Photocatalytic degradation of organic pollutants by MOFs based materials: A review

Metal framework functionalized with nitro groups and chitosan composite adsorption of Congo red

Dye pollution is a significant global environmental issue. To address this problem, various adsorbents have been employed, but traditional adsorbents often suffer from poor reusability and limited adsorption efficiency. Metal-organic frameworks (MOFs), which have emerged in recent years, have excellent physicochemical properties, but their application in wastewater treatment is limited by their polycrystalline, powdered state. In this paper, nitro functional groups were added to MIL-88B. The specific surface area of MIL-88B-NO2 obtained after the treatment was 660.98 m2/g, which was enhanced by 80 % compared with MIL-88B, with more excellent physicochemical properties. Subsequently, MIL-88B-NO2 was combined with chitosan to form the MIL-88B-NO2/CS aerogel, which addressed the problem of difficult separation of MOFs from water. The maximum adsorption amount of the aerogel for Congo Red (CR) was 878.8 mg/g. The adsorption process of CR by the adsorbent designed in this paper is consistent with the pseudo-second-order kinetic model and the Sips model, indicating that it is a complex physicochemical process. The adsorption mechanism is mainly synergistic with the effects of π-π conjugation, electrostatic attraction and hydrogen bonding. MIL-88B-NO2/CS aerogel demonstrated excellent reusability, maintaining a CR removal rate of 80 % after five adsorption-desorption cycles, indicating its promising application in dye removal.

Molecular imprinted photoresponse hybrid biocatalyst for ultrasensitive glutamate detection

A novel construction strategy for hybrid nanobiocatalyst was developed in this study by combining molecular imprinting technology with Fe3O4 nanoparticles hybrid MOF and enzyme immobilization technology. The impacts of molecular imprinting and the photothermal effect of Fe3O4 were investigated on the catalytic performance of the hybrid nanobiocatalyst. It was demonstrated that Fe3O4 nanoparticles exhibited a photothermal effect when exposed to multi-wavelength light. Leveraging the selective recognition ability of the molecular imprinting technique, the hybrid nanobiocatalyst showed a 15.8 % increase in catalytic activity for glutamate oxidase. Furthermore, under the influence of red light (650 nm), the photothermal effect induced by Fe3O4 accelerated the enzymatic reaction rate, resulting in a 23 % increase in enzyme activity. Benefiting from the specific recognition of the substrate by the Fe3O4 imprinted polymer, the hybrid nanobiocatalyst exhibited the rapid and highly sensitive detection of glutamate. Notably, this work provides an efficient strategy for constructing hybrid nanobiocatalyst with excellent properties.

Perovskite Type ABO3 Oxides in Photocatalysis, Electrocatalysis, and Solid Oxide Fuel Cells: State of the Art and Future Prospects

Since photocatalytic and electrocatalytic technologies are crucial for tackling the energy and environmental challenges, significant efforts have been put into exploring advanced catalysts. Among them, perovskite type ABO3 oxides show great promising catalytic activities because of their flexible physical and chemical properties. In this review, the fundamentals and recent progress in the synthesis of perovskite type ABO3 oxides are considered. We describe the mechanisms for electrocatalytic oxygen evolution reactions (OER), oxygen reduction reactions (ORR), hydrogen evolution reactions (HER), nitrogen reduction reactions (NRR), carbon dioxide reduction reactions (CO2RR), and metal-air batteries in details. Furthermore, the photocatalytic water splitting, CO2 conversion, pollutant degradation, and nitrogen fixation are reviewed as well. We also stress the applications of perovskite type ABO3 oxides in solid oxide fuel cells (SOFs). Finally, the optimization of perovskite type ABO3 oxides for applications in various fields and an outlook on the current and future challenges are depicted. The aim of this review is to present a broad overview of the recent advancements in the development of perovskite type ABO3 oxides-based catalysts and their applications in energy conversion and environmental remediation, as well as to present a roadmap for future development in these hot research areas.

Environmental applications of metal-organic framework-based three-dimensional macrostructures: a review

Metal-organic frameworks (MOFs) hold considerable promise for environmental remediation owing to their exceptional performance and distinctive structure. Nonetheless, the practical implementation of MOFs encounters persistent technical hurdles, notably susceptibility to loss, challenging recovery, and potential environmental toxicity arising from the fragility, insolubility, and poor processability of MOFs. MOF-based three-dimensional macrostructures (3DMs) inherit the advantageous attributes of the original MOFs, such as ultra-high specific surface area, tunable pore size, and customizable structure, while also incorporating the intriguing characteristics of bulk materials, including hierarchical structure, facile manipulation, and structural flexibility. Consequently, they exhibit rapid mass transfer and exceptional practicality, offering extensive potential applications in environmental remediation. This review presents a comprehensive overview of recent advancements in utilizing MOF-based 3DMs for environmental remediation, encompassing their fascinating characteristics, preparation strategies, and characterization methods, and highlighting their exceptional performance in pollutant adsorption, catalysis, and detection. Furthermore, existing challenges and prospects are presented to advance the utilization of MOF-based materials across various domains, particularly in environmental remediation.

Integrating Ni-MOF/g-C3N4/chitosan derived S-scheme photocatalyst for efficient visible light photodegradation of tetracycline and antibacterial activities

Nickel MOF (Ni-MOF) nanoparticles were successfully anchored onto a polymeric graphitic carbon nitride (g-C3N4) and Chitosan nanostructure (NS) using an eco-friendly and straightforward synthesis method. These newly fabricated photocatalysts were thoroughly characterized with standard techniques, revealing that the nanoscale Ni-MOF particles were uniformly deposited on the sheet-like g-C3N4 matrix. This configuration demonstrated excellent antimicrobial properties and outstanding photodegradation of tetracycline hydrochloride under visible light exposure. The MOF@GC photocatalyst exhibited robust bactericidal activity against pathogens like Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Additionally, it achieved superior visible-light-driven degradation of tetracycline in a significantly shorter time compared to other studies, with approximately 96% of the tetracycline being degraded in just 70 min under visible light. These findings suggest that the effective deposition of Ni-MOF onto the g-C3N4 structure reduces the recombination rate of photogenerated electrons and holes, thereby enhancing the photocatalytic efficiency of pure g-C3N4 under visible light. The proposed catalytic mechanism, informed by valence band (VB) and conduction band (CB) data from cyclic voltammetry measurements, further supports this conclusion. The MOF@GC photocatalyst is a promising nanostructured material for antimicrobial applications and visible-light-driven photocatalysis.

Integrating sodium cholate-modified MOF hybrid lipase and solubilization of hydrophobic candidates into a step for liganding fishing lipase inhibitors from Nelumbinis Folium

Enzyme immobilization by metal organic frameworks (MOFs) is an efficient way for screening active constituents in natural products. However, the enzyme's biocatalysis activity is usually decreased due to unfavorable conformational changes during the immobilization process. In this study, sodium cholate was firstly used as the modifier for zeolitic imidazolate framework-8 (ZIF-8) immobilized lipase to increase both the stability and activity. More importantly, with the help of solubilization of sodium cholate, a total of 3 flavonoids and 6 alkaloids candidate compounds were fished out. Their structures were identified and the enzyme inhibitory activities were verified. In addition, the binding information between the candidate compound and the enzyme was displayed by molecular docking. This study provides valuable information for the improvement of immobilized enzyme activity and functional active ingredients in complicated medicinal plant extracts.

Thoughts on the Rational Design of MOF-Guest Interactions for Future Intelligent Materials

The MOF-guest relationship is broken down in elementary phases, descriptors, and parameters. These descriptors and parameters allow precise descriptions of processes, whether they occur at the point when the guest enters the MOF, during the stay, or at the point of exiting. Description of these three phases is possible according to the location of the guest inside the MOF, the activity between MOF and guest, whether stimuli can be used, and whether a selective action can be exercised. The vocabulary provided herein can be useful to better formulate requirements when designing host-guest interactions in, and building new classes of, intelligent materials.

Applying molecular oxygen for organic pollutant degradation: Strategies, mechanisms, and perspectives

Molecular oxygen (O2) is an environmentally friendly, cost-effective, and non-toxic oxidant. Activation of O2 generates various highly oxidative reactive oxygen species (ROS), which efficiently degrade pollutants with minimal environmental impact. Despite extensive research on the application of O2 activation in environmental remediation, a comprehensive review addressing this topic is currently lacking. This review provides an informative overview of recent advancements in O2 activation, focusing on three primary strategies: photocatalytic activation, chemical activation, and electrochemical activation of O2. We elucidate the respective mechanisms of these activation methods and discuss their advantages and disadvantages. Additionally, we thoroughly analyze the influence of oxygen supply, reactive temperature, and pH on the O2 activation process. From electron transfer and energy transfer perspectives, we explore the pathways for ROS generation during O2 activation. Finally, we address the challenges faced by researchers in this field and discuss future prospects for utilizing O2 activation in pollution control applications. This detailed analysis enhances our understanding and provides valuable insights for the practical implementation of organic pollutant degradation.

A new UiO-66-NH2 MOF-based nano-immobilized DFR enzyme as a biocatalyst for the synthesis of anthocyanidins

Anthocyanidins and anthocyanins are one subclass of flavonoids in plants with diverse biological functions and have health-promoting effects. Dihydroflavonol 4-reductase (DFR) is one of the important enzymes involved in the biosynthesis of anthocyanidins and other flavonoids. Here, a new MOF-based nano-immobilized DFR enzyme acting as a nano-biocatalyst for the production of anthocyanidins in vitro was designed. We prepared UiO-66-NH2 MOF nano-carrier and recombinant DFR enzyme from genetic engineering. DFR@UiO-66-NH2 nano-immobilized enzyme was constructed based on covalent bonding under the optimum immobilization conditions of the enzyme/carrier ratio of 250 mg/g, 37 °C, pH 6.5 and fixation time of 10 min. DFR@UiO-66-NH2 was characterized and its catalytic function for the synthesis of anthocyanidins in vitro was testified using UPLC-QQQ-MS analysis. Compared with free DFR enzyme, the enzymatic reaction catalyzed by DFR@UiO-66-NH2 was more easily for manipulation in a wide range of reaction temperatures and pH values. DFR@UiO-66-NH2 had better thermal stability, enhanced adaptability, longer-term storage, outstanding tolerances to the influences of several organic reagents and Zn2+, Cu2+ and Fe2+ ions, and relatively good reusability. This work developed a new MOF-based nano-immobilized biocatalyst that had a good prospect of application in the green synthesis of anthocyanins in the future.

2D Porphyrin-Based Covalent-Organic Framework/PEG Composites: A Rational Strategy for Photocatalytic Hydrogen Evolution

Two-dimensional porphyrin-based covalent-organic frameworks (2D-por-COFs) have gained significant attention as attractive platforms for efficient solar light conversion into hydrogen production. Herein, it is found that introducing transition metal zinc and polyethylene glycol (PEG) into 2D-por-COFs can effectively improve the photocatalytic hydrogen evolution performance. The photocatalytic hydrogen evolution rate of ZnPor-COF is 2.82 times higher than that of H2Por-COF. Moreover, ZnPor-COF@PEG has the highest photocatalytic hydrogen evolution efficiency, which is 1.31 and 3.7 times that of pristine ZnPor-COF and H2Por-COF, respectively. The filling of PEG makes the layered structure of COFs more stable. PEG reduces the distortion and deformation of the carbon skeleton after the experiment of photocatalytic hydrogen evolution. The layered stacking and crystallization of 2D-por-COFs are also enhanced. Meanwhile, the presence of PEG also accelerates the transfer of excited electrons and enhances the photocatalytic hydrogen evolution activity. This strategy will provide valuable insights into the design of 2D-por-COFs as efficient solid photocatalysts for solar-driven hydrogen production.

Recent advances in photocatalytic nanomaterials for environmental remediation: Strategies, mechanisms, and future directions

Innovative and efficient strategies are urgently needed for wastewater treatment and environmental remediation. The photocatalytic degradation properties of photo-responsive nanomaterials (NMs) have become a prime candidate due to their low negative impact and photo-adjustability. Photocatalytic NMs vary in their degradation of different pollutants depending on the type of synthetic material, excitation light source, and physicochemical properties. Essentially, photocatalytic NMs excited by light produce reactive oxygen species (ROS) or metal ions that can degrade complex structure pollutants. Therefore, this review summarises the recent advances of photocatalytic NMs in the environmental application within the last 3 years, focusing on the development schemes, structural analyses, photocatalytic mechanisms, and the degradation effects of dyes, antibiotics, pesticides, phenolic compounds, metals, hormones, and other contaminants. The limitations and future directions are also explained. This review hopes to provide a possible pathway for the subsequent development of novel and efficient photocatalytic NMs to cope with complex and variable polluted environments.

Construction of Ternary Ce Metal-Organic Framework/Bi/BiOCl Heterojunction towards Optimized Photocatalytic Performance

Photocatalysis is the most promising green approach to solve antibiotic pollution in water, but the actual treatment effect is limited by photocatalytic activity. Herein, Bi and BiOCl were loaded onto the surface of Ce-MOF (metal-organic framework) using an electrostatic adsorption method, and a special ternary heterojunction of Ce/Bi/BiOCl was successfully prepared as a photocatalyst for the degradation of tetracycline (TC). FTIR demonstrated that the obtained photocatalyst contains functional groups such as -COOH belonging to Ce-MOF and characteristic crystal planes of Bi and BiOCl, indicating the successful construction of a ternary photocatalyst. The results of UV-vis absorption spectra confirm that the band gap of Ce/Bi/BiOCl heterojunction is reduced from 3.35 eV to 2.7 eV, resulting in an enhanced light absorption capability in the visible light region. The special ternary heterojunction constructed by Ce-MOF, Bi, and BiOCl could achieve a narrow band gap and reasonable band structure, thereby enhancing the separation of photogenerated charges. Consequently, the photocatalytic performance of the Ce/Bi/BiOCl ternary heterojunction was significantly enhanced compared to Ce-MOF, Bi, and BiOCl. Therefore, Ce/Bi/BiOCl can achieve a photocatalytic degradation rate of 97.7% within 20 min, which is much better than Bi (14.8%) and BiOCl (67.9%). This work successfully constructed MOF-based ternary photocatalysts and revealed the relationship between ternary heterojunctions and photocatalytic activity. This provides inspiration for constructing other heterogeneous catalysts for use in the field of photocatalysis.

Ti4+ Ions-Doped Metal-Organic Framework (MOF-74) for Photoreduction of Carbon Dioxide

The development of efficient and sustainable methods for reducing carbon dioxide (CO2) and converting it into valuable hydrocarbons has gained significant attention. In this study, researchers focused on Ti4+-doped metal-organic framework (MOF-74) photocatalysts. The incorporation of Ti4+ ions into the MOF-74 structure was achieved through a one-pot hydrothermal method. By replacing Zn2+ ions with Ti4+ ions in a substitutional manner, researchers have aimed to enhance the photocatalytic activity of the CO2 reduction. The obtained Ti4+-doped MOF-74 photocatalysts exhibited a significantly improved performance in the reduction of CO2 into carbon monoxide (CO). The doping of Ti4+ ions induced energy bands below the conduction band minimum (CBM) of MOF-74, extending the visible response range and enabling the photocatalysts to utilize a broader spectrum of light for catalytic reactions. This extension of the visible response range enables photocatalysts to utilize a broader spectrum of light for catalytic reactions. The incorporation of Ti4+ ions not only extends the visible response range but also suppresses charge carrier recombination. This work provides valuable insights into the design principles of MOF-based photocatalysts and paves the way for their practical implementation in addressing the energy crisis and reducing greenhouse gas emissions.

A review on development and modification strategies of MOFs Z-scheme heterojunction for photocatalytic wastewater treatment, water splitting, and DFT calculations

Increasing water pollution and decreasing energy reserves have emerged as growing concerns for the environment. These pollution are due to the dangerous effects of numerous pollutants on humans and aquatic organisms, such as hydrocarbons, biphenyls, pesticides, dyes, pharmaceuticals, and metal ions. On the other hand, the need for a clean environment, finding alternatives to fossil and renewable fuels is very important. Hydrogen (H2) is regarded as a viable and promising substitute for fossil fuels, and a range of methodologies have been devised to generate this particular source of energy. Metal-organic frameworks (MOFs) are a new generation of nanoporous coordination polymers whose crystal structure is composed of the juxtaposition of organic and inorganic constituent units. Due to their flexible nature, regular structure, and high surface area, these materials have attracted much attention for removing various pollutants from water and wastewater, and water splitting. MOFs Z-scheme heterojunctions have been identified as an economical and eco-friendly method for eliminating pollutants from wastewater systems, and producing H2. Their low-cost synthesis and unique properties increase their application in various energy and environment fields. The heterojunctions possess diverse properties, such as exceptional surface area, making them ideal for degradation and separation. The development and formulation of Z-scheme heterojunctions photocatalytic systems using MOFs, which possess stable and potent redox capability, have emerged as a successful approach for addressing environmental pollution and energy shortages in recent times. Through the utilization of the benefits offered by MOFs Z-scheme heterojunctions photocatalysts, such as efficient separation and migration of charge carriers, extensive spectrum of light absorption, among other advantages, notable enhancements can be attained. This review encompasses the synthesis techniques, structure, and properties of MOFs Z-scheme heterojunctions, and their extensive use in treating various wastewaters, including dyes, pharmaceuticals, and heavy metals, and water splitting. Also, it provides an overview of the mechanisms, pathways, and various theoretical and practical aspects for MOFs Z-scheme heterojunctions. Finally, it thoroughly assesses existing challenges and suggests further research on the promising applications of MOFs Z-scheme in industrial-scale wastewater treatment.

Density functional theory-based screening of Ti4C3O2-loaded single atoms for efficient selective catalytic oxidation of formaldehyde

Indoor formaldehyde (HCHO) pollution poses a major risk to human health. Low-temperature catalytic oxidation is an effective method for HCHO removal. The high activity and selectivity of single atomic catalysts provide a possibility for the development of efficient non-precious metal catalysts. In this study, the most stable single-atom catalyst Ti-Ti4C3O2 was screened by density functional theory among many single atomic catalysts with two-dimensional (2D) monolayer Ti4C3O2 as the support. The computational results show that Ti-Ti4C3O2 is highly selective to HCHO and O2 in complex environments. The HCHO oxidation reaction pathways are proposed based on the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. According to the reaction energy and energy span models, the E-R mechanism has a lower maximum energy barrier and higher catalytic efficiency than the L-H mechanism. In addition, the stability of the Ti-Ti4C3O2 structure and active center was verified by diffusion energy barrier and ab initio molecular dynamics simulations. The above results indicate that Ti-Ti4C3O2 is a promising non-precious metal catalyst. The present study provides detailed theoretical insights into the catalytic oxidation of HCHO by Ti-Ti4C3O2, as well as an idea for the development of efficient non-precious metal catalysts based on 2D materials.

Streamlined fabrication of AuPtRh trimetallic nanoparticles supported on Ti3C2MXene for enhanced photocatalytic activity in cephalosporins degradation

The escalating prevalence of cephalosporin antibiotics in wastewater poses a serious threat to public health and environmental balance. Thus, it is crucial to develop effective methods for removing cephalosporin antibiotics from water sources. Herein, we propose the use of AuPtRh trimetallic nanoparticles supported on Ti3C2MXene as a photocatalyst for the degradation of cephalosporin antibiotics. Initially, AuPtRh nanoparticles were uniformly grown onto Ti3C2MXene sheets using one-step reduction technique. The prepared AuPtRh/Ti3C2MXene exhibited a complete degradation of cefixime and ceftriaxone sodium, while an impressive degradation efficiency of 91.58 % for cephalexin was achieved after 60 min of exposure to visible light, surpassing the performance of its individual AuPtRh nanoparticles and Ti3C2MXene. The enhanced photoactivity of AuPtRh/Ti3C2MXene was resulted from improved light absorption capacity and efficient generation, separation, and transfer of charge carriers driven by the formation of heterojunction between AuPtRh and Ti3C2MXene. Electron paramagnetic resonance and radicals trapping experiments results revealed that •O2- and h+ are the principal reactive species governing the degradation of cephalosporins. The photocatalyst exhibited excellent stability and could be reused four times without significant loss in efficiency. Our study highlights the potential of MXene composites for environmental remediation, offering insights into designing sustainable AuPtRh/Ti3C2MXene photocatalyst for water pollutant degradation.

Biomedical application of metal-organic frameworks (MOFs) in cancer therapy: Stimuli-responsive and biomimetic nanocomposites in targeted delivery, phototherapy and diagnosis

The nanotechnology is an interdisciplinary field that has become a hot topic in cancer therapy. Metal-organic frameworks (MOFs) are porous materials and hybrid composites consisted of organic linkers and metal cations. Despite the wide application of MOFs in other fields, the potential of MOFs for purpose of cancer therapy has been revealed by the recent studies. High surface area and porosity, significant drug loading and encapsulation efficiency are among the benefits of using MOFs in drug delivery. MOFs can deliver genes/drugs with selective targeting of tumor cells that can be achieved through functionalization with ligands. The photosensitizers and photo-responsive nanostructures including carbon dots and gold nanoparticles can be loaded in/on MOFs to cause phototherapy-mediated tumor ablation. The immunogenic cell death induction and increased infiltration of cytotoxic CD8+ and CD4+ T cells can be accelerated by MOF platforms in providing immunotherapy of tumor cells. The stimuli-responsive MOF platforms responsive to pH, redox, enzyme and ion can accelerate release of therapeutics in tumor site. Moreover, MOF nanocomposites can be modified ligands and green polymers to improve their selectivity and biocompatibility for cancer therapy. The application of MOFs for the detection of cancer-related biomarkers can participate in the early diagnosis of patients.

Decoration of viscose fibers with silver nanoparticle-based titanium-organic framework for use in environmental applications

To effectively remove pharmaceuticals, nitroaromatic compounds, and dyes from wastewater, an efficient multifunctional material was created based on silver nanoparticles (Ag) and MIL-125-NH2 (MOF) immobilized on viscose fibers (VF) as a support substrate. Firstly, silver nanoparticles (Ag) were immobilized on the surface of viscose fibers (VF) via in situ synthesis using trisodium citrate (TSC) as a reducing agent to create (VF-Ag). Then, VF and VF-Ag were decorated with the titanium metal-organic framework MIL-125-NH2 (MOF) to create VF-MOF and VF-Ag-MOF. The influence of VF-Ag, VF-MOF, and VF-Ag-MOF on the sonocatalytic or sonophotocatalytic degradation of sulfa drugs was investigated. The results show that VF-Ag-MOF showed excellent sonocatalytic and sonophotocatalytic activity towards the degradation of sulfa drugs compared to VF-Ag and VF-MOF. Furthermore, sonophotodegradation showed a dramatic enhancement in the efficiency of degradation of sulfa drugs compared to sonodegradation. The sonophotodegradation degradation percentage of sulfanilamide, sulfadiazine, and sulfamethazine drugs in the presence of VF-Ag-MOF was 65, 90, and 95 after 45 min of ultrasonic and visible light irradiation. The catalytic activity of VF-Ag, VF-MOF, and VF-Ag-MOF was evaluated through the conversion of p-nitrophenol (4-NP) to p-aminophenol (4-AP). The results demonstrate that VF-Ag-MOF had the highest catalytic activity, followed by VF-Ag and VF-MOF. The conversion percentage of 4-NP to 4-AP was 69%. The catalytic or photocatalytic effects of VF-Ag, VF-MOF, and VF-Ag-MOF on the elimination of methylene blue (MB) dye were investigated. The results demonstrate that VF-Ag-MOF showed high efficiency in removing the MB dye through the reduction (65%) or photodegradation (71%) after 60 min. VF-Ag-MOF composites structure-activity relationships represent that doping within silver NPs enhanced the photocatalytic activity of MIL-125-NH2, which could be explained as follows: (i) Due to the formation of a Schottky barrier at the junction between MIL-125-NH2 and Ag NPs, the photogenerated electrons in the conduction band of MIL-125-NH2 were supposed to be quickly transferred to the valence band of the Ag NPs, and subsequently, the electrons were transferred to the conduction band of Ag NPs. This considerable electron transferring process, which is reported as Z scheme heterojunction, can efficiently suppress the recombination of electron/hole pairs in VF-Ag-MIL-125-NH2 composites. (ii) Sufficient separation between the photogenerated charge carriers (holes and electrons) and avoiding their recombination enhanced the photocatalytic activity of composites.

A novel target-triggered signal chemiluminescence kit for thrombin detection based on fusiform Au/MIL-53(Fe)

In this work, a fusiform Au/MIL-53(Fe) catalyst was used to construct a chemiluminescence (CL) kit for the sensitive and rapid detection of thrombin (THR). The porous silica microspheres encapsulated with luminol in holes by thrombin aptamer (THR-APT/Luminol/SPSiO2) and the fusiform Au/MIL-53(Fe) modified with thrombin aptamer complementary chains (Au/MIL-53(Fe)-SSDNA) were prepared. Then, a CL kit for THR detection was constructed by using the prepared composites. When thrombin is added to the reaction system, it binds to its aptamer (THR-APT) to open the holes of SPSiO2, which cause luminol and Au/MIL-53(Fe) release. Released luminol enters the detection system and triggers the reaction of luminol-H2O2-NaOH with the catalyst of Au/MIL-53(Fe), and produces a CL signal. The detection limit and the linear range of the kit were 4.7 × 10-15 M and 1.5 × 10-14 - 3.5 × 10-10 M, respectively. The CL kit also showed high stability, selectivity and reproducibility, and was successfully applied to the determination of THR in serum samples. Therefore, the proposed method for detecting THR has great application potential in the diagnosis of blood-related disease markers.

Design of bifunctional ultrathin MnO2 nanofilm with laccase-like activity for sensing environmental pollutants containing phenol groups

Laccase-catalyzed oxidative reactions are increasingly examined as a reliable approach to environmental analysis and remediation, and it is urgent to widen metal category to compensate huge gap in the number of studies on copper- and non-copper laccase mimics. Herein, two-dimensional ultrathin MnO2 nanofilm (Mn-uNF) was designed via a chemical deposition and alkali etching process. Similar to Cu-laccase, Mn-uNF can oxidize phenols via a one-electron-transfer reaction of Mn(III) and accelerate the MnIII/MnIV state cycle through an unconventional oxygen reduction process. The excellent laccase-like performance of Mn-uNF can be ascribed to the abundant atomically dispersed Vo-assisted Mn(III) and surface -OH species, which was confirmed by characterizations and DFT calculation. Further, a facile dual-function colorimetric platform was designed for array sensing of o-, m-, and p-dihydroxybenzene isomers and one-step discrimination of tetracyclines containing phenol groups. These findings provide reasonable guidance for the design of a nanozyme with active Mn sites as a new family member of highly efficient copper-free laccase mimics.

A heterostructural MoS2QDs@UiO-66 nanocomposite for the highly efficient photocatalytic degradation of methylene blue under visible light and simulated sunlight

The development of recyclable photocatalysts with high activity and stability has piqued the interest of researchers in the field of wastewater treatment. In this study, an ultrasonic probe approach was used to immerse a sequence of heterojunctions formed by metal-organic frameworks (UiO-66) and different amounts of molybdenum disulfide quantum dots (MoS2QDs), resulting in a highly recyclable MoS2QDs@UiO-66 photocatalyst. Multiple advanced techniques, such as XPS, XRD, TEM, XRF, and UV-vis spectrophotometry, were used to characterize and confirm the successful preparation of UIO-66 impregnated with MoS2QDs. The results indicated that the best heterostructure catalyst exhibited superior efficiency in the photocatalytic degradation of methylene blue (MB) in water, achieving approximately 99% removal within 30 minutes under simulated sunlight, while approximately 97% removal under visible light. The outstanding photocatalytic performance is predominantly attributed to the photoinduced separation of carriers in this heterostructure system. This study proposes a unique, simple, and low-cost method for improving the degradation performance of organic contaminants in water.

Recent Progress of Covalent Organic Frameworks-Based Materials in Photocatalytic Applications: A Review

Covalent organic frameworks (COFs) are one type of porous organic materials linked by covalent bonds. COFs materials exhibit many outstanding characteristics such as high porosity, high chemical and thermal stability, large specific surface area, efficient electron transfer efficiency, and the ability for predesigned structures. These exceptional advantages enable COFs materials to exhibit remarkable performance in photocatalysis. Additionally, the activity of COFs materials as photocatalysts can be significantly upgraded by ion doping and the formation of heterojunctions. This paper summarizes the latest research progress on COF-based materials applied in photocatalytic systems. Initially, typical structures and preparation methods of COFs are analyzed and compared. Moreover, the essential principles of photocatalytic reactions over COFs-based materials and the latest research developments in photocatalytic hydrogen production, CO2 reduction, pollutants elimination, organic transformation, and overall water splitting are indicated. At last, the outlook and challenges of COF-based materials in photocatalysis are discussed. This review is intended to permit instructive guidance for the efficient use of photocatalysis based on COFs in the future.

Facile fabrication of plasmonic Ag/ZIF-8: an efficient catalyst for investigation of antibacterial, haemolytic and photocatalytic degradation of antibiotics

Present article represents the fabrication of plasmonic Ag/ZIF-8 composite and its effect on antibacterial, haemolytic and photocatalytic degradation of antibiotics. Ag/ZIF-8 was prepared by varying molar concentrations (1 mM, 2.5 mM, and 5 mM) of AgNO3 into ZIF-8 using NaBH4 as a reducing agent by the sol-gel process. The material was then characterised using the XRD, XPS, FTIR, SEM, HRTEM, UVDRS, BET and EIS techniques. When it comes to breaking down the antibiotic CIP, the optimised Ag2.5/ZIF-8 exhibits the strongest photocatalytic capability, with a degradation efficiency of 82.3% after 90 minutes. Due to LSPR (Localised Surface Plasmon Resonance) as well as the efficient movement and separation of the interfaces of photo-generated charge carriers in Ag2.5/ZIF-8 may be the causes of this increase in photocatalytic degradation. The effect of several parameters, such as pH, a variety of catalysts, varying dose concentrations, scavenging and sustainability are being investigated. The para benzoquinone (OH˙) and citric acid (h+) the primary active species in the photocatalytic breakdown pathway, according to trapping study. Whereas, Ag5/ZIF-8 was optimised for greater antibacterial activity against S. aureus and E. coli due to the synergistic impact of Ag+ and Zn2+ in Ag5/ZIF-8 and in haemolytic experiment, all samples were discovered to be non-toxic to blood cells. Overall, the synthesised compound was discovered to be a reusable, affordable catalyst for water remediation that can also be used in biomedicine.

A green and facile one-step hydration method based on ZIF-8-PDA to prepare melamine composite sponges with excellent hydrophobicity for oil-water separation

Frequent crude oil spills and illegal discharges of industrial organic pollutants cause serious damage to the ecological environment and considerable loss of valuable resources. Therefore, there is an urgent need to develop efficient strategies to separate and recover oils or reagents from sewage. Herein, a green, facile and rapid one-step hydration method was applied to obtain the composite sponge (ZIF-8-PDA@MS) that monodispersed zeolitic imidazolate framework-8 nanoparticles with high porosity and large specific surface area were firmly loaded onto the melamine sponge by ligand exchange and the self-assembly of dopamine. The water contact angle of ZIF-8-PDA@MS with multiscale hierarchical porous structure could reach 162°, which remained stable over a long period of time and a wide pH range. ZIF-8-PDA@MS displayed excellent adsorption capacities (up to 85.45-168.95 g⋅g^-1), and could be reused at least 40 times. Besides, ZIF-8-PDA@MS exhibited remarkable photothermal effect. Simultaneously, Silver nanoparticle-immobilized composite sponges were also prepared via in-situ reduction of silver ions to inhibit bacterial contamination. The composite sponge developed in this work can be used not only for the treatment of industrial sewage, but also for the emergency response of large-scale marine oil spill accidents, which has inestimable practical value for water decontamination.

Post-synthesis introduction of dual functional groups in metal-organic framework for enhanced adsorption of moxifloxacin antibiotic

Highly effective removal of antibiotics from aqueous solution is of importance while still faces challenge. Herein, we report a novel metal-organic framework (MOF) adsorbent, MOF-808-SIPA (SIPA, 5-sulfoisophthalic acid), constructed via post-synthesis exchange strategy. On the basis, dual active groups including sulfonic acid and carboxyl groups are successfully introduced. The novel MOF-808-SIPA exhibits a high adsorption capacity of 287.1 mg g^-1 for moxifloxacin hydrochloride (MOX·HCl), superior to that (174.6 mg g^-1) of the pristine MOF-808-AA (AA, acetic acid). Besides, MOF-808-SIPA shows rapid adsorption equilibrium of ∼ 30 min, strong anti-interference ability from pH and inorganic ions, and feasible regeneration. The superiority renders MOF-808-SIPA a potential adsorbent for MOX removal. Density function theory (DFT) calculation and experiment confirm that H-bond interaction contributes largely to the excellent adsorption in MOF-808-SIPA. Our work provides a guideline for designing high-efficiency MOF-based adsorbent.

Promoted elimination of metronidazole in ferrous ions activated peroxydisulfate process by gallic acid complexation

We applied gallic acid (GA) as the complexing agent to stabilizing the regeneration of Fe²⁺ during the Fe²⁺/peroxydisulfate (PDS) Fenton-like reaction for promoting the removal of metronidazole (MTZ). This research evaluated the elimination of MTZ by optimizing the dose of GA and Fe²⁺ and pH condition. MTZ removal reached 83% at the GA: Fe²⁺ molar ratio of 1:1 (30 μM) and initial pH 5 and 6.2 after 120 min, and the kinetics showed two degradation phases (k_obs1 = 0.09636 for the rapid stage and k_obs2 = 0.01056 for the slow stage). The Fe²⁺ and GA complexes could expand the range of pH applicability and effectively stabilize the regeneration of Fe²⁺, which ultimately promoted the decontamination of MTZ. Sulfate radical (SO₄^.-), hydroxyl radicals, and singlet oxygen were proved to exist in this ternary system and contribute to MTZ removal, and SO₄^.- played the dominant role. Furthermore, the possible pathways and mechanisms for MTZ degradation were proposed, and the simulation result indicated that the toxicity of degradation intermediates of MTZ were declined. The GA assisted Fe²⁺/PDS system provided an improved promising advanced oxidation process for organic wastewater disposal.

Thiol-decorated defective metal-organic framework for effective removal of mercury(II) ion

Removal of mercury (Hg) ion from water is important while still faces challenges in capacity and adsorption speed. Herein, using thiol-containing mercaptoacetic acid (MA) as the template, we constructed a novel metal-organic framework (MOF) adsorbent, Zr-MSA-MA (MSA, mercaptosuccinic acid). Unlike other monodentate acids such as acetic acid and formic acid, MA benefits to maintain high-content binding sites, in the meantime of defect formation. On the basis, Zr-MSA-MA exhibits a high adsorption capacity of 714.8 mg g^-1 for Hg²⁺ and fast adsorption kinetics, superior to other MOF-based adsorbents. Co-existing metal ions and pH have only slight interference for the adsorption behavior. Besides, the adsorption is proved to an endothermic reaction and the adsorbent can be regenerated based on a simple elution. Further analysis indicates the strong chemical bonding of Hg²⁺ and -SH is the main adsorption mechanism. Thus, our work demonstrates the Zr-MSA-MA can serve as a potential adsorbent for Hg²⁺, and provides a novel strategy to construct defective adsorbent via using active group-containing template.

Design of an S-scheme photo-catalyst utilizing a Cu-doped perovskite and MOF-5 for simultaneous degradation of organic pollutants under LED light irradiation: Application of EXRSM method for spectra separation and BBD-RSM modeling

Heterojunction photo-catalysts have attracted significant attention in solar energy conversion due to their ability to reduce suppressing electron-hole pairs and improve catalytic capability. Herein, we designed an S-scheme photo-catalyst by encapsulating a Cu-doped perovskite inside the pores of MOF-5 for the first time, exhibiting excellent efficiency in a pollutant degradation process. The pristine MOF cannot act in the visible light region because of its wide bandgap. However, the encapsulation modified its bandgap and but also increased its photo-catalytic activity. Simultaneous photo-degradation of two organic contaminants, methylene blue (MB) and paracetamol (PA), was investigated to evaluate the catalytic activity of this composite. As a challenge, the UV-vis spectra of PA strongly overlapped with MB in a binary mixture preventing direct measurement of its concentration without previous separation via conventional methodologies. Hence, we used a simple and fast technique called the extended ratio subtraction method (EXRSM) to separate their absorption spectra. The statistical investigations established that it could resolve the issue of signal overlapping. Also, a statistical approach, Box-Behnken (BBD-RSM), was used to model and optimize the degradation process providing a better way to explain the effect and interactions of main parameters on degradation efficiency. Now, an empirical model for each pollutant can make a relationship between them. The photo-degradation yield was obtained at 67.12% and 87.96% for PA and MB, respectively, under optimum conditions. Furthermore, the kinetics and mechanism of reaction were investigated, and the results revealed that it follows a pseudo-first-order model for each pollutant.

In-situ construction of Zr-based metal-organic framework core-shell heterostructure for photocatalytic degradation of organic pollutants

Photocatalysis is an eco-friendly promising approach to the degradation of textile dyes. The majority of reported studies involved remediation of dyes with an initial concentration ≤50 mg/L, which was away from the existing values in textile wastewater. Herein, a simple solvothermal route was utilized to synthesize CoFe2O4@UiO-66 core-shell heterojunction photocatalyst for the first time. The photocatalytic performance of the as-synthesized catalysts was assessed through the photodegradation of methylene blue (MB) and methyl orange (MO) dyes at an initial concentration (100 mg/L). Under simulated solar irradiation, improved photocatalytic performance was accomplished by as-obtained CoFe2O4@UiO-66 heterojunction compared to bare UiO-66 and CoFe2O4. The overall removal efficiency of dyes (100 mg/L) over CoFe2O4@UiO-66 (50 mg/L) reached >60% within 180 min. The optical and photoelectrochemical measurements showed an enhanced visible light absorption capacity as well as effective interfacial charge separation and transfer over CoFe2O4@UiO-66, emphasizing the successful construction of heterojunction. The degradation mechanism was further explored, which revealed the contribution of holes (h+), superoxide (•O2 -), and hydroxyl (•OH) radicals in the degradation process, however, h+ were the predominant reactive species. This work might open up new insights for designing MOF-based core-shell heterostructured photocatalysts for the remediation of industrial organic pollutants.

Hotspots analysis and perspectives of Prussian blue analogues (PBAs) in environment and energy in recent 20 years by CiteSpace

Prussian blue analogs (PBAs), a type of metal-organic frameworks (MOFs), have attracted much attention because of their large specific surface area, high porosity, easy synthesis, and low cost. This paper presents the first review of PBAs by applying the bibliometric visualization software CiteSpace. The co-occurrence, co-citation, and clustering analysis of 2214 articles in the Web of Science database on the topic of "Prussian blue analogs" over the past 20 years were performed. The results provide a comprehensive overview of the evolution of the research hotspots for this material, and most importantly, it is identified that the research hotspots and trends for PBAs materials are concentrated in the environmental and energy fields. For example, the material is used as an adsorbent or catalyst to reduce pollutants, produce clean energy, or for energy storage applications such as batteries or supercapacitors. Finally, some outlooks are provided on the future research trends of this material in the environmental and energy fields, presenting the challenges faced by this material. For instance, the conductivity and corrosion resistance of the material needs to be improved and secondary contamination should be decreased or even avoided. It is believed that this paper would provide a comprehensive, systematic, and dynamic overview of the research of PBAs, and promote the future research of PBAs in the fields of environment and energy.

Efficient and Stable Catalytic Hydrogen Evolution of ZrO2/CdSe-DETA Nanocomposites under Visible Light

Composite photocatalysts are crucial for photocatalytic hydrogen evolution. In this work, ZrO2/CdSe-diethylenetriamine (ZrO2/CdSe-DETA) heterojunction nanocomposites are synthesized, and efficiently and stably catalyzed hydrogen evolution under visible light. X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscope (HRTEM) confirm the formation of heterojunctions between ZrO2 (ZO) and CdSe-DETA (CS). Ultraviolet–visible spectroscopy diffuse reflectance spectra (UV-vis DRS), Mott–Schottky, and theoretical calculations confirm that the mechanism at the heterojunction of the ZrO2/CdSe-DETA (ZO/CS) nanocomposites is Type-I. Among the ZO/CS nanocomposites (ZO/CS-0.4, ZO/CS-0.6, and ZO/CS-0.8; in the nanocomposites, the mass ratio of ZO to CS is 0.1:0.0765, 0.1:0.1148, and 0.1:0.1531, respectively). ZO/CS-0.6 nanocomposite has the best photocatalytic hydrogen evolution activity (4.27 mmol g−1 h−1), which is significantly higher than ZO (trace) and CS (1.75 mmol g−1 h−1). Within four cycles, the ZO/CS-0.6 nanocomposite maintains an efficient catalytic hydrogen evolution rate. Due to the existence of the heterojunction of the composites, the photogenerated electron-hole pairs can be effectively separated, which accelerates the photocatalytic hydrogen evolution reaction and reduces the progress of photocorrosion. This work reveals the feasibility of ZO/CS nanocomposite photocatalysts for hydrogen evolution.

Direct photolysis of diclofenac under simulated sunlight: Transformation pathway and biological concerns

Topical diclofenac gels are frequently applied on human skin and, consequently are exposed to sunlight during outdoor activities. The degradation of diclofenac (DCF) with sunlight exposure is known to occur but the detailed transformation characteristics and biological concerns have not been comprehensively investigated. In the present work, the transformation products during diclofenac photolysis were identified with the aid of ultra-performance liquid chromatography coupled with triple time-of-flight mass spectrometry (UPLC-TripleTOF). Biological concerns, including microtoxicity, genotoxicity, cytotoxicity and antiestrogenicity were examined with multiple in-vitro bioassays. Spearman correlation analysis was conducted to obtain further insight into the contributions of photolysis products to overall biological concerns. The results demonstrated that diclofenac was readily degraded under sunlight to form five main photolysis products via substitution, dechlorination, dehydroxylation, homodimerization and heterodimerization. Products P1, P2 and P5 were reported previously, while two dimer products (P3 and P4) are innovative products and have not been found in prior studies. A significant elevation in the microtoxicity was found during the photolysis of diclofenac, resulting mainly from the carbazole-containing photolysis products P2, P3, P4 and P5. Genotoxicity and antiestrogenicity declined along with the reduction of diclofenac, indicating that no photolysis products were genotoxic or anti-estrogenic. Modest cytotoxicity to the human skin epidermis cell line was observed and attributed to the formation of intermediate species. This outcome highlighted the biological concerns of diclofenac to human health when exposed to sunlight.

Metal-organic framework (MOF)-5/CuO@ZnIn2S4 core-shell Z-scheme tandem heterojunctions for improved charge separation and enhanced photocatalytic performance

Interface engineering is regarded as an effective strategy for charge separation. Metal-organic framework (MOF)-5/CuO@ZnIn₂S₄ core-shell Z-scheme tandem heterojunctions with a three-dimensional floral spherical shape are prepared by a two-step solvothermal and oxidative method. The flower spherical core-shell structure enhances multiple reflections and refractions of light and thus improves light utilization efficiently. In addition, this core-shell structure can supply sufficient active sites for photocatalytic reactions. Meanwhile, the composition of Z-scheme tandem heterojunctions and the photothermal effect contributed to the spatial charge separation and accelerated the photocatalytic process. The photocatalytic hydrogen production rate of MOF-5/CuO@ZnIn₂S₄ (1938.3 μmol g^-1 h^-1) is 18 times higher than that of pristine MOF-5, and the photocatalytic degradation efficiency of 2,4-dichlorophenol and phenol can reach up to 98.7% and 97.3%, respectively. In addition, multiple cycle experiments demonstrate high stability, which is favorable 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.

Study on visible light photocatalytic performance of MIL-100(Fe) modified by carbon nanodots

The emerging porous material metal organic framework (MOFs) has caught researchers' attention in the field of photocatalysis. In this study, a visible light-driven carbon nanodots/MIL-100(Fe) photocatalytic material was prepared by in situ synthesis method. The study found that the composite material loaded with 2.5 mg C-dots (2.5-carbon nanodots/MIL-100(Fe)) showed the best tetracycline degradation efficiency with 4.2 times higher than that of MIL-100(Fe) materials in a neutral environment. The superiority of 2.5-carbon nanodots/MIL-100(Fe) in degrading tetracycline is attributed to the fact that C-dots have the ability to act as acceptors and donors of electrons, thus promoting electron transfer and inhibiting electron-hole recombination. Moreover, the 2.5-carbon nanodots/MIL-100(Fe) also showed high stability after five cycles of the photodegradation reaction. The quenching experiment proved that the main active substances that degrade tetracycline were O₂^- and h⁺. The study of carbon nanodots /MIL-100(Fe) composite materials provides new thoughts and methods for the removal of organic pollutants.