Performance of metal–organic frameworks for the adsorptive removal of potentially toxic elements in a water system: a critical review

Switchable metal extractant integrated miniaturized 3D-printed device: A semi-online multi-metal separation system for matrix-free ICP-MS analysis

BACKGROUND

This study tackles the critical challenges in metal analysis by presenting an innovative miniaturized metal extraction device prototype. This device features a functional nanocomposite (FNC) enhanced 3D-printed polylactic acid (PLA) metal extractant (FNC@3D PLA). The research is motivated by the constraints of traditional solid-phase extraction (SPE) methods, specifically their limitations in handling competitive metal ion environments and matrix interference during inductively coupled plasma mass spectrometry (ICP-MS) analysis. The designed prototype aims to overcome these challenges and enhance the extraction efficiency of diverse metals.

RESULTS

The FNC, designed to incorporate various functional groups critical for metal ion extraction efficiency, was meticulously engineered through the reaction of acid-treated and delaminated graphitic carbon nitride nanosheets (Thiol-gCN NSs) with 3-mercaptopropyl trimethoxysilane (MPTMS). The competitive metal ion extraction efficiency of FNC@3D PLA was demonstrated, showcasing notable limit of detection values of 3.2 ± 0.7 ng mL-1 and 8.57 ± 3.05 ng mL-1 for Cu and Ag, respectively. Furthermore, the miniaturized 3D-printed metal-preconcentration setup incorporating FNC@3D PLA exhibited favorable intraday relative standard deviation (RSD) percentage (%) values ranging from 1.23 to 8.6 for both Cu and Ag. Interday RSD % between 1.41 and 8.14 were observed under spiked real urine sample conditions. The sustainability and robustness of the proposed approach were underscored by substantial recovery % values exhibited by FNC@3D PLA, even after eight consecutive regeneration processes.

SIGNIFICANCE

This study significantly contributes to the advancement of analytical methodologies by providing a reliable and efficient platform for metal extraction and preconcentration in practical metal analysis applications. Developed FNC@3D PLA system demonstrates its potential to address the challenges associated with SPE in metal analysis, especially in complex sample matrices. We believe implications of this research can be extended to various fields, from environmental monitoring to clinical diagnostics, where accurate and reliable metal analysis is paramount.

The effect of synthesis conditions on the in situ grown MIL-100(Fe)-chitosan beads: Interplay between structural properties and arsenic adsorption

Efficient sequestration of arsenic from drinking water is a global need. Herein we report eco-friendly porous hybrid adsorbent beads for removal of arsenic, through in situ synthesis of MIL-100(Fe) in the chitosan solvogel. To understand the structural vs. performance correlation, series of hybrid adsorbents were synthesized by modulating synthesis conditions like temperature, crystallization time, and concentration. Adsorbents were investigated using PXRD, FT-IR, SEM, and ICP-OES. Intriguing correlation between crystallinity and adsorption performance was observed as low and high crystalline MIL-100(Fe)-chitosan (ChitFe5 and ChitFe7, respectively) exhibited exceptional adsorption towards As5+ by removing it from water with 99% efficiency, whereas for As3+ species removal of about 85% was afforded. Adsorption isotherms indicated that increase in crystallinity (ChitFe5 -> ChitFe7), adsorption capacities of As5+ and As3+ increased from 23.2 to 64.5, and from 28.1 to 35.3 mg/g, respectively. Selectivity tests of the adsorbents towards As5+ and As3+ over competitive anions in the equimolar competitive systems having nitrates, sulfates, and carbonates demonstrated that the performance of the absorbents was fully maintained, relative to the control system. Through this study a highly selective and efficient adsorbent for arsenic species is designed and a clear insight into the structural tuning and its effect on adsorption performance is provided.

Controlled Growth of Highly Defected Zirconium-Metal-Organic Frameworks via a Reaction-Diffusion System for Water Remediation

The relentless growth of metal-organic framework (MOF) chemistry is paralleled by the persistent urge to control the MOFs physical and chemical properties. While this control is mostly achieved by solvothermal syntheses, room temperature procedures stand out as more convenient and sustainable pathways for the production of MOF materials. Herein, a novel approach to control the crystal size and defect numbers of a dihydroxy-functionalized zirconium-based metal-organic framework (UiO-66(OH)2) at room temperature is reported. Through a reaction-diffusion method in a 1D system, zirconium salt was diffused into an agar gel matrix containing the organic linker to form nanocrystals of UiO-66(OH)2 with tailored structural features that include crystal size distribution, surface area, and defect number. By variation of the synthesis parameters of the system, hierarchical MOF nanocrystals with an average size ranging from 30 nm up to 270 nm and surface areas between 201 and 500 m2 g-1 were obtained in a one-pot synthetic route. To stress the importance of crystal size, morphology, and structural defects on the adsorption properties of UiO-66(OH)2, the adsorption capacity of the MOF toward methylene blue dye was tested with the largest and most defected crystals achieving the best performance of 202 mg/g. The distinctive structural characteristics including the hierarchical micromesoporous frameworks, the nanosized particles, and the highly defective crystals obtained by our synthesis procedure are deemed challenging through the conventional synthesis methods. This work paves the way for engineering MOF crystals with tunable physical and chemical properties, using a green synthesis procedure, for their advantageous use in many desirable applications.

On the adsorption characteristics and mechanism of methylene blue by ball mill modified biochar

In this study, modified biochar (BRB) was prepared from rice straw by ball milling technique and used for the adsorption of methylene blue (MB) in wastewater. The BRB was characterized by SEM, FTIR and XPS, and the adsorption model and Box-Behnken design were used to optimize the five influencing factors. The results showed that the ball milling technique could increase the content of functional groups (-OH, C=C and C-O, etc.) and aromatic structures on the surface of biochar, thus facilitating the removal of MB. The isotherm model was consistent with the Langmuir adsorption model (R2 = 0.947) and the maximum adsorption capacity was 50.27 mg/g. The adsorption kinetics was consistent with the pseudo-second-order kinetic model (R2 = 1) and the adsorption rate was mainly controlled by chemisorption. The thermodynamic model confirmed that the adsorption process was a spontaneous heat absorption reaction. The maximum adsorption efficiency was 99.78% under the optimal conditions (40℃, pH 8, reaction time = 90 min, dosing amount = 0.1 mg), and the adsorption efficiency could be improved by increasing the pH and BRB dosing amount. The surface functional groups and crystal structure properties of BRB were the main determinants of adsorption, and it was clarified that physical adsorption, electrostatic attraction and π-π interaction were the main mechanisms for the adsorption of MB by BRB. The main mechanisms were clarified. Therefore, BRB is an economic, efficient and green adsorption material with good potential for the removal of dye pollutants in the aqueous environment.

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.

Role of soil organic matter on the retention and mobility of common plastic additives, Di(2-ethylhexyl) phthalate, bisphenol A and benzophenone, in soil

The objectives of this study were to assess the role of soil organic matter on retaining plastic additives, Di(2-ethylhexyl) phthalate (DEHP), Bisphenol A (BPA) and Benzophenone (BP), to postulate the retention mechanisms and mobility in soil. Batch experiments were conducted for red yellow podzolic soil (OM) and soil subjected to high temperature oxidation at 600 °C for 2 h to remove total organic matter (OMR). Pristine soil, which contains organic matter abbreviated as OM (soil with organic matter) whereas total organic matter removed soil is abbreviated as OMR (organic matter removed soil). The pH edge and kinetic experiments were conducted with 20 g/L soil suspension spiked with 10 mg/L of each additive, whereas 1-20 mg/L concentration range was used in isotherm experiments and analyzed using high performance liquid chromatography. DEHP demonstrated the highest retention, 331 and 615.16 mg/kg in OM and OMR soils respectively, at pH 6.6. However, BPA and BP showed highest retentions of 132 and 128 mg/kg, respectively around pH 4.3 in pristine soil. DEHP interaction with soil OM indicated weak physical bonding whereas chemisorption to OMR soil. In the case of BPA, physisorption governed its interaction with both soil organic matter and mineral fraction. Nevertheless, BP demonstrated chemical interactions with OM and minerals. Desorption of DEHP was close to 100% however, BPA and BP were <15%. Overall, DEHP and BPA could be easily released into soil water and possibly be available for plant uptake while, BP is immobilized in soil.

Efficient removal of veterinary drugs from aqueous solutions using magnetically separable carbonaceous materials derived from cobalt and iron metal-organic frameworks

Rapid synthesis of carbon-based magnetic materials derived from cobalt and iron metal-organic frameworks (MOFs), ZIF-67, and MIL-100(Fe), by microwave-assisted method, followed by carbonization under a N₂ atmosphere is described in this study. The carbon-derived MOFs (CDMs) were evaluated for the removal of the emerging pollutants sulfadiazine (SDZ) and flumequine (FLU) used as veterinary drugs. The study aimed to link the adsorption behavior with their surface properties and elemental composition. C-ZIF-67 and C-MIL-100(Fe) showed hierarchical porous structures with specific surface areas of 295.6 and 163.4 m² g^-1, respectively. The Raman spectra of the CDMs show the characteristic D and G bands associated with defect-rich carbon and sp² graphitic carbon, respectively. The CDMs exhibit cobalt species (Co₃O₄, CoO, and Co) in C-ZIF-67 and iron species (Fe₂O₃, Fe₃O₄, and Fe) in C-MIL-100 (Fe) which are related to the magnetic behavior of CDMs. C-ZIF-67 and C-MIL-100 (Fe) had saturation magnetization values of 22.9 and 53.7 emu g^-1, respectively, allowing easy solid-liquid separation using a magnet. SDZ and FLU removal rates on CDMs follow pseudo-second-order kinetics, and adsorption isotherms fit the Langmuir model based on regression coefficient values. Adsorption thermodynamics calculations showed that the adsorption of SDZ and FLU by CDMs was a thermodynamically favorable process. Therefore, these properties of C-ZIF-67 and C-MIL-100 (Fe) and their regeneration ability facilitate their use as adsorbents for emerging pollutants.

Insights into the statistical physics modeling and fractal like kinetic approach for the adsorption of As(III) on coordination polymer gel based on zirconium(IV) and 2-thiobarbituric acid

A novel coordination polymer gel based on zirconium(IV) and 2-thiobarbituric (ZrTBA) was synthesized and explored its potential to remediate As(III) from water. Box-Behnken design with desirability function and genetic algorithm yielded the optimized conditions (initial concentration=194 mg L^-1, dosage = 42.2 mg, time= 95 min and pH = 4.9) for maximum removal efficiency (99.19 %). The experimental saturation capacity for As(III) was 178.30 mg g^-1. The steric parameter n > 1 of the best fitted statistical physics model: monolayer with two energies (R² = 0.987-0.992) suggested multimolecular mechanism with vertical orientation of As(III) molecules onto the two active sites. XPS and FTIR confirmed the two active sites being zirconium and oxygen. The adsorption energies (E₁ = 35.81-37.63 kJ/mol; E₂ = 29.50-36.49 kJ/mol) and isosteric heat of adsorption indicated that physical forces governed the As(III) uptake. DFT calculations implied that the weak electrostatic interaction and hydrogen bonding were involved. The best fitted (R²>0.99) fractal like pseudo first order model established energetic heterogeneity. ZrTBA showed excellent removal efficiency in the presence of potential interfering ions and could be used up to 5 cycles of adsorption-desorption with < 8 % loss in the efficiency. ZrTBA removed ≥96.06 % As(III) from real water samples spiked at different levels of As(III).

Exploring the Potential of a Highly Scalable Metal-Organic Framework CALF-20 for Selective Gas Adsorption at Low Pressure

In this study, the ability of the highly scalable metal-organic framework (MOF) CALF-20 to adsorb polar and non-polar gases at low pressure was investigated using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The results from the simulated adsorption isotherms revealed that the highest loading was achieved for SO₂ and Cl₂, while the lowest loading was found for F₂ molecules. The analysis of interaction energies indicated that SO₂ molecules were able to form the strongest adsorbent-adsorbate interactions and had a tight molecular packing due to their polarity and angular structure. Additionally, Cl₂ gas was found to be highly adsorbed due to its large van der Waals surface and strong chemical affinity in CALF-20 pores. MD simulations showed that SO₂ and Cl₂ had the lowest mobility inside CALF-20 pores. The values of the Henry coefficient and isosteric heat of adsorption confirmed that CALF-20 could selectively adsorb SO₂ and Cl₂. Based on the results, it was concluded that CALF-20 is a suitable adsorbent for SO₂ and Cl₂ but not for F₂. This research emphasizes the importance of molecular size, geometry, and polarity in determining the suitability of a porous material as an adsorbent for specific adsorbates.

Metal-Organic Frameworks as Potential Agents for Extraction and Delivery of Pesticides and Agrochemicals

Pesticide contamination is a global issue, affecting nearly 44% of the global farming population, and disproportionately affecting farmers and agricultural workers in developing countries. Despite this, global pesticide usage is on the rise, with the growing demand of global food production with increasing population. Different types of porous materials, such as carbon and zeolites, have been explored for the remediation of pesticides from the environment. However, there are some limitations with these materials, especially due to lack of functional groups and relatively modest surface areas. In this regard, metal-organic frameworks (MOFs) provide us with a better alternative to conventionally used porous materials due to their versatile and highly porous structure. Recently, a number of MOFs have been studied for the extraction of pesticides from the environment as well as for targeted and controlled release of agrochemicals. Different types of pesticides and conditions have been investigated, and MOFs have proved their potential in agricultural applications. In this review, the latest studies on delivery and extraction of pesticides using MOFs are systematically reviewed, along with some recent studies on greener ways of pest control through the slow release of chemical compounds from MOF composites. Finally, we present our insights into the key issues concerning the development and translational applications of using MOFs for targeted delivery and pesticide control.

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

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

Impact of industrial effluents on the environment and human health and their remediation using MOFs-based hybrid membrane filtration techniques

The hazardous risk posed by industrial effluent discharge into the ecosystem has raised a plethora of environmental issues, public health, and safety concerns. The effluents from industries such as tanning, leather, petrochemicals, pharmaceuticals, and textiles are create significant stress on the aquatic ecosystem, which induces significant toxicity, involved in endocrine disruptions, and inhibits reproductive functions. Therefore, this review presented an overall abridgment of the effects of these effluents and their ability to synergize with modern pollutants such as pharmaceuticals, cosmetic chemicals, nanoparticles, and heavy metals. We further emphasize the metal organic framework (MOF) based membrane filtration approach for remediation of industrial effluents in comparison to the traditional remediation process. The MOF based-hybrid membrane filters provide higher reusability, better adsorption, and superior removal rates through the implication of nanotechnology, while the traditional remediation process offers poorer filtration rates and stability.

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

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

A sustainable Decision Support System for soil bioremediation of toluene incorporating UN sustainable development goals

Decision Support System (DSS) is a novel approach for smart, sustainable controlling of environmental phenomena and purification processes. Toluene is one of the most widely used petroleum products, which adversely impacts on human health. In this study, Fusarium Solani fungi are utilized as the engine of the toluene bioremediation procedure for the monitoring part of DSS. Experiments are optimized by Central Composite Design (CCD) - Response Surface Methodology (RSM), and the behavior of the mentioned fungi is estimated by M5 Pruned model tree (M5P), Gaussian Processes (GP), and Sequential Minimal Optimization (SMOreg) algorithms as the prediction section of DSS. Finally, the control stage of DSS is provided by integrated Petri Net modeling and Failure Modes and Effects Analysis (FMEA). The findings showed that Aeration Intensity (AI) and Fungi load/Biological Waste (F/BW) are the most influential mechanical and biological factors, with P-value of 0.0001 and 0.0003, respectively. Likewise, the optimal values of main mechanical parameters include AI, and the space between pipes (S) are equal to 13.76 m³/h and 15.99 cm, respectively. Also, the optimum conditions of biological features containing F/BW and pH are 0.001 mg/g and 7.56. In accordance with the kinetic study, bioremediation of toluene by Fusarium Solani is done based on a first-order reaction with a 0.034 s-1 kinetic coefficient. Finally, the machine learning practices showed that the GP (R2 = 0.98) and M5P (R2 = 0.94) have the most precision for predicting Removal Percentage (RP) for mechanical and biological factors, respectively. At the end of the present research, it is found that by controlling seven possible risk factors in bioremediation operation through the FMEA- Petri Net technique, efficiency of the process can be adjusted to optimum value.

Layer-by-layer coating of MIL-100(Fe) on a cotton fabric for purification of water-soluble dyes by the combined effect of adsorption and photocatalytic degradation

Efforts have been made for sustainable development of adsorbents to purify organic contaminants from wastewater. In this study, a MIL-100(Fe) based textile that acts as a reusable adsorbent and photocatalytic agent was developed by synthesizing MIL-100(Fe) onto a cotton fabric by the layer-by-layer (LBL) process using water-based solutions. As the number of LBL cycles increased, the add-on's of MIL-100(Fe) showed a drastic increase up to 8 cycles, then showed gradual increases with further treatments. The overall adsorption performance was enhanced with the increased MIL-100(Fe) add-on's, but the specific adsorption efficiency per unit mass of MIL-100(Fe) was reduced as the LBL cycles increased, implying the reduced average adsorption efficiency with a thicker coating. To examine the reusability of the adsorbent, desorption efficiency of RhB was measured. The desorption after the first-time adsorption was not efficient due to the strong binding inside the pores. For the later cycles of adsorption–desorption, desorption occurred more efficiently, probably because RhB molecules were adhered mostly at the outer surface of the MOF layer. Simultaneously, MIL-100(Fe)@cotton demonstrated the photocatalytic degradation performance against RhB in the presence of H₂O₂ by the Fenton reaction. With the combined effect of adsorption and photodegradation, the developed fabric attained 96% removal efficiency for RhB dissolved in water. This study demonstrates an environmentally responsible process of developing a MIL-100(Fe) coated fabric that is readily available for effective removal of organic foulants in water. This fabrication method can be applied as a scalable manufacturing of metal–organic framework-based photocatalytic adsorbent textiles.

A MIL-100(Fe)-based water purifying textile that functions by dual action of adsorption and photocatalytic activity is designed via a layer-by-layer process without using toxic organic solvents.

Colloidal biochar for enhanced adsorption of antibiotic ciprofloxacin in aqueous and synthetic hydrolyzed human urine matrices

Objectives of the present research were to examine the capacity of disc-milled high lignin biochar colloids (CBC) for the removal of ciprofloxacin (CPX) from aqueous solution and synthetic hydrolyzed human urine. In this study, adsorption of CPX was tested against the initial pH (3-10), ionic strength (0.001-0.1 M NaNO₃), resident time (up to 8 h), initial CPX concentration (5-100 mg/L) and temperature (25, 35, and 45 °C). The surface morphology was examined using Brunauer-Emmett-Teller (BET) specific surface area. The CBC was observed to be < 300 nm whereas the BET surface area was 284 m²/g. Best CPX adsorption demonstrated at pH 5-6 and however, indicated ionic strength dependency. Experimental kinetics data in aqueous media were well-fitted to the pseudo-second-order (r² of 0.98), while the Hill and Langmuir isotherm models best described the isotherm data (r² of 0.95 and 0.94, respectively) confirming chemisorption followed by physisorption interactions. The thermodynamics results indicate that CPX adsorption onto CBC is spontaneous (-ΔG), endothermic (+ΔH) and has increased randomness (+ΔS) in the aqueous system. The kinetic experimental data in synthetic urine matrix was fitted with Elovich (r² = 0.99) and fractional power (r² = 0.96) models whereas Hills (r² = 0.99) and Langmuir (r² = 0.97) models were the most fitted with isotherm data suggesting the adsorption of CPX on the CBC by chemisorption mechanisms. In conclusion, CBC demonstrated effective removal of CPX indicating its potential to be used in wastewater treatment.

MIL series of metal organic frameworks (MOFs) as novel adsorbents for heavy metals in water: A review

With large specific surface area, abundant adsorption sites, flexible pore structure, and good water stability, Materials of Institute Lavoisier frameworks (MILs) have attracted increasing attention as effective environmental adsorbents. This review systematically analyzes and recapitulates recent progress in the synthesis and application of MIL-based adsorbents for the removal of aqueous heavy metal ions. Commonly used solvothermal, microwave, electrochemical, ultrasonic, and mechanochemical syntheses of MILs are first summarized and compared. Instead of focusing on adsorption process parameters, adsorption performances and governing mechanisms of virgin MILs, functional MILs, MIL-based composites, and carbonized MILs to representative metal(loid) ions (chromium, arsenic, lead, cadmium, and mercury) in water under various conditions are then systematically reviewed and discussed. In the end, this work also outlines prospects and future directions to promote the applications of MILs in treating heavy metal contaminated water.

High-performance and selective adsorption of ZIF-8/MIL-100 hybrids towards organic pollutants

Environmental contamination by organic pollutants has become a pressing concern. In this study, metal-organic framework composites with a core-shell structure of MIL-100 wrapped around ZIF-8 (ZIF-MIL hybrids) were synthesized and characterized for their effectiveness to remove organic pollutants. First, a sequence of routine characterizations will examine the ZIF-MIL series samples' physicochemical properties and morphological characteristics. Then, the adsorption capacities of ZIF-MIL towards organic pollutants, including cationic dyes (methylene blue (MB), and rhodamine B (RHB)), anionic dyes (methyl orange (MO)), neutral pollutants (Sudan III (SD-III), tetracycline (TC) and amoxicillin (AMX)), were investigated. Among the ZIF-MIL series, ZIF-MIL-4 has an excellent specific surface area with high uptake of TC (1288 mg g^-1) and RHB (1181 mg g^-1). Based on the adsorption data from kinetic and dynamic studies, the adsorption process was closest to the pseudo-second-order kinetic model and Freundlich isotherm. In terms of thermodynamic parameter values, the adsorption of TC is an endothermic and spontaneous process, while the adsorption of RHB is an exothermic and spontaneous process. Furthermore, the reusability and selectivity studies of ZIF-MIL-4 towards TC and RHB exhibited significant regeneration ability and high selectivity. The effects of ionic strength and pH on pollutant removal efficiency were also tested. The experimental results showed that the main interactions between ZIF-MIL-4 and RHB or TC were weak coordination, electrostatic, hydrogen bonding, and π-π stacking interactions. Thus, the proposed MOF hybrid, by forming mixtures with other MOFs, can be a potential purifier with improved adsorption capacity and selectivity for organic pollutants as well as self-reusability.

Metal-organic frameworks for active food packaging. A review

Food wastage is a major concern for sustainable health and agriculture. To reduce food waste, classical preservation techniques such as drying, pasteurization, freeze-drying, fermentation, and microwave are available. Nonetheless, these techniques display shortcomings such as alteration of food and taste. Such shortcomings may be solved by active food packaging, which involves the incorporation of active agents into the packaging material. Recently, metal-organic frameworks, a class of porous hybrid supramolecular materials, have been developed as an active agent to extend food shelf life and maintain safety. Here, we review metal-organic frameworks in active packaging as oxygen scavengers, antimicrobials, moisture absorbers, and ethylene scavengers. We present methods of incorporation of metal-organic frameworks into packaging materials and their applications.

Modern Carbon-Based Materials for Adsorptive Removal of Organic and Inorganic Pollutants from Water and Wastewater

Currently, a serious threat for living organisms and human life in particular, is water contamination with persistent organic and inorganic pollutants. To date, several techniques have been adopted to remove/treat organics and toxic contaminants. Adsorption is one of the most effective and economical methods for this purpose. Generally, porous materials are considered as appropriate adsorbents for water purification. Conventional adsorbents such as activated carbons have a limited possibility of surface modification (texture and functionality), and their adsorption capacity is difficult to control. Therefore, despite the significant progress achieved in the development of the systems for water remediation, there is still a need for novel adsorptive materials with tunable functional characteristics. This review addresses the new trends in the development of new adsorbent materials. Herein, modern carbon-based materials, such as graphene, oxidized carbon, carbon nanotubes, biomass-derived carbonaceous matrices-biochars as well as their composites with metal-organic frameworks (MOFs) and MOF-derived highly-ordered carbons are considered as advanced adsorbents for removal of hazardous organics from drinking water, process water, and leachate. The review is focused on the preparation and modification of these next-generation carbon-based adsorbents and analysis of their adsorption performance including possible adsorption mechanisms. Simultaneously, some weak points of modern carbon-based adsorbents are analyzed as well as the routes to conquer them. For instance, for removal of large quantities of pollutants, the combination of adsorption and other methods, like sedimentation may be recommended. A number of efficient strategies for further enhancing the adsorption performance of the carbon-based adsorbents, in particular, integrating approaches and further rational functionalization, including composing these adsorbents (of two or even three types) can be recommended. The cost reduction and efficient regeneration must also be in the focus of future research endeavors. The targeted optimization of the discussed carbon-based adsorbents associated with detailed studies of the adsorption process, especially, for multicomponent adsorbate solution, will pave a bright avenue for efficient water remediation.

Construction of a Tl(I) voltammetric sensor based on ZIF-67 nanocrystals: optimization of operational conditions via response surface design

An electroanalytical sensor was constructed constituted on a carbon paste electrode (CPE) with a ZIF-67 modifier and devoted to the quantification of Tl(I). Several characterization tests including XRD, BET, FT-IR, SEM/EDS/mapping, TEM, impedance spectroscopy (EIS), and cyclic voltammetry (CV) were performed on the synthesized ZIF-67 nanocrystals and CPE matrix. Central composite design (CCD) was used to assess the impact of variables affecting the sensor response, including the weight percent of ZIF-67 (14%), the pH of the thallium accumulation solution (6.4), and accumulation time (315 s) as well as the accumulation potential (-1.2 V). The direct linear relationship between the sensor response and the concentration of Tl(I) is in the interval of 1.0×10^-10 to 5.0×10^-7 M (coefficient of determination = 0.9994). The detection limit is approximately 1.0 × 10^-11 M. The right selection of the MOF makes this sensor highly resistant to the interference of other ions. High selectivity against common interferences in the measurement of thallium (such as Pb(II) and Cd(II)) is an important feature of this sensor. To confirm the performance of the prepared sensor, the amount of thallium in the real sample was determined.

Discriminatory behavior of a rhodamine 6G decorated mesoporous silica based multiple cation sensor towards Cu2+ and Hg2+vis-à-vis Al3+, Cr3+ and Fe3+: selective removal of Cu2+ and Hg2+ from aqueous media

Selective identification of metal ions as well as their removal is possible when a sensing unit is anchored to a solid support. In this paper, functionalized mesoporous silica with a pendant rhodamine 6G moiety (R6FMS) has been obtained by successive grafting of an aldehyde derivative of bisphenol A followed by rhodamine 6G over a 3-aminopropyl anchored mesoporous silica framework. The materials have been characterized by powder X-ray diffraction, nitrogen sorption and electron microscopy studies, FT-IR and solid state MAS NMR spectral studies, and thermal analysis. In ethanol, the colorless silica material gives pink coloration in the presence of Al3+, Cr3+, Fe3+ and Cu2+ which is also clearly evident from the generation of an absorption peak at 525 nm. Upon excitation at 500 nm, the fluorescence intensity of the probe increases by 36-, 17-, 40- and 89-fold in the presence of Al3+, Cr3+, Fe3+ and Cu2+ ions, respectively. This suggests that R6FMS is a colorimetric and fluorescent chemosensor for these cations in ethanol. However, when the solvent is changed from ethanol to water, it becomes a selective chemosensor only for Cu2+ and Hg2+, by the generation of a pink color and strong fluorescence at ca. 550 nm, thereby discriminating the trivalent cations. Cations induce the opening of the spirolactam ring resulting in pink coloration and strong fluorescence. The quantum yield and lifetime of the probe have been increased considerably in the presence of these cations in ethanol as well as in aqueous media. The detection limit values for these cations range from 10-6 to 10-8 M. R6FMS has been used to remove Hg2+ and Cu2+ from their aqueous solution with a maximum adsorption capacity of 35 mg g-1 and 148 mg g-1 for Cu2+ and Hg2+, respectively.

Fabrication and application of a MIL-68(In)-NH2 incorporated high internal phase emulsion polymeric monolith as a solid phase extraction adsorbent in triazine herbicide residue analysis

In this work, a metal–organic framework MIL-68(In)–NH₂ incorporated high internal phase emulsion polymeric monolith (MIL-68(In)–NH₂/polyHIPE) was prepared and applied as a solid phase extraction adsorbent for the extraction and detection of trace triazine herbicides in environmental water samples by coupling with HPLC-UV detection. The fabricated material showed good adsorption for simazine, prometryn, and prometon in water samples because of π–π interactions and hydrogen bonding interactions. Under optimal conditions, the maximum adsorption capacity of simazine, prometon and prometryn was 800 μg g⁻¹, 800 μg g⁻¹ and 6.01 mg g⁻¹, respectively. The linearities were 10–800 ng mL⁻¹ for simazine, prometon and prometryn. The limits of detection were 31–97 ng L⁻¹, and the recoveries were 85.6–118.2% at four spiked levels with relative standard deviations lower than 5.0%. The method has a high sensitivity for the determination of three triazine herbicides in environmental water samples.

MIL-68(In)–NH₂ incorporated high internal phase emulsion polymeric monoliths were fabricated and applied to extract and determine triazine herbicide residues in environmental water samples.

Carbon-based adsorbents for fluoroquinolone removal from water and wastewater: A critical review

This review summarizes the adsorptive removal of Fluoroquinolones (FQ) from water and wastewater. The influence of different physicochemical parameters on the adsorptive removal of FQ-based compounds is detailed. Further, the mechanisms involved in the adsorption of FQ-based antibiotics on various adsorbents are succinctly described. As the first of its kind, this paper emphasizes the performance of each adsorbent for FQ-type antibiotic removal based on partition coefficients of the adsorbents that is a more sensitive parameter than adsorption capacity for comparing the performances of adsorbents under various adsorbate concentrations and heterogeneous environmental conditions. It was found that π-π electron donor-acceptor interactions, electrostatic interactions, and pore-filling were the most prominent mechanisms for FQ adsorption by carbon and clay-based adsorbents. Among all the categories of adsorbents reviewed, graphene showed the highest performance for the removal of FQ antibiotics from water and wastewater. Based on the current state of knowledge, this review fills the gap through methodolically understanding the mechanism for further improvement of FQ antibiotics adsorption performance from water and wastewater.

Removal of decidedly lethal metal arsenic from water using metal organic frameworks: a critical review

Water contamination is worldwide issue, undermining whole biosphere, influencing life of a large number of individuals all over the world. Water contamination is one of the chief worldwide danger issues for death, sickness, and constant decrease of accessible drinkable water around the world. Among the others, presence of arsenic, is considered as the most widely recognized lethal contaminant in water bodies and poses a serious threat not exclusively to humans but also towards aquatic lives. Hence, steps must be taken to decrease quantity of arsenic in water to permissible limits. Recently, metal-organic frameworks (MOFs) with outstanding stability, sorption capacities, and ecofriendly performance have empowered enormous improvements in capturing substantial metal particles. MOFs have been affirmed as good performance adsorbents for arsenic removal having extended surface area and displayed remarkable results as reported in literature. In this review we look at MOFs which have been recently produced and considered for potential applications in arsenic metal expulsion. We have delivered a summary of up-to-date abilities as well as significant characteristics of MOFs used for this removal. In this review conventional and advanced materials applied to treat water by adsorptive method are also discussed briefly.

Sea urchin-like FeOOH functionalized electrochemical CNT filter for one-step arsenite decontamination

Advanced nanotechnologies for efficient arsenic decontamination remain largely underdeveloped. The most abundant inorganic arsenic species are neutrally-charged arsenate, As(III), and negatively-charged arsenite, As(V). Compared with As(V), As(III) is 60 times more toxic and more difficult to remove due to high mobility. Herein, an electrochemical filtration system was rationally designed for one-step As(III) decontamination. The key to this technology is a functional electroactive carbon nanotube (CNT) filter functionalized with sea urchin-like FeOOH. With the assistance of electric field, CNT-FeOOH anodic filter can in situ transform As(III) to less toxic As(V) while passing through. Then, as-produced As(V) could be effectively sequestrated by FeOOH. The sufficient exposed sorption sites, flow-through design, and filter's electrochemical reactivity synergistically guaranteed a rapid arsenic removal kinetic. The underlying working mechanism was unveiled based on systematic experimental investigations and theoretical calculations. The system efficacy can be adapted across a wide pH range and environmental matrixes. Exhausted CNT-FeOOH filters could be effectively regenerated by chemical washing with diluted NaOH solution. Outcomes of the present study are dedicated to provide a straightforward and effective strategy by integrating electrochemistry, nanotechnology, and membrane separation for the removal of arsenic and other similar heavy metals from water bodies.

Simultaneous fluorescence determination of bisphenol A and its halogenated analogs based on a molecularly imprinted paper-based analytical device and a segment detection strategy

Bisphenol A (BPA) and its halogenated analogs tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA) are common environmental contaminants and a method for their simultaneous determination is urgently needed. A paper-based analytical device (PAD) was prepared using a metal-organic framework of UiO-66-NH₂ coated with molecularly imprinted polymers (MIPs) using TBBPA as a template. The maximum adsorption capacity was 120.94 mg g^-1 and the imprinting factor was 4.07. The selective recognition ability of this PAD enabled the effective separation of TBBPA, TCBPA and BPA based on paper chromatography. Subsequently, the PAD cut into segments were used individually to determine the presence of target chemicals using a highly sensitive fluorescent method. Under ultraviolet light irradiation, UiO-66-NH₂ acts as a photocatalyst to produce reactive oxygen species (ROS) that degrade TBBPA, TCBPA or BPA in the imprinted cavities and the fluorescent signal of 2',7'-dichlorodihydrofluorescein diacetate (H₂DCFDA) added as a ROS probe enabled the indirect determination of target chemicals. This method could determine BPA and its halogenated analogs in dust samples simultaneously with detection limits ranging from 0.14 to 0.30 ng g^-1. The intraday relative standard deviation (RSD) was ≤6.8% and interday RSD was ≤8.1%. The recoveries ranged from 91.0 to 105.6% with RSD values that were ≤7.5%. The results stemmed from this method were consistent with those obtained from LC-MS/MS. It is an environmentally-friendly approach due to the degradation of target pollutants and possesses many advantages such as high selectivity, low cost and easy-to-fabrication.

Effective Removal of Clenbuterol and Ractopamine from Water with a Stable Al(III)-Based Metal-Organic Framework

Clenbuterol (CLE) and ractopamine (RAC) are two kinds of typical β₂-adrenergic agonists which pose a serious threat to the health of human beings. In this work, 10 kinds of metal-organic frameworks (MOFs) with high stability and various pore features are screened to assess adsorption performance for CLE and RAC. An Al(III)-MOF (BUT-19) with abundant ethyl groups exhibits exceptional performance in removing CLE and RAC from water. The maximum adsorption capacity for CLE and RAC are up to 294.1 and 366.3 mg/g under the optimum adsorption conditions, respectively. Meanwhile, the adsorption mechanism effects of pH, temperature, and coexisted ions are investigated systematically. It is found that the MOF pore size and weak hydrogen-bond interactions between CLE/RAC molecules and the MOF are the main causes leading to the extraordinary adsorption. This study provides a new idea for the purposeful design and synthesis of MOFs for removing environmental pollutants and sheds light on the depuration of contaminated water.

Study of the adsorption of an organic pollutant onto a microporous metal organic framework

In this study, the microporous metal organic framework-5 (MOF-5) has been synthesized to be used to remove methyl orange by adsorption. The adsorption experiments exhibit a good adsorption capacity at a catalyst dose of 0.1 g L^-1 and for an initial concentration of 200 mg L^-1, whereas the performance is stable over a wide pH range. The equilibrium adsorption data showed a sigmoidal course, which is well fitted by the Dubinin-Astakhov model applicable for physical adsorption processes (E = 0.055 kJ mol^-1) onto heterogeneous surfaces and a more homogeneous pore structure (n = 9.9), with a maximum adsorption capacity of 1248.35 mg g^-1. As can be observed from the evaluation of the kinetic data, the surface of the adsorbent is heterogeneous with different active sites for methyl orange (MO) adsorption. Moreover, based on the rate constant, it can be suggested that there is a specific interaction like electrostatic interaction between MO and the adsorbent for rapid and high uptake of the dye, whereas the adsorption phenomenon is reversible. According to the adsorption mechanisms, intra-particle and film diffusion models simultaneously controlled the rate sorption, which was confirmed by the calculated intra-particle diffusion and the film diffusion coefficients. The evaluation of the thermodynamic parameters revealed that the MO adsorption is spontaneous, endothermic and the randomness increases with the adsorption of MO.

Review: Efficiently performing periodic elements with modern adsorption technologies for arsenic removal

Arsenic (As) toxicity is a global phenomenon, and it is continuously threatening human life. Arsenic remains in the Earth's crust in the forms of rocks and minerals, which can be released into water. In addition, anthropogenic activity also contributes to increase of As concentration in water. Arsenic-contaminated water is used as a raw water for drinking water treatment plants in many parts of the world especially Bangladesh and India. Based on extensive literature study, adsorption is the superior method of arsenic removal from water and Fe is the most researched periodic element in different adsorbent. Oxides and hydroxides of Fe-based adsorbents have been reported to have excellent adsorptive capacity to reduce As concentration to below recommended level. In addition, Fe-based adsorbents were found less expensive and not to have any toxicity after treatment. Most of the available commercial adsorbents were also found to be Fe based. Nanoparticles of Fe-, Ti-, Cu-, and Zr-based adsorbents have been found superior As removal capacity. Mixed element-based adsorbents (Fe-Mn, Fe-Ti, Fe-Cu, Fe-Zr, Fe-Cu-Y, Fe-Mg, etc.) removed As efficiently from water. Oxidation of AsO₃^3- to AsO₄^3-and adsorption of oxidized As on the mixed element-based adsorbent occurred by different adsorbents. Metal organic frameworks have also been confirmed as good performance adsorbents for As but had a limited application due to nano-crystallinity. However, using porous materials having extended surface area as carrier for nano-sized adsorbents could alleviate the separation problem of the used adsorbent after treatment and displayed outstanding removal performances.