Schiff base-functionalized metal-organic frameworks as an efficient adsorbent for the decontamination of heavy metal ions in water

Adsorptive removal of heavy metal ions from water is an energy- and cost-effective water decontamination technology. Schiff base functionalities can be incorporated into the pore cages of metal-organic frameworks (MOFs) via direct synthesis, post-synthetic modification, and composite formation. Such incorporation can efficiently enhance the interactions between the MOF adsorbent and target heavy metal ions to promote the selective adsorption of the latter. Accordingly, Schiff base-functionalized MOFs have great potential to selectively remove a particular metal ion from the aqueous solutions in the presence of coexisting (interfering) metal ions through the binding sites within their pore cages. Schiff base-functionalized MOFs can bind divalent metal ions (e.g., Pb(II), Co(II), Cu(II), Cd (II), and Hg (II)) more strongly than trivalent metal ions (e.g., Cr(III)). The adsorption capacity range of Schiff base-functionalized MOFs for divalent ions is thus much more broad (22.4-713 mg g-1) than that of trivalent metal ions (118-127 mg g-1). To evaluate the adsorption performance between different adsorbents, the two parameters (i.e., adsorption capacity and partition coefficient (PC)) are derived and used for comparison. Further, the possible interactions between the Schiff base sites and the target heavy metal ions are discussed to help understand the associated removal mechanisms. This review delivers actionable knowledge for developing Schiff-base functionalized MOFs toward the adsorptive removal of heavy metal ions in water in line with their performance evaluation and associated removal mechanisms. Finally, this review highlights the challenges and forthcoming research and development needs of Schiff base-functionalized MOFs for diverse fields of operations.

Green Ultrasound-Assisted Synthesis of Rare-Earth-Based MOFs

Rare-earth (RE)-based metal organic frameworks (MOFs) are quickly gaining popularity as flexible functional materials in a variety of technological fields. These MOFs are useful for more than just conventional uses like gas sensors and catalyst materials; in fact, they also show significant promise in emerging technologies including photovoltaics, optical, and biomedical applications. Using yttrium and europium as ionic host centres and dopants, respectively, and 1,3,5-benzenetricarboxylic acid (H3-BTC) as an organic linker, we describe a simple and green approach for the fabrication of RE-MOFs. Specifically, Y-BTCs and Eu-doped Y-BTCs MOFs have been synthesised in a single step using an eco-friendly method that makes use of ultrasound technology. To establish a correlation between the morphological and structural properties and reaction conditions, a range of distinct reaction periods has been employed for the synthetic processes. Detailed analyses of the synthesised samples through powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), and Fourier-transform infrared spectroscopy (FT-IR) have confirmed the phase formation. Furthermore, thermal analyses such as thermogravimetric analysis (TGA) have been employed to evaluate the thermal stability and structural modifications of the Y-BTC and Eu-doped Y-BTC samples. Finally, the luminescent properties of the synthesised samples doped with Eu3+ have been assessed, providing an evaluation of their characteristics. As a proof of concept, an Eu-doped Y-BTC sample has been applied for the sensing of nitrobenzene as a molecule test of nitro derivatives.

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.

MIL-161 Metal-Organic Framework for Efficient Au(III) Recovery from Secondary Resources: Performance, Mechanism, and DFT Calculations

The recovery of precious metals from secondary resources is significant economically and environmentally. However, their separation is still challenging because they often occur in complex metal ion mixtures. The poor selectivity of adsorbents for gold in complicated solutions prevents further application of adsorption technology. In this study, a Zr-based MOF adsorbent, MIL-161, was synthesized using s-tetrazine dicarboxylic acid (H₂STz) as an organic ligand. MIL-161 demonstrated a high adsorption capacity of up to 446.49 mg/g and outstanding selectivity for gold(III) in a simulated electronic waste solution as a result of the presence of sulfur- and nitrogen-containing groups. In addition, the MIL-161 adsorbents were characterized using Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TG), Brunner-Emment-Teller (BET), and X-ray photoelectron spectroscopy (XPS). Additionally, the adsorption kinetics, isotherms, and thermodynamics of the MOF adsorbents were also thoroughly examined. More importantly, the experimental results and DFT calculations indicate that chelation and electrostatic interactions are the main adsorption mechanisms.

Detection of anthrax biomarker and metallic ions in aqueous media using spherical-shaped lanthanide infinite coordination polymers

We report a lanthanide-based infinite coordination polymer (ICP) system synthesized using pyrazole-3,5-dicarboxylic acid as linker, malonic acid as coordination modulator and water as solvent. The precursors self-assembly into microspherical particles, which are water-stable and exhibit excellent dispersibility. Bimetallic samples based on Tb³⁺ doped with Eu³⁺ were investigated as ratiometric dipicolinic acid (DPA) sensors, which is a biomarker for Bacillus anthracis spores. Along with the calibration curves, a detection in a real sample extracted from Bacillus subtilis (model organism) was performed. The samples proved to be highly sensitive and selective for ratiometric DPA detection. In a secondary study, the monometallic sample containing only Tb³⁺ was also investigated as a sensor for ionic species in aqueous media. The Cr³⁺, Fe³⁺, Cu²⁺, and Cr₂O₇^2- ionic species could be detected in water by luminescence quenching mechanism. Therefore, we found that the reported ICP system can be judiciously constructed in order to act as a multimodal probe for several chemical species.

Synthesis and Characterization of Mesoporous Silica Modified with Purpald and Its Application in the Preconcentration of Cu2+ and Cd2+ from Aqueous Samples through Solid-Phase Extraction

The synthesis of an organofunctionalized mesoporous silica was accomplished by a two-step process involving (1) the co-condensation of a silylant agent at the surface of silica, followed by (2) the immobilization of Purpald (ligand) at the organic termination of the silytant agent. The characterization of the organofunctionalized material indicated the presence of NH2 groups, and the immobilization of the ligand was confirmed by 29Si- and 13C-nuclear magnetic resonance. The material’s surface area was determined as 370 m2 g−1. Batch adsorption experiments enabled the determination of optimum pH conditions for the adsorption of Cu(II) and Cd(II). Under optimal pH, the pseudo-second-order kinetic model and Langmuir model provided the best correlations to describe the materials adsorption behavior, suggesting a chemisorption mechanism. When tested in continuous-flow preconcentration experiments, the flow rate and eluent concentration demonstrated to affect the removal of Cu(II) and Cd(II), while the buffer concentration had an effect only over the adsorption of Cu(II). Under optimized preconcentration conditions, it was possible both to determine the concentrations of Cu(II) and Cd(II) in samples such as mineral water, ground water, tap water and river water. Ions commonly found in drinking and natural waters (Na+, K+, Ca2+, Mg2+, Fe3+, Ba2+, Cl−, SO42−, HCO3−, and H2PO4−) did not affect the preconcentration of any of the studied analytes. Reutilization experiments indicated that the adsorbent material can withstand at least 40 adsorption/desorption preconcentration cycles with no efficiency loss.

Overview on recent advances of magnetic metal-organic framework (MMOF) composites in removal of heavy metals from aqueous system

Developing a novel, simple, and cost-effective analytical technique with high enrichment capacity and selectivity is crucial for environmental monitoring and remediation. Metal-organic frameworks (MOFs) are porous coordination polymers that are self-assembly synthesized from organic linkers and inorganic metal ions/metal clusters. Magnetic metal-organic framework (MMOF) composites are promising candidate among the new-generation sorbent materials available for magnetic solid-phase extraction (MSPE) of environmental contaminants due to their superparamagnetism properties, high crystallinity, permanent porosity, ultrahigh specific surface area, adaptable pore shape/sizes, tunable functionality, designable framework topology, rapid and ultrahigh adsorption capacity, and reusability. In this review, we focus on recent scientific progress in the removal of heavy metal ions present in contaminated aquatic system by using MMOF composites. Different types of MMOFs, their synthetic approaches, and various properties that are harnessed for removal of heavy metal ions from contaminated water are discussed briefly. Adsorption mechanisms involved, adsorption capacity, and regeneration of the MMOF sorbents as well as recovery of heavy metal ions adsorbed that are reported in the last ten years have been discussed in this review. Moreover, particular prospects, challenges, and opportunities in future development of MMOFs towards their greener synthetic approaches for their practical industrial applications have critically been considered in this review.

Multifunctional nanomaterials and nanocomposites for sensing and monitoring of environmentally hazardous heavy metal contaminants

The applications of conventional sensors are limited by the long response time, high cost, large detection limit, low sensitivity, complicated usage and low selectivity. These sensors are nowadays replaced by Nanocomposite-based modalities and nanomaterials which are known for their high selectivity and physical and chemical properties. These nanosensors effectively detect heavy metal contaminants in the environment as the discharge of heavy metals into natural water as a result of human activity has become a global epidemic. Exposure to these toxic metals might induce many health-related complications, including kidney failure, brain injury, immune disorders, muscle paleness, cardiac damage, nervous system impairment and limb paralysis. Therefore, designing and developing novel sensing systems for the detection and recognition of these harmful metals in various environmental matrices, particularly water, is of extremely important. Emerging nanotechnological approaches in the past two decades have played a key role in overcoming environmentally-related problems. Nanomaterial-based fabrication of chemical nanosensors has widely been applied as a powerful analytical tool for sensing heavy metals. Portability, high sensitivity, on-site detection capability, better device performance and selectivity are all advantages of these nanosensors. The detection and selectivity have been improved using molecular recognition probes for selective binding on different nanostructures. This study aims to evaluate the sensing properties of various nanomaterials such as metal-organic frameworks, fluorescent materials, metal-based nanoparticles, carbon-based nanomaterials and quantum dots and graphene-based nanomaterials and quantum dots for heavy metal ions recognition. All these nano-architectures are frequently served as effective fluorescence probes to directly (or by modification with some large or small biomolecules) sense heavy metal ions for improved selectivity. However, efforts are still needed for the simultaneous designing of multiple metal ion-based detection systems, exclusively in colorimetric or optical fluorescence nanosensors for heavy metal cations.

Biomass-derived carbon dots as a sensitive and selective dual detection platform for fluoroquinolones and tetracyclines

A novel carbon dot (CD) was synthesized through the facile and simple hydrothermal method from Curcuma amada, as the precursor for the first time. These CDs with an average diameter of 4.6 nm display blue fluorescence, with excitation/emission maxima at 360/445 nm and a quantum yield of 14.1%. It exhibited high stability under different conditions and was characterized using various techniques. These CDs can be employed as a dual-sensing platform to detect tetracyclines and fluoroquinolones, two antibiotic classes. Even though antibiotics are regarded as an inevitable commodity, overuse and improper management of discarded antibiotics pose a severe threat to the environment. Herein, we developed a dual-sensing, biocompatible sensor with high selectivity and sensitivity to detect antibiotics. CD was employed as a fluorescence probe and detected tetracycline and fluoroquinolone antibiotic through inner filter effect-based fluorescence quenching and hydrogen bonding-based enhancement process, respectively. The linear range was 0-16 μM and the detection limit was 33 nM for tetracycline and 2 nM for fluoroquinolone antibiotic. As an electrochemical probe, CD selectively detected tetracycline with a lower detection limit of 0.5 nM over a linear range of 0-16 μM. Using both methods, a real sample analysis of the developed sensor exhibited accurate reliability and precision.

A Flower-like In2O3 Catalyst Derived via Metal-Organic Frameworks for Photocatalytic Applications

The most pressing concerns in environmental remediation are the design and development of catalysts with benign, low-cost, and efficient photocatalytic activity. The present study effectively generated a flower-like indium oxide (In₂O₃-MF) catalyst employing a convenient MOF-based solvothermal self-assembly technique. The In₂O₃-MF photocatalyst exhibits a flower-like structure, according to morphology and structural analysis. The enhanced photocatalytic activity of the In₂O₃-MF catalyst for 4-nitrophenol (4-NP) and methylene blue (MB) is likely due to its unique 3D structure, which includes a large surface area (486.95 m² g^-1), a wide spectrum response, and the prevention of electron-hole recombination compared to In₂O₃-MR (indium oxide-micro rod) and In₂O₃-MD (indium oxide-micro disc). In the presence of NaBH₄ and visible light, the catalytic performances of the In₂O₃-MF, In₂O₃-MR, and In₂O₃-MD catalysts for the reduction of 4-NP and MB degradation were investigated. Using In₂O₃-MF as a catalyst, we were able to achieve a 99.32 percent reduction of 4-NP in 20 min and 99.2 percent degradation of MB in 3 min. Interestingly, the conversion rates of catalytic 4-NP and MB were still larger than 95 and 96 percent after five consecutive cycles of catalytic tests, suggesting that the In₂O₃-MF catalyst has outstanding catalytic performance and a high reutilization rate.

Highly efficient and selective capture Pb(II) through a novel metal-organic framework containing bifunctional groups

The design and development of materials with a selective adsorption capacity for Pb(II) are very important for environmental governance and ecological safety. In this work, a novel 3D metal-organic framework ([Cd₂H₄L₄Cl₂SO₄]·4H₂O, Cd-MOF) is constructed using a multiple pyrazole heterocycles tetraphenylethylene-based ligand (H₄L₄) and CdSO₄ which containing Pb(II) adsorption sites (SO₄^2-). Studies have shown that the Cd-MOF has outstanding stability, and its maximum adsorption value of Pb(II) can be as high as 845.55 mg/g, which is higher than that of most MOFs or MOFs modified materials. It is worth emphasizing that the Cd-MOF have excellent recyclability due to the unique adsorption mechanism of the Cd-MOF. Thermodynamic studies have shown that Pb(II) adsorption of the Cd-MOF is a spontaneous endothermic process. Specific selective adsorption, exceptional stability and remarkable recyclability make the Cd-MOF a potential material for industrial capture and recovery of Pb(II) from water.

Recent advances in the application of water-stable metal-organic frameworks: Adsorption and photocatalytic reduction of heavy metal in water

Heavy metals pollution in water is a global environmental issue, which has threatened the human health and environment. Thus, it is important to remove them under practical water environment. In recent years, metal-organic frameworks (MOFs) with water-stable properties have attracted wide interest with regard to the capture of hazardous heavy metal ions in water. In this review, the synthesis strategy and postsynthesis modification preparation methods are first summarized for water-stable MOFs (WMOFs), and then the recent advances on the adsorption and photocatalytic reduction of heavy metal ions in water by WMOFs are reviewed. In contrast to the conventional adsorption materials, WMOFs not only have excellent adsorption properties, but also lead to photocatalytic reduction of heavy metal ions. WMOFs have coupling and synergistic effects on the adsorption and photocatalysis of heavy metal ions in water, which make it more effective in treating single pollutants or different pollutants. In addition, by introducing appropriate functional groups into MOFs or synthesizing MOF-based composites, the stability and ability to remove heavy metal ions of MOFs can be effectively enhanced. Although WMOFs and WMOF-based composites have made great progress in removing heavy metal ions from water, they still face many problems and challenges, and their application potential needs to be further improved in future research. Finally, this review aims at promoting the development and practical application of heavy metal ions removal in water by WMOFs.

Decorating S-doped Cu-La bimetallic oxides with UIO-66 to increase the As(III) adsorption capacity via synchronous oxidation and adsorption

Arsenite (As(III)) is more toxic and difficult to remove than arsenate (As(V)). In this study, an S-doped Cu-La bimetallic oxide (S-CuLaO) decorated with metal-organic framework (MOF) composite (S-CuLaO@UIO-66) was synthesized and applied for the adsorption of As(III). The maximum adsorption capacity of As(III) by S-CuLaO@UIO-66 was as high as 171 mg/g, which was much higher compared with other MOF compounds reported to date. The UIO-66 support improved the dispersion and reduced the size of the S-CuLaO particles, which increased the number of exposed adsorption reactive sites. Study of the mechanism revealed that the synchronous oxidation and adsorption significantly increased the removal of As(III). O₂^∙- was produced by the receiving electron from the dissolved oxygen from Cu(I) in S-CuLaO, which converted As(III) to As(V). Furthermore, the stability and reusability S-CuLaO@UIO-66 (without regeneration) was investigated at a low As(III) concentration (approximately 1000 µg/L) in deionized water and well water. The residual arsenic concentration ranged from 0.8 to 2.8 μg/L in deionized water and 3-58.2 μg/L in well water within 240 min during three cycles. Generally, this study suggests that combining an optimal oxide with a stable MOF is a promising approach for the fabrication of composite adsorbents.

Ratiometric fluorescence detection of sulfide ions based on lanthanide coordination polymer using guanosine diphosphate as ligand

The efficiency of energy transfer from guanine nucleotide to terbium ion (Tb³⁺) is affected by the phosphate group significantly. Compared with the biomolecules 5'-GMP (guanosine monophosphate), guanosine diphosphate (GDP) exhibits better sensitize ability to Tb³⁺ ions luminescence. Assisted with the carboxycoumarin ligand, we synthesized a more stable optical Coumarin@GDP-Tb polymer with the characteristic emission peaks located on 440 nm and 545 nm in this work. The Coumarin@GDP-Tb polymer is not only rich in metal binding sites, but also maintains a moderate ionic binding force, which helps metal ions to bind or leave it easily. Experiment result shows that Coumarin@GDP-Tb polymer has the appropriate binding force for Fe²⁺ ions, which can be destroyed by sulfur ions (S^2-) as the formation of FeS precipitation. Based on this, Coumarin@GDP-Tb was designed as the ratio fluorescence probe for sulfur ions detection, where the fluorescence at 545 nm can be selectively quenched by Fe²⁺ ions, while that at 440 nm was unaffected, in the presence of S^2- ions, the quenched fluorescence can be recovered remarkably. With the increasing S^2- ions from 0.1-45 μM, the ratio of fluorescence intensity at 545 nm to 440 nm (F₅₄₅/F₄₄₀) is linear to S^2- concentration, and the detection limit of S^2- was calculated to be 0.073 μM. Contrast to those fluorescence probes with single wavelength emission, Coumarin@GDP-Tb displays a comparable sensitivity, the introduced self-adjust wavelength improved the detection accuracy efficiently. The above 98.1 % recovery rates of S^2- ions in the actual water sample demonstrated the practicability of Coumarin@GDP-Tb fluorescence probe.

Nanomaterial-based fluorescent sensors for the detection of lead ions

Lead (Pb) poisoning has been a scourge to the human to pose sighnificant health risks (e.g., organ disorders, carcinogenicity, and genotoxicity) as observed from many different parts of the world, especially in developing countries. The demand for accurate sensors for its detection, especially in environmental media (soil, water, food, etc.) has hence been growing steadily over the years. The potential utility of fluorescent nanosensors as an important analytical tool is recognized due to their astonishing characteristics (e.g., high sensitivity/selectivity, enhanced detection performance, low cost, portability, and rapid on-site detection ability). This review is organized to offer insight into the recent developments in fluorescent nanosensing technology for the detection of lead ions (Pb²⁺). To this end, different types of nanomaterials explored for such applications have been classified and evaluated with respect to performance, especially in terms of sensitivity. This review will help researchers gain a better knowledge on the status and importance of optical nanosensors so as to remediate the contamination of lead and associated problems. The technical challenges and prospects in the development of nanosensing systems for Pb²⁺ are also discussed.

Characterization of Fe-based sediments received from chemical pre-treatment of hydrometallurgical waste leachate from the recycling of alkaline batteries

The waste leachate from the hydrometallurgical recycling of spent batteries contains a significant amount of undesirable iron that needs to be precipitated before the recovery of target metals. The produced Fe-sediments are usually disposed of or stored at the treatment site as waste and are often poorly managed. This work estimates the environmental stability and application potential of Fe-sediments produced from highly acidic hydrometallurgical leachate during the recycling of spent alkaline batteries. After pH neutralization of the leachate by Na₂CO₃, a primary Fe-sediment (PFS), mainly composed of highly unstable metal (i.e., Fe, Zn, and Mn) sulfates, was obtained. The subsequent rinsing of this unstable PFS sediment led to the production of a secondary Fe-sediment (SFS), which was composed of an amorphous-phased ferric iron sulfate hydrate - Fe₁₆O₁₆(SO₄)₃(OH)₁₀·10H₂O. The results of single extraction using chemical reagents and biological dissolution by iron-transforming bacteria confirmed that despite most of the ions in PFS were dissolvable, the processed SFS was environmentally safe. The sorption efficiency of SFS towards Pb(II) and As(V) (up to ~ 99% and 94%, respectively, with an initial concentration of 100 mg/L) was found to be promising, suggesting the high potential for economical reuse of SFS.

Ln-MOFs with window-shaped channels based on triazine tricarboxylic acid as a linker for the highly efficient capture of cationic dyes and iodine

Seven isostructural complexes were synthesized under solvothermal condition by the 4,4′,4′′ ((1,3,5-triazine-2,4,6-triyl)tri(azanediyl))tribenzoic acid and rare earth metal ions. It is found that 1 exhibits the adsorption capacity of 758.72 mg g⁻¹ to iodine.

A critical review on recent developments in MOF adsorbents for the elimination of toxic heavy metals from aqueous solutions

Effective and substantial remediation of contaminants especially heavy metals from water is still a big challenge in terms of both environmental and biological perspectives because of their adverse effects on the human health. Many techniques including adsorption, ion exchange, co-precipitation, chemical reduction, ultrafiltration, etc. are reported for eliminating heavy metal ions from the water. However, adsorption has preferred because of its simple and easy handlings. Several types of adsorbents are observed and documented well for the purpose. Recently, highly porous metal-organic frameworks (MOFs) were developed by incorporating metals and organic ligands together and claimed as potent adsorbents for the remediation of highly toxic heavy metals from the aqueous solutions due to their unique features like greater surface area, high chemical stability, green and reuse material, etc. In this review, the authors discussed systematically some recent developments about secure MOFs to eliminate the toxic metals such as arsenic (both arsenite and arsenate), chromium(VI), cadmium (Cd), mercury (Hg) and lead (Pb). MOFs are observed as the most efficient adsorbents with greater selectivity as well as high adsorption capacity for metallic contamination. Graphical abstract.

Oriented oxidation of all alkanes in soils

In order to investigate the mechanism of the oriented oxidation of all alkanes by regulating organic functional groups, Fenton oxidation was performed in two soils (S1 and S2: total petroleum hydrocarbons (TPH) are 26,281 mg/kg and 12,668 mg/kg). The higher the proportion of hydroxyl radicals (OH) transferred (41 %-58 %), the more the number of oriented oxidation of alkanes, which realized the oriented oxidation of all alkanes. Meanwhile, high oriented oxidation of long alkanes and short alkanes (58 %: 3405 mg/kg and 1729 mg/kg) was observed. Protein Ⅰ in soil organic matter (SOM) was reduced by regulating CH and carboxyl group OH, which indicated that protein Ⅰ was inactive. Protein Ⅰ oxidation after regulation was decreased significantly. Protein Ⅰ was the main active organic matter to capture OH. When the relative reactivity coefficient K_TPH/SOM (the ratio of TPH oxidation to SOM oxidation) and K_{TPH/protein I} (the ratio of TPH oxidation to protein Ⅰ oxidation) were higher than 1, low oxidation of SOM and protein Ⅰ was obtained. It indicated that for the oriented oxidation of all alkanes, the high coefficient of relative reactivity for petroleum was the key for the transfer of OH from oxidizing SOM to oxidizing alkanes.

Aqueous synthesis of highly adsorptive copper-gallic acid metal-organic framework

A greener route to synthesize mesoporous copper-gallic acid metal-organic framework (CuGA MOF) than the conventional method using harmful DMF solvent was proposed in this study. Various synthesis attempts were conducted by modifying the synthesis conditions to produce CuGA MOF with comparable physical properties to a reference material (DMF-synthesized CuGA NMOF). The independent variables investigated include the molar ratio of NaOH to GA (1.1 to 4.4) and the synthesis temperature (30, 60, 90 °C). It was found that proper NaOH addition was crucial for suppressing the generation of copper oxide while maximizing the formation of CuGA MOF. On the other hand, the reaction temperature mainly affected the stability and adsorption potential of CuGA MOF. Reacting Cu, GA, and NaOH at a molar ratio of 1:1:2.2 and a temperature of 90 °C, produced mesoporous MOF (CuGA 90-2.2) with a surface area of 198.22 m2/g, a pore diameter of 8.6 nm, and a thermal stability of 219 °C. This MOF exhibited an excellent adsorption capacity for the removal of methylene blue (124.64 mg/g) and congo red (344.54 mg/g). The potential usage of CuGA 90-2.2 as a reusable adsorbent was demonstrated by its high adsorption efficiency (> 90%) after 5 adsorption-desorption cycles.

Green choline amino acid ionic liquids aqueous two-phase extraction coupled with synchronous fluorescence spectroscopy for analysis naphthalene and pyrene in water samples

A novel aqueous two-phase extraction method has been established for the determination of polycyclic aromatic hydrocarbons in water sample. This method was based on the extraction of naphthalene and pyrene from water by means of choline amino acid ionic liquids aqueous two-phase system and their determination by synchronous fluorescence spectroscopy. In synchronous fluorescence spectroscopy, the fluorescence peaks of naphthalene and pyrene were completely separated to meet the requirement of simultaneous determination. For this method, good linear calibration curves of naphthalene and pyrene were obtained in the range of 0.50-10.0, 0.05-5.0 μg mL^-1, respectively, and limits of detection were 0.211, 0.012 μg mL^-1, respectively. The proposed method was successfully applied for the simultaneous determination of naphthalene and pyrene in water samples, which was considered as an excellent green analysis according Analytical Eco-Scale.

Metal-organic frameworks based adsorbents: A review from removal perspective of various environmental contaminants from wastewater

Rapidly increasing water contamination has turned into a major threat globally. The pollutants such as organic and inorganic compounds, heavy metals, and biological organisms are among the major contributor to water pollution. Therefore, the removal of these contaminants has attracted the researchers a lot. Various methodologies are being carried out for the purpose. Among them, the metal-organic frameworks (MOFs) with several active sites and tailorable porous architectures as adsorbents or photocatalytic removal agents is a fast-growing class of coordination chemistry to remove these agents from water. To date, numerous approaches dealing with water treatment including conservative and advanced technologies have been presented. This article thoroughly reviews the application of MOFs toward how to remove the toxic agents from water. The leading objective is to present up-to-date information and references regarding MOFs based materials toward wastewater treatment applications.

A Hybrid Metal-Organic Framework-Reduced Graphene Oxide Nanomaterial for Selective Removal of Chromate from Water in an Electrochemical Process

Hexavalent chromium Cr(VI) is a highly toxic groundwater contaminant. In this study, we demonstrate a selective electrochemical process tailored for removal of Cr(VI) using a hybrid MOF@rGO nanomaterial synthesized by in situ growth of a nanocrystalline, mixed ligand octahedral metal-organic framework with cobalt metal centers, [Co₂(btec)(bipy)(DMF)₂]_n (Co-MOF), on the surface of reduced graphene oxide (rGO). The rGO provides the electric conductivity necessary for an electrode, while the Co-MOF endows highly selective adsorption sites for CrO₄^2-. When used as an anode in the treatment cycles, the MOF@rGO electrode exhibits strong selectivity for adsorption of CrO₄^2- over competing anions including Cl^-, SO₄^2-, and As(III) and achieves charge efficiency (CE) >100% due to the strong physisorption of CrO₄^2- by Co-MOF; both electro- and physisorption capacities are regenerated with the reversal of the applied voltage, when highly toxic Cr(VI) is reduced to less toxic reduced Cr species and subsequently released into brine. This approach allows easy regeneration of the nonconducting Co-MOF without any chemical addition while simultaneously transforming Cr(VI), inspiring a novel electrochemical method for highly selective degradation of toxic contaminants using tailor-designed electrodes with high affinity adsorbents.

Distribution, characteristics of extracellular polymeric substances of Phanerochaete chrysosporium under lead ion stress and the influence on Pb removal

The distribution, characteristics of extracellular polymeric substances (EPS) of Phanerochaete chrysosporium under Pb²⁺ stress and the influence on Pb removal were investigated. Polysaccharides was found to be the main composition in both soluble EPS (SEPS) and bounded EPS (BEPS). More polysaccharides and protein in BEPS were detected with the increased Pb²⁺ concentration. The ratio of Pb amount distributed in BEPS to the total Pb removed by the fungal biomass gradually decreased from 91.66 to 61.27% in group with 50 mg/L of initial Pb²⁺, but kept at about 35% or 25% in groups with higher Pb²⁺. It implies that BEPS played a certain role in the lead removal process, and the role of BEPS was relatively more important in the removal of lower concentration of Pb²⁺ and in the initial period of Pb removal. With FTIR analysis and Pb²⁺ adsorption experiment, more effective functional groups and better Pb²⁺ adsorption capacity was demonstrated in BEPS than in SEPS. SEM-EDS analysis demonstrated that part of Pb immobilized in BEPS was in the form of Pb precipitation. The increased molecular weight in SEPS and more polysaccharides in BEPS were probably beneficial for the adhesion of Pb precipitation.

Adsorption of Lead Ions by a Green AC/HKUST-1 Nanocomposite

A new nanocomposite consisting of activated carbon (AC) from the Cortaderia selloana flower and copper-based metal-organic framework (HKUST-1) was synthesized through a single-step solvothermal method and applied for the removal of lead ions from aqueous solution through adsorption. The nanocomposite, AC/HKUST-1, was characterized by Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), and Energy-Dispersive X-ray Spectroscopy (EDX) methods. The SEM images of both HKUST-1 and AC/HKUST-1 contain octahedral crystals. Different factors affecting adsorption processes, such as solution pH, contact time, adsorbent dose, and initial metal pollution concentration, were studied. The adsorption isotherm was evaluated with Freundlich and Langmuir models, and the latter was fitted with the experimental data on adsorption of lead ion. The adsorption capacity was 249.4 mg g^-1 for 15 min at pH 6.1, which is an excellent result rivalling previously reported lead adsorbents considering the conditions. These nanocomposites show considerable potential for use as a functional material in the ink formulation of lead sensors.

Capability of Bacillus Subtilis to remove Pb2+ via producing lipopeptides

Lead contamination is widely found in soil and waters, which makes great threat to animal and human health. Environmentally friendly, efficient, and economical methods for the removal of Pb²⁺ pose significant challenges for environmental protection. Bacillus subtilis lipopeptide was firstly used to remove Pb²⁺ from water. In mechanisms, the lipopeptides formed complexes and chelated with Pb²⁺ via OH, CO, OCO, and NH. In kinetics, the Pb²⁺ removal process closely followed a pseudo-first-order model, and the equilibrium Pb²⁺ adsorption capacity ranged from 112.6 to 113.7 mg/g within a temperature range of 293.13-313.13 K. The Pb²⁺ removal process could be well described by a Langmuir isotherm. The maximum Pb²⁺ removal capability of lipopeptides was 164.4 mg/g in manually metal contaminated water and 130.4 mg/g in actual wastewater. Furthermore, the lipopeptides can not only decrease the amount of lead in oats grown, but also promote oat growth under Pb²⁺ stress. The results showed that lipopeptides can be used as a highly efficient adsorbent to remove Pb²⁺ from water, which means the great potential of lipopeptides in practical environments.

High selectivity and effectiveness for removal of tetracycline and its related drug resistance in food wastewater through schwertmannite/graphene oxide catalyzed photo-Fenton-like oxidation

Selectively and effectively for removal of tetracycline (TC) and its related antibiotic resistance gene from food wastewater matrix with high-salt and high COD characteristics is highly desirable. In this work, novel schwertmannite/graphene oxide (SCH/GO) nanocomposites were synthesized through a facile oxidation-coprecipitation method. The SCH/GO nanocomposites were characterized by TEM, XRD, BET, PL, DRS, XPS and FTIR. In the presence of 1 mM H₂O₂, the SCH/GO catalyzed Fenton-like oxidation can thoroughly degrade TC under visible light irradiation, even under nature sunlight, whose second-order kinetic rate constant was about 15 times higher than that of pure SCH. SCH/GO was capable of highly selectively capturing and effectively degrading TC in the presence of similar concentration of Cl^-, NO₃^-, SO₄^2- and PO₄^3- with that of food wastewater, even at organic matters concentration of 12.5 times than that of TC. At the same time, the removal of total organic carbon (TOC) and chemical oxygen demand (COD) in aforementioned food wastewater in SCH/GO+H₂O₂+Vis system reached 27.3 % and 34.5 % after 60 min, respectively. The inhibition zone experiments authenticated that the removal of drug resistance of bacteria by TC degradation intermediates can be achieved very well without producing secondary contamination in this system.

A novel triphenylamine-based bis-Schiff bases fluorophores with AIE-Activity as the hydrazine fluorescence turn-off probes and cell imaging in live cells

Developing a specific and sensitive method for endogenous hydrazine detection in living systems is valuable to understand its various pathological events. In this work, two novel fluorescent chemosensors (C1, C3) based on triphenylamine Schiff-base derivative and reference dyes (C2, C4) were prepared in relatively high yield (more than 72% yield). The aggregation induced emission (AIE) properties of sensors were investigated through UV-Visible, dynamic light scattering, X-ray diffraction, fluorescence spectrophotometric analyses as well as scanning electron microscope images (SEM). The results indicated that probes C1 and C3 exhibited strong AIE property in DMF/H₂O (1:1, v/v) mixture system with brilliant yellow fluorescence emission (560 nm) observed under 365 nm UV lamp. The experiments of sensing indicated that probes C1 and C3 possessed the sequentially detecting abilities for hydrazine with high sensitivity, specificity as well as an extremely low detection limit (55.1 nM), which was due to blocking of AIE process of probes C1 and C3 by special chemical reaction (-CHN- moiety transformed into -CH₂-NH- group) after hydrazine addition, resulting in the increase in water solubility and a weak emission in aqueous media. Furthermore, ¹H NMR, SEM and fluorescence titration experiment was also conducted to confirm the sensing mechanism. For biological application, probes C1 and C3 presented a good bio-imaging performance and showed the similar fluorescence quenching after adding hydrazine. Therefore, the probes are suitable for the fluorescence imaging of exogenous hydrazine in HeLa cells.

High capacity Hg(II) and Pb(II) removal using MOF-based nanocomposite: Cooperative effects of pore functionalization and surface-charge modulation

Water pollution by heavy metal ions especially Hg(II) and Pb(II) is one of the most important concerns because of their harmful effects on human health and environment sustainability. Here, we developed Fe₃O₄@TMU-32 metal-organic framework (MOF)-based nanocomposite by applying pore functionalization and surface-charge modulation strategies. Based on synergic effects of these strategies, Fe₃O₄@TMU-32 nanocomposite shows very high capacity toward Hg(II) and Pb(II) metal ions. TMU-32 (with formula [Zn(OBA)(DPU)]·2DMF·H₂O where H₂OBA and DPU are (4,4'-oxybis(benzoic acid)) and 1,3-di(pyridin-4-yl)urea)) is decorated with urea functional groups containing carbonyl and amine groups that can interact with metal ions. As results, TMU-32 show very high capacity toward Hg(II) and Pb(II) ions. To improve the TMU-32 capacity toward Hg(II) and Pb(II) cations, we tried to modulate the surface-charge of TMU-32 as a host-framework. Surface-charge modulation strategy had been conducted through encapsulation of Fe₃O₄ nanoparticles by TMU-32 in an in-situ synthesis procedure and synthesis of Fe₃O₄@TMU-32 nanocomposite. Fe₃O₄@TMU-32 nanocomposite shows improved removal capacity (45 % and 54 % toward Pb(II) and Hg(II)) rather pristine TMU-32 framework because of urea decorated framework and charge modulated surface. Fe₃O₄@TMU-32 nanocomposite adsorb 1600 mg.g^-1 of Pb(II) and 905 mg.g^-1 of Hg(II) which extremely rare in the literature. Such improvement can be related to the electrostatic interaction between cationic nature of Pb(II) and Hg(II) and negative charge of the Fe₃O₄@TMU-32 adsorbent.

Dynamic proteome responses to sequential reduction of Cr(VI) and adsorption of Pb(II) by Pannonibacter phragmitetus BB

Here, the microbial responses to Cr(VI) and Pb(II) with bio-removal of the metals in water by Pannonibacter phragmitetus BB were explored. The comparative bacterial proteomics showed that the intracellular and extracellular Cr(VI) reduction proteins, Pb(II) adsorption by the lipoprotein and sugar-related bacterial proteins, as well as Pb(II) precipitation by phosphate and OH^- were vital to the bio-removal of Cr(VI) and Pb(II). Moreover, the influx and efflux channels of Cr(VI) and Cr(III), Pb(II) transporters, extracellular siderophores for Pb(II) complexation and antioxidant proteins enabled the strain BB to resist the toxicity of Cr(VI) and Pb(II). In addition, the dynamic expression levels of the proteins related to reduction and transportation of Cr(VI), and adsorption, transportation and complexation of Pb(II) were dependent on the corresponding metal, respectively. The anti-oxidative stress system, such as superoxide dismutase, and Na⁺/H⁺ antiporters played central roles in the protein-protein interaction network to resist and detoxify Cr(VI) and Pb(II). The results of our study provide a novel insight for the physiological responses of the strain BB to the combined stresses of Pb(II) and Cr(VI).

A bond energy transfer based difunctional fluorescent sensor for Cys and bisulfite

In living cells, cysteine (Cys) and bisulfite are involved in many important physiological processes. Their unbalance in vivo would lead to multiple diseases. So, it is vital to develop difuntional sensor for Cys and bisulfite. As we known, cysteine could metabolized into bisulfite by the metabolic processes of cysteine in the animal level. Therefore, we designed and synthesized a mitochondria-targeted long-wavelength ratio fluorescence sensor Z2 for Cys and bisulfite simultaneous detection. Z2 exhibitted excellent selectivity, good anti-interference, fast response and low detection limit. The sensor exhibited obviously two channels fluorescence response for Cys and bisulfite orderly. Z2 is widely used for imaging Cys and bisulfite in MCF-7 cells, zebrafish, and mice, and successfully imaging Cys metabolism in these livings. We hope this bifunctional ratio fluorescence sensor Z2 will be a useful tool to monitor Cys and SO₂ levels in living systems.

Highest and Fastest Removal Rate of PbII Ions through Rational Functionalized Decoration of a Metal-Organic Framework Cavity

To overcome the challenge of developing a multipurpose adsorbent for effective removal of toxic and carcinogenic Pb^II ions from aqueous solutions, a made-for-purpose functional group (N¹ ,N² -di(pyridine-4-yl)oxalamide) was rationally designed and incorporated into the cavities of a Zn metal-organic framework (MOF), namely, TMU-56. Large enough pore size along with high densities of strong metal chelating sites lead not only to the highest uptake capacity for Pb^II ions, but also the fastest removal rate that has ever been reported for functionalized MOFs, occurring in just 20 s. Moreover, high concentrations of lead ions favor the ion exchange reaction, resulting in a high degree of metal exchange. In addition, TMU-56 can be a practical adsorbent because of its notable performance in the simultaneous removal of several toxic and carcinogenic heavy metals from wastewater, which has rare precedence.

Enhanced chemical sensing for Cu2+ based on composites of ZIF-8 with small molecules

Two organic molecules, pyridoxal hydrazide (PAH) and salicylaldehyde based Rhodamine B hydrazone (RBS) were integrated into zeolitic imidazolate framework-8 (ZIF-8) to give composites, namely PAH/ZIF-8 and RBS/ZIF-8. The organic molecules and ZIF-8 are proposed to be assembled via hydrogen bonds and π–π stacking in the composites. The mass fraction of PAH and RBS in the composites was calculated to be 21.86% and 29.3%. The fluorescence of PAH/ZIF-8 is quenched regularly by Cu²⁺. The detection limit for Cu²⁺ was calculated to be 1.42 nM for PAH/ZIF-8, which is one order of magnitude lower than that of PAH. The detection limit for Cu²⁺ was determined to be 0.8 μM for RBS/ZIF-8, which is three times lower than that of RBS. The two composites both display high selectivity to Cu²⁺ over competing metal ions. The PAH/ZIF-8 fluorescent sensor was successfully applied to Cu²⁺ determination in environmental water. PAH/ZIF-8 exhibits excellent cell membrane permeability and low cytotoxicity in cellular imaging. The enhanced chemical sensor was designed by introducing small molecules into ZIF-8 for the specific recognition of Cu²⁺.

An enhanced chemical sensor was designed by introducing small molecules into ZIF-8 for the specific recognition of Cu²⁺.

Extraction of Metal Ions with Metal-Organic Frameworks

Metal-organic frameworks (MOFs) are crystalline porous materials composed of metal ions or clusters coordinated with organic linkers. Due to their extraordinary properties such as high porosity with homogeneous and tunable in size pores/cages, as well as high thermal and chemical stability, MOFs have gained attention in diverse analytical applications. MOFs have been coupled with a wide variety of extraction techniques including solid-phase extraction (SPE), dispersive solid-phase extraction (d-SPE), and magnetic solid-phase extraction (MSPE) for the extraction and preconcentration of metal ions from complex matrices. The low concentration levels of metal ions in real samples including food samples, environmental samples, and biological samples, as well as the increased number of potentially interfering ions, make the determination of trace levels of metal ions still challenging. A wide variety of MOF materials have been employed for the extraction of metals from sample matrices prior to their determination with spectrometric techniques.