Water Adsorption Desorption Research Articles

Optimizing Hygroscopic Metal–Organic Frameworks via EDTA‐Mediated Structural Reinforcement and Photothermal Modification

AbstractHygroscopic metal–organic frameworks (MOFs) are considered as superior moisture sorbents due to their highly adjustable and desired water adsorption/release performance, enabling effective atmospheric water harvesting (AWH) in arid regions. However, the water adsorption capacity, recycling stability, and functionality of current MOFs should be further improved to meet the requirements of practical AWH systems. Here the hydrophilicity at low relative humidity (RH) and cycling stability of MOF‐808 are simultaneously enhanced through the ethylenediaminetetraacetic acid (EDTA)‐mediated post‐modification. Based on the structural reinforcement, EDTA‐modified MOF‐808 (E‐MOF‐808) delivers a stable water uptake capacity of 0.39 g g−1 at 25% RH even after 50 water adsorption–desorption cycles, more than five times that of pristine MOF‐808. In addition, bridging by EDTA with the strong chelating ability, the E‐MOF‐808 can spontaneously capture Cu2+ for further functional improvement. Accordingly, light‐absorbing CuS nanoparticles can be in situ decorated on E‐MOF‐808 for facilitating solar‐driven water release. It is envisioned that this EDTA‐mediated function enhancement should provide valuable insights into the all‐in‐one design of versatile MOFs sorbents.

Nonalkaline Fabrication of Al-Based Metal-Organic Frameworks with Tailored Water Sorption Properties via Polymeric Hydroxy-Aluminum Basicity Modulation.

Metal-organic frameworks (MOFs) are porous crystalline materials composed of metallic nodes and organic ligands, demonstrating increasing potential in water harvesting in arid and semiarid regions. This study presents a nonalkaline, water-based, and scalable synthesis strategy designed to adjust the water sorption properties of aluminum-based MOFs (Al-MOFs), specifically, AlFum and MOF-303, by modifying the basicity of the metal source, polymeric hydroxy-aluminum, as an alternative. Characterizations, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analyses (TGA), confirmed the successful synthesis of Al-MOFs. The results revealed that high-basicity polymeric hydroxy-aluminum introduced additional mesoscopic intraparticle defects, interparticle voids, and hydrophilic surface sites to the primary microporous Al-MOFs. This led to an enhanced external surface area and uniformity in the particle size. Consequently, the water sorption performance of basicity-modulated Al-MOFs was significantly improved. Specifically, within the typical working humidity between 0.05 and 0.3, using polymeric hydroxy-aluminum of the highest basicity resulted in a 23% and 68% increase in water uptake for AlFum and MOF-303, respectively, achieving capacities of 0.43 and 0.37 g·g-1. Cyclic water adsorption-desorption tests further indicated the hydrolytic stability of prepared Al-MOFs. This study offers a novel approach to engineering MOF properties through metal source modulation, with important implications for applications in water harvesting and heat transfer.

Regulation of d‐Band Center of Ruthenium Sites via Electronic Complementary Effect of C60 Fullerene Molecules and Manganese Atoms for Efficient Alkaline Hydrogen Evolution

AbstractDeveloping advanced electrocatalysts is crucial for alkaline hydrogen evolution reaction (HER). A balance in adsorption energy for each reaction intermediate on the catalyst determines the overall catalytic rate. This balance is closely linked to the d‐band center, which is, in turn, controlled by the electronic structure of the active sites. Herein, C60 molecules with electron‐withdrawing properties and manganese (Mn) atoms with electron‐donating properties to drive charge redistribution on Ru active sites are strategically utilized. The synergistic and complementary effects of C60 and Mn regulate the d‐band centers of Ru sites to an optimal position, optimizing both the water adsorption and hydrogen desorption of the synthesized Ru catalysts. The constructed MnRu/C60‐3 catalyst exhibits a low overpotential of 8 mV at 10 mA cm−2, a large TOF value of 15.5 s−1, and a high mass activity of 2.39 A mg−1Ru at an overpotential of 100 mV in 1.0 m KOH. The anion exchange membrane water electrolyzer, assembled with MnRu/C60‐3 as the cathode, demonstrates excellent water electrolysis performance and high stability under industrial operational conditions. This work offers a fresh perspective on catalyst design principles by manipulating the d‐band centers of active sites using two complementary components.

Tubular metal–organic framework membranes enabling exceptional atmospheric water harvesting by fast air permeation

Atmospheric water harvesting (AWH) with monolithic metal–organic frameworks (MOFs) represents an industrially favorable solution to freshwater scarcity, while its water productivity is rather poor due to the limited water adsorption–desorption cycling capacity of MOFs. Herein, versatile tubular MOF membranes (TMMs) with well-aligned lamellar microstructures and containing helical porous carbon strips (PCSs) are presented. Such unique shapes and microstructures of TMMs allow the airflow to rapidly pass through TMM walls, resulting in their highly efficient surface exposure to air and dramatically accelerated atmospheric water adsorption. PCSs embedded within TMMs enable to deliver localized electrical heating (LEH) to achieve rapid and sufficient heating of the entire TMMs, endowing TMMs with highly efficient water desorption capacity. These merits synergistically impart TMMs with fast and well-controlled water adsorption–desorption cycling capabilities, enabling the TMM-based AWH devices to deliver 6.2, 3.2 and 8.6 LH2O kgTMM-1 day−1 of record-high water productivity at 20 %, 35 % and 60 % relative humidity and 25 °C, respectively. The TMM with fast air permeation and sufficient LEH capacity thus demonstrate a novel design of industry-favorable AWH sorbent towards exceptional water productivity, paving a bright avenue towards the real-world water production at scales with sorption-based AWH.

In English

Hybrid adsorbents with carbon/silica, carbon/metal oxide/silica, and carbon/metal/silica could be of interest from a practical point of view since they can effectively adsorb both polar and nonpolar compounds. Therefore, mesoporous silica gel Si–60 modified by carbonization acetylacetone or Ti, Zn, Ni, Co, Cr, Zr acetylacetonates has been studied using nitrogen and water adsorption–desorption, thermogravimetry, transmission electron microscopy, X–ray diffraction, and X–ray fluorescence methods. Grafted C/X phases consist of metal compounds (X denotes metal oxide or silicate or/and metal) and char, whose characteristics can be varied changing metal in the precursors and their amounts. The morphological, structural, and textural characteristics of C/X/SiO2, such as composition and particle size distributions of deposits, a number and kind of polar and non polar surface sites, specific surface area, pore volume, and pore size distributions depend on the type, content, and distribution of the C/X deposits. The changes in the grafted matters occur with increasing precursor and C/X concentrations and a possible catalytic effect of the X phases on the carbonization reactions. Appropriate selection of precursor structure and amounts allows one to vary and control the characteristics of whole hybrid adsorbents that is of importance from a practical point of view.

Synergistically Enabling Fast-Cycling and High-Yield Atmospheric Water Harvesting with Plasma-Treated Magnetic Flower-Like Porous Carbons.

Sorption-based atmospheric water harvesting (AWH) offers a promising solution to the water scarcity in arid regions. However, majority of the existing AWH sorbents are suffering from rather poor water productivity due to their slow water adsorption-desorption cycling capability especially when they are applied in high packing thickness. Herein, an oxygen plasma-treated magnetic flower-like porous carbon (P-MFPC) with large open surfaces, abundant surface oxygen-containing moieties, and excellent localized magnetic induction heating (LMIH) capacity is developed. These merits, together with the use of air-blowing-assisted water adsorption and LMIH-driven water desorption strategy, synergistically allow P-MFPC with 2cm of packing thickness to complete a AWH cycling in 20min and deliver a record 4.5 LH2O kg-1 day-1 of water productivity at 30% relative humidity. Synergistically enabling such an ultrafast AWH cycling at high sorbent packing thickness provides a promising way for the scalable high-yield AWH with compact AWH systems.

In-situ growth of ReS2/NiS heterostructure on Ni foam as an ultra-stable electrocatalyst for alkaline hydrogen generation

Improving water adsorption and hydrogen (H) atoms desorption capacities are critical issues for the hydrogen evolution reaction (HER) in alkaline media. Herein, a ReS2/NiS heterostructure was generated in situ on the surface of the nickel foam (NF) using a facile hydrothermal process. The combination of experimental and density functional theory (DFT) analyses revealed a charge transfer from NiS to ReS2, which directly promoted water adsorption on Ni sites in NiS as well as H desorption on S sites in ReS2. Moreover, the antioxidation capacity of the heterointerface in the catalyst improved. Therefore, the formed ReS2/NiS@NF delivered an excellent HER activity very close to that of commercial Pt/C at low current density with overpotential of 78 mV at 10 mA/cm2 while remarkably outperforming Pt/C at high current densities. The ReS2/NiS@NF also exhibited remarkable stability at 150 mA/cm2. This work provides a strategy for designing excellent electrocatalysts based on NiS.

Magnetic Stuffed Bun-Structured Metal-Organic Framework Monoliths with Noncompromised Accessible Pores and Highly Efficient Recycling Capability.

Development of industrially favorable metal-organic framework (MOF) monoliths is of paramount importance for their real-world applications. However, MOF monoliths prepared with the existing MOF shaping methods usually have seriously compromised accessible pores and suffer from inefficient and energy-intensive recycling, thereby greatly limiting their practical applications. We herein present a magnetic stuffed bun-structured MOF (mSBM) bead consisting of highly porous poly(vinyl alcohol) wraps stuffed with a binder-free powder mixture of UiO-66 and Fe3O4 nanoparticles. Such a unique structure and composition of the mSBM not only make its MOF component have a well-reserved crystal structure, surface area, and porosity and the corresponding accessible pores but also impart it with excellent localized magnetic induction heating (LMIH) capability that enables the sufficient heating and highly efficient recycling of the mSBM. These merits of mSBMs are further exemplified by assessing their atmospheric water adsorption and LMIH-driven water desorption performance. The mSBMs exhibit well-reserved atmospheric water adsorption capacities, up to 100% LMIH-driven water desorption, excellent reusability, and durability toward the practical applications. Our current work, therefore, demonstrates a new MOF shaping strategy to produce MOF monoliths with well-defined shapes, noncompromised accessible pores, and highly efficient recycling capabilities, paving a bright avenue to accelerate the practical applications of MOF monoliths.

High-yield solar-driven atmospheric water harvesting of metal-organic-framework-derived nanoporous carbon with fast-diffusion water channels.

Solar-driven, sorption-based atmospheric water harvesting (AWH) offers a cost-effective solution to freshwater scarcity in arid areas. Creating AWH devices capable of performing multiple adsorption-desorption cycles per day is crucial for increasing water production rates matching human water requirements. However, achieving rapid-cycling AWH in passive harvesters has been challenging due to sorbents' slow water adsorption-desorption dynamics. Here we report an MOF-derived nanoporous carbon, a sorbent endowed with fast sorption kinetics and excellent photothermal properties, for high-yield AWH. The optimized structure (40% adsorption sites and ~1.0 nm pore size) has superior sorption kinetics due to the minimized diffusion resistance. Moreover, the carbonaceous sorbent exhibits fast desorption kinetics enabled by efficient solar-thermal heating and high thermal conductivity. A rapid-cycling water harvester based on nanoporous carbon derived from metal-organic frameworks can produce 0.18 L kgcarbon-1 h-1 of water at 30% relative humidity under one-sun illumination. The proposed design strategy is helpful to develop high-yield, solar-driven AWH for advanced freshwater-generation systems.

Mo‐Vacancies Defect Engineering of One‐Dimensional Porous Mo2C Nanowires for Enhanced High‐Efficiency Hydrogen Evolution

AbstractThe large‐scale application of efficient water‐splitting greatly promote the development of hydrogen economy which benefit both in alleviating the energy crisis and reaching the goal of carbon neutral. To realize considerable hydrogen evolution, rational design of catalysts with controllable structure and surface composition become crucial. In this work, we proposed an enhanced active site originated from Mo‐vacancies defect in Mo2C crystal which was fabricated by the evaporation of Zn content in well‐designed one‐dimensional ZnMoO4 precursor. Density functional theory calculation and experimental results demonstrated that the formation of molybdenum vacancies in molybdenum carbide promoted the water adsorption and H2 desorption effectively, resulting in an excellent HER reaction dynamics. Moreover, one‐dimensional porous nanowires also ensured rapid mass transfer and contributed strong support for superexcellence HER performance. As expected, V−Mo2C‐900@NF exhibited extremely low overpotential (η10=43 mV) at the current density of 10 mA cm−2 and rapid reaction kinetics (Tafel slope 77.89 mV dec−1).

Ethanol Solvothermal Treatment on Graphitic Carbon Nitride Materials for Enhancing Photocatalytic Hydrogen Evolution Performance.

Recently, Pt-loaded graphic carbon nitride (g-C3N4) materials have attracted great attention as a photocatalyst for hydrogen evolution from water. The simple surface modification of g-C3N4 by hydrothermal methods improves photocatalytic performance. In this study, ethanol is used as a solvothermal solvent to modify the surface properties of g-C3N4 for the first time. The g-C3N4 is thermally treated in ethanol at different temperatures (T = 140 °C, 160 °C, 180 °C, and 220 °C), and the Pt co-catalyst is subsequently deposited on the g-C3N4 via a photodeposition method. Elemental analysis and XPS O 1s data confirm that the ethanol solvothermal treatment increased the contents of the oxygen-containing functional groups on the g-C3N4 and were proportional to the treatment temperatures. However, the XPS Pt 4f data show that the Pt2+/Pt0 value for the Pt/g-C3N4 treated at ethanol solvothermal temperature of 160 °C (Pt/CN-160) is the highest at 7.03, implying the highest hydrogen production rate of Pt/CN-160 is at 492.3 μmol g−1 h−1 because the PtO phase is favorable for the water adsorption and hydrogen desorption in the hydrogen evolution process. In addition, the electrochemical impedance spectroscopy data and the photoluminescence spectra emission peak intensify reflect that the Pt/CN-160 had a more efficient charge separation process that also enhanced the photocatalytic activity.

Core–Shell Photoanodes for Photoelectrochemical Water Oxidation

AbstractPhotoelectrochemical (PEC) water splitting into hydrogen and oxygen is a promising solution for the conversion and storage of solar energy. Because sluggish water oxidation is the bottleneck of water splitting, the design and preparation of an efficient photoanode is intensively investigated. Currently, all known photoanode materials suffer from at least one of the following drawbacks: ① low carriers separation efficiency; ② sluggish surface water oxidation reaction; ③ poor long‐term stability; ④ insufficient water adsorption and gas desorption. Core–shell configurations can endow a photoanode with improved activity and stability by coating an overlayer that plays energetic, catalytic, and/or protective roles. The construction strategy has an important effect on the activity of a core–shell photoanode. Nonetheless, the mechanism for the improvement of performance is still ambiguous and is worthy of a closer examination. In this review, the successes and challenges of core–shell photoanodes for water oxidation, focusing on synthesis strategies as well as functionalities (facilitating carrier separation, surface reaction promotion, corrosion prevention, and bubble detachment) are explored. Finally, the perspectives of this class of materials in terms of new opportunities and efforts are discussed.

Impact of H2O on the Adsorption of Hg0 on Activated Carbon.

In this work, the influence of water on the adsorption of mercury is systematically investigated on basic and washed activated carbons. Breakthrough curves were measured and temperature-programmed desorption (TPD) experiments were performed with mercury and water. Both physisorptive and chemisorptive interactions are relevant in the adsorption of mercury. The experiments show that the presence of water in the pores promotes chemisorption of mercury on washed activated carbons while there is little influence on chemisorption on basic materials. Washing exposes or forms oxygen functional groups that are chemisorptive sites for mercury. Obviously, effective chemisorption of mercury requires both the presence of water and of oxygen functional groups. As mercury chemisorption is preceded by a physisorptive step, higher physisorptive mercury loading at lower temperature (30 °C) enhances chemisorption though the reaction rate constant is smaller than at higher temperature (100 °C). Sequential adsorption and partial desorption of water at lower temperature changes the surface chemistry without inhibiting mercury physisorption. Here, the highest chemisorption rates were found. The number of desorption peaks in the TPD experiments corresponds to the number of adsorption and desorption mechanisms with different oxygen functional groups in the presence of water. The results of the TPD experiments were simulated using a transport model extended by an approach for chemisorption. The simulation results provide reaction parameters (activation energy, frequency factor, and reaction order) of each mechanism. As in many heterogeneously catalyzed reactions, the activation energy and the frequency factor are independent of mercury loading and increase with increasing temperature.

Adsorber heat exchanger using Al-fumarate beads for heat-pump applications - a transport study.

Metal-Organic Frameworks (MOFs), thanks to their type V water adsorption isotherms ("S-Shape") and large water capacities, are considered as potential breakthrough adsorbents for heat-pump applications. In particular, Al(OH)-fumarate could enable efficient regeneration at a lower temperature than silica-gel which would allow us to address the conversion of waste heat at low temperature such as found in data centers. Despite its greater adsorption capacity features, heat and mass transport limitations could jeopardize the potential performance of Al(OH)-fumarate. Heat and mass transport depend on the size of the bodies (mm range), their packing and on the pore structures, i.e. macro-mesopore volumes and sizes. This paper describes the cost-efficient and scalable synthesis and shaping processes of Al(OH)-fumarate beads of various sizes appropriate for use in water Adsorption Heat-Pumps (AHPs). The objective was to study transport limitations (i.e. mass and heat) in practical e beads which meet mechanical stability requirements. Dynamic data at the grain scale was obtained by the Large Temperature Jump method while dynamic data at the adsorber scale was obtained on a heat exchanger filled with more than 1 kg of Al(OH)-fumarate beads. Whereas the binder content had little impact on mass and heat transfer in this study, we found that Knudsen diffusion in mesopores of the grain may be the main limiting factor at the grain scale. At the adsorber scale, heat-transfer within the bed packing as well as to the heat exchanger is likely responsible for the slow adsorption and desorption kinetics which have been observed for very low desorption temperature. Finally, the dynamic aspects of the observed water adsorption isotherm shift with temperature are discussed in light of reported reversible structure modification upon temperature triggered water adsorption-desorption.

Investigating the properties of humins foams, the porous carbonaceous materials derived from biorefinery by-products

Humins as biorefineries by-product can be converted with a direct heating treatment into new rigid porous carbon materials known as humins foams. Currently, not many informations about this new material are known. Here, a preparation protocol in two steps involving foaming and carbonization is reported, while the materials have been investigated in terms of morphology, elemental content, water adsorption–desorption, stability to solvents and high temperatures, and thermal conductivity. In order to evaluate their potential uses in applications such as water purification, the pH associated to the zero charge point has been identified. Foams prepared under air ventilated condition revealed an extremely negative surface, which can be used in cation exchange applications. The surface's groups have been identified by Boehm titration, showing that this behavior can be associated to the presence of acid moieties, while the basic species result absent. The humins foams have been also tested through CO2 adsorption tests at realistic operation conditions, revealing that their performances can compete with materials reported in literature. Finally, activated carbon monoliths from carbonized humins foams using CO2 activation were tested, reaching a surface area of 1347 m2 g−1 after 20 min and 1482 m2 g−1 after 40 min of activation. These monoliths have been characterized in terms of morphology and elemental content. The results prove that the humins foams are very versatile materials, cost effective and easy to produce, with promising properties that can be further tailored for foreseen applications.

A Hydrolytically Stable Vanadium(IV) Metal–Organic Framework with Photocatalytic Bacteriostatic Activity for Autonomous Indoor Humidity Control

AbstractMetal–organic frameworks (MOFs) with long‐term stability and reversible high water uptake properties can be ideal candidates for water harvesting and indoor humidity control. Now, a mesoporous and highly stable MOF, BIT‐66 is presented that has indoor humidity control capability and a photocatalytic bacteriostatic effect. BIT‐66 (V3(O)3(H2O)(BTB)2), possesses prominent moisture tunability in the range of 45–60 % RH and a water uptake and working capacity of 71 and 55 wt %, respectively, showing good recyclability and excellent performance in water adsorption–desorption cycles. Importantly, this MOF demonstrates a unique photocatalytic bacteriostatic behavior under visible light, which can effectively ameliorate the bacteria and/or mold breeding problem in water adsorbing materials.

A Hydrolytically Stable Vanadium(IV) Metal-Organic Framework with Photocatalytic Bacteriostatic Activity for Autonomous Indoor Humidity Control.

Metal-organic frameworks (MOFs) with long-term stability and reversible high water uptake properties can be ideal candidates for water harvesting and indoor humidity control. Now, a mesoporous and highly stable MOF, BIT-66 is presented that has indoor humidity control capability and a photocatalytic bacteriostatic effect. BIT-66 (V3 (O)3 (H2 O)(BTB)2 ), possesses prominent moisture tunability in the range of 45-60 % RH and a water uptake and working capacity of 71 and 55 wt %, respectively, showing good recyclability and excellent performance in water adsorption-desorption cycles. Importantly, this MOF demonstrates a unique photocatalytic bacteriostatic behavior under visible light, which can effectively ameliorate the bacteria and/or mold breeding problem in water adsorbing materials.

Mechanistic aspects of water adsorption-desorption in porphyrin containing MOFs

Abstract Although porphyrin containing metal organic frameworks (PCMOFs) have found applications in different important fields, for example catalysis, phototherapy, adsorption etc. the mechanism of water adsorption on these materials remains unknown. In this study we analyze adsorption-desorption data on three PCMOFs. It is shown that hysteresis on adsorption-desorption isotherms is caused probably by the structural deformations. The application of SAFT-VR model to describe the experimental data is in agreement with the in - situ DRIFT insight of the process showing that the affinity between water and studied MOFS decreases as follows: CaTCPP > MgTCPP > ZnTCPP > TCPP. Application of the in-situ DRIFT method leads to important information about the nature of water material interactions showing for example the creation of aqua complexes and hydrogen bonds.

Record-Setting Sorbents for Reversible Water Uptake by Systematic Anion Exchanges in Metal-Organic Frameworks.

The reversible capture of water vapor at low humidity can enable transformative applications such as atmospheric water harvesting and heat transfer that uses water as a refrigerant, replacing environmentally detrimental hydro- and chloro-fluorocarbons. The driving force for these applications is governed by the relative humidity at which the pores of a porous material fill with water. Here, we demonstrate modulation of the onset of pore-filling in a family of metal–organic frameworks with record water sorption capacities by employing anion exchange. Unexpectedly, the replacement of the structural bridging Cl– with the more hydrophilic anions F– and OH– does not induce pore-filling at lower relative humidity, whereas the introduction of the larger Br– results in a substantial shift toward lower relative humidity. We rationalize these results in terms of pore size modifications as well as the water hydrogen bonding structure based on detailed infrared spectroscopic measurements. Fundamentally, our data suggest that, in the presence of strong nucleation sites, the thermodynamic favorability of water pore-filling depends more strongly on the pore diameter and the interface between water in the center of the pore and water bound to the pore walls than the hydrophilicity of the pore wall itself. On the basis of these results, we report two materials that exhibit record water uptake capacities in their respective humidity regions and extended stability over 400 water adsorption–desorption cycles.

Application of empirical Peleg model to study the water adsorption and mineral desorption of cocoa (Theobroma cacao) beans in water and sodium bicarbonate during debittering process

The ability of water and sodium bicarbonate solution in producing debittering cocoa bean for immediate consumption as ready to cook food and the applicability of empirical Peleg model in order to interpret the sorption data is evaluated in this study. Fermented cocoa beans were soaked and/or boiled in water and in 2% sodium bicarbonate solution with a weight to volume ratio of 1:10. Cocoa beans were withdrawn at each interval over a 6-h time period and moisture and minerals (calcium, magnesium, phosphorus and potassium) content analyzed using standard analytical methods. Bitterness was measured by sensory analysis. Peleg model was used to transform the sorption data into the mathematical equation and Peleg parameters K1, K2 and Me calculated. It has been found that boiling in water and sodium bicarbonate (2%) significantly reduces the bitterness of cocoa beans. Kinetic curves of water absorption express the characteristic shape with a fast water absorption rate at the beginning of the process follow by a decreasing rate as the equilibrium moisture is reached. Mineral desorption curves exhibited unusual pattern depending on the mineral under consideration. Application of sorption data demonstrates a predictive capacity of the Peleg model as judged by the regression coefficients. Boiling cocoa beans for 50min in 2% sodium bicarbonate and 30min in boiling water can be considered as optimal for debittering cocoa beans in order to give them palatable option to be integrated in nutrition and in none medicinal therapeutics in Cameroon.