Synthesis of Fe-THC MOFs and functionalizing MOFs by MXenes for the selective removal of lead(ii) ions from wastewater

The elimination of heavy metals, especially lead, from wastewater is vital for the environment and human health and using a proper adsorbent to achieve this goal is highly desirable. Initially, Fe-THC MOF was prepared using a simple method and functionalized using MXene for efficient, rapid, and selective elimination of lead. Different characterization tools demonstrated that Fe-THC MOF and its composite Fe-THC/MXene were successfully prepared. The adsorption outcomes showed that the maximum sorption capability was 674 mg g^-1 at 305 K and pH 4.5. The sorption kinetics obeys the pseudo-second-order kinetic model, and the sorption isotherms fit the Langmuir isotherm model. This finding suggests monolayer sorption on Fe-THC/MXene, and the rate-controlling step is chemisorption. Thermodynamic findings exhibit that sorption was a spontaneous and exothermic process. The sorption process can selectively adsorb Pb ions from aqueous media. After five adsorption-desorption tests, the adsorption efficiency of Fe-THC/MXene was still high. The sorption mechanism of lead on Fe-THC was mainly due to the interaction of lead ions with -F and -O ions and porosity of the Fe-THC/MXene composite. The -O and -F ions were derived from MXene, while the porosity was derived from the MOFs of composites. These findings confirmed that Fe-THC/MXene enables rapid, efficient, and selective elimination of lead from wastewater, which is of practical importance.

Anion-Directed Self-Assembly of Calix[4]arene-Based Silver(I) Coordination Polymers and Photocatalytic Degradation of Organic Pollutants

Coordination polymers (CPs) have recently emerged as promising candidates for heterogeneous photocatalysis due to their structural designability and tunable properties. Herein, we developed two novel Ag(I)-calix[4]arene coordination polymers with the formula {[Ag₂(μ-NO₃)L¹]}_n (CP 1) and {[AgL¹]·PF₆}_n (CP 2) (L¹ = 2-mercapto-5-methyl-1,3,4-thiadiazole resorcinol calix[4]arene). Crystallography revealed that anion coordination and self-inclusion behavior induced the cavitand and silver ions to self-assemble into well-defined CPs 1 and 2 with different topological coordination frameworks, respectively. Furthermore, CPs 1 and 2 display high photocatalytic activity for the photodegradation of rhodamine B (RhB) and methyl orange (MO) in an aqueous solution under mild conditions (WLED and UV irradiation). The comparison results demonstrate that CP 1 exhibited better photocatalytic performance than CP 2, which correlated well with the differences in their molecular structure and HOMO-LUMO energy gaps. The photocatalysis products and possible intermediates were successfully monitored and determined using mass spectrum, gas chromatography, and electron paramagnetic resonance measurements. The rational photocatalysis mechanism was further investigated and proposed.

The Versatility of Ethylene Glycol to Tune the Dimensionality and Magnetic Properties in DyIII-Anilato-Based Single-Ion Magnets

We exploit the high versatility of the solvent ethylene glycol (eg = CH₂OH-CH₂OH) acting as a ligand with three different coordination modes: terminal (κO), chelate (κ²O,O'), and bridge (1κO,2κO') to prepare a novel family of six different coordination polymers with Dy^III and three different anilato ligands (3,6-disubstituted-2,5-dihydroxy-1,4-benzoquinone dianion = C₆O₄X₂^2-, with X = H, Cl, and Br). With the X = H derivative (dhbq^2-), we have prepared [Dy₂(dhbq)₃(eg)₂(μ-eg)]·4eg·2H₂O (1), a 3D diamond-like network with a chelate and bridging eg molecules. With the X = Cl derivative (chloranilato), we have prepared [Dy₂(C₆O₄Cl₂)₃(eg)₄]·2eg·H₂O (2) and [Dy₂(C₆O₄Cl₂)₃(μ-eg)(H₂O)₄]·2eg·7H₂O (3). Compound 2 has a 2D (6,3)-gon brick-wall lattice and contains a chelate and a terminal eg molecule. Compound 3 has a 3D diamond-like topology as 1, although now the chelate eg has been replaced by two water molecules. Finally, with the X = Br derivative (bromanilato), we have obtained [Dy₂(C₆O₄Br₂)₃(eg)₂(CH₃OH)₂]·2eg·4CH₃OH (4), [Dy₂(C₆O₄Br₂)₃(eg)₄]·4eg (5), and [Dy₂(C₆O₄Br₂)₃(eg)₃(H₂O)]·2eg·H₂O (6). Compound 4 has a 2D (6,3)-gon herringbone topology and contains a chelate eg and a MeOH molecule. Compounds 5 and 6 have a 2D (6,3)-gon brick-wall topology with a chelate and a terminal eg molecules (in 5 and in one of the two independent Dy centers of 6). The other Dy center in 6 has a chelate eg and a water molecule. All the compounds show slow relaxation of the magnetization at low temperatures (in compounds 1, 2, and 5 with no applied DC field). The magnetization of compounds 1-6 relaxes through Orbach and direct mechanisms when a DC field is applied and through an Orbach and/or quantum tunneling mechanism when no DC field is applied.

Two pillared-layer metal-organic frameworks based on the pinwheel trinuclear carboxylate-clusters of Zn(II) and Co(II): synthesis, crystal structures, magnetic study, and Lewis acid catalysis

Using a dicarboxylic acid, [1,1'-biphenyl]-4,4'-dicarboxylic acid (H₂L1) and an exobidentate ligand, (1E,1'E)-N,N'-(1,4-phenylene)bis(1-(pyridin-4-yl)methanimine) (L2), two 3D interpenetrated networks, {[Zn₃(L1)₃(L2)]·9H₂O}_n (Zn-MOF) and {[Co₃(L1)₃(L2)(DMF)]·0.5DMF}_n (Co-MOF), have been prepared in good yields. The crystal structure analysis of Zn-MOF and Co-MOF revealed that both have a 3D pillared-layer structure based on pinwheel trinuclear metal-carboxylate clusters as secondary building units (SBUs). Furthermore, the structures also exhibited three-fold interpenetration. Although the overall networks in Zn-MOF and Co-MOF showed significant resemblances, there are marked differences in their crystal structures, which are associated with the coordination environment of the metal centre and the binding modes of the carboxylates. Gas adsorption studies (N₂ at 77 K and 1 bar) indicated that Co-MOF is more porous than Zn-MOF. Magnetic measurements on Co-MOF indicate a significant antiferromagnetic interaction (45 K to 303 K) between trimeric Co(II) S = 3/2 spins through syn-syn carboxylato bridges. Both MOFs were studied for the Lewis acid catalyzed Knoevenagel condensation reactions between benzaldehydes and malononitrile with an active methylene group, where Zn-MOF was found to be a better catalyst than Co-MOF. This was supported by the Monte Carlo simulations indicating the better substrate binding ability of Zn-MOF than Co-MOF.

Recent advances in application of metal-organic frameworks (MOFs) as adsorbent and catalyst in removal of persistent organic pollutants (POPs)

The presence of persistent organic pollutants (POPs) in the aquatic environment is causing widespread concern due to their bioaccumulation, toxicity, and possible environmental risk. These contaminants are produced daily in large quantities and released into water bodies. Traditional wastewater treatment plants are ineffective at degrading these pollutants. As a result, the development of long-term and effective POP removal techniques is critical. In water, adsorption removal and photocatalytic degradation of POPs have been identified as energy and cost-efficient solutions. Both technologies have received a lot of attention for their efforts to treat the world's wastewater. Photocatalytic removal of POPs is a promising, effective, and long-lasting method, while adsorption removal of persistent POPs represents a simple, practical method, particularly in decentralized systems and isolated areas. It is critical to develop new adsorbents/photocatalysts with the desired structure, tunable chemistry, and maximum adsorption sites for highly efficient removal of POPs. As a class of recently created multifunctional porous materials, Metal-organic frameworks (MOFs) offer tremendous prospects in adsorptive removal and photocatalytic degradation of POPs for water remediation. This review defines POPs and discusses current research on adsorptive and photocatalytic POP removal using emerging MOFs for each type of POPs.

The Properties of Microwave-Assisted Synthesis of Metal-Organic Frameworks and Their Applications

Metal-organic frameworks (MOF) are a class of porous materials with various functions based on their host-guest chemistry. Their selectivity, diffusion kinetics, and catalytic activity are influenced by their design and synthetic procedure. The synthesis of different MOFs has been of considerable interest during the past decade thanks to their various applications in the arena of sensors, catalysts, adsorption, and electronic devices. Among the different techniques for the synthesis of MOFs, such as the solvothermal, sonochemical, ionothermal, and mechanochemical processes, microwave-assisted synthesis has clinched a significant place in MOF synthesis. The main assets of microwave-assisted synthesis are the short reaction time, the fast rate of nucleation, and the modified properties of MOFs. The review encompasses the development of the microwave-assisted synthesis of MOFs, their properties, and their applications in various fields.

Room-temperature synthesis of nanometric and luminescent silver-MOFs

Three silver-MOFs were prepared using an optimized, room-temperature methodology starting from AgNO₃ and dicarboxylate ligands in water/ethanol yielding Ag ₂ BDC, Ag ₂ NDC (UAM-1), and Ag ₂ TDC (UAM-2) at 38%-48% (BDC, benzenedicarboxylate; NDC, 1,8-naphthalene-dicarboxylate; TDC, p-terphenyl-4,4″-dicarboxylate). They were characterized by PXRD/FT-IR/TGA/photoluminescence spectroscopy, and the former two by SEM. These materials started decomposing at 330°C, while showing stability. The crystal structure of UAM-1 was determined by PXRD, DFT calculations, and Rietveld refinement. In general, the structure was 3D, with the largest Ag-O bond interlinking 2D layers. The FT-IR spectra revealed 1450 and 1680 bands (cm^-1) of asymmetrically stretching aniso-/iso-bidentate -COO in coordination with 2/3-Ag atoms, accompanied by Ag-O bands at 780-740 cm^-1, all demonstrating the network formation. XRD and SEM showed nanometric-scale crystals in Ag₂BDC, and UAM-1 developed micrometric single-stranded/agglomerated fibrillar particles of varying nanometric widths. Luminescence spectroscopy showed emission by Ag₂BDC, which was attributed to ligand-to-metal or ligand-to-metal-metal transitions, suggesting energy transfer due to the short distance between adjacent BDC molecules. UAM-1 and UAM-2 did not show luminescence emission attributable to ligand-to-metal transition; rather, they presented only UV emission. The stabilities of Ag₂BDC and UAM-1 were evaluated in PBS/DMEM/DMEM+FBS media by XRD, which showed that they lost their crystallinity, resulting in AgCl due to soft-soft (Pearson's principle) affinity.

A systematic study of a polymer-assisted carboxylate-based MOF synthesis: multiple roles of core cross-linked PMAA-b-PMMA nanoparticles

Colloidaly stable carboxylate-based metal organic frameworks (MOFs), grown from acid decorated nanoparticles synthesized via PISA.

Robust DUT-67 material for highly efficient removal of the Cr(VI) ion from an aqueous solution

Robust DUT-67 was synthesized by the hydrothermal method and characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). To systematically study the removal of Cr(VI) ion by DUT-67, single-factor, competition ion, material regeneration, kinetic, and thermodynamic experiments were designed. The experimental results show that DUT-67 had a maximum removal rate of 96.1% and a maximum adsorption capacity of 105.42 mg g^-1 with material regeneration and outstanding selective adsorption. In addition, the process of removal of the Cr(VI) ion from an aqueous solution by DUT-67, which accorded with the pseudo-second-order kinetics model and Langmuir model, was studied, and its adsorption mechanism was reasonably explained by the theoretical calculation.

Metal-Organic Frameworks as Photocatalysts for Solar-Driven Overall Water Splitting

Metal-organic frameworks (MOFs) have been frequently used as photocatalysts for the hydrogen evolution reaction (HER) using sacrificial agents with UV-vis or visible light irradiation. The aim of the present review is to summarize the use of MOFs as solar-driven photocatalysts targeting to overcome the current efficiency limitations in overall water splitting (OWS). Initially, the fundamentals of the photocatalytic OWS under solar irradiation are presented. Then, the different strategies that can be implemented on MOFs to adapt them for solar photocatalysis for OWS are discussed in detail. Later, the most active MOFs reported until now for the solar-driven HER and/or oxygen evolution reaction (OER) are critically commented. These studies are taken as precedents for the discussion of the existing studies on the use of MOFs as photocatalysts for the OWS under visible or sunlight irradiation. The requirements to be met to use MOFs at large scale for the solar-driven OWS are also discussed. The last section of this review provides a summary of the current state of the field and comments on future prospects that could bring MOFs closer to commercial application.

Development of novel MOF-mixed matrix three-dimensional membrane capsules for eradicating potentially toxic metals from water and real electroplating wastewater

The stability and applicability of UiO-66-(NH₂)₂ metal-organic framework (MOF) nanoparticles (NPs) were successfully improved in this study by incorporating them into alginate biopolymer during the manifestation of crosslinking agents-calcium chloride and glutaraldehyde-via a simple, environment-friendly, and facile approach to eradicate potentially toxic metals (PTMs) such as Cr⁶⁺, Cr³⁺, Cu²⁺, and Cd²⁺ from water and real electroplating wastewater. Hydrophilic functional groups (i.e., -OH, -COOH, and -NH₂) are imperative in the smooth loading of UiO-66-(NH₂)₂ MOF- NPs into three-dimensional (3-D) membrane capsules (MCs). The X-ray photoelectron spectroscopy (XPS) results suggested that UiO-66-(NH₂)₂ MOF was effectively bonded in/on the capsule via electrostatic crosslinking between -H₃N⁺ and -COO^-. Scanning electron microscopy results revealed a porous honeycomb configuration of the 3-D SGMMCs (S: sodium alginate, G: glutaraldehyde, M: MOF NPs, and MCs: membrane capsules). The maximum monolayer absorption capacities for Cr⁶⁺, Cr³⁺, Cu²⁺, and Cd²⁺ were 495, 975, 1295, and 1350 mg/g, respectively. The results of Fourier transform infrared spectroscopy and XPS analyses showed that electrostatic attraction and ion exchange were the main processes for PTM removal used by the as-developed 3-D SGMMCs. The as-developed 3-D SGMMCs exhibited outstanding selectivity for removing the targeted PTMs under the specified pH/conditions and maintained >80% removal efficiency for up to six consecutive treatment cycles. Notably, > 60% removal efficiencies for Cr⁶⁺ and Cu²⁺ were observed when treating real electroplating wastewater. Therefore, the as-developed 3-D SGMMCs can be used as an exceptional multifunctional sorbent to remove and recover PTMs from real electroplating wastewater.

Nano/microplastics: Fragmentation, interaction with co-existing pollutants and their removal from wastewater using membrane processes

NANO: and microplastic (NP/MP) is one of the most challenging types of micropollutants, coming from either direct release or degradation of plastic items into ecosystems. NP/MP can adsorb hazardous pollutants (such as heavy metals and pharmaceutical compounds) and pathogens onto their surface that are consumed by humans, animals, and aquatic living organisms. This paper presents the interaction of NP/MP with other pollutants in the water environment and mechanisms involved to enable the ultimate fate of NP/MP as well as the effectiveness of metal-organic frame (MOF)-based membrane over conventional membrane processes for NP/MP removal. It is found that conventional membranes could remove MPs when their size is usually more than 1000 nm, but they are ineffective in removing NPs. These NPs have potentially greater health impacts due to their greater surface area. MOF-based membrane could effectively remove both NP and MP due to its large porous structure, high adsorption capacity, and low density. This paper also discusses some challenges associated with MOF-based membranes for NP/MP removal. Finally, we conclude a specific MOF-based ultrafiltration membrane (ED-MIL-101 (Cr)) that can potentially remove both negative and positive charged NP/MP from wastewater by electrostatic attraction and repulsion force with efficient water permeability.

Remarkable Separation of Carbofuran Pesticide from Aqueous Solution Using Free Metal Ion Variation on Aluminum-Based Metal-Organic Framework

The alarming increase in pesticide residues poses a major threat to aquatic and natural habitats. Therefore, it has become essential to design extremely operationally and economically advantageous systems for the removal of carbofuran pesticides from wastewater. Here, an aluminum-based metal-organic framework (MOF), MIL-53-NH2, and its modified forms, MIL-53-NH-ph, MIL-53-NH-ph-Fe, MIL-53-NH-ph-Zn, and MIL-53-NH-ph-Cu, have been successfully synthesized. Full characterization using IR, 1HNMR, XRD, and SEM was carried out. The prepared MOFs have been utilized as effective adsorbents for carbofuran in aqueous solutions. The various factors affecting the adsorption process (pH, time, and adsorbate concentration) were also investigated. Spectroscopic approaches were used to investigate the adsorption mechanisms. A mixture of π-π stacking contact, coordination bonding, and hydrogen bond formation can be connected to the current process. The adsorption of carbofuran from aqueous solutions was best described by pseudo-second-order kinetics and Langmuir equilibrium isotherm models. MIL-53-NH2, MIL-53-NH-Ph, MIL-53-NH-Ph-Fe, MIL-53-NH-Ph-Zn, and MIL-53-NH-Ph-Cu demonstrated adsorption capacities of 367.8, 462.1, 662.94, 717.6, and 978.6 mg g−1, respectively.

Adsorption Mechanism of Novel Porous Materials in Wastewater Treatment: A New Open Special Issue in Materials Science

The special titled Adsorption Mechanism of Novel Porous Materials in Wastewater Treatment: A New Open Special Issue in Materials aims to publish high-quality research and review articles on the basic and applied science of porous materials and make great contributions to the understanding of metal-organic frameworks (MOFs) in removing pollutants from aqueous and soil environments [...].

Deciphering the underlying mechanism of MOF-808-based abiotic catalysis enhancing biodegradability of waste activated sludge: Insights from the effects on bioconversion of extracellular organic substances into methane

Extracellular organic substances (EOSs) usually control sludge biodegradability. Metal-organic framework-808 (MOF-808), a catalyst with a high ability of catalytic hydrolysis and proton transfer, has great potential to enhance biodegradability of EOSs. In this study, the underlying mechanism of MOF-808 enhancing the biodegradability of EOSs via abiotic catalysis was investigated. Experimental results showed that protein-like and humic acid-like substances were the main organic components in EOSs, and the MOF-808 enhanced the disintegration of protein-like substances rather than humic acid-like substances. Analyses of the changes in the functional group, the secondary structure of protein-like substances, and the electron transfer of catalytically degraded EOS samples revealed that the MOF-808 enhanced the hydrolysis of EOSs protein-like substances, loosened their secondary structure, and improved the electron transfer in EOSs. Further analyses of the MOF-808 before and after the catalysis reaction revealed that the coordination of Zr sites with protein-like substance-specific active sites (such as ZrN) in the MOF-808 substantially contributed to the high-efficiency catalysis. Biochemical methane potential assays confirmed that MOF-808-based abiotic catalysis promoted the generation efficiency of methane from the EOSs. These findings can elucidate the abiotic catalytic effect of MOF-808 on sludge biodegradability during the anaerobic digestion process.

Water-stable porous Al24 Archimedean solids for removal of trace iodine

In this paper, we report a unique type of core-shell crystalline material that combines an inorganic zeolitic cage structure with a macrocyclic host arrangement and that can remove trace levels of iodine from water effectively. These unique assemblies are made up of an inorganic Archimedean truncatedhexahedron (tcu) polyhedron in the kernel which possesses six calixarene-like shell cavities. The cages have good adaptability to guests and can be assembled into a series of supramolecular structures in the crystalline state with different lattice pore shapes. Due to the unique core-shell porous structures, the compounds are not only stable in organic solvents but also in water. The characteristics of the cages enable rapid iodine capture from low concentration aqueous I₂/KI solutions (down to 4 ppm concentration). We have studied the detailed process and mechanism of iodine capture and aggregation at the molecular level. The facile synthesis, considerable adsorption capacity, recyclability, and β- and γ-radiation resistance of the cages should make these materials suitable for the extraction of iodine from aqueous effluent streams (most obviously, radioactive iodide produced by atomic power generation).

The removal of radioactive elements is important to human health and sustainable development. Here, the authors reveal the synthesis of water-stable Archimedean solids based on the earth-abundant element for the fast removal of trace iodine.

Effective adsorption of cadmium and lead using SO3H-functionalized Zr-MOFs in aqueous medium

Cadmium (Cd) and Lead (Pb) from industrial wastewater can bioaccumulate in the living organisms of water bodies, posing serious threats to human health. Therefore, efficient remediation of heavy metal ions of Cd (II) and Pb (II) in aqueous media is necessary for public health and environmental sustainability. In the present study, water stable Zirconium (Zr) based metal organic frameworks (MOFs) with SO3H functionalization were synthesized by solvothermal method and used first time for the adsorption of Cd (II) and Pb (II). Synthesis of UiO-66-SO3H, nano-sized (<100 nm) MOFs, was confirmed by FTIR, XRD, FESEM and BET. Effects of contact time, pH and temperature were investigated for adsorption of Cd (II) and Pb (II) onto SO3H-functionalized Zr-MOFs. The UiO-66-SO3H displayed notable rejections of 97% and 88% towards Cd (II) and Pb (II), respectively, after 160 min at 25 °C and pH (6) with an initial concentration of 1000 mg/L. Adsorption capacities of Cd (II) and Pb (II) were achieved as 194.9154 (mg/g) and 176.6879 (mg/g), respectively, at an initial concentration of 1000 mg/L. The Pseudo second-order kinetic model fitted well with linear regression (R2) of value 1. The mechanism was confirmed mainly as a chemisorption and coordination interaction between sulfone group (-SO3H) and metal ions Cd (IIa) and Pb (II). These results may support effective adsorption and can be studied further to enrich and recycle other heavy metals from wastewater.

Photo-controllable Ion-Gated Metal-Organic Framework MIL-53 Sub-nanochannels for Efficient Osmotic Energy Generation

By closing and opening ion channels, electric eels are able to convert ion concentration gradients into electricity. Inspired by electric eels, considerable artificial sub-nanoscale ion channels with high ion selectivity and transportation efficiency have been designed for harvesting the osmotic energy between ionic solutions of different salinities, but constructing smart ion-gated sub-nanochannels for effective ion transport is still a huge challenge. Herein, photo-controllable sub-nanochannels of metal-organic framework (MOF) NH₂-MIL-53 encapsulated with spiropyrans (SP-MIL-53) were fabricated by a facile in situ growth strategy. Interestingly, the highly ordered sub-nanochannels of SP-MIL-53 were switched on and off to efficiently regulate the ion flux by the light-driven isomerization of SP, which made it a smart ionic gate with a high on-off ratio of 16.2 in 10 mM KCl aqueous solution via UV irradiation. Moreover, the ion-gated sub-nanochannel membrane yielded a high power density of 8.3 W m^-2 under a 50-fold KCl concentration gradient in the open state. Density functional theory calculations revealed that K⁺ ions in SP-MIL-53 sub-nanochannels had a higher mobility constant (3.61 × 10^-2) with UV irradiation than without UV illumination (2.33 × 10^-22). This work provides an effective way to develop smart ion-gating sub-nanochannels for capturing salinity gradient power.

A Water-Stable Zn-MOF Used as Multiresponsive Luminescent Probe for Sensing Fe3+/Cu2+, Trinitrophenol and Colchicine in Aqueous Medium

A water-stable Zn-MOF was constructed based on H₂PBA and 1, 10-phenanthroline under solvothermal conditions. The compound exhibited a 3D (2,3,8)-connected (4³)₂(4⁶.6⁶.8¹⁵.12)(8) topology framework. The crystal structure and phase purity of the compound was verified by single crystal X-ray diffraction. Subsequently, some studies on the morphology, structure, and luminescent properties were carried out. The results showed that this compound could be used as a versatile chemosensor for Fe³⁺/Cu²⁺, trinitrophenol and colchicine via a luminescence quenching effect in an aqueous medium.

Stable magnetic CoZn/N-doped polyhedron with self-generating carbon nanotubes for highly efficient removal of bisphenols from complex wastewaters

Bisphenols have extensively been found in various environmental matrices and caused public concerns due to their endocrine-disrupting potential. Herein, we developed a ZIF-67@ZIF-8-derived CoZn/nitrogen-doped carbon (CoZn/NC) as a robust adsorbent for bisphenols in wastewaters. The self-generating carbon nanotubes and the open metal sites provided sufficient adsorption sites. The Co component endowed the derivative with strong magnetism facilitating its separation from water. CoZn/NC exhibited exceeding water stability in pH 3 - 12 solution and withstood water up to 15 days. The great applicability of CoZn/NC was validated with 16 real wastewaters from different sources (recoveries exceeding 97.9%). Fast adsorption kinetics were observed with removal efficiencies above 96.5% within 1 min. The adsorption isotherms were well fitted with the Langmuir model, with adsorption capacities of 222, 200, 193, and 321 mg g^-1 for bisphenol A, bisphenol F, bisphenol S, and bisphenol AF, respectively. Variations in external conditions, including pH 3 - 9, humic acid (50 mg L^-1), and NaCl (0.1 mol L^-1), had negligible impacts on the adsorption process. The characterizations and density functional theory computation demonstrated that electrostatic, hydrophobic, π - π, and cation- π interactions are the driving forces in this system. The as-prepared CoZn/NC exhibits great promise in real wastewater treatment.

New generation advanced nanomaterials for photocatalytic abatement of phenolic compounds

Nowadays, organic pollutants create severe problems worldwide. Phenolic compounds are the harmful pollutants that are developed from industrial effluents, thus causing several environmental problems. Low-cost materials show good potential capabilities for removal of phenolic compounds but are not so effective, so modification is required. New generation nanocatalysts are thought to be excellent for phenol removal. Removal of phenolic pollutants by photodegradation may lead to the decrement of these problematic groups. In this review, (i) a new generation of catalysts for the removal of phenolic compounds is discussed, (ii) nanocatalysts for photodegradation processes, and (iii) the mechanisms involved in photodegradation processes are also discussed. It is noticeable from the analysis that new generation catalysts for photodegradation processes have been demonstrated for high removal abilities of irrefutable phenolic compounds. Finally, future perspectives are also given in this article for the further development of next-generation catalysts.

Adsorptive removal of ibuprofen to binary and amine-functionalized UiO-66 in the aquatic environment: synergistic/antagonistic evaluation

The removal of ibuprofen (IBP) from the aqueous solution by metal-organic frameworks such as UiO-66, UiO-66-NH₂, and a binary MOF (UiO-66@5%HKUST-1) was studied. MOFs were synthesized by the solvothermal method. The synthesized MOFs were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and N₂ adsorption. BET results showed that binary MOF and UiO-66-NH₂ had a smaller surface area and were mesoporous compared to UiO-66, while UiO-66 was microporous. Quantitative investigations were conducted to understand the effect of binary and functional UiO-66 in adsorbing IBP and compared to UiO-66. The results showed that UiO-66 with 213 mg/g had the highest adsorption in comparison to other adsorbents. UiO-66-NH₂ showed the lowest adsorption (96 mg/g) due to a large decrease in the surface area. The binary MOF, despite a slight decrease in surface area (1277.6 m²/g), had lower adsorption than UiO-66 (147 mg/g) due to the antagonistic effects between the adsorbent and IBP. Furthermore, the pH of the solution had a great effect on the adsorption of IBP, and the results showed that increasing the pH values above 4 reduced the adsorption of IBP.

Recent developments in MOF and MOF based composite as potential adsorbents for removal of aqueous environmental contaminants

With the growth of globalization which has been the primary cause of water pollution, it is utmost necessary for us living being to have access to clean water for the purpose of drinking, washing and various other useful applications. With the purpose of future security and to restore our ecological balance, it is essential to give much significance towards the removal of unwanted toxic contaminants from our water resources. In this regard adsorptive removal of toxic pollutants from wastewater with porous adsorbent is regarded as one of the most promising way for water decontamination process. Metal organic frameworks (MOFs) comprising of uniformly arranged pores, abundant active sites and containing an easily tunable structure has aroused as a promising material for adsorbent to remove the unwanted contaminants from water sources. The adsorption of pollutants by the different MOFs surface are driven by various interactions including π-π, acid-base, electrostatic and H-bonding etc. On the other hand, the removal of various contaminants by MOFs is influenced by various factors including pH, temperature and initial concentration. In this review we will specifically discuss the adsorptive removal of different organic and inorganic pollutants present in our water systems with the use of MOFs as adsorbent along with the various factors and interaction mechanism manipulating the adsorption behaviour.

Nanocatalytic Biofunctional MOF Coating on Titanium Implants Promotes Osteoporotic Bone Regeneration through Cooperative Pro-osteoblastogenesis MSC Reprogramming

An elevated bone microenvironmental reactive oxygen species (ROS) level is a hallmark of osteoporosis that often leads to the dysfunction of bone-related mesenchymal stem cells (MSCs), which would induce MSC senescence and severely undermine their osteoblastic potential. Herein, we report the in situ construction of bone microenvironment-responsive biofunctional metal-organic framework (bio-MOF) coating on the titanium surface through the coordination between p-xylylenebisphosphonate (PXBP) and Ce/Sr ions by a hydrothermal method. Taking advantage of the anchored Ce and Sr ions, the AHT-Ce/SrMOF implants demonstrate on-demand superoxide dismutase and catalase-like catalytic activities to decompose ROS in MSCs and restore their mitochondrial functions. In vitro analysis showed that the AHT-Ce/SrMOF implants substantially activated the AMP-activated protein kinase (AMPK) signaling pathway in MSCs and reduced the ROS levels. Meanwhile, MSCs grown on AHT-Ce/SrMOF implants displayed significantly higher expressions of the mitochondrial fission marker (DRP1), mitochondrial fusion marker (MFN2 and OPA1), and mitophagy marker (PINK1 and LC3) than those of the AHT-CeMOF and AHT-SrMOF groups, which indicated that the bio-MOF could amend mitochondrial function in MSCs to reverse senescence. In vivo evaluations showed that the bio-MOF-coated Ti implants could restore MSC function in the implant site and promote new bone formation, leading to improved osteointegration in osteoporotic rat. This study may improve implant-mediated fracture healing in the clinics.

Controlled Thermal Release of L-Menthol with Cellulose-Acetate-Fiber-Shelled Metal-Organic Framework

Fragrances have been widely used in many customer products to improve the sensory quality and cover flavor defects. The key to the successful application of fragrance is to realize controlled fragrance release, which relies on the use of an appropriate carrier for fragrance. An ideal fragrance carrier helps to achieve the stable storage and controlled release of fragrance. In this work, a novel composite fragrance carrier with MIL-101 (Cr) as the fragrance host and cellulose acetate fiber (CAF) as the protective shell was developed. The encapsulation effect of MIL-101 (Cr) and the protective function of the CAF shell significantly improved the storage stability of L-menthol (LM). Only 5 wt % of LM was lost after 40 days of storage at room temperature. Encapsulated LM could also be effectively released upon heating due to the thermal responsiveness of CAF. In addition, the composite carrier was highly stable with neglectable Cr leaching under different conditions. The results of this work showed that the developed composite carrier could be a promising carrier for the thermally triggered release of fragrance.

Robust Carbazole-Based Rare-Earth MOFs: Tunable White-Light Emission for Temperature and DMF Sensing

Rare-earth metal-organic frameworks (RE-MOFs) are an attractive platform to construct luminescent materials for practical applications in lighting, optoelectronics, and sensing. By adjusting the metal composition in mixed RE-MOFs, one can not only realize tunable emission but also construct ratiometric luminescent sensors. As such, it is highly desirable to prepare robust RE-MOFs that display efficient, multifunctional sensing capability. In this work, we designed and synthesized a series of RE-MOFs that exhibit both excellent thermal and chemical stability due to the incorporation of a bulky tert-butyl group on a new carbazole-based ligand. By rationally tuning the molar ratio of Eu³⁺/Tb³⁺/Y³⁺, a white-light-emitting MOF was developed as an excellent thermal sensor that exhibits a temperature-induced ratiometric luminescence response between 278 and 378 K. After removing the coordinated solvent molecules via thermal treatment, the desolvated MOF materials exhibit excellent turn-on or color change sensitivity to recognize dimethylformamide (DMF) molecules. Such high sensitivity is attributed to the DMF coordination that induces the framework structure change and shifts the ligand's excited-state energy level to facilitate the ligand-to-metal energy transfer process. Taking together, NPF-700-RE represents a new class of robust, tunable luminescent materials that have great potential in white-light emission and thermal- and DMF-sensing applications.

Advances in metal-organic framework-based membranes

Membrane-based separations have garnered considerable attention owing to their high energy efficiency, low capital cost, small carbon footprint, and continuous operation mode. As a class of highly porous crystalline materials with well-defined pore systems and rich chemical functionalities, metal-organic frameworks (MOFs) have demonstrated great potential as promising membrane materials over the past few years. Different types of MOF-based membranes, including polycrystalline membranes, mixed matrix membranes (MMMs), and nanosheet-based membranes, have been developed for diversified applications with remarkable separation performances. In this comprehensive review, we first discuss the general classification of membranes and outline the historical development of MOF-based membranes. Subsequently, particular attention is devoted to design strategies for MOF-based membranes, along with detailed discussions on the latest advances on these membranes for various gas and liquid separation processes. Finally, challenges and future opportunities for the industrial implementation of these membranes are identified and outlined with the intent of providing insightful guidance on the design and fabrication of high-performance membranes in the future.

A comprehensive review on water remediation using UiO-66 MOFs and their derivatives

Metal-organic frameworks (MOFs) are a versatile class of porous materials offering unprecedented scope for chemical and structural tunability. On account of their synthetic versatility, tunable and exceptional host-guest chemistry they are widely utilized in many prominent water remediation techniques. However, some of the MOFs present low structural stabilities specifically in aqueous and harsh chemical conditions which impedes their potential application in the field. Among the currently explored MOFs, UiO-66 exhibits structural robustness and has gained immense scientific popularity. Built with a zirconium-terephthalate framework, the strong Zr-O bond coordination contributes to its stability in aqueous, chemical, and thermal conditions. Moreover, other exceptional features such as high surface area and uniform pore size add to the grand arena of porous nanomaterials. As a result of its stable nature, UiO-66 offers relaxed admittance towards various functionalization, including synthetic and post-synthetic modifications. Consequently, the adsorptive properties of these highly stable frameworks have been modulated by the addition of various functionalities. Moreover, due to the presence of catalytically active sites, the use of UiO-66 has also been extended towards the degradation of pollutants. Furthermore, to solve the practical handling issues of the crystalline powdered forms, UiO-66 has been incorporated into various membrane supports. The incorporation of UiO-66 in various matrices has enhanced the rejection, permeate flux, and anti-fouling properties of membranes. The combination of such exceptional characteristics of UiO-66 MOF has expanded its scope in targeted purification techniques. Subsequently, this review highlights the role of UiO-66 in major water purification techniques such as adsorption, photocatalytic degradation, and membrane separation. This comprehensive review is expected to shed light on the existing developments and guide the inexhaustible futuristic scope of UiO-66 MOF.

Nanoengineered metal-organic framework for adsorptive and photocatalytic mitigation of pharmaceuticals and pesticide from wastewater

Rapidly expanding water pollution has transformed into significant dangers around the world. In recent years, the pharmaceutical and agriculture field attained enormous progress to meet the necessities of health and life; however, discharge of trace amounts of pharmaceuticals and pesticides into water significantly have a negative influence on human health and the environment. Contamination with these pollutants also constitutes a great threat to the aquatic ecosystem. To deal with the harmful impacts of such pollutants, their expulsion has attracted researchers' interest a lot, and it became essential to figure out techniques suitable for the removal of these pollutants. Thus, many researchers have devoted their efforts to improving the existing technology or providing an alternative strategy to solve this environmental problem. One of the attractive materials for this purpose is metal-organic frameworks (MOFs) due to their superior high surface area, high porosity, and the tunable features of their structures and function. Among various techniques of wastewater treatment, such as biological treatment, advanced oxidation process and membrane technologies, etc., metal-organic frameworks (MOFs) materials are tailorable porous architectures and are viably used as adsorbents or photocatalysts for wastewater treatment due to their porosity, tunable internal structure, and large surface area. MOFs are synthesized by various methods such as solvo/hydrothermal, sonochemical, microwave and mechanochemical methods. Most common method used for the synthesis of MOFs is solvothermal/hydrothermal methods. Herein, this review aims at providing a comprehensive overview of the latest advances in MOFs and their derivatives, focusing on the following aspects: synthesis and applications. This review comprehensively highlights the application of MOFs and nano-MOFs to remove pharmaceuticals and pesticides from wastewater. For the past years, transition metal-based MOFs have been concentrated as photocatalyst/adsorbents in treating contaminated water. However, work on main group metal-based MOFs is not so abundant. Hence, the foremost objective of this review is to present the latest material and references concerning main group element-based MOFs and nanoscale materials derived from them towards wastewater treatment. It summarizes the possible research challenges and directions for MOFs and their derivatives as catalysts applied to wastewater treatment in the future. With the context of recent pioneering studies on main group elements-based MOFs and their derivatives; we hope to stimulate some possibilities for further development, challenges and future perspectives in this field have been highlighted.

Synthesis and characterization of a 2-periodic cadmium-based metal-organic framework: A study on reversible water adsorption

A previously-reported cadmium-based two-periodic metal-organic framework [Cd_1.5(BTC)(H₂O)_4.5]_n·nH₂O (CP1) has been re-synthesized, where H₃BTC = 1,3,5-benzenetricarboxylic acid. CP1 was characterized with single crystal X-ray diffraction (SCXRD), powder X-ray diffraction (PXRD) followed by various thermal analyses such as thermogravimetric analysis (TGA), hot stage microscopy (HSM) and differential scanning calorimetry (DSC). CP1 is composed of 2-periodic layers, which are interdigitated. Heating can effectively remove the uncoordinated and coordinated water molecules resulting in an amorphous product CP1′. The original framework can be regenerated by readsorption of water from the atmosphere, indicating that the dehydration is reversible.

Fluorinated metal-organic frameworks for gas separation

Fluorinated metal-organic frameworks (F-MOFs) as fast-growing porous materials have revolutionized the field of gas separation due to their tunable pore apertures, appealing chemical features, and excellent stability. A deep understanding of their structure-performance relationships is critical for the synthesis and development of new F-MOFs. This critical review has focused on several strategies for the precise design and synthesis of new F-MOFs with structures tuned for specific gas separation purposes. First, the basic principles and concepts of F-MOFs as well as their structure, synthesis and modification and their structure to property relationships are studied. Then, applications of F-MOFs in adsorption and membrane gas separation are discussed. A detailed account of the design and capabilities of F-MOFs for the adsorption of various gases and the governing principles is provided. In addition, the exceptional characteristics of highly stable F-MOFs with engineered pore size and tuned structures are put into perspective to fabricate selective membranes for gas separation. Systematic analysis of the position of F-MOFs in gas separation revealed that F-MOFs are benchmark materials in most of the challenging gas separations. The outlook and future directions of the science and engineering of F-MOFs and their challenges are highlighted to tackle the issues of overcoming the trade-off between capacity/permeability and selectivity for a serious move towards industrialization.

Remarkable proton conducting behavior driven by synergistic effects in acid-base conjugated MOFs impregnated with sulphuric acid molecules

The Coulomb force between protons and negative charges usually leads to low proton diffusion and poor proton conductivity. Herein, acid-base conjugated MOFs of UiO-66-SO₃^--NH₃⁺ were constructed by linking sulfonic acid and amine groups to an organic skeleton. According to the XPS and elemental analysis, the ratio of 2-aminoterephthalic acid/2-sulfoterephthalic acid was ∼1.9 in UiO-66-SO₃^--NH₃⁺. After introducing sulphuric acid molecules, the MOF-based electrolyte exhibited a remarkable proton conductivity of 5.40 × 10^-1 S cm^-1 and low activation energy of 0.15 eV at 100% RH and 90 °C. This remarkable proton conducting behavior was generated by the synergistic system in the MOF, which contained certain synergistic effects such as between -SO₃^-⋯H⁺⋯SO₄^2- and NH₃⁺⋯SO₄^2-, therefore possessing a Grotthuss mechanism, which facilitates facile proton transport.

Construction of Water-Stable Rare-Earth Organic Frameworks with Ambient High Proton Conductivity Based on Zirconium Sandwiched Heteropolytungstate

Water-stable proton-conducting materials owning excellent performances at ambient temperatures are currently one of the crucial challenges. Herein, four water-stable three-dimensional polyoxometalate-based rare-earth organic frameworks have been successfully synthesized and formulated as H{Ln₄(L)₂(H₂O)₂₁[Zr₃(OH)₃(PW₉O₃₄)₂]}·15H₂O (1-3) (Ln = La (1), Ce (2), Pr (3); L = 3,5-pyridine dicarboxylic acid), which are the first examples of MOFs constructed by a zirconium sandwiched polyoxoanion. There are abundant coordinated water molecules functionalizing the Pr^III centers, and simultaneously, plenty of lattice water molecules are fitted into the channel of the framework. A continuous H-bonding network is found between the architectures and plays an important role in stabilizing the structure. Benefiting from the consecutive H-bonding networks, compounds 1-3 showed high proton conductivities at ambient temperature (up to 1.05 × 10^-3 S·cm^-1 under 98% RH) by a synergistic effect of the combined components.

Assembly of UiO-66 onto Co-doped Fe3O4 nanoparticles to activate peroxymonosulfate for efficient degradation of fenitrothion and simultaneous in-situ adsorption of released phosphate

Although sulfate radical-based advanced oxidation processes (SR-AOPs) have shown great potential for the efficient degradation of various organic contaminants, there is few research on the removal of organophosphorus pesticides (OPPs) through SR-AOPs. In this work, Co-doped Fe₃O₄ magnetic particles encapsulated by zirconium-based metal-organic frameworks (Co-Fe₃O₄@UiO-66) were prepared and employed to activate peroxymonosulfate (PMS) for the elimination of fenitrothion (FNT) and the simultaneous in-situ adsorption of produced phosphate. The catalyst exhibited efficient catalytic performance, achieving above 90.0% removal of FNT (10 mg/L) in the presence of PMS (1 mM) within 60 min. Moreover, the produced phosphate during the degradation process was also completely adsorbed onto the catalyst. Both sulfate and hydroxyl radicals were responsible for the degradation of FNT. The degradation products of FNT in the system were identified and the possible pathways were proposed. This study represents a promising and adoptable strategy to develop other versatile composite nanomaterials in a green manner hence broadening its environmental application range, as it can not only remove OPPs by catalytic oxidation but also immobilize degraded phosphorus by adsorption.