Superior removal of arsenic from water with zirconium metal-organic framework UiO-66

Synergistic Effect of UiO-66 Directly Grown on Kombucha-Derived Bacterial Cellulose for Dye Removal

Metal-Organic Frameworks (MOFs) are particularly attractive sorbents with great potential for the removal of toxic dye pollutants from industrial wastewaters. The uniform dispersion of MOF particles on suitable substrates then represents a key condition to improve their processability and provide good accessibility to the active sites. In this work, we investigate the efficiency of a natural bacterial cellulose material derived from Kombucha (KBC) as an active functional support for growing and anchoring MOF particles with UiO-66 structures. An original hierarchical microstructure was obtained for the as-developed Kombucha cellulose/UiO-66 (KBC-UiO) composite material, with small MOF crystals (~100 nm) covering the cellulose fibers. Promising adsorption properties were demonstrated for anionic organic dyes such as fluorescein or bromophenol blue in water at pH 5 and pH 7 (more than 90% and 50% removal efficiency, respectively, after 10 min in static conditions). This performance was attributed to both the high accessibility and uniform dispersion of the MOF nanocrystals on the KBC fibers together with the synergistic effects involving the attractive adsorbing properties of UiO-66 and the surface chemistry of KBC. The results of this study provide a simple and generic approach for the design of bio-sourced adsorbents and filters for pollutants abatement and wastewater treatment.

Integration of metal organic framework nanoparticles into sodium alginate biopolymer-based three-dimensional membrane capsules for the efficient removal of toxic metal cations from water and real sewage

Sodium alginate (SA) biopolymer has been recognized as an efficient adsorbent material owing to their unique characteristics, including biodegradability, non-toxic nature, and presence of abundant hydrophilic functional groups. Accordingly, in the current research work, UiO-66-OH and UiO-66-(OH)2 metal organic framework (MOF) nanoparticles (NPs) have been integrated into SA biopolymer-based three-dimensional (3-D) membrane capsules (MCs) via a simple and facile approach to remove toxic metal cations (Cu2+ and Cd2+) from water and real sewage. The newly configured capsules were characterized by FTIR, SEM, XRD, EDX and XPS analyses techniques. Exceptional sorption properties of the as-developed capsules were ensured by evaluation of the pertinent operational parameters, i.e., contents of MOF-NPs (1-100 wt%), adsorbent dosage (0.001-0.05 g), content time (0-360 h), pH (1-8), initial concentration of metal cations (5-1000 mg/L) and reaction temperature (298.15-333.15 K) on the eradication of Cu2+ and Cd2+ metal cations. It was found that hydrophilic functional groups (-OH and -COOH) have performed an imperative role in the smooth loading of MOF-NPs into 3-D membrane capsules via intra/inter-molecular hydrogen bonding and van der waals potencies. The maximum monolayer uptake capacities (as calculated by the Langmuir isotherm model) of Cd2+ and Cu2+ by 3-D SGMMCs-OH were 940 and 1150 mg/g, respectively, and by 3-D SGMMCs-(OH)2 were 1375 and 1575 mg/g, respectively, under optimum conditions. The as-developed capsules have demonstrated superior selectivity against targeted metal cations under designated pH and maintained >80 % removal efficiency up to six consecutive treatment cycles. Removal mechanisms of metal cations by the 3-D SGMMCs-OH/(OH)2 was proposed, and electrostatic interaction, ion-exchange, inner-sphere coordination bonds/interactions, and aromatic ligands exchange were observed to be the key removal mechanisms. Notably, FTIR and XPS analysis indicated that hydroxyl groups of Zr-OH and BDC-OH/(OH)2 aromatic linkers played vital roles in Cu2+ and Cd2+ adsorption by participating in inner-sphere coordination interactions and aromatic ligands exchange mechanisms. The as-prepared capsules indicated >70 % removal efficiency of Cu2+ from real electroplating wastewater in the manifestation of other competitive metal ions and pollutants under selected experimental conditions. Thus, it was observed that newly configured 3-D SGMMCs-OH/(OH)2 have offered a valuable discernment into the development of MOFs-based water decontamination 3-D capsules for industrial applications.

Highlights in Interface of Wastewater Treatment by Utilizing Metal Organic Frameworks: Purification and Adsorption Kinetics

Polluted water has become a concern for the scientific community as it causes many severe threats to living beings. Detection or removal of contaminants present in wastewater and attaining purity of water that can be used for various purposes are a primary responsibility. Different treatment methods have already been used for the purification of sewage. There is a need for low-cost, highly selective, and reusable materials that can efficiently remove pollutants or purify contaminated water. In this regard, MOFs have shown significant potential for applications such as supercapacitors, drug delivery, gas storage, pollutant adsorption, etc. The outstanding structural diversity, substantial surface areas, and adjustable pore sizes of MOFs make them superior candidates for wastewater treatment. This Review provides an overview of the interaction science and engineering (kinetic and thermodynamic aspects with interactions) underpinning MOFs for water purification. First, fundamental strategies for the synthesis methods of MOFs, different categories, and their applicability in wastewater treatment are summarized, followed by a detailed explanation of various interaction mechanisms. Finally, current challenges and future outlooks for research on MOF materials toward the adsorption of hazardous components are discussed. A new avenue for modifying their structural characteristics for the adsorption and separation of hazardous materials, which will undoubtedly direct future work, is also summarized.

High Capacity Arsenate Removal from Real Samples Using Dihydrotetrazine Decorated Zirconium-Based Metal-Organic Frameworks

Zirconium metal-organic frameworks (Zr-MOFs) are potential candidates for decontamination of water resources from harmful pollutants due to their modulable porosity and chemical stability in aqueous solutions. Linker functionalization is an approach for tuning the host-guest chemistry of Zr-MOFs and extends their applications in environmental monitoring. In this work, the structure of UiO-66(Zr) (formulated Zr6(OH)4O4(BDC)6, BDC2- = benzene-1,4-dicarboxylate) was functionalized with dihydrotetrazine group via postsynthesis linker exchange (PSLE) method. The functionalized framework, UiO-66(Zr)-DHTZ, was applied for the removal of arsenate ions from aqueous solutions. The results show that UiO-66(Zr)-DHTZ can adsorb 583 mg g-1 of As(V) at pH = 7 after 2 h, which is significantly higher than that of the UiO-66(Zr). According to X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR), the removal mechanism is based on possible hydrogen bindings between free -C-NH and -C═N- sites of dihydrotetrazine function with -O- and -OH sites of As(V) species. Removal tests in real samples show that UiO-66(Zr)-DHTZ still has a high capacity (220 mg g-1) to As(V) ions in complex matrixes and also can decrease the concentration of As(V) below the detection limit (0.05 ppm) of the inductively coupled plasma optical emission spectroscopy (ICP-OES) method. Since the dihydrotetrazine-decorated UiO-66(Zr)-DHTZ reaches one the highest adsorption capacities to As(V) species, it can be considered a potential candidate for water treatment in real-life applications.

Elucidating anticancer drugs release from UiO-66 as a carrier through the computational approaches

The computational analysis of drug release from metal-organic frameworks (MOFs), specifically UiO-66, is the primary focus of this research. MOFs are recognized as nanocarriers due to their crystalline structure, porosity, and potential for added functionalities. The research examines the release patterns of three drugs: temozolomide, alendronate, and 5-fluorouracil, assessing various factors such as the drugs' distance from the UiO-66 centers, the interaction of drug functional groups with Zr metal ions, and the drug density throughout the nanocarrier. Findings reveal that 5-fluorouracil is located furthest from the UiO-66 center and exhibits the highest positive energy compared to the other drugs. Alendronate's density is observed to shift to the carrier surface, while 5-fluorouracil's density significantly decreases within the system. The drug density diminishes as the distance from the UiO-66 center of mass increases, suggesting a stronger positive interaction between the drugs and the nanocarrier. Moreover, Monte Carlo calculations were employed to load drugs onto the UiO-66 surface, leading to a substantial release of 5-fluorouracil from UiO-66. Quantum and Monte Carlo adsorption localization calculations were also conducted to gather data on the compounds' energy and geometry. This research underscores the potential of MOFs as nanocarriers for drug delivery and highlights the crucial role of temperature in regulating drug release from UiO-66. It provides insights into the complex dynamics of drug release and the factors influencing it, thereby emphasizing the promise of UiO-66 as a viable candidate for drug delivery. This work contributes to our understanding of UiO-66's role and sets the stage for improved performance optimization in the cancer treatment.

Multifunctional Roles of Dihydrotetrazine-Decorated Zr-MOFs in Photoluminescence and Colorimetrism for Discrimination of Arsenate and Phosphate Ions in Water

The high chemical and structural stabilities of zirconium (Zr)-based metal-organic frameworks (MOFs) in aquatic media make them ideal candidates for wastewater treatment. Rational decoration or Zr-MOFs with functional groups can significantly extend their application in this area. In this work, two well-known Zr-MOFs, UiO-66 and MIL-140-A, were functionalized with dihydrotetrazine function to increase their capability in water treatment. Investigations reveal that these two dihydrotetrazine (DHTZ)-functionalized MOFs, namely UiO-66(Zr)-DHTZ and MIL-140(Zr)-DHTZ, can be applied as a two-component array for highly selective and sensitive discrimination of arsenate (AsO43-) and phosphate (PO43-) ions in water in the presence of other anions. Photoluminescence (PL) tests using UiO-66(Zr)-DHTZ show that this MOF can detect these two anions via a ratiometric response, 1.74 for arsenate and 1.84 for phosphate at 2 μM, with superior detection limits (7.2 × 10-8 M for AsO43- and 4.3 × 10-8 M for PO43-). The ratiometric PL response of UiO-66(Zr)-DHTZ toward arsenate and phosphate anions arises possibly from the arsenate-dihydrotetrazine hydrogen bonding. In the next step, colorimetric tests using MIL-140(Zr)-DHTZ were conducted to discriminate the arsenate from phosphate with a very low detection limit at nanomolar level. This MOF undergoes a yellow-to-pink color change in the presence of arsenate ions, while no color change is observed in the presence of phosphate. This color change is observed through conversion of dihydrotetrazine sites inside the pores of MIL-140(Zr)-DHTZ into tetrazine. Altogether, the PL response of UiO-66(Zr)-DHTZ is originated from the hydrogen bond-donating/accepting character of DHTZ function, while the colorimetric response of MIL-140(Zr)-DHTZ is based on the chemical conversion of DHTZ function. This work clearly shows that the decoration of Zr-based MOFs with multicharacter functional groups can develop their application in wastewater treatment as multipurpose platforms.

Silk nanofibrils-MOF composite membranes for pollutant removal from water

Membrane separation technology is considered an effective strategy to remove pollutants in sewage. However, it remains a significant challenge to fabricate inexpensive membranes with high purification efficiency. Therefore, the present study proposes the integration of silk nanofibrils (SNFs) and polydopamine⊂metal-organic framework (PDA⊂MOF) nanoparticles to prepare self-supporting membranes, which can effectively intercept nanoparticle pollutants through the size exclusion effect and can strongly adsorb organic dyes and metal ions by SNF. In addition, PDA⊂MOF enables these membranes to adsorb small molecules and heavy metal ions during the filtration process, thereby effectively removing various pollutants from sewage. The integration of size-exclusion and adsorption capabilities enables the SNF/PDA⊂MOF membrane to remove nanoparticles, small-molecule dyes, heavy metal ions, and radioactive elements. This work provides a rational approach for the design and development of the next generation of water treatment membranes and is expected to be used in environmental, food-related, and biomedical fields.

Facile fabrication of Fe/Zr binary MOFs for arsenic removal in water: High capacity, fast kinetics and good reusability

A water-stable bimetallic Fe/Zr metal-organic framework [UiO-66(Fe/Zr)] for exceptional decontamination of arsenic in water was fabricated through a facile one-step strategy. The batch adsorption experiments revealed the excellent performances with ultrafast adsorption kinetics due to the synergistic effects of two functional centers and large surface area (498.33 m²/g). The absorption capacity of UiO-66(Fe/Zr) for arsenate [As(V)] and arsenite [As(III)] reached as high as 204.1 mg/g and 101.7 mg/g, respectively. Langmuir model was suitable to describe the adsorption behaviors of arsenic on UiO-66(Fe/Zr). The fast kinetics (adsorption equilibrium in 30 min, 10 mg/L As) and pseudo-second-order model implied the strong chemisorption between arsenic ions and UiO-66(Fe/Zr), which was further confirmed by DFT theoretical calculations. The results of FT-IR, XPS analysis and TCLP test demonstrated that arsenic was immobilized on the surface of UiO-66(Fe/Zr) through Fe/Zr-O-As bonds, and the leaching rates of the adsorbed As(III) and As(V) from the spent adsorbent were only 5.6% and 1.4%, respectively. UiO-66(Fe/Zr) can be regenerated for five cycles without obvious removal efficiency decrease. The original arsenic (1.0 mg/L) in lake and tap water was effectively removed in 2.0 hr [99.0% of As(III) and 99.8% of As(V)]. The bimetallic UiO-66(Fe/Zr) has great potentials in water deep purification of arsenic with fast kinetics and high capacity.

FeSx@MOF-808 composite for efficient As(III) removal from wastewater: behavior and mechanism

Arsenic is extremely toxic to humans with water as its carrier. One challenge for arsenic control is the complete elimination of As(III) due to its high toxicity, mobility, and solubility. Herein, an active FeS_x@MOF-808 composite was fabricated to enhance the As(III) removal for wastewater remediation. The FeS_x@MOF-808 showed better As(III) adsorptive performance (Q_e = 73.60 mg/g) compared with Fe₂S₃ (Q_e=12.38 mg/g), MOF-808 (Q_e = 27.85 mg/g), and Fe@MOF-808 (Q_e=34.26 mg/g). This can be attributed to an improved porous structure provided by MOF-808 and abundant reactive sites provided by FeS_x. Calculated by the Langmuir model (R² =0.9965), the maximum adsorption capacity (Q_max) of FeS_x@MOF-808 for As(III) removal at 298 K and pH = 7 was 203.28 ± 6.43 mg/g, which is beyond most of the traditional materials and MOFs. Additionally, FeS_x@MOF-808 exhibited good stability in a wide pH range (1-13). Results also showed that the different Fe/S ratios (1:0-1:8) and FeS_x loading amount (0.00625-0.25 mmol) have effects on the FeS_x@MOF-808 performance. By kinetics studies, XPS, and DFT calculation, the mechanisms for arsenic by FeS_x@MOF-808 were proposed. Multiple reaction mechanisms combine the adsorption by the MOF-808 support, the co-precipitation of iron oxides via hydroxyl (Fe-OH) groups, and most importantly, the precipitation through the break of Fe-S and the bond of As-S.

Correlating the Role of Nanofillers with Active Layer Properties and Performance of Thin-Film Nanocomposite Membranes

Thin-film nanocomposite (TFN) membranes are emerging water-purification membranes that could provide enhanced water permeance with similar solute removal over traditional thin-film composite (TFC) membranes. However, the effects of nanofiller incorporation on active layer physico-chemical properties have not been comprehensively studied. Accordingly, we aimed to understand the correlation between nanofillers, active layer physico-chemical properties, and membrane performance by investigating whether observed performance differences between TFN and control TFC membranes correlated with observed differences in physico-chemical properties. The effects of nanofiller loading, surface area, and size on membrane performance, along with active layer physico-chemical properties, were characterized in TFN membranes incorporated with Linde Type A (LTA) zeolite and zeolitic imidazole framework-8 (ZIF-8). Results show that nanofiller incorporation up to ~0.15 wt% resulted in higher water permeance and unchanged salt rejection, above which salt rejection decreased 0.9-25.6% and 26.1-48.3% for LTA-TFN and ZIF-8-TFN membranes, respectively. Observed changes in active layer physico-chemical properties were generally unsubstantial and did not explain observed changes in TFN membrane performance. Therefore, increased water permeance in TFN membranes could be due to preferential water transport through porous structures of nanofillers or along polymer-nanofiller interfaces. These findings offer new insights into the development of high-performance TFN membranes for water/ion separations.

Removal of Hg2+ in wastewater by grafting nitrogen/sulfur-containing molecule onto Uio-66-NH2: from synthesis to adsorption studies

The remediation of heavy metal deserves to be on the agenda, with the adsorbent design bearing the brunt of it. In this study, the molecule (4, 6-diamino-2-mercaptopyrimidine, DMP) containing thiol (-SH) and amino (-NH₂) functional groups was grafted onto Uio-66-NH₂, and a composite metal-organic framework nanomaterial (Zr(NH₂)-DMP) was synthesized via a facile post-modification scheme. The morphological characteristics and structural features of the modified adsorbent were characterized by XRD, FT-IR, FE-SEM, EDS, BET, and XPS. The characterization results verified that the post-modification scheme was successfully achieved. The adsorption experiments were carried out to investigate the removal performance of the Zr(NH₂)-DMP towards Hg²⁺ under different influencing parameters. The maximum adsorption capacity of 389.4 mg/g was obtained, and the adsorption equilibrium was achieved within 30 min at pH 6 at room temperature. Adsorption thermodynamic study indicated that the adsorption process was exothermic and spontaneous. The Zr(NH₂)-DMP exhibited excellent selectivity for Hg²⁺, and also has the potential to remove Cu²⁺, Fe²⁺, and Zn²⁺ ions. The introduction of Cl^- inhibited the removal of Hg²⁺ due to the formation of mercuric chlorides (removal efficiency reduced from 97.8 to 95.6%). The removal efficiency of up to 86.7% was obtained after four cycles. The Langmuir isotherm and Pseudo-second kinetic were more suitable for fitting the adsorption process of Hg²⁺ by Zr(NH₂)-DMP. The main removal mechanism could be attributed to the chelation between Hg²⁺ (soft acid) and nitrogen/sulfur (soft base) elements. These findings convinced that the successful synthesis of Zr(NH₂)-DMP provides an option for Hg²⁺ removal from wastewater.

A Brief Review of Recent Results in Arsenic Adsorption Process from Aquatic Environments by Metal-Organic Frameworks: Classification Based on Kinetics, Isotherms and Thermodynamics Behaviors

In nature, arsenic, a metalloid found in soil, is one of the most dangerous elements that can be combined with heavy metals. Industrial wastewater containing heavy metals is considered one of the most dangerous environmental pollutants, especially for microorganisms and human health. An overabundance of heavy metals primarily leads to disturbances in the fundamental reactions and synthesis of essential macromolecules in living organisms. Among these contaminants, the presence of arsenic in the aquatic environment has always been a global concern. As (V) and As (III) are the two most common oxidation states of inorganic arsenic ions. This research concentrates on the kinetics, isotherms, and thermodynamics of metal-organic frameworks (MOFs), which have been applied for arsenic ions uptake from aqueous solutions. This review provides an overview of the current capabilities and properties of MOFs used for arsenic removal, focusing on its kinetics and isotherms of adsorption, as well as its thermodynamic behavior in water and wastewater.

Metal-Organic Framework Aerogel for Full pH Range Operation and Trace Adsorption of Arsenic in Water

The UiO-66-NH₂ aerogel has been designed to remove As(III) and As(V) in the full pH range with a long lifetime. The efficiency of the aerogel for trace removal from river water samples at the sub-ppb level has been demonstrated. The feasibility for practical uses has been evaluated by breakthrough experiments operated at a liquid hourly space velocity (LHSV) of 38 h^-1 using a real water sample with a significant capacity of 284 mg g^-1. The UiO-66-NH₂ aerogel provides a lifetime of over 600 min, which is one of the highest lifetimes among the reported adsorbents for arsenic decontamination.

Tuning the structure of cerium-based metal-organic frameworks for efficient removal of arsenic species: The role of organic ligands

The ability of organic ligands to change the structure of metal-organic frameworks (MOFs) in nature and influence their adsorption efficiency for arsenic species is enormous. The current work was designed to investigate the adsorption performance of cerium-based MOFs with tunable structures through the use of organic ligands (Ce-MOF-66 and Ce-MOF-808) towards arsenic species from water. The structural features of Ce-MOF-66 and Ce-MOF-808 with varying crystallinity, morphology, particle size, and surface area are considerably altered by organic ligands tuning, resulting in clearly distinct arsenate (As (V)) and arsenite (As (III)) adsorption capabilities. The experimental results showed that the Langmuir adsorption capacities of As (V) by Ce-MOF-66 and Ce-MOF-808 reached 355.67 and 217.80 mg/g, respectively, while for As (III) were 5.52 and 402.10 mg/g for Ce-MOF-66 and Ce-MOF-808, respectively. Except for the impact of PO₄^3- on As (V), co-existing ions had no significant influence on adsorption, illustrating the high selectivity. Furthermore, to understand the structure and adsorption mechanism, two adsorbents were characterized by powder X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, specific surface area, Fourier transform infrared and X-ray photoelectron spectroscopy, in which identified that unsaturated sites and ligand exchange were the main adsorption mechanisms of As (V) and As (III). Overall, this research presents a novel approach for developing high-performance Ce-derived MOFs adsorbents to capture arsenic species.

A comprehensive review on water remediation using UiO-66 MOFs and their derivatives

Metal-organic frameworks (MOFs) are a versatile class of porous materials offering unprecedented scope for chemical and structural tunability. On account of their synthetic versatility, tunable and exceptional host-guest chemistry they are widely utilized in many prominent water remediation techniques. However, some of the MOFs present low structural stabilities specifically in aqueous and harsh chemical conditions which impedes their potential application in the field. Among the currently explored MOFs, UiO-66 exhibits structural robustness and has gained immense scientific popularity. Built with a zirconium-terephthalate framework, the strong Zr-O bond coordination contributes to its stability in aqueous, chemical, and thermal conditions. Moreover, other exceptional features such as high surface area and uniform pore size add to the grand arena of porous nanomaterials. As a result of its stable nature, UiO-66 offers relaxed admittance towards various functionalization, including synthetic and post-synthetic modifications. Consequently, the adsorptive properties of these highly stable frameworks have been modulated by the addition of various functionalities. Moreover, due to the presence of catalytically active sites, the use of UiO-66 has also been extended towards the degradation of pollutants. Furthermore, to solve the practical handling issues of the crystalline powdered forms, UiO-66 has been incorporated into various membrane supports. The incorporation of UiO-66 in various matrices has enhanced the rejection, permeate flux, and anti-fouling properties of membranes. The combination of such exceptional characteristics of UiO-66 MOF has expanded its scope in targeted purification techniques. Subsequently, this review highlights the role of UiO-66 in major water purification techniques such as adsorption, photocatalytic degradation, and membrane separation. This comprehensive review is expected to shed light on the existing developments and guide the inexhaustible futuristic scope of UiO-66 MOF.

Frontier Materials for Adsorption of Antimony and Arsenic in Aqueous Environments: A Review

As highly toxic and carcinogenic substances, antimony and arsenic often coexist and cause compound pollution. Heavy metal pollution in water significantly threatens human health and the ecological environment. This article elaborates on the sources and hazards of compound antimony and arsenic contamination and systematically discusses the research progress of treatment technology to remove antimony and arsenic in water. Due to the advantages of simple operation, high removal efficiency, low economic cost, and renewable solid and sustainable utilization, adsorption technology for removing antimony and arsenic from sewage stand out among many treatment technologies. The adsorption performance of adsorbent materials is the key to removing antimony and arsenic in water. Therefore, this article focused on summarizing frontier adsorption materials' characteristics, adsorption mechanism, and performance, including MOFs, COFs, graphene, and biomass materials. Then, the research and application progress of antimony and arsenic removal by frontier materials were described. The adsorption effects of various frontier adsorption materials were objectively analyzed and comparatively evaluated. Finally, the characteristics, advantages, and disadvantages of various frontier adsorption materials in removing antimony and arsenic from water were summarized to provide ideas for improving and innovating adsorption materials for water pollution treatment.

Fabrication of a Reusable Carbon Dot/Gold Nanoparticle/Metal-Organic Framework Film for Fluorescence Detection of Lead Ions in Water

Solid-state sensing platforms are desirable for the development of reusable sensors to promote public health measures such as testing for drinking water contamination. A bioinspired metal-organic framework (MOF)-based material has been developed by imitating metal-protein interactions in biological systems to attain high sensitivity and selectivity to Pb²⁺ through fluorescence sensing. A zirconium terephthalate-type framework (also known as NH₂-UiO-66) was modified with both gold nanoparticles and thiol-functionalized carbon dots to give HS-C/Au(x)/UiO-66 composites with different Au content (x) and were subsequently adapted into films that show extraordinary sensitivity to Pb²⁺. The HS-C/Au(1.4)/UiO-66 film that consists of 1.4 wt % Au shows a quenching response with the limit of detection of 80 parts per trillion and sustained performance for five cycles. Moreover, the fluorescence response of the HS-C/Au(x)/UiO-66 film to Pb²⁺ can be reversed from emission quenching to enrichment of fluorescence by increasing the Au content. The performance of the HS-C/Au(x)/UiO-66 film as a solid-state sensor demonstrates its potential for application in reusable sensing devices to ensure public safety from Pb²⁺ contamination in drinking water.

Facile fabrication of amino-functionalized MIL-68(Al) metal-organic framework for effective adsorption of arsenate (As(V))

An amino-functionalized MIL-68(Al) metal–organic framework (amino-MIL-68(Al) MOF) was synthesized by solvothermal method and then characterized by FESEM, XRD, FTIR, EDX-mapping, and BET-BJH techniques. In order to predict arsenate (As(V)) removal, a robust quadratic model (R² > 0.99, F-value = 2389.17 and p value < 0.0001) was developed by the central composite design (CCD) method and then the genetic algorithm (GA) was utilized to optimize the system response and four independent variables. The results showed that As(V) adsorption on MOF was affected by solution pH, adsorbent dose, As(V) concentration and reaction time, respectively. Predicted and experimental As(V) removal efficiencies under optimal conditions were 99.45 and 99.87%, respectively. The fitting of experimental data showed that As(V) adsorption on MOF is well described by the nonlinear form of the Langmuir isotherm and pseudo-second-order kinetic. At optimum pH 3, the maximum As(V) adsorption capacity was 74.29 mg/g. Thermodynamic studies in the temperature range of 25 to 50 °C showed that As(V) adsorption is a spontaneous endothermic process. The reusability of MOF in ten adsorption/regeneration cycles was studied and the results showed high reusability of this adsorbent. The highest interventional effect in inhibiting As(V) adsorption was related to phosphate anion. The results of this study showed that amino-MIL-68(Al) can be used as an effective MOF with a high surface area (> 1000 m²/g) and high reusability for As(V)-contaminated water.

Hydroxylation of UiO-66 Metal-Organic Frameworks for High Arsenic(III) Removal Efficiency

Zirconium clusters of UiO-66 have been hydroxylated with NaOH to generate strong binding sites for As(III) species in wastewater treatment. Hydroxylated UiO-66 provides high adsorption capacity over a wide range of pH from 1 to 10 with a maximum uptake of 204 mg g^-1, which is significantly enhanced compared to those of pristine UiO-66, acid-modulated UiO-66, and other adsorbents for use in a wide pH range of treatment processes. The local structure of hydroxylated sites and As(III) adsorption mechanism are determined by extended X-ray absorption fine structure combined with density functional theory calculations.

Adsorption-Based Removal of Sb (III) from Wastewater by Graphene Oxide-Modified Zirconium-Based Metal-Organic Framework Composites

The treatment of Sb (III) wastewater produced from mining activities is uniquely challenging and has therefore garnered increasing attention. Here, an amino-modified zirconium-based metal-organic framework material (UiO-66-NH2) and its composites were loaded onto graphene oxide (GO@UiO-66-NH2) via the hydrothermal method, after which these materials were used to adsorb Sb (III) in mine wastewater. The effects of adsorption time, pH, initial Sb (III) concentration, temperature, and adsorbent dosage on the removal performance of Sb (III) were then investigated. The adsorption processes of Sb (III) were examined via adsorption kinetic, isotherm, and thermodynamic analyses. XRD, SEM, and FTIR analyses demonstrated the presence of a porous structure and high levels of oxygen-containing functional groups on the UiO-66-NH2 and GO@UiO-66-NH2 surfaces. During the Sb (III) adsorption process, the adsorption rates of UiO-66-NH2 and GO@UiO-66-NH2 were very fast in the first 10 minutes, and the adsorption equilibrium was achieved in 12 h, with the adsorption efficiencies of 91.76% and 93.79%, respectively. At a pH of 7.0, 25°C, an initial Sb (III) concentration of 100 mg/L, and an adsorbent dosage of 0.04 g/L, the maximum Sb (III) adsorption capacities of UiO-66-NH2 and GO@UiO-66-NH2 reached 39.23 mg/g and 61.07 mg/g, respectively. The adsorption process was accurately described by the Langmuir model, meaning that the Sb (III) was adsorbed through single-layer uniform adsorption. Moreover, the adsorption process was highly consistent with the pseudo-second-order model, which was indicative of spontaneous and endothermic chemical adsorption. Additionally, the Sb (III) removal efficiency could be maintained approximately 70% after sorption-desorption recycling four times. Therefore, our study provides an economical and effective method for the removal of Sb (III) in wastewater treatment.

Engineered assembly of water-dispersible nanocatalysts enables low-cost and green CO2 capture

Catalytic solvent regeneration has attracted broad interest owing to its potential to reduce energy consumption in CO₂ separation, enabling industry to achieve emission reduction targets of the Paris Climate Accord. Despite recent advances, the development of engineered acidic nanocatalysts with unique characteristics remains a challenge. Herein, we establish a strategy to tailor the physicochemical properties of metal-organic frameworks (MOFs) for the synthesis of water-dispersible core-shell nanocatalysts with ease of use. We demonstrate that functionalized nanoclusters (Fe₃O₄-COOH) effectively induce missing-linker deficiencies and fabricate mesoporosity during the self-assembly of MOFs. Superacid sites are created by introducing chelating sulfates on the uncoordinated metal clusters, providing high proton donation capability. The obtained nanomaterials drastically reduce the energy consumption of CO₂ capture by 44.7% using only 0.1 wt.% nanocatalyst, which is a ∽10-fold improvement in efficiency compared to heterogeneous catalysts. This research represents a new avenue for the next generation of advanced nanomaterials in catalytic solvent regeneration.

Catalytic solvent regeneration is of interest to reduce energy consumption in CO2 separation, however, the development of engineered nanocatalysts remains a challenge. Here, a new avenue is presented for the next generation of advanced metal-organic frameworks (MOFs) in energy-efficient CO2 capture.

Nanomaterials as adsorbents for As(III) and As(V) removal from water: A review

Freshwater demand will rise in the next couple of decades, with an increase in worldwide population growth and industrial development. The development activities, on one side, have increased the freshwater demand. However, the ground water has been degraded. Among the various organic and inorganic contaminants, arsenic is one of the most toxic elements. Arsenic contamination in ground waters is a major issue worldwide, especially in South and Southeast Asia. Various methods have been applied to provide a remedy to arsenic contamination, including adsorption, ion exchange, oxidation, coagulation-precipitation and filtration, and membrane filtration. Out of these methods, adsorption of As(III)/As(V) using nanomaterials and biopolymers has been used on a wide scale. The present review focuses on recently used nanomaterials and biopolymer composites for As(III)/As(V) sorptive removal. As(III)/As(V) adsorption mechanisms have been explored for various sorbents. The impacts of environmental factors such as pH and co-existing ions on As(III)/As(V) removal, have been discussed. Comparison of various nanosorbents and biopolymer composites for As(III)/As(V) adsorption and regeneration of exhausted materials has been included. Overall, this review will be useful to understand the sorption mechanisms involved in As(III)/As(V) removal by nanomaterials and biopolymer composites and their comparative sorption performances.

UiO-66(Zr)-derived t-zirconia with abundant lattice defect for remarkably enhanced arsenic removal

Zirconium oxide (ZrO₂) exhibits great potential in the remediation of arsenic-polluted water. In this study, tetragonal zirconium oxide (t-ZrO₂) with high lattice defects was facilely fabricated by regulating the Zr-metal-organic framework (MOF) (UiO-66) with sodium acetate modulator and examined to adsorb arsenic from water. Benefitting from the synergistic effects of mesopores structure and lattice defect, t-ZrO₂ exhibited ultrahigh adsorption capacity and faster kinetics towards both arsenate (As(V)) and arsenite (As(III)). The Langmuir adsorption capacity for As(V) and As(III) of 147.5 mg g^-1 and 352.1 mg g^-1 on t-ZrO₂ in exothermic process, respectively, significantly outperforming reported counterparts in literature (generally ≤100 mg g^-1). The faster adsorption kinetic of both As(III) and As(V) on t-ZrO₂ is defined favorably by the pseudo-second-order model over a wide pH (3-11). Furthermore, arsenic is mainly captured by t-ZrO₂ via forming Zr-O-As bonds through occupying coordinatively unsaturated zirconium atoms adsorption sites revealed by the X-ray photoelectron spectroscopy (XPS) spectrum and Fourier-transformed infrared (FTIR) spectra analysis. This study offers a new strategy for designing ultrahigh performance Zr-MOF-derived adsorbents for capturing arsenic.

Robust Al3+ MOF with Selective As(V) Sorption and Efficient Luminescence Sensing Properties toward Cr(VI)

Herein, we report the synthesis and characterization of a new robust Al³⁺ metal-organic framework MOF, [Al(OH)(PATP)]·solvent (Al-MOF-1, with PATP^2- = 2-((pyridin-2-ylmethyl)amino)terephthalate). Al-MOF-1 exhibits excellent stability from highly acidic (pH = 2) to basic (pH = 12) aqueous solutions or in the presence of oxoanionic species [As(V) and Cr(VI)]. On the contrary, the related MIL-53(Al) MOF (Al(OH) (BDC), with BDC^2- = terephthalate) shows a partial structure collapse under these conditions, signifying the superior chemical robustness of Al-MOF-1. Al-MOF-1 was proved to be an effective sorbent toward As(V) with efficient sorption capacity (71.9 ± 3.8 mg As/g), rapid sorption kinetics (equilibrium time ≤1 min), and high selectivity in the presence of various competing anions. Furthermore, Al-MOF-1 revealed high sorption capacities for Cr(VI) species in both neutral (124.5 ± 8.6 mg Cr/g) and acidic (63 ± 2 mg Cr/g) aqueous media, combining fast kinetics and relatively good selectivity. The limited porosity (BET = 38 m²/g) and small pores (2-3 Å) of the material indicate that the sorption process occurs exclusively on the external surface of Al-MOF-1 particles. The driving force for the capture of oxoanions by Al-MOF-1 is the strong electrostatic interactions between the oxoanionic species and the positively charged surface of MOF particles. Aiming at a practical wastewater treatment, we have also immobilized Al-MOF-1 on a cotton substrate, coated with polydopamine. The fabric sorbent exhibited highly effective removal of the toxic oxoanionic species from aqueous media under either batch or dynamic (continuous flow) conditions. In addition, Al-MOF-1 was found to be a promising luminescence sensor for detecting trace amounts of Cr(VI) in real water samples, with Cr(VI) being successfully detected at concentrations well below the acceptable limits (<50 ppb). Moreover, Al-MOF-1 was demonstrated to be a sufficient water sensor in organic solvents (LOD ≤0.25% v/v). All the above indicate that Al-MOF-1 represents a multifunctional material with a multitude of potential applications, such as environmental remediation, industrial wastewater treatment, chemical analysis, and water determination in biofuels.

Increased serum levels of cadmium are associated with an elevated risk of cardiovascular disease in adults

Previous studies have determined the effects of exposure to certain heavy metals on cardiovascular disease (CVD); however, the association between cadmium exposure and CVD in adults remains unclear. The relationship between serum levels of cadmium and the risk of CVD was studied by analyzing available data from 38,223 different participants of the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2016. After adjusting for all covariates, we found that higher serum cadmium concentrations were positively related to both the overall risk of CVD (odds ratio (OR): 1.45; 95% confidence interval (CI): 1.22, 1.72; p for trend <0.001) and the risks of its subtypes, including congestive heart failure, coronary heart disease, heart attack, and stroke. Elevated cadmium levels were associated with increased levels of lipids and inflammatory factors, including blood triglycerides, total cholesterol, white blood cells (WBCs), and C-reactive protein (CRP). Our study provided epidemiological evidence that cadmium may increase the risk of CVD by elevating blood lipids and inflammation.

Outstanding fluoride removal from aqueous solution by a La-based adsorbent†

A La-based adsorbent was prepared with La(NO₃)₃·6H₂O, 2-methylimidazole and DMF via amide-hydrolysis and used for fluoride decontamination from aqueous water. The obtained adsorbent was lanthanum methanoate (La(COOH)₃). The effects of pH value, initial F⁻ concentration and interfering ions on defluoridation properties of as-prepared La(COOH)₃ were assessed through batch adsorption tests. The adsorption kinetics, isotherm models and thermodynamics were employed to verify the order, nature and feasibility of La(COOH)₃ towards fluoride removal. The results imply that La(COOH)₃ is preferable for defluoridation over a wide pH range of 2 to 9 without interference. Simultaneously, the defluoridation process of La(HCOO)₃ accords to the pseudo-second order model and Langmuir isotherm, revealing chemical adsorption is the main control step. The maximum fluoride capture capacities of La(COOH)₃ at 30, 40 and 50 °C are 245.02, 260.40 and 268.99 mg g⁻¹, respectively. The mechanism for defluoridation by La(COOH)₃ was revealed by PXRD and XPS. To summarize, the as-synthesized La based adsorbent could serve as a promising adsorbent for defluoridation from complex fluoride-rich water.

A La-based adsorbent was prepared with La(NO₃)₃·6H₂O, 2-methylimidazole and DMF via amide-hydrolysis and used for fluoride decontamination from aqueous water.

Generating Catalytic Sites in UiO-66 through Defect Engineering

UiO-66 is regarded as an epitome of metal-organic frameworks (MOFs) because of its stability. Defect engineering has been used as a toolbox to alter the performance of MOFs. UiO-66 is among the most widely explored MOFs because of its capability to bear a high number of defects without undergoing structural collapse. Several representative works in the field of MOF-based defect engineering are available based on UiO-66. In this review, more emphasis is given toward the construction of catalytic sites by engineering defects in UiO-66 as a representative including all the detailed synthesis procedures for inducing defects, and the characterization techniques used to analyze these defects in UiO-66 are discussed. Furthermore, a comprehensive review for the defects themselves and the support using defects in catalysis is provided to accentuate the importance of defect engineering.

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.

Electrospun metal-organic frameworks hybrid nanofiber membrane for efficient removal of As(III) and As(V) from water

Metal-organic frameworks (MOFs) have been widely applied for pollutants removal in water. However, the powdered MOFs are always suffered from aggregation during use and difficult collection after use. These problems discount their efficiency and inhibit their reusability. In this work, Zr-based MOF (UiO-66) was successfully imprisoned into a water-stable polyacrylonitrile (PAN) substrate by electrospinning. The containing UiO-66 hybrid membrane was confirmed by instrumental characterizations and its stability was also investigated by ICP-OES analysis. The obtained composite membrane can efficiently remove both arsenite (AsIII) and arsenate (AsV) from water under natural pH conditions. The adsorption kinetic fitted well with pseudo-second-order model and was dominated by chemisorption. Its adsorption isotherm can be described by Langmuir model. The maximal adsorption capacities of the hybrid membrane for As(V) and As(III) were 42.17 mg/g and 32.90 mg/g, respectively. Our results demonstrated that the MOFs-dispersed electrospun nanofiber membrane can greatly inherit the MOFs' original adsorption properties and exhibits good regenerability without loss of MOFs. Electrospinning is an effective and practical method for the preparation of MOFs hybrid membrane, which makes the composite very easy to be collected after use.

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.

Removal of arsenic from aqueous solution by novel iron and iron-zirconium modified activated carbon derived from chemical carbonization of Tectona grandis sawdust: Isotherm, kinetic, thermodynamic and breakthrough curve modelling

The aim of the present study was: development of activated carbon modified with iron (Fe@AC) and modified with iron and zirconium (Fe-Zr@AC) from the Tectona grandis sawdust (TGS) waste biomass and its potential applicability for the removal of As (III) from contaminated water by batch and column mode. The biomass waste was pre-treated with ferric chloride (FeCl₃) and the mixture of FeCl₃ and zirconium oxide (ZrO₂) and then pyrolyzed at 500 °C for 2 h. The properties of both bioadsorbents were comprehensively characterized by using Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), Fourier transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), Particle Size analysis (PSA), point of zero charge (pH_ZPC), Brunauer-Emmett-Teller (BET) to prove successful impregnation of the Fe and Zr on the surface of AC of TGS. FTIR analysis clearly indicates the Fe and Fe-Zr complexation on biosorbents surface and biosorption of As (III). The results revealed that maximum As (III) removal was achieved 86.35% by Fe-Zr@AC (3 g/L dose, pH-7.0, temperature-25 °C and concentration 0.5 mg/L). However, maximum removal of As (III) was attained ~75% by Fe@AC (with dose-4g/L, pH-7.0, temperature-25 °C and concentration 0.5 mg/L) at the initial concentration of 0.5 mg/L of As (III). Fe-Zr@AC exhibits higher efficiency with q_max value 1.206 mg/g than Fe@AC with the q_max value 0.679 mg/g for the removal of As(III). While in the column study, Fe-Zr@AC exhibited 98.8% removal at flow rate of 5 mL/min and bed height of 5 cm. Biosorption Isotherm and Kinetics were fitted good with Langmuir isotherm (R² ≥ 0.99) and followed pseudo-second-order (R² ≥ 0.99). The regeneration study indicates that the prepared biosorbents efficiently recycled up to five cycles. Therefore, Fe@AC and Fe-Zr@AC derived from TGS has been showed to be novel, effective, and economical biosorbent. The collective benefits of easy development, good affinity towards As (III), good separability, reusability, and inexpensive of magnetized Fe@AC and Fe-Zr@AC make it a novel biosorbent. The application of Fe-Zr@AC for the removal of As (III) from the water was very efficient its concentration in the solution after treatment was found below the 10 μg/L as per the guideline WHO.

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

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