Salting-in species induced self-assembly of stable MOFs

Exploring the effects of excipients on complex coacervation

Complex coacervation is an associative liquid-liquid phase separation phenomenon that takes place due to the electrostatic complexation of oppositely-charged polyelectrolytes and the entropic gains associated with the release of bound counterions and rearrangement of solvent. The aqueous nature of coacervation has resulted in its broad use in systems requiring high biocompatibility. The significance of electrostatic interactions in coacervates has meant that studies investigating the phase behaviors of these systems have tended to focus on parameters such as the charge stoichiometry of the polyions, the solution pH, and the ionic strength. However, the equilibrium that exists between the polymer-rich coacervate phase and the polymer-poor supernatant phase represents a balance among attractive electrostatic interactions and excluded volume repulsions as well as osmotic pressure effects. As such, we hypothesize that it should be possible to tune coacervate phase behavior via the addition of non-electrostatic excipients which would partition between the two phases and potentially alter both the solvent quality and the osmotic pressure balance. In particular, our work focuses on small molecule excipients such as sugars, amino acids, and other additives that have a history of use in vaccine formulation. We quantified the ability of these excipients to partition into the coacervate phase, and their potential for destabilizing the phase separation. Furthermore, we demonstrate that these additives can be combined with complex coacervation in the context of a virus formulation.

Multi-enzymatic biomimetic cerium-based MOFs mediated precision chemodynamic synergistic antibacteria and tissue repair for MRSA-infected wounds

Antibiotic-resistant pathogens represent a significant global public health challenge, particularly in refractory infections associated with biofilms. Urgent development of innovative, safe, and therapeutically adaptive strategies to combat these resistant biofilms is essential. We present a novel biomimetic antibacterial system inspired by the multifunctional enzymatic properties of cerium-based metal-organic frameworks. This system utilizes the inherent oxidase and peroxidase activities of a nanozyme to generate reactive oxygen species (ROS) for bacterial eradication, while its phosphate-ester hydrolase activity disrupts bacterial genetic material and energy metabolism. By the reversible covalent binding between boronic acid groups and cis-diol groups on bacterial surfaces, combined with abundant cerium catalytic sites from the porous structure and the potent antibacterial effects of sanguinarine, we enhance targeted antibacterial activity. This system effectively penetrates extracellular polymeric substances (EPS) and demonstrates precise regulation of ROS, allowing for localized delivery of ROS and sanguinarine for biofilm eradication. Transcriptomic analyses indicate that this approach disrupts the cellular environment, impairs energy metabolism, inhibits bacterial attachment to EPS, and promotes biofilm dispersion by modulating drug resistance-related genes. In vivo experiments confirm that this nanocatalyst composite effectively treats biofilm-induced wounds with efficacy comparable to vancomycin, presenting a promising solution for managing chronic infections caused by antibiotic-resistant biofilms.

Harnessing the Hofmeister Effect for Dynamic Self-Assembly of Supramolecular Hydrogels

Dynamic regulation of intermolecular interactions is essential for the creation of dynamic supramolecular materials with lifelike self-regulating functions. Yet specific ion effect, which is known to possess potent effect on intermolecular interactions, has remained unexplored for such a purpose. Here, we demonstrate our access to dynamic self-assembly of supramolecular hydrogels by orchestrating the Hofmeister effect through a simple enzymatic reaction. The involved gelators containing carboxylate moieties self-assemble into hydrogel (Gel1) at acidic pH and dissolve at basic pH. We surprisingly find that the dissolved gelators at basic pH can be driven to self-assemble into hydrogel (Gel2) by kosmotropic ions through the disruption of gelator-water interactions. By coupling to the enzymatic hydrolysis of urea, Gel1 gradually disintegrates over time because of the production of basic NH3. However, interestingly, with the accumulation of kosmotropic ions, NH4 + and CO3 2-, the dissolved gelators are driven to self-assemble into Gel2, realizing a self-regulating gel-sol-gel transition process. The transition rate and stiffness of Gel2 are tunable by adjusting the concentrations of urea or urease. This work may shed light on the creation of lifelike self-regulating supramolecular materials using Hofmeister effect for many enticing applications such as ion-programmed biosensing and drug delivery.

Light-Responsive Nanoemulsion-Guided Assembly of Honeycomb Hierarchically Macro/mesoporous Metal-Organic Framework Nanoarchitectures

Despite that soft template pathways are promising avenues for synthesizing hierarchically porous metal-organic framework (MOF) nanoparticles, smart-responsive-directed assembly strategies have been rarely extended to fabricate well-defined hierarchical macro/mesoporosities in MOF architectures. Herein, a novel light-responsive nanoemulsion-guided strategy is reported to prepare honeycomb hierarchically porous UiO-66 nanoparticles (UiO-66 HHPNPs) with macro/mesoporosities transition using poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (F127, PEO106PPO70PEO106) and azobenzene (Azo) as a light-responsive soft template. By facilely tuning the concentration of Azo and light irradiation (e.g., 365 nm ultraviolet light), the assembled UiO-66 HHPNPs varies from microporous architectures to macro/mesoporous dendritic architectures with an average pore size expanding from 14 to 135 nm. It is worth noting that the cis-trans configuration transformation of Azo under the irradiation of 475 nm blue light results in the shrunken micelles and thus rapid template removal from macro/mesoporous architectures of UiO-66 HHPNPs. Additionally, a light-responsive soft template can also alter the pore structures of other MOF nanoparticles (e.g., zirconium-based UiO-66). Importantly, the resultant macro/mesoporous UiO-66 HHPNPs reveal superior catalytic activity than the microporous UiO-66 HHPNPs in the 3,3',5,5'-tetramethylbenzidine catalytic reaction system. This newfangled light-induced template assembly technique paves an attractive way for the rational design of multimodal macro/mesoporous architectures and thus renders them broad applications.

Scalable and Low-Energy Synthesis of Metal-Organic Frameworks by a Seed-Mediated Approach

The synthesis of metal-organic frameworks (MOFs) by low energy input has been a long-term target for practical applications yet remains a great challenge. Herein, we developed a low-energy MOF growth strategy at a temperature down to 50 °C by simply introducing seeds into the reaction system. The MOFs are continuously grown on the surface of the seeds at a growth rate dozens of times higher than that of conventional solvothermal synthesis at low temperature, while the resulting MOFs possess high crystallinity, porosity, and stability similar to solvothermal seeds. Remarkably, the obtained MOFs feature high-density structural defects with Lewis acidity, thereby displaying more than one order of magnitude higher activity than the MOFs obtained by the conventional solvothermal method in the iodination reaction of substituted arenes. This low-energy synthetic approach is readily scaled up, which would be a significant step forward in the dream of the MOF industry.

Investigation the effect of exchange solvents on the adsorption performances of Ce-MOFs towards organic dyes

Cerium-based MOFs (Ce-MOFs) are regarded as attractive porous materials showing various structures, excellent thermal and chemical stability, tunable porous properties, and simple synthetic methods that are useful for wastewater treatment applications. Hence, in the present work, we synthesized a series of Ce-MOFs through a fast and green synthetic method at room temperature using water as a green solvent. Four different solvents including ethanol, chloroform, acetone, and methanol were used in the solvent-exchange process to engineer the properties of prepared Ce-MOFs. The influence of different exchange solvents on the crystalline structure, porous structure, thermal stability, and surface morphology of Ce-MOFs was studied systematically. It was found that exchange solvents can significantly affect the chemical and physical properties of prepared Ce-MOFs. Using ethanol as an exchange solvent results in the production of highly crystalline MOF that has the highest surface area (843 m2/g) and pore volume (0.7518 cm3/g) compared to other prepared Ce-MOFs. The dye adsorption experiments revealed that the activated sample by acetone (Ce-MOF-4) exhibited the highest adsorption capacities toward both anionic (270.27 mg/g for Congo Red (CR)) and cationic (227.27 mg/g for Malachite Green (MG)) dyes. This MOF adsorbs both organic dyes via different mechanisms including hydrogen bonding, pore-filling, π-π stacking, coordination, and electrostatic interactions. Moreover, it exhibited good structural stability in acidic solution, neutral solution, and during consecutive adsorption-desorption cycles, confirming its potential to be applied as a stable adsorbent for simultaneous removal of cationic and anionic organic dyes from water.

Construction of Compartmentalized Meso/Micro Spaces in Hierarchically Porous MOFs with Long-Chain Functional Ligands Inspired by Biological Signal Amplification

The creation of spatially coupled meso-/microenvironments with biomimetic compartmentalized functionalities is of great significance to achieve efficient signal transduction and amplification. Herein, using a soft-template strategy, UiO-67-type hierarchically mesoporous metal-organic frameworks (HMMOFs) were constructed to satisfy the requirements of such an artificial system. The key to the successful synthesis of HMUiO-67 is rooted in the utilization of the preformed cerium-oxo clusters as metal precursors, aligning the growth of MOF crystals with the mild conditions required for the self-assembly of the soft template. The adoption of long-chain functional 2,2'-bipyridine-5,5'-dicarboxylic acid ligands not only resulted in larger microporous sizes, facilitating the transport of various cascade reaction intermediates, but also provided anchorages for the introduction of enzyme-mimicking active sites. A cascade amplification system was designed based on the developed HMUiO-67, in which enzyme cascade reactions were initiated and relayed by a target analyte in the separate but coupled meso/micro spaces. As a proof of concept, natural acetylcholinesterase (AChE) and Cu-based laccase mimetics were integrated into HMMOFs, establishing a spatially coupled nanoreactor. The activity of AChE was triggered by the target analyte of carbaryl, while the amplified products of AChE catalysis mediated the activity of biomimetic enzyme in the closely proximate microporous spaces, producing further amplification of detectable signal. This enabled the entire cascade system to respond to minimal carbaryl with a limit of detection as low as approximately 2 nM. Such a model of cascade amplification is expected to set a conceptual guideline for the rational design of various bioreactors, serving as a sensitive response system for quantifying numerous target analytes.

Biphasic interface templated synthesis of wrinkled MOFs for the construction of cascade sensing platform based on the encapsulated gold nanoclusters and enzymes

The design and construction of MOFs with flower-like structure could afford sufficient space for the immobilization of guests with large size and interconnected transport channels for their mass diffusion although it remains a challenge. Herein, wrinkled Ce-based hierarchically porous UiO-66 (Ce-WUiO-66) with good crystallinity was successfully synthesized for the first time using bicontinuous emulsion composed of 1-heptanol, water and F127 (PEO106PPO70PEO106) surfactant as a template. F127 played a key role in the formation of emulsions as a stabilizer, and meanwhile its PEO segments interacted with MOF precursors to guide the evolvement of crystallized pore walls. Through controlling the ratios of heptanol to water and the salinity, the distances of the pleat openings and the morphology of the resultant Ce-WUiO-66 were facilely regulated. In virtue of its highly open radial structure, Ce-WUiO-66 could serve as an ideal platform for loading multiple substances to build a cascade sensing system. As a proof of concept, we designed an amino acid (AA) cascade probe by co-immobilizing gold nanoclusters (AuNCs) and LAA oxidase into Ce-WUiO-66. The aggregation-induced-emission enhancement resulted from the encapsulation of AuNCs into Ce-WUiO-66 significantly improved the detection sensitivity and the detection limit of corresponding substrates reached as low as 10-8 M. The proposed biphasic interface assembly strategy is hopefully to provide a new route for the rational design of MOFs with various open pore structure and broaden their potential applications with multiple large-size substances involved besides the currently exemplified cascade sensing platform.

Structural engineering in hierarchical nanoarchitectures of metal-organic frameworks and their derivatives

Metal-organic frameworks (MOFs) have attracted much attention owing to their tuneable structures, high surface areas, and good functionalization. Nanoreactors derived from various MOFs are now widely used in heterogeneous catalysis, electrocatalysis and photocatalysis. The nanoarchitectures of MOFs and their derivatives have a great impact on mass and energy transfer pathways, thus affecting the activity and selectivity of the catalysts. In this review, we intend to provide a universal survey of reported methods to synthesize MOF-based core-satellite, core-shell, yolk-shell and hollow-shell structures or their derivatives in recent years and present a continuous evolution among them. We hope that this review could provide some perspectives for exploring new facile methods to prepare different hierarchical nanoarchitectures of MOFs or their derivatives.

From nano- to macroarchitectures: designing and constructing MOF-derived porous materials for persulfate-based advanced oxidation processes

Persulfate-based advanced oxidation processes (PS-AOPs) have gained significant attention as an effective approach for the elimination of emerging organic contaminants (EOCs) in water treatment. Metal-organic frameworks (MOFs) and their derivatives are regarded as promising catalysts for activating peroxydisulfate (PDS) and peroxymonosulfate (PMS) due to their tunable and diverse structure and composition. By the rational nanoarchitectured design of MOF-derived nanomaterials, the excellent performance and customized functions can be achieved. However, the intrinsic fine powder form and agglomeration ability of MOF-derived nanomaterials have limited their practical engineering application. Recently, a great deal of effort has been put into shaping MOFs into macroscopic objects without sacrificing the performance. This review presents recent advances in the design and synthetic strategies of MOF-derived nano- and macroarchitectures for PS-AOPs to degrade EOCs. Firstly, the strategies of preparing MOF-derived diverse nanoarchitectures including hierarchically porous, hollow, yolk-shell, and multi-shell structures are comprehensively summarized. Subsequently, the approaches of manufacturing MOF-based macroarchitectures are introduced in detail. Moreover, the PS-AOP application and mechanisms of MOF-derived nano- and macromaterials as catalysts to eliminate EOCs are discussed. Finally, the prospects and challenges of MOF-derived materials in PS-AOPs are discussed. This work will hopefully guide the design and development of MOF-derived porous materials in SR-AOPs.

Uncoordinated amino groups of MIL-101 anchoring cobalt porphyrins for highly selective CO2 electroreduction

Electrocatalytic carbon dioxide reduction reaction (CO2RR) presents a sustainable route to address energy crisis and environmental issues, where the rational design of catalysts remains crucial. Metal-organic frameworks (MOFs) with high CO2 capture capacities have immense potential as CO2RR electrocatalysts but suffer from poor activity. Herein we report a redox-active cobalt protoporphyrin grafted MIL-101(Cr)-NH2 for CO2 electroreduction. Material characterizations reveal that porphyrin molecules are covalently attached to uncoordinated amino groups of the parent MOF without compromising its well-defined porous structure. Furthermore, in situ spectroscopic techniques suggest inherited CO2 concentrate ability and more abundant adsorbed carbonate species on the modified MOF. As a result, a maximum CO Faradaic efficiency (FECO) up to 97.1% and a turnover frequency of 0.63 s-1 are achieved, together with FECO above 90% within a wide potential window of 300 mV. This work sheds new light on the coupling of MOFs with molecular catalysts to enhance catalytic performances.

Hofmeister Effect Promoted the Introduction of Tunable Large Mesopores in MOFs at Low Temperature for Femtomolar ALP Detection

In addressing the demand for hierarchically mesoporous metal-organic frameworks (HMMOFs) with adjustable large mesopores, a method based on the synergistic effects of low-temperature microemulsions and Hofmeister ions is developed. Low temperature dramatically enhanced the solubility of hydrophobic solvent in the microemulsion core, enlarging the mesopores in HMMOFs replica. Meanwhile, Hofmeister salt-in ions continuously controlled mesopore expansion by modulating the permeability of swelling agent into the microemulsion core. The large mesopores up to 33 nm provided sufficient space for the alkaline phosphatase (ALP) enrichment, and retained the remaining channel to facilitate the free mass diffusion. Leveraging these advantages, a colorimetric sensor is successfully developed using large-mesopore HMMOFs for femtomolar ALP detection based on the enrichment and cycling amplification principles. The sensor exhibited a linear detection range of 100 to 7500 fm and a limit of detection of 42 fm, presenting over 4000 times higher sensitivity than classic para-nitrophenyl phosphate colorimetric methods. Such high sensitivity highlights the importance of adjustable mesoporous structures of HMMOFs in advanced sensing applications, and prefigures their potential for detecting large biomolecules in diagnostics and biomedical research.

Green Synthesis of Cerium-Based Metal-Organic Framework (Ce-UiO-66 MOF) for Wastewater Treatment

Green synthesis of metal-organic frameworks (MOFs) in aqueous solutions under ambient conditions with reduced production costs and environmental effects is an efficient technique to transfer lab-scale production to industrial large scale. Hence, this work proposes a green, low-cost, sustainable, rapid, and innovative synthetic strategy to produce cerium-based (Ce-UiO-66) MOFs under ambient conditions in the presence of water as a green solvent. This synthetic strategy exhibits great potential compared to conventional solvothermal synthetic techniques, and it does not need external activation energy and organic solvents, which can achieve the standards of green chemistry. Ce-UiO-66 MOF was synthesized successfully and utilized as a green adsorbent to efficiently eliminate anionic Congo Red (CR) dye from dye-containing wastewater. The experimental adsorption results were well matched to the pseudo-second-order kinetic and Langmuir isotherm models, in which the maximum CR adsorption capacity was measured to be about 285.71 mg/g. To evidence the applicability of Ce-UiO-66 MOFs in CR adsorption, the CR adsorption reaction was performed in the presence of interfering pollutants [e.g., salts (NaCl, KCl, and MgCl2) and cationic organic dyes (Malachite Green (MG) and Methylene Blue (MB)], where the results prove the promising adsorption performances of Ce-UiO-66 MOFs toward CR dye. Interestingly, the synthesized adsorbent exhibited high structural stability during repeated adsorption-desorption cycles, where the surface area of MOFs decreased from 555 to 376 m2/g after three cycles, while its CR adsorption capacity decreased by only 10% compared to that of the fresh adsorbent. All these outstanding properties indicate that the Ce-UiO-66 MOFs will be an effective adsorbent for water and wastewater treatment applications.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Hofmeister Effects Shine in Nanoscience

Hofmeister effects play a crucial role in nanoscience by affecting the physicochemical and biochemical processes. Thus far, numerous wonderful applications from various aspects of nanoscience have been developed based on the mechanism of Hofmeister effects, such as hydrogel/aerogel engineering, battery design, nanosynthesis, nanomotors, ion sensors, supramolecular chemistry, colloid and interface science, nanomedicine, and transport behaviors, etc. In this review, for the first time, the progress of applying Hofmeister effects is systematically introduced and summarized in nanoscience. It is aimed to provide a comprehensive guideline for future researchers to design more useful Hofmeister effects-based nanosystems.

Internalization of the Metal-Organic Framework MIL-101(Cr)-NH2 by a Freshwater Alga and Transfer to Zooplankton

The common metal-organic framework (MOF) MIL-101(Cr)-NH₂ has attracted considerable attention due to its great potential applications in the environmental field. Nevertheless, its behavior and fate in aquatic systems are unknown. This study quantified and visualized the interactions of MIL-101(Cr)-NH₂ with the freshwater phytoplanktonic alga Chlamydomonas reinhardtii and its potential trophic transfer to zooplankton. The unicellular alga absorbed and accumulated the MOF by surface attachment, forming agglomerates and eventually cosettling out from water. Bioimaging revealed that MIL-101(Cr)-NH₂ was internalized by the algal cells and mainly occurred in the pyrenoid. Without algae in a freshwater system, MIL-101(Cr)-NH₂ was ingested by Daphnia magna, showing steadily increasing concentrations approaching 1-9% of dry body weight. Addition of algae substantially suppressed D. magna uptake of MIL-101(Cr)-NH₂ by 63.8-97.9%. Such inhibition could be explained by the competitive uptake of MOF by the algae and the inductive effects of algal food on MOF elimination by D. magna. The MOF (≤1 mg/L) ingested by D. magna was centered in the gut regions, whereas large MOF or algae-MOF aggregates were adsorbed onto the carapace and appendages, including the antennae, at 10 mg/L. Overall, the algae were the major targets for MIL-101(Cr)-NH₂, with nearly all algal cells settling out at 10 mg/L within 24 h. The possibility of trophic transfer of MIL-101(Cr)-NH₂ to D. magna in aquatic systems with algae present was limited due to its low accumulation potential and short retention time in D. magna.

Room temperature design of Ce(iv)-MOFs: from photocatalytic HER and OER to overall water splitting under simulated sunlight irradiation

A new synthetic approach is reported to synthesize redox-active Ce(iv) MOFs at room temperature for efficient and reusable photo-induced overall water splitting.

Mechanistic Principles for Engineering Hierarchical Porous Metal-Organic Frameworks

Metal-organic frameworks (MOFs) have generated tremendous research interest in the past two decades, due to their high surface areas, tailorable active sites, and tunable structures. Hierarchical porous MOFs (HP-MOFs) with two or more pore systems are particularly attractive, benefiting from improved active site accessibility and enhanced mass diffusivity in applications involving bulk molecules. This review outlines the mechanistic principles used for the rational design of HP-MOFs, current techniques used to measure their hierarchical porosities, as well as their emerging applications. We then critically summarize the current challenges in this field and provide a contemporary perspective on the technological innovations that would address current synthetic challenges in the field of HP-MOFs. The aim of this review is to provide an in-depth understanding of the formation mechanisms, materials chemistry, and structural and chemical properties of HP-MOFs while exploring ways to enhance the performance of current MOF materials in a range of fields.

Hierarchical large-pore MOFs templated from poly(ethylene oxide)-b-polystyrene diblock copolymer with tuneable pore sizes

Diblock copolymer poly(ethylene oxide)-b-poly(styrene) (PEO-b-PS) was adopted to template the synthesis of hierarchically porous Ce-based metal-organic frameworks (MOFs) for the first time. By extending the synergistic effect of Hofmeister ions and soft templates into the water-rich system, UiO-66 type Ce-MOFs with a mesopore size of about 15 nm were achieved. Mesopore size could be further tuned up to approximately 23 nm upon introducing 1,3,5-trimethylbenzene to the micelle core of PEO-b-PS.

Hierarchically Porous MOFs Synthesized by Soft-Template Strategies

The past few decades have been witnessing the rapid research boom of metal-organic frameworks (MOFs), which are assembled from metal nodes and multitopic organic linkers. In virtue of their modular assembly mode, they can be tailored according to desired functions to satisfy numerous potential applications. However, most initially reported MOFs were restricted to the microporous regime, limiting their practical applications with bulk molecules involved. Therefore, the research attention was immediately directed toward enlarging the intrinsic pore size of frameworks by extending the secondary building units or organic ligands. Unfortunately, the synthesis of more extended ligands is frequently tedious, and the most resultant MOFs are not sufficiently stable, restricting their popularization. The soft-template strategy is recognized as a promising avenue to produce hierarchically porous MOFs (HPMOFs), although early attempts generally failed due to the incompatibility between the surfactant self-assembly and guided crystallization process of MOF precursors in the organic phase. Therefore, developing a rational soft-template strategy to achieve the precise control of morphology and porosity of HPMOFs is of great significance.In this Account, we present our recent progress on the development and applications of HPMOFs prepared by soft-template strategies. We highlight the key issues upon using the soft-template strategy to synthesize HPMOFs. To enhance the interaction between the template and MOF precursor, a long-chain monocarboxylic acid strategy is introduced to synthesize HPMOFs with irregular mesopores in the organic phase. Then, to improve the order of mesopores, an aqueous-phase synthesis method using amphoteric surfactants as templates is developed to prepare ordered HPMOFs. To further enlarge the pore size and make the synthesis conditions of MOFs compatible with the self-assembly of surfactants, a salting-in species-induced self-assembly strategy is proposed and coupled with the structure-directing properties of copolymer templates to synthesize a series of HPMOFs with large mesopores and even macropores. This salting-in ion-mediated self-assembly (SIMS) strategy paves the way to modify the pore size, pore structure, morphology, and chemical composition of HPMOFs. The separated but intimately interconnected hierarchical pores in the resultant HPMOFs can not only realize rapid mass transport but also isolate different-size guest molecules so that they are competent for a broad range of applications including protein digestion, cascade catalysis, enzyme-assisted substrate sensing, and DNA cleavage. Finally, the limitations, challenges, and future developments of this rapidly evolving field are described. This Account with a highlight to the soft-template strategies not only provides interesting insights to understand the assembly process between templates and MOFs but also inspires an optimization of the properties of HPMOFs from diverse aspects for desired applications.

DFT study of common anions adsorption at graphene surface due to anion-π interaction

Using density functional theory (DFT) calculations, we researched the different anions adsorption on the graphene and found that anions can be stably adsorbed on the graphene surface due to the anion-π interaction. The adsorption energy decreased as the order of HPO₄^2- > SO₄^2- > F^- > CH₃COO^- > ClO₃^- > NO₃^- > ClO₄^- > SCN^- > Cl^- > Br^-. The adsorption energy markedly increased as the valence of anion increased from negative monovalence (< -20 kcal/mol) to negative bivalence (> -40 kcal/mol). The energy decomposition analysis (EDA) showed that anion-π interaction is mainly induced by orbital effect. This work provides new insights for understanding Hofmeister effect at graphene interface from the molecular level and indicates that the anion-π interaction cannot be ignored at the interface, especially for the substrate with π-electron-rich carbon-based nanomaterials.

Nanoemulsion-directed growth of MOFs with versatile architectures for the heterogeneous regeneration of coenzymes

As one of the most appealing strategies for the synthesis of nanomaterials with various architectures, emulsion-directed methods have been rarely used to control the structure of metal-organic frameworks (MOFs). Herein, we report a versatile salt-assisted nanoemulsion-guided assembly to achieve continuous architecture transition of hierarchical Zr-based MOFs. The morphology of nanoemulsion can be facilely regulated by tuning the feed ratio of a dual-surfactant and the introduced amount of compatible hydrophobic compounds, which directs the assembly of MOFs with various architectures such as bowl-like mesoporous particle, dendritic nanospheres, walnut-shaped particles, crumpled nanosheets and nanodisks. The developed dendritic nanospheres with highly open and large mesochannels is successfully used as matrix for the co-immobilization of coenzymes and corresponding enzymes to realize the in situ heterogeneous regeneration of NAD⁺. This strategy is expected to pave a way for exploring sophisticated hierarchical MOFs which can be competent for practical applications with bulk molecules involved.

Controlling the structure of hierarchical metal-organic frameworks via soft template remains a challenge. Here, the authors report a salt-assisted nanoemulsion-guided strategy to achieve continuous structure transition of hierarchical Zr-based MOFs.

The chemistry behind room temperature synthesis of hafnium and cerium UiO-66 derivatives

RT formation of Hf and Ce UiO-66 derivatives is investigated using a one-step method where the linker and metal salt are simply combined, and a two-step method where the inorganic component is pre-heated to form metal clusters.

The electrostatic origins of specific ion effects: quantifying the Hofmeister series for anions

Life as we know it is dependent upon water, or more specifically salty water. Without dissolved ions, the interactions between biological molecules are insufficiently complex to support life. This complexity is intimately tied to the variation in properties induced by the presence of different ions. These specific ion effects, widely known as Hofmeister effects, have been known for more than 100 years. They are ubiquitous throughout the chemical, biological and physical sciences. The origin of these effects and their relative strengths is still hotly debated. Here we reconsider the origins of specific ion effects through the lens of Coulomb interactions and establish a foundation for anion effects in aqueous and non-aqueous environments. We show that, for anions, the Hofmeister series can be explained and quantified by consideration of site-specific electrostatic interactions. This can simply be approximated by the radial charge density of the anion, which we have calculated for commonly reported ions. This broadly quantifies previously unpredictable specific ion effects, including those known to influence solution properties, virus activities and reaction rates. Furthermore, in non-aqueous solvents, the relative magnitude of the anion series is dependent on the Lewis acidity of the solvent, as measured by the Gutmann Acceptor Number. Analogous SIEs for cations bear limited correlation with their radial charge density, highlighting a fundamental asymmetry in the origins of specific ion effects for anions and cations, due to competing non-Coulombic phenomena.

Metal-Organic Framework-Based Hierarchically Porous Materials: Synthesis and Applications

Metal-organic frameworks (MOFs) have been widely recognized as one of the most fascinating classes of materials from science and engineering perspectives, benefiting from their high porosity and well-defined and tailored structures and components at the atomic level. Although their intrinsic micropores endow size-selective capability and high surface area, etc., the narrow pores limit their applications toward diffusion-control and large-size species involved processes. In recent years, the construction of hierarchically porous MOFs (HP-MOFs), MOF-based hierarchically porous composites, and MOF-based hierarchically porous derivatives has captured widespread interest to extend the applications of conventional MOF-based materials. In this Review, the recent advances in the design, synthesis, and functional applications of MOF-based hierarchically porous materials are summarized. Their structural characters toward various applications, including catalysis, gas storage and separation, air filtration, sewage treatment, sensing and energy storage, have been demonstrated with typical reports. The comparison of HP-MOFs with traditional porous materials (e.g., zeolite, porous silica, carbons, metal oxides, and polymers), subsisting challenges, as well as future directions in this research field, are also indicated.

Accelerated and scalable synthesis of UiO-66(Zr) with the assistance of inorganic salts under solvent-free conditions

The synthesis of UIO-66 (Zr) and its functionalized materials can be accelerated and scalable under solvent-free condition with the assistance of inorganic salts.

Counteranions in the Stimulation Solution Alter the Dynamics of Exocytosis Consistent with the Hofmeister Series

We show that the Hofmeister series of ions can be used to explain the cellular changes in exocytosis observed by single-cell amperometry for different counteranions. The formation, expansion, and closing of the membrane fusion pore during exocytosis was found to be strongly dependent on the counteranion species in solution. With stimulation of chaotropic anions (e.g., ClO₄^–), the expansion and closing time of the fusion pore are longer, suggesting chaotropes can extend the duration of exocytosis compared with kosmotropic anions (e.g., Cl^–). At a concentration of 30 mM, the two parameters (e.g., t_1/2 and t_fall) that define the duration of exocytosis vary with the Hofmeister series (Cl^– < Br^– < NO₃^– ≤ ClO₄^– < SCN^–). More interestingly, fewer (e.g., N_foot/N_events) and smaller (e.g., I_foot) prespike events are observed when chaotropes are counterions in the stimulation solution, and the values can be sorted by the reverse Hofmeister series (Cl^– ≥ Br^– > NO₃^– > ClO₄^– > SCN^–). Based on ion specificity, an adsorption-repulsion mechanism, we suggest that the exocytotic Hofmeister series effect originates from a looser swelling lipid bilayer structure due to the adsorption and electrostatic repulsion of chaotropes on the hydrophobic portion of the membrane. Our results provide a chemical link between the Hofmeister series and the cellular process of neurotransmitter release via exocytosis and provide a better physical framework to understand this important phenomenon.

Hofmeister Series: Insights of Ion Specificity from Amphiphilic Assembly and Interface Property

Hofmeister series (HS), ion specific effect, or lyotropic sequence acts as a pivotal part in a number of biological and physicochemical phenomena, e.g., changing the solubility of hydrophobic solutes, the cloud points of polymers and nonionic surfactants, the activities of various enzymes, the action of ions on an ion-channel, and the surface tension of electrolyte solutions, etc. This review focused on how ion specificity influences the critical micelle concentration (CMC) and how the thermoresponsive behavior of surfactants, and the dynamic transition of the aggregate, controls the aggregate transition and gel formation and tunes the properties of air/water interfaces (Langmuir monolayer and interfacial free energy). Recent progress of the ion specific effect in bulk phase and at interfaces in amphiphilic systems and gels is summarized. Applications and a molecular level theoretical explanation of HS are discussed comprehensively. This review is aimed to supply a fresh and comprehensive understanding of Hofmiester phenomena in surfactants, polymers, colloids, and interface science and to provide a guideline to design the microstructures and templates for preparation of nanomaterials.

The chemistry of Ce-based metal-organic frameworks

Metal-organic frameworks (MOFs) have gained widespread attention due to their modular construction that allows the tuning of their properties. Within this vast class of compounds, metal carboxylates containing tri- and tetravalent metal ions have been in the focus of many studies due to their often high thermal and chemical stabilities. Cerium has a rich chemistry, which depends strongly on its oxidation state. Ce(iii) exhibits properties typically observed for rare earth elements, while Ce(iv) is mostly known for its oxidation behaviour. In MOF chemistry this is reflected in their unique optical and catalytic properties. The synthetic parameters for Ce(iii)- and Ce(iv)-MOFs also differ substantially and conditions must be chosen to prevent reduction of Ce(iv) for the formation of the latter. Ce(iii)-MOFs are usually reported in comprehensive studies together with those constructed with other RE elements and normally they are isostructural. They exhibit a greater structural diversity, which is reflected in the larger variety of inorganic building units. In contrast, the synthesis conditions of Ce(iv)-MOFs were only recently (2015) established. These lead selectively to hexanuclear Ce-O clusters that are well-known for Zr-MOFs and therefore very similar structural and isoreticluar chemistry is found. Hence Ce(iv)-MOFs exhibit often high porosity, while only a few porous Ce(iii)-MOFs have been described. Some of these show structural flexibility which makes them interesting for separation processes. For Ce(iv)-MOFs the redox properties are most relevant. Thus, they are intensively discussed for catalytic, photocatalytic and sensing applications. In this perspective, the synthesis, structural chemistry and properties of Ce-MOFs are summarized.

Selective CO2 or CH4 adsorption of two anionic bcu-MOFs with two different counterions: experimental and simulation studies

Two new bcu-MOFs with counterions tuned from Li(H₂O)₄⁺ to DMA⁺ have been successfully synthesized and their selective CO₂ or CH₄ adsorption over N₂ gas has been systematically investigated in-depth by both experimental and simulation studies.