Thiol- and Amine-Incorporated UIO-66-NH2 as an Efficient Adsorbent for the Removal of Mercury(II) and Phosphate Ions from Aqueous Solutions

Multiple signal-enhanced electrochemiluminescence aptamer sensors based on carboxylated ruthenium (II) complexes for acetamiprid detection

BACKGROUND

Rapid and sensitive detection for acetamiprid, a kind of widely used neonicotinoid insecticide, is very meaningful for the development of modern agriculture and the protection of human health. Highly stable electrochemiluminescence (ECL) materials are one of the key factors in ECL sensing technology. ECL materials prepared by porous materials (e.g., MOFs) coated with chromophores have been used for ECL sensing detection, but these materials have poor stability because the chromophores escape when they are in aqueous solution. Therefore, the development of highly stable ECL materials is of great significance to improve the sensitivity of ECL sensing technology.

RESULTS

In this work, by combining etched metal-organic frameworks (E-UIO-66-NH2) as carrier with Tris(4,4'-dicarboxylic acid-2,2'-bipyridine)Ru(II) chloride (Ru(dcbpy)32+) as signal probe via amide bonds, highly stable nanocomposites (E-UIO-66-NH2-Ru) with excellent ECL performance were firstly prepared. Then, using MoS2 loaded with AuNPs as substrate material and co-reactant promoter, a signal off-on-off ECL aptamer sensor was prepared for sensitive detection of acetamiprid. Due to the excellent catalytic activity of E-UIO-66-NH2-Ru and MoS2@Au towards K2S2O8, the ECL signals can be enhanced by multiple signal enhancement pathways, the prepared ECL aptamer sensor could achieve sensitive detection of acetamiprid in the linear range of 10-13 to10-7 mol L-1, with the limit of detection (LOD) of 2.78ⅹ10-15 mol L-1 (S/N = 3). After the evaluation of actual sample testing, this sensing platform was proven to be an effective method for the detection of acetamiprid in food and agricultural products.

SIGNIFICANCE AND NOVELTY

The E-UIO-66-NH2-Ru prepared by linking Ru(dcbpy)32+ to E-UIO-66-NH2 via amide bonding has very high stability. The synergistic catalytic effect of MoS2 and AuNPs enhanced the ECL signal. By exploring the sensing mechanism and evaluating the actual sample tests, the proposed signal "on-off" ECL sensing strategy was proved to be an effective and excellent ECL sensing method for sensitive and stable detection of acetamiprid.

Cysteamine-Anchored MOF through Post-Synthetic Modification Strategy for the Effective Removal of Mercury from Water

The introduction of cysteamine functionality, referred to as Q-ZIF-67-SH, was successfully achieved through postsynthetic modification while maintaining the structural and thermal stability of the quasi metal-organic framework Q-ZIF-67. By subjecting ZIF-67 to controlled partial deligandation at 310 °C under an air atmosphere, a substantial number of unsaturated cobalt sites were generated within the quasi ZIF-67 (Q-ZIF-67) structure. These unsaturated cobalt sites facilitated effective coordination with cysteamine, resulting in the development of the thiol-functionalized framework Q-ZIF-67-SH. The potential of these metal-organic frameworks (MOFs) for the adsorptive removal of hazardous Hg(II) was investigated. Various factors, such as the type of sorbent, pH, adsorbent dosage, initial concentration of Hg(II), and presence of coexisting ions, were thoroughly examined and comprehensively explained. Thiol-anchored MOF significantly enhanced the efficiency of Hg(II) removal, achieving an impressive removal rate of up to 99.2%. Furthermore, it demonstrated a maximum adsorption capacity of 994 mg g-1 and a distribution coefficient of 2.5 × 106 mL g-1. A good correspondence with pseudo-second-order kinetics and the Langmuir model was observed through the fitting of adsorption kinetics and the isotherm model. The thermodynamic data strongly indicate that the adsorptive removal of Hg(II) is characterized by endothermicity and spontaneity. This signifies that the process is energetically favorable and has potential for efficient Hg(II) removal. Therefore, the Q-ZIF-67-SH sorbent emerges as a promising and advantageous option for the removal of Hg(II) from water.

Hydrothermal synthesis of Mg/Al-layered double hydroxide modified water hyacinth hydrochar for remediation of wastewater containing mordant brown dye

A high-performance dye adsorbent of Mg/Al-layered double hydroxide modified water hyacinth hydrochar (MgAl@WH) was synthesized by a simple hydrothermal method. The surface functional groups, elemental composition, crystalline structure, and surface morphology of the prepared (MgAl@WH) were determined using different analytical techniques. The characterization results revealed that the (MgAl@WH) hydrochar surface offered more active adsorption sites, facilitating the mordant brown (anionic dye) adsorption, leading to its superior performance with much higher uptake capability (311.0 mg g-1 at 298 K) than Mg/Al double hydroxide nanosheets (MgAl DLHs, 80.2 mg g-1 at 298 K) and dried water hyacinth (WH, 10.0 mg g-1 at 298 K). The adsorption behavior of MgAL@WH follows the pseudo second order kinetic model (R2 = 0.999) and Langmuir isotherm model (R2 = 0.999). Moreover, MgAl@WH bonded efficiently with mordant brown dye via hydrogen bonding and interlayer anion exchange with monolayer formation. Additionally, the recycling tests revealed that the MgAl@WH can be reused over 10 cycles without significant change in the removal efficiency. Based on the obtained findings, Mg/Al-layered double hydroxide modified water hyacinth hydrochar (MgAl@WH), for its economic and environmental benefits, has recently been used as an efficient adsorbent to remediate industrial wastewater containing anionic dyes.

Recent advancements in modifications of metal-organic frameworks-based materials for enhanced water purification and contaminant detection

Metal-organic frameworks (MOFs) have emerged as a key focus in water treatment and monitoring due to their unique structural features, including extensive surface area, customizable porosity, reversible adsorption, and high catalytic efficiency. While numerous reviews have discussed MOFs in environmental remediation, this review specifically addresses recent advancements in modifying MOFs to enhance their effectiveness in water purification and monitoring. It underscores their roles as adsorbents, photocatalysts, and in luminescent and electrochemical sensing. Advancements such as pore modification, defect engineering, and functionalization, combined synergistically with advanced materials, have led to the development of recyclable MOF-based nano-adsorbents, Z-scheme photocatalytic systems, nanocomposites, and hybrid materials. These innovations have broadened the spectrum of removable contaminants and improved material recyclability. Additionally, this review delves into the creation of multifunctional MOF materials, the development of robust MOF variants, and the simplification of synthesis methods, marking significant progress in MOF sensor technology. Furthermore, the review addresses current challenges in this field and proposes potential future research directions and practical applications. The growing research interest in MOFs underscores the need for an updated synthesis of knowledge in this area, focusing on both current challenges and future opportunities in water remediation.

A novel ionic liquid-entrapped MIL-101(Cr) framework with enhanced removal efficiency towards phosphate from aqueous solution

Developing adsorbent materials with high adsorptive dephosphorization (ADP) is significant for treating phosphate from aqueous solutions and eutrophic water. Herein, the MIL-101(Cr) framework was entrapped ionic liquid (IL) of 1-butyl-3-methylimidazoliumbromide ionic liquid ([C4mem]+[Br]-) using a ship-in-a-bottle approach to obtain novel adsorbents [C4mem]+[Br]-@MIL-101(Cr) contained varied IL contents, namely C4mem@MIL-101. The characterization results revealed that the formed [C4mem]+[Br]- molecules interacted with the MIL-101(Cr) frameworks, enhanced their stability, and offered additional adsorption sites. The batch adsorptions of phosphate showed that the optimized C4mem@MIL-101 adsorbent loaded with ~ 7% IL-based N content had the highest phosphate absorbing capacity of ~ 200 mg/g, outperforming the pristine MIL-101(Cr) and other adsorbents. The ADP efficiency was facilitated in the acidic media, where the phosphate ions of H2PO4- and HPO42- captured onto the C4mem@MIL-101 via several interactions, including electrostatic attraction, H-bonds, and chemical interactions. In the meantime, the coexisting anions diminished the phosphate adsorption because they competed with the pollutants at adsorption sites. Furthermore, phosphate treatment under the continuous fixed-bed conditions showed that 1 g of the polyvinyl alcohol (PVA)-mixed C4mem@MIL-101 pellets purified 25 l of water containing phosphate with a 1 mg/l concentration. The results suggest that the novel [C4mem]+[Br]-@MIL-101(Cr) structure had a high potential for treating phosphate in aqueous solutions.

Functionalization of Defective Zr Metal-Organic Frameworks for Water Decontamination: Mechanistic Insight into the Competitive Roles of -NH2 and -SH Sites in Removal of As(III) Species

Direct removal of trivalent arsenic, As(III), arsenite, or H3AsO3, is a great challenge in accessing clean sources of water. Different methodologies and materials were applied in this regard, but among them, direct removal of As(III) species using a metal-organic framework (MOF)-based adsorbent shows a great deal of potential. Although some studies were conducted on As(III) removal using MOFs, studies of functional groups are still quite rare. For this purpose, three novel functionalized defective Zr-MOFs, using UiO-66 [Zr6(OH)4O4(BDC)6, where BDC2- = benzene-1,4-dicarboxylate], were fabricated to investigate the competitive or cooperative roles of the free -NH2 and/or -SH site in the removal of As(III). UiO-66 was functionalized with monocarboxylate linkers, including glycine (Gly, NH2-CH2-COOH), cysteine [Cys, SH(CH2)-NH2(CH)-COOH], and mercaptopropionic acid [Mer, SH-(CH2)2-COOH]. Gly@UiO-66, Cys@UiO-66, and Mer@UiO-66 were applied for the direct removal of As(III) species. Although Cys@UiO-66 is functionalized with both amine and thiol functional groups, Gly@UiO-66 has a higher adsorption capacity (301.4 mg g-1) with respect to As(III), which is among the best reported values. This is due to the fact that (1) the affinity of amine sites in Gly@UiO-66 for As(III) is higher than that of thiol sites in Mer@UiO-66 and (2) Cys@UiO-66 has a very small surface area compared to that of Gly@UiO-66. Mechanistic studies using X-ray photoelectron spectroscopy and vibrational spectroscopy reveal that not only the functionalization and chemical nature of the function but also other parameters such as the protonation-deprotonation mechanisms and chemical state of the function are other critical factors for designing a functional MOF-based adsorbent with high affinity for and maximum capacity with respect to the target analyte.

Harnessing the Chemical Functionality of Metal-Organic Frameworks Toward Removal of Aqueous Pollutants

Wastewater treatment has been bestowed with a plethora of materials; among them, metal-organic frameworks (MOFs) are one such kind with exceptional properties. Besides their application in gas adsorption and storage, they are applied in many fields. In orientation toward wastewater treatment, MOFs have been and are being successfully employed to capture a variety of aqueous pollutants, including both organic and inorganic ones. This review sheds light on the postsynthetic modifications (PSMs) performed over MOFs to adsorb and degrade recalcitrant. Modifications performed on the metal nodes and the linkers have been explained with reference to some widely used chemical modifications like alkylation, amination, thiol addition, tandem modifications, and coordinate modifications. The boost in pollutant removal efficacy, reaction rate, adsorption capacity, and selectivity for the modified MOFs is highlighted. The rationale and the robustness of micromotor MOFs, i.e., MOFs with motor activity, and their potential application in the capture of toxic pollutants are also presented for readers. This review also discusses the challenges and future recommendations to be considered in performing PSM over a MOF concerning wastewater treatment.

Phosphate adsorption by metal organic frameworks: Insights from a systematic review, meta-analysis, and predictive modelling with artificial neural networks

This comprehensive study analysed 55 articles published between 2011 and 2022 on the use of metal organic frameworks (MOFs) for phosphate adsorption. The study found that the performance of MOFs in phosphate adsorption is influenced by various factors such as the type of MOF, synthesis method, modification/alteration, and operational conditions (initial concentration, adsorbent dose, pH, contact time, and temperature). Most of the MOFs have a wide range of theoretical maximum adsorption capacity for phosphate, but their long-term use in phosphorus recovery may be limited due to the adsorption mechanisms being dominated by inner sphere complexation. The study employed machine learning to construct artificial neural network (ANN) models for predicting phosphate adsorption capacity based on input features from operation and synthesis procedures. The initial phosphate concentration was the most important input from the operational features, while the modulator agent was consistently relevant during MOF synthesis. The models showed strong fitting for most MOF types recorded for the study, such as UIO-66, MIL-100, ZIF-8, Al-MOFs, La-MOFs, and Ce-MOFs. Overall, this study provides valuable insights for the design of MOF adsorbents for phosphate adsorption and offers guidance for future research in this area.

Novel Zn metal-organic framework with the thiazole sites for fast and efficient removal of heavy metal ions from water

Pollution of water by heavy metal ions such as Pb2+ and Hg2+ is considered as an important issue, because of the potential toxic effects these ions impose on environmental ecosystems and human health. A new Zn-based metal-organic framework, [Zn2(DPTTZ) (OBA)2] (IUST-2), was synthesized through a solvothermal method by the reaction of 2, 5-di (4- pyridyl) thiazolo [5, 4-d] thiazole ligand (DPTTZ), the "V-shape" 4,4'-oxybis (benzoic acid) ligand (OBA) and zinc nitrate (Zn(NO3)2·6H2O). This novel MOF has been characterized by several analysis techniques such as fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA), powder x-ray diffraction (PXRD), thermogravimetry analysis (TGA), differential thermal analysis (DTA), field emission scanning electron microscopy (FE-SEM), Brunauer-Emmett-Teller (BET) surface area analysis and single-crystal X-ray diffraction (SXRD). This 3D MOF was tested for removing Pb2+ and Hg2+ ions from water. The factors that were investigated on the elimination of Pb2+ and Hg2+ ions were of pH, adsorption time, and the effect of initial ions concentration. According to the results, this particular Zn-MOF had significant performance in eliminating Pb2+ and Hg2+ ions from water with a removal efficiency of more than 97% and 87% within 3 min, respectively.

Facilitated Adsorption of Mercury(II) and Chromium(VI) Ions over Functionalized Carbon Nanotubes

By considering the importance of water and its purity, herein, a powerful adsorbent has been developed for the adsorption of two toxic contaminants that commonly exist in water, viz., divalent mercury and hexavalent chromium. The efficient adsorbent, CNTs-PLA-Pd, was prepared by covalent grafting polylactic acid to carbon nanotubes and subsequent deposition of palladium nanoparticles. The CNTs-PLA-Pd could adsorb Hg(II), and Cr(VI) entirely exists in water. The adsorption rate for Hg(II) and Cr(VI) was rapid at initial stage, followed by gradual decrease, and attained the equilibrium. The Hg(II) and Cr(VI) adsorption was perceived within 50 min and 80 min, respectively with CNTs-PLA-Pd,. Further, experimental data for Hg(II) and Cr(VI) adsorption was analyzed, and kinetic parameters were estimated using pseudo-first and second-order models. The adsorption process of Hg(II) and Cr(VI) followed the pseudo-second-order kinetics, and the rate-limiting step in the adsorption was chemisorption. The Weber-Morris intraparticle pore diffusion model revealed that the Hg(II) and Cr(VI) adsorption over CNTs-PLA-Pd occurs through multiple phases. The experimental equilibrium parameters for the Hg(II) and Cr(VI) adsorption were estimated by Langmuir, Freundlich, and Temkin isotherms models. All three models were well suited and demonstrated that Hg(II) and Cr(VI) adsorption over CNTs-PLA-Pd transpires through monolayer molecular covering and chemisorption.

Green Synthesis of Silver Nanoparticles Using Acacia ehrenbergiana Plant Cortex Extract for Efficient Removal of Rhodamine B Cationic Dye from Wastewater and the Evaluation of Antimicrobial Activity

Silver nanoparticles (Ag-NPs) exhibit vast potential in numerous applications, such as wastewater treatment and catalysis. In this study, we report the green synthesis of Ag-NPs using Acacia ehrenbergiana plant cortex extract to reduce cationic Rhodamine B (RhB) dye and for antibacterial and antifungal applications. The green synthesis of Ag-NPs involves three main phases: activation, growth, and termination. The shape and morphologies of the prepared Ag-NPs were studied through different analytical techniques. The results confirmed the successful preparation of Ag-NPs with a particle size distribution ranging from 1 to 40 nm. The Ag-NPs were used as a heterogeneous catalyst to reduce RhB dye from aqueous solutions in the presence of sodium borohydride (NaBH₄). The results showed that 96% of catalytic reduction can be accomplished within 32 min using 20 μL of 0.05% Ag-NPs aqueous suspension in 100 μL of 1 mM RhB solution, 2 mL of deionized water, and 1 mL of 10 mM NaBH₄ solution. The results followed a zero-order chemical kinetic (R² = 0.98) with reaction rate constant k as 0.059 mol L^-1 s^-1. Furthermore, the Ag-NPs were used as antibacterial and antifungal agents against 16 Gram-positive and Gram-negative bacteria as well as 1 fungus. The green synthesis of Ag-NPs is environmentally friendly and inexpensive, as well as yields highly stabilized nanoparticles by phytochemicals. The substantial results of catalytic reductions and antimicrobial activity reflect the novelty of the prepared Ag-NPs. These nanoparticles entrench the dye and effectively remove the microorganisms from polluted water.

Preparation of metal organic frameworks modified chitosan composite with high capacity for Hg(II) adsorption

In this study, a novel modified chitosan composite adsorbent (UNCS) was prepared by crosslinking between chitosan and metal organic frameworks (MOFs) material UiO-66-NH₂ using epichlorohydrin as crosslinker. The influence of the prepared conditions was investigated. The structure and morphology of the composite were characterized by FT-IR, XRD, SEM, TGA, BET and zeta potential analysis. Effects of different variables for adsorption of Hg(II) on this adsorbent were explored. The kinetic studies indicated that the adsorption process followed the pseudo-second-order kinetic model and the adsorption equilibrium could be reached within 2 h. The adsorption was mainly controlled by chemical process. Adsorption isothermal studies illustrated that the adsorption fitted Langmuir isotherm model, implying the homogeneous adsorption on the surface of the adsorbent. The adsorbent exhibited high uptake and the maximum capacity from Langmuir model could reach 896.8 mg g^-1 at pH 6. Thermodynamic studies showed the spontaneous nature and exothermic nature of the adsorption process. Additionally, the removal of Hg(II) on UNCS could achieve over 90 %. The adsorption-desorption cycled experiments indicated the appropriate reusability of the adsorbent. Hence, this adsorbent would be promising for the removal of Hg(II) from wastewater.

Catalytic metal-organic framework-melamine foam composite as an efficient material for the elimination of organic pollutants

Water-insoluble organic pollutants in environment, such as sea oil spill, industrial reagents, and the abused organic pesticides, bring great risks to global water systems, which thus requires effective approaches for organic pollutant elimination. In this study, we report a catalytic metal-organic framework (MOF)-melamine foam (MF) composite material (DDT-UiO-66-NH₂@MF) showing excellent oil-water separation performance and enzyme-like degradation ability toward organophosphorus pesticides. The fabrication of DDT-UiO-66-NH₂@MF is based on the immobilization of a MOF-derived nanozyme (UiO-66-NH₂) on MF sponge, and followed by the hydrophobic modification of UiO-66-NH₂ by 1-dodecanethiol (DDT). The obtained DDT-UiO-66-NH₂@MF thus displayed superhydrophobic/superhydrophilic property with a high water contact angle (WCA = 144.6°) and specific adsorption capacity toward various oils/organic solvents (62.2-119.8 g/g), which leads to a continuous oil-water separation on a simple device. In the meanwhile, owing to the enzyme-like property of UiO-66-NH₂, DDT-UiO-66-NH₂@MF also displayed good ability to hydrolyze paraoxon under mild conditions, which facilitates the elimination of toxic pesticide residuals in water systems. This work provides a simple, efficient, and green approach for the separation and treatment of water-insoluble organic pollutants, as well as expands the use of MOFs-MF sponge composite materials in environmental sustainability.

Metal-organic frameworks for food contaminant adsorption and detection

Metal-organic framework materials (MOFs) have been widely used in food contamination adsorption and detection due to their large specific surface area, specific pore structure and flexible post-modification. MOFs with specific pore size can be targeted for selective adsorption of some contaminants and can be used as pretreatment and pre-concentration steps to purify samples and enrich target analytes for food contamination detection to improve the detection efficiency. In addition, MOFs, as a new functional material, play an important role in developing new rapid detection methods that are simple, portable, inexpensive and with high sensitivity and accuracy. The aim of this paper is to summarize the latest and insightful research results on MOFs for the adsorption and detection of food contaminants. By summarizing Zn-based, Cu-based and Zr-based MOFs with low cost, easily available raw materials and convenient synthesis conditions, we describe their principles and discuss their applications in chemical and biological contaminant adsorption and sensing detection in terms of stability, adsorption capacity and sensitivity. Finally, we present the limitations and challenges of MOFs in food detection, hoping to provide some ideas for future development.

Triazine-Based Functionalized Activated Carbon Prepared from Water Hyacinth for the Removal of Hg2+, Pb2+, and Cd2+ Ions from Water

A novel chelating adsorbent, based on the functionalization of activated carbon (AC) derived from water hyacinth (WH) with melamine thiourea (MT) to form melamine thiourea-modified activated carbon (MT-MAC), is used for the effective removal of Hg²⁺, Pb²⁺, and Cd²⁺ from aqueous solution. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) theory confirm the successful functionalization of AC with the melamine thiourea chelating ligand through the amidation reaction between the carboxyl groups of oxidized activated carbon (OAC) and the amino groups of melamine thiourea (MT) in the presence of dicyclohexylcarbodiimide (DCC) as a coupling agent. The prepared MT-MAC exhibited extensive potential for the adsorption of the toxic metal ions Hg²⁺, Pb²⁺, and Cd²⁺ from wastewater. The MT-MAC showed high capacities for the adsorption of Hg²⁺ (292.6 mg·g^-1), Pb²⁺ (237.4 mg·g^-1), and Cd²⁺ (97.9 mg·g^-1) from aqueous solution. Additionally, 100% removal efficiency of Hg²⁺ at pH 5.5 was observed at very low initial concentrations (25-1000 ppb).The experimental sorption data could be fitted well with the Langmuir isotherm model, suggesting a monolayer adsorption behavior. The kinetic data of the chemisorption mechanism realized by the melamine thiourea groups grafted onto the activated carbon surface have a perfect match with the pseudo-second-order (PSO) kinetic model. In a mixed solution of metal ions containing 50 ppm of each ion, MT-MAC showed a removal of 97.0% Hg²⁺, 68% Pb²⁺, 45.0% Cd²⁺, 17.0% Cu²⁺, 7.0% Ni²⁺, and 5.0% Zn²⁺. Consequently, MT-MAC has exceptional selectivity for Hg²⁺ ions from the mixed metal ion solutions. The MT-MAC adsorbent showed high stability even after three adsorption-desorption cycles. According to the results obtained, the use of the MT-MAC adsorbent for the adsorption of Pb²⁺, Hg²⁺, and Cd²⁺ metal ions from polluted water is promising.