Photocatalytic active metal–organic framework and its derivatives for solar-driven environmental remediation and renewable energy

Boosted visible-light-induced photo-Fenton degradation of organic pollutants over a novel direct Z-scheme NH2-MIL-125(Ti)@FeOCl heterojunction catalyst

Improving the charge separation, charge transfer, and effective utilization is crucial in a photocatalysis system. Herein, we prepared a novel direct Z-scheme NH2-MIL-125(Ti)@FeOCl (Ti-MOF@FeOCl) composite photocatalyst through a simple method. The prepared composite catalyst was utilized in the photo-Fenton degradation of Rhodamine B (RhB) and ciprofloxacin (CIP). The Ti-MOF@FeOCl (10FeTi-MOF) catalyst exhibited the highest catalytic performance and degraded 99.1 and 66% of RhB and CIP, respectively. However, the pure NH2-MIL-125(Ti) (Ti-MOF) and FeOCl catalysts achieved only 50 and 92% of RhB and 50 and 37% of CIP, respectively. The higher catalytic activities of the Ti-MOF@FeOCl composite catalyst could be due to the electronic structure improvements, photoinduced charge separations, and charge transfer abilities in the catalyst system. The composite catalysts have also enhanced adsorption and visible light-responsive properties, allowing for efficient degradation. Furthermore, the electron paramagnetic resonance (EPR) signals, the reactive species trapping experiments, and Mott-Schottky (M - S) measurements revealed that the photogenerated superoxide radical (•O2-), hydroxyl radical (•OH), and holes (h+) played a vital role in the degradation process. The results also demonstrated that the Ti-MOF@FeOCl heterojunction composite catalysts could be a promising photo-Fenton catalyst system for the environmental remediation. Environmental implications The discharging of toxic contaminants such as organic dyes, antibiotics, and other emerging pollutants to the environment deteriorates the ecosystem. Specifically, the residues of organic pollutants recognized as a threat to ecosystem and a cause for carcinogenic effects. Among them, ciprofloxacin is one of antibiotics which has biological resistance, and metabolize partially in the human or animal bodies. It is also difficult to degrade ciprofloxacin completely with traditional treatment methods. Similarly, organic dyes are also toxic and a cause for carcinogenic effects. Therefore, effective degradation of organic pollutants such as RhB and ciprofloxacin with appropriate method is crucial.

Enhancement of Synergistic Photocatalytic Performance by Anchoring Cadmium Sulfide on Nanosphere Structured Coordination Polymers

Precisely tuning how and where a reaction occurs in a one-step selective system is important but challenging owing to the similar electronic environments in multiple active sites. In this work, highly selective and effective reaction sites were obtained by generating copper coordination polymers (Cu-CP) of a range of sizes and morphologies, from bulk solid crystals (1) to uniform nanosphere structures (1a), by controlling the amount of surfactant hexadecyl trimethylammonium bromide (CTAB). The results indicated that the morphology and size of the uniform nanosphere structures were affected by the proportion of CTAB; uniform distribution of nanosphere structures was achieved with a premade building carrier when the content of CTAB was 0.005 mmol, generating a well-established platform. Photocatalytic cadmium sulfide (CdS) was then immobilized on the surface of the premade platform unit 1a through an in situ process to generate CdS@1a composites with well-dispersed catalytic CdS active sites. Furthermore, the well-defined CdS@1a composite platform was utilized as photocatalysts to explore the selective one-step depolymerization reaction under blue-light irradiation. Notably, the CdS0.149@1a composite, which featured a unique structure with evenly dispersed, closely spaced catalytic sites, exhibiting remarkable photoelectrochemical behaviors for selective one-step depolymerization of lignin model substances to aromatic monomer phenol and acetophenone framework products. This work demonstrates the use of an inherently morphological process to construct outstanding photocatalysts that could enable a wide range of photocatalytic reactions.

A Review of Metal-Organic Frameworks Derived Hollow-Structured Photocatalysts: Synthesis and Applications

Photocatalysis is a most important approach to addressing global energy shortages and environmental issues due to its environmentally friendly and sustainable properties. The key to realizing efficient photocatalysis relies on developing appropriate catalysts with high efficiency and chemical stability. Among various photocatalysts, Metal-organic frameworks (MOFs)-derived hollow-structured materials have drawn increased attention in photocatalysis based on advantages like more active sites, strong light absorption, efficient transfer of pho-induced charges, excellent stability, high electrical conductivity, and better biocompatibility. Specifically, MOFs-derived hollow-structured materials are widely utilized in photocatalytic CO2 reduction (CO2RR), hydrogen evolution (HER), nitrogen fixation (NRR), degradation, and other reactions. This review starts with the development story of MOFs, the commonly adopted synthesis strategies of MOFs-derived hollow materials, and the latest research progress in various photocatalytic applications are also introduced in detail. Ultimately, the challenges of MOFs-derived hollow-structured materials in practical photocatalytic applications are also prospected. This review holds great potential for developing more applicable and efficient MOFs-derived hollow-structured photocatalysts.

Simple fluorochromic detection of chromium with ascorbic acid functionalized luminescent Bio-MOF-1

The bioaccumulation of various heavy metals in the environment and agriculture is posing serious hazards to human health. Hexavalent chromium is one of the most encountered heavy metal pollutants. The routine monitoring of Cr(VI) via simple methods assumes great analytical significance in sectors like environmental safety, food quality, etc. This study reports a novel biocompatible and luminescent metal-organic framework (ascorbic acid functionalized Bio-MOF-1) based "Turn-on" nanoprobe for rapid and sensitive optical detection of Cr(VI). Bio-MOF-1 has been synthesized, functionalized with ascorbic acid (AA), and then comprehensively characterized for its key material properties. The presence of Cr(VI) results in the photoluminescence recovery of Bio-MOF-1/AA. Using the above approach, Cr(VI) is detected over a wide concentration range of 0.02 to 20 ng mL-1, with the limit of detection being 0.01 ng mL-1. The nanoprobe is capable of detecting Cr(VI) in real water as well as in some spiked food samples. Hence, the ascorbic acid functionalized Bio-MOF-1 nanoprobe is established as a potential on-field detection tool for Cr(VI).

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.

Innovative enhancement of electron tunneling synergy in carbon-doped Ta2O5CuO photocatalyst with nematic liquid crystal for safe drinking water

This study focuses on enhancing the photocatalytic properties of carbon-doped Ta2O5CuO (C-Ta2O5CuO) nanocomposites for drinking water purification. The nanocomposites were fabricated by depositing C-Ta2O5CuO onto Nematic Liquid Crystal Polaroid (NLCP) obtained from a discarded laptop monitor, employing the sputter deposition method. The X-ray diffraction (XRD) and High-resolution transmission electron microscopy (HRTEM) determined the nanocomposite thin films' crystallinity and structural properties. The EDX and XPS analyses confirmed the elemental composition and reality of the Cu-incorporated Ta2O5 nanocomposites, respectively. The combination of electron tunneling enhancement provided by the NLCP and graphitic carbon led to exceptional photocatalytic performance. This was particularly evident in the efficient degradation of P-Rosaniline Hydrochloride (PRH) dye in an aqueous medium. C-Ta2O5CuO catalytic activities were estimated at various dye concentrations, repeatability, reusability with time, and kinetics. Coating's stability and long-term activity in photocatalysis reactions were also tested. Additionally, Cu present in the C-Ta2O5CuO and ˙OH radicals exhibited remarkable bactericidal activity. They displayed significant antibacterial efficacy against both gram-positive Escherichia coli (E. coli) and gram-negative Staphylococcus aureus (S. aureus) bacteria. These findings have significant implications for the development of advanced materials with potent photocatalytic and antibacterial properties, holding promise for improving drinking water quality and addressing environmental and health challenges.

Rational construction of visible-light-driven perylene diimides/Fe2O3@C derived from MIL-88A (Fe) heterojunction with S-scheme electron transfer pathway to activate peroxymonosulfate for degradation of antibiotics

The novel composite photocatalytic material perylene diimides/Fe2O3@C (PDIs/Fe2O3@C) was constructed by a simple hydrothermal-calcination method and an oil bath method. 20 % PDIs/Fe2O3@C displayed a 16.4-fold increase in the rate of tetracycline (TC) removal over Fe2O3@C at 8 min. The main factor that enhanced photocatalytic performance was due to the combination of PDIs with Fe2O3@C, which effectively improved the phenomenon during the self-assembly of highly agglomerative PDIs, increased the specific surface area of Fe2O3@C, exposed more reaction sites, and promoted the activation of peroxymonosulfate (PMS) by Fe2+/Fe3+; and secondly, the composite of two different materials, both organic and inorganic, which effectively promoted the photogenerated electron transfer and the separation of electron-hole pairs, the a new S-scheme electron transport pathway is formed, which effectively promoted the photogenerated electron transfer as well as the e--h+ separation, which was more favorable for the activation of PMS. The whole reaction pathway and product toxicity were thoroughly evaluated by Fukui function calculations, Liquid Chromatograph Mass Spectrometer (LC-MS), and Toxicity Estimation Software Tool (T.E.S.T.) simulation results, which demonstrated the rationality of the degradation pathway and the greatly reduced product toxicity. Moreover, the composites were effective and versatile for all other antibiotics (chlortetracycline (CTC), ciprofloxacin (CIP) and sulfadiazine (SDZ)). As an advanced oxidation process, the activation of PDIs/Fe2O3@C under visible light shows its potential application in pollutant degradation, which provides new perspectives and ideas for further effective treatment of real wastewater.

Visible light-driven oxidation of non-native substrate by laccase attached on Ru-based metal-organic frameworks

Light-induced electron transfer can broaden the substrate range of metalloenzyme. However, the efficiency of photo-enzyme coupling is limited by the poor combination of photosensitizer or photocatalyst with enzyme. Herein, we prepared the nano-photocatalyst MIL-125-NH2@Ru(bpy) by in site embedding ruthenium pyridine-diimine complex [Ru(bpy)3]2+ into metal organic frameworks MIL-125-NH2 and associated it with multicopper oxidase (MCO) laccase. Compared to [Ru(bpy)3]2+, the coupling efficiency of MIL-125-NH2@Ru(bpy)3 for enzymatic oxygen reduction increased by 35.7%. A series of characterizations confirmed that the amino group of laccase formed chemical bonds with the surface defects or hydrophobic groups of MIL-125-NH2@Ru(bpy)3. Consequently, the tight binding accelerated the quenching process and electron transfer between laccase and the immobilized ruthenium pyridine-diimine complex. This work would open an avenue for the synthesis of MOFs photocatalyst towards photo-enzyme coupling.

Vibrational dynamics as an essential determinant of the thermal stability of zinc zeolitic imidazolate lattices

Thermal stability and kinetics of zeolitic imidazolate frameworks (ZIFs) are crucial for their applications as energetic materials. Here, the effect of microscopic vibrational dynamics on the thermal stability of ZIFs is demonstrated by using simple tools. Specifically, we explored the thermal kinetics based on Flynn-Wall-Ozawa and Kissinger's methods. The study comprises a combination of structure-related effects such as topology, density, and alkyl substitution with respect to vibrational dynamics in ZIFs. The results exhibit a linear correlation between the vibrational dynamics of the linkers and activation energy, I.E. stabilization of ZIFs, in the polymorphic Zn(EtIm)2 series. At the same time, thermal destabilization was observed with the growing alkyl chain and was further probed by IR spectroscopy.

MOF-Based Photocatalytic Membrane for Water Purification: A Review

Photocatalytic membranes can effectively integrate membrane separation and photocatalytic degradation processes to provide an eco-friendly solution for efficient water purification. It is of great significance to develop highly efficient photocatalytic membranes driven by visible light to ensure the long-term stability of membrane separation systems and the maximum utilization of solar energy. Metal-organic framework (MOF) is an emerging photocatalyst with a well-defined structure and tunable chemical properties, showing a broad application prospect in the construction of high-performance photocatalytic membranes. Herein, this work provides a comprehensive review of recent advancements in MOF-based photocatalytic membranes. Initially, this work outlines the main tailoring strategies that facilitate the enhancement of the photocatalytic activity of MOF-based photocatalysts. Next, this work introduces commonly used methods for fabricating MOF-based photocatalytic membranes. Subsequently, this work discusses the application and mechanisms of MOF-based photocatalytic membranes toward organic pollutant degradation, metal ion removal, and membrane fouling mitigation. Finally, challenges in developing MOF-based photocatalytic membranes and their practical applications are presented, while also pointing out future research directions toward overcoming these existing limitations.

Ultrasonic processing of WO3 nanosheets integrated Ti3C2 MXene 2D-2D based heterojunctions with synergistic effects for enhanced water splitting and environmental remediation

This article describes a straightforward chemical procedure that involves hydrothermal and ultrasonic treatments to create a new 2D/2D ultrathin WO3/Ti3C2 heterojunctions. The features of the fabricated heterojunctions were characterized and examined by field emission electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), optical absorption spectroscopy (UV-Vis). By photodegrading an organic dye under the influence of visible light, the photocatalytic degradation capabilities of the heterojunctions were also investigated. The performance of WO3/Ti3C2 was superior to that of bare WO3, with a removal rate of 94% and a kinetic rate constant (k) that was approximately 3 times that of WO3. The creation of 2D/2D heterojunction was observed to encourage the spatial charge separation and increase the surface reactive sites, to result with the increased photocatalytic activity in WO3/Ti3C2 heterojunction. The photocurrent values discovered through photoelectrochemical studies further indicated Ti3C2's active function in enhancing water-splitting performance. The impedance analysis examined by an electrochemical method revealed that heterojunctions might be helpful in accelerating the migration of charges quickly to get the outcomes seen.

A review of metal-organic framework (MOF) materials as an effective photocatalyst for degradation of organic pollutants

Water plays a vital role in all aspects of life. Recently, water pollution has increased exponentially due to various organic and inorganic pollutants. Organic pollutants are hard to degrade; therefore, cost-effective and sustainable approaches are needed to degrade these pollutants. Organic dyes are the major source of organic pollutants from coloring industries. The photoactive metal-organic frameworks (MOFs) offer an ultimate strategy for constructing photocatalysts to degrade pollutants present in wastewater. Therefore, tuning the metal ions/clusters and organic ligands for the better photocatalytic activity of MOFs is a tremendous approach for wastewater treatment. This review comprehensively reports various MOFs and their composites, especially POM-based MOF composites, for the enhanced photocatalytic degradation of organic pollutants in the aqueous phase. A brief discussion on various theoretical aspects such as density functional theory (DFT) and machine learning (ML) related to MOF and MOF composite-based photocatalysts has been presented. Thus, this article may eventually pave the way for applying different structural features to modulate novel porous materials for enhanced photodegradation properties toward organic pollutants.

Reticular framework materials for photocatalytic organic reactions

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

Impact of Cobalt Doping on the Structural, Optical, and Dielectric Properties of MgAl2O4 Spinel Material

Nanomaterials (NMs) with structural, optical, and dielectric properties are called functional or smart materials and have favorable applications in various fields of material science and nanotechnology. Pure and Co-doped MgAl2O4 were synthesized by using the sol-gel combustion method. A systematic investigation was carried out to understand the effects of the Co concentration on the crystalline phase, morphology, and optical and dielectric properties of Co-doped MgAl2O4. X-ray diffraction confirmed the cubic spinel structure with the Fd3̅m space group, and there was no impurity phase, while the surface morphology of the samples was investigated by scanning electron microscopy. The dielectric properties of the synthesized material are investigated using an LCR meter with respect to the variation in frequency (1-2 GHz), and their elemental composition has been examined through the energy-dispersive X-ray technique. The existence of the metal-oxygen Mg-Al-O bond has been confirmed by Fourier transform infrared spectroscopy. The value of the dielectric constant decreases with the increasing frequency and Co concentration. The optical behaviors of the Co2+-doped MgAl2O4 reveal that the optical properties were enhanced by increasing the cobalt concentration, which ultimately led to a narrower band gap, which make them exquisite and suitable for energy storage applications, especially for super capacitors. This work aims to focus on the effect of cobalt ions in different concentrations on structural, optical, and dielectric properties.

Recent progress on plant extract-mediated biosynthesis of ZnO-based nanocatalysts for environmental remediation: Challenges and future outlooks

The plant extract mediated green synthesis of nanomaterials has attracts enormous interest due to its cost-effectiveness, greener, and environmentally friendly. It is also considered as an alternative and facile method in which the phytochemicals can be used as a natural capping and reducing agents and helped to produce nanomaterials with high surface area, different sizes, and shapes. One of the materials fabricated using green methods is zinc oxide (ZnO) semiconductor due to its enormous applications in different field areas. In this review, an overview of recent progress on green synthesized ZnO-based catalysts and various modification methods for the purpose of enhancing the catalytic activity of ZnO and the corresponding structural-activity and interactions towards the removal of pollutants are highlighted. Particularly, the plant extract mediated ZnO-based photocatalysts application for the removal of pollutants via photocatalytic degradation, reduction reaction, and adsorption mechanism are demonstrated. Besides, the opportunities, challenges, and future outlooks of ZnO-based materials for environmental remediation with green and sustainable methods are also included. We believe that this review is a timely and comprehensive review on the recent progress related to plant extract mediated ZnO-based nanocatalysts synthesis and applications for environmental remediation.

Effect of Functional Group Modifications on the Photocatalytic Performance of g-C3 N4

In recent years, photocatalysis has received increasing attention in alleviating energy scarcity and environmental treatment, and graphite carbon nitride (g-C₃ N₄ ) is used as an ideal photocatalyst. However, it still remains numerous challenges to obtain the desirable photocatalytic performance of intrinsic g-C₃ N₄ . Functional group functionalization, formed by introducing functional groups into the bulk structure, is one of the common modification techniques to modulate the carrier dynamics and increases the number of active sites, offering new opportunities to break the limits for structure-to-performance relationship of g-C₃ N₄ . Nevertheless, the general overview of the advance of functional group modification of g-C₃ N₄ is less reported yet. In order to better understand the structure-to-performance relationship at the molecular level, a review of the latest development of functional group modification is urgently needed. In this review, the functional group modification of g-C₃ N₄ in terms of structures, properties, and photocatalytic activity is mainly focused, as well as their mechanism of reaction from the molecular level insights is explained. Second, the recent progress of the application of introducing functional groups in g-C₃ N₄ is introduced and examples are given. Finally, the difficulties and challenges are presented, and based on this, an outlook on the future research development direction is shown.

Efficient photocatalytic hydrogen peroxide production induced by the strong internal electric field of all-organic S-scheme heterojunction

Light-driven reaction of oxygen and water to hydrogen peroxide (H₂O₂) is an environmental protection method, which can convert solar energy into green products. In this work, perylene-3, 4, 9, 10-tetracarboxylic diimide (PDINH) could be recrystallized in situ on the surface of porous carbon nitride (PCN), to obtain an all-organic S-scheme heterojunction (PDINH/PCN). The design of the hierarchical porous photocatalyst improved the mass transfer, enhanced the light absorption and increased specific surface area. Moreover, the construction of the S-scheme heterojunction at the interface of PDINH and PCN exhibited suitable band, which facilitated the separation and transfer of carriers. The H₂O₂ production rate was up to 922.4 μmol g^-1h^-1, which was 2.6 and 53.3 times higher than that of PCN and PDINH. Therefore, the all-organic S-scheme heterojunction provides an insight for improving the photocatalytic H₂O₂ production.

Water stable MOFs as emerging class of porous materials for potential environmental applications

Metal-organic frameworks (MOFs) are extensively recognized for their wide applications in a variety of fields such as water purification, adsorption, sensing, catalysis and drug delivery. The fundamental characteristics of the majority of MOFs, such as their structure and shape, are known to be sensitively impacted by water or moisture. As a result, a thorough evaluation of the stability of MOFs in respect to factors linked to these property changes is required. It is quite rare for MOFs in their early stages to have strong water-stability, which is necessary for the commercialization and development of wider applications of this interesting material. Also, numerous applications in presence of water have progressed considerably as a "proof of concept" stage in the past and a growing number of water-stable MOFs (WSMOFs) have been discovered in recent years. This review discusses the variables and processes that affect the aqueous stability of several MOFs, including imidazolate and carboxylate frameworks. Accordingly, this article will assist researchers in accurately evaluating how water affects the stability of MOFs so that effective techniques can be identified for the advancement of water-stable metal-organic frameworks (WSMOFs) and for their effective applications toward a variety of fields.

Photocatalytic reduction of low-concentration CO2 by metal-organic frameworks

Direct conversion of diluted CO₂ to value-added chemical stocks and fuels with solar energy is an energy-saving approach to relieve global warming and realize a carbon-neutral cycle. The exploration of catalysts with both efficient CO₂ adsorption and reduction ability is significant to achieving this goal. Metal-organic frameworks (MOFs) are emerging in the field of low-concentration CO₂ reduction due to their highly tunable structure, high porosity, abundant active sites and excellent CO₂ adsorption capacity. This highlight outlines the advantages of MOFs for low-pressure CO₂ adsorption and the strategies to improve the photocatalytic performance of MOF materials at low CO₂ concentrations, including the functionalization of organic ligands, regulation of metal nodes and preparation of MOF composites or derivatives. This paper aims to provide possible avenues for the rational design and development of catalysts with the ability to reduce low-concentration CO₂ efficiently for practical applications.

Recent Progress of Metal-Organic Frameworks and Metal-Organic Frameworks-Based Heterostructures as Photocatalysts

In the field of photocatalysis, metal-organic frameworks (MOFs) have drawn a lot of attention. MOFs have a number of advantages over conventional semiconductors, including high specific surface area, large number of active sites, and an easily tunable porous structure. In this perspective review, different synthesis methods used to prepare MOFs and MOFs-based heterostructures have been discussed. Apart from this, the application of MOFs and MOFs-based heterostructures as photocatalysts for photocatalytic degradation of different types of pollutants have been compiled. This paper also highlights the different strategies that have been developed to modify and regulate pristine MOFs for improved photocatalytic performance. The MOFs modifications may result in better visible light absorption, effective photo-generated charge carriers (e-/h+), separation and transfer as well as improved recyclability. Despite that, there are still many obstacles and challenges that need to be addressed. In order to meet the requirements of using MOFs and MOFs-based heterostructures in photocatalysis for low-cost practical applications, future development and prospects have also been discussed.