UiO-66: An Advanced Platform for Investigating the Influence of Functionalization in the Adsorption Removal of Pharmaceutical Waste

Effective removal of perfluorooctanoic acid from water using PVA@UiO-66-NH2/GO composite materials via adsorption

This study introduces an innovative approach using highly efficient nanocomposite materials to effectively remove PFAS from water, demonstrating remarkable adsorption capabilities. The nanocomposite was synthesized by integrating a zirconium-based metal-organic framework (MOF) called UiO-66 with graphene oxide (GO) within a polyvinyl alcohol (PVA) matrix. The resulting PVA@UiO-66/GO material features flower-like UiO-66 MOF crystals embedded in the PVA and GO matrix. Various kinetic models were applied to determine the rate constants and adsorption capacities, with the Langmuir isotherm indicating an adsorption capacity of 9.904 mg/g. Thermodynamic analysis confirmed the process's spontaneity and exothermic nature. The UiO-66-NH2/GO/PVA composite also demonstrated high reusability, maintaining substantial PFOA removal efficiency across multiple cycles, with optimal reduction occurring at approximately pH 5. Overall, the PVA@UiO-66/GO composites offer an effective, sustainable, and environmentally friendly solution for PFAS removal in water purification.

Innovations in metal-organic frameworks (MOFs): Pioneering adsorption approaches for persistent organic pollutant (POP) removal

Adsorption is a promising way to remove persistent organic pollutants (POPs), a major environmental issue. With their high porosity and vast surface areas, MOFs are suited for POP removal due to their excellent adsorption capabilities. This review addresses the intricate principles of MOF-mediated adsorption and helps to future attempts to mitigate organic water pollution. This review examines the complicated concepts of MOF-mediated adsorption, including MOF synthesis methodologies, adsorption mechanisms, and material tunability and adaptability. MOFs' ability to adsorb POPs via electrostatic forces, acid-base interactions, hydrogen bonds, and pi-pi interactions is elaborated. This review demonstrates its versatility in eliminating many types of contaminants. Functionalizing, adding metal nanoparticles, or changing MOFs after they are created can improve their performance and remove contaminants. This paper also discusses MOF-based pollutant removal issues and future prospects, including adsorption capacity, selectivity, scale-up for practical application, stability, and recovery. These obstacles can be overcome by rationally designing MOFs, developing composite materials, and improving material production and characterization. Overall, MOF technology research and innovation hold considerable promise for environmental pollution solutions and sustainable remediation. Desorption and regeneration in MOFs are also included in the review, along with methods for improving pollutant removal efficiency and sustainability. Case studies of effective MOF regeneration and scaling up for practical deployment are discussed, along with future ideas for addressing these hurdles.

Molecular Simulation Studies of Pharmaceutical Pollutant Removal (Rosuvastatin and Simvastatin) Using Novel Modified-MOF Nanostructures (UIO-66, UIO-66/Chitosan, and UIO-66/Oxidized Chitosan)

The ubiquitous presence of pharmaceutical pollutants in the environment significantly threatens human health and aquatic ecosystems. Conventional wastewater treatment processes often fall short of effectively removing these emerging contaminants. Therefore, the development of high-performance adsorbents is crucial for environmental remediation. This research utilizes molecular simulation to explore the potential of novel modified metal-organic frameworks (MOFs) in pharmaceutical pollutant removal, paving the way for the design of efficient wastewater treatment strategies. Utilizing UIO-66, a robust MOF, as the base material, we developed UIO-66 functionalized with chitosan (CHI) and oxidized chitosan (OCHI). These modified MOFs' physical and chemical properties were first investigated through various characterization techniques. Subsequently, molecular dynamics simulation (MDS) and Monte Carlo simulation (MCS) were employed to elucidate the adsorption mechanisms of rosuvastatin (ROSU) and simvastatin (SIMV), two prevalent pharmaceutical pollutants, onto these nanostructures. MCS calculations demonstrated a significant enhancement in the adsorption energy by incorporating CHI and OCHI into UIO-66. This increased ROSU from -14,522 to -16,459 kcal/mol and SIMV from -17,652 to -21,207 kcal/mol. Moreover, MDS reveals ROSU rejection rates in neat UIO-66 to be at 40%, rising to 60 and 70% with CHI and OCHI. Accumulation rates increase from 4 Å in UIO-66 to 6 and 9 Å in UIO-CHI and UIO-OCHI. Concentration analysis shows SIMV rejection surges from 50 to 90%, with accumulation rates increasing from 6 to 11 Å with CHI and OCHI in UIO-66. Functionalizing UIO-66 with CHI and OCHI significantly enhanced the adsorption capacity and selectivity for ROSU and SIMV. Abundant hydroxyl and amino groups facilitated strong interactions, improving performance over that of unmodified UIO-66. Surface functionalization plays a vital role in customizing the MOFs for pharmaceutical pollutant removal. These insights guide next-gen adsorbent development, offering high efficiency and selectivity for wastewater treatment.

Rapid and selective removal of aristolochic acid I in natural products by vinylene-linked iCOF resins

Rapid, efficient, and selective removal of toxicants such as aristolochic acid I (AAI) from complex natural product systems is of great significance for the safe use of herbal medicines or medicine-food plants. Addressing this challenge, we develop a high-performance separation approach based on ionic covalent organic frameworks (iCOFs) to separate and remove AAI. Two vinylene-linked iCOFs (NKCOF-46-Br- and NKCOF-55-Br-) with high crystallinity are fabricated in a green and scalable fashion via a melt polymerization synthesis method. The resulting materials exhibit a uniform morphology, high stability, fast equilibrium time, and superior affinity and selectivity for AAI. Compared to conventional separation media, NKCOF-46-Br- and NKCOF-55-Br- achieve the record high adsorption capacities of 246.0 mg g-1 and 178.4 mg g-1, respectively. Various investigations reveal that the positively charged framework and favorable pore microenvironment of iCOFs contribute to their high selectivity and adsorption efficiency. Moreover, the iCOFs exhibit excellent biocompatibility by in vivo toxicity assays. This study paves a new avenue for the rapid, selective and efficient removal of toxicants from complex natural systems.

Nanoscale designing of metal organic framework moieties as efficient tools for environmental decontamination

Environmental pollutants, being a major and detrimental component of the ecological imbalance, need to be controlled. Serious health issues can get intensified due to contaminants present in the air, water, and soil. Accurate and rapid monitoring of environmental pollutants is imperative for the detoxification of the environment and hence living beings. Metal-organic frameworks (MOFs) are a class of porous and highly diverse adsorbent materials with tunable surface area and diverse functionality. Similarly, the conversion of MOFs into nanoscale regime leads to the formation of nanometal-organic frameworks (NMOFs) with increased selectivity, sensitivity, detection ability, and portability. The present review majorly focuses on a variety of synthetic methods including the ex situ and in situ synthesis of MOF nanocomposites and direct synthesis of NMOFs. Furthermore, a variety of applications such as nanoabsorbent, nanocatalysts, and nanosensors for different dyes, antibiotics, toxic ions, gases, pesticides, etc., are described along with illustrations. An initiative is depicted hereby using nanostructures of MOFs to decontaminate hazardous environmental toxicants.

Aptamers dimerization inspired biomimetic clamp assay towards impedimetric SARS-CoV-2 antigen detection

Antigen-detecting rapid diagnostic testing (Ag-RDT) has contributed to containing the spread of SARS-CoV-2 variants of concern (VOCs). In this study, we proposed a biomimetic clamp assay for impedimetric SARS-CoV-2 nucleocapsid protein (Np) detection. The DNA biomimetic clamp (DNA-BC) is formed by a pair of Np aptamers connected via a T₂₀ spacer. The 5'- terminal of the DNA-BC is phosphate-modified and then anchored on the surface of the screen-printed gold electrode, which has been pre-coated with Au@UiO-66-NH₂. The integrated DNA-material sensing biochip is fabricated through the strong Zr-O-P bonds to form a clamp-type impedimetric aptasensor. It is demonstrated that the aptasensor could achieve Np detection in one step within 11 min and shows pronounced sensitivity with a detection limit of 0.31 pg mL^-1. Above all, the aptasensor displays great specificity and stability under physiological conditions as well as various water environments. It is a potentially promising strategy to exploit reliable Ag-RDT products to confront the ongoing epidemic.

Investigation of the Influence of Functionalization Strategy on Urea 2D MOF Catalytic Performance

Urea-functionalized MOFs with unique properties have recently been used as efficient platforms to conduct organocatalytic reactions. To gain more insight into the key factors which govern an efficient organocatalytic reaction in urea-MOFs, two different urea-containing 2D MOFs TMU-58 ([Zn(L1)(oba)].CH₃CN) and TMU-83 ([Zn(L2)(oba)].DMF), where L1 = (1E,5E)-1,5-bis(1-(pyridine-4-ylethylidene)carbonohydrazide, L2 = (1E,5E)-1,5-bis(1-(pyridine-4-ylmethylene)carbonohydrazide, and oba = 4,4'-oxybisbenzoic acid, with abundant accessible active sites, were selected and examined in the methanolysis of styrene oxide. TMU-58 with the ability to form a two-point H-bond with different substrates revealed a high organocatalytic efficiency in the regioselective ring opening of styrene oxide. The catalytic activation of epoxide oxygen by the urea N-H functional sites, followed by the nucleophilic attack of methanol at the benzylic carbon led to the formation of 2-methoxy-2-phenylethanol as the major product. DFT calculations were also performed to investigate the acidic strength of the urea hydrogens in both TMU-58 and TMU-83 structures as a major factor to conduct an efficient catalytic reaction. The results indicated the more acidic nature of the urea hydrogens in TMU-83; however, its catalytic efficiency was remarkably reduced due to the inappropriate orientation of the active interaction sites within the framework revealing the importance of proper orientation of the urea hydrogens in conducting an efficient organocatalytic reaction. The current study provides a comparative study on the function-property relationship in 2D MOF assemblies which has not been explored so far.

Adsorptive removal of aromatic diamines from water using metal-organic frameworks functionalized with a nitro group

Adsorptive removal of aromatic diamines such as methylenedianiline (MDA) and p-phenylenediamine (PPD) was firstly investigated with nitro-functionalized metal-organic frameworks (MOFs, MIL-101(Cr)-NO₂). The MIL-101(Cr)-NO₂ showed much better performances in the removal of MDA and PPD, in both adsorption capacity and kinetics, than any other adsorbents. For example, MIL-101(Cr)-NO₂ had a much higher maximum adsorption capacity for MDA (1111 mg·g^-1) than activated carbon (208 mg·g^-1) or a reported adsorbent (391 mg·g^-1). Based on experimental results, hydrogen bonding (especially, via the formation of a 6-membered ring (6-MR) between -NO₂ of the adsorbent and -NH₂ of the adsorbates) could be suggested as the main mechanism to interpret the noticeable adsorption of the diamines. Importantly, this is the first example to confirm that MOFs with nitro group can be a competitive adsorbent to remove organics composed of amino group, especially via making 6-MR through hydrogen bonding. Higher adsorption of MDA than that of PPD over MIL-101(Cr)-NO₂ might be explained with π-π interaction between aromatic rings (π-lean aromatics of MOF and π-rich aromatics of the adsorbates). Moreover, MIL-101(Cr)-NO₂ could be recycled after simple washing, suggesting the potential use of the MOF in adsorptive purification of contaminated water with organics with amino groups.

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.

Crystal Structures of Ce(IV) Nitrates with Bis(2-pyrrolidone) Linker Molecules Deposited from Aqueous Solutions with Different HNO3 Concentrations

We investigated the molecular and crystal structures of Ce(IV) compounds deposited under different [HNO₃] with bis(2-pyrrolidone) linker molecules having a trans-1,4-cyclohexyl bridging moiety (L). As a result, we found that, after loading L, Ce(IV) in HNO₃(aq) exclusively provides one of different crystalline phases, (HL)₂[Ce(NO₃)₆] or [Ce₂(μ-O)-(NO₃)₆(L)₂]_n 2D MOF, depending on [HNO₃]. The former has been obtained at [HNO₃] = 4.70-9.00 M and is isomorphous with the analogous (HL)₂[An(NO₃)₆] we reported previously. In contrast, the deposition of the latter phase at the lower [HNO₃] conditions (1.00-4.30 M) demonstrates that hydrolysis and oxolation of Ce⁴⁺ proceed even below pH 0 to provide a [Ce-O-Ce]⁶⁺ unit included in this compound. These different Ce(IV) phases are exchangeable with each other under soaking in HNO₃(aq), implying that chemical equilibria of dissolution/deposition of these crystalline phases and hydrolysis and oxolation of Ce⁴⁺ and its complexation with NO₃^- occur in parallel. Indeed, such coordination chemistry of Ce(IV) in HNO₃(aq) was well corroborated by ¹⁷O NMR, Raman, and IR spectroscopy.

Recent trends and challenges with the synthesis of membranes: Industrial opportunities towards environmental remediation

The industrial and agricultural revolution has posed a serious and potential threat to environment. The industrial and agricultural pollutants are directly released into the environment. This issue has clinched the scientists to work on different materials in order to decontaminate the environment. Among all other techniques, the membrane filtration technology has fascinated researchers to overcome the pollution by its promising features. This review elaborated various membrane synthesis approaches along with their mechanism of filtration, their applications towards environmental remediation such as removal of heavy metals, degradation of dyes, pharma waste, organic pollutants, as well as gas sensing applications. The membrane synthesis using different sort of materials in which inorganic, carbon materials, polymers and metal organic framework (MOFs) are highlighted. These materials have been involved in synthesis of membrane to make it more cost effective and productive to remove such hazardous materials from wastewater. Based on the reported literature, it has been found that inorganic and polymer membranes are facing issues of brittleness and swelling prior to the industrial scale applications related to the high temperature and pressure which needs to be addressed to enhance the permeation performance.

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.

Superficially capped amino metal-organic framework for efficient solid-phase microextraction of perfluorinated alkyl substances

Perfluorinated alkyl substances (PFASs) were ubiquitously in the surface and groundwater. It is crucial and urgent to develop a rapid and ultrasensitive analysis method for the quantification of trace-level PFASs. Herein, a highly hydrophobic sorbent by capping phenylsilane groups on the surfaces of NH₂-UiO-66(Zr) nanocrystals was used for efficient solid-phase microextraction (SPME) of PFASs in water samples. It was found that the superficially capped nanocrystals (NH₂-UiO-66(Zr)-hp) exhibited both faster extraction kinetics and higher enrichment capacity than the non-capped nanocrystals. The extraction of eleven kinds of PFASs by NH₂-UiO-66(Zr)-hp fiber reached equilibrium in 20 min. The enrichment factors of the NH₂-UiO-66(Zr)-hp fiber ranged from 6.5 to 48, with a preference for long-chain PFASs over short-chain PFASs. It was proposed that superficial capping eliminated competitive moisture adsorption on the surfaces of the non-capped nanocrystals, thus facilitating the adsorption of PFASs through hydrophobic interaction. By using this new sorbent, the limits of detection of the SPME method as low as 0.035 to 0.616 ng·L^-1 were achieved for the target PFASs. The recoveries of PFASs in the environmental water samples were 80.9%-120%. This study presents a new strategy for developing an efficient sorbent for PFASs by surface hydrophobic modification.

Adsorptive removal of herbicides with similar structures from water over nitrogen-enriched carbon, derived from melamine@metal-azolate framework-6

Based on the recent concern on the pollution of water bodies with herbicides, adsorptive removal of typical herbicides with similar chemical structures, e. g. clofibric acid (CLFA), methylchlorophenoxypropionic acid or mecoprop (MCPP) and 2,4-dichlorophenoxyacetic acid (2,4-D) from water was studied using a porous nitrogen-enriched carbon. To prepare the nitrogen-enriched carbon, pyrolysis of a melamine (MLM) incorporated metal-azolate framework-6 (MLM(x)@MAF6; x = 0-50 M % of the ligand 2-ethylimidazole for MAF6), that was prepared for the first time via an in situ method, was carried out. The MLM(x)@MAF6-derived carbons (MDC6M(x)s) were characterized and used in the removal of CLFA, MCPP and 2,4-D from water. We found that the MDC6M(25), obtained from MLM(25)@MAF6 with 25% MLM (as the optimum precursor composition), showed the highest maximum adsorption capacity (Q₀) of 1031 mg/g for CLFA, compared with any reported adsorbents, so far. The physicochemical properties of CLFA, as well as adsorbents and adsorptions under wide pH conditions, were employed to propose a plausible adsorption mechanism including hydrogen bonding. Remarkably, the porous carbon with enriched nitrogen, derived from MAF6 loaded MLM via in situ method, was very competitive in herbicides adsorption because of the contribution of well-dispersed nitrogen sties on the adsorbent. Finally, MDC6M(25) was suggested as a potential adsorbent for the removal of herbcides, including CLFA, MCPP and 2,4-D, from water, which is highly attractive to mitigate the environmental issue, especially, water pollution by various herbicides.

Cerium based UiO-66 MOF as a multipollutant adsorbent for universal water purification

Herein, we demonstrate the use of cerium (Ce)-UiO-66 metal organic framework (MOF) for the removal of a variety of potentially toxic pollutants. The Ce-UiO-66 MOF, with similar framework topologies to Zr-UiO-66, has not been explored for its adsorptive properties in water remediation. The replacement of Zr metal center with Ce yields a MOF that can be synthesized in shorter durations with lesser energy consumptions and with excellent multipollutant adsorption properties. Further, the Ce-UiO-66 MOF was also studied for its adsorption abilities in the binary component system. Interestingly, the adsorbent showed higher adsorption capacities in the presence of other pollutants. Removal studies for other potentially toxic anionic and cationic dyes showed that the Ce-UiO-66 MOF has a wide range of contaminant removal abilities. Investigations of individual adsorption capacities revealed that the Ce-UiO-66 MOF has a maximum adsorption capacity of 793.7 mg/g for congo red (CR), 110 mg/g for methylene blue (MB), 66.1 mg/g for fluoride (F^-), 30 mg/g for Cr⁶⁺ and 485.4 mg/g for the pharmaceutical waste diclofenac sodium (DCF). To imply the practical applications of the Ce-UiO-66 MOF we have also demonstrated an adaptable filter that could separate all the potentially toxic pollutants.

Metal-Organic Gel-Modulated Synthesis of Hierarchically Porous Molecularly Imprinted Polymers for Efficient Removal of Sildenafil from Water

Molecularly imprinted polymers (MIPs) with high specific recognition capability are promising in environmental remediation. However, traditional MIPs usually show poor specific binding affinity toward templates in pure aqueous medium, thus greatly limiting their practical applications in wastewater treatment. Herein, we proposed a facile and versatile method to synthesize a water-compatible hierarchically porous MIP (HP-MIP), in which a metal-organic gel (MOG) was formed by in situ assembly and acted as a removable structural modulator. Remarkably, the integration of the MOG modulator and template imprinting defects significantly improved the specific template binding affinity of HP-MIP in water. The adsorption behavior of HP-MIP fitted well with the heterogeneous Freundlich isotherm, suggesting that HP-MIP possessed greater site heterogeneity to sildenafil than HP-NIP, which confirmed the efficiency of HP-MIP for the removal of sildenafil from water. This approach provides an important pathway to prepare water-compatible porous MIP for efficient removal of highly toxic organic pollutants from wastewater.

Advanced applications of Zr-based MOFs in the removal of water pollutants

The global water pollution is caused by the increase of industrial and agricultural activities, which have produced various toxic pollutants. Pollutants in water generally consist of metal ions, pharmaceuticals and personal care products (PPCPs), oil spills, organic dyes, and other organic pollutants. Amongst the adsorbents that have been developed to deal with pollutants in water, Zr-based metal-organic frameworks (MOFs) have drawn scientists' great attention due to their excellent stability and adjustable functionalization. Herein, the present review article introduces the synthetic methods of functionalized Zr-based MOFs and summarizes their applications in water pollution treatment. It also clarifies the interactions and removal mechanisms between pollutants and Zr-based MOFs. The use of these MOFs with eminent adsorption ability and recycling performance have been discussed in detail. Zr-based MOFs also face some challenges such as high cost, lack of real water environment applications, selective removal of pollutants, and low ability to remove composite pollutants. Future research should focus on addressing these issues. Although there is still a blank of the practical utility of Zr-based MOFs on a commercial scale, the research reported to date clearly shows that they are very promising materials for the water treatment.

Adsorptive removal of hazardous organics from water and fuel with functionalized metal-organic frameworks: Contribution of functional groups

The purification of contaminated water and fuel is very important for our sustainability. Adsorptive removal has attracted significant attention because of possible applications in industry and the rapid development of metal-organic frameworks (MOFs), which can be competitive adsorbents. In this review, the possible/competitive purification of water (contaminated with organics) and fuel (composed of S- and N-Containing compounds) via adsorption using MOFs, especially those with various functional groups (FGs), will be discussed. The contribution of FGs such as -OH, -COOH, -SO₃H, -NH₂, and -NH₃⁺ to adsorption/purification will be analyzed in detail, not only to understand the plausible adsorption mechanism but also to utilize specific FGs in adsorption. Moreover, methods for introducing FGs onto MOFs will be summarized. Finally, the prospects for both adsorption/removal and emerging fields will be suggested. Studies for practical applications in industry with shaped MOFs from inexpensive route will be important. The solution pH should be considered for the adsorption of aqueous solution. Applications of MOFs in other fields like storage/delivery and enrichment of analytes might be deeply studied.

Modulating the regioselectivity of solid-state photodimerization in coordination polymer crystals

Coordination polymers [Cd(1,4-bpeb)(L1)] (1), [Zn2(1,4-bpeb)2(L2)2(SO42-)2] (2) and [Cd(1,4-bpeb)(L3)] (H2O) (3) (H2L1, 3-[2-(3-hydroxy-phenoxymethyl)-benzyloxy]-benzoic acid; HL2, 1H-Indazole-3-carboxylic acid; H3L3, benzene-1,2,3-tricarboxylic acid; 1,4-bpeb, 1,4-bis[2-(4-pyridyl)vinyl]benzene have been synthesized under solvothermal conditions. Complexes 1-3 underwent photodimerization in the solid-state to give quantitative yields of single isomeric products. The choice of carboxyl ligands L and metal center determined the arrangement of 1,4-bpeb ligands, which in turn directed the regiochemistry of the final photoproducts. The solid-state network structures of cadmium based 1 and 3 had 1,4-bpeb pairs aligned face-to-face with both C[double bond, length as m-dash]C centres in each ligand at an appropriate distance and alignment for photodimerization to give the corresponding para-[2.2]cyclophane (pCP) exclusively. By contrast, compound 2 possessed dinuclear (ZnSO4)2 metallocycles that positioned the 1,4-bpeb "arms" face-to-face, but with C[double bond, length as m-dash]C centres offset at an appropriate distance for only one pair to undergo [2 + 2] cycloaddition to yield a single stereoisomer of the monocyclobutane photo-product bpbpvpcb. This work highlights crystal engineering design principles that can be used to facilitate regio- and stereospecificity in solid-state transformations.

Insights to perfluorooctanoic acid adsorption micro-mechanism over Fe-based metal organic frameworks: Combining computational calculation with response surface methodology

Adsorption performance, interfacial interaction mechanism and contribution of pores concerning PFOA adsorption to Fe-based metal-organic frameworks (MOFs) including Fe-BTC, MIL-100-Fe and MIL-101-Fe are investigated using experiments and computational calculation at molecular level even electronic level. Fe-BTC (418 mg/g) with more Lewis acid sites demonstrates higher adsorption capacity of PFOA in comparison with MIL-100-Fe (349 mg/g) and MIL-101-Fe (370 mg/g). Adsorption isotherms and kinetics indicate presence of monolayer adsorption and chemisorption in adsorption process. The pH dependence of PFOA adsorption to Fe-based MOFs is statistically revealed by experiments and analysis of variance of response surface methodology (RSM). XPS spectra of MOF-PFOA corroborate that decreasing binding energy of Fe2p and increasing binding energy of F1s, suggesting the presence of Lewis acid/base complexing (LAB) and hydrophobic interaction in adsorption process. Differential charge demonstrates that Fe center and benzene of organic ligands are respectively electron acceptor and donor in adsorption process. Electronic level mechanism finds that LAB complexing dominates adsorption process due to highest overlap of electron cloud. Smaller pores such as triangle and pentagonal pores of Fe-based MOFs contribute to the load of PFOA, while larger hexagonal one enable PFOA to enter into cages, as revealed by computational calculation.

Environmental threatening concern and efficient removal of pharmaceutically active compounds using metal-organic frameworks as adsorbents

An alarming number of contaminants of emerging concern, including active residues from pharmaceuticals and personal care products (PPCPs), are increasingly being introduced in water systems and environmental matrices due to unavoidable outcomes of modern-day lifestyle. Most of the PPCPs based contaminants are not completely eliminated during the currently used water/wastewater treatment processes. Therefore, highly selective and significant removal of PPCPs from environmental matrices remains a scientific challenge. In recent years, a wide range of metal-organic frameworks (MOFs) and MOF-based nanocomposites have been designed and envisioned for environmental remediation applications. MOF-derived novel cues had shown an adsorptive capability for the extraction and removal of an array of trace constituents in environmental samples. Noteworthy features such as substantial surface area, size, dispersibility, tunable structure, and repeated use capability provide MOFs-derived platform a superiority over in-practice conventional adsorptive materials. This review provides a comprehensive evaluation of the efficient removal or mitigation of various categories of PPCPs by diverse types of MOF-derived adsorbents with suitable examples. The growing research investigations in this direction paves the way for designing more efficient porous nanomaterials that would be useful for the elimination of PPCPs, and separation perspectives.

Pore-Functionalized and Hydrolytically Robust Cd(II)-Metal-Organic Framework for Highly Selective, Multicyclic CO2 Adsorption and Fast-Responsive Luminescent Monitoring of Fe(III) and Cr(VI) Ions with Notable Sensitivity and Reusability

Metal-organic frameworks (MOFs) show a distinctive pre-eminence over other heterogeneous systems for adsorption of carbon dioxide (CO₂) gas and fluorescence detection of water contaminating ions, where integration of both these attributes along with enhancement of pore functionality and water stability is crucial for potential applications related to environmental remediation. Pore functionalization has been achieved in a 2-fold interpenetrated, mixed-ligand Cd(II)-framework [Cd_1.5(L)₂(bpy)(NO₃)]·2DMF·2H₂O (CSMCRI-5) (HL = 4-(4-carboxyphenyl)-1,2,4-triazole, bpy = 4,4'-bipyridine, DMF = dimethylformamide, CSMCRI = Central Salt & Marine Chemicals Research Institute) by utilizing a bifunctional ligand HL. The bpy-pillared framework, containing diverse Cd(II) nodes, optimum sized voids, and free N-atom affixed one-dimensional porous channels, shows notable structural robustness in diverse organic solvents and water. In spite of a negligible surface area, the activated MOF (5a) exhibits good CO₂ uptake and highly selective CO₂ adsorption over N₂ (259.94) and CH₄ (14.34) alongside minor loss during multiple CO₂ adsorption-desorption cycles. Luminescence studies demonstrate extremely selective and ultrafast sensing of Fe³⁺ ions in the aqueous phase with notable quenching (1.13 × 10⁴ M^-1) as well as an impressive 98 ppb limit of detection (LOD). Importantly, Fe³⁺ detection is exclusively retained under simulated physiological conditions. The framework further serves as a quick-responsive scaffold for toxic CrO₄^2- and Cr₂O₇^2- anions, where individual quenching constants (CrO₄^2-: 1.73 × 10⁴ M^-1; Cr₂O₇^2-: 5.42 × 10⁴ M^-1) and LOD values (CrO₄^2-: 280 ppb; Cr₂O₇^2-: 320 ppb) rank among the best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress vivid monitoring of all these aqueous pollutants by a handy paper-strip method, besides outstanding applicability of 5a toward their recyclable detection. Mechanism of selective quenching is comprehensively investigated in light of the absorption of the excitation/emission energy of the host framework by an individual studied analyte.

Fabrication of (4, 10) and (4, 12)-Connected Multifunctional Zirconium Metal-Organic Frameworks for the Targeted Adsorption of a Guest Molecule

Following the principle of a topology guide, a zirconium MOF (PCN-207) based on the H₄TPTA ligand (tetramethyl(4,4',4″,4‴-(pyrazine-2,3,5,6-tetrayl))tetrabenzoic acid) with C₂ symmetry and an 8-connected Zr₆(μ_3-OH)₈(OH)₈]⁸⁺ cluster with D_4h symmetry has been synthesized. PCN-206 can also be obtained by modulating the benzoic acid usage to change the flexibility of the H₄TPTA ligand. The unique positions of 8-connected Zr₆ clusters in the flu and scu networks and the flexibility of the tetratopic primary linker enable the precise insertion of fumarate (FA), 1,4-benzenedicarboxylic acid (H₂BDC), and even 2,6-naphthalenedicarboxylic acid (H₂NDC) in a one-pot reaction. Auxiliary linkers are used to generate new MOF structures or topologies or to split the pore spaces, which may significantly change the porosity and chemical and physical properties of scaffold MOFs. The results provide a successful strategy for the rational design of multicomponent Zr-MOFs. Because of differences in composition and configuration between structures, PCN-207 shows the highest separation capability of light hydrocarbons; moreover, PCN-206 exhibits the highest adsorption capacity of 2,4-D and DCF among MOFs at present.

Design of l-Cysteine Functionalized UiO-66 MOFs for Selective Adsorption of Hg(II) in Aqueous Medium

Mercury ions can cause a series of hazards to humans and the environment, even in trace amounts. Here, we designed a novel adsorbent (Cys-UiO-66) by functionalizing NH₂-UiO-66 with l-cysteine for selective removal of Hg(II) from solution. The Cys-UiO-66 was characterized by different instruments. The adsorption property of Cys-UiO-66 was evaluated by batch methods. The maximum adsorption capacity was 350.14 mg/g at pH 5.0. Furthermore, the adsorption isotherm and kinetics models were in accord with the Langmuir and pseudo-second-order models, respectively, evidencing that the adsorption behavior was dominated by monolayer chemisorption. The Cys-UiO-66 had better affinity for Hg(II) than other coexisting ions in wastewater and could be regenerated for at least five cycles. The results prove that Cys-UiO-66 is a talented and efficient sorbent for mercury ions.