Recent Advances in Metal-Organic Frameworks Derived Nanocomposites for Photocatalytic Applications in Energy and Environment

In vivo study of chelating agent-modified nano zero-valent iron: Biodistribution and toxicity in mice

In this study, the distribution and toxicity of nanoscale zero valent iron (nZVI) and nZVIs coated with citric acid and sodium tripolyphosphate (CA-nZVI and STPP-nZVI) in mice were investigated. nZVIs were primarily found in the livers and spleens, followed by the lungs, hearts, and kidneys. Histologic analysis revealed no significant histopathologic abnormalities or lesions in all organs except the liver at 14th d gavage. nZVIs did not have a noticeable impact on the body weight of the mice or the weight of their organs. Compared with the control group, there were no significant changes in hematology indexes in the nZVIs groups. However, the nZVIs groups exhibited varying levels of elevation in alanine aminotransferase, aspartate aminotransferase, and creatinine, suggesting liver and kidney inflammation in mice. The up-regulation of Nuclear Factor erythroid 2-Related Factor 2 and Heme oxygenase 1 in the nZVIs groups may be a response to nZVIs-induced oxidative stress. Immunohistochemical analysis confirmed the inflammatory response induced by the three nZVI groups. Chelating agents did not have a significant impact on the distribution or toxicity of nZVIs in mice. This study contributes to a comprehensive and detailed insight into nZVI toxicity in the environmental field.

Metal-Organic Frameworks-Derived Nanocarbon Materials and Nanometal Oxides for Photocatalytic Applications

Harnessing low-density solar energy and converting it into high-density chemical energy through photocatalysis has emerged as a promising avenue for the production of chemicals and remediation of environmental pollution, which contributes to alleviating the overreliance on fossil fuels. In recent years, metal-organic frameworks (MOFs) have gained widespread application in the field of photocatalysis due to their photostability, tunable structures, and responsiveness in the visible light range. However, most MOFs exhibit relatively low response to light, limiting their practical applications. MOFs-derived nanomaterials not only retain the inherent advantages of pristine MOFs but also show enhanced light adsorption and responsiveness. This review categorizes and summarizes MOFs-derived nanomaterials, including nanocarbons and nanometal oxides, providing representative examples for the synthetic strategies of each category. Subsequently, the recent research progress on MOFs-derived materials in photocatalytic applications are systematically introduced, specifically in the areas of photocatalytic water splitting to H2, photocatalytic CO2 reduction, and photocatalytic water treatment. The corresponding mechanisms involved in each photocatalytic reaction are elaborated in detail. Finally, the review discusses the challenges and further directions faced by MOFs-derived nanomaterials in the field of photocatalysis, highlighting their potential role in advancing sustainable energy production and environmental remediation.

Multifunctional photocatalyst of graphitic carbon embedded with Fe2O3/Fe3O4 nanocrystals derived from lichen for efficient photodegradation of tetracycline and methyl blue

We propose a feasible and economical method of constructing biomass-based multifunctional photocatalysts with excellent adsorption performance and high photodegradation abilities toward tetracycline (TC) and methyl blue (MB) under visible light. A series of novel hybrids of porous graphitic carbon embedded with Fe2O3/Fe3O4 nanocrystals (denoted as Fe2O3/Fe3O4@C) were derived from lichen doped with different dosages of Fe3+ by calcination at 700°C under a N2 atmosphere. The Fe2O3/Fe3O4@C hybrids exhibited nanoflake-like shapes, mesoporous structures, and efficient visible light harvesting, thus indicating enhanced adsorption ability and photoactivity toward pollutants. The formed Fe2O3/Fe3O4 heterojunction improved the separation efficiency and inhibited the recombination of photogenerated carriers, whereas the carbon network improved the transfer of photogenerated electrons. Under optimised conditions, the Fe2O3/Fe3O4@C-1 hybrid demonstrated enhanced photodegradation efficiencies of 96.4% for TC and 100% for MB under visible light. In addition, electron spin resonance and trapping measurements were performed to identify active species and determine the photocatalytic mechanism toward pollutants. •O2- and •OH were the active species involved, playing critical roles in the TC and MB photodegradation processes. In addition, a bacterium test revealed that the products of TC degradation by Fe2O3/Fe3O4@C-1 showed low biological toxicity. This work provides a promising preparation strategy or biomass-based photocatalysts for application in environmental pollutant treatment.

Binder-Free MOF-Based and MOF-Derived Nanoarrays for Flexible Electrochemical Energy Storage: Progress and Perspectives

The fast development of Internet of Things and the rapid advent of next-generation versatile wearable electronics require cost-effective and highly-efficient electroactive materials for flexible electrochemical energy storage devices. Among various electroactive materials, binder-free nanostructured arrays have attracted widespread attention. Featured with growing on a conductive and flexible substrate without using inactive and insulating binders, binder-free 3D nanoarray electrodes facilitate fast electron/ion transportation and rapid reaction kinetics with more exposed active sites, maintain structure integrity of electrodes even under bending or twisted conditions, readily release generated joule heat during charge/discharge cycles and achieve enhanced gravimetric capacity of the whole device. Binder-free metal-organic framework (MOF) nanoarrays and/or MOF-derived nanoarrays with high surface area and unique porous structure have emerged with great potential in energy storage field and been extensively exploited in recent years. In this review, common substrates used for binder-free nanoarrays are compared and discussed. Various MOF-based and MOF-derived nanoarrays, including metal oxides, sulfides, selenides, nitrides, phosphides and nitrogen-doped carbons, are surveyed and their electrochemical performance along with their applications in flexible energy storage are analyzed and overviewed. In addition, key technical issues and outlooks on future development of MOF-based and MOF-derived nanoarrays toward flexible energy storage are also offered.

Enhancing the photocatalytic performance of a rutile unit featuring a titanium-oxide cluster by Pb2+ doping

Titanium-oxide clusters (TOCs) are well-defined molecular models for TiO2 materials and provide the opportunity to study the structure-activity relationships of TiO2. Here, we report a new Pb-doped TOC, Ti12Pb2, which resembles a two-layer decker of the {TiTi6} structural units of rutile TiO2 with two Ti4+ ions replaced by two Pb2+ ions. Its electronic structure, photoresponse, and photocatalytic performances were investigated and compared with those of the Ti14 cluster, which is isostructural to Ti12Pb2. Our results indicate that Pb2+ does not affect the electronic structure, but it greatly enhances the photocatalytic activity by improving the charge-separation and interfacial charge-transfer properties of the TOC. The successful synthesis of Ti12Pb2 highlights the roles of closed-shell heterometal ions in the construction of new TOCs. Our mechanism may be an inspiration for understanding the structure-activity relationships of closed-shell heterometal-doped TiO2.

Recent progress of MOF-functionalized nanocomposites: From structure to properties

Metal-organic frameworks (MOFs) are novel crystalline porous materials assembled from metal ions and organic ligands. The adaptability of their design and the fine-tuning of the pore structures make them stand out in porous materials. Furthermore, by integrating MOF guest functional materials with other hosts, the novel composites have synergistic benefits in numerous fields such as batteries, supercapacitors, catalysis, gas storage and separation, sensors, and drug delivery. This article starts by examining the structural relationship between the host and guest materials, providing a comprehensive overview of the research advancements in various types of MOF-functionalized composites reported to date. The review focuses specifically on four types of spatial structures, including MOFs being (1) embedded in nanopores, (2) immobilized on surface, (3) coated as shells and (4) assembled into hybrids. In addition, specific design ideas for these four MOF-based composites are presented. Some of them involve in situ synthesis method, solvothermal method, etc. The specific properties and applications of these materials are also mentioned. Finally, a brief summary of the advantages of these four types of MOF composites is given. Hopefully, this article will help researchers in the design of MOF composite structures.

g-C3N4/Ag@AgCl with Z-scheme heterojunction and Ag electron bridge for enhanced photocatalytic degradation of tetracycline wastewater

Building Z-scheme heterojunctions with an electron bridge is a favored function for increasing photocatalytic activity. A facile approach for preparing g-C3N4/Ag@AgCl ternary heterojunctions by co-precipitation and photoreduction was established in this work. First, via co-precipitation, AgCl was modified on the surface of g-C3N4 to create a broad contact area between AgCl and g-C3N4. The AgCl is then reduced to Ag via an in-situ photoreduction technique, resulting in the formation of a ternary composite. The experimental results showed that when g-C3N4 modified 25% of the Ag@AgCl, that is, g-C3N4/Ag@AgCl-25 had the best photocatalytic performance, 94.9% of TC was degraded within 240 min, and the reaction rate to TC was 0.1214 min-1, which was 4.49 times and 8.12 times higher than that of g-C3N4 and Ag/AgCl, respectively. The excellent photocatalytic performance of g-C3N4/Ag@AgCl is attributed to the LSPR effect of Ag NPs and O-doping g-C3N4, which broadens the absorbance performance of g-C3N4, the establishment of Z-type heterojunctions between AgCl NPs and g-C3N4 NSs and Ag NPs as an electron transport bridge accelerate the photogenerated electrons transfer between AgCl and g-C3N4.

Construction of Low-Cost Z-Scheme Heterojunction Cu2O/PCN-250 Photocatalysts Simultaneously for the Enhanced Photoreduction of CO2 to Alcohols and Photooxidation of Water

Solar-driven high-efficiency conversion of CO2 with water vapor into high-value-added alcohols is a promising approach for reducing CO2 emissions and achieving carbon neutrality. However, the rapid recombination of photogenerated carriers and low CO2 adsorption capacity of photocatalysts are usually the factors that limit their applicability. Herein, a series of low-cost Z-scheme heterostructures Cu2O/PCN-250-x are constructed by in situ growth of ultrasmall Cu2O nanoparticles on PCN-250. A systematic investigation revealed that there is a strong interaction between Cu2O nanoparticles and PCN-250. The resulting Cu2O/PCN-250-2 exhibits excellent photogenerated carrier separation efficiency and CO2 adsorption capacity, which dramatically promote the conversion of CO2 into alcohols. Notably, the total yield of 268 μmol gcat-1 for the production of CH3OH and CH3H2OH is superior to that of isolated PCN-250 and Cu2O. This study provides a new perspective for the design of a Cu2O nanoparticle/metal-organic framework Z-scheme heterojunction for the reduction of CO2 to alcohols with water vapor.

Controlled Partial Linker Thermolysis in Metal-Organic Framework UiO-66-NH2 to Give a Single-Site Copper Photocatalyst for the Functionalization of Terminal Alkynes

Metal-organic frameworks (MOFs) with expanding porosity and tailored pore environments are intriguing for catalytic applications. We report herein a straightforward method of controlled partial linker thermolysis to introduce desirable mesopores into mono-ligand MOFs, which is different from the classical thermolyzing method that starts from mixed-linker MOFs. UiO-66-NH2 , after partial ligand thermolysis, exhibits significant mesoporosity, retained crystal structure, improved charge photogeneration and abundant anchoring sites, which is ideal to explore single-site photocatalysis. Atomically dispersed Cu is then accommodated in the tailored pore. The resulting single-site Cu catalyst exhibits excellent performance for photocatalytic alkylation and oxidation coupling for the functionalization of terminal alkynes. The study highlights the advantage of controlled partial linker thermolysis to synthesize hierarchical MOFs to achieve the advanced single-site photocatalysis.

Application of a novel composite of Fe3O4@SiO2/PAEDTC surrounded by MIL-101(Fe) for photocatalytic degradation of penicillin G under visible light

The novel photocatalyst of Fe3O4@SiO2/PAEDTC@MIL-101(Fe) was prepared based on the sol-gel method, and its structure and morphology were determined by SEM mapping, TEM, XRD, FTIR, and N2 adsorption-desorption analyses. The photocatalytic activity of nanocomposite was evaluated in comparison with other particles as well as adsorption and photolysis processes. The effect of operating parameters showed that the complete degradation of penicillin G (PNG) can be provided at a photocatalyst dosage of 0.6 g/L, radiation intensity of 36 W, pH of 5, and time of 60 min. In the optimum condition, 84% TOC removal was attained and the BOD5/COD rate for the treated effluent was above 0.4, which was representative of the high biodegradability of the treated effluent compared to the raw sample. The findings of energy consumption showed that PNG can be easily and effectively treated by the photocatalytic process based on magnetic MIL-101(Fe) with electrical energy per order between 10 and 20.87 kWh/m3. Due to the excellent interaction between the MIL-101(Fe) and Fe3O4@SiO2/PAEDTC, the photocatalyst stability test showed a recyclability of the particles for 5 consecutive reaction cycles with a minimum reduction of 7%. Solution treated with photocatalyst under UV and visible light sources explained that the toxicity of the effluent after treatment is significantly reduced with the growth of Escherichia coli. Scavenging experiments showed that •OH radical and hole (h+) are the main agents in degrading PNG to CO2, H2O, and biodegradable and low-toxicity products. Finally, the findings of the diagnostic analysis and comparative experiments proved that with the interaction of Fe3O4@SiO2, NH2, and MIL-101(Fe), a lower band gap can be prepared for more absorption of photons and pollutant and also more and faster production of active radicals.

Thermally Induced Orderly Alignment of Porphyrin Photoactive Motifs in Metal-Organic Frameworks for Boosting Photocatalytic CO2 Reduction

Efficient transfer of charge carriers through a fast transport pathway is crucial to excellent photocatalytic reduction performance in solar-driven CO2 reduction, but it is still challenging to effectively modulate the electronic transport pathway between photoactive motifs by feasible chemical means. In this work, we propose a thermally induced strategy to precisely modulate the fast electron transport pathway formed between the photoactive motifs of a porphyrin metal-organic framework using thorium ion with large ionic radius and high coordination number as the coordination-labile metal node. As a result, the stacking pattern of porphyrin molecules in the framework before and after the crystal transformations has changed dramatically, which leads to significant differences in the separation efficiency of photogenerated carriers in MOFs. The rate of photocatalytic reduction of CO2 to CO by IHEP-22(Co) reaches 350.9 μmol·h-1·g-1, which is 3.60 times that of IHEP-21(Co) and 1.46 times that of IHEP-23(Co). Photoelectrochemical characterizations and theoretical calculations suggest that the electron transport channels formed between porphyrin molecules inhibit the recombination of photogenerated carriers, resulting in high performance for photocatalytic CO2 reduction. The interaction mechanism of CO2 with IHEP-22(Co) was clarified by using in-situ electron paramagnetic resonance, in-situ diffuse reflectance infrared Fourier transform spectroscopy, in-situ extended X-ray absorption fine structure spectroscopy, and theoretical calculations. These results provide a new method to regulate the efficient separation and migration of charge carriers in CO2 reduction photocatalysts and will be helpful to guide the design and synthesis of photocatalysts with superior performance for the production of solar fuels.

Guest-Induced Multilevel Charge Transport Strategy for Developing Metal-Organic Frameworks to Boost Photocatalytic CO2 Reduction

Encapsulating photogenerated charge-hopping nodes and space transport bridges within metal-organic frameworks (MOFs) is a promising method of boosting the photocatalytic performance. Herein, this work embeds electron transfer media (9,10-bis(4-pyridyl)anthracene (BPAN)) in MOF cavities to build multi-level electron transfer paths. The MOF cavities are accurately regulated to investigate the significance of the multi-level electron transfer paths in the process of CO2 photoreduction by evaluating the difference in the number of guest media. The prepared MOFs, {[Co(BPAN)(1,4-dicarboxybenzene)(H2 O)2 ]·BPAN·2H2 O} and {[Co(BPAN)2 (4,4'-biphenyldicarboxylic acid)2 (H2 O)2 ]·2BPAN·2H2 O} (denoted as BPAN-Co-1 and BPAN-Co-2), exhibit efficient visible-light-driven CO2 conversion properties. The CO photoreduction efficacy of BPAN-Co-2 (5598 µmol g-1  h-1 ) is superior to that of most reported MOF-based catalysts. In addition, the enhanced CO2 photoreduction ability is supported by density functional theory (DFT). This work illustrates the feasibility of realizing charge separation characteristics in MOF catalysts at the molecular level, and provides new insight for designing high-performance MOFs for artificial photosynthesis.

Photocatalytic Activity and Thermal Stability of Hybrid Metal-Polymer-Coordinated Complexes Derived from Gallic Acid and Ethylenediamine

Three new hybrid metal-polymer-coordinated complexes (MPCs) of copper(II), cobalt(II), and nickel(II) ions with an organic polymer derived from gallic acid and ethylenediamine (GAEtH) were synthesized. The structures of GAEtH and MPCs were characterized with FT-IR, ultraviolet (UV)-Vis, ¹H and ¹³C NMR spectroscopy, and elemental and thermogravimetric analysis. The results reveal that the organic polymer GAEtH exhibits an infinite one-dimensional chain structure, while the hybrid MPCs have a double chain structure, with the two chains joined by metal ions. The thermodynamic and kinetic parameters of the thermal degradation stages were determined by the Coats Redfern method, and the photocatalytic behaviors of the MPCs were investigated through the decomposition of methyl orange dye under UV irradiation.

Visible-Light-Driven Photocatalytic Dehydrogenation of Alcohols on TiO2 via Ligand-to-Metal Charge Transfer for Coproduction of H2 and Aldehydes

Developing visible-light-driven photocatalysts for the catalytic dehydrogenation of organics is of great significance for sustainable solar energy utilization. Here, we first report that aromatic alcohols could be efficiently split into H₂ and aldehydes over TiO₂ under visible-light irradiation through a ligand-to-metal charge transfer (LMCT) mechanism. A series of TiO₂ catalysts with different surface contents of the hydroxyl group (-OH) have been synthesized by controlling the hydrothermal and calcination synthesis methods. An optimal H₂ production rate of 18.6 μmol h^-1 is obtained on TiO₂ synthesized from the hydrothermal method with a high content of surface -OH. Experimental characterizations and comparison studies reveal that the surface -OH markedly influences the formation of LMCT complexes and thus changes the visible-light-driven photocatalytic performance. This work is anticipated to inspire further research endeavors in the design and fabrication of visible-light-driven photocatalyst systems based on the LMCT mechanism to realize the simultaneous synthesis of clean fuel and fine chemicals.

Electrocatalytic transformation of oxygen to hydroxyl radicals via three-electron pathway using nitrogen-doped carbon nanotube-encapsulated nickel nanocatalysts for effective organic decontamination

The selective electrochemical reduction of oxygen (O₂) via 3e^- pathway for the production of hydroxyl radicals (HO) is a promising alternative to conventional electro-Fenton process. Here, we developed a nitrogen-doped CNT-encapsulated Ni nanoparticle electrocatalyst (Ni@N-CNT) with high O₂ reduction selectivity for the generation of HO^•via 3e^- pathway. Exposed graphitized N on the CNT shell, and Ni nanoparticles encapsulated within the tip of the N-CNT, played a key role in the generation of H₂O₂ intermediate (*HOOH) via a 2e^- oxygen reduction reaction. Meanwhile, those encapsulated Ni nanoparticles at the tip of the N-CNT facilitated the sequential HO^• generation by directly decomposing the electrogenerated *H₂O₂ in a 1e^- reduction reaction on the N-CNT shell without inducing Fenton reaction. Improved bisphenol A (BPA) degradation efficiency were observed when compared with conventional batch system (97.5% vs 66.4%). Trials using Ni@N-CNT in a flow-through configuration demonstrated a complete removal of BPA within 30 min (k = 0.12 min^-1) with a limited energy consumption of 0.068 kW·h·g^-1 TOC.

Oxygen defects and S-scheme heterojunctions synergistically promote the photocatalytic hydrogen evolution activity and stability of WO2.72/Zn0.5Cd0.5S-DETA nanocomposites

The study analyzed the impact of oxygen defects and S-scheme heterojunction on the performance and stability of WO_2.72/Zn_0.5Cd_0.5S-DETA (WO/ZCS) nanocomposites photocatalysts for hydrogen evolution. Results showed that ZCS alone under visible light had good photocatalytic hydrogen evolution activity (1.762 mmol g^-1h^-1) and stability (79.5 % activity retention rate after seven cycles, 21 h). The WO₃/ZCS nanocomposites with S-scheme heterojunction had better hydrogen evolution activity (2.287 mmol g^-1h^-1), but poor stability (41.6 % activity retention rate). The WO/ZCS nanocomposites with S-scheme heterojunction and oxygen defects showed excellent photocatalytic hydrogen evolution activity (3.94 mmol g^-1h^-1) and stability (89.7 % activity retention rate). The specific surface area measurement and ultraviolet-visible spectroscopy diffuse reflectance spectroscopy indicate that oxygen defects lead to larger specific surface area and improved light absorption, respectively. The charge density difference confirms the existence of the S-scheme heterojunction and the amount of charge transfer, which accelerates the separation of photogenerated electron-hole pairs and enhances the utilization efficiency of light and charge. This study offers a new approach using the synergistic impact of oxygen defects and S-scheme heterojunction to enhance the photocatalytic hydrogen evolution activity and stability.

Construction of ZnIn2S4/MOF-525 heterojunction system to enhance photocatalytic degradation of tetracycline

Zirconium-based porphyrin metal organic frameworks (Zr-PMOFs) had attracted attention in the field of photocatalysis in recent years. However, the recombination of photogenerated carriers of monomer PMOF limits its performance of photocatalytic organic pollutants degradation. Metal sulfide has a suitable visible band gap, which can form a heterojunction with MOF materials to enhance the photocatalytic efficiency of MOF. Therefore, a typical metal sulfide semiconductor ZnIn₂S₄ (ZIS) was introduced into a Zr-MOF (MOF-525) by solvothermal method to prepare a series of ZIS/MOF-525 (ZIS/MOF-525-1, ZIS/MOF-525-2, ZIS/MOF-525-3 and ZIS/MOF-525-4) composite photocatalysts in this work. The results of characterization analysis, optical analysis and electrochemical analysis showed that the interface of ZIS/MOF-525 formed a typical type-II heterojunction, which accelerated the electron transport rate and effectively inhibited the recombination of photogenerated e^- and h⁺ in MOF-525. The optimal removal efficiency of tetracycline (TC) by ZIS/MOF-525-3 (the mass of MOF-525 is 30 mg) reached 93.8% under 60 min visible light illumination, which was greater than that of pure MOF-525 (37.2%) and ZnIn₂S₄ (70.0%), and it still maintained good stability after five cycles reusing experiment. This work provides feasible insight for the preparation of novel and efficient PMOF-based photocatalysts in the future.

Topologically Porous Heterostructures for Photo/Photothermal Catalysis of Clean Energy Conversion

As a straightforward way to fix solar energy, photo/photothermal catalysis with semiconductor provides a promising way to settle the energy shortage and environmental crisis in many fields, especially in clean energy conversion. Topologically porous heterostructures (TPHs), featured with well-defined pores and mainly composed by the derivatives of some precursors with specific morphology, are a major part of hierarchical materials in photo/photothermal catalysis and provide a versatile platform to construct efficient photocatalysts for their enhanced light absorption, accelerated charges transfer, improved stability, and promoted mass transportation. Therefore, a comprehensive and timely review on the advantages and recent applications of the TPHs is of great importance to forecast the potential applications and research trend in the future. This review initially demonstrates the advantages of TPHs in photo/photothermal catalysis. Then the universal classifications and design strategies of TPHs are emphasized. Besides, the applications and mechanisms of photo/photothermal catalysis in hydrogen evolution from water splitting and CO_x hydrogenation over TPHs are carefully reviewed and highlighted. Finally, the challenges and perspectives of TPHs in photo/photothermal catalysis are also critically discussed.

Interfacial intimacy and internal electric field modulated S-scheme Sv-ZnS/ZnIn2S4 photocatalyst for efficient H2 evolution and CO2 reduction

The construction of S-scheme heterojunctions is an effective approach to realize artificial photocatalytic processes. For the higher solar energy conversion efficiency, current research focuses on improving the interfacial intimacy and precisely modulating the strength of the internal electric field (IEF). To address this issue, we propose a novel MOF-based synthesis and derivation strategy. The heterojunction obtained by this strategy tends to form an intimate interface and a tunable IEF, which facilitates the transfer and separation of photogenerated carriers. Herein, a ZnS/ZnIn₂S₄ (ZIS) S-Scheme heterojunction containing sulfur vacancies (Sv) was successfully synthesized, and its good photocatalytic hydrogen evolution reaction (HER) and CO₂ reduction reaction (CO₂RR) activity confirmed the feasibility of this strategy. The prepared Sv-ZnS/ZIS exhibits an apparent quantum yield of 19.8 ± 1.0 % at 420 nm and a hydrogen evolution rate of 2912.3 ± 185.9 μmol g^-1h^-1, which is 9.0 and 33.6 times higher than pure ZIS and Sv-ZnS, respectively. Furthermore, the yield of photoreduction CO₂ to CO reaches 2075.7 ± 63.0 μmol g^-1h^-1 with a CO selectivity of 93.0 ± 0.8 %. This work provides new sights for the rational design and construction of S-scheme photocatalysts with sulfur vacancies for efficient photocatalysis.

Recent advances in Metal Organic Framework (MOF)-based hierarchical composites for water treatment by adsorptional photocatalysis: A review

Architecting a desirable and highly efficient nanocomposite for applications like adsorption, catalysis, etc. has always been a challenge. Metal Organic Framework (MOF)-based hierarchical composite has perceived popularity as an advanced adsorbent and catalyst. Hierarchically structured MOF material can be modulated to allow the surface interaction (external or internal) of MOF with the molecules of interest. They are well endowed with tunable functionality, high porosity, and increased surface area epitomizing mass transfer and mechanical stability of the fabricated nanostructure. Additionally, the anticipated optimization of nanocomposite can only be acquired by a thorough understanding of the synthesis techniques. This review starts with a brief introduction to MOF and the requirement for advanced nanocomposites after the setback faced by conventional MOF structures. Further, we discussed the background of MOF-based hierarchical composites followed by synthetic techniques including chemical and thermal treatment. It is important to rationally validate the successful nanocomposite fabrication by characterization techniques, an overview of challenges, and future perspectives associated with MOF-based hierarchically structured nanocomposite.

Constructing tightly integrated conductive metal-organic framework/covalent triazine framework heterostructure by coordination bonds for photocatalytic hydrogen evolution

The construction of tightly integrated heterostructures with metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) has been confirmed to be an effective way for improved hydrogen evolution. However, the reported tightly integrated MOF/COF hybrids were usually limited to the covalent connection of COFs with aldehyde groups and NH₂-MOF via Schiff base reaction, restricting the development of MOF/COF hybrids. Herein, a covalent triazine framework (CTF-1), a subtype of crystalline COFs, was integrated with a conductive two-dimensional (2D) MOF (Ni-CAT-1) by a novel coordinating connection mode for significantly enhanced visible-light-driven hydrogen evolution. The terminal amidine groups in the CTF-1 layers offer dual N sites for the coordination of metal ions, which provides the potential of coordinating connection between CTF-1 and Ni-CAT-1. The conductive 2D Ni-CAT-1 in Ni-CAT-1/CTF-1 hybrids effectively facilitates the separation of photogenerated carriers of CTF-1 component, and the resultant hybrid materials show significantly enhanced photocatalytic hydrogen evolution activity. In particular, the Ni-CAT-1/CTF-1 (1:19) sample exhibits the maximum hydrogen evolution rate of 8.03 mmol g^-1h^-1, which is about four times higher than that of the parent CTF-1 (1.96 mmol g^-1h^-1). The enhanced photocatalytic activity of Ni-CAT-1/CTF-1 is mainly attributed to the incorporation of conductive MOF which leads to the formation of a Z-Scheme heterostructure, promoting the electron transfer in hybrid materials. The coordinating combination mode of Ni-CAT-1 and CTF-1 in this work provides a novel strategy for constructing tightly integrated MOF/COF hybrid materials.

ZnO Nanoparticles Modified by Carbon Quantum Dots for the Photocatalytic Removal of Synthetic Pigment Pollutants

Synthetic pigment pollutants caused by the rapid development of the modern food industry have become a serious threat to people's health and quality of life. Environmentally friendly ZnO-based photocatalytic degradation exhibits satisfactory efficiency, but some shortcomings of large band gap and rapid charge recombination reduce the removal of synthetic pigment pollutants. Here, carbon quantum dots (CQDs) with unique up-conversion luminescence were applied to decorate ZnO nanoparticles to effectively construct the CQDs/ZnO composites via a facile and efficient route. The ZnO nanoparticles with a spherical-like shape obtained from a zinc-based metal organic framework (zeolitic imidazolate framework-8, ZIF-8) were coated by uniformly dispersive quantum dots. Compared with single ZnO particles, the obtained CQDs/ZnO composites exhibit enhanced light absorption capacity, decreased photoluminescence (PL) intensity, and improved visible-light degradation for rhodamine B (RhB) with the large apparent rate constant (k _app). The largest k _app value in the CQDs/ZnO composite obtained from 75 mg of ZnO nanoparticles and 12.5 mL of the CQDs solution (∼1 mg·mL^-1) was 2.6 times that in ZnO nanoparticles. This phenomenon may be attributed to the introduction of CQDs, leading to the narrowed band gap, an extended lifetime, and the charge separation. This work provides an economical and clean strategy to design visible-light-responsive ZnO-based photocatalysts, which is expected to be used for the removal of synthetic pigment pollutants in food industry.

Mechanistic investigation of cellulose regulating the morphology and photocatalytic activity of Al-doped ZnO

The morphology of metal oxide is a crucial factor for improving of catalysis properties. As a renewable and environmentally friendly biomass material, cellulose has been widely used to induce the morphology of semiconductors. The contributions of cellulose hydroxyl groups and spatial hindrance in tailoring Al doped ZnO (AZO) morphologies were investigated. The morphology of AZO could be gradually induced from flake-like to flower-like with the increase of cellulose hydroxyl content per unit volume. At the same time, the changes in spatial hindrance had no apparent effect on the morphology of AZO. So the cellulose hydroxyl groups that act to induce the in situ growth of AZO nanoparticles on cellulose substrates. The results further confirmed the strong interaction between cellulose hydroxyl groups and Zn²⁺. In addition, the photocatalytic activities of Al-doped ZnO/cellulose nanocomposites (AZOC) with different morphologies were evaluated by the degradation of bisphenol A (BPA). The high hydroxyl contents of cellulose substrates contributed to the growth of flower-like AZO with high light utilization and photocatalytic activity. This work proposed cleaner strategies to modify semiconductor morphologies for photocatalysis by regulating the content of cellulose hydroxyl contents.

MOF-Derived Defective Co3O4 Nanosheets in Carbon Nitride Nanocomposites for CO2 Photoreduction and H2 Production

In photocatalysis, especially in CO₂ reduction and H₂ production, the development of multicomponent nanomaterials provides great opportunities to tune many critical parameters toward increased activity. This work reports the development of tunable organic/inorganic heterojunctions comprised of cobalt oxides (Co₃O₄) of varying morphology and modified carbon nitride (CN), targeting on optimizing their response under UV-visible irradiation. MOF structures were used as precursors for the synthesis of Co₃O₄. A facile solvothermal approach allowed the development of ultrathin two-dimensional (2D) Co₃O₄ nanosheets (Co₃O₄-NS). The optimized CN and Co₃O₄ structures were coupled forming heterojunctions, and the content of each part was optimized. Activity was significantly improved in the nanocomposites bearing Co₃O₄-NS compared with the corresponding bulk Co₃O₄/CN composites. Transient absorption spectroscopy revealed a 100-fold increase in charge carrier lifetime on Co₃O₄-NS sites in the composite compared with the bare Co₃O₄-NS. The improved photocatalytic activity in H₂ production and CO₂ reduction is linked with (a) the larger interface imposed from the matching 2D structure of Co₃O₄-NS and the planar surface of CN, (b) improvements in charge carrier lifetime, and (c) the enhanced CO₂ adsorption. The study highlights the importance of MOF structures used as precursors in forming advanced materials and the stepwise functionalization of the individual parts in nanocomposites for the development of materials with superior activity.

Rational Construction of Metal Organic Framework Hybrid Assemblies for Visible Light-Driven CO2 Conversion

Photocatalytic reduction of CO₂ to value-added chemicals is known to be a promising approach for CO₂ conversion. The design and preparation of ideal photocatalysts for CO₂ conversion are of pivotal significance for the sustainable development of the whole society. In this work, we integrated two functional organic linkers to prepare a novel metal organic framework (MOF) photocatalyst {[Co(9,10-bis(4-pyridyl)anthracene)_0.5(bpda)]·4DMF} (Co-MOF). The existence of anthryl and amino groups leads to a wide range of visible light absorption and efficient separation of photogenerated electrons. To extend the lifetime of photogenerated electrons in the photocatalytic system, we modified Co-MOF particles onto g-C₃N₄. As expected, Co-MOF/g-C₃N₄ composites exhibited an ultrahigh selectivity (more than 97%) in the photocatalytic process, and the highest CO production rate (1824 μmol/g/h) was 7.1 and 27.2 times of Co-MOFs and g-C₃N₄, respectively. What's more, we also discussed the reaction mechanism of the Co-MOF/g-C₃N₄ photocatalytic CO₂ reduction, and this work paves the pathway for designing photocatalysts with ideal CO₂ reduction performance.

Femtosecond transient absorption spectroscopy investigation into the electron transfer mechanism in photocatalysis

Femtosecond transient absorption spectroscopy (fs-TAS) is a powerful technique for monitoring the electron transfer kinetics in photocatalysis. Several important works have successfully elucidated the electron transfer mechanism in heterojunction photocatalysts (HPs) using fs-TAS measurements, and thus a timely summary of recent advances is essential. This feature article starts with a thorough interpretation of the operating principle of fs-TAS equipment, and the fundamentals of the fs-TAS spectra. Subsequently, the applications of fs-TAS in analyzing the dynamics of photogenerated carriers in semiconductor/metal HPs, semiconductor/carbon HPs, semiconductor/semiconductor HPs, and multicomponent HPs are discussed in sequence. Finally, the significance of fs-TAS in revealing the ultrafast interfacial electron transfer process in HPs is summarized, and further research on the applications of fs-TAS in photocatalysis is proposed. This feature article will provide deep insight into the mechanism of the enhanced photocatalytic performance of HPs from the perspective of electron transfer kinetics.

The Therapeutic Potential of Algal Nanoparticles: A Brief Review

Recently, the green synthesis of metallic nanoparticles (NPs) has received tremendous attention as a simple approach. The green pathway of biogenic synthesis of metallic NPs through microbes may provide a sustainable and environmentally friendly protocol. Green technology is the most innovative technology for various biological activities and lacks toxic effects. Reports have shown the algae-mediated synthesis of metal NPs. Algae are widely used for biosynthesis as they grow fast; they produce biomass on average ten times that of plants and are easily utilized experimentally. In the future, the production of metal NPs by different microalgae and their biological activity can be explored in diverse areas such as catalysis, medical diagnosis, and anti-biofilm applications.

Progress and perspectives on 1D nanostructured catalysts applied in photo(electro)catalytic reduction of CO2

Reducing CO₂ into value-added chemicals and fuels by artificial photosynthesis (photocatalysis and photoelectrocatalysis) is one of the considerable solutions to global environmental and energy issues. One-dimensional (1D) nanostructured catalysts (nanowires, nanorods, nanotubes and so on.) have attracted extensive attention due to their superior light-harvesting ability, co-catalyst loading capacity, and high carrier separation rate. This review analyzed the basic principle of the photo(electro)catalytic CO₂ reduction reaction (CO₂ RR) briefly. The preparation methods and properties of 1D nanostructured catalysts are introduced. Next, the applications of 1D nanostructured catalysts in the field of photo(electro)catalytic CO₂ RR are introduced in detail. In particular, we introduced the design of composite catalysts with 1D nanostructures, for example loading 0D, 1D, 2D, and 3D materials on a 1D nanostructured semiconductor to construct a heterojunction to optimize the photo-response range, carrier separation and transport efficiency, CO₂ adsorption and activation capacity, and stability of the catalyst. Finally, the development prospects of 1D nanostructured catalysts are discussed and summarized. This review can provide guidance for the rational design of advanced catalysts for photo(electro)catalytic CO₂ RR.

Fast Cross-Linked Hydrogel as a Green Light-Activated Photocatalyst for Localized Biofilm Disruption and Brush-Free Tooth Whitening

Biofilm-driven caries and tooth discoloration are two major problems in oral health care. The current methods have the disadvantages of insufficient biofilm targeting and irreversible enamel damage. Herein, an injectable sodium alginate hydrogel membrane doped with bismuth oxychloride (Bi₁₂O₁₇Cl₂) and cubic cuprous oxide (Cu₂O) nanoparticles was designed to simultaneously achieve local tooth whitening and biofilm removal through a photodynamic dental therapy process. This fast cross-linked hydrogel could form a biofilm removal coating on the target tooth surface precisely. Afterward, reactive oxygen species was effectively released on demand under green light, which could not only eradicate the biofilm but also whiten the tooth non-destructively in a facile manner without significant damage to both the enamel and biological cells. After the usage, the removal of this hydrogel can also enhance the effect of biofilm destruction and caries prevention.

Derivatives of metal-organic frameworks for heterogeneous Fenton-like processes: From preparation to performance and mechanisms in wastewater purification - A mini review

Organic pollution is an ever-growing issue in aquatic environment, Fenton-like processes have gained widespread acceptance due to their high oxidative potential and environmental compatibility. Derivatives of metal-organic frameworks (MOFs) are emerging heterogeneous Fenton-like catalysts, which have advantages of large surface area, diversity of structures, and abundant active sites. This work focuses on the recent advances in MOFs derivatives including metal compounds and metal incorporated carbons for Fenton-like processes. First, preparation strategies, structures and compositions are introduced. And then, the removal of organic pollutant in Fenton, electro-Fenton, and photo-Fenton process catalyzed by MOFs derivative is summarized, respectively. The contents particularly devote efforts to build connections among preparation, structures, compositions, and performance. Furthermore, the mechanisms of improving performance are discussed in detail. Finally, the perspectives of MOFs derivatives toward Fenton-like applications are proposed.

Bimetallic Co-Mo sulfide/carbon composites derived from polyoxometalate encapsulated polydopamine-decorated ZIF nanocubes for efficient hydrogen and oxygen evolution

The increased call for carbon neutrality by 2050 makes it compelling to develop emission-free alternative energy sources. Green hydrogen produced from water electrolyzers using renewable electricity is of great importance, and the development of efficient transition-metal-based materials for hydrogen production by electrolysis is highly desirable. In this report, a new approach to produce defect-rich and ultra-fine bimetallic Co-Mo sulfides/carbon composites from polyoxometalates@ZIF-67@polydopamine nanocubes via carbonization/sulfurization, which are highly active for hydrogen and oxygen evolution reactions (HER and OER), have been successfully developed. The coating of polydopamine (PDA) on the surface of the acid-sensitive ZIF-67 cubes can prevent the over-dissociation of ZIF-67 caused by the encapsulated phosphomolybdic acid (PMA) etching through PDA chelating with the PMA molecules. Meanwhile, the partially dissociated Co²⁺ from ZIF-67 can be captured by the coated PDA via chelation, resulting in more evenly dispersed active sites throughout the heterogeneous composite after pyrolysis. The optimized bimetallic composite CoMoS-600 exhibits a prominent improvement in HER (with an overpotential of -0.235 V vs. RHE at a current density of 10 mA cm^-2) and OER performance (with an overpotential of 0.350 V vs. RHE at a current density of 10 mA cm^-2), due to the synergistic effect of ultra-fine defect-rich Co-Mo-S nanoparticle active sites and N,S-codoped porous carbons in the composites. Moreover, this synthesis approach can be readily expanded to other acidic polyoxometalates to produce HER and OER active bimetallic Co-W sulfide/carbon composites by replacing PMA with phosphotungstic acid. This new synthesis strategy to modify acid-sensitive ZIFs with selected compounds offers an alternative approach to develop novel transition metal sulfide/carbon composites for various applications.

Recent Progress in the Synthesis and Applications of Composite Photocatalysts: A Critical Review

Photocatalysis is an advanced technique that transforms solar energy into sustainable fuels and oxidizes pollutants via the aid of semiconductor photocatalysts. The main scientific and technological challenges for effective photocatalysis are the stability, robustness, and efficiency of semiconductor photocatalysts. For practical applications, researchers are trying to develop highly efficient and stable photocatalysts. Since the literature is highly scattered, it is urgent to write a critical review that summarizes the state-of-the-art progress in the design of a variety of semiconductor composite photocatalysts for energy and environmental applications. Herein, a comprehensive review is presented that summarizes an overview, history, mechanism, advantages, and challenges of semiconductor photocatalysis. Further, the recent advancements in the design of heterostructure photocatalysts including alloy quantum dots based composites, carbon based composites including carbon nanotubes, carbon quantum dots, graphitic carbon nitride, and graphene, covalent-organic frameworks based composites, metal based composites including metal carbides, metal halide perovskites, metal nitrides, metal oxides, metal phosphides, and metal sulfides, metal-organic frameworks based composites, plasmonic materials based composites and single atom based composites for CO₂ conversion, H₂ evolution, and pollutants oxidation are discussed elaborately. Finally, perspectives for further improvement in the design of composite materials for efficient photocatalysis are provided.

Post-synthetic modification of aluminum trimesate and copper trimesate with TiO2 nanoparticles for photocatalytic applications

Organic pollutants have been a significant source of concern in recent years due to their facile dissemination and harmful effects. In this work, two different metal-organic frameworks (MOFs) were initially prepared by hydrothermal treatment, namely aluminum trimesate (MIL-100(Al)) and copper trimesate (HKUST-1). These materials were subsequently submitted to a post-synthetic modification step to grow titania nanoparticles on their surface. Anatase nanoparticles with sizes around 5 nm were successfully anchored on MIL-100(Al), and the concentration of TiO₂ in this sample was about 68 wt.%. This is the first time that this composite (TiO₂@MIL-100(Al)) is reported in the literature. It showed an improved photocatalytic activity, removing 90% of methylene blue (k _app = 1.29 h^-1), 55% of sodium diclofenac (k _app = 0.21 h^-1), and 62% of ibuprofen (k _app = 0.37 h^-1) after four hours of illumination with UV-A light. A significant concentration (14 µM) of reactive oxygen species (ROS) was detected for this composite. HKUST-1 showed a structural collapse during its post-synthetic modification, leading to a non-porous material and providing fewer sites for the heterogeneous nucleation of titania. This behavior led to a low concentration of rutile nanoparticles on HKUST-1 (9 wt.%). However, the obtained composite (TiO₂@HKUST) also showed an improved photoactivity compared to HKUST-1, increasing the photodegradation rates evaluated for methylene blue (0.05 h^-1 vs. 0.29 h^-1), sodium diclofenac (negligible vs. 0.03 h^-1), and ibuprofen (0.01 h^-1 vs. 0.02 h^-1). This work brings new insights concerning the preparation of photocatalysts by growing semiconductor nanoparticles on trimesate-based MOFs.

Cerium versus zirconium UiO66 metal–organic frameworks coupled with CdS for H2 evolution under visible light

Metal–organic frameworks (MOFs) as highly porous photocatalysts have received increasing attention.

Hierarchically Porous ZnO/g-C3N4 S-Scheme Heterojunction Photocatalyst for Efficient H2O2 Production

The design of photocatalysts with hierarchical pore sizes is an effective method to improve mass transport, enhance light absorption, and increase specific surface area. Moreover, the construction of a heterojunction at the interface of two semiconductor photocatalysts with suitable band positions plays a crucial role in separating and transporting charge carriers. Herein, ZIF-8 and urea are used as precursors to prepare hierarchically porous ZnO/g-C₃N₄ S-scheme heterojunction photocatalysts through a two-step calcination method. This S-scheme heterojunction photocatalyst shows high activity toward photocatalytic H₂O₂ production, which is 3.4 and 5.0 times higher than that of pure g-C₃N₄ and ZnO, respectively. The mechanism of charge transfer and separation within the S-scheme heterojunction is studied by Kelvin probe, in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), and electron paramagnetic resonance (EPR). This research provides an idea of designing S-scheme heterojunction photocatalysts with hierarchical pores in efficient photocatalytic hydrogen peroxide production.