Optimizing Pt Electronic States through Formation of a Schottky Junction on Non‐reducible Metal–Organic Frameworks for Enhanced Photocatalysis

Polythiophene-coated carbon nano boxes for efficient platinum-based catalysts for methanol electrooxidation

To improve the efficiency of the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs), it is essential to develop catalysts with high catalytic activity. However, constructing polyatomic doped carbon nanomaterials and understanding the interaction mechanisms between dopant elements remain significant challenges. In this study, we propose nitrogen-doped carbon nanobox (CNB) derived from Zeolitic Imidazolate Framework-67 (ZIF-67) crystals as precursors to serve as carriers for highly efficient platinum nanoparticles (Pt NPs). We synthesized platinum/poly(3,4-propylenedioxythiophene)/carbon nanobox (Pt/PProDOT/CNB) composites by wrapping CNB around PProDOT films via in situ oxidative polymerization. This unique structural design provides several advantages to the catalyst, including a large active surface area, numerous accessible electrocatalytic active centers, an optimized electronic structure, and good electronic conductivity. The Pt/PProDOT/CNB composites demonstrated excellent methanol oxidation performance, with a remarkable mass activity (MA) of 1639.9 mA mg-1Pt and a high electrochemical active surface area (ECSA) of 160.8 m2/g. Furthermore, the catalyst exhibited good CO resistance and outstanding durability.

Encapsulating fullerene into Ti-based metal-organic frameworks with anchored atomically dispersed Pt cocatalysts for efficient hydrogen evolution

Ti-based Metal-organic frameworks (Ti-MOF) have been extensively investigated for producing hydrogen via solar water splitting, while their intrinsic activities are still retarded by the poor performance of photocarriers separation and utilization. Herein, a donor-acceptor (D-A) supramolecular photocatalyst is successfully constructed via encapsulating fullerene (C60) into MIL-125-NH2 and meanwhile depositing individual Pt atoms as cocatalyst. The as-prepared C60@MIL-125-NH2-Pt exhibits remarkable activity in photocatalytic water splitting, with a H2 formation rate of 1180 μmol g-1 h-1, which is ∼ 12 times higher than that of the pristine MIL-125-NH2. Further investigations indicate that the host-guest interactions between C60 and MIL-125-NH2 strengthen the built-in electric field, which greatly facilitates the separation and migration of photogenerated charge carriers. In addition, the cocatalyst of individual Pt atoms not only further promotes the separation and transport of carriers but also enhances the contact between water and the catalyst. All of these factors directly contribute to the superior activity of C60@MIL-125-NH2-Pt. This work provides a new perspective for constructing D-A supramolecular photocatalysts for enhanced charge separation and making full use of photoelectrons to realize efficient hydrogen production.

C3N4/Se-CNTs as Advanced Metal-Free Catalysts for the Photoassisted Electrocatalytic Oxygen Evolution Reaction

Photoassisted electrocatalysis is a frontier direction of electrocatalysis for promoting energy conversion. In this work, a metal-free C3N4/Se-CNTs is reported as a novel catalyst for photoassisted electrocatalytic oxygen evolution reaction (OER). C3N4 has an appropriate bandgap, high specific surface area, and long-term stability. CNTs can modulate the electronic environment of C3N4 by strong π-π interaction and greatly enhance the separation efficiency of photogenerated carriers. The distributed Se nanoparticles in CNTs can further increase the charge transfer ability. As a metal-free catalyst, the C3N4/Se-CNTs exhibits an overpotential of 231 mV at a current density of 10 mA cm-2 and a small Tafel slope of 52 mV dec-1 under illumination, which ranks among the best catalysts for photoassisted OER performance, surpassing most noble and transition metal-based catalysts. The result demonstrates the great potential of C3N4-based catalysts in the photoassisted OER process and provides a new perspective to explore the excellent metal-free OER catalysts.

Immobilization of Metal Nanoparticles to an Ultrathin Two-Dimensional Conjugated Metal-Organic Framework for Synergistic Electrocatalysis

Metal-organic frameworks (MOFs) have been considered as promising hosts for immobilizing ultrafine metal nanoparticles (MNPs) due to their high surface area and porosity. However, electrochemical applications of such emerging composites are severely limited by the poor electrical conductivity and large size of the MOFs. Herein, we report the general synthesis of incorporating various MNPs into a conjugated MOF ultrathin nanosheet (Cu-TCPP UNS) matrix, which not only prevents agglomeration and restricts the growth of MNPs but also benefits the exposure of active sites and the transport of electrons. Specifically, the obtained PtCu@Cu-TCPP UNSs exhibited nearly two times higher mass activity for the methanol oxidation reaction (MOR) than the commercial Pt/C catalyst. Mechanistic studies reveal that the strong interaction between MNPs and Cu-TCPP promotes the oxidation of the CO intermediate. Moreover, the PtCu@Cu-TCPP UNSs can be employed as bifunctional electrocatalysts to couple MOR with the hydrogen evolution reaction for highly efficient hydrogen production.

Spatially Separate Center-to-Surround Radiation Structure Induced Tandem Electron Transfer Effect for Stable and Enhanced Photocatalysis

Spatially separate anchoring redox cocatalysts on the photocatalyst to shunt the charge migration paths is an effective route to regulate the charge flow. Differently, we herein introduce an artificially synthesized Sun-planet-like spatially separated center-to-surround radiation photosensitizer-cocatalyst structure to regulate electron flow in a tandem manner. A single Au sphere acts as the Sun/photosensitizer in the center, and small Pt particles scatter around as the planets/cocatalyst, both of which are fixed inside the MOF crystal. Such a structure can not only simultaneously increase the light harvesting capacity and electron migration kinetics but also optimize the electron transfer pathway to minimize the electron migration distance, so that the hot electrons generated by Au can be quickly transferred to Pt through MOF before annihilation, leading to a significant photoactivity promotion.

Metal-organic frameworks for organic transformations by photocatalysis and photothermal catalysis

Organic transformation by light-driven catalysis, especially, photocatalysis and photothermal catalysis, denoted as photo(thermal) catalysis, is an efficient, green, and economical route to produce value-added compounds. In recent years, owing to their diverse structure types, tunable pore sizes, and abundant active sites, metal-organic framework (MOF)-based photo(thermal) catalysis has attracted broad interest in organic transformations. In this review, we provide a comprehensive and systematic overview of MOF-based photo(thermal) catalysis for organic transformations. First, the general mechanisms, unique advantages, and strategies to improve the performance of MOFs in photo(thermal) catalysis are discussed. Then, outstanding examples of organic transformations over MOF-based photo(thermal) catalysis are introduced according to the reaction type. In addition, several representative advanced characterization techniques used for revealing the charge reaction kinetics and reaction intermediates of MOF-based organic transformations by photo(thermal) catalysis are presented. Finally, the prospects and challenges in this field are proposed. This review aims to inspire the rational design and development of MOF-based materials with improved performance in organic transformations by photocatalysis and photothermal catalysis.

Harnessing the Synergistic Interplay between Atomic-Scale Vacancies and Ligand Effect to Optimize the Oxygen Reduction Activity and Tolerance Performance

Defect engineering is an effective strategy for regulating the electrocatalysis of nanomaterials, yet it is seldom considered for modulating Pt-based electrocatalysts for the oxygen reduction reaction (ORR). In this study, we designed Ni-doped vacancy-rich Pt nanoparticles anchored on nitrogen-doped graphene (Vac-NiPt NPs/NG) with a low Pt loading of 3.5 wt . % and a Ni/Pt ratio of 0.038 : 1. Physical characterizations confirmed the presence of abundant atomic-scale vacancies in the Pt NPs induces long-range lattice distortions, and the Ni dopant generates a ligand effect resulting in electronic transfer from Ni to Pt. Experimental results and theoretical calculations indicated that atomic-scale vacancies mainly contributed the tolerance performances towards CO and CH3OH, the ligand effect derived from a tiny of Ni dopant accelerated the transformation from *O to *OH species, thereby improved the ORR activity without compromising the tolerance capabilities. Benefiting from the synergistic interplay between atomic-scale vacancies and ligand effect, as-prepared Vac-NiPt NPs/NG exhibited improved ORR activity, sufficient tolerance capabilities, and excellent durability. This study offers a new avenue for modulating the electrocatalytic activity of metal-based nanomaterials.

Synergistic Effects of MOFs and Noble Metals in Photocatalytic Reactions: Mechanisms and Applications

Photocatalytic technology can efficiently convert solar energy to chemical energy and this process is considered as one of the green and sustainable technology for practical implementation. In recent years, metal-organic frameworks (MOFs) have attracted widespread attention due to their unique advantages and have been widely applied in the field of photocatalysis. Among them, noble metals have contributed significant advances to the field as effective catalysts in photocatalytic reactions. Importantly, noble metals can also form a synergistic catalytic effect with MOFs to further improve the efficiency of photocatalytic reactions. However, how to precisely control the synergistic effect between MOFs and noble metals to improve the photocatalytic performance of materials still needs to be further studied. In this review, the synergistic effects of MOFs and noble metal catalysts in photocatalytic reactions are firstly summarized in terms of noble metal nanoparticles, noble metal monoatoms, noble metal compounds, and noble metal complexes, and focus on the mechanisms and advantages of these synergistic effects, so as to provide useful guidance for the further research and application of MOFs and contribute to the development of the field of photocatalysis.

Modifying Parallel Excitations into One Framework for C(sp3)─H Bond Activation with Energy Combined More Than Two Photons

Natural photosynthesis enzymes utilize energies of several photons for challenging oxidation of water, whereas artificial photo-catalysis typically involves only single-photon excitation. Herein, a multiphoton excitation strategy is reported that combines parallel photo-excitations with a photoinduced electron transfer process for the activation of C(sp3)─H bonds, including methane. The metal-organic framework Fe3-MOF is designed to consolidate 4,4',4″-nitrilotrisbenzoic units for the photoactivation of dioxygen and trinuclear iron clusters as the HAT precursor for photoactivating alkanes. Under visible light irradiation, the dyes and iron clusters absorbed parallel photons simultaneously to reach their excited states, respectively, generating 1O2 via energy transfer and chlorine radical via ligand-to-metal charge transfer. The further excitation of organic dyes leads to the reduction of 1O2 into O2 •- through a photoinduced electron transfer, guaranteeing an extra multiphoton oxygen activation manner. The chlorine radical abstracts a hydrogen atom from alkanes, generating the carbon radical for further oxidation transformation. Accordingly, the total oxidation conversion of alkane utilizing three photoexcitation processes combines the energies of more than two photons. This new platform synergistically combines a consecutive excited photoredox organic dye and a HAT catalyst to combine the energies of more than two photons, providing a promising multiphoton catalysis strategy under energy saving, and high efficiency.

Exclusive generation of a superoxide radical by a porous aromatic framework for fast photocatalytic decontamination of mustard gas simulant in room air

Mustard gas and other chemical warfare agents (CWAs) are a global threat to public security, arising from unpredictable emergencies and chemical spill accidents. So far, photocatalysts such as metal clusters, polyoxometalates and porous solids have been exploited for oxidative degradation of mustard gas, commonly with 1O2 as reactive species. However, the production of 1O2 is oxygen-dependent and requires a high oxygen concentration to sustain the detoxication process. For safety and operation process considerations, it is always preferable to rapidly detoxify dangerous chemicals in the atmosphere of room air. In this work, a porous aromatic framework, PAF-68, was synthesized as a metal-free photocatalyst. In the presence of PAF-68, fast detoxication occurred in typical room air atmosphere. The half-life (t 1/2) for the complete conversion of mustard gas simulant to nontoxic product in room air was only 1.7 min, which is comparable to the performance in pure oxygen, surpassing that of any other porous photocatalysts. It was found that ˙O2 - rather than 1O2 is the predominant reactive species initiated by PAF-68 for mustard gas detoxication. Unlike the formation of 1O2 which prefers the environment of pure oxygen, generation of the ˙O2 - is an oxygen-independent process. It is suggested that amorphous PAFs possess low exciton binding energy and long decay lifetime, which facilitate the generation of ˙O2 -, and this offers a general design strategy to detoxifying chemical warfare agents under real-world conditions.

Atomically Contacted Cs3Bi2Br9 QDs@UiO-66 Composite for Photocatalytic CO2 Reduction

Metal halide perovskite quantum dots (QDs) are widely studied in the field of photocatalytic CO2 due to their strong light absorption and long carrier migration length. However, it can not exhibit high catalytic performance because of the radiative recombination and the lack of effective catalytic sites. Metal organic frameworks (MOFs) encapsulated QDs can not only solve the aforementioned problems, but also maintain their own unique characteristics with ultra-high specific surfaces area and abundant metal sites. In this work, lead-free bismuth-based halide perovskite QDs are encapsulated into Zr-based MOF (UiO-66), which combines the advantages with high power conversion efficiency of QDs and the high surface area and porosity of UiO-66. In addition, benefiting from the close contact between the Cs3Bi2Br9 QDs and the UiO-66 enables the photogenerated electrons in the QDs to be rapidly transferred to the MOF. As a result, the Cs3Bi2Br9@UiO-66 composite exhibits a higher yield for photocatalytic CO2 reduction than that of the prepared large-sized composite of Cs3Bi2Br9 and UiO-66.

Photoelectrochemical analysis of Pb2+ based on Au@PTCA Schottky junction with Pb2+-G quadruplex structure

Herein, a novel photoelectrochemical (PEC) aptasensor using gold nanoparticles@3,4,9,10-perylene tetracarboxylic (Au@PTCA) Schottky junction as the effective optoelectronic material and lead ion (Pb2+)-G quadruplex structure as the efficient quencher was constructed for the detection of Pb2+ with high sensitivity and excellent selectivity. Au@PTCA Schottky junction, which was proposed by the in situ reduction of Au NPs on the PTCA surface, exhibited a strong unidirectional conductivity, which could generate a significantly enhanced PEC signal compared with the pure PTCA. The Pb2+-G quadruplex structure with a large spatial hindrance effect was formed when the target Pb2+ was present owing to the occurrence of the specific recognition between Pb2+ and its aptamer S1. The formation of a Pb2+-G quadruplex structure effectively quenched the initial signal generated by the Au@PTCA Schottky junction, which was derived from restricted electron transport and light transmission. The obtained prominently decreased PEC signal could achieve the quantitative detection of Pb2+ from 0.5 pM to 500 nM, with a low detection limit of 0.17 pM. The preparation time of this PEC aptasensor was 13 h, and the time for PEC measurement depended on the illumination time, which switched off-on-off for 10 s-20 s-10 s. The study proposed here with high sensitivity and excellent selectivity for Pb2+ analysis offered a novel and reliable tool for environmental monitoring related to heavy metal ions.

Surface-Grafted Single-Atomic Pt-Nx Complex with a Precisely Regulating Coordination Sphere for Efficient Electron Acceptor-Inducing Interfacial Electron Transfer

Based on the electron-withdrawing effect of the Pt(bpy)Cl2 molecule, a simple post-modification amide reaction was firstly used to graft it onto the surface of NH2-MIL-125, which performed as a highly efficient electron acceptor that induced the conversion of the photoinduced charge migration pathway from internal BDC→TiOx migration to external BDC→PtNx migration, significantly improving the efficiency of photoinduced electron transfer and separation. Furthermore, precisely regulating over the first coordination sphere of Pt single atoms was achieved using further post-modification with additional bipyridine to investigate the effect of Pt-Nx coordination numbers on reaction activity. The as-synthesized NML-PtN2 exhibited superior photocatalytic hydrogen evolution activity of 7.608 mmol g-1 h-1, a remarkable improvement of 225 and 2.26 times compared to pristine NH2-MIL-125 and NML-PtN4, respectively. In addition, the superior apparent quantum yield of 4.01 % (390 nm) and turnover frequency of 190.3 h-1 (0.78 wt % Pt SA; 129 times compared to Pt nanoparticles/NML) revealed the high solar utilization efficiency and hydrogen evolution activity of the material. And macroscopic color changes caused by the transition of carrier migration paths was first observed. It holds profound significance for the design of MOF-Molecule catalysts with efficient charge carrier separation and precise regulation of single-atom coordination sphere.

Water-Stable High-Entropy Metal-Organic Framework Nanosheets for Photocatalytic Hydrogen Production

Metal-organic frameworks (MOFs) have emerged as promising platforms for photocatalytic hydrogen evolution reaction (HER) due to their fascinating physiochemical properties. Rationally engineering the compositions and structures of MOFs can provide abundant opportunities for their optimization. In recent years, high-entropy materials (HEMs) have demonstrated great potential in the energy and environment fields. However, there is still no report on the development of high-entropy MOFs (HE-MOFs) for photocatalytic HER in aqueous solution. Herein, the authors report the synthesis of a novel p-type HE-MOFs single crystal (HE-MOF-SC) and the corresponding HE-MOFs nanosheets (HE-MOF-NS) capable of realizing visible-light-driven photocatalytic HER. Both HE-MOF-SC and HE-MOF-NS exhibit higher photocatalytic HER activity than all the single-metal MOFs, which are supposed to be ascribed to the interplay between the different metal nodes in the HE-MOFs that enables more efficient charge transfer. Moreover, impressively, the HE-MOF-NS demonstrates much higher photocatalytic activity than the HE-MOF-SC due to its thin thickness and enhanced surface area. At optimum conditions, the rate of H2 evolution on the HE-MOF-NS is ≈13.24 mmol h-1 g-1, which is among the highest values reported for water-stable MOF photocatalysts. This work highlights the importance of developing advanced high-entropy materials toward enhanced photocatalysis.

MoO3/MIL-125-NH2 with boosted peroxidase-like activity for electrochemical staphylococcus aureus sensing via specific recognition of bacteriophages

Herein, novel nanozyme mimics MoO3/MIL-125-NH2 were reported and conjugated with bacteriophages as a new electrochemical probe for high sensitivity and specific electrochemical detection of staphylococcus aureus. The excellent peroxidase-like activity of MoO3/MIL-125-NH2 composites was attributed to the integration of MIL-125-NH2 with MoO3, which can boost the generation of superoxide radicals (O• 2-) and thus promote the oxidation of TMB in the presence of H2O2. In this work, two bacteriophages named SapYZU04 and SapYZU10 were isolated from sewage samples by using staphylococcus aureus YZUsa12 as the host. In comparison, MoO3/MIL-125-NH2@SapYZU04 was selected as a recognition agent. The DPV current declined linearly with staphylococcus aureus YZUsa12 concentration in the range of 101-108 CFU mL-1, with a low detection limit of 16 CFU mL-1 (S/N = 3). 20 strains including 13 host strains and 7 non-host strains were used to evaluate the selectivity of the proposed sensor. Regardless of the differences in the degrees of lytic performance for phage SapYZU04, all selected host strains can be screened with merely the same DPV current. Host spectrum-oriented bacteriophage sensing is of great importance for the practical application of bacteriophage-based biosensors in the future.

Naphthalene-based donor-acceptor covalent organic frameworks as an electron distribution regulator for boosting photocatalysis

By incorporating the electron-rich naphthalene and electron-deficient triazine as an electron donor and an electron acceptor, a new donor-acceptor covalent organic framework as an electron distribution regulator was obtained for boosting photocatalytically oxidative coupling of benzylamines and selective oxidation of thioethers under the irradiation of green light (520 nm).

Copper Phenylacetylide and TiO2 Modification for an Efficient Visible-Light-Driven Oxidative Coupling of Amines

The selective oxidation of amines to imines under mild conditions has attracted much attention. Our study reveals that copper phenylacetylide (PhC2Cu) could serve as an efficient photocatalyst for imine synthesis under visible-light irradiation (>400 nm). Utilizing benzylamine as a model reactant, PhC2Cu achieves an imine yield of 50.4%, which is 5 times higher than that of P25 under the same conditions and comparable to the yield obtained by the 3 wt % Au/P25 photocatalyst (55.4%). Further loading 3.9 nm TiO2 onto PhC2Cu through tetrabutyl titanate hydrolysis increases the imine yield to 84.7%, with a Ti:Cu atomic ratio of 3.65%. Control experiments, photoluminescence (PL) spectra, optical pump terahertz probe (OPTP) spectra, and electron spin resonance (ESR) tests confirm that the optimized TiO2 modification promotes the separation of excited carriers and electron transfer in PhC2Cu and facilitates the activation of surface oxygen, thereby enhancing the formation of superoxide radicals, a key active oxygen species in the reaction system. This work presents a promising strategy for efficient imine synthesis via amine coupling and expands the application field of PhC2Cu-based photocatalysts.

Tailoring Charge Flow in Carbon-Defective Cu-MOF with Pd Nanoparticles: A Boost for Visible Light Organic Photoelectrochemical Transistor in Bioanalysis

The photoactive material was of significant importance in organic photoelectrochemical transistor (OPECT) bioanalysis as it influences the photoinduced voltage and the μC* product, resulting in a varying sensor sensitivity. The utilization of metal-organic frameworks (MOFs) as photoactive materials in OPECT analysis is promising, yet it remains a grand challenge due to the inherently narrow light absorption range and high electron-hole recombination rate. Herein, Pd NPs were encapsulated as electron acceptors into the Cu-MOF using a double-solvent method, followed by pyrolysis at the proper temperature. After pyrolysis, Cu-MOF transformed into a carbon defect-rich composite of CuO and Cu2O while retaining its high porosity and structural morphology. The resulting carbon defect-rich pyrolysis Cu-MOF (p-Cu-MOF) served as an active support, facilitating the separation of electrons and holes. The photoelectrons trigger the electron transfer of adjacent active metal components and the formation of a Schottky junction between Pd and the MOFs. This effect induces the electron donation from the MOFs. Moreover, Pd/pyrolysis Cu-MOF exhibits significantly higher visible light absorption, better water stability, and higher electrical conductivity compared to Cu-MOF and Pd/Cu-MOF. An OPECT sensor was fabricated by utilizing Pd/p-Cu-MOF as the photoactive material and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the channel material on an integrated laser-etched FTO. The aptamer was used as the recognition element, enabling sensitive and efficient detection of residual isocarbophos.

Molecular Stacking Dependent Molecular Oxygen Activation in Supramolecular Polymeric Photocatalysts

Here, we showed that supramolecular assemblies based on perylene diimides (PDIs) are able to activate molecular oxygen through both the electron transfer and energy transfer pathways, which consequently leads to the formation of superoxide radicals (·O2-) and singlet oxygen species (1O2), respectively. These reactive oxygen species (ROS) can effectively lead to oxidative coupling of benzylamine and oxidation of 2-chloroethyl sulfide (CEES). We have designed and synthesized PDIs with similar molecular structures yet differing by the molecular stacking modes. We found that the photooxidation activities of the PDI supramolecular assemblies are inversely associated with the photoluminescence wavelength difference between the assemblies and the monomers (Δλ) quantitatively, and a smaller Δλ results in a higher catalytic efficiency accordingly. Overall, this work contributes to the design and fabrication of high performance photocatalysts based on metal-free organic materials.

Metal-Free Activation of Molecular Oxygen by Quaternary Ammonium-Based Ionic Liquid: A Detail Mechanistic Study

Most oxidation processes in common organic synthesis and chemical biology require transition metal catalysts or metalloenzymes. Herein, we report a detailed mechanistic study of a metal-free oxygen (O2) activation protocol on benzylamine/alcohols using simple quaternary alkylammonium-based ionic liquids to produce products such as amide, aldehyde, imine, and in some cases, even aromatized products. NMR and various control experiments established the product formation and reaction mechanism, which involved the conversion of molecular oxygen into a hydroperoxyl radical via a proton-coupled electron transfer process. Detection of hydrogen peroxide in the reaction medium using colorimetric analysis supported the proposed mechanism of oxygen activation. Furthermore, first-principles calculations using density functional theory (DFT) revealed that reaction coordinates and transition state spin densities have a unique spin conversion of triplet oxygen leading to formation of singlet products via a minimum energy crossing point. In addition to DFT, domain-based local pair natural orbital coupled cluster, (DLPNO-CCSD(T)), and complete active space self-consistent field, CASSCF(20,14) methods complemented the above findings. Partial density of states analysis showed stabilization of π* orbital of oxygen in the presence of ionic liquid, making it susceptible to hydrogen abstraction in a mild, metal-free condition. Inductively coupled plasma atomic emission spectroscopic (ICP-AES) analysis of reactant and ionic liquids clearly showed the absence of any significant transition metal contamination. The current results described the origin of O2 activation within the context of molecular orbital (MO) theory and opened up a new avenue for the use of ionic liquids as inexpensive, multifunctional and high-performance alternative to metal-based catalysts for O2 activation.

Modulating the Electronic States of Pt Nanoparticles on Reducible Metal-Organic Frameworks for Boosting the Oxidation of Volatile Organic Compounds

The adsorption and activation of pollutant molecules and oxygen play a critical role in the oxidation reaction of volatile organic compounds (VOCs). In this study, superior adsorption and activation ability was achieved by modulating the interaction between Pt nanoparticles (NPs) and UiO-66 (U6) through the spatial position effect. Pt@U6 exhibits excellent activity in toluene, acetone, propane, and aldehyde oxidation reactions. Spectroscopic studies, 16O2/18O2 kinetic isotopic experiments, and density functional theory (DFT) results jointly reveal that the encapsulated Pt NPs of Pt@U6 possess higher electron density and d-band center, which is conducive for the adsorption and dissociation of oxygen. The toluene oxidation reaction and DFT results indicate that Pt@U6 is more favorable to activate the C-H of toluene and the C═C of maleic anhydride, while Pt/U6 with lower electron density and d-band center exhibits a higher oxygen dissociation temperature and higher reactant activation energy barriers. This study provides a deep insight into the architecture-performance relation of Pt-based catalysts for the catalytic oxidation of VOCs.

Rational design of bimetallic sites in covalent organic frameworks for efficient photocatalytic oxidative coupling of amines

The conversion of organic compounds by photocatalysis under mild conditions is an environment-friendly alternative for organic transformations. In this work, the bimetallic covalent organic framework coordinated by Sr2+ and Fe2+ in the porphyrin centers with molar ratio of 2:1 (COF-Sr2Fe1) was synthesized through a two-step reaction. Under the synergistic regulation of Sr2+ and Fe2+, the separation of photogenerated charges and visible light absorption for COF-Sr2Fe1 were significantly promoted, and thus COF-Sr2Fe1 exhibited efficient photocatalytic performance towards benzylamine oxidative coupling reaction with a yield of 97 %, much higher than that of the nonmetallic covalent organic framework COF-366. Moreover, it was found that the Fe site displayed higher dehydrogenation ability and the Sr site displayed higher CN coupling ability through the density functional theory (DFT) calculations, thereby making the dehydrogenation and CN coupling steps more controllable for benzylamine oxidative coupling reaction by COF-Sr2Fe1. This work provides a strategy for designing efficient covalent organic frameworks photocatalysts, and helps to understand the oxidative coupling of amines more deeply.

Photocatalytic degradation of chlorinated organic pollutants by ZnS@ZIF-8 composite through hydrogen peroxide generation by activating dioxygen under simulated sunlight irradiation

Photocatalytic hydrogen peroxide (H2O2) production and its application in advanced oxidation processes (AOPs) are regarded as low-cost and environmentally friendly wastewater treatment processes. Herein, by modifying a small amount of sulphide on the zeolitic imidazolate framework-8 (ZIF-8), a ZnS@ZIF-8 composite and used for photocatalytic H2O2 production to degrade chlorinated organic pollutants under simulated sunlight (SSL). ZnS@ZIF-8 composite could enhance the separation of photo-induced charge carriers, promote electron transfer from zinc sulphide (ZnS) to ZIF-8, which exhibited good selectivity for the two-electron oxygen reduction reaction (2e--ORR) and two-electron water oxidation (2e--WOR) pathways. Based on oxygen (O2) activation, the developed ZnS@ZIF-8/O2/SSL system could achieve 6.43 mmol/L H2O2 production within 150 min, which was approximately 8.66 and 10.36 times higher than that of the ZnS/O2/SSL and ZIF-8/O2/SSL systems, respectively. In the ZnS@ZIF-8/O2/SSL system, the ORR, WOR and H2O2 photolysis led to the generation of hydroxyl radical (•OH), while the photochemical behavior of ZnS in ZnS@ZIF-8 composite resulted in the generation of active hydrogen (*H). Benefitting from the high concentration of H2O2 and the coexistence of redox species in the ZnS@ZIF-8/O2/SSL system, various chlorinated organic pollutants could be dechlorinated and mineralized. In addition, a possible mechanism for photocatalytic H2O2 production was also proposed. Importantly, the proposed process did not involve an additional sacrificial agent or Fenton-like catalysts. This work provides insights into the potential application of ZnS@ZIF-8 composite for H2O2 production and wastewater treatment.

In Situ Polymerization of Antibacterial Modification Polyamide 66 with Au@Cu2O-ZnO Ternary Heterojunction

In situ polymerization has proven to be an effective route through which to introduce function materials into polyamide materials. In this work, a nano-heterojunction material was evenly dispersed in PA66 via in situ polymerization methods to yield the antimicrobial PA66. The composites showed excellent antibacterial activity against Staphylococcus aureus and Escherichia coli, with strong mechanical properties. Fourier transform infrared spectroscopy (FTIR) showed that metal ions reacted with oxygen-containing functional groups. In addition, the shift of oxygen peaks in XPS spectra confirmed the occurrence of a complexation reaction. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) confirmed the effect of nano-heterojunction, which induced crystallization. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed uniform dispersion of heterojunctions in PA66. Tensile testing revealed decreased toughness with higher loadings. The nanocomposite polyamide material has good processing properties which can be processed into thin films, molds, and wires without changing the morphology, and can be widely used in a variety of fields.

Progress and Perspectives on Promising Covalent-Organic Frameworks (COFs) Materials for Energy Storage Capacity

In recent years, a new class of highly crystalline advanced permeable materials covalent-organic frameworks (COFs) have garnered a great deal of attention thanks to their remarkable properties, such as their large surface area, highly ordered pores and channels, and controllable crystalline structures. The lower physical stability and electrical conductivity, however, prevent them from being widely used in applications like photocatalytic activities and innovative energy storage and conversion devices. For this reason, many studies have focused on finding ways to improve upon these interesting materials while also minimizing their drawbacks. This review article begins with a brief introduction to the history and major milestones of COFs development before moving on to a comprehensive exploration of the various synthesis methods and recent successes and signposts of their potential applications in carbon dioxide (CO2 ) sequestration, supercapacitors (SCs), lithium-ion batteries (LIBs), and hydrogen production (H2 -energy). In conclusion, the difficulties and potential of future developing with highly efficient COFs ideas for photocatalytic as well as electrochemical energy storage applications are highlighted.

Electronic configuration inversion in CdIn2S4 for efficient photocatalytic hydrogen peroxide generation coupled with selective benzylamine oxidation

Vacancies engineering has sparked a huge interest in enhancing photocatalytic activity, but monovacancy simultaneously conducts as either electron or hole acceptor and redox reaction, worsening charge transfer and catalytic performance. Here, the concept of electronic inversion has been proposed through the simultaneous introduction of surface oxygen and S vacancies in CdIn2S4 (OSv-CIS). Consequently, under mild conditions, the well-designed OSv-CIS-200 demonstrated a strong rate of N-benzylidenebenzylamine production (2972.07 µmol g-1 h-1) coupled with Hydrogen peroxide (H2O2) synthesis (2362.33 µmol g-1 h-1) (PIH), which is 12.4 times higher than that of CdIn2S4. Density functional theory (DFT) simulation and characterization studies demonstrate that oxygen is introduced into the lattice on the surface of the material, reversing the charge distribution of the S vacancy and enhancing the polarity of the total charge distribution. It not only provides a huge built-in electric field (BEF) for guiding the orientation of the charge transfer, but also acts as a long-distance active site to accelerate reaction and prevent H2O2 decomposition. Our work offers a straightforward connection between the atomic defect and intrinsic properties for designing high-efficiency materials.

PEDOT-embellished Ti3C2Tx nanosheet supported Pt-Pd bimetallic nanoparticles as efficient and stable methanol oxidation electrocatalysts

Exploiting high-efficiency and durable electrocatalysts toward the methanol oxidation reaction (MOR) is crucial for the advancement of direct methanol fuel cells (DMFCs). Herein, we demonstrate the loading of platinum-palladium bimetallic nanoparticles (Pt-Pd NPs) onto poly(3,4-ethylenedioxythiophene) (PEDOT)-embellished titanium carbide (Ti3C2Tx) nanosheets as the electrocatalyst (Ti3C2Tx/PEDOT/Pt-Pd) via a facile and rapid chemical reduction-assisted one-pot hydrothermal process. The structural and morphological analyses of Ti3C2Tx/PEDOT/Pt-Pd indicate that the three-dimensional (3D) hybrid structure formed between PEDOT and Ti3C2Tx provides a sizable active surface and more active sites, which enhances the homogeneous dispersion of the Pt-Pd NPs and facilitates mass transfer. The Schottky junctions formed between PEDOT and Pt-Pd NPs contribute to charge transfer. The electronic effects and synergistic interactions between the support and catalyst favor the electrocatalytic activity of the catalyst. The electrochemical test results reveal that the Ti3C2Tx/PEDOT/Pt-Pd catalyst has prominent electrocatalytic capability for the MOR. Compared with Ti3C2Tx/Pt-Pd and commercial Pt/C catalysts, the Ti3C2Tx/PEDOT/Pt-Pd catalyst has a larger electrochemical activity surface area (ECSA = 122 m2 g-1) and higher mass activity (MA = 1445.4 mA mg-1), as well as better CO tolerance and more reliable long-term durability (a peak current density retention of 71% after 5200 s).

Photothermal Effect- and Interfacial Chemical Bond-Modulated NiOx/Ta3N5 Heterojunction for Efficient CO2 Photoreduction

Photothermal catalysis, which combines light promotion and thermal activation, is a promising approach for converting CO2 into fuels. However, the development of photothermal catalysts with effective light-to-heat conversion, strong charge transfer ability, and suitable active sites remains a challenge. Herein, the photothermal effect- and interfacial N-Ni/Ta-O bond-modulated heterostructure composed of oxygen vacancy-rich NiOx and Ta3N5 was rationally fabricated for efficient photothermal catalytic CO2 reduction. Beyond the charge separation capability conferred by the NiOx/Ta3N5 heterojunction, we observed that the N-Ni and Ta-O bonds linking NiOx and Ta3N5 form a spatial charge transfer channel, which enhances the interfacial electron transfer. Additionally, the presence of surface oxygen vacancies in NiOx induced nonradiative relaxation, resulting in a pronounced photothermal effect that locally heated the catalyst and accelerated the reaction kinetically. Leveraging these favorable factors, the NiOx/Ta3N5 hybrids exhibit remarkably elevated activity (≈32.3 μmol·g-1·h-1) in the conversion of CO2 to CH4 with near-unity selectivity, surpassing the performance of bare Ta3N5 by over 14 times. This study unveils the synergistic effect of photothermal and interfacial chemical bonds in the photothermal-photocatalytic heterojunction system, offering a novel approach to enhance the reaction kinetics of various catalysts.

The Effect of Linker-to-Metal Energy Transfer on the Photooxidation Performance of an Isostructural Series of Pyrene-Based Rare-Earth Metal-Organic Frameworks

The tetratopic linker, 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4 TBAPy) along with rare-earth (RE) ions is used for the synthesis of 9 isostructures of a metal-organic framework (MOF) with shp topology, named RE-CU-10 (RE = Y(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Tm(III), Yb(III), and Lu(III)). The synthesis of each RE-CU-10 analogue requires different reaction conditions to achieve phase pure products. Single crystal X-ray diffraction indicates the presence of a RE9 -cluster in Y- to Tm-CU-10, while a RE11 -cluster is observed for Yb- and Lu-CU-10. The photooxidation performance of RE-CU-10 analogues is evaluated, observing competition between linker-to-metal energy transfer versus the generation of singlet oxygen. The singlet oxygen produced is used to detoxify a mustard gas simulant 2-chloroethylethyl sulfide, with half-lives ranging from 4.0 to 5.8 min, some of the fastest reported to date using UV-irradiation and < 1 mol% catalyst, in methanol under O2 saturation.

Bi/Mn-Doped BiOCl Nanosheets Self-Assembled Microspheres toward Optimized Photocatalytic Performance

Doping engineering of metallic elements is of significant importance in photocatalysis, especially in the transition element range where metals possess empty 'd' orbitals that readily absorb electrons and increase carrier concentration. The doping of Mn ions produces dipole interactions that change the local structure of BiOCl, thus increasing the specific surface area of BiOCl and the number of mesoporous distributions, and providing a broader platform and richer surface active sites for catalytic reactions. The combination of Mn doping and metal Bi reduces the forbidden bandwidth of BiOCl, thereby increasing the absorption in the light region and strengthening the photocatalytic ability of BiOCl. The degradation of norfloxacin by Bi/Mn-doped BiOCl can reach 86.5% within 10 min. The synergistic effect of Mn doping and Bi metal can change the internal energy level and increase light absorption simultaneously. The photocatalytic system created by such a dual-technology combination has promising applications in environmental remediation.

Modulating Charges of Dual Sites in Multivariate Metal-Organic Frameworks for Boosting Selective Aerobic Epoxidation of Alkenes

Selective aerobic epoxidation of alkenes without any additives is of great industrial importance but still challenging because the competitive side reactions including C═C bond cleavage and isomerization are difficult to avoid. Here, we show fabricating Cu(I) single sites in pristine multivariate metal-organic frameworks (known as CuCo-MOF-74) via partial reduction of Cu(II) to Cu(I) ions during solvothermal reaction. Impressively, CuCo-MOF-74 is characteristic with single Cu(I), Cu(II), and Co(II) sites, and they exhibit the substantially enhanced selectivity of styrene oxide up to 87.6% using air as an oxidant at almost complete conversion of styrene, ∼25.8% selectivity increased over Co-MOF-74, as well as good catalytic stability. Contrast experiments and theoretical calculation indicate that Cu(I) sites contribute to the substantially enhanced selectivity of epoxides catalyzed by Co(II) sites. The adsorption of two O₂ molecules on dual Co(II) and Cu(I) sites is favorable, and the projected density of state of the Co-3d orbital is closer to the Fermi level by modulating with Cu(I) sites for promoting the activation of O₂ compared with dual-site Cu(II) and Co(II) and Co(II) and Co(II), thus contributing to the epoxidation of the C═C bond. When other kinds of alkenes are used as substrates, the excellent selectivity of various epoxides is also achieved over CuCo-MOF-74. We also prove the universality of fabricating Cu(I) sites in other MOF-74 with various divalent metal nodes.

Spatial Specific Janus S-Scheme Photocatalyst with Enhanced H2 O2 Production Performance

Photocatalytic oxygen reduction reaction (ORR) for H₂ O₂ production in the absence of sacrificing agents is a green approach and of great significance, where the design of photocatalysts with high performance is the central task. Herein, a spatial specific S-scheme heterojunction design by introducing a novel semiconducting pair with a S-scheme mechanism in a purpose-designed Janus core-shell-structured hollow morphology is reported. In this design, TiO₂ nanocrystals are grown inside the inner wall of resorcinol-formaldehyde (RF) resin hollow nanocakes with a reverse bumpy ball morphology (TiO₂ @RF). The S-scheme heterojunction preserves the high redox ability of the TiO₂ and RF pair, the spatial specific Janus design enhances the charge separation, promotes active site exposure, and reduces the H₂ O₂ decomposition to a large extent. The TiO₂ @RF photocatalyst shows a high H₂ O₂ yield of 66.6 mM g^-1  h^-1 and solar-to-chemical conversion efficiency of 1.11%, superior to another Janus structure (RF@TiO₂ ) with the same heterojunction but a reversed Janus spatial arrangement, and most reported photocatalysts under similar reaction conditions. The work has paved the way toward the design of next-generation photocatalysts for green synthesis of H₂ O₂ production.

Enhanced Alkene Selectivity for Transfer Semihydrogenation of Alkynes over Electron-Deficient Pt Nanoparticles Encapsulated in Hollow Silica Nanospheres

In this work, we report that Pt nanoparticles confined in hollow porous silica nanospheres (Pt@HPSNs) function as highly selective catalysts for the transfer hydrogenation of phenylacetylene to styrene with ammonia borane. Relative to the deep hydrogenation of phenylacetylene to ethylbenzene over the supported Pt/SiO2, Pt@HPSNs exhibit above 88% of styrene selectivity at nearly 100% of phenylacetylene conversions, and the high selectivity of Pt@HPSNs can be maintained even at high ammonia borane/phenylacetylene ratios and longer reaction time. The Pt 4f X-ray photoelectron spectrum of Pt@HPSNs shows a remarkable ∼1.5 eV shift to high binding energy, proving the nature of electron deficiency of such encapsulated Pt nanoparticles. Combined with extremely minor transfer hydrogenation of styrene to ethylbenzene when styrene as substrates, the enhanced styrene selectivity of Pt@HPSNs is ascribed to the electron deficiency of encapsulated Pt nanoparticles, which leads to the fast desorption of styrene and thus avoids deep hydrogenation.

Functionalized MOF-Based Photocatalysts for CO2 Reduction

Metal-organic frameworks (MOFs) materials have become a research forefront in the field of photocatalytic CO₂ reduction attributed to their ultra-high specific surface area, adjustable structure, and abundant catalytic active sites. Particularly, MOFs can be facilely tuned to match CO₂ photoreduction by utilizing post-modification of metal nodes, functionalization of organic linkers, and combination with other active materials. Herein, the recent advances in the construction strategy of MOF-based photocatalysts materials for CO₂ reduction are highlighted. Some systematic modification strategies on MOF-based photocatalysts are also discussed, such as modification of metal sites and organic ligands, construction of heterojunction, introduction of single/dual-atom, and strain engineering. Finally, the future development directions of MOF-based photocatalysts in the field of CO₂ reduction are presented.

Metal-Organic Framework-Based Photocatalysis for Solar Fuel Production

Metal-organic frameworks (MOFs) represent a novel class of crystalline inorganic-organic hybrid materials with tunable semiconducting behavior. MOFs have potential for application in photocatalysis to produce sustainable solar fuels, owing to their unique structural advantages (such as clarity and modifiability) that can facilitate a deeper understanding of the structure-activity relationship in photocatalysis. This review takes the photocatalytic active sites as a particular perspective, summarizing the progress of MOF-based photocatalysis for solar fuel production; mainly including three categories of solar-chemical conversions, photocatalytic water splitting to hydrogen fuel, photocatalytic carbon dioxide reduction to hydrocarbon fuels, and photocatalytic nitrogen fixation to high-energy fuel carriers such as ammonia. This review focuses on the types of active sites in MOF-based photocatalysts and discusses their enhanced activity based on the well-defined structure of MOFs, offering deep insights into MOF-based photocatalysis.

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

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

Reversibly Phase-Transformative Zeolitic Imidazolate Framework-108 and the Membrane Separation Utility

Reversible phase transformations (RPTs) of metal-organic frameworks not only create material diversity but also promise a self-restoration of crystals in a controllable manner. However, there are only limited examples because seeking for a convenient and effective trigger for RPTs, especially for RPTs with respect to spatiotemporal harmony in cleavage and reconstruction of metal-linker chemical bonds, is challenging. In this work, we found that zeolitic imidazolate framework (ZIF)-108 with Zn-N coordination bonds showing moderate strength was an ideal platform. We reported three crystal phases of ZIF-108, namely, sodalite (SOD), diamondoid (DIA), and large pore_sodalite (lp_SOD) topologies, and identified RPTs between phases: (1) when exposed to water or water vapor, the SOD structure could transform to a compact DIA version as a result of the decomposition of four-membered rings and synchronous reorganization of six-membered rings. Then, the DIA structure could also return back to SOD when soaked in dimethylformamide (DMF) or DMF vapor. (2) High-temperature treatment of SOD gives rise to lp_SOD, which then reverts to SOD by DMF. (3) lp_SOD could also be compressed into the DIA phase by water or water vapor and can then be restored via a two-step treatment, namely, soaking in DMF (DIA → SOD) right before a high-temperature therapy (SOD → lp_SOD). From the perspective of the separation utility, we found that the lp_SOD version of ZIF-108, relative to SOD-structured ZIF-108, can produce mixed matrix membranes having an interesting interfacial structure with the polymer chains, though both share the same chemical composition. We verified that the large pore of lp_SOD can allow being penetrated by polymer chains, which contributed to not only reinforcing the bi-phase interface but also sharpening the molecule sieve properties of fillers toward CO₂ and CH₄.