Facile Synthesis of Polyaniline@UiO-66 Nanohybrids for Efficient and Rapid Adsorption of Methyl Orange from Aqueous Media

Investigation the effect of exchange solvents on the adsorption performances of Ce-MOFs towards organic dyes

Cerium-based MOFs (Ce-MOFs) are regarded as attractive porous materials showing various structures, excellent thermal and chemical stability, tunable porous properties, and simple synthetic methods that are useful for wastewater treatment applications. Hence, in the present work, we synthesized a series of Ce-MOFs through a fast and green synthetic method at room temperature using water as a green solvent. Four different solvents including ethanol, chloroform, acetone, and methanol were used in the solvent-exchange process to engineer the properties of prepared Ce-MOFs. The influence of different exchange solvents on the crystalline structure, porous structure, thermal stability, and surface morphology of Ce-MOFs was studied systematically. It was found that exchange solvents can significantly affect the chemical and physical properties of prepared Ce-MOFs. Using ethanol as an exchange solvent results in the production of highly crystalline MOF that has the highest surface area (843 m2/g) and pore volume (0.7518 cm3/g) compared to other prepared Ce-MOFs. The dye adsorption experiments revealed that the activated sample by acetone (Ce-MOF-4) exhibited the highest adsorption capacities toward both anionic (270.27 mg/g for Congo Red (CR)) and cationic (227.27 mg/g for Malachite Green (MG)) dyes. This MOF adsorbs both organic dyes via different mechanisms including hydrogen bonding, pore-filling, π-π stacking, coordination, and electrostatic interactions. Moreover, it exhibited good structural stability in acidic solution, neutral solution, and during consecutive adsorption-desorption cycles, confirming its potential to be applied as a stable adsorbent for simultaneous removal of cationic and anionic organic dyes from water.

3D-Printed MOF Monoliths: Fabrication Strategies and Environmental Applications

Metal-organic frameworks (MOFs) have been extensively considered as one of the most promising types of porous and crystalline organic-inorganic materials, thanks to their large specific surface area, high porosity, tailorable structures and compositions, diverse functionalities, and well-controlled pore/size distribution. However, most developed MOFs are in powder forms, which still have some technical challenges, including abrasion, dustiness, low packing densities, clogging, mass/heat transfer limitation, environmental pollution, and mechanical instability during the packing process, that restrict their applicability in industrial applications. Therefore, in recent years, attention has focused on techniques to convert MOF powders into macroscopic materials like beads, membranes, monoliths, gel/sponges, and nanofibers to overcome these challenges.Three-dimensional (3D) printing technology has achieved much interest because it can produce many high-resolution macroscopic frameworks with complex shapes and geometries from digital models. Therefore, this review summarizes the combination of different 3D printing strategies with MOFs and MOF-based materials for fabricating 3D-printed MOF monoliths and their environmental applications, emphasizing water treatment and gas adsorption/separation applications. Herein, the various strategies for the fabrication of 3D-printed MOF monoliths, such as direct ink writing, seed-assisted in-situ growth, coordination replication from solid precursors, matrix incorporation, selective laser sintering, and digital light processing, are described with the relevant examples. Finally, future directions and challenges of 3D-printed MOF monoliths are also presented to better plan future trajectories in the shaping of MOF materials with improved control over the structure, composition, and textural properties of 3D-printed MOF monoliths.

Removal of Anionic Methyl Orange Dye from Water by Poly[2-methyl-1H-indole] Derivatives: Investigation of Kinetics and Isotherms of Adsorption

The adsorption properties toward methyl orange (MO) were evaluated for poly[2-methyl-1H-indole] and its derivatives. The influence of pH, ionic strength of solution, composition, and amount of sorbent on the adsorption of MO dye was investigated; the kinetics of dye adsorption was studied. The adsorption isotherms were analyzed using different models of sorption equilibrium. The presence of chemical interaction between polyindoles and dye was proved by IR and UV spectroscopy methods. The sorption of MO with polymers is realized mainly due to the formation of electrostatic interactions between the sulfogroup of the dye and the imino group of the sorbent. Microphotographs demonstrate the change in the morphology of polyindoles after adsorption, which further confirms the structural changes in the polymers. It was found that the main factors affecting the sorption capacity of the studied materials are the position and nature of substituents in the polymers and the sorption conditions. For example, polyindoles containing a methoxy group in their structure (o-OMePIn and m-OMePIn) have the best sorption activity. These polymers are effective in adsorbing dyes, which means that they can be used in wastewater treatment.

Fabrication of Bacterial Cellulose/Chitosan-MIL-100(Fe) Composite for Adsorptive Removal of Dacarbazine

In this research, a polymeric composite based on a chitosan/bacterial cellulose (CS/BC) matrix filled with MIL-100(Fe) particles was prepared to solve the recyclability of issue MIL-100(Fe) particles and utilized as an efficient adsorbent for removing dacarbazine (DTIC) from wastewater. The adsorption capacity of the composite (CS/BC-MIL) was higher than both MIL-100(Fe) and the CS/BC polymeric matrix. The adsorption performance of the fabricated composite was evaluated through kinetics and isotherm studies. While isotherm studies revealed that the adsorption of DTIC onto the adsorbent can be well described by the Freundlich model, kinetics studies indicated that a combination of factors, rather than a single rate-limiting factor, are responsible for the adsorption rate. Thermodynamics investigation showed that the adsorption of DTIC to CS/BC-MIL composite is exothermic and occurs spontaneously. Additionally, due to the negative entropy change, it was established that the adsorption is governed by the enthalpy change. Exploring the solution chemistry revealed that the optimum pH for the adsorption process was about 4. Moreover, the CS/BC-MIL can selectively adsorb DTIC in the presence of other pharmaceuticals like doxorubicin (DOX). Furthermore, regeneration investigations disclosed that the composite holds its structural features and has an acceptable adsorption capacity after several cycles of adsorption/desorption.

Novel ZIF-8/CNC Nanohybrid with an Interconnected Structure: Toward a Sustainable Adsorbent for Efficient Removal of Cd(II) Ions

Water pollution, especially by heavy metals, continues to pose significant challenges, emphasizing the urgency to develop sustainable processes to remove pollutants while developing sustainable materials derived from renewable sources. In the present research, a nanoscale adsorbent was prepared to remove cadmium (Cd(II)) ions from wastewater by hybridizing zeolitic imidazolate framework-8 (ZIF-8) with a cellulose nanocrystal (CNC). The prepared nanohybrid exhibited an interconnected structure in which the ZIF-8 particles were connected to each other via CNC nanoneedles. The hybridization of ZIF-8 with CNC caused a significant enhancement in the adsorption performance of the fabricated nanohybrid compared to pure ZIF-8, increasing its adsorption capacity by nearly 36%. The adsorption of ZIF/CNC followed the Langmuir isotherm model and pseudo-second-order kinetics models, remarking homogeneous adsorption onto the surface of ZIF/CNC, where chemisorption controlled the rate of adsorption. The thermodynamic study uncovered that the adsorption is spontaneous, endothermic, and entropy-governed as the randomness was increased at the solid-liquid interface. Additionally, the influence of operating variables, such as temperature, adsorbent dosage, pH, and ionic strength, was studied to mimic the adsorption capabilities of the adsorbent in real conditions. Accordingly, the optimum conditions were found to be at 45 °C and pH = 7 with a dosage of 0.4 g/L for the adsorbent. Moreover, the adsorption in a multimetal solution showed that the ZIF/CNC nanohybrid can remove various heavy metals, including Cd(II), Fe(III), Cu(II), and Pb(II) ions simultaneously. Finally, the regeneration study confirmed the great potential of the ZIF/CNC nanohybrid, which retained 94% of its initial adsorption capacity after 5 consecutive adsorption/desorption cycles.

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.

Interface synthesis of Cu-BTC/PVDF hybrid membranes and their selective adsorption activity toward Congo red

Considering the surface affinity of MOFs and separation advantages of polymer membranes, herein, a one-step interface synthesis strategy is used in the construction of Cu-BTC/PVDF hybrid membranes, in which Cu2+ ions and 1,3,5-benzenetricarboxylic acid (H3BTC) were dissolved in ionized water and n-octanol separately, and polyvinylidene fluoride (PVDF) films were laid at the interface of two immiscible solvents. As a result, Cu-BTC was generated and readily self-assembled inside the PVDF films. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and the Brunauer-Emmett-Teller (BET) method were used to characterize Cu-BTC/PVDF hybrid membranes, and Congo red (CR) was selected as the target dye to evaluate the surface adsorption activity of the hybrid membranes. Batch adsorption tests under various conditions were conducted to optimize the adsorption capacity, adsorption kinetics, isotherms and thermodynamics, which were analyzed to further explore the adsorption behavior. Based on this, the adsorption mechanism was discussed. It is worth noting that because of the π-π stacking interaction and hydrogen bonding, an extraordinary adsorption capacity of CR was achieved, and the good separation advantage and the cyclic adsorption performances endow the resulting Cu-BTC/PVDF hybrid membranes with promising applications in the removal of organic dyes from practical wastewater.

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.

Effect of a Zr-Based Metal-Organic Framework Structure on the Properties of Its Composite with Polyaniline

Composites of polyaniline (PANI) and Zr-based metal-organic frameworks (MOFs), UiO-66 and UiO-66-NH2, were synthesized by the oxidative polymerization of aniline in the presence of MOF templates with the MOF content in the resulting materials (78.2 and 86.7 wt %, respectively) close to the theoretical value (91.5 wt %). Scanning electron microscopy and transmission electron microscopy showed that the morphology of the composites was set by the morphology of the MOFs, whose structure was mostly preserved after the synthesis, based on the X-ray diffraction data. Vibrational and NMR spectroscopies pointed out that MOFs participate in the protonation of PANI and conducting polymer chains were grafted to amino groups of UiO-66-NH2. Unlike PANI-UiO-66, cyclic voltammograms of PANI-UiO-66-NH2 showed a well-resolved redox peak at around ≈0 V, pointing at the pseudocapacitive behavior. The gravimetric capacitance of PANI-UiO-66-NH2, normalized per mass of the active material, was also found to be higher compared to that of pristine PANI (79.8 and 50.5 F g-1, respectively, at 5 mV s-1). The introduction of MOFs into the composites with PANI significantly improved the cycling stability of the materials over 1000 cycles compared to the pristine conducting polymer, with the residual gravimetric capacitance being ≥100 and 77%, respectively. Thus, the electrochemical performance of the prepared PANI-MOF composites makes them attractive materials for application in energy storage.

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.