A facile approach to fabricate an immobilized-phosphate zirconium-based metal-organic framework composite (UiO-66-P) and its activity in the adsorption and separation of organic dyes

Using eugenol scaffold to explore the explosive sensing properties of Cd(II)-based coordination polymers: experimental studies and real sample analysis

Eugenol, the major constituent of clove oil, has been explored as an essential natural ingredient for ages owing to its versatile pharmacological properties. However, to date, the coordination chemistry of eugenol derivatives has not been much explored. In the present work, an eugenol-based Schiff base ligand (HL) was synthesized and structurally confirmed through ESI-MS, NMR, and FT-IR spectroscopy studies. Consequently, the N,O-donor chelating ligand HL was coordinated with Cd2+, in the presence of bridging pseudohalides (thiocyanate, SCN-, and dicyanamide, N(CN)2-) to synthesize two luminescent coordination polymers (CPs 1 and 2): [Cd2(L)2(X)2]n (where HL = 4-allyl-2-(((2-(benzylamino)ethyl) imino)methyl)-6-methoxyphenol and Xs are bridging pseudohalides, i.e., SCN- and N(CN)2-) on a Cd-eugenol scaffold. The CPs depicted structural diversity, bulk-phase purity, thermal stability, and the presence of interlayer supramolecular C-H⋯π interactions together with C-H⋯S (for CP 1) and C-H⋯N (for CP 2) interactions. The CPs further exemplified themselves as selective and sensitive 'turn-off' probes towards trinitrophenol (TNP) (quenching efficiency: 82.02% and 83.86% for 1 and 2) among a pool of hazardous nitroaromatic compounds (NACs). Accordingly, 1 and 2 exhibited an ultralow limit of detection (LOD) of 0.29 and 0.15 μM, with high quenching constants (KSV) of 5.91 × 104 and 17.60 × 104 M-1, respectively. In addition, TNP sensing events were evidenced to be recyclable and exhibited fast response (∼31 s, 1, and ∼40 s, 2), which increased its real-world viability. Vapor phase TNP sensing was also accomplished upon drop-casted CP films. Experimental investigations and theoretical DFT study confirmed the cooperative occurrence of RET-IFE-PET-collisional quenching and non-covalent π⋯π stacking as key factors involved in the TNP sensing performance. The competency of 1 and 2 in the detection of TNP from several complex environmental matrices (CEMs), viz. matchstick powder, river and sewage water, and soil specimens, was also established with good recovery (∼66-86% and ∼68-93% for 1 and 2, respectively) and high KSV values (3.90-11.39 × 104 and 6.17-18.79 × 104 M-1 for 1 and 2, respectively).

Superior Adsorptive Removal of Anionic Azo Dyes from Aqueous Solutions Using Sulfonic Acid Group-Modified MIL-101@Graphene Oxide Composite

It is critical to remove organic contaminants from wastewater released by the printing and dyeing industry for addressing water pollution issue. Therefore, the fabrication of new adsorbents with excellent removal efficiencies is an urgent task. A composite of MIL-101 partially functionalized with -SO3H (MIL-101-SO3H) and graphene oxide (GO) was prepared by assembling MIL-101-SO3H truncated octahedrons on the GO framework. The synthesized MIL-101-SO3H@GO has a superior adsorption efficiency for anionic azo dyes. The maximum adsorption capacities of MIL-101-SO3H@GO-1 for Congo red, methyl orange, acid orange 7, and acid orange G reached 2711.3, 818.8, 551.2, and 319.8 mg/g, respectively, which are considerably higher than those obtained using unmodified MIL-101. This is because additional interactions that promote azo dye adsorption, such as hydrogen bonding between the dye and the sulfonic acid groups of MIL-101-SO3H or the carboxyl groups of GO, were induced, and agglomerate pores that accommodated the dye were formed in the composite. The ultrahigh removal efficiency of the composite for azo dyes is mainly driven by hydrogen bonding, electrostatic interactions, π-π stacking between the MIL-101-SO3H@GO and dye molecules, synergistic interactions at the interface of GO and MIL-101-SO3H microcrystals, and the pore-filling effect. Understanding these driving forces for dye adsorption can contribute to the development of sustainable and functionally modified metal-organic framework composite adsorbents.

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

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

One-Step Synthesis of Al-Doped UiO-66 Nanoparticle for Enhanced Removal of Organic Dyes from Wastewater

In this study, a series of Al-doped metal-organic frameworks (Al_xZr_(1-x)-UiO-66) were synthesized through a one-step solvothermal method. Various characterization techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and N₂ sorption measurement, suggested that the Al doping was uniform and barely influenced the crystallinity, chemical stability, and thermal stability of the materials. Two cationic dyes, safranine T (ST) and methylene blue (MB), were selected for investigating the adsorption performances of Al-doped UiO-66 materials. Al_0.3Zr_0.7-UiO-66 exhibited 9.63 and 5.54 times higher adsorption capacities than UiO-66, 498 mg/g and 251 mg/g for ST and MB, respectively. The improved adsorption performance can be attributed to π-π interaction, hydrogen bond, and the coordination between the dye and Al-doped MOF. The pseudo-second-order and Langmuir models explained the adsorption process well, which indicated that the dye adsorption on Al_0.3Zr_0.7-UiO-66 mostly occurred through chemisorption on homogeneous surfaces. A thermodynamic study indicated the adsorption process was spontaneous and endothermic. The adsorption capacity did not decrease significantly after four cycles.

NIR light-propelled bullet-shaped carbon hollow nanomotors with controllable shell thickness for the enhanced dye removal

Materials with asymmetric nanostructures have attracted tremendous research attention due to their unique structural characteristics, excellent physicochemical properties, and promising prospects. However, it is still difficult to design and fabricate bullet-shaped nanostructure due to its structural complexity. Herein, for the first time, we successfully constructed NIR light-propelled bullet-shaped hollow carbon nanomotors (BHCNs) with an open mouth on the bottom of nano-bullet for the enhanced dye removal, by employing bullet-shaped silica nanoparticles (B-SiO₂ NPs) as a hard template. BHCNs were formed by the growth of polydopamine (PDA) layer on the heterogeneous surface of B-SiO₂ NPs, followed by the carbonization of PDA and subsequent selective etching of SiO₂. The shell thickness of BHCNs was able to be facilely controlled from ≈ 14 to 30 nm by tuning the added amount of dopamine. The combination of streamlined bullet-shaped nanostructure with good photothermal conversion efficiency of carbon materials facilitated the generation of asymmetric thermal gradient field around itself, thus driving the motion of BHCNs by self-thermophoresis. Noteworthily, the diffusion coefficient (De) and velocity of BCHNs with shell thickness of 15 nm (BHCNs-15) reached to 43.8 μm⋅cm^-2 and 11.4 μm⋅s^-1, respectively, under the illumination of 808 nm NIR laser with the power density of 1.5 W⋅cm^-2. The NIR laser propulsion caused BCHNs-15 to enhance the removal efficiency (53.4% vs. 25.4%) of methylene blue (MB) as a typical dye because the faster velocity could produce the higher micromixing role between carbon adsorbent and MB. Such a smart design of the streamlined nanomotors may provide a promising potential in environmental treatment, biomedical and biosensing applications.

Adsorption of Methyl Orange on a Novel Palygorskite/UiO-66 Nanocomposite

Herein, a novel composite material containing UiO-66 and palygorskite (Pal) clay mineral was prepared using a facile one-pot synthesis process. The material was studied using a variety of techniques and applied as did not affect the structure of the metal-organic framework (MOF) part, but induced a small increase in specific surface area. The developed Pal/UiO-66 composite presented excellent adsorption efficiency against MO removal, as evidenced by detailed kinetic and isotherm experiments. An impressive maximum adsorption capacity at equilibrium was evidenced; 340 mg g−1 at pH = 5 and T = 25 °C. This corresponds to a 34.5 % increase compared with pure UiO-66, considering only the MOF content. Furthermore, the Pal/UiO-66 composite was proven stable and highly recyclable, losing less than 9% of the removal capacity after five consecutive cycles. The study highlights the synergistic effect of the coupling of MOF structures with low-cost and abundant clay minerals for the development of advanced absorbents.

Fine-tuning the dye adsorption capacity of UiO-66 by a mixed-ligand approach

The mixed ligand synthetic approach offers an alternative to engineering a specific character in metal-organic framework (MOFs) materials. Herein, we synthesized and characterized a well-known prototype zirconium-based-MOF, so-called UiO-66, and its mixed ligand derivatives UiO-66-xATA, where x is mole fraction (0.5, 0.75, and 1.0) and ATA is 2-animoterephthalate. The study investigates whether the dye adsorption capacity can be tuned/enhanced by the ATA ligand substitution into the framework. We found that, at room temperature, UiO-66-0.75ATA shows the highest adsorption capacity toward various dye solutions, including methylene blue (MB), indigo carmine (IC), and congo red (CR). The optimum adsorption conditions in all four materials were in a common trend where their adsorption capacities can be increased with decreasing pH and adsorbent dose, increasing IC concentration, contact time, and temperature. Pseudo-second order kinetics model fits best with their adsorption data, where UiO-66-ATA has the fastest adsorption rate. Langmuir and Freundlich isotherms were found best to describe adsorption behavior in ATA-containing UiO-66 and UiO-66, respectively, where adsorption processes were found to be physisorption. Confirming by thermodynamic studies, the adsorption in all four materials occurred spontaneously, driven by entropy. Computational studies showed ligand to metal charge transfer where the distribution of electron densities was varied with the amount of functionalized ligand. Adsorption mechanism is proposed as a synergistic interplay between electrostatic interaction and hydrogen bonding. The findings in this work broaden the potential strategy to fine-tune the dye adsorption capacity in MOF materials.

Functionally modified metal–organic frameworks for the removal of toxic dyes from wastewater

This review highlights recent advancement in functional modified (FM) MOFs as superior adsorbents for the removal of dyes, classifying them by various modification strategies. The adsorption interactions affected by the FM approach are summarized.

Multifunctional Fe3O4/TiO2/NH2-UiO-66 with integrated interfacial features for favorable phosphate adsorption

Excessive use and discharge of phosphate are the decisive factors leading to water eutrophication, and adsorption is deemed among the most effective methods in phosphorus capture. This study prepared the...

Adsorptive removal of dyes from wastewater using a metal-organic framework: A review

Water pollution from synthetic dyes is a growing environmental concern because many dyes have carcinogenic effects on humans and aquatic life. Adsorption is a widely used technology for the separation and removal of dyes from wastewater. However, the dye removal process using conventional adsorbents is not sufficiently efficient for industrial wastewater. Metal-organic frameworks (MOFs) addresses these drawbacks. MOF showed excellent dye removal and degradation capacity owing to its multifunctionality, water-stability, large surface area, tunable pore size and recyclability. Magnetic MOFs retained excellent performance up to several consecutive cycles. Modified MOFs performed as Fenton-like catalysis process which generated abundant reactive radicals that degraded complex organic dyes into simple and less toxic forms which were further adsorbed onto the MOF. This review systematically compiles in-depth studies on the adsorptive removal of dyes from wastewater, MOF adsorption mechanisms, major influencing factors, to adsorption efficiency of MOFs. While all MOFs adsorb dyes through electrostatic attraction, the type of MOF, presence of functional groups, ligands, and pH significantly control the adsorption mechanism. Before developing an MOF, optimization and upgradation of factors and interaction between available adsorption site and adsorbate is needed. Finally, the prospects and new frontiers of MOFs in sustainable water treatment is discussed.

M, Shahid M, AlDamen MA, Khalid M, Akram M. Cationic dye adsorption and separation at discrete molecular level: first example of an iron cluster with rapid and selective adsorption of methylene blue from aqueous system

A novel Fe₆ cluster was designed as a rare example of any discrete molecule as a highly efficient, selective and rapid functional material for the adsorption of cationic dyes, i.e. methylene blue (MB), from contaminated water bodies.

Ni(ii)-Based one dimensional coordination polymers for environmental remediation: design, topology, magnetism and the selective adsorption of cationic dyes

Two coordination polymers are designed in order to exploit them for the separation of cationic and anionic dyes effectively and rapidly.

A new water-insoluble coordination polymer as efficient dye adsorbent and olefin epoxidation catalyst

A new water-insoluble bi-metallic coordination polymer was simply prepared via polymerization-precipitation of molybdenum complex building blocks with Zn²⁺ cation. The linker was a di-carboxylic acid consisting of two coordination sites i.e. N,O and COO^- suitable for coordinating to MoO₂ unit and Zn²⁺, respectively. Characterization of the prepared coordination polymer was carried out with various physicochemical methods which confirmed the proposed structure. The prepared coordination polymer preferentially adsorbed methylene blue (more than 92% of methylene blue after 2 min) relative to methyl orange and can be reused at least four times without any loss of adsorption efficiency. The adsorption process of both dyes followed the pseudo-second order kinetic equation. Additionally, the obtained coordination polymer catalyzed epoxidation of olefins with tert-butylhydroperoxide (TBHP) quantitatively with excellent selectivity (>99%) under mild reaction conditions.

A novel self-assembled Na{Cu12Zn4} multifunctional material: first report of a discrete coordination compound for detection of Ca2+ions and selective adsorption of cationic dyes in water

A novel discrete Na{Cu₁₂Zn₄} unit is discovered with the ability to sense calcium ions (with ultra-low detection limit) as well as to adsorb cationic dyes in the aqueous phase with high performance.

Selective Dye Adsorption by Zeolitic Imidazolate Framework-8 Loaded UiO-66-NH2

In this study, Zeolitic Imidazolate Framework-8 (ZIF-8)-loaded UiO-66-NH₂ was synthesized, characterized, and analyzed for its potential to efficiently remove dyes. The selective adsorption on ZIF-8-loaded UiO-66-NH₂ or its parent MOFs (UiO-66-NH₂ and ZIF-8) in the mixed dyes solution was explored, including anionic dye (methyl orange (MO)) and cationic dyes (methylene blue (MB) and rhodamine B (RhB)). ZIF-8-loaded UiO-66-NH₂ displayed much better selectivity to MB than its parent MOFs. Adsorption capacity of ZIF-8-loaded UiO-66-NH₂ (173 mg/g) toward MB was found to be 215% higher than UiO-66-NH₂ (55 mg/g). A kinetics study based on adsorption data demonstrated that the adsorption process most closely matched with the model of pseudo-second-order kinetic and Langmuir isotherm. The adsorption was an exothermic and spontaneous physical process as revealed by the values of thermodynamic parameters. Furthermore, reusability of ZIF-8-loaded UiO-66-NH₂ was investigated and revealed the significant regeneration efficiency in adsorption capacity for MB even after four adsorption cycles. Experimental results proved that the interaction between ZIF-8-loaded UiO-66-NH₂ and MB was mainly affected by the mechanism, for instance, electrostatic interaction as well as π–π stacking interactions.

Three-in-one is really better: exploring the sensing and adsorption properties in a newly designed metal-organic system incorporating a copper(ii) ion

A 2-D copper(ii)-based coordination polymer, [Cu(SCN)(hmp)]_n CP (1), was crystallized via the slow evaporation method after the reaction of CuSO₄·5H₂O, 2-pyridinemethanol (hmpH), sodium thiocyanate and sodium hydroxide in water for functional applications. CP (1) was characterized via elemental analysis, FTIR, PXRD, magnetic, EPR, crystallographic and TGA studies. The crystal structure and EPR data confirmed a square pyramidal geometry around the Cu(ii) ions. The topological analysis revealed that CP 1 has a {6^{^}3} point symbol with a [6.6.6] extended point symbol and 3-c net, uninodal net having hcb and Shubnikov hexagonal plane net/(6,3) type of uncommon topology. The magnetic studies suggested the strong antiferromagnetic nature of CP (1). The fluorescence sensing property of CP (1) was investigated with different nitro aromatic compounds and hazardous metal ions. CP (1) demonstrated high selectivity and sensitivity towards nitrobenzene, even in the presence of other competitive nitro aromatics. In addition, CP (1) showed excellent selectivity and sensitivity toward Fe³⁺ over other metal ions. The possible detection mechanisms were proposed employing UV-visible and fluorescence spectroscopy and DFT calculations. CP (1) also showed excellent recyclability towards both analytes, and its initial intensity was almost regained after several washings. Moreover, CP (1) acted as an excellent adsorbent material for natural dyes with different charges and sizes, i.e., methylene blue (MB), methyl orange (MO) and Rhodamine-B. Furthermore, CP (1) was utilized repeatedly for the effective adsorption of MB from wastewater without significant loss in its adsorption capacity. Hence, the present CP (1) was designed to relate coordination chemistry with various functional applications of interest.

Recent advances on porous organic frameworks for the adsorptive removal of hazardous materials

Environmental pollution is one of the most serious problems facing mankind today, and has attracted widespread attention worldwide. The burgeoning class of crystalline porous organic framework materials, metal-organic frameworks and covalent organic frameworks present promising application potential in areas related to pollution control due to their interesting surface properties. In this review, the literature of the past five years on the adsorptive removal of various hazardous materials, mainly including heavy metal ions, harmful gases, organic dyes, pharmaceutical and personal care products, and radionuclides from the environment by using COFs and MOFs, is summarized. The adsorption mechanisms are also discussed to help understand their adsorption performance and selectivity. Additionally, some insightful suggestions are given to enhance the performance of MOFs and COFs in the adsorptive removal of various hazardous materials.

Superior adsorptive removal of anionic dyes by MIL-101 analogues: the effect of free carboxylic acid groups in the pore channels

MIL-101-COOH nanoparticles functionalized with free carboxylic acid groups exhibited superior CR, MO, and AC adsorption capacities via their distinctive adsorption mechanisms.

Ce-doped UiO-67 nanocrystals with improved adsorption property for removal of organic dyes

In this study, we report the synthesis of Ce-doped UiO-67 nanocrystals via one-step hydrothermal method and their potential use for waste water treatment to remove organic dyes. The as-prepared samples were characterized by using SEM, TEM, FT-IR, XRD, XPS and TG techniques and the results demonstrate the formation of the framework structure of the Ce-doped UiO-67. The adsorption study of the material shows that the Ce-doped UiO-67 nanoparticles preferentially adsorb the cationic dyes such as rhodamine B and malachite green rather than the anionic dyes such as methyl orange. Adsorption capacities are 754.4, 589.2 and 191.6 mg g⁻¹ for rhodamine B, malachite green and methyl orange respectively. Based on its zeta potential and adsorption isotherm, it is understood that Ce doping increases its electrostatic interactions, and as a consequence, improves the adsorption capacity for cationic dyes. In addition, it is found that a pseudo-second-order kinetics and the Langmuir isothermal model were suitable for describing the adsorption behavior of cationic dyes onto the Ce-doped UiO-67.

The Ce-doped UiO-67 nanocrystals were successfully synthesized via a one-step hydrothermal method. Ce doping increases the negative charge on the surface of the material, thus the adsorbent exhibits high adsorption capacity to cationic dyes.

Facile preparation of UiO-66 /PAM monoliths via CO2-in-water HIPEs and their applications

A novel clean method to synthesis a composite monolith was developed. Given its amphiphilic property, UiO-66 can emulsify water and CO2 to format a high internal phase emulsion (HIPE) under certain conditions. These UiO-66-emulsified Pickering HIPEs can be used as templates to prepare interconnected macroporous MOF/polymer composite monoliths. The effects of UiO-66 amount, cross-linking agent concentration, and CO2-water ratio on UiO-66/PAM structures were investigated. Then, the as-synthesized MOF/PAM composites were characterized by TGA, XRD, SEM, and FT-IR analyses, as well as rheological and DMA measurements. The results indicated that the composites are interconnected with hierarchical pores, and the diameter of the voids is 10-50 μm. The directly prepared monoliths exhibited relatively high stresses at 82% strain and recovered their shape quickly. The adsorption capacity of the composites for methylene blue (MB) is 50 mg g-1 at a faster adsorption rate. The monoliths also exhibit underlying applications in edible oil-water separation.

Effect of particle size distribution of UiO-67 nano/microcrystals on the adsorption of organic dyes from aqueous solution

UiO-67 nano/microcrystals with different particle size distributions (PSDs) were successfully obtained by a simple solvothermal method.