Caesium adsorption on a zeolitic imidazolate framework (ZIF-8) functionalized by ferrocyanide

Effective retention of cesium ions from aqueous environment using morphologically modified kaolinite nanostructures: experimental and theoretical studies

Kaolinite can undergo a controlled morphological modification process into exfoliated nanosilicate sheets (EXK) and silicate nanotubes (KNTs). The modified structures were assessed as potential effective adsorbents for the retention of Cs+ ions. The impact of the modification process on the retention properties was assessed based on conventional and advanced equilibrium studies, considering the related steric and energetic functions. The synthetic KNTs exhibit a retention capacity of 249.7 mg g-1 as compared to EXK (199.8 mg g-1), which is significantly higher than raw kaolinite (73.8 mg g-1). The kinetic modeling demonstrates the high effectiveness of the pseudo-first-order kinetic model (R2 > 0.9) to illustrate the sequestration reactions of Cs+ ions by K, EXK, and KNTs. The enhancement effect of the modification processes can be illustrated based on the statistical investigations. The presence of active and vacant receptors enhanced greatly from 19.4 mg g-1 for KA to 40.8 mg g-1 for EXK and 46.9 mg g-1 for KNTs at 298 K. This validates the significant impact of the modification procedures on the specific surface area, reaction interface, and reacting chemical groups' exposure. This also appeared in the enhancement of the reactivity of their surfaces to be able to uptake 10 Cs+ ions by KNTs and 5 ions by EXK as compared to 4 ions by kaolinite. The thermodynamic and energetic parameters (Gaussian energy < 8.6 kJ mol-1; uptake energy < 40 kJ mol-1) show that the physical processes are dominant, which have spontaneous and exothermic properties. The synthetic EXK and KNT structures validate the high elimination performance of the retention of Cs+ either in the existence of additional anions or cations.

Engineering a defect-rich Prussian blue analog composite for enhanced Cs+ removal performance

Using a novel, irregular honeycombed N-doped porous carbon (NPC) as a support and defect inducer, defect-rich Zn-PBA was formed in situ and evenly anchored on the surface of NPC to obtain a defect-rich Zn-PBA/NPC composite. This composite demonstrated an ultrafast Cs+ adsorption rate that reached equilibrium within 60 s as well as excellent adsorption capacity, stability and reusability. The adsorption mechanism indicated that Cs+ was quickly adsorbed via the defect sites close to the Zn-PBA crystal face accompanied by K(OH2)+ elimination.

Cation-Intercalated Lamellar MoS2 Adsorbent Enables Highly Selective Capture of Cesium

Highly selective capture of cesium (Cs+) from complex aqueous solutions has become increasingly important owing to its (133Cs) indispensable role in some cutting-edge technologies and the environmental mobility of radioactive nuclide (137Cs) from nuclear wastewater. Herein, we report the development of cation-intercalated lamellar MoS2 as an effective Cs+ adsorbent with the advantages of facile synthesis and highly tunable layer spacing. Two types of cations, including Na+ and NH4+, were employed for the intercalations between adjacent layers of MoS2. The results demonstrated that the adsorption capacity of the NH4+-intercalated material (M-NH4+, 134 mg/g) for Cs+ clearly outperformed the others due to higher loading percentages of cations and larger layer spacing. The cesium partition coefficients for M-NH4+ in the presence of 100-fold competing ions all exceed 1 × 103 mL/g. A simulated complex aqueous solution containing 15.37 mg/L Cs+ and highly excess of competing ions Li+, Na+, K+, Mg2+, and Ca2+ (20-306 times higher) was introduced to prove the practical application potential using our best-performing M-NH4+, showing a good to excellent partition ability of Cs+ among other cations, especially for Cs/K and Cs/Na with separation factors of 58 and 212, respectively. The adsorption and selectivity mechanisms were clearly elucidated using various advanced techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. These results revealed that the good selectivity for Cs+ can be ascribed to the differences in Lewis acidities, hydration energy, cation sizes, and in particular, the divergence of coordination modes which was successfully achieved after tuning the layer distance via the cation intercalation strategy. In addition, the material has fast kinetics (<30 min), wide range of pH tolerance (4-10), and good reusability. Overall, our studies point out that the tunable lamellar MoS2-based materials are promising adsorbents for Cs+ capture and separation.

Dittmarite-type magnesium phosphates for highly efficient capture of Cs. JOURNAL OF HAZARDOUS MATERIALS 2023;453:131385. [PMID: 37043858 DOI: 10.1016/j.jhazmat.2023.131385] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The presence of cesium ions (Cs⁺) in radioactive wastewater has attracted considerable attention owing to their extreme toxic effects. Thus, there is an urgent need to develop adsorbents for Cs⁺ with high adsorption capacities (q). While phosphate-based adsorbents have advantages for their disposal, previous adsorbents have shown limited q because of their limited capacity for ion exchange, despite showing high theoretical q values. In this study, two dittmarite-type magnesium phosphates, KMgPO₄·H₂O (KMP) and NH₄MgPO₄·H₂O (NMP), were synthesized because of their ability to contain readily exchangeable cations in their interlayers. KMP and NMP demonstrated remarkable adsorption capacities for Cs⁺ (q_e^KMP = 630 mg g^-1 and q_e^NMP = 711 mg g^-1), which were the highest among all reported adsorbents and are ∼84 % of their theoretical values. Their distribution coefficients in waters with high divalent ion concentrations were low, which limits their use for the adsorption of Cs⁺ from such environments. After adsorption, KMP and NMP were structurally transformed into struvite-type CsMgPO₄·6H₂O (CsMP), which has two different stacking structures, either cubic or hexagonal, depending on the pH of the solution. The high q values of KMP and NMP enable them to reduce the volume of radioactive waste for disposal.

Effective adsorptive removal of sulfamethoxazole (SMX) from aqueous solution by ZIF-8 derived adsorbent ZC-0.5

Efficient removal of antibiotics from the aquatic environment is urgently needed due to their obstinate accumulation and non-biodegradability. In this study, a mesoporous carbon material (ZC-0.5) was successfully synthesized for the adsorption of sulfamethoxazole (SMX), one of the major antibiotics for the treatment of human and animal infections. ZIF-8 as the precursor of ZC-0.5, specifically, using cetyl trimethyl ammonium bromide (CTAB) and sodium laurate (SL) as dual templates and carbonizing at 800 ℃. This novel adsorbent exhibited a high proportion of mesopore (75.64%) and a large specific surface area (1459.73 m²·g^-1). The adsorption experiment examined the reusability of ZC-0.5 and that it could retain superior maximum adsorption capacities (167.45 mg∙L^-1) after five cycles of adsorption and desorption. The adsorption process satisfied the pseudo-second-order kinetic (PSO) and mixed first- and second-order kinetic (MOE). It also satisfied the Freundlich and Sips isotherm models. Moreover, thermodynamic calculation indicated the adsorption process was spontaneous, endothermal, and entropy-increasing. Furthermore, plausible adsorption mechanisms were explained through van der Waals force, electrostatic interaction, hydrophobic force, π-π interaction, and hydrogen bond. This work offers a new efficient adsorbent for antibiotic elimination.

Estimation of 137Cs Distribution and Recovery Using Various Types of Sorbents in the Black Sea Surface Layer

Monitoring 137Cs in seawater is necessary for the timely detection of radioactive contamination. The possibility of sorption and the sorption efficiency of 137Cs from seawater were studied for the first time during several cruises of the R/V (research vessel) Professor Vodyanitsky using various types of sorbents based on transition metal ferrocyanides (Anfezh, Niket, Uniket, FSS, FD-M, FIC, Termoxid 35, NKF-C) and zirconium phosphate (Termoxid 3A). The influence of the seawater flow rate and volume of the sorbent used for the recovery of 137Cs was estimated. The ferrocyanide sorbents Niket, Uniket, Termoxid 35, and FIC showed the best sorption efficiency (60–100%) at a seawater flow rate of 2–4 column volumes per minute. The data obtained during three cruises on the R/V Professor Vodyanitsky were analyzed. A detailed (28 sampling points) spatial distribution of 137Cs in the Black Sea along the southern coast of Crimea was studied using the sorbents that showed the best characteristics. An increase in 137Cs activity in the study area was not found, and the average activity was 9.01 ± 0.87 Bq/m3.

Three-dimension titanium phosphate aerogel for selective removal of radioactive strontium(II) from contaminated waters

The effective removal of radioactive strontium (especially ⁹⁰Sr) from nuclear wastewater is crucial to environmental safety. Nevertheless, materials with excellent selectivity in Sr removal remain a challenge since the similarity with alkaline earth metal ions in the liquid phase. In this work, a novel titanium phosphate (TiP) aerogel was investigated for Sr(II) removal from the radioactive wastewater based on the sol-gel method and supercritical drying technique. The TiP aerogel has amorphous, three-dimensional and mesoporous structures with abundant phosphate groups, which was confirmed by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FT-IR). The adsorbent exhibited high efficiency and selectivity for the removal of Sr(II) with an extensive distribution coefficient up to 4740.03 mL/g. The adsorption equilibrium reached within 10 min and the maximum adsorption capacity was 373.6 mg/g at pH 5. And the kinetics and thermodynamics data fitted well with the pseudo-second-order model and Langmuir model respectively. It can be attributed to the rapid trapping and slow intraparticle diffusion of Sr(II) inside the mesoporous channels of the TiP aerogel. Furthermore, TiP aerogel exhibited over 80% removal for 50 mg/L Sr²⁺ in real water systems (seawater, lake water and tap water). X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy revealed that strong ionic bonding formed during Sr(II) adsorption with the phosphate group on TiP aerogel. These results indicated that TiP aerogel is a promising high-capacity adsorbent for the effective and selective capture of Sr(II) from radioactive wastewater.

Beyond Pristine Metal-Organic Frameworks: Preparation of Hollow MOFs and Their Composites for Catalysis, Sensing, and Adsorption Removal Applications

Metal-organic frameworks (MOFs) have been broadly applied to numerous domains with a substantial surface area, tunable pore size, and multiple unsaturated metal sites. Recently, hollow MOFs have greatly attracted the scientific community due to their internal cavities and gradient pore structures. Hollow MOFs have a higher tunability, faster mass-transfer rates, and more accessible active sites when compared to traditional, solid MOFs. Hollow MOFs are also considered to be candidates for some functional material carriers. For example, composite materials such as hollow MOFs and metal nanoparticles, metal oxides, and enzymes have been prepared. These composite materials integrate the characteristics of hollow MOFs with functional materials and are broadly used in many aspects. This review describes the preparation strategies of hollow MOFs and their composites as well as their applications in organic catalysis, electrochemical sensing, and adsorption separation. Finally, we hope that this review provides meaningful knowledge about hollow-MOF composites and their derivatives and offers many valuable references to develop hollow-MOF-based applied materials.

ZIF-8 metal organic framework materials as a superb platform for the removal and photocatalytic degradation of organic pollutants: a review

Metal organic frameworks (MOFs) are attracting significant attention for applications including adsorption, chemical sensing, gas separation, photocatalysis, electrocatalysis and catalysis. In particular, zeolitic imidazolate framework 8 (ZIF-8), which is composed of zinc ions and imidazolate ligands, have been applied in different areas of catalysis due to its outstanding structural and textural properties. It possesses a highly porous structure and chemical and thermal stability under varying reaction conditions. When used alone in the reaction medium, the ZIF-8 particles tend to agglomerate, which inhibits their removal efficiency and selectivity. This results in their mediocre reusability and separation from aqueous conditions. Thus, to overcome these drawbacks, several well-designed ZIF-8 structures have emerged by forming composites and heterostructures and doping. This review focuses on the recent advances on the use of ZIF-8 structures (doping, composites, heterostructures, etc.) in the removal and photodegradation of persistent organic pollutants. We focus on the adsorption and photocatalysis of three main organic pollutants (methylene blue, rhodamine B, and malachite green). Finally, the key challenges, prospects and future directions are outlined to give insights into game-changing breakthroughs in this area.

Cesium removal from wastewater: High-efficient and reusable adsorbent K1.93Ti0.22Sn3S6.43

Efficient and quick removal of radioactive Cs⁺ from wastewater is significant for the safe use of nuclear energy and human health. A novel adsorbent K_1.93Ti_0.22Sn₃S_6.43 (KTSS) was developed for Cs⁺ removal from complex natural water systems. The working mechanism of KTSS for removing Cs⁺ was the synergistic effect of ion exchange and the Cs⋯S binding, which was proved by several characterization techniques. KTSS showed ultrafast kinetics for Cs⁺ adsorption within 1 min with a removal rate of 99%. Meanwhile, KTSS exhibited a higher adsorption capacity of 450.12 mg/g than many other adsorbents to remove Cs⁺ and possessed excellent chemical stability in a wide pH range of 3-12. Thanks to the natural affinity arising from the S^2- ligands, KTSS displayed excellent selectivity for Cs⁺ even in different complex water systems. The separation factors between Cs⁺ and the coexisting ions of Na⁺, K⁺, Mg²⁺, Ca²⁺ were ranged from 408.61 to 7448.20. Fortunately, by eluting with NaNO₃ the adsorbent could realize the green regeneration and cyclic utilization. Furthermore, it was found that KTSS had tremendous advantages in the removal of Cs⁺ in comparison with the other adsorbents. Consequently, it should be considered that KTSS obtained in this study has great potential in applying ultrafast and high-efficient removal of Cs⁺ from wastewater.

New insight into the co-adsorption of oxytetracycline and Pb(II) using magnetic metal-organic frameworks composites in aqueous environment: co-adsorption mechanisms and application potentials

The present study aimed to investigate the co-adsorption and application of water stabilized Fe₃O₄@ZIF-8 composite with magnetic cubic crystal structure. This new material was successfully prepared by facile modification strategy and rational design, which was used for simultaneous adsorption of oxytetracycline (OTC) and Pb(II) in aqueous solution. The co-adsorption behavior and mechanism of the composite for OTC and Pb(II) were systematically investigated by characterization techniques and batch experiments, and its application potential was effectively evaluated. The results showed that the synthesized Fe₃O₄@ZIF-8 composite innovatively retained the cubic crystal structure of ZIF-8 and was successfully loaded on the surface of Fe₃O₄ particles with small particle size to form a core-shell structure. The Fe₃O₄@ZIF-8 composite possessed a large specific surface area (1722 m²/g), magnetic separation performance (13.4 emu/g), and rich functional groups. The co-adsorption of OTC and Pb(II) on Fe₃O₄@ZIF-8 had fast reaction kinetics (equilibrium within 90 min) and large adsorption capacity (310.29 mg/g and 276.06 mg/g respectively). The adsorption process for both contaminants followed pseudo-second order kinetics and Langmuir isotherm models and had synergistic and competitive effects at the same time. π-π stacking and electrostatic interaction were the main mechanisms of adsorption. Fe₃O₄@ZIF-8 had good adsorption performance after cyclic adsorption for 4 times and it performed well in the treatment of real waste water. This study provided a new sight for the control of combined pollution of OTC and Pb(II) and proved Fe₃O₄@ZIF-8 composites have great application potentials for complex wastewater treatment.

Sorption methods in marine radiochemistry

The review presents the general methodology of using sorption methods to solve problems of marine radiochemistry, including sampling, preconcentration and radiochemical preparation and methods for measuring the activity of radionuclides. The possible methodological errors at various stages of sampling and sample concentration are discussed. The most widely used artificial (90Sr, 134Cs, 137Cs, 239Pu, 240Pu), natural (210Pb, 210Po; radium quartet: 223Ra, 224Ra, 226Ra, 228Ra; thorium isotopes, mainly 234Th) and cosmogenic (7Be, 32P, 33P) radiotracers are considered. The sorption of uranium from seawater is not addressed, since its concentration in seawater is usually calculated from the known dependence of uranium concentration on seawater salinity.

The bibliography includes 200 references.

Significant improvement of the lithium-ion conductivity of solid-state electrolytes by fabricating large pore volume hollow ZIF-8

Metal-organic frameworks (MOFs) emerging as a type of functional material have been widely used in electrochemical energy storage and conversion in recent years. Hollow MOFs with a large pore volume and surface area can increase the contact area between active materials and electrolytes, thus improving the ionic conductivity of the materials. Herein, we obtained a kind of hollow MOF (ZIF-8) using carboxylate-terminated polystyrene microspheres as exterior templates. Transmission electron microscopy and N₂ adsorption/desorption analysis revealed that the average cavity diameter of hollow ZIF-8 is 1 μm. Moreover, hollow ZIF-8 exhibits excellent electrochemical quality with an ionic conductivity of 7.36 × 10^-4 S cm^-1, a lithium ion transference number of 0.83 and an activation energy of 0.15 eV in a wide stable electrochemical window of 2.0-6.5 V at room temperature. Compared with the traditional non-hollow ZIF-8, the electrochemical performance has been improved obviously. Consequently, our strategy of fabrication of large pore volume hollow MOFs provides a new perspective for the development of solid electrolytes with excellent lithium ionic conductivity.

Peptide-Mediated Synthesis of Zeolitic Imidazolate Framework-8: Effect of Molecular Hydrophobicity, Charge Number and Charge Location

Three amphiphilic peptides with varied molecular hydrophobicity, charge number and charge location have been designed as regulators to modulate the crystal growth of zeolitic imidazolate framework-8 (ZIF-8). All three peptides can interact with ZIF-8 to inhibit {100} facet growth and produce truncated cubic crystals. The peptide's molecular hydrophobicity plays a dominant role in defining the final morphology and size of the ZIF-8 crystals. The peptides with less charge and higher hydrophobicity can promote nuclei formation and crystal growth to give smaller ZIF-8 crystals. However, the charge located in the center of the molecular hydrophobic region has little effect on the crystal nucleation and growth due to the shielding of its charge by molecular aggregation. The study provides insights into the effect of molecular charge and hydrophobicity on ZIF-8 crystal growth and is helpful for guiding the molecular design for regulating the synthesis of metal-organic framework materials.

Amino-functionalized POSS nanocage-intercalated titanium carbide (Ti3C2Tx) MXene stacks for efficient cesium and strontium radionuclide sequestration

In this work, we prepared two-dimensional (2D) stack-structured aminopropylIsobutyl polyhedral oligomeric silsesquioxane (POSS-NH₂) intercalated titanium carbide (Ti₃C₂T_x) MXene material (Ti₃C₂T_x/POSS-NH₂) using a post-intercalation strategy as a potential adsorbent for the removal of cesium (Cs⁺) and strontium (Sr²⁺) ions from aqueous solutions. Ti₃C₂T_x/POSS-NH₂ exhibited unprecedented adsorption capacities of 148 and 172 mg g^-1 for Cs⁺ and Sr²⁺ ions, respectively. Batch adsorption experimental data well fitted the Freundlich isotherm model, which revealed multilayer adsorption of Cs⁺ and Sr²⁺ ions onto heterogeneous -OH, -F, -O, and -NH₂ adsorption sites of Ti₃C₂T_x/POSS-NH₂ with different energies. Ti₃C₂T_x/POSS-NH₂ exhibited rapid Cs⁺/Sr²⁺ ions adsorption kinetics and attained equilibrium within 30 min. Also, Ti₃C₂T_x/POSS-NH₂ exhibited recyclable capability over three cycles and remarkable selectivities of 89% and 93% for Cs⁺ and Sr²⁺ ions, respectively, in the presence of co-existing mono- and divalent cations. We suggest the high adsorption capacity of Ti₃C₂T_x/POSS-NH₂ might be due to the synergistic effects of (i) increased inter-lamellar distance between Ti₃C₂T_x galleries due to POSS-NH₂ intercalation, enabling diffusion and encapsulation of large numbers of Cs⁺/Sr²⁺ ions, (ii) strong complexation of amine (-NH₂) groups of POSS-NH₂ with Cs⁺/Sr²⁺ ions, and (iii) the presence of large numbers of heterogeneous surface functional groups (e.g., -OH, -F, and -O), which resulted in the adsorptions of Cs⁺/Sr²⁺ ions through electrostatic, ion exchange, and surface complexation mechanisms. Given the extraordinary adsorption capacities observed, intercalation appears to be a promising strategy for the effective removal of radioactive Cs⁺ and Sr²⁺ ions from aqueous media.

Catalytic conversion of seawater to fuels: Eliminating N vacancies in g-C3N4 to promote photocatalytic hydrogen production

The use of solar energy to decompose seawater and produce hydrogen is of great significance in solving the energy crisis. Numerous studies have shown that vacancies can significantly improve photocatalytic activity due to their electron-rich nature. However, our recent research has shown that materials with vacancies are not suitable for photocatalytic reactions in seawater. In this study, g-C₃N₄ with rich N vacancies was selected as the research object, and urea was used as the precursor; in this system, the N vacancies in g-C₃N₄ could be effectively reduced by the addition of ZIF-8 (ZCNQx). The activity of ZCNQ40 was 5.6 times higher than that of g-C₃N₄ in fresh seawater, but only 3.1 times higher in freshwater. Based on the analysis of the experimental results, we believe that g-C₃N₄ has a limiting relationship between H+ adsorption catalysis and H₂ product desorption. In addition, seawater contains many heteroatoms that will also compete with proton (H+) reduction. The results of our study show that catalysts with vacancies are not necessarily suitable for catalytic reactions in seawater media. This research will stimulate new ideas for research into the conversion of solar energy to chemical energy in seawater media.

The Era of Nanomaterials: A Safe Solution or a Risk for Marine Environmental Pollution?

In recent years, the application of engineered nanomaterials (ENMs) in environmental remediation gained increasing attention. Due to their large surface area and high reactivity, ENMs offer the potential for the efficient removal of pollutants from environmental matrices with better performances compared to conventional techniques. However, their fate and safety upon environmental application, which can be associated with their release into the environment, are largely unknown. It is essential to develop systems that can predict ENM interactions with biological systems, their overall environmental and human health impact. Until now, Life-Cycle Assessment (LCA) tools have been employed to investigate ENMs potential environmental impact, from raw material production, design and to their final disposal. However, LCA studies focused on the environmental impact of the production phase lacking information on their environmental impact deriving from in situ employment. A recently developed eco-design framework aimed to fill this knowledge gap by using ecotoxicological tools that allow the assessment of potential hazards posed by ENMs to natural ecosystems and wildlife. In the present review, we illustrate the development of the eco-design framework and review the application of ecotoxicology as a valuable strategy to develop ecosafe ENMs for environmental remediation. Furthermore, we critically describe the currently available ENMs for marine environment remediation and discuss their pros and cons in safe environmental applications together with the need to balance benefits and risks promoting an environmentally safe nanoremediation (ecosafe) for the future.