Metal-Organic Framework-Based Composite for Photocatalytic Detection of Prevalent Pollutant

Photocatalytic properties of 2,5-furandicarboxylic acid (FDCA), a model organic molecule used for biopolymer production, are reported for the first time. Further integration of FDCA into metal-organic framework (MOF) structures and subsequent silver-based photoactivation leads to the next generation of hybrids with controlled morphologies, capable of forming sensorial platforms for prevalent phenol contaminant detection. The mechanisms that allow photocatalytic functionality are driven by the charge carrier generation in the organic molecule (either in its alone or integrated form) and depend on sample's physical and chemical properties as confirmed by scanning and transmission electron microscopy, Fourier transform infrared and X-ray photoelectron spectroscopy, and X-ray diffraction, respectively. Electrochemical analysis using cyclic voltammetry confirmed high sensitivity for p-nitrophenol (p-NP) detection as dictated by the selective electron migration at a user-controlled electrode interface. Considering the wide usage of p-NP and its increased discharge shown to lead to harmful effects on both the environment and biosystems, this new detection method is envisioned to allow effective control and regulation of such compound release, all under low-cost and environmentally friendly conditions.

Bipyridyl-Containing Cadmium-Organic Frameworks for Efficient Photocatalytic Oxidation of Benzylamine

Metal-organic frameworks (MOFs) have attracted increased research attention in photocatalysis due to their great potential in light harvest and conversion. However, the organic transformations as photocatalyzed by MOFs under mild conditions yet remain a challenge. Herein, three bipyridyl-containing cadmium-organic frameworks Cd(dcbpy) (dcbpy = 2,2'-bipyridine-5,5'-dicarboxylate), Cd(bdc)(bpy) (bdc = 1,4-benzenedicarboxylate; bpy = 2,2'-bipyridyl), and Cd(bdc)(2Me-bpy) (2Me-bpy = 4,4'-dimethyl-2,2'-bipyridyl) were synthesized for the first time. The bpy-containing Cd-MOFs have strong light harvest abilities and suitable photocatalysis energy potentials, making them highly active and selective for the photo-oxidation of benzylamine to N-benzylbenzaldimine under mild conditions, i.e., using atmospheric air as oxidant, at room temperature, and in the absence of any photosensitizer or cocatalyst. It provides an efficient, economical, and green way for the direct oxidation of amines to produce imines.

Enhanced photocatalytic performance of a Ti-based metal-organic framework for hydrogen production: Hybridization with ZnCr-LDH nanosheets

Novel hybrid composites of NH₂-MIL-125(Ti) and ZnCr-layered double hydroxide nanosheets (ZnCr-LDH NSs) are developed for use as visible-light-active photocatalysts for hydrogen production based on water photolysis. The hybrid composites are obtained by growing NH₂-MIL-125(Ti) in the presence of exfoliated ZnCr-LDH NSs using a solvothermal reaction. Hybridization of NH₂-MIL-125(Ti) with exfoliated ZnCr-LDH NSs leads to significant effects on the morphology and optical properties of NH₂-MIL-125(Ti). To find the optimum photocatalytic activity for hydrogen production by the hybrid composite photocatalysts, the content of ZnCr-LDH in this work is controlled. Compared to that of pristine NH₂-MIL-125(Ti) and ZnCr-LDH, the hybrid composites exhibit an improved photocatalytic activity for hydrogen production under visible-light irradiation. In addition, the hybrid composite photocatalyst shows excellent photo-chemical stability. The improved photocatalytic activity is believed to benefit from the synergy of strong electronic coupling between NH₂-MIL-125(Ti) and ZnCr-LDH NSs, expanded light absorption and band alignment to enhance the lifetime of photo-induced electrons and holes.

A two-dimensional metal-organic framework accelerating visible-light-driven H2 production

The rapid consumption of non-renewable fossil fuels and the relevant critical environmental issues have significantly boosted the demand for clean, renewable and carbon-free energy sources. The conversion of solar energy into green hydrogen (H2) via photocatalytic water splitting stands out as a promising, cost-effective and environmentally friendly technology. However, the realization of large-scale solar-driven photocatalytic H2 production relies on the development of inexpensive, efficient and stable photocatalysts. Here, for the first time, we report the fabrication of Zn0.8Cd0.2S (ZCS) nanoparticles (NPs) dispersed Co-based metal-organic layers (CMLs) using an easy self-assembly approach. The as-synthesized ZCS/CML composite shows a remarkable visible-light-induced H2-production activity of 18 102 μmol h-1 g-1, 492% higher than that of pure ZCS. A series of advanced characterization studies, e.g., synchrotron-based X-ray absorption near edge structure and time-resolved photoluminescence spectroscopy, disclose that the strong electronic interaction between ZCS and CML and the abundant reactive sites on the CML lead to the significantly improved photocatalytic H2-production activity. Our contribution not only demonstrates the application of CML as an earth-abundant support and promoter to tremendously boost photocatalytic H2 production without noble-metal co-catalysts, but also sheds light on the tailored design and synthesis of metal-organic-layer based materials for energy conversion and storage.

Bi-metal-organic frameworks type II heterostructures for enhanced photocatalytic styrene oxidation

Fabricating heterostructures enhances the photocatalytic performance of metal-organic frameworks (MOFs) due to their excellent light absorption and high efficient charge transfer capacity. In this study, we designed and implemented three-dimensional dendritic UiO-66-NH2@MIL-101(Fe) (UOML) heterostructures as catalysts for photocatalytic styrene oxidation. The UOML catalysts exhibited a well-matched band gap structure and efficient catalytic interface, leading to a remarkable photoexcited carrier separation and catalytic activity. Our results present a promising insight for synthesizing novel MOFs-based catalysts and their applications.

WO3 in suit embed into MIL-101 for enhancement charge carrier separation of photocatalyst

Compositing nanoparticles photo-catalyst with enormous surface areas metal–organic framework (MOF) will greatly improve photocatalytic performances. Herein, WO₃ nanoparticles are partly embedded into pores of MIL-101 or only supported on the outside of representative MIL-101, which were defined as embedded structure WO₃@MIL-101@WO₃ and coating structure WO₃&MIL-101 respectively. Different pH, concentration and loading percentage were researched. XRD, TEM and BET were carried to analyze the composites. Compared with the pristine WO₃, all WO₃ loaded MOF nanocomposites exhibited remarkable enhancing for the efficiency of photocatalytic degradation methylene blue under visible light. Their activity of the same loading percentage WO₃ in embedded structure and coating structure have increased for 9 and 3 times respectively compared with pure WO₃. The WO₃@MIL-101@WO₃ has 3 times higher efficiency than WO₃&MIL-101, because the shorter electron-transport distance can make a contribution to electron–hole separation. The further mechanism involved has been investigated by radical quantify experiment, XPS and photoluminescence spectroscopy.

Metal-Organic Frameworks for Photocatalysis and Photothermal Catalysis

To meet the ever-increasing global demand for energy, conversion of solar energy to chemical/thermal energy is very promising. Light-mediated catalysis, including photocatalysis (organic transformations, water splitting, CO₂ reduction, etc.) and photothermal catalysis play key roles in solar to chemical/thermal energy conversion via the light-matter interaction. The major challenges in traditional semiconductor photocatalysts include insufficient sunlight utilization, charge carrier recombination, limited exposure of active sites, and particularly the difficulty of understanding the structure-activity relationship. Metal-organic frameworks (MOFs), featuring semiconductor-like behavior, have recently captured broad interest toward photocatalysis and photothermal catalysis because of their well-defined and tailorable porous structures, high surface areas, etc. These advantages are beneficial for rational structural modulation for improved light harvesting and charge separation as well as other effects, greatly helping to address the aforementioned challenges and especially facilitating the establishment of the structure-activity relationship. Therefore, it is increasingly important to summarize this research field and provide in-depth insight into MOF-based photocatalysis and photothermal catalysis to accelerate the future development. In this Account, we have summarized the recent advances in these two directly relevant applications, photocatalysis and photothermal catalysis, mainly focusing on the results in our lab. Given the unique structural features of MOFs, we have put an emphasis on rational material design to optimize the components and performance and to understand related mechanisms behind the enhanced activity. This Account starts by presenting an overview of solar energy conversion by catalysis. We explain why MOFs can be promising photocatalysts and exemplify the semiconductor-like behavior of MOFs. More importantly, we show that MOFs provide a powerful platform to study photocatalysis, in which the involved three key processes, namely, light harvesting, electron-hole separation, and surface redox reactions, can be rationally improved. Meanwhile, the structure-activity relationship and charge separation dynamics are illustrated in this part. In addition, MOFs for photothermal catalysis have been introduced that are based on the photothermal effect of plasmonic metals and/or MOFs, together with light-driven electronic state optimization of active sites, toward enhanced heterogeneous organic reactions. Finally, our brief outlooks on the current challenges and future development of MOF photocatalysis and photothermal catalysis are provided. It is believed that this Account will afford significant understanding and inspirations toward solar energy conversion over MOF-based catalysts.

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

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

Controlled growth of ZnS/ZnO heterojunctions on porous biomass carbons via one-step carbothermal reduction enables visible-light-driven photocatalytic H2 production

Controlled growth of ZnS/ZnO heterojunctions on porous biomass carbons has been achieved via a one-step carbothermal reduction strategy.

Different functional group modified zirconium frameworks for the photocatalytic reduction of carbon dioxide

UiO-68-PSMs of UiO-68-F, UiO-68-CH₃ and UiO-68-OCH₃ achieved by post-synthetic modification were found to show different activity for photocatalytic CO₂ reduction.

A mesoporous NNN-pincer-based metal–organic framework scaffold for the preparation of noble-metal-free catalysts

A terpyridine-based mesoporous 3D MOF was synthesized as a general scaffold for catalyst preparation.

Photo-induced electron transfer in a metal–organic framework: a new approach towards a highly sensitive luminescent probe for Fe3+

By utilizing the d-PET process between ligands 4,4′-bimbp and H₂pta in a Co-based mixed-ligand MOF, ZJU-109, a fluorescent turn-on sensor for Fe³⁺ with a detection limit as low as 0.053 μM has been demonstrated.

Oxygen-free water-promoted selective photocatalytic oxidative coupling of amines

A novel oxygen-free photocatalytic selective oxidative coupling of amines to produce imines was successfully performed with water as the primary oxidant at room temperature.

A fluorescent conjugated polymer photocatalyst based on Knoevenagel polycondensation for hydrogen production

An organic polymer photocatalyst (p-P) for hydrogen production was designed and synthesized through Knoevenagel condensation with a high yield.

Metal–organic framework-derived heterojunctions as nanocatalysts for photocatalytic hydrogen production

A summary of using the pore chemistry or surface chemistry of MOFs to construct heterojunction nanocatalysts for photocatalytic hydrogen production.

Metal-Organic Frameworks Encapsulating Active Nanoparticles as Emerging Composites for Catalysis: Recent Progress and Perspectives

Beyond conventional porous materials, metal-organic frameworks (MOFs) have aroused great interest in the construction of nanocatalysts with the characteristics of catalytically active nanoparticles (NPs) confined into the cavities/channels of MOFs or surrounded by MOFs. The advantages of adopting MOFs as the encapsulating matrix are multifold: uniform and long-range ordered cavities can effectively promote the mass transfer and diffusion of substrates and products, while the diverse metal nodes and tunable organic linkers may enable outstanding synergy functions with the encapsulated active NPs. Herein, some key issues related to MOFs for catalysis are discussed. Then, state-of-the art progress in the encapsulation of catalytically active NPs by MOFs as well as their synergy functions for enhanced catalytic performance in the fields of thermo-, photo-, and electrocatalysis are summarized. Notably, encapsulation-structured nanocatalysts exhibit distinct advantages over conventional supported catalysts, especially in terms of the catalytic selectivity and stability. Finally, challenges and future developments in MOF-based encapsulation-structured nanocatalysts are proposed. The aim is to deliver better insight into the design of well-defined nanocatalysts with atomically accurate structures and high performance in challenging reactions.

Autoluminescent Metal-Organic Frameworks (MOFs): Self-Photoemission of a Highly Stable Thorium MOF

A novel thorium(IV) metal-organic framework (MOF), Th(2,6-naphtalenedicarboxylate)₂, has been synthesized via solvothermal reaction of thorium nitrate and 2,6-naphtalendicarboxilyc acid. This compound shows a new structural arrangement with an interesting topology and an excellent thermal resistance, as the framework is stable in air up to 450 °C. Most notably, this MOF, combining the radioactivity of its metal center and the scintillation property of the ligand, has been proven capable of spontaneous photon emission.

Metal-Organic Frameworks with Organogold(III) Complexes for Photocatalytic Amine Oxidation with Enhanced Efficiency and Selectivity

Luminescent organogold(III) complex Au^III with highly emissive triplet excited state was encapsulated in two metal-organic frameworks (MOFs) with different pore sizes and structures (MOF1 and ZJU-28). Compared with the Au^III complex in solution, the resultant composites Au^III @MOF1 and Au^III @ZJU-28 exhibit enhanced emission intensity, lifetime, and quantum yield. Under irradiation, Au^III @MOFs are efficient, selective, and recyclable catalysts for light-induced aerobic C-N bond formation. When used as a heterogeneous catalyst for oxidizing secondary amines to the corresponding imines, Au^III @ZJU-28 achieved high TONs of 876-1548, which are about 2.8-3.5 times higher than that of the homogenous Au^III complex. In addition, different selectivities in oxidizing mixed substrates is realized by means of different host MOFs, and thus encapsulating the Au^III complex in an appropriate MOF allowed the desired product to be obtained. Inherent shortcomings of homogeneous catalysts in cyclic use are also overcome by using composite catalysts, and high conversion of the Au^III @ZJU-28 catalyst was still observed after ten cycles.

Conductive Leaflike Cobalt Metal-Organic Framework Nanoarray on Carbon Cloth as a Flexible and Versatile Anode toward Both Electrocatalytic Glucose and Water Oxidation

Transition metal-organic frameworks (MOFs), on account of their unique inherent properties of large pore volume, high specific surface area, tunable pores, and good catalytic activity, have been highly regarded as superior catalysts recently for water electrolysis, supercapacitors, batteries, sensors, and so on. Herein, we report on a cobalt MOF phase with 3D well-aligned nanosheets array architecture on carbon cloth (Co-MOF NS/CC), fabricated by a facile ambient liquid-phase deposition, could serve as a self-standing Janus catalytic electrode toward both glucose and water oxidation. It shows good glucose-sensing performance with low determination limit and large detection range. Also, it exhibits high water-oxidation efficiency with low overpotential and good durability. This work demonstrates the potential of utilizing transition-metal based well-aligned MOF nanoarrays for electrocatalytic oxidation.

Design of Single-Site Photocatalysts by Using Metal-Organic Frameworks as a Matrix

Single-site photocatalysts generally display excellent photocatalytic activity and considerably high stability compared with homogeneous catalytic systems. A rational structural design of single-site photocatalysts with isolated, uniform, and spatially separated active sites in a given solid is of prime importance to achieve high photocatalytic activity. Intense attention has been focused on the design and fabrication of single-site photocatalysts by using porous materials as a platform. Metal-organic frameworks (MOFs) have great potential in the design and fabrication of single-site photocatalysts due to their remarkable porosity, ultrahigh surface area, extraordinary tailorability, and significant diversity. MOFs can provide an abundant number of binding sites to anchor active sites, which results in a significant enhancement in photocatalytic performance. In this focus review, the development of single-site MOF photocatalysts that perform important and challenging chemical redox reactions, such as photocatalytic H2 production, photocatalytic CO2 conversion, and organic transformations, is summarized thoroughly. Successful strategies for the construction of single-site MOF photocatalysts are summarized and major challenges in their practical applications are noted.

Enhanced visible light photocatalytic non-oxygen coupling of amines to imines integrated with hydrogen production over Ni/CdS nanoparticles

Non-oxygen coupling of amines to imines, initiated by hydrogen evolution over Ni/CdS nanoparticles with visible light, smoothly happens. Outstanding catalytic performance was achieved, originating from integrating effect of coupling reaction and solar-driven reduction of aqueous protons.

Macroscopic and microscopic investigation of uranium elimination by Ca–Mg–Al-layered double hydroxide supported nanoscale zero valent iron

Ca–Mg–Al-LDH/nZVI nanocomposites showed excellent U(vi) removal performance from aqueous solutions through the coordination of reduction and adsorption reactions.