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

Facile fabrication of electrospun hybrid nanofibers integrated cellulose, chitosan with ZIF-8 for efficient remediation of copper ions

To removal copper ions (Cu2+) from wastewater, structurally stable microcrystalline cellulose (MCC)/chitosan (CS)/zeolitic imidazole framework-8 (ZIF-8) hybrid nanofibers were fabricated by mixing electrospinning (MCC/CS/ZIF-8) and in-situ grown of ZIF-8 on electrospun nanofibers (I-MCC/CS/ZIF-8). The microstructure, porosity, thermal stability, crystal structure, surface wettability, chemical groups of hybrid nanofibers as well as their adsorption performance, isotherms, and kinetics were characterized and analyzed. The rhombohedral ZIF-8 at the optimum synthesis ratio was evenly bounded to nanofibers, corresponding to an average diameter of 775.81 nm. The introduction of ZIF-8 effectively improved the thermal stability of biomass polysaccharide nanofibers, maintained beneficial hydrophilicity (25.08°), increased their specific surface area by 16.51 times, and provided abundant potential active sites for Cu2+ adsorption. The adsorption performance of I-MCC/CS/ZIF-8 was superior to that of MCC/CS/ZIF-8, achieving the maximum Cu2+ adsorption capacity of 204.08 mg g-1 at pH = 5, which conformed to both the Langmuir model and the pseudo-second-order kinetic model. The enhanced mechanism for Cu2+ adsorption can be attributed to the sufficient channels of porous network and the strong hydrogen bonding facilitating physical adsorption, as well as the effective chemical adsorption resulting from the rapid growth of ultrathin lamellar copper oxide‑zinc oxide heterojunctions with nanoflower-like shapes.

A chitosan/MOF hybrid monolith with improved stability and enhanced adsorption performances via a pre-frozen crosslinking route

In wastewater remediation by adsorption, three-dimensional porous MOF (metal-organic frame)/polymer hybrid monoliths have been demonstrated to be promising absorbents with effective adsorption and recovery capacities. However, MOF/polymer monoliths often suffer from obvious decrease of porous structures due to large shrinkage during dry at room temperature, weakening the accessibility of active sites for adsorption. Here, a so-called pre-frozen crosslinking process is employed for fabrication of a chitosan/UiO-66 monolith, of which shrinkage is restrained markedly during drying in the air, and the shape of the monolith can be kept intact in 6.3 M acetic acid (CH3COOH), deionized water and 1 M sodium hydroxide (NaOH) for 60 days. Furthermore, the monolith achieves an adsorption capacity of 55.50 mg g-1 for methylchlorophenoxypropionic acid (MCPP) from its aqueous solution, increasing by 55.6% compared with UiO-66 particles, and the maximum adsorption capacity is 256.41 mg g-1.

Fabrication of Fe-doped UiO-66-NH2@b-TiO2 Z-scheme heterojunction for enhanced visible light-driven degradation of VSCs and antibiotics

Volatile sulfur compounds (VSCs) and sulfur-containing antibiotic wastewater are pervasive environmental pollutants that pose significant risks to atmospheric and aquatic ecosystems. Traditional photocatalysts often lack the versatility to simultaneously address multiple pollutants, highlighting the need for multifunctional materials. A novel FeUiO-66-NH2@b-TiO2 composite with a Z-scheme heterojunction has been developed as a highly efficient and tunable visible-light photocatalyst for the degradation of both VSCs and sulfur-containing antibiotics. The composite was synthesized through a one-pot hydrothermal method, and its photocatalytic performance was optimized by varying the ratio of FeUiO-66-NH2 to b-TiO2. The Z-scheme heterojunction facilitates effective separation and transfer of photogenerated carriers, significantly enhancing the material's photocatalytic activity. The material's structure and photoresponse were evaluated using XRD and FTIR. Under visible light, the composite exhibited remarkable degradation performance. For example, FU1T6 achieved complete degradation of CH3SH within 20 min, while FU3T1 degraded 90 % of the antibiotic cefixime within 140 min. Moreover, the material demonstrated excellent degradation efficiency for other cephalosporins and amoxicillin, proving its broad-spectrum capability for sulfur-containing antibiotics. This study highlights the FeUiO-66-NH2@b-TiO2 composite as a promising candidate for the treatment of complex environmental pollutants, including odorous gases and antibiotic wastewater. The results suggest that material design, particularly the integration of the Z-scheme heterojunction, enables multifunctional pollutant treatment, contributing significantly to environmental protection and public health. These findings provide an innovative strategy for tackling diverse sulfur-based pollutants in environmental remediation.

Rapid screening of acetylcholinesterase inhibitors in Qi-Fu-Yin using magnetic metal-organic frameworks immobilized with acetylcholinesterase

Current immobilization approaches for ligand fishing often experience challenges such as limited protein loading capacity and difficulties in the recycling process. To overcome these challenges, we synthesized a magnetic metal-organic frameworks (MMOFs) composite, which can be rapidly separated and has a large specific surface area, and employed it to immobilize acetylcholinesterase (AChE). The synthesized MMOFs@AChE composite exhibited a high immobilization yield (129.7 mg/g) and excellent relative activity recovery (88.1 %). Furthermore, immobilized AChE can improve its resistance to alkaline environments and high temperatures. After being stored at 4 °C for a month, the immobilized enzyme maintained 91.4 % of its original activity, significantly higher than the free enzyme (77.6 %). Furthermore, it preserved more than 80 % of its initial activity after five cycles and 68.7 % after eight cycles. The composite MMOFs@AChE was then incubated with Qi-Fu-Yin extract to fish for ligands binding to AChE. Notably, Qi-Fu-Yin can alleviate Alzheimer's disease (AD) symptoms by modulating the AChE pathway, while active compounds remain unclear. Sixteen potential AChE inhibitors were identified through UHPLC-Q-Exactive-Orbitrap-MS/MS. The results of ligand fishing were validated through molecular docking studies, molecular dynamics simulation, surface plasmon resonance and AChE inhibitory activity assays. The screened compounds may exert inhibitory effects on AChE by altering the spatial configuration of the catalytic site or by influencing the binding of the substrate to the catalytic site, catalytic anionic site and peripheral anionic site regions. The MMOFs@AChE-based ligand fishing platform offers an efficient, effective, and convenient approach for enzymatic inhibitors discovery from natural products.

Simultaneous removal of cationic and anionic dyes by highly efficient and recyclable ZIF-67/expanded vermiculite (ZIF-67/EV) composites

This study focuses on the synthesis of composite materials using Zeolitic imidazolate frameworks (ZIF-67) nanoparticles as an effective adsorbent, along with different concentrations (2-10%) of thermally expanded vermiculite (EV) as a low-cost and natural adsorbent substrate. The pristine materials and their composites were fully characterized using XRD, FTIR, BET, SEM, zeta potential, and EDS techniques. The pseudo-second-order kinetic model described both organic dyes' adsorption on synthesized adsorbents. Accordingly, the calculated adsorption capacities of Congo Red (CR) and Malachite Green (MG) dyes over the synthesized adsorbents were found to be about 22.72 and 49.02 mg/g for pure EV, 100 and 100 mg/g for pure ZIF-67, 90.91 and 100 mg/g for ZIF-67/EV-2, 100 and 100 mg/g for ZIF-67/EV-5, 95.24 and 99.01 mg/g for ZIF-67/EV-7, and 92.59 and 97.09 mg/g for ZIF-67/EV-10, respectively. The Langmuir isotherm model fits experimental isotherm data best in the studied temperature range (298-313 K). Among the synthesized adsorbent materials, the ZIF-67/EV-5 composite (containing 5% EV flakes) showed the highest maximum adsorption capacities of 1428.6 and 1114.2 mg/g for MG and CR dyes at pH 7 and 298 K. Moreover, it showed the highest removal efficiency (up to 99.5%) toward both cationic MG and anionic CR dyes in the binary mixture of both dyes. Finally, the regeneration and recyclability of this composite showed a 12% decrease in dye removal after five adsorption cycles. The synthesized ZIF-67/EV composites may therefore be used as efficient and inexpensive adsorbent materials for the simultaneous removal of cationic and anionic dyes from contaminated water. PRACTITIONER POINTS: ZIF-67/expanded vermiculite composites were synthesized and used to simultaneously remove cationic and anionic dyes from wastewater. Kinetics, isotherms, and thermodynamics of adsorption were studied showing good removal of both dyes. The ZIF-67/EV-5 composite achieved maximum adsorption capacities of 1428.6 and 1114.2 mg/g for cationic Malachite Green and anionic Congo Red dyes, respectively. Various interactions like π-π stacking and coordination are proposed as mechanisms of adsorption. The composite showed good selectivity in separating dyes and maintained high removal efficiency even after 5 reuse cycles.

Dihydrotetrazine-Functionalized Zirconium-Based Metal-Organic Frameworks for High-Capacity Oil Denitrogenation

High structural stability, dual organic-inorganic nature, and tunability in chemical functionality are promising characteristics of zirconium-based metal-organic frameworks (Zr-MOFs). These properties assist Zr-MOFs in extending their applications in various fields, especially adsorptive removal of pollutants. In this work, two well-known Zr-MOFs (UiO-66(Zr) and MIL-140(Zr) with the formula Zr6O4(OH)4(BDC)6, H2BDC is benzene 1,4-dicarboxylic acid) were synthesized and decorated with a dihydrotetrazine functional group through postsynthesis linker exchange (PSLE). Two dihydrotetrazine (DHTZ)-functionalized frameworks, UiO-66(Zr)-DHTZ and MIL-140(Zr)-DHTZ, were applied for the removal of quinoline (Qui) and indole (Ind) from the model oil. The results of adsorption experiments at room temperature display that these functionalized Zr-MOFs have significantly improved removal capacities for Qui (875% for UiO-66(Zr)-DHTZ and 303% for MIL-140(Zr)-DHTZ) and Ind (722% for UiO-66(Zr)-DHTZ and 257% for MIL-140(Zr)-DHTZ). Mechanistic studies based on X-ray photoelectron (XPS) and Fourier-transform infrared (FT-IR) spectroscopies reveal that there is a specific kind of host-guest interaction between dihydrotetrazine and nitrogen-containing compounds (NCCs). UiO-66(Zr)-DHTZ adsorbs 1426 mg·g-1 Qui and 1176 mg·g-1 Ind, while MIL-140(Zr)-DHTZ adsorbs 619 mg·g-1 Qui and 511 mg·g-1 Ind. The lower adsorption capacities of MIL-140(Zr)-DHTZ compared to UiO-66(Zr)-DHTZ are related to its lower surface area (783 m2·g-1 versus 330 m2·g-1). The recyclability of the frameworks goes up to five cycles without any significant decrease in the removal capacity. These results indicate that dihydrotetrazine-functionalized Zr-MOFs are highly stable platforms with superior adsorption capacity compared to basic and neutral NCCs.

Pore Characteristics and Dye Adsorption Mechanism of Functionalized UiO-66s with Various Ratios of Amino Groups

A series of UiO-66 samples with various amino functional group ratios were prepared by modulating the proportion of terephthalic acid (H2BDC) and aminoterephthalic acid (H2BDC-NH2) ligands, and the microstructure of the samples and dependence of methyl orange (MO) adsorption properties on the amino group content were investigated by X-ray diffraction, scanning electron microscopy, FTIR spectra, nitrogen adsorption, positron annihilation lifetime spectroscopy, and UV-vis spectra. The results showed that as the ratio of amino groups increased, the specific surface area and total porosity of the samples decreased, primarily due to decrement in the crystallinity as well as the bulky effect of amino groups in inherent pores. Interestingly, the amino-functionalized samples possessed considerable adsorption capacity of MO even in alkaline conditions due to the hydrogen bonding between the MO and -NH2 groups. The adsorption kinetics, isotherms, and thermodynamics revealed that MOs' adsorption process in amino-functionalized UiO-66s was exothermic, obeying a Langmuir-type adsorption dominated by chemisorption. UiO-66-NH2-0.4 (H2BDC:H2BDC-NH2 = 2:3) exhibited the best adsorption performance, with a maximum adsorption capacity of 336.7 mg/g, and the adsorption capacity was slightly decreased with increasing salt concentration in solution. UiO-66-NH2-0.4 could be easily regenerated by washing with a mixed solution of ethanol and water. The results demonstrated that although amino groups led to relatively less crystallinity and lower micropore volumes, the strong electrostatic attraction and hydrogen bonding between amino groups and MOs enhanced the adsorption capacity of MOs in amino-functionalized UiO-66s, in which MOs were adsorbed in two types of inherent pores, as shown by a significant decrement in positronium annihilation in them upon MO adsorption.

Preparation of Guanidine-Grafted NH2-MIL-101(Fe)/Polyvinylidene Fluoride Mixed Matrix Membranes for Adsorption of Pb2+ for Isopropanol Purification

Electronic-grade isopropyl alcohol is widely utilized in the cleaning of semiconductors and microelectronic components. Removing ions like Pb2+ is crucial since the presence of impurities may cause degradation of electronics, increased failure rates, and short circuits. Membrane materials offer a number of advantages in the field of adsorption separation; however, the lack of adsorption sites results in limited adsorption capacity. In the current work, guanidino-grafted NH2-MIL-101(Fe) was incorporated into polyvinylidene fluoride (PVDF) to prepare MOF/PVDF mixed matrix membranes (NM/PVDF) for the removal of Pb2+ from isopropanol. Benefiting from the larger specific surface area and more lone electron pairs in the guanidine group, the Pb2+ adsorption capacity of the as-prepared NM/PVDF membrane was 29.4458 mg/g, which was higher than that of the NH2-MIL-101(Fe)/PVDF membrane (20.9306 mg/g) and the pure PVDF membrane (6.7324 mg/g). The NM/PVDF membrane was able to reduce the concentration of Pb2+ from 500 to 86.73 ppb. This work highlights the potential of guanidine-grafted Fe-based MOFs/PVDF membranes as adsorbents for acquisition of electronic-grade solvents.

Novel three-dimensional fibrous covalent organic frameworks constructed via silver amalgam bridging for efficient organic dye adsorption and removal

The construction of covalent organic frameworks (COFs) with unique structures has great significance in exploring the structure-function relationship and extending their potential applications. Fibrous COFs have demonstrated superior performance in specific application scenarios owing to the distinctive three-dimensional (3D) structure. Herein, we report a facile strategy for the fabrication of 3D COF nanofiber by exploiting silver amalgam as a bridging agent to assemble one-dimensional-extended PA-COF modules into a tubular structure. Dimensions of the obtained 3D COF nanofiber were predicted by DFT calculations, and the nanofiber was endowed with the merits of favorable uniformity and high stability. Due to the enhanced exposure of conjugatable binding sites for dye retention offered by the novel 3D architecture, the PA-COF nanofiber exhibits fast adsorption (within 5 min) and superior adsorption capacity to various organic dyes, e.g., 1717 mg g-1 for methylene blue (MB) and 978.3 mg g-1 for methyl orange (MO). Moreover, the PA-COF nanofiber shows excellent reusability in dye adsorption, which makes it a potential medium for removing dye pollutants from wastewater. This work presents an effective strategy to construct COF materials with unique architecture and potential prospects in the fields of separation and wastewater treatment.

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.

Cu-Co bimetallic organic framework as effective adsorbents for enhanced adsorptive removal of tetracycline antibiotics

In this study, the removal effect of a new MOF-on MOF adsorbent based on Cu-Co bimetallic organic frameworks on tetracycline antibiotics (TCs) in water system was studied. The adsorbent (Cu-MOF@Co-MOF) were synthesized by solvothermal and self-assembly method at different concentrations of Co2+/Cu2+. The characterization results of SEM, XRD, XPS, FTIR and BET indicated that the MOF-on MOF structure of Cu-MOF@Co-MOF exhibited the best recombination and physicochemical properties when the molar ratio of Co2+: Cu2+ is 5:1. In addition, the Cu-MOF@Co-MOF have a high specific surface area and bimetallic clusters, which can achieve multi-target synergistic adsorption of TCs. Based on above advantages, Cu-MOF@Co-MOF provided a strong affinity and could efficiently adsorb more than 80% of pollutants in just 5 to 15 min using only 10 mg of the adsorbent. The adsorption capacity of tetracycline and doxycycline was 434.78 and 476.19 mg/g, respectively, showing satisfactory adsorption performance. The fitting results of the experimental data were more consistent with the Langmuir isotherm model and pseudo-second-order kinetic model, indicating that the adsorption process of TC and DOX occurred at the homogeneous adsorption site and was mainly controlled by chemisorption. Thermodynamic experiments showed that Cu-MOF@Co-MOF was thermodynamically advantageous for the removal of TCs, and the whole process was spontaneous. The excellent adsorption capacity and rapid adsorption kinetics indicate the prepared MOF-on MOF adsorbent can adsorb TCs economically and quickly, and have satisfactory application prospects for removing TCs in practical environments. The results of the study pave a new way for preparing novel MOFs-based water treatment materials with great potential for efficient removal.

Facile synthesis of lignin-based Fe-MOF for fast adsorption of methyl orange

To rapidly remove dyes from wastewater, iron-based metal-organic frameworks modified with phenolated lignin (NH2-MIL@L) were prepared by a one-step hydrothermal method. Analyses of the chemical structure and adsorption mechanism of the NH2-MIL@L proved the successful introduction of lignin and the enhancement of its adsorption sites. Compared with NH2-MIL-101-Fe without phenolated lignin, the modification with lignin increased the methyl orange (MO) adsorption rate of NH2-MIL@L. For the best adsorbent, NH2-MIL@L4, the MO adsorption efficiency in MO solution reached 95.09% within 5 min. NH2-MIL@L4 reached adsorption equilibrium within 90 min, exhibiting an MO adsorption capacity of 195.31 mg/g. The process followed pseudo-second-order kinetics and the Dubinin-Radushkevich model. MO adsorption efficiency of NH2-MIL@L4 was maintained at 89.87% after six adsorption-desorption cycles. In mixed solutions of MO and methylene blue (MB), NH2-MIL@L4 achieved an MO adsorption of 94.02% at 5 min and reached MO adsorption equilibrium within 15 min with an MO adsorption capacity of 438.6 mg/g, while the MB adsorption equilibrium was established at 90 min with an MB adsorption rate and capacity of 95.60% and 481.34 mg/g, respectively. NH2-MIL@L4 sustained its excellent adsorption efficiency after six adsorption-desorption cycles (91.2% for MO and 93.4% for MB). The process of MO adsorption by NH2-MIL@L4 followed the Temkin model and pseudo-second-order kinetics, while MB adsorption followed the Dubinin-Radushkevich model and pseudo-second-order kinetics. Electrostatic interactions, π-π interactions, hydrogen bonding, and synergistic interactions affected the MO adsorption process of NH2-MIL@L4.

Structure-Assisted Boronic Acid Implanted Mesoporous Metal-Organic Frameworks for Specific Extraction of cis-Diol Molecules

cis-Diol-containing molecules, an essential type of compounds in living organisms, have attracted intensive research interest from various fields. The analysis of cis-diol-containing molecules is still suffering from some drawbacks, including low abundance and abundant interference. Metal-organic frameworks (MOFs) have proven to be an ideal sorbent for sample preparation. However, most of the reported MOFs are mainly restricted to a microporous regime (pore size <2 nm), which greatly limits the application. Herein, a facile strategy is established to construction of boronate affinity MOFs via the postsynthetic ligand-exchange process. Owing to the fact that the ligand-exchange process was assisted by the structural integrity of the primitive metal-organic framework and the great compatibility of click chemistry, the obtained EPBA-PCN-333(Fe) is able to realize the maximum maintaining the porosity and crystallinity of the parent material. Several intriguing features of EPBA-PCN-333(Fe) (e.g., excellent selectivity, efficient diffusion, good accessibility, and size exclusion effect) are experimentally demonstrated via a series of cis-diol-containing molecules with different molecular sizes (small molecules, glycopeptides, and glycoproteins). The binding performance of EPBA-PCN-333(Fe) is evaluated by employing catechol as the test molecule (binding capacity: 0.25 mmol/g, LOD: 200 ng/mL). Finally, the real-world applications of EPBA-PCN-333(Fe) were demonstrated by the detection of nucleosides of human urine samples.

A Drop-and-Drain Method for Convenient and Efficient Fabrication of MOF/Fiber Composites

The fabrication of flexible composites by integrating metal-organic frameworks (MOFs) with flexible substrates is a critical strategy for developing advanced materials with excellent feasibility and processability. These flexible MOF-based composites play a particularly important role in the separation and purification processes. However, several drawbacks remain challenge to overcome such as long processing time, high-cost, complicated processes, or harsh reaction conditions. In this paper, a convenient and efficient method is reported for fabricating MOF/fiber composites using a simple drop-and-drain (D&D) process. By exploiting the electrostatic interactions between the positively charged MOF particles and negatively charged fiber-based flexible substrates, a uniform coating of MOF on flexible fibers are achieved. This is accomplished by allowing the MOF ink to drop and drain through a substrate using a custom-made Teflon cell. Additionally, the D&D method enables the production of multiple layers of composites in a single-step process. UiO-66 and ZIF-8 submicroparticles and various substrates such as cotton-pad, cotton-fabric, nylon-fabric, PET-fabric, and filter-paper are employed to create flexible MOF/fiber composites. These composites demonstrate outstanding capacities for capturing negatively charged organic dyes, including methyl orange and indigo carmine. Furthermore, the MOF/fiber composites can be reused for dye capture after a simple washing process.

Highlights in Interface of Wastewater Treatment by Utilizing Metal Organic Frameworks: Purification and Adsorption Kinetics

Polluted water has become a concern for the scientific community as it causes many severe threats to living beings. Detection or removal of contaminants present in wastewater and attaining purity of water that can be used for various purposes are a primary responsibility. Different treatment methods have already been used for the purification of sewage. There is a need for low-cost, highly selective, and reusable materials that can efficiently remove pollutants or purify contaminated water. In this regard, MOFs have shown significant potential for applications such as supercapacitors, drug delivery, gas storage, pollutant adsorption, etc. The outstanding structural diversity, substantial surface areas, and adjustable pore sizes of MOFs make them superior candidates for wastewater treatment. This Review provides an overview of the interaction science and engineering (kinetic and thermodynamic aspects with interactions) underpinning MOFs for water purification. First, fundamental strategies for the synthesis methods of MOFs, different categories, and their applicability in wastewater treatment are summarized, followed by a detailed explanation of various interaction mechanisms. Finally, current challenges and future outlooks for research on MOF materials toward the adsorption of hazardous components are discussed. A new avenue for modifying their structural characteristics for the adsorption and separation of hazardous materials, which will undoubtedly direct future work, is also summarized.

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.