CO2/CH4 separation by mixed-matrix membranes holding functionalized NH2-MIL-101(Al) nanoparticles: Effect of amino-silane functionalization

New generation mixed matrix membrane for CO2 separation: Transition from binary to quaternary mixed matrix membrane

Contemporary advances in material development associated with membrane gas separation refer to the cost-effective fabrication of high-performance, defect-free mixed matrix membranes (MMMs). For clean energy production, natural gas purification, and CO2 capture from flue gas systems, constituting a functional integration of polymer matrix and inorganic filler materials find huge applications. The broad domain of research and development of MMMs focused on the selection of appropriate materials, inexpensive membrane fabrication, and comparative study with other gas separation membranes for real-world applications. This study addressed a comprehensive review of the advanced MMMs wrapping various facets of membrane material selection; polymer and filler particle morphology and compatibility between the phases and the relevance of several fillers in the assembly of MMMs are analyzed. Further, the research on binary MMMs, their problems, and solutions to overcome these challenges have also been discussed. Finally, the future directions and scope of work on quaternary MMM are scrutinized in the article.

Reduction of sulfur in fuel oil using Fe2O3 hybrid nanoadsorbent by solvent deasphalting and optimization of operational parameters with CCD

The present study investigated and tested the effect of adding three types of nanoadsorbents (multi-walled carbon nanotubes (MWCNT)) in pure form, multi-walled carbon nanotubes with Fe2O3 particles (MWCNT-Fe2O3) hybrid, and Silanated-Fe2O3 hybrid to heavy fuel oil to reduce sulfur using a deasphalting process with solvent. First, all three types of nanoadsorbents were synthesized. Then, the Central Composite Design (CCD) method was used to identify the parameters effective in deasphalting, such as the type of nanoadsorbent, the weight percentage of nanoadsorbent, and the solvent-to-fuel ratio, and to obtain their optimal values. Based on the optimization result, under laboratory temperature and pressure conditions, the highest percentage of sulfur reduction in deasphalted fuel (DAO) was obtained by adding 2.5% by weight of silanated-Fe2O3 nano-adsorbent and with a solvent-to-fuel ratio of 7.7 (The weight percentage of sulfur in DAO decreased from 3.5% by weight to 2.46%, indicating a decrease of 30%). Additionally, by increasing the temperature to 70 °C, in optimal conditions, the results revealed that the remaining sulfur percentage in DAO decreased to 2.13% by weight, indicating a decrease of 40%. Synthesized nanoadsorbents and asphaltene particles adsorbed on the surfaces of nanoadsorbents were evaluated by XRD, FTIR, FESEM, and TEM techniques.

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.

Magnetic Nitrogen-Rich UiO-66 Metal-Organic Framework: An Efficient Adsorbent for Water Treatment

The postsynthetic modification of metal-organic frameworks (MOFs) has opened up a promising area to widen their water treatment application. However, their polycrystalline powdery state still restricts their widespread industrial-scale applications. Herein, the magnetization of UiO-66-NH₂ is reported as a promising approach to facilitate the separation of the used MOFs after water treatment. A two-step postmodification procedure employing 2,4,6-trichloro-1,3,5-triazine (TCT) and 5-phenyl-1H-tetrazole (PTZ) agents was introduced to level up the adsorption performance of the magnetic nanocomposite. Despite a decrement in porosity and specific surface area of the designed MOFs (m-UiO-66-TCT) compared to neat UiO-66-NH₂, it outweighs in adsorption capacity. It was observed that m-UiO-66-TCT has an adsorption capacity of ≈298 mg/g for methyl orange (MO) with facile MOF separation using an external magnet. Pseudo-second-order kinetic model and Freundlich isotherm models suitably interpret the experimental data. Thermodynamic studies showed that MO removal using m-UiO-66-TCT is spontaneous and thermodynamically favorable at higher temperatures. The m-UiO-66-TCT composite exhibited easy separation, high adsorption capacity, and good recyclability, rendering it an attractive candidate for the adsorptive removal of MO dye from aqueous environments.

A comprehensive review on zeolite-based mixed matrix membranes for CO2/CH4 separation

Biogas consisting of carbon dioxide/methane (CO₂/CH₄) gas mixtures has emerged as an alternative renewable fuel to natural gas. The presence of CO₂ can decrease the calorific value and generate greenhouse gas. Hence, separating CO₂ from CH₄ is a vital step in enhancing the use of biogas. Zeolite and zeolite-based mixed matrix membrane (MMM) is considered an auspicious candidate for CO₂/CH₄ separation due to thermal and chemical stability. This review initially addresses the development of zeolite and zeolite-based MMM for the CO₂/CH₄ separation. The highest performance in terms of CO₂ permeance and CO₂/CH₄ selectivity was achieved using zeolite and zeolite-based MMM, which exhibited CO₂ permeance in the range of 2.0 × 10^{- 7}-7.0 × 10^{- 6} mol m^{- 2} s^{- 1} Pa^{- 1} with CO₂/CH₄ selectivity ranging from 3 to 300. Current trends directed toward improving CO₂/CH₄ selectivity via modification methods including post-treatment, ion-exchanged, amino silane-grafted, and ionic liquid encapsulated of zeolite-based MMM. Those modification methods improved the defect-free and interfacial adhesions between zeolite particulates and polymer matrices and subsequently enhanced the CO₂/CH₄ selectivity. The modifications via ionic liquid and silane methods more influenced the CO₂/CH₄ selectivity with 90 and 660, respectively. This review also focuses on the possible applications of zeolite-based MMM, which include the purification and treatment of water as well as biomedical applications. Lastly, future advances and opportunities for gas separation applications are also briefly discussed. This review aims to share knowledge regarding zeolite-based MMM and inspire new industrial applications.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Adsorption Behavior of a Gd-Based Metal-Organic Framework toward the Quercetin Drug: Effect of the Activation Condition

A carboxylate gadolinium-based metal-organic framework (Gd-MOF) is an exceptional candidate for magnetic resonance imaging agents, but its low drug adsorption capacity hinders this MOF from being used as a theragnostic agent. In this work, the Gd-MOF was synthesized by a simple solvothermal method. Then, different activation situations, including various solvents over different time periods, were applied to enhance the specific surface area of the synthesized MOF. Different characterization analyses such as X-ray diffraction and Brunauer-Emmett-Teller along with experimental quercetin adsorption tests were done to study the crystalline and physical properties of various activated MOFs. In the following, the MOF activated by ethanol for 3 days (3d-E) was chosen as the best activated MOF due to its crystallinity, highest specific surface area, and drug adsorption capacity. More explorations were done for the selected MOF, including the drug adsorption isotherm, thermodynamics, and pH effect of adsorption. The results show that the activation process substantially affects the crystallinity, morphology, specific surface area, and drug adsorption capacity of Gd-MOFs. An optimized activation condition is proposed in this work, which shows an impressive enhancement of the specific surface area of Gd-MOFs just by simple solvent exchange method employment.

Development of Amine-Functionalized Metal-Organic Frameworks Hollow Fiber Mixed Matrix Membranes for CO2 and CH4 Separation: A Review

CO2 separation from raw natural gas can be achieved through the use of the promising membrane-based technology. Polymeric membranes are a known method for separating CO2 but suffer from trade-offs between its permeability and selectivity. Therefore, through the use of mixed matrix membranes (MMMs) which utilizes inorganic or hybrid fillers such as metal-organic frameworks (MOFs) in polymeric matrix, the permeability and selectivity trade-off can be overcome and possibly surpass the Robeson Upper Bounds. In this study, various types of MOFs are explored in terms of its structure and properties such as thermal and chemical stability. Next, the use of amine and non-amine functionalized MOFs in MMMs development are compared in order to investigate the effects of amine functionalization on the membrane gas separation performance for flat sheet and hollow fiber configurations as reported in the literature. Moreover, the gas transport properties and various challenges faced by hollow fiber mixed matrix membranes (HFMMMs) are discussed. In addition, the utilization of amine functionalization MOF for mitigating the challenges faced is included. Finally, the future directions of amine-functionalized MOF HFMMMs are discussed for the fields of CO2 separation.

RSM Modeling and Optimization of CO2 Separation from High CO2 Feed Concentration over Functionalized Membrane

The challenges in developing high CO₂ gas fields are governed by several factors such as reservoir condition, feed gas composition, operational pressure and temperature, and selection of appropriate technologies for bulk CO₂ separation. Thus, in this work, we report an optimization study on the separation of CO₂ from CH₄ at high CO₂ feed concentration over a functionalized mixed matrix membrane using a statistical tool, response surface methodology (RSM) statistical coupled with central composite design (CCD). The functionalized mixed matrix membrane containing NH₂-MIL-125 (Ti) and 6FDA-durene, fabricated in our previous study, was used to perform the separation performance under three operational parameters, namely, feed pressure, temperature, and CO₂ feed concentration, ranging from 3.5–12.5 bar, 30.0–50.0 °C and 15–70 mol%, respectively. The CO₂ permeability and CO₂/CH₄ separation factor obtained from the experimental work were varied from 293.2–794.4 Barrer and 5.3–13.0, respectively. In addition, the optimum operational parameters were found at a feed pressure of 12.5 bar, a temperature of 34.7 °C, and a CO₂ feed concentration of 70 mol%, which yielded the highest CO₂ permeability of 609.3 Barrer and a CO₂/CH₄ separation factor of 11.6. The average errors between the experimental data and data predicted by the model for CO₂ permeability and CO₂/CH₄ separation factor were 5.1% and 3.3%, respectively, confirming the validity of the proposed model. Overall, the findings of this work provide insights into the future utilization of NH₂-MIL-125 (Ti)/6FDA-based mixed matrix membranes in real natural gas purification applications.