Recent advances of metal-organic framework-based and derivative materials in the heterogeneous catalytic removal of volatile organic compounds

Two Thiophene-Functionalized Co-MOFs as Green Heterogeneous Catalysts for the Biginelli Reaction

Two Co(II) metal-organic frameworks (Co-MOFs), namely, [Co(DMTDC)(bimb)]n (Co-MOF-1) and {[Co(DPTDC)(bimb)(H2O)]·2DMF}n (Co-MOF-2) (H2DMTDC = 3,4-dimethylthieno[2,3-b]thiophene-2,5-dicarboxylic acid, H2DPTDC = 3,4-diphenylthieno[2,3-b]thiophene-2,5-dicarboxylic acid, bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene), were obtained by the reaction of flexible N-containing ligand bimb and two structurally related thiophene-containing ligands H2DMTDC and H2DPTDC, respectively. These Co-MOFs displayed a 3D framework and porous structure, respectively. Co-MOF-1 and the activated sample Co-MOF-2' could act as green heterogeneous catalysts for the one-pot multicomponent Biginelli reaction, specifically the dehydration condensation process involving aldehydes, acetoacetates, and urea to yield dihydropyrimidin-2(1H)-ones. The reaction has advantages such as solvent-free conditions, water as only byproduct, readily accessible starting materials, excellent functional group compatibility, and simple operation. Both catalysts exhibited a wide substrate scope and maintained significant catalytic activity over five cycles. The special catalytic performance may be ascribed to functional groups within the ligand.

Recent advances and applications of stimuli-responsive nanomaterials for water treatment: A comprehensive review

The development of stimuli-responsive nanomaterials holds immense promise for enhancing the efficiency and effectiveness of water treatment processes. These smart materials exhibit a remarkable ability to respond to specific external stimuli, such as light, pH, or magnetic fields, and trigger the controlled release of encapsulated pollutants. By precisely regulating the release kinetics, these nanomaterials can effectively target and eliminate contaminants without compromising the integrity of the water system. This review article provides a comprehensive overview of the advancements in light-activated and pH-sensitive nanomaterials for controlled pollutant release in water treatment. It delves into the fundamental principles underlying these materials' stimuli-responsive behaviour, exploring the design strategies and applications in various water treatment scenarios. In particular, the article indicates how integrating stimuli-responsive nanomaterials into existing water treatment technologies can significantly enhance their performance, leading to more sustainable and cost-effective solutions. The synergy between these advanced materials and traditional treatment methods could pave the way for innovative approaches to water purification, offering enhanced selectivity and efficiency. Furthermore, the review highlights the critical challenges and future directions in this rapidly evolving field, emphasizing the need for further research and development to fully realize the potential of these materials in addressing the pressing challenges of water purification.

Controllable Synthesis of Manganese Organic Phosphate with Different Morphologies and Their Derivatives for Supercapacitors

Morphological control of metal-organic frameworks (MOFs) at the micro/nanoscopic scale is critical for optimizing the electrochemical properties of them and their derivatives. In this study, manganese organic phosphate (Mn-MOP) with three distinct two-dimensional (2D) morphologies was synthesized by varying the molar ratio of Mn2+ to phenyl phosphonic acid, and one of the morphologies is a unique palm leaf shape. In addition, a series of 2D Mn-MOP derivatives were obtained by calcination in air at different temperatures. Electrochemical studies showed that 2D Mn-MOP derivative calcined at 550 °C and exhibited a superior specific capacitance of 230.9 F g-1 at 0.5 A g-1 in 3 M KOH electrolyte. The aqueous asymmetric supercapacitor and the constructed flexible solid-state device demonstrated excellent rate performance. This performance reveals the promising application of 2D Mn-MOP materials for energy storage.

Highly efficient Cu(II) coordination polymer catalyst for the conversion of hazardous volatile organic compounds

Three novel coordination polymers (CPs), namely [Cu(μ-1κO,2κN-L)2]n (1), [Zn (μ-1κO,2κN-L)2(H2O)2]n (2) and [Cd (μ-1κOO',2κN-L)2]n (3) [where HL = 4-(pyrimidin-5-ylcarbamoyl)benzoic acid], were synthesized and characterized by elemental analysis, ATR-IR, TGA, XPS and single-crystal X-ray diffraction. Despite having the same organic ligand, the various metal cations had an impact in the subsequent frameworks. Hirshfeld surface analysis was performed to investigate the intermolecular interactions and to examine the stability of the crystal structures of the three polymers. Their catalytic performances were screened for the peroxidative oxidation of Volatile Organic Compounds (VOCs), with toluene and p-xylene selected as model substrates. Tert-butyl hydroperoxide (t-BuOOH or TBHP) (aq. 70 %) was employed as the oxidant. The catalytic oxidation of toluene yielded benzyl alcohol, benzaldehyde and benzoic acid. The copper CP 1 exhibited the highest total yield for toluene oxidation, reaching approximately 36% in an aqueous medium. For p-xylene oxidation, tolualdehyde, methylbenzyl alcohol, and toluic acid were produced as the primary products, accompanied by minor ones. The experiments were conducted under diverse conditions, manipulating key parameters such as the choice of solvent (water or acetonitrile), type of oxidant (t-BuOOH or H2O2), the concentration of the oxidant and reaction temperature. In the presence of catalyst 1, a maximum total yield of ca. 80% was achieved for p-xylene oxidation.

Multi-metallic MOF based composites for environmental applications: synergizing metal centers and interactions

The escalating threat of environmental issues to both nature and humanity over the past two decades underscores the urgency of addressing environmental pollutants. Metal-organic frameworks (MOFs) have emerged as highly promising materials for tackling these challenges. Since their rise in popularity, extensive research has been conducted on MOFs, spanning from design and synthesis to a wide array of applications, such as environmental remediation, gas storage and separation, catalysis, sensors, biomedical and drug delivery systems, energy storage and conversion, and optoelectronic devices, etc. MOFs possess a multitude of advantageous properties such as large specific surface area, tunable porosity, diverse pore structures, multi-channel design, and molecular sieve capabilities, etc., making them particularly attractive for environmental applications. MOF-based composites inherit the excellent properties of MOFs and also exhibit unique physicochemical properties and structures. The tailoring of central coordinated metal ions in MOFs is critical for their adaptability in environmental applications. Although many reviews on monometallic, bimetallic, and polymetallic MOFs have been published, few reviews focusing on MOF-based composites with monometallic, bimetallic, and multi-metallic centers in the context of environmental pollutant treatment have been reported. This review addresses this gap by providing an in-depth overview of the recent progress in MOF-based composites, emphasizing their applications in hazardous gas sensing, electromagnetic wave absorption (EMWA), and pollutant degradation in both aqueous and atmospheric environments and highlighting the importance of the number and type of metal centers present. Additionally, the various categories of MOFs are summarized. MOF-based composites demonstrate significant promise in addressing environmental challenges, and this review provides a clear and valuable perspective on their potential in environmental applications.

Efficacious destruction of typical aromatic hydrocarbons over CoMn/Ni foam monolithic catalysts with boosted activity and water resistance

Developing cost-effective monolith catalyst with superior low-temperature activity is critical for oxidative efficacious removal of industrial volatile organic compounds (VOCs). However, the complexity of the industrial flue gas conditions demands the need for high moisture tolerance, which is challenging. Herein, CoMn-Metal Organic Framework (CoMn-MOF) was in situ grown on Ni foam (NiF) at room temperature to synthesize the cost-effective monolith catalyst. The optimized catalyst, Co1Mn1/NiF, exhibited excellent performance in toluene oxidation (T90 = 239 °C) due to the substitution of manganese into the cobalt lattice. This substitution weakened the Co-O bond strength, creating more oxygen vacancies and increasing the active oxygen species content. Additionally, experimentally and computationally evidence revealed that the mutual inhibiting effect of three typical aromatic hydrocarbons (benzene, toluene and m-xylene) over the Co1Mn1/NiF catalyst was attributed to the competitive adsorption occurring on the active site. Furthermore, the Co1Mn1/NiF catalyst also presents outstanding water resistance, particularly at a concentration of 3 vol%, where the activity is even enhanced. This was attributed to the lower water adsorption and dissociation energy derived from the interaction between the bimetals. Results demonstrate that the dissociation of water vapor enables more reactive oxygen species to participate in the reaction which reduces the formation of intermediates and facilitates the reaction. This investigation provides new insights into the preparation of oxygen vacancy-rich monolith catalysts with high water resistance for practical applications.

Collaborative adsorption and photocatalytic degradation of high concentration pharmaceutical pollutants in water using a novel dendritic fibrous nano-silica modified with chitosan and UiO-66

This study presents a novel hybrid mesoporous material for degrading drug pollutants in water. The hybrid materials, derived from UiO-66 metal-organic framework and chitosan, coated on nano-silica, showed excellent drug adsorption through hydrogen-bonding interactions and efficient photodegradation of antibiotics. The hybrid material's enhanced conductivity and reduced band gap significantly improved pollution reduction by minimising electron-hole recombination. This allows for more efficient charge transport and better light absorption, boosting the material's ability to break down pollutants. Structural and morphological analyses were conducted using various techniques, including scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Optimising the adsorption-photodegradation process involved investigating pH, catalyst dose, and radiation time. Non-linear optimisation revealed an efficiency exceeding 85 % for 400 mg/L tetracycline and doxycycline, the model antibiotics. The optimal parameters for maximal elimination were determined as pH = 4.3, hybrid mesosphere dose = 4.0 mg/mL, and radiation time = 10 min. Kinetic studies favored pseudo-second-order diffusion models over pseudo-first-order models. The hybrid mesosphere showed sustained efficiency after three cycles and performed well in real aqueous samples, removing over 80 % of each antibiotic. This study demonstrates the potential of the hybrid mesoporous material for removing pharmaceutical pollutants in water systems.

Fluorination modification enhanced the water resistance of Universitetet i Oslo-67 for multiple volatile organic compounds adsorption under high humidity conditions: Mechanism study

The construction of metal-organic frameworks (MOFs) with highly efficient capture for volatile organic compounds (VOCs) adsorption under humid conditions is a significant yet formidable task. Herein, series of fluorinated UiO-67 modified with trifluoroacetic acid (TFA) and 4-fluorobenzoic acid were successfully synthesized for VOCs adsorption under high humidity conditions. Experiments results showed that UiO-67 modified with 4-fluorobenzoic acid (67-F) presented excellent adsorption capacity of 345 mg/g for toluene adsorption and exhibited great water resistance (10.0 vol% H2O, 374 mg/g toluene adsorption capacity). Characterization results indicated that the introduction of 4-fluorobenzoic acid induced the competitive coordination between 4-fluorobenzoic acid and 4,4-biphenyl dicarboxylic acid (BPDC) with Zr4+, causing the formation of abundant defects to provide extra adsorption sites. Meanwhile, the benzene ring in 4-fluorobenzoic acid enhanced the π-π conjugation, causing the further promotion of VOCs adsorption capacity. More importantly, the water resistance mechanism was investigated and elucidated that the introduction of F decreased the surface energy of 67-F and its affinity with water. Meanwhile, the metal complex induced by the fluorinated modification produced an electron-dense pore environment, which greatly improved its chemical and water stability. This work provided a strategy for preparing an adsorbent with high water resistance for real-world VOCs adsorption at high humidity conditions.

Synthesis, Characterization, and Catalytic Performance of a New Heterobimetallic Y/Tb Metal-Organic Framework with High Catalytic Activity

A three-dimensional heterobimetallic porous structure with the formula {[Y3.5Tb1.5L6(OH)3(H2O)1.5 (DMF)1.5] n ·1.5H2O·DMF} n (L = 3-amino-4-hydroxybenzoate) (Y/Tb-MOF) has been synthesized and characterized by single crystal and powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), inductively coupled plasma mass spectrometry (ICP-MS), electrophoretic mobility, and Fourier transform infrared (FTIR) spectroscopy. The structure presents two metal environments: a bioaugmented isosceles wedge (mm2) MO8 and a tricapped trigonal prism (-6m2) MN3O6. These configurations facilitate the creation of channels with a diameter of 10.7 Å, enabling its utilization as an active catalyst where the heterobimetallic nature of the assembly will be explored. This mixed-metal metal-organic framework has been tested in the cycloaddition of epoxides with carbon dioxide as well as in the cyanosilylation and hydroboration reactions of carbonylic substrates. Additionally, a monometallic Tb-MOF analogue has been synthesized for comparative evaluation of their catalytic performances. Both the mixed metal and monometallic variants exhibit outstanding activity in the cyanosilylation and hydroboration of carbonyls and in the synthesis of carbonates under CO2 pressure. However, only the latter exhibits high recyclability.

Engineering Co3O4@3DOM LaCoO3 multistage-pore nanoreactor with superior SO2 resistance for toluene catalytic combustion

Sulfur dioxide poisoning is a significant factor in catalyst deactivation during the catalytic combustion of volatile organic compounds. In this study, we prepared the LaCoO3 and Co3O4 composite catalysts using both the Ship-in-Bottle and Building-Bottle-Around-Ship approaches. Three-dimensionally ordered macropores (3DOM LaCoO3) were utilized as nanoreactors to protect the active sites during the catalytic combustion of toluene, preventing SO2 poisoning. Additionally, we grew ZIF-67 confined in the nanoreactor to create a multistage-pore structure. The Co3O4@3DOM LaCoO3 catalysts exhibited excellent activity in the complete catalytic oxidation of toluene. Various characterization studies confirmed the presence of a significant number of Co3+ species and an abundance of surface weak acid sites in the Co3O4@3DOM LaCoO3 catalysts, which synergistically enhanced the conversion of VOCs at low temperatures. Notably, the multistage pore structure provided a favorable reaction environment, accelerating the adsorption and diffusion of toluene and intermediates, resulting in excellent sulfur resistance of the catalysts. Moreover, XPS analysis confirmed a strong interaction between Co3O4 and LaCoO3, promoting rapid electron transfer and increasing the activation of O2-. In situ DRIFTS experiments verified that toluene mainly follows the MvK mechanism over Co3O4@3DOM LaCoO3 catalysts, indicating the following reaction pathway: toluene adsorption → benzyl alcohol → benzaldehyde → benzoate → anhydride → CO2 and H2O.

Sustainable conversion of polyethylene plastic bottles into terephthalic acid, synthesis of coated MIL-101 metal-organic framework and catalytic degradation of pollutant dyes

Persistent environmental colored compounds, resistant to biodegradation, accumulate and harm eco-systems. Developing effective methods to break down these pollutants is crucial. This study introduces Ag-MIL-101 (Ag-MIL-101) as a composite and reusable catalyst that efficiently degrades specific colored organic pollutants (COPs) like Methylene blue (MB), 4-Nitrophenol (4-NP), and 4-Nitroaniline (4-NA) using sodium borohydride at room temperature. The MIL-101 was synthesized using Terephthalic acid (TPA) derived from the degradation of Polyethylene Terephthalate (PET) plastic waste, with the assistance of zinc chloride. To further investigation, the kinetics of degradation reaction was studied under optimized conditions in the presence of Ag-MIL-101 as catalyst. Our results demonstrated the remarkable efficiency of the degradation process, with over 93% degradation achieved within just 8 min. The catalyst was characterized using FTIR, XRD, FESEM, and TEM. In this study, the average particle size of Ag-MIL-101 was determined using SEM and XRD analysis. These methods allow us to accurately and precisely determine the particle size. We determined the reaction rate constants for the degradation of each COP using a pseudo first-order kinetic equation, with values of 0.585, 0.597 and 0.302 min-1 for MB, 4-NP, and 4-NA, respectively. We also evaluated the recyclability of the catalyst and found that it could be reused for up to three cycles with only a slight decrease in efficiency (10-15%). Overall, our findings highlight the promising application of Ag-MIL-101 as an effective catalyst for the degradation of COPs, emphasizing the importance of optimizing reaction conditions to achieve enhanced efficiency.

Adsorption studies of tetracycline hydrochloride and diclofenac sodium on NH2-MIL-53(Al/Zr) sodium alginate gel spheres

Metal-organic frameworks are emerging inorganic-organic hybrid materials that can be self-assembled from metal ions and organic ligands via coordination bonds. These materials possess large specific surface area, tunable pore structure, abundant active center, diversity of functional groups as well as high mechanical and thermal stability which promote their applications in adsorption and catalysis studies. In this study, NH2-MIL-53(Al/Zr) was prepared and embedded into sodium alginate gel spheres (NH2-MIL-53(Al/Zr)-SA) and its adsorption properties towards TC and DCF in solution were investigated. According to XRD and FTIR analysis, the structure of the raw material was not changed after making the gel spheres. The maximum adsorption towards TC (pH =3) and DCF (pH =5) reached 98.5 mg·g-1 and 192 mg·g-1, respectively. The process was consistent with Langmuir and Freundlich, suggesting that there was both monolayer and multilayer adsorption which infers the presence of physical adsorption (intra-particle diffusion) and non-homogeneous chemical adsorption. The thermodynamic parameters showed that the adsorption process was a spontaneous entropy increasing reaction. The regeneration rate of spent NH2-MIL-53(Al/Zr)-SA could still reach 99.1 % after three cycles, indicating good regeneration performance. This study can provide a basis for the application of NH2-MIL-53(Al/Zr)-SA in wastewater treatment.

Construction of greenly biodegradable bacterial cellulose/UiO-66-NH2 composite separators for efficient enhancing performance of lithium-ion battery

The disposal of waste lithium batteries, especially waste separators, has always been a problem, incineration and burial will cause environmental pollution, therefore, the development of degradable and high-performance separators has become an important challenge. Herein, UiO-66-NH2 particles were successfully anchored onto bacterial cellulose (BC) separators by epichlorohydrin (ECH) as a crosslinker, then a BC/UiO-66-NH2 composite separator was prepared by vacuum filtration. The ammonia groups (-NH2) from UiO-66-NH2 can form hydrogen bonds with PF6- in the electrolyte, promoting lithium-ion transference. Additionally, UiO-66-NH2 can store the electrolyte and tune the porosity of the separator. The lithium ion migration number (0.62) of the battery assembled with BC/UiO-66-NH2 composite separator increased by 50 % compared to the battery assembled with commercial PP separator (0.45). The discharge specific capacity of the battery assembled with BC/UIO-66-NH2 composite separator after 50 charge and discharge cycles is 145.4 mAh/g, which is higher than the average discharge specific capacity of 114.3 mAh/g of the battery assembled with PP separator. When the current density is 2C, the minimum discharge capacity of the battery assembled with BC/UiO-66-NH2 composite separator is 85.3 mAh/g. The electrochemical performance of the BC/UiO-66-NH2 composite separator is significantly better than that of the commercial PP separator. In addition, -NH2 can offer a nitrogen source to facilitate degradation of the BC separators, whereby the BC/UiO-66-NH2 composite separator could be completely degraded in 15 days.

MOFs as versatile scaffolds to explore environmental contaminants based on their luminescence bustle

Metal-Organic Frameworks (MOFs) with luminescent properties hold significant promise for environmental remediation. This review critically examines recent research on these materials design, synthesis, and applications, mainly focusing on their role in combating environmental pollutants. Through a comprehensive analysis of metal ions, ligands, and framework compositions, the review discusses the importance of tailored design and synthesis approaches in achieving desired luminescent characteristics. Key findings highlight the effectiveness of luminous MOFs as fluorescent sensors for a wide range of contaminants, including heavy metals, reactive species, antibiotics, and explosives. Considering all this, the review discusses future research needs and opportunities in the field of luminous MOFs. It emphasizes the importance of developing multifunctional materials, refining design methodologies, exploring sensing mechanisms, and ensuring environmental compatibility, scalability, and affordability. By providing insights into the current state of research and outlining future directions, this review is a valuable resource for researchers seeking to address environmental challenges using MOF-based solutions.

Adsorption of perfluoroalkyl substances on deep eutectic solvent-based amorphous metal-organic framework: Structure and mechanism

Perfluoroalkyl substances (PFASs) are a class of emerging organic pollutants characterized by high toxicity, environmental persistence, and widespread detection in water sources. The removal of PFASs from water is a matter of global concern, given their detrimental impact on both the environment and public health. Many commonly used PFAS adsorbents demonstrate limited adsorption capacities and/or slow adsorption kinetics. Therefore, there is an urgent need for the development of efficient adsorbents. For the first time, this work systematically investigated the performance of a deep eutectic solvent (DES)-based amorphous metal-organic framework (MOF) for the adsorption of PFASs with different carbon-chain lengths under the state of the mixture in aquatic environments. The adsorption mechanism was probed by a suite of adsorption kinetics studies, adsorption isotherm profiling, spectral characterization, and ab initio molecular dynamics (AIMD) simulations, revealing that PFAS adsorption is driven by synergistic capturing effects including acid/base coordination, CF-π (carbon-fluorine-π), hydrogen bonding, and hydrophobic interactions. Furthermore, the adsorption processes of short-chain and long-chain targets were found to involve different rate-controlling steps and interaction sites. Hydrophobic interactions facilitated the swift arrival of long-chain PFASs at the coordinatively interacting sites between carboxyl termini and Lewis acid Zr unsaturated sites, thanks to their lower reaction barriers. On the other hand, the adsorption of short-chain PFASs primarily relied on a Zr hydroxyl-based ligand exchange force, which would take place at Brønsted acid sites. The existence of massive structural disorder in amorphous UiO-66 led to the development of larger pores, thus improving the accessibility of abundant adsorption sites and facilitating adsorption and diffusion. The presence of multiple types of interactions and flexible structure in defect-rich amorphous UiO-66 significantly increased the exposure of functional groups to the adsorbates. Additionally, this material possessed outstanding regeneration efficiency and outperformed other MOF-based adsorbents with high affinity for targets. It enhances our understanding of the adsorption performances and mechanisms of amorphous materials toward PFASs, thereby paving the way for designing more efficient PFAS adsorbents.

Defects materials of Institut Lavoisier-125(Ti) materials enhanced photocatalytic activity for toluene and chlorobenzene mixtures degradation: Mechanism study

In this paper, the effect of three monocarboxylic acids on MIL-125 synthesis was systematically investigated and the results were discussed in detail. X-ray diffractometry (XRD) and nitrogen adsorption-desorption curves indicated that small molecule acids (acetic acid, propionic acid and butyric acid) affected the morphology of MIL-125 and induced lamellar pores and structural defects in the crystals. Thermogravimetric measurements confirmed the presence of acid-regulated defective metal-organic frameworks (MOFs). Electrochemical tests and density function theory calculations indicated that acid modulation could change the forbidden bandwidth of the material. The acid modification strategy effectively promoted the transfer of photogenerated electrons and enhanced the adsorption and activation of O2 and H2O molecules, generating reactive radicals. The modified MOFs also showed excellent performance in the removal of mixed toluene and chlorobenzene. The degradation pathways of the mixture were analyzed by in situ infrared (IR) and gas chromatography-mass spectrometry (GC-MS). The mixture was converted to chlorophenolic intermediates in the presence of reactive oxygen species, further decomposed to form ethers and ethanol, and finally formed small molecules such as carbon dioxide and water. A feasible method was provided for the preparation of photocatalysts for the treatment of mixed VOCs.

Photocatalytic oxidation of formaldehyde under visible light using BiVO4-TiO2 synthesized via ultrasonic blending

Formaldehyde (HCHO) is one of the primary indoor air pollutants, and efficiently eliminating it, especially at low concentrations, remains challenging. In this study, BiVO4-TiO2 catalyst was developed using ultrasonic blending technology for the photocatalytic oxidation of low-level indoor HCHO. The crystal structure, surface morphology, element distribution, and active oxidation species of the catalyst were examined using XRD, SEM, TEM, UV-Vis, EDS, and ESR techniques. Our results demonstrated that the BiVO4-TiO2 catalyst, prepared by ultrasonic blending, exhibited good oxidation performance and stability. The HCHO concentration reduced from 1.050 to 0.030 mg/m3 within 48 h, achieving a removal rate of 97.1%. The synergy between BiVO4 and TiO2 enhanced the efficiency of separating photogenerated carriers and minimized the likelihood of recombination between photogenerated electrons and holes. Additionally, this synergy significantly enhanced the presence of hydroxyl radicals (·OH) on the catalyst, resulting in an oxidation performance superior to that of either BiVO4 or TiO2. Our research offers valuable insights for the development of new photocatalysts to address HCHO pollution.

Efficient spatial separation of charge carriers over Sv-ZnIn2S4/NH2-MIL-88B(Fe) S-scheme heterojunctions for enhanced photocatalytic H2 evolution and antibiotics removal performance

The exploration of highly efficient sunlight-assisted photocatalyst for photodegradation of organic contaminants or energy conversion is strongly encouraged. In this work, we designed a novel three-dimensional spindle-like Sv-ZIS@NMFe heterojunction made of amino functionalized NH2-MIL-88B(Fe) (NMFe) and ZnIn2S4 nanosheets with abundant sulfur vacancies (Sv-ZIS). The structural properties of NMFe materials, such as a clearly defined system of pores and cavities, were retained by the Sv-ZIS@NMFe composites. Additionally, the incorporation of sulfur vacancies, -NH2 functional groups, and well-matched energy level positions led to various synergistic effects that considerably enhanced internal electron transformation and migration, as well as improved adsorption performance. Consequently, under visible light irradiation, the optimized sample exhibited superior hydrogen production activity and tetracycline hydrochloride photodegradation performance. At last, density functional theory calculations was used to further elucidated the possible photoreactivity mechanism. This study demonstrates that the Sv-ZIS@NMFe heterojunction materials formed by ZnIn2S4 with suitable sulfur vacancies and amino functionalized Fe-MOFs have promising applications in photocatalysis.

Enhancing air treatment through controlled fabrication of transition metal-doped titanium dioxide nanocomposites for photocatalytic toluene degradation

Rapid industrial growth and urbanization have resulted in a significant rise in environmental pollution issues, particularly indoor air pollutants. As a result, it is crucial to design and develop technologies and/or catalysts that are not only cost-effective but also promising high performance and practical applicability. However, achieving this goal has been so far remained a challenging task. Herein, a series of transition metal M - TiO2 (M = W, Fe, Mn) nanocrystals was prepared for photocatalytic degradation of volatile organic compounds (VOCs), i.e., toluene. Of the nanocomposites tested, W-TiO2 showed significantly improved photocatalytic activity for VOC degradation under UV irradiation compared to the others. In particular, the optimized W dopant amount of 0.5 wt% resulted in the outstanding degradation performance of toluene (96%) for the obtained W-TiO2(0.5%) nanocomposite. Moreover, W-TiO2(0.5%) nanocomposite exhibited good stability for 32 h working under high toluene concentration (10 ppm) compared to the pristine TiO2. The current work demonstrates the potential usage of M - TiO2 nanocrystals, particularly W-TiO2(0.5%), as a promising photocatalyst for efficient VOCs degradation.

Insight into modified CeMn based catalysts for efficient degradation of toluene by in situ infrared

Trace activated carbon (AC) and diatomaceous earth (DE) were used as structural promoters to be incorporated into Ce-Mn-based solid-solution catalysts by the redox precipitation method. The modified catalysts exhibit superior reducibility, with abundant Ce3+, Mn3+and reactive oxygen species, which are facilitated to the migration of oxygen and the generation of oxygen vacancies. In particular, the catalytic combustion temperatures of 90 % toluene (3000 ppm) on Ce1Mn3Ox-AC/DE were 84 °C (dry) and 123 °C (10 vol% H2O), respectively. The role of lattice oxygen and adsorbed oxygen was revealed by in situ DRIFTS. Additionally, in situ DRIFTS was employed to verify that the degradation of toluene by Ce1Mn3Ox-AC/DE satisfied the Langmuir-Hinshelwood (L-H) mechanism and the Mars-Van Krevelen (MvK) mechanism. The possible reaction pathway was elucidated (toluene → benzyl alcohol → benzoic acid → maleic anhydride → CO2 + H2O). Furthermore, final products attributed to toluene oxidation were detected by in situ DRIFTS at 50 °C in the absence of oxygen, confirming that the catalyst possessed outstanding performance at low temperatures beyond mere adsorption.

Two isostructural Zn/Co-MOFs with penetrating structures: multifunctional properties of both luminescence sensing and conversion of CO2 into cyclic carbonates

Two new metal-organic frameworks (MOFs), namely, {[Zn(HL)(bpea)]·DMF}n (Zn-MOF-1) and {[Co(HL)(bpea)]·DMF}n (Co-MOF-2) (H3L = 3-(3,5-dicarboxybenzyloxy)benzoic acid, bpea = 1,2-di(pyridyl)ethane), were obtained by the reaction of H3L and N-containing ligand bpea with Zn(NO3)2·6H2O and Co(NO3)2·6H2O, respectively. The isomorphic Zn-MOF-1 and Co-MOF-2 featured a 3D penetrating framework with different stabilities, luminescence, and catalytic properties. Luminescence measurement indicated that Zn-MOF-1 could be used to detect Al3+ through a turn-on effect with a detection limit of 0.42 μM. The sensing mechanism experiments showed that the enhanced luminescence of Zn-MOF-1 toward Al3+ may be due to the weak interaction between Al3+ and Zn-MOF-1 and the absorbance-caused enhancement (ACE) mechanism. Meanwhile, both Zn-MOF-1 and Co-MOF-2 showed interesting CO2 adsorption properties and could catalyze the cycloaddition of CO2 to epoxides resulting in 96 and 92% ideal products within 12 hours, respectively. They can be cycled up to 5 times without significant loss of catalytic efficiency.

Defective UiO-66 metal-organic gels for optimizing gaseous toluene capture

Developing high-performance sorbents for volatile organic compounds (VOCs) is urgently required for environmental cleaning and personnel protection. Zirconium-based metal-organic frameworks (Zr-MOFs) have been deemed attractive candidates for gaseous toluene capture due to their superior stability and high adsorption capacity. However, the practical application of powdered Zr-MOFs is hindered by inherent limitations. Here, we report a series of defective UiO-66 metal-organic gels (G66-X) with variable missing linker deficiency by altering the modulator concentration. The defect concentration of the adsorbents has a significant impact on the porosity and gaseous toluene adsorption capacity. Dynamic breakthrough results reveal that G66-9 demonstrates optimal breakthrough time of 336 min/g and uptake amount of 334 mg/g, outperforming those of many other typical toluene adsorbents. The breakthrough times and the uptake capacities dramatically decrease with the increase of adsorption temperature. An outstanding regeneration performance of adsorbents can almost maintain even after five adsorption-desorption cycles.

Effect of amino functional groups on the surface properties and Lewis's acid base parameters of UiO-66(NH2) by inverse gas chromatography

Amino-functionalized metal organic frameworks (MOFs) have attracted much attention for various applications such as carbon dioxide capture, water remediation and catalysis. The focus of this study is to determine the surface and Lewis's acid-base properties of UiO-66(NH2) crystals by the inverse gas chromatography (IGC) technique at infinite dilution. The latter was applied to evaluate the dispersive component of the surface energy γ s d ( T ) by using thermal model and several molecular models. The obtained results proved that γ s d ( T ) decreases when the temperature increases. The best results were achieved by using the thermal model that takes into account the effect of the temperature on the surface areas of the organic molecules. We also observed a decrease of the Gibbs surface free energy of adsorption by increasing the temperature of the different organic solvents. The polar interactions of UiO-66(NH2) were obtained by using the methods of Saint-Flour Papirer, Donnet et al., Brendlé-Papirer and the different molecular models. The Lewis's acid base constants K A and K D were further calculated by determining the different variables of adsorption of the probes on the solid surface and the obtained values were 1.07 and 0.45 for K A and K D respectively, with an acid-base ratio (KA/KD) of 2.38. These values showed the high acidic surface of the solid substrate; whereas, the values of the entropic acid base parameters, ω A , ω D and ω A / ω D respectively equal to 1.0 × 10 - 3 , 3.8 × 10 - 4 and 2.73 , also highlighted the important acidity of UiO-66-(NH2) surface. These important findings suggest that the surface defects (missing linkers and/or clusters) in UiO-66(NH2) are the main determining factor of the acid-base properties of UiO-66 based structures.

Simultaneous catalytic oxidation of toluene and CO over Cu-V/Al-Ce catalysts: Physicochemical properties-activity relationship and simultaneous oxidation mechanism

Cu-V/Al-Ce with varying ratios of Al2O3/CeO2 were prepared to study the simultaneous catalytic oxidation of toluene and CO. Experimental results show that Cu-V/20Al-80Ce exhibits optimal simultaneous oxidation activity and good durability. This superior performance is related to Cu-Ce, V-Ce, and Al-Ce interactions, which facilitate the exposure of active centers, the creation of oxygen vacanicies, and efficient electron transfer. The mutual influence between toluene and CO during the simultaneous oxidation is then demonstrated. Toluene hinders CO oxidation through the competitive adsorption and the consumption of reactive oxygen species. CO enhances toluene oxidation, which is comprehensively explained by affecting the competition between the desorption and oxidation of benzaldehyde. Despite the mutual influence between toluene and CO, the pathways of CO and toluene oxidation are mutually independent. Toluene oxidation proceeds sequentially from toluene to benzyl alcohol, benzaldehyde, benzoate, and finally to CO2. Before being completely oxidized to CO2, CO is initially converted to carboxylic acid, hydrogen carbonate, free carbonate ion, bidentate formate, and monodentate carbonate.

Atomic-level design of metalloenzyme-like active pockets in metal-organic frameworks for bioinspired catalysis

Natural metalloenzymes with astonishing reaction activity and specificity underpin essential life transformations. Nevertheless, enzymes only operate under mild conditions to keep sophisticated structures active, limiting their potential applications. Artificial metalloenzymes that recapitulate the catalytic activity of enzymes can not only circumvent the enzymatic fragility but also bring versatile functions into practice. Among them, metal-organic frameworks (MOFs) featuring diverse and site-isolated metal sites and supramolecular structures have emerged as promising candidates for metalloenzymes to move toward unparalleled properties and behaviour of enzymes. In this review, we systematically summarize the significant advances in MOF-based metalloenzyme mimics with a special emphasis on active pocket engineering at the atomic level, including primary catalytic sites and secondary coordination spheres. Then, the deep understanding of catalytic mechanisms and their advanced applications are discussed. Finally, a perspective on this emerging frontier research is provided to advance bioinspired catalysis.

Au doped metal organic frameworks as di-functional photocatalysts for clearing organics in wastewater

Along with the development of productive forces, the use of organic compounds including diversified dyes and multiple drugs has become more and more commonly, resulting in the accelerating water contamination. Herein in this paper, Au doped PCN 224 are designed as bi-functional wastewater treatment agents to absorb and decompose organics molecules efficiently under light irradiation. After inserted with Au, the PCN 224 nanoparticles, which is kind of porous, stable and photosensitive metal-organic framework, show enhanced photodegradeability. Because the Au inserted could inhibit the re-combination of electrons and holes by absorbing photo-electrons; decrease the nanoparticles' band gap, and finally produce much more free radicals. In the meanwhile, due to the lower binding energy between S and Au, the Au modified PCN 224 perform better in absorbing organic compounds consisted of S contained heterocyclic ring (such as methylene blue). This work provides new insights into the precious design of materials in clearing organic compounds.

Facet-specific NiCo2O4/Fe2O3 p-n heterojunction with promising triethylamine sensing properties

Semiconductor gas sensing materials with specific crystal facets exposure have attracted researchers' attention recently. However, related research mainly focuses on single metal oxide semiconductor. The research on crystal facets designing of semiconductor p-n heterojunction is still highly challenging. Herein, based on NiCo2O4 octahedral nanocrystals with high-energy {111} crystal facets as substrate, Fe2O3 nanorods with {001} crystal facets were decorated to obtain a facet-specific NiCo2O4/Fe2O3 p-n heterojunction. The p-n heterojunction showed promising triethylamine sensing properties with a high response of 70 (Ra/Rg, 100 ppm) at 300 °C, which was about 57 and 10 times higher than that of pristine NiCo2O4 and Fe2O3, respectively. Theoretical calculation suggested that the electronic coupling effect formed by d-orbitals of Co-Fe in heterojunction strengthened the influence on the orbitals of N site in triethylamine, which improved the triethylamine adsorption and interface charge transfer. The results indicate that crystal facets designing of NiCo2O4 and Fe2O3 can achieve synergistic optimization of surface/interface characteristics of p-n heterojunction, thereby achieving a comprehensive improvement in gas sensing performance. This study not only provides a high performance triethylamine sensing material, but also greatly enriches the gas sensing mechanism of p-n heterojunction at the atomic and electronic levels.

Study on adsorption of salicylic acid and sulfosalicylic acid by MOF-sodium alginate gel beads obtained in a green way

A composite (ZS-UiO-66-NH2) zirconium crosslinked sodium alginate gel beads (ZS)-metal-organic skeleton (UiO-66-NH2) were prepared in this study through in-situ growth under simple, green and mild conditions for removal of the salicylic acid (SA) and sulfosalicylic acid (SSA) from water. The physicochemical properties of ZS-UiO-66-NH2 were characterized using various analytical methods. The influencing factors in the adsorption process including pH of solution, amount of adsorbent, coexisting ions, adsorption time, reaction temperature and equilibrium concentration of SA/SSA were performed in batch adsorption. The experimental results indicated that ZS-UiO-66-NH2 had high stability and could achieve efficient adsorption of SA/SSA in broad pH range (2-9) and salinity (0-0.2 mol·L-1). SA and SSA adsorbed on the composite at 293 K reached high values of 193 and 167 mg·g-1 from Langmuir model, respectively. Kinetic and isotherm studies demonstrated that the adsorption processes were mainly multilayer heterogeneous chemisorption. Thermodynamic data manifested that the two processes were exothermic and spontaneous with increasing entropy. ZS-UiO-66-NH2 can effectively remove SA/SSA from simulated wastewater under different pH and can be reused after elution with a NaHCO3 solution (5 mmol·L-1). The ZS-UiO-66-NH2 composite has great potential for removing SA/SSA from actual water bodies.

Effect of benzoic acid and dopamine hydrochloride as a modulator in the water resistance of Universitetet i Oslo-67: Adsorption performance and mechanism

The severe hazards on ecological environment and human body caused by volatile organic compounds (VOCs) have attracted worldwide substantial attention. In this research, a series of novel modified Universitetet i Oslo-67 (UiO-67) with water resistance were prepared and characterized, which had modified by benzoic acid and dopamine hydrochloride (67-ben-DH). On this basis, the adsorption performance, adsorption kinetics, defect engineering and water resistance of adsorbent were investigated. The results indicated that the excellent pore structure and specific surface area of 67-ben-DH-6 (molar ratio of Zr4+ to DH was 1:6) were retained while the adsorption performance and water resistance of the adsorbent were improved. Due to more defects, excellent adsorption diffusion and strong π-π interactions of 67-ben-DH-6, it performed the maximum adsorption capacity of toluene (793 mg g-1). Furthermore, the outstanding water resistance was attributed to the fact that N element of DH reduced the affinity of the adsorbent with water. Finally, the density functional theory (DFT) calculations showed that the adsorbent 67-ben-DH-6 had the maximum adsorption energy for toluene (-99.4 kJ mol-1) and the minimum adsorption energy for water (-17.8 kJ mol-1). Thus, the potential mechanism of 67-ben-DH for efficient toluene adsorption and water resistance was verified from a microscopic perspective.

Synthesis of an efficient MOF catalyst for the degradation of OPDs using TPA derived from PET waste bottles

In this study, a method for degrading PET-waste plastic bottles using ZnCl2:Urea as a catalyst was developed, resulting in high conversion (87%). The terephthalic acid obtained from the degradation of Waste PET Bottles (WPTs) was combined with copper and zinc salts to synthesize bimetallic metal-organic frameworks (MOF). The effectiveness of a bimetallic Cu-Zn(BDC)-MOF in catalyzing the reduction reaction of organic pollutant dyes (OPDs) was investigated, and the degradation efficiency of individual dyes was optimized, achieving over 95% degradation within 6-12 min under optimal conditions. Various techniques, including FT-IR, XRD, FE-SEM, EDS, and TEM were used to characterize the synthesized MOF. Results showed that the catalytic activity of Cu-Zn-MOF in reduction reaction of OPDs was enhanced by increasing the copper content. The reaction kinetics were investigated following pseudo-first-order kinetics with rate constants of 0.581, 0.43, 0.37, and 0.30 min-1 for Methylene Blue (MB), Methyl Orange (MO), 4-Nitrophenol (4-NP), and 4-Nitroaniline (4-NA), respectively. The investigations revealed that the produced catalyst exhibited excellent stability and recoverability, while its activity remained well-preserved even after undergoing three reuse cycles.

Post-Synthetic Modification of Zr-based Metal-Organic Frameworks with Imidazole: Variable Optical Behavior and Sensing

UiO-66-NH2 -IM, a fluorescent metal-organic framework (MOF), was synthesized by post-synthetic modification of UiO-66-NH2 with 2-imidazole carboxaldehyde via a Schiff base reaction. It was examined using various characterization techniques (PXRD, FTIR, NMR, SEM, TGA, UV-Vis DRS, and photoluminescence spectroscopy). The emissive feature of UiO-66-NH2 -IM was utilized to detect volatile organic compounds (VOCs), metal ions, and anions, such as acetone, Fe3+ , and carbonate (CO3 2- ). Acetone turns off the high luminescence of UiO-66-NH2 -IM in DMSO, with the limit of detection (LOD) being 3.6 ppm. Similarly, Fe3+ in an aqueous medium is detected at LOD=0.67 μM (0.04 ppm) via quenching. On the contrary, CO3 2- in an aqueous medium significantly enhances the luminescence of UiO-66-NH2 -IM, which is detected with extremely high sensitivity (LOD=1.16 μM, i. e., 0.07 ppm). Large Stern-Volmer constant, Ksv , and low LOD values indicate excellent sensitivity of the post-synthetic MOF. Experimental data supported by density functional theory (DFT) calculations discern photo-induced electron transfer (PET), resonance energy transfer (RET), inner filter effect (IFE), or proton abstraction as putative sensing mechanisms. NMR and computational studies propose a proton abstraction mechanism for luminescence enhancement with CO3 2- . Moreover, the optical behavior of the post-synthetic material toward analytes is recyclable.

Effective photocatalytic degradation of amphotericin B and naproxen from aqueous solutions using carbon quantum dots combined in MIL-88B(Fe) under visible light

A photocatalytic adsorbent composed of carbon dots (CD) embedded in a metal-organic framework (MOF) of MIL-88 B(Fe) was prepared by solvothermal technique. The synthesized CD@MIL-88 B(Fe) was characterized by different X-ray-based microscopic and spectroscopic methods, as well as electrochemical impedance spectroscopy, UV-Vis, FT-IR, DRS, TGA, and photoluminescence (PL) analysis. The prepared adsorbent showed a remarkable photocatalytic activity for eliminating amphotericin B (AmB) and naproxen (Nap) from aqueous solutions under visible light, reaching up to 92% and 90% removal, respectively, with an RSD value of around 5%. The parameters affecting the degradation process of pharmaceuticals were investigated. The optimal conditions for the degradation process were determined, including pH values (3 and 4 for AmB and Nap), photocatalyst concentration (0.2 g L-1), and H2O2 concentration (40-50 mM). Reactive oxidative species were also identified (·OH, ·O2) by examination of different scavengers. The adsorption isotherm and kinetic studies reveal that the synthesized photocatalyst exhibits dual functionality as an effective adsorbent (with maximum adsorption capacities of 42.5 and 121.5 mg g-1 for AmB and Nap) and a photocatalytic agent for removal purposes.

Metal-organic frameworks as photocatalysts in energetic and environmental applications

Metal-organic frameworks (MOFs) are an exciting new class of porous materials with great potential for photocatalytic applications in the environmental and energy sectors. MOFs provide significant advantages over more traditional materials when used as photocatalysts due to their high surface area, adaptable topologies, and functional ability. In this article, we summarize current developments in the use of MOFs as photocatalysts for a variety of applications, such as CO2 reduction, water splitting, pollutant degradation, and hydrogen production. We discuss the fundamental properties of MOFs that make them ideal for photocatalytic applications, as well as strategies for improving their performance. The opportunities and challenges presented by this rapidly expanding field are also highlighted.

Simple ultrasonic integration of shapeable, rebuildable, and multifunctional MIL-53(Fe)@cellulose composite for remediation of aqueous contaminants

Metal-organic frames (MOFs) have been recognized as one of the best candidates in the remediation of aqueous contaminants, while the fragile powder shape restricts the practical implementation. In this work, a shapeable, rebuildable, and multifunctional MOF composite (MIL-53@CF) was prepared from MIL-53 (Fe) and cellulose fiber (CF) using a simple ultrasonic method for adsorption and photocatalytic degradation of organic pollutants in wastewater. The results showed MIL-53(Fe) crystals were uniformly growth on CF surfaces and bonded with surface nanofibrils of CF through physical crosslinking and hydrogen bonding. Because of the high bonding strength, the MIL-53@CF composite exhibited an excellent compressive strength (3.53 MPa). More importantly, the MIL-53@CF composite was rebuildable through mechanical destruction followed by re-ultrasonication, suggesting the excellent reusability of MIL-53@CF for water remediation. The MIL-53@CF composite also had high adsorption capacities for methyl orange (884.6 mg·g-1), methylene blue (198.3 mg·g-1), and tetracycline (106.4 mg·g-1). MIL-53@CF composite could degrade TC through photocatalysis. The photocatalytic degradation mechanism was attributed to the Fe(II)/Fe(III) transform cycle reaction of MIL-53 crystal located on MIL-53@CF. Furthermore, the mechanical property and remoldability of MIL-53@CF composite increased its practicability. Comprehensively, MIL-53@CF composite provided a possible strategy to practically apply MOF in the remediation of aqueous contaminants.

Recent Advances in Metal-Organic Framework (MOF)-Based Photocatalysts: Design Strategies and Applications in Heavy Metal Control

The heavy metal contamination of water systems has become a major environmental concern worldwide. Photocatalysis using metal-organic frameworks (MOFs) has emerged as a promising approach for heavy metal remediation, owing to the ability of MOFs to fully degrade contaminants through redox reactions that are driven by photogenerated charge carriers. This review provides a comprehensive analysis of recent developments in MOF-based photocatalysts for removing and decontaminating heavy metals from water. The tunable nature of MOFs allows the rational design of composition and features to enhance light harvesting, charge separation, pollutant absorptivity, and photocatalytic activities. Key strategies employed include metal coordination tuning, organic ligand functionalization, heteroatom doping, plasmonic nanoparticle incorporation, defect engineering, and morphology control. The mechanisms involved in the interactions between MOF photocatalysts and heavy metal contaminants are discussed, including light absorption, charge carrier separation, metal ion adsorption, and photocatalytic redox reactions. The review highlights diverse applications of MOF photocatalysts in treating heavy metals such as lead, mercury, chromium, cadmium, silver, arsenic, nickel, etc. in water remediation. Kinetic modeling provides vital insights into the complex interplay between coupled processes such as adsorption and photocatalytic degradation that influence treatment efficiency. Life cycle assessment (LCA) is also crucial for evaluating the sustainability of MOF-based technologies. By elucidating the latest advances, current challenges, and future opportunities, this review provides insights into the potential of MOF-based photocatalysts as a sustainable technology for addressing the critical issue of heavy metal pollution in water systems. Ongoing efforts are needed to address the issues of stability, recyclability, scalable synthesis, and practical reactor engineering.

Recent progress in high-performance environmental impacts of the removal of radionuclides from wastewater based on metal-organic frameworks: a review

The nuclear industry is rapidly developing and the effective management of nuclear waste and monitoring the nuclear fuel cycle are crucial. The presence of various radionuclides such as uranium (U), europium (Eu), technetium (Tc), iodine (I), thorium (Th), cesium (Cs), and strontium (Sr) in the environment is a major concern, and the development of materials with high adsorption capacity and selectivity is essential for their effective removal. Metal-organic frameworks (MOFs) have recently emerged as promising materials for removing radioactive elements from water resources due to their unique properties such as tunable pore size, high surface area, and chemical structure. This review provides an extensive analysis of the potential of MOFs as adsorbents for purifying various radionuclides rather than using different techniques such as precipitation, filtration, ion exchange, electrolysis, solvent extraction, and flotation. This review discusses various MOF fabrication methods, focusing on minimizing environmental impacts when using organic solvents and solvent-free methods, and covers the mechanism of MOF adsorption towards radionuclides, including macroscopic and microscopic views. It also examines the effectiveness of MOFs in removing radionuclides from wastewater, their behavior on exposure to high radiation, and their renewability and reusability. We conclude by emphasizing the need for further research to optimize the performance of MOFs and expand their use in real-world applications. Overall, this review provides valuable insights into the potential of MOFs as efficient and durable materials for removing radioactive elements from water resources, addressing a critical issue in the nuclear industry.

Analysis of Radioactive Iodine Trapping Mechanism by Zinc-Based Metal-Organic Frameworks with Various N-Containing Carboxylate Ligands

This study aimed to develop effective adsorbents for capturing radioactive iodine in nuclear power waste gas. Two zinc metal-organic frameworks (Zn-MOFs) were synthesized and found to have favorable properties such as a large surface area, thermal stability, surface rich in π-electron-containing nitrogen, and redox potential. Adsorption experiments revealed maximum capacities of 1.25 and 1.96 g g^-1 for the MOFs at 75 °C, with the pseudo-second-order kinetic model fitting the data well. The Langmuir equation provided a better fit in cyclohexane, with maximum adsorption amounts of 249 and 358 mg g^-1 for Zn-MOF-1 and Zn-MOF-2, respectively. The MOFs were also stable during six cycles of adsorption and desorption. Furthermore, electron transfer occurred due to the synergistic adsorption of Zn, N, and O atoms, resulting in the conversion of some iodine to polyiodide. Zn-MOF-2 exhibited better chemisorption than Zn-MOF-1 due to a smaller highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap. Notably, it was discovered that N-containing radicals had stronger interactions with iodine compared to radicals without N. These findings provide valuable insights into MOF synthesis and environmental protection.

Activation of Co-O bond in (110) facet exposed Co3O4 by Cu doping for the boost of propane catalytic oxidation

Defects engineering in metal oxide is an important avenue for the promotion of VOCs catalytic oxidation. Herein, the influence of crystal facet of Co₃O₄ is first investigated for the propane oxidation. An intelligent Cu doping is subsequently performed in the most active (110) facet exposed Co₃O₄ catalyst. The optimized Cu-Co₃O₄-110-3 catalyst exhibits a prominently enhanced activity with propane conversion rate of 1.9 μmol g^-1 s^-1 at reaction temperature of 192 °C and the propane mass space velocity of 60,000 mL g^-1 h^-1, about 2.4 times that of the pristine Co₃O₄. Systematic experimental characterizations (XAS, EPR, Raman, TPR, XPS, etc.) combined with density functional theory calculations point out that the incorporated Cu could increase the electrophilicity of nearby O atom and implant beneficial defect structures (lattice distortion, coordination unsaturation, abundant oxygen vacancies, etc.), which could significantly activate Co-O bond in Co₃O₄, leading to the facilitated generation of active oxygen species as well as promoted oxidation ability. This study could set an illuminating paradigm for the boost of the intrinsic oxidation activity by the precise defect construction in Co₃O₄ catalyst, which will help drive ahead the pursuit of non-precious metal catalyst for VOCs abatement.

Facile fabrication of PMIA composite separator with bi-functional sodium-alginate coating layer for synergistically increasing performance of lithium-ion batteries

Lack of safety and unenough electrochemical performance have been known as a fundamental obstacle limiting the extensive application of lithium-ion batteries (LIBs). It is really preferable but challenging to fabricate thermal-response separator with shutdown function for high-performance LIBs. Herein, a thermal-response sodium-alginate modified PMIA (Na-Alg/PMIA) composite separator with shutdown function was designed and prepared by non-solvent phase induced separation (NIPs). PMIA and Na-Alg are combined by hydrogen bonding. While Na-Alg increases polar groups and makes Li⁺ easy to be transported, a small amount of Na⁺ can provide Li⁺ active sites, accelerate Li⁺ deposition coating and effectively inhibit the formation of Li dendrites. The as-prepared Na-Alg/PMIA composite separators can close pores at 200 °C and maintain dimensional integrity without obvious thermal shrinkage. In addition, the Na-Alg/PMIA composite separators has excellent wettability and ionic conductivity, resulting in high specific capacity and retention during the charge-discharge cycles. After 50 cycles, the capacity retention of cells with the Na-Alg/PMIA-20 composite separator is 84.3 %. At 2 C, cells with the Na-Alg/PMIA-20 composite separators still held 101.1 mAh g^-1. This facile yet effective method improves the electrochemical performance while ensuring the safety of the LIBs, which provides ideas for the commercial application of PMIA separators.

Synthesis of PMIA/MIL-101(Cr) composite separators with high Li+ transmission for boosting safety and electrochemical performance of lithium-ion batteries

Energy storage devices require separators with sufficient lithium-ion transfer and restrained lithium dendrite growth. Herein, PMIA separators tuned using MIL-101(Cr) (PMIA/MIL-101) were designed and fabricated by a one-step casting process. At 150 °C, the Cr³⁺ in the MIL-101(Cr) framework sheds two water molecules to form an active metal site that complexes with PF₆^- in the electrolyte on the solid/liquid interface, leading to improved Li⁺ transport. The Li⁺ transference number of the PMIA/MIL-101 composite separator was found to be 0.65, which is about 3 times higher than that of the pure PMIA separator (0.23). Additionally, MIL-101(Cr) can modulate the pore size and porosity of the PMIA separator, while its porous structure also functions as additional storage space for the electrolyte, enhancing the electrochemical performance of the PMIA separator. After 50 charge/discharge cycles, batteries assembled using the PMIA/MIL-101 composite separator and the PMIA separator presented a discharge specific capacity of 120.4 and 108.6 mAh/g, respectively. The battery assembled using PMIA/MIL-101 composite separator significantly outperformed both the batteries assembled from pure PMIA and commercial PP separators in terms of cycling performance at 2 C, displaying a discharge specific capacity of 1.5 times that of the battery assembled from PP separators. The chemical complexation of Cr³⁺ and PF₆^- plays a critical role to improve the electrochemical performance of the PMIA/MIL-101 composite separator. The tunability and enhanced properties of the PMIA/MIL-101 composite separator make it a promising candidate for use in energy storage devices.

Unraveling the role of Co3O4 facet for photothermal catalytic oxidation of methanol via operando spectroscopy and theoretical investigation

Tubular, pie- and bread-shaped forms of Co₃O₄ with exposed {110}, {112} and {111} facets were prepared and compared in their photothermal catalytic performance and reaction pathways during the oxidation of methanol. Among them, the Co₃O₄ with exposed {110} facet exhibited the best photothermal catalytic performance (95% methanol conversion, 93% CO₂ yield) under solar irradiation, while also maintaining good stability and moisture resistance. Reaction mechanism studies showed that the {110} facets had a strong adsorption capacity for formaldehyde, which facilitated its conversion to formate. The transformation of formaldehyde to formate species was the key step. The key step on the {110} facet was conversion of formaldehyde to a mono-dentate formate species, while conversion on the {112} and {111} facets was mainly to bi-dentate formate species. This study demonstrated that the design of preferential exposed crystal facet can regulate the pathway of photothermal catalytic reaction and realize efficient solar energy utilization.

Enhanced Visible-Light Photocatalytic Activities of CeVO4-V2O3 Composite: Effect of Ethylene Glycol

CeVO4-V2O3 composites were prepared by simple hydrothermal method, and the effects of ethylene glycol(EG) on the products were studied by XRD, N2 adsorption–desorption, SEM, EDS, XPS, PL and UV-vis spectra. The characterization reveals a slight decrease in surface area and a slight enhancement of visible light absorption in the final sample, while the crystalline phase, morphology and separation efficiency of the collective carriers are severely affected by the EG. At the same time, the photocatalytic effect of CeVO4-V2O3 composites was evaluated by the degradation rate of methylene blue (MB) under simulated visible light. The sample for 10 mL EG obtained the highest efficiency of 96.9%, while the one for 15 mL EG showed the lowest efficiency of 67.5% within 300 min. The trapping experiments and ESR experiment showed that the contribution of active species to the photocatalytic degradation of MB was ∙OH > h+ > ∙O2− in descending order, and a possible degradation mechanism was proposed.

Organophosphate Esters (OPEs) Flame Retardants in Water: A Review of Photocatalysis, Adsorption, and Biological Degradation

As a substitute for banned brominated flame retardants (BFRs), the use of organophosphate esters (OPEs) increased year by year with the increase in industrial production and living demand. It was inevitable that OPEs would be discharged into wastewater in excess, which posed a great threat to the health of human beings and aquatic organisms. In the past few decades, people used various methods to remove refractory OPEs. This paper reviewed the photocatalysis method, the adsorption method with wide applicability, and the biological method mainly relying on enzymolysis and hydrolysis to degrade OPEs in water. All three of these methods had the advantages of high removal efficiency and environmental protection for various organic pollutants. The degradation efficiency of OPEs, degradation mechanisms, and conversion products of OPEs by three methods were discussed and summarized. Finally, the development prospects and challenges of OPEs’ degradation technology were discussed.

Urea-H2O2 defect engineering of δ-MnO2 for propane photothermal oxidation: Structure-activity relationship and synergetic mechanism determination

Photothermal catalysis has an advantage in effective and economical elimination technology of volatile organic compounds (VOCs) in the ascendant. Herein, various surface defect engineering routes were adopted to enhance the low-temperature propane oxidation of δ-MnO₂. Compared to reducing etchants urea and vitamin C, δ-MnO₂ treated with urea - H₂O₂ exhibited an excellent thermal (T₉₀ = 240 ℃) and photothermal (T₉₀ = 196 ℃) activities of propane oxidation. Urea - H₂O₂ treatment provided high concentration of Mn⁴⁺ and surface-active oxygen (Mn⁴⁺-O_sur) species as surface-active sites, and produced numerous oxygen vacancies to improve charge separation and superoxide species generation capacity. Thus, the photothermal conversion efficiency and low-temperature reducibility were remarkably enhanced. Furthermore, the photothermal synergistic catalytic mechanism was proposed based on in-situ diffuse reflectance infrared Fourier transform spectroscopy and control experiments. The strategy here offered insight into the rational design of efficient transition catalysts, and in-depth understanding of the photothermal catalytic VOCs removal mechanism.

Review of Emission Characteristics and Purification Methods of Volatile Organic Compounds (VOCs) in Cooking Oil Fume

Volatile organic compounds (VOCs) in cooking oil fumes need to be efficiently removed due to the significant damage they cause to the environment and human health. This review discusses the emission characteristics, which are influenced by different cooking temperatures, cooking oils, and cuisines. Then, various cooking oil fume purification methods are mainly classified into physical capture, chemical decomposition, and combination methods. VOCs removal rate, system operability, secondary pollution, application area, and cost are compared. The catalytic combustion method was found to have the advantages of high VOC removal efficiency, environmental protection, and low cost. Therefore, the last part of this review focuses on the research progress of the catalytic combustion method and summarizes its mechanisms and catalysts. The Marse-van Krevelen (MVK), Langmuir-Hinshelwood (L-H), and Eley-Rideal (E-R) mechanisms are analyzed. Noble metal and non-noble metal catalysts are commonly used. The former showed excellent activity at low temperatures due to its strong adsorption and electron transfer abilities, but the high price limits its application. The transition metals primarily comprise the latter, including single metal and composite metal catalysts. Compared to single metal catalysts, the interaction between metals in composite metal catalysts can further enhance the catalytic performance.