular temperature changes is crucial for exploring temperature-related biological processes. Fluorescence probe is an ideal tool for observing temperature changes in cells, which has many advantages, such as high sensitivity, good selectivity, and noninvasive, and thus aroused the great interest of researchers. In this paper, we summarize the recent progress of organic small molecule temperature-sensitive fluorescence probes in recent years was reviewed. Particularly, we describe the common response mode to the temperature and the practical applications of the probe in living cells and even animal models. Moreover, an outlook regarding temperature detection in clinical applications is discussed. The temperature-sensitive fluorescent probe is a "black box" to many researchers. This review aims to open a window on the prospect of the noninvasive in vivo detection of temperature which is helpful to deeper understand this rich research area.

Facile and stable fabrication of wafer-scale, ultra-black c-silicon with 3D nano/micro hybrid structures for solar cells

Three-dimensional (3D) silicon (Si) nanostructures have attracted much attention in solar cells due to their excellent broadband and omnidirectional light-harvesting properties. However, the development of 3D Si nanostructures is still plagued by the trade-off between structural complexity and fabrication difficulty. Herein, we proposed a facile and stable approach toward the fabrication of wafer-scale, ultra-black crystalline silicon (c-Si) with nano/micro hybrid structures. The distinguishing advantage of this approach is that it allows the formation of 3D Si nano/micro hybrid structures in a single-round process, avoiding the need for multiple iterations of lithography, coating, and etching required in conventional processes. The nano/micro hybrid structure arrays we fabricated show a low reflectance of <1% in the 600-1000 nm wavelength range and absorb 98.82% of incident light in the visible and near-infrared regions from 400 to 1100 nm under AM 1.5 G illumination. Solar cells made from nano/micro hybrid 3D structure arrays have an efficiency improvement of about 11.4% compared to those made from mono-micropillar arrays, and they have potential applications in high-performance photovoltaic devices.

Self-Reconstructed Metal-Organic Framework Heterojunction for Switchable Oxygen Evolution Reaction

Designing metal-organic framework (MOF)-based catalysts with superior oxygen evolution reaction (OER) activity and robust durability simultaneously is highly required yet very challenging due to the limited intrinsic activity and their elusive evolution under harsh OER conditions. Herein, a steady self-reconstructed MOF heterojunction is constructed via redox electrochemistry and topology-guided strategy. Thanks to the inhibiting effect from hydrogen bonds of Ni-BDC-1 (BDC=1,4-benzenedicarboxylic acid), the obatained MOF heterojunction shows greatly improved OER activity with low overpotential of 225 mV at 10 mA cm^-2 , relative to the totally reconstructed Ni-BDC-3 (332 mV). Density function theory calculations reveal that the formed built-in electric field in the MOF heterojunction remarkably optimizes the ad/desorption free energy of active Ni sites. Moreover, such MOF heterojunction shows superior durability attributed to the shielding effect of the surface-evolved NiOOH coating.