Enhanced Water Stability Research Articles

Enhanced water stability of MOFs via multiple hydrogen bonds and their application in water harvesting.

A mechanism based on multiple hydrogen bonds was proposed to describe the great water stability of some hydrated Cu paddle-wheel-based MOFs, which was demonstrated through density functional theory (DFT) calculations and single-crystal X-ray diffraction (SCXRD) of water-loaded MOFs. This mechanism endowed Cu-TDPAT with exceptional water stability and outstanding atmospheric water harvesting capability.

Enhanced water stability and catalytic activity of Fe-based metal–organic frameworks with co-ligands for 2,4-dichlorophenol degradation

Fe-based metal–organic frameworks (MOFs) have good photocatalytic performance, environmental friendliness, low cost, and abundance. However, their applications are limited by low water stability, particularly in the presence of light irradiation and oxidizing agents. In this study, we present a MIL-53(Fe)-based MOF using 1,4-naphthalene dicarboxylic (1,4-NDC) and 1,4-benzenedicarboxylic (H2BDC) acid co-ligands, denoted MIL-53(Fe)-Nx, where Nx represents the ratio of 1,4-NDC. This MOF exhibits high water stability and good photocatalytic activity because of the hydrophobicity of naphthalene. The removal and mineralization rates for 100 mg/L 2,4-dichlorophenol reached 100% and 22%, respectively, within 60 min. After three cycles of use, the Fe leached into the solution from the catalysts was significantly lower than the maximum permissible limit indicated in the European Union standard. Of note, 1,4-NDC can be used to make a rigid MOF, thereby improving the crystallinity, porosity, and hydrophobicity of the resultant materials. It also significantly reduced the bandgap energy and improved the charge separation efficiency of the catalysts. This study provides a route to enhance the water stability of Fe-based MOFs via a mixed-ligand strategy to expand their applications in pollutant control.

Synergistically enhanced water-resistive perovskite nanocrystals for cell nucleus imaging and acid phosphatase detection

Despite the impressive success of metal halide perovskite nanocrystals (NCs) in diverse fields, such as solar cells, light-emitting diodes, photodetectors, and so forth, their intrinsic sensitivity to water limits the extending applications in aqueous systems. Herein, enhanced water stability is achieved for NH2-PEG-COOH capped Mn2+-doped CsPbCl3/CsPb2Cl5 core/shell NCs through the synergistic effect of ion doping, core/shell construction and polymer encapsulation. The NH2-PEG-COOH encapsulation is validated crucial for the formation of CsPbCl3/CsPb2Cl5 core/shell structure, since it retains contact for CsPbCl3 NCs with trace water, and guarantees a slow water-etching process, triggering the CsPbCl3 to CsPb2Cl5 transformation. Thanks to the high formation energy induced by Mn2+ doping, CsPbCl3/CsPb2Cl5 hetero core/shell construction and NH2-PEG-COOH protective barrier, the obtained NCs exhibit unattenuated photoluminescence quantum yield after dipped in water for 15 days. Based on the robust water stability, the NH2-PEG-COOH capped Mn2+-doped CsPbCl3/CsPb2Cl5 NCs work well in cell nucleus imaging and acid phosphatase detection. This work not only produces a novel perovskite fluorescence probe in aqueous systems but also provides a general and effective combination strategy to enhance the water stability of perovskite materials.

Easy-regeneration Mn-doped ZIF-67 derivate adsorbent with ultra-high adsorption capacity for tetracycline hydrochloride in wastewater

Adsorption capacity and reusability are critical to the practical applications of metal–organic framework (MOF)-based adsorbents. In this work, an easy-regeneration ZIF-67 derivate adsorbent (Mn-ZIF-400) was synthesized by calcining the manganese-modified MOF ZIF-67 (Mn-ZIF-67) precursor at 400 °C in air for the first time. Mn-ZIF-400 reveals an ultra-high adsorption capacity for tetracycline hydrochloride (TCH) (qmax = 1191.5 mg⋅g−1 at 308 K at pH = 4) in a wide pH range (pH = 3–10) owing to its great surface area (816.2 m2⋅g−1), surface polyvalent metal ions (Co2+/Co3+, Mn2+/ Mn 3+/ Mn4+), abundant surface oxygen species (including –COOH, –OH etc.) and π-electrons from benzene-ring. The adsorption mechanism of TCH on Mn-ZIF-400 belongs to the monolayer chemisorption mainly by π-π conjugation/π-cation interactions, hydrogen/coordination bonding, and pore filling. It also can maintain high adsorption performance in an actual aqueous environment. More importantly, Mn-ZIF-400 showed enhanced water stability and reusability after modification and no obvious loss in adsorption capacity in four recycles via simple water washing, being a promising adsorbent for antibiotic elimination.

The effect of dopants (Fe, Al) on the low-temperature activity and SO2 tolerance in solvothermally synthesized MnOx NH3-SCR catalysts

Fe-doped MnOx catalyst prepared by a preferred solvothermal method displayed noticeably better low-temperature (LT) NH3-SCR performance and water stability than an analogously prepared Al-doped MnOx catalyst. The SCR activity of both catalysts decreased markedly when exposed to SO2, but the resultant MnFeOx-S catalyst retained higher LT activity than MnAlOx-S and recovered significantly more of its original activity after thermal regeneration (400 °C). Comprehensive characterization confirmed that the deactivation of the catalysts was governed by formation of stable metal sulfates, which only decomposed to a minor extent upon thermal treatment although Al doping lowered the thermal stability of the adsorbed sulfur species. Additionally, Fe doping was found to facilitate electron transfer between Mn and Fe ions and weaken the interaction between active sites and deposited sulfates during the heating procedure, which promoted re-oxidation of Mn2+ to catalytically active Mn3+/Mn4+. Altogether, the altered redox properties resulted in improved LT SCR performance, enhanced water stability, higher SO2 tolerance and superior regeneration of the MnFeOx catalyst.

A Symmetry Concept for the Self-Assembly Synthesis of Mn-MIL-100 Using a Capping Agent and Its Adsorption Performance with Methylene Blue

In this study, a facile strategy of regulated self-assembly synthesis of Mn-MIL-100, using sodium acetate (CH3COONa) as a mono-dentate ligand capping agent (CA), was proposed. The as-prepared product is denoted Mn-MIL-100-CA. The coordination modulation of CH3COONa, led by its interference in the connectivity and symmetry of the metal centers and organic nodes, plays a vital role in the synthesis process. The crystallinity, morphology, topology, and properties of such MOF products were improved, since the self-assembly process of Mn-MIL-100-CA was promoted and regulated effectively. The materials were systematically characterized via XRD, SEM, N2 isotherms, XPS, and TGA in terms of crystallization behavior, morphology, topology, chemical composition, and thermal and water stability. The ability of Mn-MIL-100 and Mn-MIL-100-CA to remove methylene blue (MB) from an aqueous solution was investigated using a UV–vis spectrophotometer. The results indicate that with the addition of a molar ratio of 50% CH3COONa, Mn-MIL-100-CA particles developed a regularly symmetrical morphology, i.e., ‘spherical pyramid-like structure’ crystals with a dimension of 2~5 μm. Their specific surface area and pore volume increased by 59.2% and 56.7%, respectively. The increased proportion of Mn3+ implies reduced crystal defects and improved crystal structural order and integrity, and therefore an enhanced water stability. Mn-MIL-100-CA exhibited excellent adsorption performance towards MB from aqueous solution. The equilibrium adsorption value was as high as 1079.9 mg/g, which is 44.7% higher than that of Mn-MIL-100 without the addition of CA. The good adsorption capacity and excellent water stability mean that Mn-MIL-100-CA has great potential for the practical removal of MB dye pollutants from water.

Highly water-stable MOF-74 synthesized by in-situ trace polymer modification

MOF-74 family is unstable in humid environment because its coordination bond between metal ions and oxygen atoms is relatively weak. This limits the practical application of MOF-74 material. Therefore, improving the water vapor/water stability of MOF-74 is crucial for their use in practical applications. In this work, we propose a strategy involving a trace polymer in-situ modified MOF-74. During the in-situ synthesis, polyvinylamineacid (PCH) was introduced into the structure of MOF-74 (PCH-MOF-74, PMOF-74) to form a hydrophobic environment around the unsaturated metal sites to enhance water stability. After immersion in water or acid, PMOF-74 can maintain most of the original crystal structure and gas adsorption capacity. The experimental results show that the successful incorporation of PCH into MOF can effectively improve the water vapor/water stability of MOF structures, and it is also worth further improving and enhancing the structural stability of other MOF materials with metal sites.

CuBTC Metal-Organic Framework Decorated with FeBTC Nanoparticles with Enhance Water Stability for Environmental Remediation Applications.

Metal-organic frameworks (MOFs) based on Cu-benzene tricarboxylate (CuBTC) are widely used for gas storage and removal applications. However, they readily lose their crystal structures under humid conditions, limiting their practical applications. This structural decomposition reduces the specific surface area, gas adsorption capability, and recyclability of CuBTC considerably. In this study, a stable MOF against water exposure was designed based on FeBTC nanoparticle-covered CuBTC (FeCuBTC). A simple one-pot solvothermal process that enables the epitaxial growth of FeBTC on the CuBTC surface was proposed. Structural and morphological analyses after water exposure revealed that the water stability of FeCuBTC was better than that of CuBTC, which completely lost its crystallinity. This observed improvement in the water stability of the synthesized MOF proved to be beneficial for the adsorption of formaldehyde under humid conditions. The proposed strategy herein is simple yet highly effective in the design of hetero-bimetallic MOFs with considerably improved water resistance and extended applicability for environmental remediation processes.

In situ growth strategy to construct perovskite quantum dot@covalent organic framework composites with enhanced water stability

Metal halide perovskite quantum dots (QDs) have excellent optoelectronic properties; however, their poor stability under water or thermal conditions remains an obstacle to commercialization. Here, we used a carboxyl functional group (−COOH) to enhance the ability of a covalent organic framework (COF) to adsorb lead ions and grow CH3NH3PbBr3 (MAPbBr3) QDs in situ into a mesoporous carboxyl-functionalized COF to construct MAPbBr3 QDs@COF core–shell-like composites to improve the stability of perovskites. Owing to the protection of the COF, the as-prepared composites exhibited enhanced water stability, and the characteristic fluorescence was maintained for more than 15 d. These MAPbBr3 QDs@COF composites can be used to fabricate white light-emitting diodes with a color comparable to natural white emission. This work demonstrates the importance of functional groups for the in situ growth of perovskite QDs, and coating with a porous structure is an effective way to improve the stability of metal halide perovskites.

Facile in Situ Polymer Functionalization Approach for Constructing Water-Resistant Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have been widely investigated for their use in separation, such as gas adsorption or biotechnology. However, numerous MOFs are unstable in aqueous environment or humid conditions, significantly hindering their practical application. While current methods for enhancing MOF water stability can largely decrease the pore structural parameters, herein, we proposed a strategy of in situ trace polymer functionalization for enhancing the MOF stability and demonstrated that the water stability of four common MOFs can be enhanced greatly by incorporating hydrophobic PSfCOOH molecules into the framework through a one-step synthesis. A series of investigations into the local chemical structure and bonding environment suggest that the enhanced water stability arises from the construction of hydrophobic microenvironments and the steric hindrance around the metal sites. The prepared Cu-BTC-PSfCOOH remained intact after being immersed in water for even 10 days, preserving 90% of its original pore structural parameter, such as Brunauer–Emmett–Teller (BET) surface areas. Moreover, 88% of the initial BET surface areas can be maintained after one-day immersion in 6 M HCl solution. The strategy is also demonstrated to be efficient in enhancing the water stability of three other typical MOFs, showing good universality in constructing water-resistant MOFs.

Optimising Starch Transformation in Aquafeed Extrusion for Enhanced Water Stability and Performance

The physical quality of aquafeed pellets is paramount for the health and performance of aquatic species in aquaculture systems. Starch, a small, but necessary component of aquafeed, plays a crucial role in creating durable and water-stable pellets. This paper investigates the complex relationship between starch transformation during extrusion cooking and its influence on water stability. Through a series of experiments involving various extrusion parameters, including three melt moisture levels and three screw speeds, the study reveals that the key to producing water-stable aquafeed lies in optimizing starch gelatinization and minimizing dextrinization. High screw speeds, in conjunction with moderate to high melt moisture levels, facilitate starch gelatinization while avoiding dextrinization, resulting in pellets with superior water stability. Conversely, low melt moisture levels at any screw speed or any melt moisture at low screw speeds lead to poor water stability due to increased dextrinization or suboptimal gelatinization levels. The research also underscores the critical role of the glass transition of starch. Starch in its semi-crystalline state is found to be more susceptible to shear degradation during extrusion. Therefore, rapidly elevating the raw material's temperature above its glass transition temperature is crucial for achieving water-stable aquafeed.

Ultrasmall water-stable CsPbBr3 quantum dots with high intensity blue emission enabled by zeolite confinement engineering.

Ultrasmall CsPbBr3 perovskite quantum dots (PQDs) as promising blue-emitting materials are highly desired for full-color display and lighting applications, but their inferior efficiency and poor ambient stability hinder extensive applications. Herein, a "break-and-repair" strategy has been developed to tightly confine monodispersed ultrasmall CsPbBr3 PQDs in a zeolite. In this strategy, the CsPbBr3 PQDs are introduced into the zeolite via a high temperature evaporation method, wherein the perovskite precursors break the zeolite framework, and amino acids and silane are then used to fix the damaged framework and lock the perovskite QDs within the matrix. By modulating the synthetic conditions to control the growth of CsPbBr3, PQDs with ultrasmall size of 2 nm have been obtained in the zeolite, giving emission centered at 460 nm with a high quantum yield of 76.93%. Strikingly, the PQDs@zeolite composite exhibits water-induced reversible photoluminescence promoted by the coordination between the amino acids and PQDs in a dynamic manner, achieving enhanced water stability (14 days in aqueous solution). This work provides a new perspective for the synthesis of water-stable blue-emitting perovskite composites for potential applications in lighting fields.

Graphene oxide nanosheets augment silk fibroin aerogels for enhanced water stability and oil adsorption.

Nanocomposite aerogels exhibit high porosity and large interfacial surface areas, enabling enhanced chemical transport and reactivity. Such mesoporous architectures can be prepared by freeze-casting naturally-derived biopolymers such as silk fibroin, but often form mechanically weak structures that degrade in water, which limits their performance under ambient conditions. Adding 2D material fillers such as graphene oxide (GO) or transition metal carbides (e.g. MXene) could potentially reinforce these aerogels via stronger intermolecular interactions with the polymeric binder. Here, we show that freeze-casting of GO nanosheets with silk fibroin results in a highly water-stable, mechanically robust aerogel, with considerably enhanced properties relative to silk-only or silk-MXene aerogels. These silk-GO aerogels exhibit high contact angles with water and are highly water stable. Moreover, aerogels can adsorb up 25-35 times their mass in oil, and can be used robustly for selective oil separation from water. This increased stability may occur due to strengthened intermolecular interactions such as hydrogen bonding, despite the random coil and α-helix conformation of silk fibroin, which is typically more soluble in water. Finally, we show these aerogels can be prepared at scale by freeze-casting on a copper mesh. Ultimately, we envision that these multicomponent aerogels could be widely utilized for molecular separations and environmental sensing, as well as for thermal insulation and electrical conductivity.

Broccoli-shaped Cu-BTC/biochar composite with enhanced water stability for toluene adsorption: Influence of humid air aging

Insufficient water stability is an important problem restricting the practical application of metal–organic frameworks (MOFs) in the field of volatile organic compounds (VOCs) adsorption. In this work, a copper(II) benzene-1,3,5-tricarboxylate MOF (Cu-BTC)/biochar composite with improved water stability was obtained by a facile one-pot method for toluene adsorption applications. Different from the traditional regular octahedral configuration, Cu-BTC was scattered on biochar in the form of broccoli-shaped microspheres. The influence of humid air aging on the physiochemical and toluene adsorption properties of Cu-BTC and Cu-BTC/biochar composites under different periods were explored. The results show that the inner structure of Cu-BTC degrades with the micropores transformed into meso-macropores under the humid air aging. Moreover, the BET surface area was reduced by 63.2 % and 94.7 % after 3-month and 6-month aging, respectively, which could eventually lead to a serious decline (76.3 % and 96.5 %) in the adsorption capacities of toluene. It can also be found that compared to traditional octahedral Cu-BTC, the degradation process of broccoli-shaped Cu-BTC/biochar is effectively slowed down, which shows better moisture stability. The retention rates of toluene adsorption capacities for broccoli-shaped Cu-BTC/biochar were 57.7 % and 17.1 % after 3-month and 6-month aging, respectively. This study is helpful for better improving the water stability of MOFs materials used for VOCs adsorption.

Persulfate-based visible photocatalysis with a novel stability enhanced Fe-based metal-organic framework

Enhancing the water stability is the critical issue for metal–organic frameworks to explore their potential as photocatalysts for water treatment. In this study, a postsynthetic modification (PSM) method was applied, and MIL-101(Fe)–NH2 was modified to form a new MIL-101(Fe)-1-(4-(methyl)phenyl)urea (named MIL-101(Fe)-MPU). Chemical structure analyses confirmed a conversion from amino group to urea group. After PSM, grafting of a carbamido-benzene-methyl arm increased the surface hydrophobicity of MIL-101(Fe)-MPU with a large contact angle (> 100°). As a consequence, MIL-101(Fe)-MPU presented a better water stability compared to MIL-101(Fe)–NH2. After a 72-h liquid water exposure, chemical skeleton structure of MIL-101(Fe)-MPU were retained. In the presences of visible light and persulfate, both MIL-101(Fe)–NH2 and MIL-101(Fe)-MPU demonstrated equivalent photocatalysis degradation efficiencies of ciprofloxacin (CIP) in water matrix. The removal of CIP fit a quasi-first-order kinetic with apparent rate constants at 0.0440 min−1 (MIL-101(Fe)–NH2) and 0.0396 min−1 (MIL-101(Fe)-MPU). The dominant reaction mechanism in light/MIL-101(Fe)-MPU/S2O82− system was verified to be visible photocatalysis, including OH· and SO4·- oxidation. In general, MIL-101(Fe)-MPU presented an enhanced water stability, contributing to its potential photocatalysis applications in water treatments.

Fe doped bimetallic HKUST-1 MOF with enhanced water stability for trapping Pb(II) with high adsorption capacity

• Fe doped HKUST-1 MOF was synthesised with varying concentrations of Fe. • Increased metal-ligand bonding in presence of Fe improved the structural stability. • Improved hydrolytic stability for Fe 0.05 HKUST-1 MOF for up to 10 hrs. • Fe 0.05 HKUST-1 MOF exhibited a Pb(II) adsorption performance of > 550 mg g −1. HKUST-1 Metal-Organic Framework (MOF), due to its coordinatively unsaturated metal sites, high surface area and microporosity, is one the most prominent MOF candidates. Our study investigates the consequence of doping iron into HKUST-1 MOF on its hydrostability, and demonstrates its usability for Pb(II) removal. A simple one-pot solvothermal process was used to synthesize Fe doped HKUST-1 MOF with varying dopant concentrations of Fe (5–20 mol%). Through various characterisation techniques (XPS, XRD, FTIR, ICP-OES) and MD simulations we demonstrated the incorporation of Fe into the HKUST-1 framework, which happened through Fe substituting the Cu(II) sites. Water stability studies using experimental and modelling approaches demonstrated that partial substituted Fe-HKUST-1 MOFs have a greater surface area retention with very little loss in crystallinity as compared to pristine HKUST-1 MOF. Fe substitution of as low as 5 mol% yielded a significant enhancement in the hydrostability of HKUST-1 MOFs, wherein the structure was intact for up to 10 hrs of water treatment. Similarly, 5 mol% Fe doping had a 53% reduction in the amount of Cu being leached out from the HKUST-1 MOF framework. Fe doped HKUST-1 MOFs showed exceptionally high Pb(II) selectivity, Pb(II) removal efficiency of > 90%, and a high Pb(II) adsorption capacity of 565 mg g −1 . This study opens up the possibility of using doping as a strategy to enhance the hydrostability of HKUST-1 MOF and in the process improve its applicability for environmental remediation applications.

Zn/Co-ZIF reinforced sugarcane bagasse aerogel for highly efficient catalytic activation of peroxymonosulfate

Sugarcane bagasse is the main solid waste of sugar extraction industry. However, there are less eco-friendly treatment methods for this kind of waste material. Most of them have been burned and this is a challenge for effective utilization of sugarcane. Herein, Zn/Co-ZIF nanoparticles are loaded onto the aerogel obtained from bagasse cellulose by doping method to form pomegranate-like structure products, i.e., Zn/Co-ZIF@GEL. By simulating the pomegranate-biomimetic structure, the leaching of cobalt ions is suppressed and enhanced its catalytic activity. Also, Zn/Co-ZIF@GEL behaves outstanding peroxymonosulfate (PMS) activation reactivity to degrade Rhodamine B (RhB) with achieving 100% removal rate in 30 min with enhanced water stability. The outer wrapping of nanoparticles by aerogel exhibits excellent reusability and the removal rate remains above 92% after 4 cycles. X-ray photoelectron spectroscopy (XPS) verifies the electron transfer between the heterostructures of Zn and Co could ensure the catalyst continues to complete the redox cycle with synergistic effect. Electron paramagnetic resonance (EPR) further investigates the non-radical singlet oxygen is the predominant degradation pathway of RhB. This work provides a new strategy for improved bagasse derivate ZIF catalytic application.

Magnetic all-inorganic perovskite nanocrystals demonstrating well-defined hybrid structure and superhydrophobic behavior towards movable and stable photoluminescence

As an emerging light-harvesting and light-emitting materials, all-inorganic perovskite nanocrystals (AIPNCs) have attracted widespread attentions in optoelectronic materials and devices. However, great challenges exist for the fabrication of novel AIPNCs demonstrating magnetic properties. Here, magnetic AIPNCs (M-AIPNC) with well-defined hybrid nanostructures of Fe3O4@SiO2@AIPNC are proposed. The core-shell structured chemical encapsulation and the in-situ crystal growth are designed to fabricate the magnetic substrate of Fe3O4@SiO2 and to link the AIPNCs, respectively. The as-prepared M-AIPNCs display brilliant blue, green and red photoluminescence by adjusting the chemical compositions of AIPNCs. The M-AIPNCs also demonstrate enhanced water stability due to their surficial hydrophobicity. The photoluminescence of Fe3O4@SiO2@AIPNC in the heating process exhibits a power exponential temperature response, and can be recovered in the cooling process. Most importantly, the M-AIPNCs can realize the mobile photoluminescence driven by a remote magnetic field. The M-AIPNCs with multi-colored fluorescence, excellent fluorescence stability, reversible temperature response and non-contact motion control provide a brand-new strategy to create the next generation of intelligent optical materials.

Precise Construction of Stable Bimetallic Metal–Organic Frameworks with Single-Site Ti(IV) Incorporation in Nodes for Efficient Photocatalytic Oxygen Evolution

Precise Construction of Stable Bimetallic Metal–Organic Frameworks with Single-Site Ti(IV) Incorporation in Nodes for Efficient Photocatalytic Oxygen Evolution

Halide Perovskite Nanocrystals with Enhanced Water Stability for Upconversion Imaging in a Living Cell.

Halide perovskite nanomaterials are widely used in optoelectronics and photonics due to their outstanding luminescent properties, whereas their strong multiphoton absorption makes them prospective for bioimaging. Nonetheless, instability of perovskites in aqueous solutions is an important limitation that prevents their application in biology and medicine. Here, we demonstrate fluorescence and upconversion imaging in living cells by employing CsPbBr3 nanocrystals (NCs) that show an improved water-resistance (at least for 24 h) after their coating as individual particles with various silica-based shells. The obtained phTEOS-TMOS@CsPbBr3 NCs possess high quality, which we confirm with high-resolution transmission and scanning transmission electron microscopy, X-ray diffraction analysis, Fourier-transform infrared and energy-dispersive X-ray spectroscopies, as well as with fluorescence optical microscopy. The developed platform can make the halide perovskite NCs suitable for various bioimaging applications.