Surface Area Of Metal-organic Frameworks Research Articles

Effect of Zr-based metal–organic framework (MOF-808) on strength development of cement pastes and its phase transition on mechanisms of cement hydration

Nanostructured materials can regulate the performance of cement-based materials at the nanoscale and thus attract intense interest in the cement community. However, there are still few studies on modifiable and large specific surface area metal–organic frameworks (MOFs) to regulate cement properties, which are still in the preliminary exploration stage. In this work, the nanoporous Zr(IV)-based MOF-808-modified cement-based composites have been investigated, focusing on the effects of MOFs on various aspects of compressive strength and microstructure of hardened cement pastes as well as cement hydration, and so on. Results showed that MOF-808 can chemically adsorb Ca2+, Fe3+, and Al3+ released from cement, and the adsorption capacity of Ca2+ increased greatly when the crystalline MOF-808 was transformed into an amorphous state. With the MOF-808 dosage of 0.15 wt%, the compressive strength at 3, 7, and 28 d increased by 15.56%, 25.53%, and 13.03% in comparison with the Blank group, respectively. Additionally, MOF-808 delayed the hydration of cement, reduced the heat of hydration, and shortened the delay time, which was reduced when the dosage of MOF-808 was increased. The addition of MOF-808 promoted the generation of C-S-H gels, refined the pore structure within the hardened cement paste, and reduced the content of pores larger than 10 μm. Finally, the influence mechanism of MOF-808 on cement hydration and strength development was proposed.

Construction of 2D MOF nanosheets with missing-linker defects for enhanced supercapacitor performance

Metal-Organic Frameworks (MOFs) are highly promising as electrode materials for supercapacitor development due to their large specific surface areas and tunable pore structures. Nevertheless, the intrinsic poor conductivity and suboptimal electrochemical performance of MOFs present substantial challenges. Traditional pyrolysis methods often compromise the inherent characteristics of MOFs. Consequently, a reasonable design of the original MOFs is a promising approach to enhancing its performance. This study commenced with pristine two-dimensional (2D) Ni-BTC (BTC = Trimesic acid) and improved their electrical conductivity and active site accessibility by embedding isophthalic acid (IPA) as missing linkers, resulting in defective Ni-BTC/IPA-x. The physicochemical properties of Ni-BTC/IPA were systematically characterized. The results indicate that defects effectively modulate the electronic structure of the metal center, pore structures, and specific surface areas of MOFs, which is conducive to improving supercapacitor performance. Electrochemical measurements reveal that Ni-BTC/IPA-3 exhibits an exceptional specific capacity of 1209 F g−1 at 0.5 A g−1, demonstrating a rate performance of 70.8 %. Furthermore, hybrid supercapacitor (HSC) devices, incorporating the Ni-BTC/IPA-3, possess an energy density of 30 Wh kg−1 at a power density of 1775.8 W kg−1. These HSC devices successfully power multi-colored light-emitting diodes (LEDs), highlighting their significant potential for practical energy storage applications.

Vapor-phase zeolitic imidazolate framework-8 growth on fibrous polymer substrates

The use of metal-organic frameworks (MOFs) in practical applications is often hindered by synthesis related challenges. Conventional solution-based approaches rely on hazardous solvents and often form powders that are difficult to integrate into practical devices. On the other hand, vapor-phase approaches generally result in MOF films on silicon substrates that make it difficult to characterize the MOF surface area, which is an important quality indicator. We address these challenges by introducing a solvent-free synthesis method to form MOF–fiber composites, which can be more easily integrated into devices. Additionally, these vapor-phase-formed MOF–fiber composites are compatible with Brunauer–Emmett–Teller surface area analysis to characterize MOF quality. Atomic layer deposition is used to form a ZnO film on polypropylene, polyester, and nylon fibrous substrates, which is subsequently converted to zeolitic imidazolate framework-8 (ZIF-8) using 2-methylimidazole vapor. We describe the effects of the ZnO film thickness and MOF conversion conditions on MOF crystallinity and surface area. We report a ZIF-8 surface area of ∼1300 m2/gMOF, which is comparable to reported surface areas of ∼1250–1600 m2/gMOF from conventional synthesis techniques, demonstrating good quality of the solvent-free MOF–fiber composites. We expect these results to extend vapor-phase MOF formation to new, practical substrates for advanced sensing and catalytic applications.

Green Synthesis of Cerium-Based Metal-Organic Framework (Ce-UiO-66 MOF) for Wastewater Treatment.

Green synthesis of metal-organic frameworks (MOFs) in aqueous solutions under ambient conditions with reduced production costs and environmental effects is an efficient technique to transfer lab-scale production to industrial large scale. Hence, this work proposes a green, low-cost, sustainable, rapid, and innovative synthetic strategy to produce cerium-based (Ce-UiO-66) MOFs under ambient conditions in the presence of water as a green solvent. This synthetic strategy exhibits great potential compared to conventional solvothermal synthetic techniques, and it does not need external activation energy and organic solvents, which can achieve the standards of green chemistry. Ce-UiO-66 MOF was synthesized successfully and utilized as a green adsorbent to efficiently eliminate anionic Congo Red (CR) dye from dye-containing wastewater. The experimental adsorption results were well matched to the pseudo-second-order kinetic and Langmuir isotherm models, in which the maximum CR adsorption capacity was measured to be about 285.71 mg/g. To evidence the applicability of Ce-UiO-66 MOFs in CR adsorption, the CR adsorption reaction was performed in the presence of interfering pollutants [e.g., salts (NaCl, KCl, and MgCl2) and cationic organic dyes (Malachite Green (MG) and Methylene Blue (MB)], where the results prove the promising adsorption performances of Ce-UiO-66 MOFs toward CR dye. Interestingly, the synthesized adsorbent exhibited high structural stability during repeated adsorption-desorption cycles, where the surface area of MOFs decreased from 555 to 376 m2/g after three cycles, while its CR adsorption capacity decreased by only 10% compared to that of the fresh adsorbent. All these outstanding properties indicate that the Ce-UiO-66 MOFs will be an effective adsorbent for water and wastewater treatment applications.

MOFs-derived TiO2 composite ZnIn2S4 to construct Z-scheme heterojunction for efficient photocatalytic hydrogen evolution under visible light

The ultra-high specific surface area of metal-organic frameworks (MOFs) with a large number of mesopores makes them good platforms for photocatalytic reactions. The materials derived from MOFs can usually retain the original framework structure and have more reaction sites. TiO2 is a practical and stable photocatalyst, but its wide bandgap (3.2 eV) results in low utilization of solar energy. ZnIn2S4 (ZIS) has a suitable bandgap (2.4 eV) and well visible light absorption, which could be a good photocatalytic material, but its chemical stability is poor. In this paper, a simple route was used to composite porous MOF-derived TiO2 with ZIS to prepare a core-shell-like Z-scheme heterojunction composite photocatalyst to produce hydrogen via photocatalysis. Porous TiO2 provided a larger specific surface area and fuller close contact with ZIS. The direct Z-scheme heterojunction greatly improved the separation and migration of carriers, and ZIS/TiO2 presented the superior hydrogen evolution rate under visible light (λ＞400 nm) which was 2.1515 mmol/g/h, which is twice that of ZIS and 119.5 times that of MOF-derived TiO2. Various methods such as in-situ XPS and theoretical calculation were used to deeply explore the heterojunction types of the photocatalyst and its photocatalytic mechanism. This study presents the enormous research potential of MOF-derived materials for photocatalysis and the superiority of Z-scheme heterojunction composite materials.

Prediction of arsenic adsorption onto metal organic frameworks and adsorption mechanisms interpretation by machine learning

Metal–organic frameworks (MOFs) are promising adsorbents for the removal of arsenic (As) from wastewater. The As removal efficiency is influenced by several factors, such as the textural properties of MOFs, adsorption conditions, and As species. Examining all of the relevant factors through traditional experiments is challenging. To predict the As adsorption capacities of MOFs toward organic, inorganic, and total As and reveal the adsorption mechanisms, four machine learning-based models were developed, with the adsorption conditions, MOF properties, and characteristics of different As species as inputs. The results demonstrated that the extreme gradient boosting (XGBoost) model exhibited the best predictive performance (test R2 = 0.93–0.96). The validation experiments demonstrated the high accuracy of the inorganic As-based XGBoost model. The feature importance analysis showed that the concentration of As, the surface area of MOFs, and the pH of the solution were the three key factors governing inorganic-As adsorption, while those governing organic-As adsorption were the concentration of As, the pHpzc value of MOFs, and the oxidation state of the metal clusters. The formation of coordination complexes between As and MOFs is possibly the major adsorption mechanism for both inorganic and organic As. However, electrostatic interaction may have a greater effect on organic-As adsorption than on inorganic-As adsorption. Overall, this study provides a new strategy for evaluating As adsorption on MOFs and discovering the underlying decisive factors and adsorption mechanisms, thereby facilitating the investigation of As wastewater treatment.

The mega-merger strategy: M@COF core-shell hybrid materials for facilitating CO2 capture and conversion to monocyclic and polycyclic carbonates

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have garnered significant attention for their potential in CO2 capture and conversion, owing to their unique properties. However, these materials suffer from inherent drawbacks such as poor stability and catalytic activity, leading to unsatisfactory utilization efficiency. In this work, we fabricated a series of novel M@COF hybrid materials by growing pyridine-based COFs with varying thicknesses on NH2-UiO-66 cores. These materials exhibited large specific surface areas and favorable chemical stability. The combination of the high specific surface area of MOF and the multiple interacting π-π stacking interactions of COF in these M@COF hybrid materials resulted in significantly enhanced CO2 adsorption performance, surpassing that of individual parent MOF or COF. In addition, an ion-functionalized M@COF-0.15-Br was fabricated through a simple post-synthesis modification. The presence of abundant ion active sites and interfacial synergistic effects in M@COF-0.15-Br effectively facilitated activation of reactants, enabling efficient catalytic conversion of CO2 to monocyclic and polycyclic carbonates. Consequently, the superior CO2 capture and conversion achieved using this M@COF core-shell hybrid material offers a new approach to design advanced functional materials with optimized structures for CO2 capture and conversion.

Selective extraction of apixaban from plasma by dispersive solid-phase microextraction using magnetic metal organic framework combined with molecularly imprinted polymer nanocomposite.

This research aims to synthesize a specific and efficient sorbent to use in the extraction of apixaban from human plasma samples and its determination by high-performance liquid chromatography-tandem mass spectrometry. High specific surface area of metal-organic framework, magnetic property of iron oxide nanoparticles, selectively of molecular imprinted polymer toward the analyte, and the combination of dispersive solid-phase extraction method with a sensitive analysis system provided an efficient analytical method. In this study, first, a molecularly imprinted polymer combined with magnetic metal organic framework nanocomposite was prepared and then characterized using different techniques. Then the sorbent particles were used for selective extraction of the analyte from plasma samples. The efficiency of the method was improved by optimizing effective parameters. According to the validation results, wide linear range (1.02-200ng mL-1 ), acceptable coefficient of determination (0.9938), low limit of detection (0.32ng mL-1 ) and limit of quantification (1.02ng mL-1 ), high extraction recovery (78%), and good precision (relative standard deviations ≤ 2.9% for intra- (n=6) and interday (n=6) precisions) were obtainable using the proposed method. These outcomes showed the high potential of the proposed method for screening apixaban in the human plasma samples.

Screening the Specific Surface Area for Metal-Organic Frameworks by Cataluminescence

Metal-organic frameworks (MOFs) are famous for their large surface area, which is responsible for the dispersed active sites and decent behaviors in gas adsorption, storage, and catalytic reactions. However, it remains a great challenge to acquire a cost-effective and accurate evaluation on the surface area for the MOFs. In this work, we have proposed cataluminescence (CTL) to evaluate the specific surface area for the MOFs, based on the adsorption–desorption and the catalytic reaction of ethanol. Aluminum-based MOFs with large-pore (lp), narrow-pore (np), and medium-pore (mp-130, mp-140, and mp-150 synthesized under 130, 140, and 150 °C) have been prepared. Distinguished CTL signals were acquired from ethanol in the presence of these MOFs: lp > mp-150 > mp-130 > mp-140 > np. Note that the CTL intensities were positively correlated with the specific surface areas of these MOFs acquired by the Brunauer–Emmett–Teller (BET) method. The distinct specific surface area of MOFs determined the capacity to accommodate and activate ethanol, leading to the varied CTL intensity signals. Therefore, the proposed CTL could be utilized for the rapid and accurate evaluation of the specific surface area for MOFs. It is believed that this CTL strategy showed great possibilities in the structural evaluation for various porous materials.

One-step fabrication of hydrophobic metal-organic framework@covalent organic framework hybrid as sorbent for high-performance solid-phase extraction of flavonoids

Metal-organic framework (MOF) and covalent organic framework (COF) exhibit excellent extraction performance in sample pretreatment, but their wider application is hindered by some inherent drawbacks. Herein, we successfully synthesized a novel MOF@COF hybrid material with large specific surface area, good chemical stability and reusability, which is suitable as a solid phase extraction (SPE) sorbent for the efficient extraction of flavonoids. Importantly, due to the synergistic effect, the obtained MOF@COF hybrid material showing a higher extraction efficiency than individual MOF and COF. This is mainly due to the obtained MOF@COF hybrid material combines the high specific surface area of MOF and multiple interactions (hydrophobic interaction, hydrogen bonding and π-π stacking interaction) with flavonoids conferred by the COF structure. Then, a sensitive analytical method for flavonoids with ideal linear range (1–500 ng mL−1), low detection limit (0.15–0.41 ng mL−1) and good repeatability (2.64–6.20%) was developed under optimized conditions. In addition, the MOF@COF hybrid sorbent has better selectivity for hydrophobic targets containing multiple hydrogen bond acceptors/donors. Finally, the established method was applied to the determination of flavonoids in different food samples, and satisfactory recoveries (81.4–102.1%) were obtained, which initially confirmed its applicability.

Computational Screening of Metal-Organic Frameworks for Ammonia Capture from H2/N2/NH3 Mixtures.

The separation of ammonia from H2/N2/NH3 mixtures is an important step in ammonia decomposition for hydrogen production and ammonia synthesis from H2 and N2 based nonaqueous technologies. Metal–organic frameworks (MOFs) are considered as potential materials for capturing ammonia. In the present work, high-throughput screening of 2932 Computation-Ready Experimental MOFs (CoRE MOFs) was carried out for ammonia capture from H2/N2/NH3 mixtures by Grand Canonical Monte Carlo (GCMC) simulations. It was found that the high-performing MOFs are characterized by tube-like channels, moderate LCD (largest cavity diameter) (4–7.5 Å), and high Qst0(NH3) (the isosteric heat of NH3 adsorption) (>45 kJ/mol). MOFs with high NH3 adsorption capacity often feature moderate surface area, while the surface area of MOFs with high NH3 selectivity is relatively lower, which limits the NH3 adsorption capacity. Qst0 and the Henry’s constant (KH) are two energy descriptors describing the interactions between adsorbents and adsorbates. The former has a stronger correlation with the adsorption selectivity, while the latter has a stronger correlation with the adsorption capacity. By analyzing the molecular density distribution of adsorbates in high-performing MOFs, it was found that unsaturated coordinated metal sites provide the main functional binding sites for NH3. Most MOFs with high NH3 selectivity have multiple different metal nodes or other atoms except C, O, and H, such as N and P. Multiple metal nodes and nonmetallic atoms provide more functional binding sites. Finally, the adsorption behavior with various concentrations of gas mixtures was examined to verify the universality of the screening calculations, and the effect of framework flexibility on adsorption performance was explored.

Machine learning approaches for predicting arsenic adsorption from water using porous metal–organic frameworks

Arsenic in drinking water is a serious threat for human health due to its toxic nature and therefore, its eliminating is highly necessary. In this study, the ability of different novel and robust machine learning (ML) approaches, including Light Gradient Boosting Machine (LightGBM), Extreme Gradient Boosting, Gradient Boosting Decision Tree, and Random Forest was implemented to predict the adsorptive removal of arsenate [As(V)] from wastewater over 13 different metal–organic frameworks (MOFs). A large experimental dataset was collected under various conditions. The adsorbent dosage, contact time, initial arsenic concentration, adsorbent surface area, temperature, solution pH, and the presence of anions were considered as input variables, and adsorptive removal of As(V) was selected as the output of the models. The developed models were evaluated using various statistical criteria. The obtained results indicated that the LightGBM model provided the most accurate and reliable response to predict As(V) adsorption by MOFs and possesses R2, RMSE, STD, and AAPRE (%) of 0.9958, 2.0688, 0.0628, and 2.88, respectively. The expected trends of As(V) removal with increasing initial concentration, solution pH, temperature, and coexistence of anions were predicted reasonably by the LightGBM model. Sensitivity analysis revealed that the adsorption process adversely relates to the initial As(V) concentration and directly depends on the MOFs surface area and dosage. This study proves that ML approaches are capable to manage complicated problems with large datasets and can be affordable alternatives for expensive and time-consuming experimental wastewater treatment processes.

Noncovalent Surface Modification of Metal-Organic Frameworks: Unscrambling Adsorption Properties via Isothermal Titration Calorimetry.

Despite the importance of noncovalent interactions in the utilization of metal-organic frameworks (MOFs), using these interactions to functionalize MOFs has rarely been explored. The ease of functionalization and potential for surface-selective functionalization makes modification via noncovalent interactions promising for the creation of porous photocatalytic assemblies. Using isothermal titration calorimetry, photoluminescence measurements, and desorption experiments, we have explored the nature and magnitude of the interactions of [Ru(bpy)2(bpy-R)]2+-functionalized dyes with the surface of MIL-96, where R = C3, C8, C12, and C18 alkyl chains of either straight-chain or cyclic conformations. The orientation of the dyes appears to be flat against the surface with respect to the long alkyl chains, and the surface concentration approaches a monolayer at high initial concentrations of dye. Strangely, the dodecyl-functionalized dye, despite having a smaller interaction energy and larger footprint than either octyl-functionalized dye, achieves the highest maximum surface concentration. Based on photoluminescence spectra, desorption experiments, and ITC data, we believe this is due to the core of the dye being lifted from the surface as the chain length increases. Our understanding of these interactions is important for further utilization of this method for the functionalization of the internal and external surface areas of MOFs.

Inner filter effect on amino-functionalized metal-organic framework for the selective detection of tetracycline

The use of tetracycline (TC) for the treatment of infectious diseases caused by bacteria has been humongous over the past few decades. However, the presence of untreated TC in freshwater leads to antimicrobial resistance. To prevent this concern from damaging the freshwater system, a stable sensor with high selectivity and rapid detection towards TC is desirable. Metal-Organic Frameworks (MOFs) are organic-inorganic hybrid structures with excellent stability, multifunctional ability, and tuneable pore structure that find extensive applications in detection techniques. The structural adaptability, excellent porosity and large surface area of MOFs prove advantageous in terms of adsorption of antibiotics. With this insight, a highly stable Zn-based Luminescent Metal-Organic Framework (LMOF) for the selective detection of tetracycline was developed. It is worth mentioning that, the LMOF-based sensor showed no depreciation in luminescence activity and can be reused more than 10 times. Moreover, a very low detection limit of 0.11 μM and a Stern-Volmer quenching constant (Ksv) value of 1.16 × 104 M−1 indicate its sensitivity precision towards TC detection. A significant inner filter effect of TC was observed in addition to adsorption of TC on the MOF through hydrogen bonding. Further, test strips based on IRMOF-3 showed satisfactory recovery in real-time samples. Thus, the stimuli-responsive sensor reports a simple strategy for excellent sensing performance towards TC.

Toxicological Impact and in Vivo Tracing of Rhodamine Functionalised ZIF-8 Nanoparticles.

Metal Organic Frameworks (MOFs) are extensively used for a wide range of applications due to their exceptionally high surface area. MOF particles are conventionally in micron size, but the nanosized MOFs show good transportation/mobility due to their small size, and when combined with the high surface area of MOFs, it makes MOF nanoparticles an ideal candidate to study for environmental remediation. Therefore, it is important to study the ecotoxicological impact of these MOFs. In this study, we developed rhodamine labelled nanoparticles of zinc imidazolate metal organic framework (ZIF-8 MOFs) as a means of in vivo tracing the MOF translocation in C. elegans. Rhodamine B isothiocyanate functionalized ZIF-8 MOFs nanoparticles (RBITC@ZIF-8 MOF nanoparticles; size 44 ± 7 nm) were fed to the worms naturally within a concentration range of 0.16–16.4 μg mg−1. Fluorescence was detected in the pharyngeal and gut lumen regions of the worms after 4 h of treatment, for exposure concentrations >0.163 μg mg−1. A higher intensity of fluorescence was observed at the end of 24 h for all exposure concentrations. Worms treated with RBITC@ZIF-8 MOF concentrations of ≥1.63 μg mg−1 for 24 h showed a bright stable fluorescence signal at the tail region. The uptake of RBITC@ZIF-8 MOF for an exposure concentration of 0.163, 1.63, and 8.2 μg mg−1 was found to be 52.1, 11.4 and 28.6%, respectively. Through this study, we showed that RBITC@ZIF-8 MOFs can be exposed to C. elegans and imaged at low concentrations of ∼0.16 μg mg−1.

Poly(sodium 4-styrenesulfonate) brushes-functionalized UiO-66-NH2 metal-organic framework for high and selective adsorption of dyes

Advanced adsorbents with high adsorption capacity and adsorption selectivity are desirable. Here, a Zr-based metal-organic framework (MOF), UiO-66-NH2 @poly(sodium 4-styrenesulfonate, Nass), was synthesized using the high surface area of MOFs as a substrate and the high grafting density of surface initiated-atom transfer radical polymerization (SI-ATRP). UiO-66-NH2 @poly(Nass) was used to adsorb different dyes. The maximum adsorption capacity (Qm) of methylene blue (MB) and basic fuchsine (BF) was 299.8 and 789.2 mg·g−1, respectively, which were higher than those of Sudan I (SD I, 6.340 mg·g−1), neutral red (NR, 188.1 mg·g−1), methyl orange (MO, 199.5 mg·g−1), and acid chrome blue K (AK, 122.3 mg·g−1). The adsorption isotherms and kinetics were investigated, and it was confirmed that the Langmuir isotherm and the pseudosecond-order kinetic model fit our adsorbents. In the binary mixed solution, the removal rate (R) of MB reached 64.44%, while that of MO was only 3.340% for MB/MO. R was 64.29% for MB and 21.97% for AK for MB/AK and 97.45% for BF and 30.03% for MO for BF/MO, verifying the preferential selectivity to adsorb basic dyes. The superior adsorption was ascribed to multiple interactions, including electrostatic interaction, hydrogen bonding, and π–π accumulation. In addition, the effect of grafting poly(Nass) on the pore size of UiO-66-NH2 was studied. The excellent stability showed that the R dropped by less than 15.62% after five consecutive cycles. The UiO-66-NH2 @poly(Nass) was applied in the determination of MB and BF in water, crucian carp, and green shrimp. Good linearity was observed for MB (R2 = 0.9971) and BF (R2 = 0.9993) in the range of 0.2–30 and 0.5–50 μg·mL-1, respectively, with satisfactory recoveries (in the range of 87.45–101.3% for MB and 90.34–98.86% for BF), achieving favorable practicability.

Synthesis, Characterization, and Application of Magnetized Lanthanum (III)-Based Metal-Organic Framework for the Organic Dye Removal from Water

A hybrid composite based on metal-organic framework (MOF) was chemically fabricated by embedding the magnetic Fe3O4 nanoparticles within amino-functionalized porous La-MOF (MOF/NH2) to produce a highly efficient and reusable composite of MOF/NH2/Fe3O4. Different proper techniques were used for the characterization of surface morphology and chemical arrangement of the prepared MOF/NH2/Fe3O4 composite. The characterization results using various techniques including Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), Brunauer, Emmett, and Teller analysis (BET), and vibrating sample magnetometer (VSM) approved the successful fabrication of MOF with amino arms on its surface besides the well magnetization using magnetic nanoparticles. The MOF/NH2/Fe3O4 composite showed enhanced adsorption capacity (618 mg/g) toward methyl orange (MO) anionic dye which is higher than many commercial reported adsorbents due to the presence of many types of adsorption sites (NH2 groups and lanthanum sites), large surface area of MOF, and the synergetic effect of magnetic nanoparticles. Moreover, the MOF/NH2/Fe3O4 composite showed selective adsorption of MO dye from dye mixtures owing to the electrostatic attraction. Also, the MOF/NH2/Fe3O4 composite retained over 90% of its efficiency for the dye removal even after six successive cycles. So, the present study provided a practical strategy for the design of functional MOF hybrid composites. Furthermore, due to the adaptability of its architectural form, it is a potential adsorbent material for industrial wastewater treatment uses.

MOFs have a new trick

Metal-organic frameworks (MOFs) are mostly pockets of empty space within a honeycomb structure of organic linkers and metal ions. Most scientists might assume such materials are incapable of conducting charge, but surprisingly, some MOFs do it well. That little-known, unexpected property , which scientists are trying to understand, is pushing MOFs into new territory. A small but quickly growing number of researchers is exploiting the rare combination of porosity, high surface area, and charge conductivity in these materials to create electronic sensors, charge storage devices, electrocatalysts, and other applications traditionally outside MOFs’ purview. For 25 years, chemists have been finding applications that take advantage of the extreme surface areas of metal-organic frameworks (MOFs). In just 1 g of some of these porous materials, the areas can reach nearly 8,000 m 2 —larger than a standard soccer pitch. That’s far greater than the surface area packed inside zeolites, activated carbon, and

Towards estimation of CO2 adsorption on highly porous MOF-based adsorbents using gaussian process regression approach

In recent years, new developments in controlling greenhouse gas emissions have been implemented to address the global climate conservation concern. Indeed, the earth's average temperature is being increased mainly due to burning fossil fuels, explicitly releasing high amounts of CO2 into the atmosphere. Therefore, effective capture techniques are needed to reduce the concentration of CO2. In this regard, metal organic frameworks (MOFs) have been known as the promising materials for CO2 adsorption. Hence, study on the impact of the adsorption conditions along with the MOFs structural properties on their ability in the CO2 adsorption will open new doors for their further application in CO2 separation technologies as well. However, the high cost of the corresponding experimental study together with the instrument's error, render the use of computational methods quite beneficial. Therefore, the present study proposes a Gaussian process regression model with four kernel functions to estimate the CO2 adsorption in terms of pressure, temperature, pore volume, and surface area of MOFs. In doing so, 506 CO2 uptake values in the literature have been collected and assessed. The proposed GPR models performed very well in which the exponential kernel function, was shown as the best predictive tool with R2 value of 1. Also, the sensitivity analysis was employed to investigate the effectiveness of input variables on the CO2 adsorption, through which it was determined that pressure is the most determining parameter. As the main result, the accurate estimate of CO2 adsorption by different MOFs is obtained by briefly employing the artificial intelligence concept tools.

Synthesis and environmental applications of defective metal organic frameworks

Metal organic frameworks (MOFs) are attracting increasing attention in the field of pollution control due to their inherent characteristics, such as high porosity, large specific surface areas, and tunable structure and composition. Though more than 20000 kinds of MOFs structures have been reported so far, the majority of them are regular and composed of different kinds of building units. Defect engineering in MOFs is an exciting concept for tailoring material properties, which opens up novel opportunities in practical application. Defects are usually present in MOFs, which would alter the performance of MOFs by changing surface properties, pore structure, and the number of active sites. Since defects can enhance the performance of MOFs in adsorption and catalytic degradation of pollutants, various methods for designing and generating defects have been employed. Based on selected reports spanning the last decades, this review focuses on the most recent and significant developments in the classification of defects in MOFs and methods of introducing defects into MOFs. According to the composition of MOFs, defects can be divided into missing-linkers defect and missing-clusters defect. The main methods of introducing defects into MOFs include de novo synthesis and post-synthetic treatment. De novo synthesis method includes mixed linker approach, modulation approach and fast crystal growth approach. Post-synthetic treatment method involves acid/base treatment approach, harsh activation approach, solvent-assisted linker exchange and mechanical treatment approach. The use of defective MOFs as adsorbent and catalyst in pollutant removal is also highlighted. Because single physical-chemical characterization has its limitations, researchers adopt various techniques to characterize the existence and concentration of defects, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), etc. Reasonable defects could be controlled by adjusting the synthesis conditions in an attempt to obtain MOFs with excellent performance in adsorption and catalysis. At the hand of adsorption, the adsorption of pollutants in water and gases onto defective MOFs is mainly affected by pore distribution, specific surface area and surface charge. The introduction of missing-linkers defect or missing-clusters defect would make the regular pore structure into locally disordered structure, and create new micropores, mesopores even macropores. Thereby, the pore volume and specific surface area of MOFs are increased, and then enhancing the adsorption performance. In view of photocatalysis, introducing defects into photo-responsive MOFs can not only promote the transfer of photo-generated electrons, but also inhibit electron-hole recombination, and even optimize the energy band structure, which synergistically results in the improvement of photocatalytic performance. From the perspective of chemical catalysis, the pores formed by missing-linkers defect or missing-clusters defect in MOFs would expose the interior surface, which creates additional catalytic sites for pollutants reaching, and then enhances the catalysis performance of MOFs. In short, defective MOFs have a wide range of applications in the fields of adsorption and catalysis. After summarizing the recent progress of the field, the advantages and shortcomings of present defective MOFs in pollution control are presented. On the basis of this, it is apparent that further deepening the basic theoretical study of defective MOFs will be helpful for its wide applications. The defect engineering of MOFs is beneficial for further industrialization. Finally, some potential research topics in construction of defects in MOFs for environmental application have also been proposed in the review.