Ce-based heterogeneous catalysts by partial thermal decomposition of Ce-MOFs in activation of peroxymonosulfate for the removal of organic pollutants under visible light

Inner transition metal-modulated metal organic frameworks (IT-MOFs) and their derived nanomaterials: a strategic approach towards stupendous photocatalysis

Photocatalysis, as an amenable and effective process, can be adopted for pollution remediation and to alleviate the ongoing energy crisis. In this case, recently, metal organic frameworks (MOFs) have attracted increasing attention in the field of photocatalysis owning to their unique characteristics including large specific surface area, tuneable pore architecture, mouldable framework composition, tuneable band structure, and exceptional photon absorption tendency complimented with superior anti-recombination of excitons. Among the plethora of frameworks, inner transition metal based-MOFs (IT-MOFs) have started to garner significant traction as photocatalysts due to their distinct characteristics compared to conventional transition metal-based frameworks. Typically, IT-MOFs have the tendency to generate high nuclearity clusters and possess abundant Lewis acidic sites, together with mixed valency, which aids in easily converting redox couples, thereby making them a suitable candidate for various photocatalytic reactions. Therefore, in this contribution, we aim to summarise the excellent photocatalytic performance of IT-MOFs and their composites accompanied by a thorough discussion of their topological changes with a variation in the structure of the metal cluster, fabrication routes, morphological features, and physico-chemical properties together with a brief discussion of computational findings. Moreover, we attempt to explore the scientific understanding of the functionalities of IT-MOFs and their composites with detailed mechanistic pathways for in-depth clarity towards photocatalysis. Furthermore, we present a comprehensive analysis of IT-MOFs for various crucial photocatalytic applications such as H₂/O₂ evolution, organic pollutant degradation, organic transformation, and N₂ and CO₂ reduction. In addition, we discuss the measures employed to enhance their performance with some future directions to address the challenges with IT-MOF-based nanomaterials.

Ligand Modulation on the Various Structures of Three Zinc(II)-Based Coordination Polymers for Antibiotics Degradation

The efficient removal of organic contaminants from wastewater is, nowadays, a prominent area of study due to its biological as well as environmental significance. Antibiotics are now found in wastewater because of their high use, which has become a source of aquatic pollution. These antibiotics have dangerous implications for people’s health. Hence, effective pharmaceutical removal from wastewater and contaminated water bodies, especially the removal of antibiotics, is of major interest to global research organizations. This is why it is necessary to investigate this class of toxic material in wastewater discharge. We synthesized three different coordination polymers (CPs) in the presence of various assistant carboxylate linkers, namely, [Zn(Hbtc)(dip)]n (1), [Zn4(1,2-bdc)4(dip)4]n (2), and [Zn(1,4-bdc)(dip)]n (3) (3,5-di(1H-imidazol-1-yl)pyridine = dip, 1,3,5-benzenetricarboxylic acid = H3btc, 1,2-benzenedicarboxylic acid = 1,2-H2bdc, and 1,4-benzendicarboxylic acid = 1,4-bdc). These CPs were characterized by using different techniques, including single-crystal X-ray diffraction. The structural studies demonstrated that in 2, there are four Zn(II) centers and both centers are in different coordination environments (Zn2 has distorted tetrahedral geometry, whereas Zn1, Zn3, and Zn4 have square pyramidal geometry). Hirshfeld surfaces analysis revealed that different types of intermolecular interactions (C⋯C, H⋯C, H⋯H, O⋯C, N⋯H, and O⋯H) are present in the synthesized CPs. We examined the different antibiotics, such as metronidazole (MDZ), nitrofurazone (NFZ), dimetridazole (DTZ), sulfasalazine(SLA), and oxytetracycline (OXY), degradation behaviors of the synthesized CPs, which showed remarkable degradation efficiency. 1 showed photocatalytic behavior toward the NFZ antibiotic in an aqueous media. This study also showed that these catalysts are stable and reusable under mild conditions.

Removal of pharmaceutical and personal care products (PPCPs) by MOF-derived carbons: A review

Nowadays, the increasing demand for pharmaceuticals and personal care products (PPCPs) has resulted in the uncontrolled release of large amounts of PPCPs into the environment, which poses a great challenge to the existing wastewater treatment technologies. Therefore, novel materials for efficient treatment of PPCPs need to be developed urgently. MOF-derived carbons (MDCs), have many advantages such as high mechanical strength, excellent water stability, large specific surface area, excellent electron transfer capability, and environmental friendliness. These advantages give MDCs an excellent ability to remove PPCPs. In this review, the effects of different substances on the properties and functions of MDCs are discussed. In addition, representative applications of MDCs and composites for the removal of PPCPs in the field of adsorption and catalysis are summarized. Finally, the future challenges of MDCs and composites are foreseen.

CeO2 Nanoparticle-Loaded MnO2 Nanoflowers for Selective Catalytic Reduction of NOx with NH3 at Low Temperatures

CeO₂ nanoparticle-loaded MnO₂ nanoflowers, prepared by a hydrothermal method followed by an adsorption-calcination technique, were utilized for selective catalytic reduction (SCR) of NO_x with NH₃ at low temperatures. The effects of Ce/Mn ratio and thermal calcination temperature on the NH₃-SCR activity of the CeO₂-MnO₂ nanocomposites were studied comprehensively. The as-prepared CeO₂-MnO₂ catalysts show high NO_x reduction efficiency in the temperature range of 150-300 °C, with a complete NO_x conversion at 200 °C for the optimal sample. The excellent NH₃-SCR performance could be ascribed to high surface area, intimate contact, and strong synergistic interaction between CeO₂ nanoparticles and MnO₂ nanoflowers of the well-designed composite catalyst. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs) characterizations evidence that the SCR reaction on the surface of the CeO₂-MnO₂ nanocomposites mainly follows the Langmuir-Hinshelwood (L-H) mechanism. Our work provides useful guidance for the development of composite oxide-based low temperature NH₃-SCR catalysts.

Peroxymonosulphate Activation by Basolite® F-300 for Escherichia coli Disinfection and Antipyrine Degradation

In this study, the removal of persistent emerging and dangerous pollutants (pharmaceuticals and pathogens) in synthetic wastewater was evaluated by the application of heterogeneous Advanced Oxidation Processes. To do that, a Metal-Organic Framework (MOF), Basolite^® F-300 was selected as a catalyst and combined with peroxymonosulfate (PMS) as oxidants in order to generate sulphate radicals. Several key parameters such as the PMS and Basolite^® F-300 concentration were evaluated and optimized using a Central Composite Experimental Design for response surface methodology for the inactivation of Escherichia coli. The assessment of the degradation of an analgesic and antipyretic pharmaceutical, antipyrine, revealed that is necessary to increase the concentration of PMS and amount of Basolite^® F-300, in order to diminish the treatment time. Finally, the PMS-Basolite^® F-300 system can be used for at least four cycles without a reduction in its ability to disinfect and degrade persistent emerging and dangerous pollutants such as pharmaceuticals and pathogens.

Applications of Metal-Organic Frameworks in Water Treatment: A Review

The ever-expanding scale of industry and agriculture has led to the gradual increase of pollutants (e.g., heavy metal ions, synthetic dyes, and antibiotics) in water resources, and the ecology and wastewater are grave problems that need to be solved urgently and has attracted widespread attention from the research community and industry in recent years. Metal-organic frameworks (MOFs) are a type of organic-inorganic hybrid material with a distinctive 3D network crystal structure. Lately, MOFs have made striking progress in the fields of adsorption, catalytic degradation, and biomedicine on account of their large specific surface and well-developed pore structure. This review summarizes the latest research achievements in the preparation of pristine MOFs, MOF composites, and MOF derivatives for various applications including the removal of heavy metal ions, organic dyes, and other harmful substances in sewage. Furthermore, the working mechanisms of utilizing adsorption, photocatalytic degradation, and membrane separation technologies are also briefly described for specific pollutants removal from sewage. It is expected that this review will provide inspiration and references for the synthesis of pristine MOFs as well as their composites and derivatives with excellent water treatment performance.

Synthesis of Mackinawite (FeSm) and its heterogeneous Fenton-like catalytic degradation performance of rhodamine B

In this work, Mackinawite (FeS_m) was synthesized by homogeneous precipitation method, and flower-like nanoparticles formed by the aggregation of nanosheets with a preferred orientation along the (001) plane. The heterogeneous Fenton-like degradation performance of FeS_m on rhodamine B (RhB) was investigated, results illustrated that RhB degradation was the synergistic effect of adsorption, Fenton, and a heterogeneous Fenton-like reaction. In repeated experiments, the reduction of reactivity was attributed to the oxidation of FeS_m into lepidocrocite, whereas lepidocrocite has relatively low hydroxyl radicals (•OH) production reactivity. Thus, it showed excellent degradation effects in long-time degradation of RhB. Photoluminescence technology and free radical capture experiments demonstrated that •OH produced on the surface of catalyst was the main active species to remove RhB. In addition, the Fe species on the surface of FeS_m was the main active center for surface-mediated reactions. A total organic carbon test revealed that the degradation was not complete and degradation intermediates were formed. Liquid chromatography-mass spectrometry technology was used to identify the degradation intermediates. On this basis, possible degradation pathways were proposed.

A new 3D 8-connected Cd(ii) MOF as a potent photocatalyst for oxytetracycline antibiotic degradation

1 exhibits the best photocatalytic decomposition efficiency towards antibiotic OXY. The plausible photocatalytic mechanism has been explained with the help of the density of states calculations and Hirshfeld surface analysis.

Investigation of the preparation and reactivity of metal-organic frameworks of cerium and pyridine-2,4,6-tricarboxylate

The synthesis of three coordination polymers of cerium(III) and the ligand pyridine-2,4,6-tricarboxylate (PTC) is reported. Two of the materials crystallise under hydrothermal conditions at 180 °C, with [Ce(PTC)(H₂O)₂]·1.5H₂O, (1), being formed on extended periods of reaction time, 3 days or longer, and Ce(PTC)(H₂O)₃, (2), crystallising after 1 day. Both phases contain Ce(III) but are prepared using the Ce(IV) salt Ce(SO₄)₂·4H₂O as reagent. Under solvothermal conditions (mixed water-N,N-dimethylformamide (DMF)), the phase [Ce(PTC)(H₂O)(DMF)]·H₂O (3) is crystallised. The structures of the three materials are resolved by single crystal X-ray diffraction, with the phase purity of the samples determined by powder X-ray diffraction and thermogravimetric analysis. (1) is constructed from helical chains cross-linked by the PTC linkers to give a three-dimensional structure that contains clusters of water molecules in channels that are hydrogen-bonded to each other and to additional waters that are coordinated to cerium. (2) also contains nine-coordinate cerium but these are linked to give a dense framework, in which water is directly coordinated to cerium. (3) contains corner-shared nine-coordinate cerium centres, linked to give a framework in which Ce-coordinated DMF fills space. Upon heating the material (1) in air all water is irreversibly lost to give a poorly crystalline anhydrous phase Ce(PTC), as deduced from X-ray thermodiffractometry and thermogravimetric analysis. The material (1), however, is hydrothermally stable, and is also stable under oxidising conditions, where immersion in 30% H₂O₂ gives no loss in crystallinity. Oxidation of around 50% of surface Ce to the +4 oxidation state is thus possible, as evidenced by X-ray photoelectron spectroscopy, which is accompanied by a colour change from yellow to orange. Photocatalytic activity of (1) is screened and the material shows effective degradation of methyl orange.

Regulation of electronic structures of MOF-derived carbon via ligand adjustment for enhanced Fenton-like reactions

Peroxymonosulfate (PMS)-based Fenton-like reactions are widely used for wastewater remediation. Metal-free carbonaceous activators can avoid the secondary pollution caused by metal leaching but often suffer from insufficient activity due to limited active centers and mass transfer barriers. Here, we prepared a series of heteroatom (N, S, F)-doped, highly porous carbonaceous materials (UC-X, X = N, S, F) by pyrolyzing UiO-66 precursors assembled by various organic ligands. Density functional theory calculations showed that the heteroatoms modulated the electronic structures of the carbon plane. UC-X exhibited significantly enhanced PMS activation capability compared with the undoped counterpart, in the efficiency order of UC-N > UC-S > UC-F > UC. UC-N (calcined at 1000°C) showed the best PMS activation, exceeding that of commonly used carbocatalysts. The prominent performance of UC-N originated from its unique porous structure and homogeneously dispersed graphitic N moieties. Trapping experiments and electron spin resonance showed a nonradical degradation pathway in the UC-N/PMS system, through which organics were oxidized by donating electrons to UC-N/PMS* metastable complexes. This work not only reports a universal way to access high-performance, metal-free PMS activators but also provides insight into the underlying mechanism of the carbon-activated PMS process.

Cobalt-Enhanced Mass Transfer and Catalytic Production of Sulfate Radicals in MOF-Derived CeO2 • Co3 O4 Nanoflowers for Efficient Degradation of Antibiotics

Antibiotics discharge has been a critical issue as the abuse in clinical disease treatment and aquaculture industry. Advanced oxidation process (AOPs) is regarded as a promising approach to degrade organic pollutants from wastewater, however, the catalysts for AOPs always present low activities, and uncontrollable porosities, thus hindering their further wider applications. In this work, an aliovalent-substitution strategy is employed in metal-organic framework (MOF) precursors assembly, aiming to introduce Co(II/III) into Ce-O clusters which could modify the structure of the clusters, then change the crystallization, enlarge the surface area, and regulate the morphology. The introduction of Co(II/III) also enlarges the pore size for mass transfer and enriches the active sites for the production of sulfate radicals (SO₄^• - ) in MOF-derived catalysts, leading to excellent performance in antibiotics removal. Significantly, the CeO₂ •Co₃ O₄ nanoflowers could efficiently enhance the generation of sulfate radical SO₄^• - and promote the norfloxacin removal efficiency to 99% within 20 min. The CeO₂ •Co₃ O₄ nanoflowers also present remarkable universality toward various antibiotics and organic pollutants. The aliovalent-substitution strategy is anticipated to find wide use in the exploration of high-performance MOF-derived catalysts for various applications.

Cu2O nanoparticles anchored on carbon for the efficient removal of propofol from operating room wastewater via peroxymonosulfate activation: efficiency, mechanism, and pathway

Anesthetic drug wastage has increasingly become the main resource of operating room sewage, which poses a great risk to the safety of humans and other organisms. Propofol is the most widely used anesthetic drug in the world, and also occupies the largest proportion of the total anesthetic wastage in the operating room. In this work, a 2D Cu₂O anchored carbon catalyst (Cu₂O@NC) was prepared by the assembly-pyrolysis process and successfully applied to peroxymonosulfate (PMS) activation. We took propofol as a typical example and investigated the removal activity through heterostructure-enhanced advanced oxidation processes (AOPs). Through the degradation process, propofol can be removed from 20 ppm to ultralow levels within 5 min using the PMS/Cu₂O@NC system. The degradation pathway of propofol was deduced through quantum chemical calculation and LC/GC-MS results. The final products were verified as CO₂ and H₂O. Moreover, sulfate radicals (SO₄˙⁻) proved to be the dominant reactive oxidation species by radical scavenger experiments and ESR results. In addition, it has great universality for various pharmaceuticals such as tetracycline (TC), amoxicillin (AMX), cephalexin (CPX), and norfloxacin (NFX). Our work provided the possibility to treat operation room sewage in a rapid, high-efficiency, and feasible way.

The 2D Cu₂O@NC catalyst obtained by thermal decomposition of MOF, could effectively enhance the propofol removal from wastewater by activating peroxymonosulfate in the advanced oxidation process.