A metal-OH group modification strategy to prepare highly-hydrophobic MIL-53-Al for efficient acetone capture under humid conditions

Derivatives of Br-doped metal-organic framework for improved acetaldehyde adsorption-photocatalytic oxidation

Different Br-doped metal-organic frameworks (MOFs) derived (Brx@UiO-66) have been prepared by heat treatment using UiO-66 as the precursor. The experimental results showed that Br0.2@UiO-66 exhibited the best photocatalytic oxidation and adsorption performances toward acetaldehyde. In the dynamic system, the acetaldehyde removal rate and adsorption capacity of Br0.2@UiO-66 were 93.2 % and 230.59 mg/g, respectively. The improvement of the photocatalytic performance can be attributed to the presence of Br ions and CBr bonds, which facilitated the rapid separation of electrons and holes and the production of •O2-. In addition, Br0.2@UiO-66 had a better adsorption performance than 300UiO-66, mainly because of the increased Lewis acidity of the metal active sites due to Br doping. Radical capture experiments indicated that •O2- and e- were the primary active substances in acetaldehyde oxidation, and allowed establishing the possible mechanism of acetaldehyde oxidation. This work shows that MOFs can have high catalytic oxidation performances toward volatile organic compounds (VOCs) while retaining their adsorption capacity, and can be used for practical applications in the adsorption-catalytic integrated degradation of VOCs.

Nano-lamellar H-ZSM-5 molecular sieves for enhanced indoor air purification: Synthesis and adsorption characterization

BACKGROUND

The rapid growth of cities has been accompanied by problems with urban air quality, making air pollution challenging to manage. In this situation, people focus on indoor building materials to improve air quality.

OBJECTIVE

In this paper, a novel bola-type surfactant was synthesized and used as a template, using ethyl orthosilicate and sodium meta-aluminate as the silicon and aluminum source, in the ratio of n(NaOH): n(NaAIO2): n(SiO2): n(SDA): n(H2O) as 30:2.5:120:5:4800.

METHODS

Hydrothermal preparation of ZSM-5 molecular sieves with a nanosheet structure (H-ZSM-5) was accomplished. The manufactured lamellar ZSM-5 molecular sieves were examined using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and adsorption and desorption techniques.

RESULTS

Traditional microporous ZSM-5 had a considerably lower static adsorption of formaldehyde molecules. The findings demonstrated that the nano-lamellar H-ZSM-5 molecular sieve can purify and eliminate larger molecular VOCs inside because it has the ability to adsorb larger molecular diameter VOCs. Additionally, the effectiveness of the adsorption was assessed using toluene vapour molecules with higher molecular diameters.

CONCLUSION

The findings demonstrate that the nanosheet H-ZSM-5 molecular sieve can remove bigger molecule VOCs from indoor air and can be utilised to purify indoor spaces. This study offers a fresh approach to indoor environmental cleanup by demonstrating the capability of nano-lamellar H-ZSM-5 molecular sieves for molecular adsorption.

Development of hybrid MIL-53(Al)@CBS for ternary adsorption of tetracyclines antibiotics in water: Physical interpretation of the adsorption mechanism

In this study, a hybrid material, MIL-53(Al)@CBS, was synthesized via the solvothermal method, involving the growth of MIL-53(Al) crystals on cocoa bean shell residues (CBS). Physicochemical characterization techniques, including TGA, BET, FTIR, XRD, and SEM, confirmed successful hybridization. MIL-53(Al)@CBS was employed as an adsorbent for antibiotics (oxytetracycline, tetracycline, chlortetracycline) separation from aqueous solutions. Parameters like pH, adsorbent dose, concentration, time, and temperature were systematically evaluated. FTIR revealed π-π interactions and hydrogen bonds between tetracyclines and the adsorbent. MIL-53(Al)@CBS exhibited adsorption, with removal rates up to 98.92%, 99.04%, and 98.24% for OTC, TC, and CTC, respectively. Kinetics suggested adsorption depends on active site availability, with TC adsorbing fastest. Microscopic models showed adsorption on three distinct active site types with different affinities without competition or adherence to the Langmuir hypothesis. Importantly, MIL-53(Al)@CBS maintained high adsorption capacity even after ten washing cycles, highlighting its potential for water treatment.

Composite poly(ethylene oxide)-based solid electrolyte with consecutive and fast ion transport channels constructed by upper-dimensional MIL-53(Al) nanofibers

Novel structural designs for metal organic frameworks (MOFs) are expected to improve ion-transport behavior in composite solid electrolytes. Herein, upper-dimensional MIL-53(Al) nanofibers (MNFs, MIL-53 belongs to the MIL (Material Institute Lavoisier) group) with flower-like nanoflake structures have been designed and constructed via modified hydrothermal coordination. The optimized MNFs with high surface area and porosity can form abundant interfaces with poly(ethylene oxide) (PEO) matrix. The plasticization of MNFs to the PEO matrix will facilitate segmental movement of PEO chains to facilitate Li+ conduction. The unsaturated open metal centers of MNFs can effectively capture bis(trifluoromethanesulfonyl)imide anions (TFSI-) to deliver more free lithium ions for transfer. Moreover, the upper-dimensional nanofiber structure endows lithium ions with a long-range and consecutive transport pathway. The obtained composite solid electrolyte (MNFs@PEO) presents a high ionic conductivity of 4.1 × 10-4 S cm-1 and a great Li+ transference number of 0.4 at 60 °C. The electrolyte also exhibits a stable Li plating/stripping behavior over 1000 h at 0.1 mA cm-1 with inhibited Li dendrite growth. Furthermore, the Li/LiFePO4 and Li/LiNi0.8Mn0.1Co0.1O2 batteries with MNFs@PEO as electrolytes both display great cycling stabilities with high-capacity retention, indicating their potential applications in lithium metal batteries. The study will put forward new inspirations for designing advanced MOF-based composite solid electrolytes.

Unveiling the MIL-53(Al) MOF: Tuning Photoluminescence and Structural Properties via Volatile Organic Compounds Interactions

MIL-53(Al) is a metal-organic framework (MOF) with unique properties, including structural flexibility, thermal stability, and luminescence. Its ability to adsorb volatile organic compounds (VOCs) and water vapor makes it a promising platform for sensing applications. This study investigated the adsorption mechanism of MIL-53(Al) with different VOCs, including ketones, alcohols, aromatics, and water molecules, focusing on structural transformations due to pore size variation and photoluminescence properties. The reported results assess MIL-53(Al) selectivity towards different VOCs and provide insights into their fundamental properties and potential applications in sensing.

Nanoarchitectonics Design Strategy of Metal-Organic Framework and Bio-Metal-Organic Framework Composites for Advanced Wastewater Treatment through Adsorption

Freshwater depletion is an alarm for finding an eco-friendly solution to treat wastewater for drinking and domestic applications. Though several methods like chlorination, filtration, and coagulation-sedimentation are conventionally employed for water treatment, these methods need to be improved as they are not environmentally friendly, rely on chemicals, and are ineffective for all kinds of pollutants. These problems can be addressed by employing an alternative solution that is effective for efficient water treatment and favors commercial aspects. Metal organic frameworks (MOFs), an emerging porous material, possess high stability, pore size tunability, greater surface area, and active sites. These MOFs can be tailored; thus, they can be customized according to the target pollutant. Hence, MOFs can be employed as adsorbents that effectively target different pollutants. Bio-MOFs are a kind of MOFs that are incorporated with biomolecules, which also possess properties of MOFs and are used as a nontoxic adsorbent. In this review, we elaborate on the interaction between MOFs and target pollutants, the role of linkers in the adsorption of contaminants, tailoring strategy that can be employed on MOFs and Bio-MOFs to target specific pollutants, and we also highlight the effect of environmental matrices on adsorption of pollutants by MOFs.

Recent trends in wastewater treatment by using metal-organic frameworks (MOFs) and their composites: A critical view-point

Respecting the basic need of clean and safe water on earth for every individual, it is necessary to take auspicious steps for waste-water treatment. Recently, metal-organic frameworks (MOFs) are considered as promising material because of their intrinsic features including the porosity and high surface area. Further, structural tunability of MOFs by following the principles of reticular chemistry, the MOFs can be functionalized for the high adsorption performance as well as adsorptive removal of target materials. However, there are still some major concerns associated with MOFs limiting their commercialization as promising adsorbents for waste-water treatment. The cost, toxicity and regenerability are the major issues to be addressed for MOFs to get insightful results. In this article, we have concise the current strategies to enhance the adsorption capacity of MOFs during the water-treatment for the removal of toxic dyes, pharmaceuticals, and heavy metals. Further, we have also discussed the role of metallic nodes, linkers and associated functional groups for effective removal of toxic water pollutants. In addition to conformist overview, we have critically analyzed the MOFs as adsorbents in terms of toxicity, cost and regenerability. These factors are utmost important to address before commercialization of MOFs as adsorbents for water-treatment. Finally, some future perspectives are discussed to give directions for potential research.

Mutual inhibition effects on the synchronous conversion of benzene, toluene, and xylene over MnOx catalysts

Advancing the practical application of catalytic oxidation technology demands for illustrating the synchronous conversion behavior of various volatile organic compounds (VOCs) over catalysts. Here, the mutual effects of benzene, toluene and xylene (BTX) were examined for their synchronous conversion on the surface of the MnO₂ nanowire. Competitive adsorption of xylene (absorption energy (E_ads): -0.889 eV) facilitated its prior conversion and impeded the oxidization of toluene and benzene over the catalyst. The turnover frequencies were 0.52 min^-1 (benzene), 0.90 min^-1 (toluene) and 2.42 min^-1 (xylene) for mixed BTX conversion over the MnO₂. Doping MnO₂ with K⁺, Na⁺ and Ca²⁺ could enhance its ability to oxidize the individual VOCs but did not alter the conversion mechanism of mixed BTX over the catalyst. When reducing the competitive effects in the adsorption of BTX, the oxidation performance of catalysts would depend on their ability to oxidize toluene and benzene. K-MnO₂ showed superior properties, i.e. specific surface area, highly low-valent Mn species, high lattice oxygen content, and abundant oxygen vacancy, and then exhibited superior performance during long-term operation (90% conversion in 800 min). The present study uncovered the co-conversion mechanism of multiple VOCs and significantly leveraged the catalytic oxidization technology for VOCs removal in practical application.

Novel strategies for the formulation and processing of aluminum metal-organic framework-based sensing systems toward environmental monitoring of metal ions

Aluminum is a relatively inexpensive and abundant metal for the mass production of metal-organic frameworks (MOFs). Aluminum-based MOFs (Al-MOFs) have drawn a good deal of research interest due to their unique properties for diverse applications (e.g., excellent chemical and structural stability). This review has been organized to highlight the current progress achieved in the synthesis/functionalization of Al-MOF materials with the special emphasis on their sensing application, especially toward metal ion pollutants in the liquid phase. To learn more about the utility of Al-MOF-based sensing systems, their performances have been evaluated for diverse metallic components in reference to many other types of sensing systems (in terms of the key quality assurance (QA) criteria such as limit of detection (LOD)). Finally, the challenges and outlook for Al-MOF-based sensing systems are discussed to help expand their real-world applications.

Dynamic Adsorption/Desorption of NOx on MFI Zeolites: Effects of Relative Humidity and Si/Al Ratio

Adsorption is a potential technology that is expected to meet NO_x ultra-low emission standards and achieve the recovery of NO₂. In this study, the adsorption/desorption behavior of NO_x with competitive gases (e.g., H₂O(g) and CO₂) was studied on MFI zeolites with different Si/Al ratios and under different relative humidity (0~90% RH). Sample characterization of self-synthesizing zeolites was conducted by means of X-ray diffraction, Ar adsorption-desorption, and field emission scanning electron microscopy. The results showed that low-silica HZSM-5(35) showed the highest NO_x adsorption capacity of 297.8 μmol/g (RH = 0) and 35.4 μmol/g (RH = 90%) compared to that of other adsorbents, and the efficiency loss factor of NO_x adsorption capacity at 90%RH ranged from 85.3% to 88.1%. A water-resistance strategy was proposed for NO_x multicomponent competitive adsorption combined with dynamic breakthrough tests and static water vapor adsorption. The presence of 14% O₂ and lower adsorption temperature (25 °C) favored NO_x adsorption, while higher CO₂ concentrations (~10.5%) had less effect. The roll-up factor (η) was positively correlated with lower Si/Al ratios and higher H₂O(g) concentrations. Unlike Silicalite-1, HZSM-5(35) exhibited an acceptable industrial desorption temperature window of NO₂ (255~265 °C). This paper aims to provide a theoretical guideline for the rational selection of NO_x adsorbents for practical applications.

Synthesis of Hierarchical-Porous Fluorinated Metal-Organic Frameworks with Superior Toluene Adsorption Properties

Constructing metal-organic frameworks (MOFs) with high volatile organic compounds (VOCs) adsorption capacity and excellent water resistance remain challenging. Herein, a monocarboxylic acid-assisted mixed ligands strategy was designed to synthesize a novel fluorinated MOFs, MIL-53 (Al). The monocarboxylic acid promoted crystallization and produced abundant crystal defects, which increased pore volume. Moreover, the competitive coordination between tetrafluoroterephthalic acid and 1,4-dicarboxybenzene was moderated by monocarboxylic modulators, significantly improving the hydrophobicity. The toluene uptake of the optimal sample reached 254.85 mg g^-1 under humid conditions, increased by 33.56 % of MIL-53(Al), and the Q_Wet /Q_Dry (the ratio of adsorption quality under wet to adsorption quality under dry) was 0.92, remarkably surpassing that of origin MIL-53 (0.72). The recycle experiment showed superior reusability with no performance degradation after 10 recycle under RH=50 % (relative humidity). The adsorptive kinetic and thermodynamic analysis proves that the adsorption process is controlled by surface mono-layer adsorption and pore diffusion. The fluorine group affects the internal diffusion, which weakens the transfer rate. This strategy opens a new prospect of obtaining hierarchical functional MOFs for meeting the VOCs uptake under the practical application.

Highly efficient amino-functionalized aluminum-based metal organic frameworks mesoporous nanorods for selective extraction of hydrocortisone in pharmaceutical wastewater

Hydrocortisone (HC), as a common steroid hormone drug, is also one of the key intermediates involved in the synthesis of multiple steroid hormone drugs. Residual HC in pharmaceutical wastewater frequently pollutes environmental water as steroid hormone contaminant and possesses great threat to human health as well as sustainable development of the ecosystem. Herein, in order to develop a highly efficient adsorbent system for selective enrichment and detection of HC in pharmaceutical wastewater, a novel amino-functionalized aluminum-based metal organic frameworks (Al-MOFs@NH₂) mesoporous nanorod is fabricated, in which 2-aminoterephthalic acid plays a dual role as organic linker and functional modification unit. The resultant Al-MOFs@NH₂ not only exhibits stable mesoporous structure but also has large specific surface area (849.76 m² g^-1) and plentiful binding sites, which significantly increases the adsorption capacity for HC. Under the promotion of hydrogen bonding and hydrophobic interaction together, Al-MOFs@NH₂ possesses high adsorption capacity (218.53 mg g^-1) for HC, as well as shows satisfactory selectivity for HC and other steroid hormones. Moreover, a method using Al-MOFs@NH₂ as solid phase extraction adsorbents combined with high performance liquid chromatography (HPLC) has been developed to specifically enrich and detect trace amount of HC in pharmaceutical wastewater. The developed method has a low limit of detection (LOD) (0.5×10^-3 μg mL^-1) and shows satisfactory recoveries for HC (75.9%-102.5%) with an acceptable relative standard deviation (RSD). These results demonstrate that the facile one-step preparation and excellent adsorption capacity makes Al-MOFs@NH₂ attractive to capture and remove environmental steroid hormone pollutants. More importantly, the method proposed in this work is expected to provide a prospective solution for analysis of strong bioactive contaminants in pharmaceutical wastewater.

One-step fabrication of novel MIL-53(Fe, Al) for synergistic adsorption-photocatalytic degradation of tetracycline

Bimetallic MOFs (MIL-53 (Fe, Al)) were successfully fabricated via a facile one-step solvothermal method for the removal of tetracycline (TC) from aqueous solutions. Tetracycline adsorption and photocatalytic experiments indicate that the optimum bimetallic synthetic molar ratio is 3:2 (40%MIL-53(Fe, Al)). The adsorption data are well fitted by the Freundlich model and pseudo-second-order adsorption kinetics. 40%MIL-53(Fe, Al) has an adsorption capacity of up to 402.033 mg/g. After the dark adsorption phase, 10 mg of 40%MIL-53(Fe, Al) can remove 94.33% of the tetracycline in a 70 mL aqueous solution (20 mg/L) under 50 min irradiation, while only 71.39% and 81.82% of the tetracycline are removed by MIL-53(Fe) and MIL-53(Al) under the same conditions. In addition, 40%MIL-53(Fe, Al) exhibits a significant adsorption-photocatalytic synergy (under direct irradiation without a dark adsorption phase), in which the pseudo-first-order kinetic constant increases by a factor of 3.11. Quenching experiments and ESR characterization indicate that ·O₂^-, ·OH, and h⁺ are the main active species in the photocatalytic process. Meanwhile, 40%MIL-53(Fe, Al) demonstrates good stability, with a tetracycline removal rate that still reaches 83.70% after 4 cycles. These results suggest that the prepared 40%MIL-53(Fe, Al) catalyst is a novel adsorption-photocatalytic material that can be used for the efficient treatment of tetracycline.