Heavy metal ions' poisoning behavior-inspired etched UiO-66/CTS aerogel for Pb(II) and Cd(II) removal from aqueous and apple juice

Multifunction hydrogen-bonded organic framework aerogel platform for detection and removal of heavy metal ions in pear juice

Heavy metal ions (HMIs) in food pose significant health risks due to their bioaccumulation and toxicity, necessitating effective detection and remediation methods. This study explores a multifunctional hydrogen-bonded organic framework (HOF-16) wrapped in sodium alginate (SA) to form a stable HOF-16/SA aerogel for detecting and removing HMIs in pear juice. The HOF-16 fluorescence probe exhibits excellent sensitivity with limits of detection of 0.49, 0.60, and 0.44 μmol/L for Pb(II), Cu(II), and Cd(II), respectively. The maximum adsorption capacities of HOF-16/SA aerogel for Pb(II), Cu(II), and Cd(II) are 284.69, 248.08, and 183.94 mg/g, respectively. The removal efficiency of HOF-16/SA aerogel for HMIs in pear juice exceeds 98 % without negative impacts. Sensitive detection of HMIs is attributed to the fluorescence quenching effect caused by electron transfer, while electrostatic interactions and complexation enhance the effective adsorption performance. This study provides a HOF-aerogel platform with great potential for detecting and removing HMIs from food matrix.

Intelligent sensing platform based on europium-doped carbon dots for dual-functional detection of ciprofloxacin/Ga3+ and its tracking in vivo

Ciprofloxacin (CIP) and gallium (Ga) are widely used in many fields and their excessive presences will pose serious threats to the environment and life health. Therefore, developing an intelligent detection method for rapidly tracking and determination of CIP and Ga3⁺ concentration in environments and organisms is of great significance. In this work, a europium-doped carbon dots (Eu-CDs) with unique structure and performances was prepared by a one-pot hydrothermal method. Eu-CDs can efficiently overcome the problem of aggregation-induced fluorescence quenching in complex environments to track CIP and Ga3⁺ with highly sensitivity. The "antenna effect" of non-radiative energy transfer is introduced to explain the pathway on fluorescence transition of Eu-CDs through DFT theoretical calculations and mechanism investigations, which provide a theoretical basis for the design and development of novel carbon dots with specific functions. Eu-CDs can successfully be applied to fluorescence imaging in organisms, moreover, it also exhibits excellent application potentials in the field of anti-tumor and antibacterial. In addition, a portable intelligent detection platform based on Eu-CDs-hydrogel device have been developed, which provides a new strategy for rapidly detection of CIP and Ga3⁺ in real samples.

Synergistic and simultaneous removal of heavy metal ions over waste bamboo shoot particles encapsulated carboxymethyl cellulose/gelatin composite hydrogel

Carboxymethyl cellulose (CMC) hydrogels are commonly used for heavy metal removal due to their abundant hydroxyl and carboxyl groups. However, pristine CMC hydrogels always suffer from low gel strength and limited adsorption properties in large-scale applications. In this study, to improve the gel strength and heavy metal ions removal capacity, fish gelatin and bamboo shoot particle (BSP) were introduced to CMC hydrogels, respectively. The formation of the composite hydrogel with enhanced gel strength was primarily driven by hydrogen bonding, which exhibited an increase strain resistance with a critical strain value up to 214.68 %. As expected, the composite hydrogel can effectively remove Cd2+, Hg2+, and Pb2+ from aqueous solutions simultaneously. The physical adsorption process of heavy metals by the composite hydrogel was well described by the pseudo-second-order kinetic model, while the Langmuir model indicated maximum adsorption capacities of 147.7 mg/g for Cd2+, 88.62 mg/g for Hg2+, and 163.89 mg/g for Pb2+. Notably, the composite hydrogel exhibited enhanced recyclability, maintaining its efficacy for up to at least five cycles. This study underscores the potential of using naturally occurring biodegradable materials for the removal of heavy metals, and paved ways for heavy metal removal at industrial levels.

Metal-Organic Framework and Covalent-Organic Framework-Based Aerogels: Synthesis, Functionality, and Applications

Metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs)-based aerogels are garnering significant attention owing to their unique chemical and structural properties. These materials harmoniously combine the advantages of MOFs and COFs-such as high surface area, customizable porosity, and varied chemical functionality-with the lightweight and structured porosity characteristic of aerogels. This combination opens up new avenues for advanced applications in fields where material efficiency and enhanced functionality are critical. This review provides a comparative overview of the synthetic strategies utilized to produce pristine MOF/COF aerogels as well as MOF/COF-based hybrid aerogels, which are functionalized with molecular precursors and nanoscale materials. The versatility of these aerogels positions them as promising candidates for addressing complex challenges in environmental remediation, energy storage and conversion, sustainable water-energy technologies, and chemical separations. Furthermore, this study discusses the current challenges and future prospects related to the synthesis techniques and applications of MOF/COF aerogels.

Selective adsorption of oxidized yeast glucan for Pb2+: Influencing factors, adsorption site and mechanism

This work investigated the influencing factors and mechanism of Pb2+ adsorbed by oxidized yeast glucan (OYG). Firstly, OYG showed greater Pb2+ adsorption performance than yeast glucan, and the adsorption capacity was greater with the oxidation degree increased. The optimal pH range for Pb2+ adsorption was 6-7. The adsorption capacity of Pb2+ reached its maximum of 86.68 and 96.88 mg/g for 20 mg of OYG1 and OYG2, respectively. In addition, OYG exhibited selective adsorption, with adsorption capacity in the order: Pb2+ > Cd2+ > Cu2+ > Ca2+. Then adsorption isotherm was established by fitting Langmuir and Freundlich isotherm adsorption models. Freundlich model could better fit the adsorption process of lead by OYG, indicating that the adsorption process was heterogeneous. According to the Langmuir model, the maximum lead adsorption capacities of OYG1 and OYG2 at 298 K were 100.70 and 131.06 mg/g, respectively. Thermodynamic data indicated a spontaneous endothermic process (ΔG < 0, ΔH > 0), accompanied by increased system disorder (ΔS > 0), involving physical and chemical adsorptions. Finally, FT-IR and XPS results revealed -COOH and -OH were the primary adsorption sites in OYG, and the interaction between these groups and Pb2+ was mainly achieved by electrostatic interaction (or ion-dipole interaction).

Defect-Engineered MOF-801/Sodium Alginate Aerogel Beads for Boosting Adsorption of Pb(II)

Metal-organic frameworks (MOFs) are attractive adsorbents for heavy metal capture due to their superior stability, easy modification, and adjustable pore size. However, their inherent microporous structure poses challenges in achieving a higher adsorption capacity. Defect engineering is considered a simple method to create hierarchical MOFs with larger pores. Here, we employed l-aspartic acid as a mixed linker to bind Zr4+ clusters in competition with fumaric acid of MOF-801 to create defects, and the pore size was increased from 4.66 to 15.65 nm. Mercaptosuccinic acid was subsequently used as a postexchange ligand to graft the resultant MOF-801 by acid-ammonia condensation to further expand the pore size to 22.73 nm. Notably, the -NH2, -COOH, and -SH groups contributed by these two ligands increased the adsorption sites for Pb(II). The obtained defective MOF-801 with larger pores was thereafter loaded onto sodium alginate to form aerogel beads as adsorbents, and an adsorption capacity of 375.48 mg/g for Pb(II) was achieved, which is ∼51 times that of pristine MOF-801. The aerogel beads also exhibited outstanding reusability with a removal efficiency of ∼90.23% after 5 cycles of use. The adsorption mechanism of Pb(II) included ion-exchange interaction, as well as chelation interactions of Pb-O, Pb-NH2, and Pb-S. The versatile combination of defect engineering and composite beads provides novel inspirations for MOF modification for boosting heavy metal adsorption.

Recent Progress in MOF-Aerogel Fabrication and Applications

Recent advancements in metal-organic frameworks (MOFs) underscore their significant potential in chemical and materials research, owing to their remarkable properties and diverse structures. Despite challenges like intrinsic brittleness, powdered crystalline nature, and limited stability impeding direct applications, MOF-based aerogels have shown superior performance in various areas, particularly in water treatment and contaminant removal. This review highlights the latest progress in MOF-based aerogels, with a focus on hybrid systems incorporating materials like graphene, carbon nanotube, silica, and cellulose in MOF aerogels, which enhance their functional properties. The manifold advantages of MOF-based aerogels in energy storage, adsorption, and catalysis are discussed, with an emphasizing on their improved stability, processability, and ease of handling. This review aims to unlock the potential of MOF-based aerogels and their real-world applications. Aerogels are expected to reshape the technological landscape of MOFs through enhanced stability, adaptability, and efficiency.

Synergistic Etching and Hydrogen Bonding-Induced Self-Assembly of MXene/MOF Hybrid Aerogel for Flexible Room-Temperature Gas Sensing

Limited by insufficient active sites and restricted mechanical strength, designing reliable and wearable gas sensors with high activity and ductility remains a challenge for detecting hazardous gases. In this work, a thermally induced and solvent-assisted oxyanion etching strategy was implemented for selective pore opening in a rigid microporous Cu-based metal-organic framework (referred to as CuM). A conductive CuM/MXene aerogel was then self-assembled through cooperative hydrogen bonding interactions between the carbonyl oxygen atom in PVP grafted on the surface of defect-rich Cu-BTC and the surface functional hydroxyl group on MXene. A flexible NO2 sensing performance using the CuM/MXene aerogel hybridized sodium alginate hydrogel is finally achieved, demonstrating extraordinary sensitivity (S = 52.47 toward 50 ppm of NO2), good selectivity, and rapid response/recovery time (0.9/4.5 s) at room temperature. Compared with commercial sensors, the relative error is less than 7.7%, thereby exhibiting significant potential for application in monitoring toxic and harmful gases. This work not only provides insights for guiding rational synthesis of ideal structure models from MOF composites but also inspires the development of high-performance flexible gas sensors for potential multiscenario applications.

Conversion of Phosphogypsum into Porous Calcium Silicate Hydrate for the Removal and Recycling of Pb(II) and Cd(II) from Wastewater

The discharge of lead and cadmium wastewater, along with the pollution caused by phosphogypsum, represents a particularly urgent environmental issue. This study employed a straightforward hydrothermal method to convert phosphogypsum into porous calcium silicate hydrate (P-CSH), which was then used to remove and recover Pb(II) and Cd(II) from wastewater. The adsorption capacities of P-CSH for Pb(II) and Cd(II) were notably high at 989.3 mg/g and 290.3 mg/g, respectively. The adsorption processes adhered to the pseudo-second-order kinetics model and the Langmuir isotherm model. Due to identical adsorption sites on P-CSH for both Pb(II) and Cd(II), competitive interaction occurred when both ions were present simultaneously. Additionally, the adsorption efficacy was minimally impacted by the presence of common coexisting cations in wastewater. The dominant mechanisms for removing Pb(II) and Cd(II) via P-CSH were chemical precipitation and surface complexation. Moreover, the adsorbed heavy metals were efficiently separated and reclaimed from the wastewater through a stepwise desorption process. The primary components of the residue from stepwise desorption were quartz and amorphous SiO2. Following dissolution via pressurized alkaline leaching, this residue could be recycled for synthesizing P-CSH. This research offered a new strategy for the resourceful use of phosphogypsum and heavy metal wastewater.

Lanthanide MOFs based portable fluorescence sensing platform: Quantitative and visual detection of ciprofloxacin and Al3

In the current context of water environmental monitoring and pollution control, there's a crucial need for rapid and simple methods to detect multi-pollutant. We herein report an easy one-step hydrothermal synthesis method to produce Eu-based metal-organic frameworks (Eu MOFs), which was used as a fluorescent probe to detect the aquatic environmental pollutants of ciprofloxacin (CIP) and aluminum ions (Al3+). This fluorescent sensor enabled the cascade detection of CIP and Al3+ through fluorescence enhancement and ratio fluorescence response, respectively. The introduction of CIP significantly turned on the characteristic fluorescence of Eu MOFs at 595 nm and 616 nm through the "antenna effect". Based on this, the sensor enables quantitative detection of CIP within a linear range of 0-120 μM with a LOD as low as 50.421 nM. In the presence of Al3+, the fluorescence emission of Eu MOFs-CIP was sharply turned off due to strong Al3+ coordination with CIP, while the blue fluorescence emission of CIP was remarkably enhanced. And thus allowing ratio fluorescence quantitative detection of Al3+ (LOD = 2.681 μM). The introduction of CIP and Al3+ in cascade resulted in distinct fluorescence color changes from colorless to red and eventually to blue, exhibiting pronounced fluorescence characteristics. This observable phenomenon enables the visual detection of CIP and Al3+ in both aqueous phase and paper test strips. By combining the analysis of fluorescence chromaticity with the use of a smartphone, the fluorescence color of test papers allows for simple quantitative determination, which provides a convenient and accessible approach for quantifying CIP and Al3+ in water environments.

Nano‑selenium functionalized chitosan gel beads for Hg(II) removal from apple juice

The presence of potentially toxic elements and compounds poses threats to the quality and safety of fruit juices. Among these, Hg(II) is considered as one of the most poisonous heavy metals to human health. Traditional chitosan-based and selenide-based adsorbents face challenges such as poor adsorption capacity and inconvenient separation in juice applications. In this study, we prepared nano‑selenium functionalized chitosan gel beads (nanoSe@CBs) and illustrated the synergistic promotions between chitosan and nanoSe in removing Hg(II) from apple juice. The preparation conditions, adsorption behaviors, and adsorption mechanism of nanoSe@CBs were systematically investigated. The results revealed that the adsorption process was primarily controlled by chemical adsorption. At the 0.1 % dosage, the adsorbent exhibited high uptake, and the maximum adsorption capacity from the Langmuir isotherm model could reach 376.5 mg/g at room temperature. The adsorbent maintained high adsorption efficiency (> 90 %) across a wide range of Hg(II) concentrations (0.01 to 10 mg/L) and was unaffected by organic acids present in apple juice. Additionally, nanoSe@CBs showed negligible effects on the quality of apple juice. Overall, nanoSe@CBs open up possibilities to be used as a safe, low-cost and highly-efficient adsorbent for the removal of Hg(II) from juices and other liquid foods.

Carrageenan-based multifunctional packaging films containing Zn-carbon dots/anthocyanin derived from Kohlrabi peel for monitoring quality and extending the shelf life of shrimps

Carrageenan-based active/intelligent packaging films containing anthocyanin and ZnO-doped CD (Zn-CD) from purple Kohlrabi peels were prepared for freshness monitoring and shelf-life extension of shrimp, and the influence of additives on the films' physical, functional, and structural properties was investigated. The films showed excellent UV blocking ability (85.2% of UV-A and 99.4% of UV-B) and high antioxidant effect (∼99% for ABTS and ∼ 58.6% for DPPH radical scavenging activity) and showed strong antibacterial activity to stop the growth (100%) of L. monocytogenes and to reduce the growth of E. coli by 8.1 log CFU/mL after 12 h of incubation. In shrimp packaging experiments, the films were evident in the freshness monitoring, reduced spoilage, and increased shelf life. This study suggests that next-generation biopolymer films impregnated with biomass-derived CDs and natural colorants will provide broad directions for ensuring safety and extending shelf life to meet the accelerating demand for packaging products.

PVA/PAA/DMTD electrospun nanofibrous membrane for the selective adsorption of Pb(II) ions in liquid foods

Lead (Pb(II)) contamination is common in liquid foods and can result from Pb(II) being present in the raw materials or during handling processes. However, due to the complexity of food matrices, there is limited data available concerning Pb(II) ion removal from food sources. This study focused on fabricating a PVA/PAA/DMTD electrospun nanofibrous membrane (ENFM) to efficiently and selectively remove Pb(II) ions from liquid foods. The PVA/PAA/DMTD ENFM had a maximum adsorption capacity of 138.3 mg/g for Pb(II) ions and demonstrated high selectivity toward the removal of Pb(II) ions. Negative values of the Gibbs free energy (ΔG°) showed that the spontaneous nature of the adsorption process was feasible at different temperatures. Moreover, it successfully removed Pb(II) ions from selected samples of commercially available drinks. Therefore, this adsorbent exhibits significant potential for removing Pb(II) ions from liquid food products, thereby reducing daily dietary exposure to Pb(II).

Current technologies for heavy metal removal from food and environmental resources

Exposure to heavy metals in water and food poses a significant threat to human well-being, necessitating the efficient removal of these contaminants. The process of urban development exacerbates heavy metal pollution, thereby increasing risks to both human health and ecosystems. Heavy metals have the capacity to enter the food chain, undergo bioaccumulation and magnify, ultimately resulting in adverse effects on human health. Therefore, implementing effective pollution control measures and adopting sustainable practices are crucial for mitigating exposure and associated health risks. Various innovative approaches, including adsorption, ion exchange, and electrochemical technology, are currently being actively investigated to cope with the issue of heavy metal contamination. These innovative methods offer benefits such as efficient recycling, cost-effectiveness and environmental friendliness. In this review, we summarize recent advances for removing heavy metals from water, soil and food, providing valuable guidance for environmental engineers and researchers seeking to address contamination challenges.

A portable sensor for glucose detection in Huangshui based on blossom-shaped bimetallic organic framework loaded with silver nanoparticles combined with machine learning

In this work, we propose a blossom-like Ni, Co bimetallic metal-organic framework (NiCo-MOF) synthesized hydrothermally and decorated with silver nanoparticles (AgNPs) via chemical reduction for electrochemical enzyme-free glucose sensing. The NiCo-MOF nanostructures had large specific surface area and good sensing performance. The AgNPs enhanced the electrochemical performance of the MOF, resulting in excellent electrochemical activity. The sensor exhibited sensitivities of 1191.84 and 271.19 μA mM-1 cm-2 in the linear ranges of 0.005-1.125 and 1.525-5.325 mM, respectively, with a detection limit of 2.3 μM. The sensor was successfully applied for glucose determination in Huangshui (HS) using an artificial neural network as machine learning (ML) model. The R2 value near 1, low RMSE, and high RPD values of the proposed ML model demonstrate its excellent fitting and prediction performance. This will provide a fast and portable intelligent sensing analysis technology for the detection of glucose in HS.

A novel hydrangea-like magnetic composite Fe3O4@MnO2@ZIF-67 for efficient selective adsorption of Pd(II) from metallurgical wastewater

The selective adsorption of palladium from wastewater is a feasible solution to solving palladium pollution and resource scarcity. Because traditional solvent extraction methods often involve the use of considerable amounts of organic solvents, research is focused on investigating adsorption techniques that can selectively remove palladium from wastewater. In this paper, the magnetic composite Fe3O4@MnO2@ZIF-67 was synthesized and its performance for the adsorption of Pd(II) in acidic water was investigated. Fe3O4@MnO2@ZIF-67 was characterized by various analytical methods such as TEM, SEM, EDS, BET, XRD, FTIR, zeta potential analysis, VSM, and TGA. The effects of palladium ion concentration, contact time, pH, and temperature on adsorption were evaluated. The kinetics were shown to follow the pseudo-second-order kinetic model and Elovich model, and the rate-limiting step was chemisorption. Thermodynamic studies showed that increasing the temperature promoted the adsorption of Pd(II), and the maximum uptake capacity of Fe3O4@MnO2@ZIF-67 for Pd(II) was 531.91 mg g-1. Interestingly, Fe3O4@MnO2@ZIF-67 exhibited superior selectivity for Pd(II) in the presence of Ir(IV), Pt(IV), and Rh(III). The adsorbent can be used repeatedly for selective adsorption of palladium. Even at the fifth cycle, the uptake rate of Pd(II) remained as high as 83.1%, and it showed a favorable adsorption capacity and selectivity for Pd(II) in real metallurgical wastewater. The adsorption mechanism was analyzed by SEM, FTIR, XRD, XPS, and DFT calculations, which indicated that electrostatic interactions and coordination with nitrogen-containing groups were involved. Fe3O4@MnO2@ZIF-67 is a promising adsorbent for the efficient adsorption and selective separation of palladium ions.

Remediation of Cu and As contaminated water and soil utilizing biochar supported layered double hydroxide: Mechanisms and soil environment altering

Preparing materials for simultaneous remediation of anionic and cationic heavy metals contamination has always been the focus of research. Herein a biochar supported FeMnMg layered double hydroxide (LDH) composites (LB) for simultaneous remediation of copper and arsenic contamination in water and soil has been assembled by a facile co-precipitation approach. Both adsorption isotherm and kinetics studies of heavy metals removal by LB were applied to look into the adsorption performance of adsorbents in water. Moreover, the adsorption mechanisms of Cu and As by LB were investigated, showing that Cu in aqueous solution was removed by the isomorphic substitution, precipitation and electrostatic adsorption while As was removed by complexation. In addition, the availability of Cu and As in the soil incubation experiments was reduced by 35.54%-63.00% and 8.39%-29.04%, respectively by using LB. Meanwhile, the addition of LB increased the activities of urease and sucrase by 93.78%-374.35% and 84.35%-520.04%, respectively, of which 1% of the dosage was the best. A phenomenon was found that the richness and structure of microbial community became vigorous within 1% dosage of LB, which indirectly enhanced the passivation and stabilization of heavy metals. These results indicated that the soil environment was significantly improved by LB. This research demonstrates that LB would be an imaginably forceful material for the remediation of anionic and cationic heavy metals in contaminated water and soil.

Fe3O4@uio66 core-shell composite for detection of electrolyte leakage from lithium-ion batteries

Fe₃O₄is an environmentally friendly gas sensing material with high response, but the cross-response to various analytes and poor thermal stability limit its practical applications. In this work, we prepared Fe₃O₄@uio66 core-shell composite via a facile method. The selective response to volatile organic compounds, especially to electrolyte vapors of lithium-ion batteries, as well as long-term stability of Fe₃O₄@uio66 has been dramatically enhanced compared to pure Fe₃O₄, due to the preconcentrator feature and thermal stability of the uio66 thin shell. Real-time detection of electrolyte leakage for an actual punctured lithium-ion battery was further demonstrated. The Fe₃O₄@uio66 sensor, after aging for 3 months, was able to detect the electrolyte leakage in 30 s, while the voltage of the punctured battery was maintained at the same level as that of a pristine battery over 6 h. This practical test results verified ability of the Fe₃O₄@uio66 sensor with long-term aging stability for hours of early safety warning of lithium-ion batteries.

Highly efficient Cd(Ⅱ) removal using 3D N-doped carbon derived from MOFs: Performance and mechanisms

Cadmium (Cd) removal is imperative to ensure the safety of aquatic-ecosystem, yet its effective removal technology has remained elusive by far. To address this concern, three-dimensional N-doped carbon (NC) polyhedrons affording ample porosity is fabricated based upon the thermal carbonization and KOH activation of zeolitic imidazolate framework-8 (ZIF-8) precursor. Thus-derived activated NC (a-NC) adsorbent not only overcomes the inherent instability of ZIF-8 but also harvests a maximum Cd(Ⅱ) adsorption capacity of 370.2 mg g^-1, which evidently surpasses those of bare NC counterpart as well as previously reported adsorbents. Impressively, a-NC achieves ca. 100% removal of aqueous Cd(Ⅱ) in a broad working pH range (5-9), and particularly attains stable performances (81-92%) in various realistic water. Theoretical calculations in combination with experimental characterizations further offer mechanistic insight into the enhanced removal exerted by a-NC. Notably, owing to the increased specific surface area (3041 vs. 389 m² g^-1) and enhanced sp² carbon content (91.7 vs. 68.8%) of a-NC as compared to NC, advanced Cd(Ⅱ) adsorption via a-NC can be exhibited. Our designed a-NC material harnessing favorable recycling capability would be in particular attractive in the realm of practical Cd(Ⅱ) remediation.

Porphyrin-Based Conjugated Microporous Polymers for Highly Efficient Adsorption of Metal Ions

The capture and elimination of anions and cations from water have attracted a great deal of attention and are quite vital for clean production and environmental remediation. In this work, we present the synthesis of four porphyrin (Por)-based conjugated microporous polymers (CMPs, namely, Por-CMP-1-4), which were produced through a Sonogashira-Hagihara linked response using porphyrin and acetylene aromatic compounds as building blocks and used as absorbents to eliminate metal ions from water. The as-synthesized Por-CMP-1-4 exhibit an amorphous porous structure and outstanding caloric and physicochemical properties. Taking advantage of their larger specific surface areas, i.e., 541.47, 614.58, 382.38, and 677.90 m² g^-1 for Por-CMP-1-4, respectively, and their chelating active site that originated from the porphyrin ring, Por-CMP-1-4 show better Zn²⁺, Cu²⁺, and Pb²⁺ adsorption ability. Among them, Por-CMP-3 has the greatest adsorbability of 640 mg g^-1 for Zn²⁺, with an adsorption efficiency of 80%, whereas its adsorption capacities for Cu²⁺ and Pb²⁺ ions were both 334 mg g^-1, with an adsorption efficiency of 42% for Cu²⁺ and Pb²⁺. Employing Por-CMP-3 as a representative example, its adsorption kinetics has been systematically investigated. The adsorption behavior of Por-CMP-3 with respect to the Zn²⁺ ion is shown to exhibit pseudo-first-order kinetics and Langmuir isotherm modes. Meanwhile, the adsorption mechanism is discussed in detail, and it was thought it might be chelation, in which the nitrogen atoms with a single pair of electrons on the porphyrin ring interacted with metal ions to form stable chelation coordination bonds, thus removing metal ions selectively and effectively. Furthermore, Por-CMP-3 exhibited good reusability, retaining 60% of its Zn²⁺ removal rate after four continuous adsorptions.

Self-propelled nanomotors based on hierarchical metal-organic framework composites for the removal of heavy metal ions

The outstanding performance efficiency for the removal of heavy metal ions in solution is governed by various factors: (a) sufficient contact probability between heavy metal ions and the adsorbent, (b) convenient diffusion/accessibility of heavy metal ions to the surface and the interior of the adsorbent, and (c) abundant binding sites for heavy metal ions on the adsorbent. We designed an efficient MnFe₂O₄ @MIL-53 @UiO-66 @MnO₂ adsorbent for Pb(II) and Cd(II) removal. The adsorbents were fabricated by merging self-propelled nanomotors, exploiting hierarchical structure, and using a metal-organic framework (MOF) composite to simultaneously meet the three requirements. The sufficient contact probability between Pb(II)/Cd(II) and MnFe₂O₄ @MIL-53 @UiO-66 @MnO₂ was achieved via the self-propelled movement of MnFe₂O₄ @MIL-53 @UiO-66 @MnO₂ which was induced by the catalytic decomposition of H₂O₂ by MnO₂. The convenient diffusion/accessibility of Pb(II)/Cd(II) on the surface and interior of MnFe₂O₄ @MIL-53 @UiO-66 @MnO₂ was achieved by exploiting the properties of the hierarchical structure of MnFe₂O₄ @MIL-53 @UiO-66 @MnO₂. Abundant binding sites (-COOH) on MIL-53 and UiO-66 composites were present for the binding of the Pb(II)/Cd(II) ions to the adsorbent. The adsorption capacities of the nanomotor adsorbent for Pb(II) and Cd(II) were 1018 and 440.8 mg g^-1 at 25 °C, respectively. Additionally, the complex formed of MnFe₂O₄ and MIL-53 endowed the adsorbent with easy-recyclable properties under the influence of an external magnet. The nanomotors exhibit satisfactory removal performances for Pb(II) and Cd(II).

Improper Estimation of Thermodynamic Parameters in Adsorption Studies with Distribution Coefficient KD (qe/Ce) or Freundlich Constant (KF): Considerations from the Derivation of Dimensionless Thermodynamic Equilibrium Constant and Suggestions

Adsorption processes often include three important components: kinetics, isotherm, and thermodynamics. In the study of solid–liquid adsorption, “standard” thermodynamic equilibrium constant $\left(K_{\text{Eq}}^{\text{o}}\right.$ ; dimensionless) plays an essential role in accurately calculating three thermodynamic parameters: the standard Gibbs energy change (∆G°; kJ/mol), the standard change in enthalpy (∆H°; kJ/mol), and the standard change in entropy [∆S°; J/(mol × K)] of an adsorption process. Misconception of the derivation of the $K_{\text{Eq}}^{\text{o}}$ constant that can cause calculative errors in values (magnitude and sign) of the thermodynamic parameters has been intensively reflected through certain kinds of papers (i.e., letters to editor, discussions, short communications, and correspondence like comment/rebuttal). The distribution coefficient (KD) and Freundlich constant (KF) have been intensively applied for calculating the thermodynamic parameters. However, a critical question is whether KD or KF is equal to $K_{\text{Eq}}^{\text{o}}$ . This paper gives (1) thorough discussion on the derivation of thermodynamic equilibrium constant of solid–liquid adsorption process, (2) reasonable explanation on the inconsistency of (direct and indirect) application of KD or KF for calculating the thermodynamic parameters based on the derivation of $K_{\text{Eq}}^{\text{o}}$ , and (3) helpful suggestions for improving the quality of papers published in this field.

Research progress in the removal of heavy metals by modified chitosan

Chitosan and its modifiers have been widely studied for their good biocompatibility and excellent adsorption properties for heavy metal ions. The synthesis and application of modified chitosan, the effects of process variables (such as pH, amount of adsorbent, temperature, contact time, etc.), adsorption kinetics, thermodynamics and the adsorption mechanism on the removal of heavy metal ions are reviewed. The purpose is to provide the latest information about chitosan as adsorbent and to promote the synthesis of modified chitosan and its application in the removal of heavy metals.

Magnetic solid-phase extraction based on zirconium-based metal-organic frameworks for simultaneous enantiomeric determination of eight chiral pesticides in water and fruit juices

A novel multi-residue method, magnetic solid-phase extraction combined with LC-MS/MS, was proposed for simultaneous enantiomeric determination of eight chiral pesticides in water and fruit juices. Fe₃O₄@C@UiO-66 was firstly used to extract and enrich pesticides, showing excellent adsorption capacity, which was proved by adsorption kinetic and thermodynamic experiments. Multiple extraction parameters were optimized by Plackett-Burman and Box-Behnken design. Under optimized conditions, good linearity (1.0-200 ng L^-1, R² ≥ 0.9953) for all analytes, detection limits (0.10 to 0.35 ng L^-1), quantitation limits (0.35 to 1.00 ng L^-1), recoveries (83.68-95.99%), and precision (intra-day RSD ≤ 7.06%, inter-day RSD ≤ 9.40%) were obtained, meeting the requirements of pesticides residues analysis. It is worth mentioning that eight chiral pesticides can be separated quickly within 19 min. The above results indicate that the proposed method with satisfactory sensitivity and accuracy has the potential for routine analysis of chiral pesticide residues in aqueous samples.

Passivation of multiple heavy metals in lead-zinc tailings facilitated by straw biochar-loaded N-doped carbon aerogel nanoparticles: Mechanisms and microbial community evolution

Heavy metal (HM) soil pollution has become an increasingly serious problem with the development of industries. Application of biochar in HMs remediation from contaminated environment has attracted considerable research attention during the past decade. Although the mechanism of HMs passivation with biochar has been investigated, effects and mechanisms of interaction among soil-indigenous microbes and novel carbon matrix composites for HMs adsorption and passivation are still unclear. Four different biochar-loaded aerogels, namely, BNCA-1-600, BNCA-1-900, BNCA-2-600, and BNCA-2-900, were synthesized in this study. Adsorption capacity of four kinds of synthetic materials and two types of contrast biochars (BC600 and BC900) to HMs in aqueous solution, passivation capacity of HMs in soil, and effects on soil organic matter and microbial community were explored. Results showed that BNCA-2-900 exhibits excellent adsorption property and a maximum removal capacity of 205.07 mg·g^-1 at 25 °C for Pb(II), 105.56 mg·g^-1 for Cd(II), and 137.89 mg·g^-1 for Zn(II). Leaching concentration of HMs in contaminated soil can meet the national standard of China (GB/T 5085.3-2007) within 120 days. Results of this study confirmed that the additive BNCA-2-900 and coexistence of indigenous microorganisms can effectively reduce bioavailability of HMs. Another potential mechanism may be to remove the passivation of HMs by porous structure and surface functional groups as well as improve the content of organic matter and microbial abundance. The research results may provide a novel perceptive for the development of functional materials and strategies for eco-friendly and sustainable multiple HMs remediation in contaminated soil and water by using a combination of carbon matrix composites and soil-indigenous microorganisms.

Emitter-Quencher Pair of Single Atomic Co Sites and Monolayer Titanium Carbide MXenes for Luminol Chemiluminescent Reactions

A facile, one-step doping protocol was adopted to synthesize Co single atomic site catalysts (SASCs) in UiO-66 metal-organic frameworks. In view of highly uniform active sites of Co-O₆ moieties, the SASCs specifically contribute to catalyzing the generation of a large amount of singlet oxygen instead of superoxide or hydroxyl radicals, which endows Co SASCs with a the remarkable enhancement effect (∼3775 times) on luminol chemiluminescent (CL) emission. Interestingly, monolayer titanium carbide MXenes can drastically quench the CL signal of the Co SASC-boosted luminol reaction by ∼94.6% as highly efficient luminescent absorbents. Furthermore, the emitter-quencher pair of Co SASCs and titanium carbide MXenes was successfully adopted to develop an immunoassay method for cardiac troponin I (cTnI) on an immunochromatographic test strip platform. With a sandwich immunoreaction mode, a titanium carbide MXene-labeled cTnI tracer antibody was captured on the test line of a test strip, which significantly inhibited the CL response of the Co SACs-boosted luminol system. The dynamic range for quantitating cTnI is 1.0-100 pg mL^-1, with a detection limit of 0.33 pg mL^-1 (3σ). The test strip was successfully used to detect cTnI in human serum samples collected from cardiopathy patients. This proof-of-principle work manifests both the CL enhancement of SASCs and the quenching behavior of MXenes, which shows the thrilling prospects of combinational usage of the two functionalized nanomaterials for tracking biological recognition events.

Cu-Based Conductive MOF Grown in situ on Cu Foam as a Highly Selective and Stable Non-Enzymatic Glucose Sensor

A non-enzymatic electrochemical sensor for glucose detection is executed by using a conductive metal–organic framework (MOF) Cu-MOF, which is built from the 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) ligand and copper acetate by hydrothermal reaction. The Cu-MOF demonstrates superior electrocatalytic activity for glucose oxidation under alkaline pH conditions. As an excellent non-enzymatic sensor, the Cu-MOF grown on Cu foam (Cu-MOF/CF) displays an ultra-low detection limit of 0.076 μM through a wide concentration range (0.001–0.95 mM) and a strong sensitivity of 30,030 mA μM⁻¹ cm⁻². Overall, the Cu-MOF/CF exhibits a low detection limit, high selectivity, excellent stability, fast response time, and good practical application feasibility for glucose detection and can promote the development of MOF materials in the field of electrochemical sensors.

Wood-inspired nanocellulose aerogel adsorbents with excellent selective pollutants capture, superfast adsorption, and easy regeneration

Heavy metal ions can cause a series of hazards to environment and humans. Herein, we developed a wood-inspired nanocellulose aerogel adsorbent with excellent selective capability, superfast adsorption, and easy regeneration. The premise for the design is that the biomimetic honeycomb architecture and specific covalent bonding networks can provide the adsorbent with structural and mechanical integrity yet superfast removal of target contaminants. The as-obtained adsorbent showed the maximum adsorption capacity for Pb(II), Cu(II), Zn(II), Cd(II), and Mn(II) of 571 mg g^-1, 462 mg g^-1, 361 mg g^-1, 263 mg g^-1, and 208 mg g^-1, respectively. The adsorbent could remove Pb(II) species with super-rapid speed (87% and 100% of its equilibrium uptake in 2 min and 10 min, respectively). Furthermore, the adsorption isotherm and kinetics models were in accord with the Langmuir and pseudo-second-order models, indicating that the adsorption behavior was dominated by monolayer chemisorption. The aerogel adsorbent had better affinity for Pb(II) than other coexisting ions in wastewater and could be regenerated for at least five cycles. Such a wood-inspired aerogel adsorbent holds great potential in the application of contaminant cleaning.