A post-functional Ti-based MOFs composite for selective removal of Pb (II) from water

Novel electrocatalytic capacitive deionization with catalytic electrodes for selective phosphonate degradation: Performance and mechanism

Phosphonate is becoming a global interest and concern owing to its environment risk and potential value. Degradation of phosphonate into phosphate followed by the recovery is regarded as a promising strategy to control phosphonate pollution, relieve phosphorus crisis, and promote phosphorus cycle. Given these objectives, an anion-membrane-coated-electrode (A-MCE) doped with Fe-Co based carbon catalyst and cation-membrane-coated-electrode (C-MCE) doped with carbon-based catalyst were prepared as catalytic electrodes, and a novel electrocatalytic capacitive deionization (E-CDI) was developed. During charging process, phosphonate was enriched around A-MCE surface based on electrostatic attraction, ligand exchange, and hydrogen bond. Meanwhile, Fe2+ and Co2+ were self-oxidized into Fe3+ and Co3+, forming a complex with enriched phosphonate and enabling an intramolecular electron transfer process for phosphonate degradation. Additionally, benefiting from the stable dissolved oxygen and high oxygen reduction reaction activity of C-MCE, hydrogen peroxide accumulated in E-CDI (158 μM) and thus hydroxyl radicals (·OH) were generated by activation. E-CDI provided an ideal platform for the effective reaction between ·OH and phosphonate, avoiding the loss of ·OH and triggering selective degradation of most phosphonate. After charging for 70 min, approximately 89.9% of phosphonate was degraded into phosphate, and phosphate was subsequently adsorbed by A-MCE. Results also showed that phosphonate degradation was highly dependent on solution pH and voltage, and was insignificantly affected by electrolyte concentration. Compared to traditional advanced oxidation processes, E-CDI exhibited a higher degradation efficiency, lower cost, and less sensitive to co-existed ions in treating simulated wastewaters. Self-enhanced and selective degradation of phosphonate, and in-situ phosphate adsorption were simultaneously achieved for the first time by a E-CDI system, showing high promise in treating organic-containing saline wastewaters.

Manganese dioxide decorated kiwi peel powder for efficient removal of lead from aqueous solutions, blood and Traditional Chinese Medicine extracts

For human health and environment safety, it is of great significance to develop novel materials with high effectiveness for removal of lead from not only aqueous solutions but also human body and traditional Chinese medicines. Here, functional kiwi peel composite, manganese dioxide decorated kiwi peel powder (MKPP), is proposed for the removal of Pb2+ effectively. The adsorption of Pb2+ in aqueous solution is a highly selective and endothermic process and kinetically follows a pseudo-second-order model, which can reach equilibrium with the capacity of 192.7 mg/g within 10 min. Comprehensive factors of hydration energy, charge-to-radius ratio and softness of Pb2+ make a stronger affinity between MKPP and Pb2+. The possible adsorption mechanism involves covalent bond, electrostatic force and chelation, etc. MKPP can be efficiently regenerated and reused with high adsorption efficiency after five cycles. Besides, MKPP can remove over 97% of Pb2+ from real water samples. MKPP can also alleviate lead poisoning to a certain extent and make the Pb level of TCM extract meet the safety standard. This work highlights that MKPP is a promising adsorbent for the removal of Pb2+ and provides an efficient strategy for reusing kiwi peel as well as dealing with the problem of Pb pollution.

Heavy metal sequestration from wastewater by metal-organic frameworks: a state-of-the-art review of recent progress

Metal-organic frameworks (MOFs) have emerged as highly promising adsorbents for removing heavy metals from wastewater due to their tunable structures, high surface areas, and exceptional adsorption capacities. This review meticulously examines and summarizes recent advancements in producing and utilizing MOF-based adsorbents for sequestering heavy metal ions from water. It begins by outlining and contrasting commonly employed methods for synthesizing MOFs, such as solvothermal, microwave, electrochemical, ultrasonic, and mechanochemical. Rather than delving into the specifics of adsorption process parameters, the focus shifts to analyzing the adsorption capabilities and underlying mechanisms against critical metal(loid) ions like chromium, arsenic, lead, cadmium, and mercury under various environmental conditions. Additionally, this article discusses strategies to optimize MOF performance, scale-up production, and address environmental implications. The comprehensive review aims to enhance the understanding of MOF-based adsorption for heavy metal remediation and stimulate further research in this critical field. In brief, this review article presents a comprehensive overview of the contemporary information on MOFs as an effective adsorbent and the challenges being faced by these adsorbents for heavy metal mitigation (including stability, cost, environmental issues, and optimization), targeting to develop a vital reference for future MOF research.

New design to enhance phosphonate selective removal from water by MOF confined in hyper-cross-linked resin

Although polymeric anion exchange resins can remove phosphonates, they lack selectivity for target phosphonates and are susceptible to interference by anions and other substances. Here, we developed a novel strategy via confining MIL-101(Fe)-NH2 inside commercial resins IRA-900 for high-efficient and precise phosphonate removal, accompanying with the improvement of the stability and recovery of MIL-101(Fe)-NH2. The obtained nanocomposite MIL-101(Fe)-NH2@IRA-900 (MFNI) exhibited significantly enhanced phosphonate removal in the presence of competing anions (Cl-, SO42-, NO3- and CO32-) and natural organic matter (humic acid) at high concentrations (2-4 times of phosphonate concentration). Moreover, MFNI displayed the highest phosphonate adsorption capacity (12.9 mg P/g) and the fastest adsorption kinetics (120 min) than hydrated ferric oxides modified IRA-900 (HFOI) (6.7 mg P/g, 180 min), MIL-101(Fe)-NH2 (7.6 mg P/g, 240 min) and IRA-900 (5.6 mg P/g, 360 min). Such higher adsorption affinity and anti-interference ability came from the synergistic effect of the host IRA-900 (hydrogen-bond interaction and electrostatic attraction) and the embedded MIL-101(Fe)-NH2 (ligand exchange). The depleted MFNI could be regenerated with a binary NaOH-NaCl solution and reused without significant loss of capacity. Column adsorption runs by using MFNI indicated the fresh MFNI could achieve 100 % removal of PPOA in 10.5 h continuously feeding, which offered the possibility of achieving potential large-scale applications. In general, a new MOF-confined design approach was practiced to achieve selective elimination of phosphates and to improve the stability and recovery of MOF.

Selective adsorption of mercury ion from water by a novel functionalized magnetic Ti based metal-organic framework composite

In the context of industrialization and severe wastewater pollution, mercury ions pose a major threat due to their high toxicity. However, traditional adsorbents and common metal-organic framework (MOF) materials have limited effectiveness. This study focuses on combining magnetic materials with functionalized titanium-based MOF composite (SNN-MIL-125(Ti)@Fe3O4) to improve mercury ion adsorption. Through comprehensive characterization and analysis, the adsorption performance and mechanism of the material were studied. The optimal adsorption of the material was achieved at pH 5, exhibiting a pseudo-second-order adsorption model and the Hill theoretical capacity of 668.98 mg/g. Hill and Tempkin models confirmed the presence of chemical and physical adsorption sites on the material surface. Thermodynamic experiments showed a spontaneous endothermic process. Despite the presence of interfering ions, the material exhibited high selectivity for mercury ions. After four cycles, adsorption performance decreased by only 8%, indicating excellent reusability. Nitrogen- and sulfur-containing functional groups played a key role in mercury ion adsorption. In conclusion, SNN-MIL-125(Ti)@Fe3O4, as a magnetic MOF adsorption material, showed potential for effective remediation of mercury-contaminated wastewater. This study contributes to the development of efficient adsorption materials and enhances the understanding of their mechanism.

Regulating steric hindrance in difunctionalized porous aromatic frameworks for the selective separation of Pb(II)

Efficient and selective removal of Pb(II) from wastewater with complex matrix remains a challenging task. Porous aromatic frameworks (PAFs) with predesigned functional building blocks provide a favorable platform for the selective separation of Pb(II). Herein, the bifunctional SPAFs with the introduction of -OH and -SO3H were synthesized through rationally optimizing their steric hindrance. As a result, the SPAF-0.75 exhibits favorable adsorption capacity of Pb(II) (212.34 mg g-1), which is 22 times larger than pristine framework. Competition experiment indicates that SPAF-0.75 possess the selective removal of Pb(II) without interfering from co-existing metal ions. The removal rate of SPAF-0.75 still retain at 100% after six successive cycles. The DFT calculation illustrates that -OH and -SO3H are co-participate in the process of capturing Pb(II), revealing SPAF-0.75 preferred removal of Pb(II) owing to the lowest adsorption energy (ΔEab = -3.99 eV). This study extend the understanding of the structure-property relationship and facilitate new possibilities for PAFs.

Lignin-modified metal-organic framework as an effective adsorbent for the removal of methyl orange

Herein, lignin-modified metal-organic frameworks (NH2-UIO@L) are prepared using a one-step synthesis as sorbents for the removal of organic dyes from water. The introduction of lignin improved the adsorption sites. NH2-UIO@L2 adsorption of MO conforms to Langmuir model, and the adsorption capacity of NH2-UIO@L2 on MO was 214.13 mg·L-1 with an adsorption efficiency up to 99.28 %, which was significantly higher than values for other adsorbents. Due to hydrogen bonds, π-π interactions and electrostatic interactions, MO was effectively removed by NH2-UIO@L2 and its adsorption efficiency is maintained at 90.55 % after six cycles. The adsorption kinetics showed that the NH2-UIO@L2 adsorption of MO was chemical adsorption and controlled by intraparticle diffusion and external mass transfer. Further, the adsorption performance of NH2-UIO@L2 on MO and MB in mixed MO/MB solution was investigated. The adsorption capacity of NH2-UIO@L2 in mixed MO/MB solution was 207.04 mg·L-1 for MO and 243.31 mg·L-1 for MB; the adsorption of NH2-UIO@L2 on MO followed the Dubinin-Radushkevich and pseudo-second-order models, and the adsorption on MB followed the Temkin and pseudo-second-order models. Hydrogen bonds, π-π interactions, and pore filling are all implicated in the removal of MO and MB. In particular, the electrostatic attraction between MB and MO improves the adsorption efficiency of NH2-UIO@L2 on MB. NH2-UIO@L2 has good reusability, maintaining an adsorption efficiency of 97.66 % for MO and up to 99.15 % for MB after six cycles. Its simple preparation and superior adsorption suggest that NH2-UIO@L2 has considerable potential to remove organic dyes from wastewater.

Tuning the Dual Active Sites of Functionalized UiO-66 for Selective Adsorption of Yb(III)

The recovery of rare earth elements (REEs) from discharged electronic devices or mineral waste water is highly essential but still facing challenges. In this work, two amino-functionalized carboxyl-UiO-66 (UiO-66-COOH-TETA and UiO-66-(COOH)₂-ED) prepared via the postmodification method were employed as the adsorbents for Yb(III) capture. The experimental results revealed their superior adsorption capacities of 161.5 and 202.6 mg/g, respectively. Meanwhile, their adsorption processes can be described by the pseudo-second-order kinetic model and Langmuir model. Effects of initial pH and temperature on adsorptions were systematically evaluated, affording an optimal operating condition (i.e., pH of 5.5-6, T of 65 °C, t of 10 h). Moreover, the fabricated materials exhibited great reusability after five adsorption-regeneration cycles. UiO-66-COOH-TETA demonstrated good separation selectivity for Yb(III) over light REEs (i.e., 3.98 of Yb/Ce, 3.51 of Yb/Nd). Based on the density functional theory calculations and characterization analysis (XPS, Zeta, mapping, and IR), the adsorption mechanisms were mainly attributed to significant electrostatic attraction and strong surface complexation between N and O sites and Yb(III).

Defective SO3H-MIL-101(Cr) for capturing different cationic metal ions: Performances and mechanisms

For broad-spectrum adsorption and capture toward cationic metal ions, a facile strategy was adopted to fabricate defective SO₃H-MIL-101(Cr) (SS-SO₃H-MIL-101(Cr)-X, X = 2, 3, 4) with enhanced vacancies using seignette salt (SS) as the modulating agent. The boosted adsorption performances of SS-SO₃H-MIL-101(Cr)-X toward eight different ions, including Ag⁺, Cs⁺, Pb²⁺, Cd²⁺, Ba²⁺, Sr²⁺, Eu³⁺ and La³⁺ in both individual component and mixed component systems, could be ascribed to the effective mass transfer resulting from the exposure of defective sites. Especially, the optimal SS-SO₃H-MIL-101(Cr)-3 could remove all the selected metal cations to below the permissible limits required by the World Health Organization (WHO) in the continuous-flow water treatment system. Furthermore, SS-SO₃H-MIL-101(Cr)-3 exhibited good adsorption capacity (189.6 mg·g^-1) toward Pb²⁺ under neutral condition and excellent desorption recirculation performance (removal efficiency > 95% after 5 cycles). Moreover, the adsorption mechanism involved the electrostatic adsorption and coordinative interactions resulting from complexation between the adsorption active sites and targeted cations (like Cr-O-M and S-O-M), which were explored systematically via both X-ray photoelectron spectroscopy (XPS) determination and density functional theory (DFT) calculations. Overall, this work provided guidance for modulating SS-SO₃H-MIL-101(Cr)-X to promote its potential application in widespread metal cations removal from wastewater.

Application of a Novel Au@ZIF-8 Composite in the Detection of Bisphenol A by Surface-Enhanced Raman Spectroscopy

Bisphenol A (BPA) is an endocrine disruptor which is widely present in fish under the influence of environmental pollution. It is essential to establish a rapid detection method for BPA. Zeolitic imidazolate framework (ZIF-8) is a typical metal-organic framework material (MOFs) with a strong adsorption capacity, which can effectively adsorb harmful substances in food. Combining MOFs and surface-enhanced Raman spectroscopy (SERS) can achieve rapid and accurate screening of toxic substances. In this study, a rapid detection method for BPA was established by preparing a new reinforced substrate Au@ZIF-8. The SERS detection method was optimized by combining SERS technology with ZIF-8. The Raman peak at 1172 cm^-1 was used as the characteristic quantitative peak, and the lowest detection concentration of BPA was as low as 0.1 mg/L. In the concentration range of 0.1~10 mg/L, the linear relationship between SERS peak intensity and the concentration of BPA was good, and R² was 0.9954. This novel SERS substrate was proven to have great potential in rapidly detecting BPA in food.

Excellent capture of Pb(II) and Cu(II) by hierarchical nanoadsorbent Fe3O4@SiO2@PAA-SO3H: A combined experimental and theoretical study

A novel magnetic nanoadsorbent (Fe₃O₄@SiO₂@PAA-SO₃H) was synthesized by grafting acrylic acid and sulfonic group to Fe₃O₄@SiO₂ using a facile cross-link technology. The adsorbent presented water-stability and biocompatibility in wastewater, which exhibited high-selectivity capture for Pb(II) and Cu(II) of 182.5 mg/g and 250.7 mg/g, respectively, at pH 6.0. Furthermore, the adsorption-desorption processes show that nanoadsorbent still retains high uptake capacity after 6 cycles, revealing structural stability and advanced recycling. Effects from other ions existed weak interference in removal of Pb(II) and Cu(II). Meanwhile, the mechanism was further analyzed from both electrostatic potential (ESP) and average local ionization energy (ALIE) based on the density functional theory (DFT). The results indicate that interaction among nanoadsorbent and heavy metal ions is bridged by oxygen active sites. As the Fe₃O₄@SiO₂@PAA-SO₃H adsorbent is a hierarchical, highly water-dispersible and biocompatible adsorbent, it is a potential new treatment option for wastewater.

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.

Efficient Removal of Pb2+ from Water by Bamboo-Derived Thin-Walled Hollow Ellipsoidal Carbon-Based Adsorbent

Lead ion (Pb²⁺) is one of the most common water pollutants. Herein, with bamboo as the raw material, we fabricate a thin-walled hollow ellipsoidal carbon-based adsorbent (CPCs900) containing abundant O-containing groups and carbon defects and having a specific surface area as large as 730.87 m² g^-1. CPCs900 shows a capacity of 37.26 mg g^-1 for adsorbing Pb²⁺ in water and an efficiency of 98.13% for removing Pb²⁺ from water. This is much better than the activated carbon commonly used for removing Pb²⁺ from water (12.19 mg g^-1, 30.48%). The bond interaction of Pb²⁺ with the O-containing groups on CPCs900 and the electrostatic interaction of Pb²⁺ with the electron-rich carbon defects on CPCs900 could be the main forces to drive Pb²⁺ adsorption on CPCs900. The outstanding adsorption performance of CPCs900 could be due to the abundant O-containing groups and carbon defects as well as the large specific surface area of CPCs900. Bamboo has a large reserve and a low price. The present work successfully converts bamboo into adsorbents with outstanding performances in removing Pb²⁺ from water. This is of great significance for meeting the huge industrial demand on highly efficient adsorbents for removing toxic metal ions from water.