Water Loadings Research Articles

Phase transfer catalysts shift the pathway to transmetalation in biphasic Suzuki-Miyaura cross-couplings

The Suzuki-Miyaura coupling is a widely used C-C bond forming reaction. Numerous mechanistic studies have enabled the use of low catalyst loadings and broad functional group tolerance. However, the dominant mode of transmetalation remains controversial and likely depends on the conditions employed. Herein we detail a mechanistic study of the palladium-catalyzed Suzuki-Miyaura coupling under biphasic conditions. The use of phase transfer catalysts results in a remarkable 12-fold rate enhancement in the targeted system. A shift from an oxo-palladium based transmetalation to a boronate-based pathway lies at the root of this activity. Furthermore, a study of the impact of different water loadings reveals reducing the proportion of the aqueous phase increases the reaction rate, contrary to reaction conditions typically employed in the literature. The importance of these findings is highlighted by achieving an exceptionally broad substrate scope with benzylic electrophiles using a 10-fold reduction in catalyst loading relative to literature precedent.

Assessing flood-depth effects on water quality, nutrient uptake, carbon sequestration, and rice yield cultivated on Histosols

In the Everglades Agricultural Area (EAA), Florida, cultivating rice in flooded paddies is becoming increasingly popular to conserve water and soil health. Flood depth is a critical factor affecting the discharged water quality, soil carbon, and yield production. However, few studies have comprehensively investigated the optimal flood depth in EAA, considering multi-functional indices. To address this gap, we investigated drainage water quality, water quantity, nutrient uptake, soil carbon, and rice yield in rice paddies in histosol soils over a two-year period at four flood depths (5, 10, 15, and 20 ​cm). For each flood depth, averaged over two years, total outflow loadings of suspended solids, nitrogen, phosphorus, and potassium were significantly reduced by 40 ​%, 38 ​%, 36 ​%, and 32 ​%, respectively, compared to inflow water loadings (p ​< ​0.001). Soil organic carbon (SOC) in 5, 10, 15, and 20 ​cm flood treatments increased annually at a rate of 3.85 ​%, 5.64 ​%, 6.86 ​%, and 6.86 ​%, respectively; for these same treatments, soil active organic carbon (AOC) decreased annually at rates of 11.75 ​%, 8.63 ​%, 20.07 ​%, and 8.48 ​%, and rice grain yield was 4488, 5103, 5450, and 5386 ​kg ​ha−1, respectively. Overall, considering the water quality, SOC, AOC, and rice yield production, irrigating rice paddies at a flood depth of 15 ​cm most effectively improves water quality, increases carbon sequestration, reduces active carbon, and yields more rice than other flood depths. By evaluating the effects of flood depth on the soil–water–plant nexus in a holistic manner, we propose a more sustainable and environmentally friendly mode of rice cultivation within the EAA.

Optimum relative humidity enhances CO2 uptake in diamine-appended M2(dobpdc)

Diamine-appended M2(dobpdc) metal–organic frameworks (MOFs) are a promising class of CO2 adsorbents, but the impact of relative humidity (RH) on their adsorption performance has yet to be carefully studied. We evaluated the CO2 uptake of (2-ampd)2M2(dobpdc) at varying relative humidities and associated water loadings using gravimetric and breakthrough adsorption methods. A significant enhancement in uptake is observed between 20 and 40 % RH, with an optimum of 30 % RH, at which a maximum CO2 uptake of 5.7 ± 0.2 mmol/g is achieved at 0.044 atm of CO2. These uptakes – which are above 1 CO2:diamine – suggest that humidity promotes an additional sorption mechanism beyond the well-known cooperative insertion between the metal and diamine. Temperature-programmed desorption and IR spectroscopy also indicated a second adsorption site accounting for the additional uptake, hypothesized to be carbamic acid pairs on the free amine within the MOF channel. Further increasing the humidity to 50 % RH resulted in a dramatic loss of capacity due to water-filled pores at these high humidity conditions. These results reveal the potential for a mixed mechanism in (2-ampd)2M2(dobpdc) promoted by humidity and highlight an optimum humidity range that will maximize the MOF’s utilization in CO2 capture applications.

Functionalization, protonation and ligand extension on MIL-53 (Al) MOFs to boost water adsorption and thermal energy storage for heat transformations

Understanding the relationship between the geometry of metal–organic frameworks (MOFs) and the shape of H2O adsorption isotherms is of utmost importance to control the hydrophilic and hydrophobic behaviors of water in MOFs with adsorption/desorption kinetics to realize their applications in thermal energy storage (TES). The MOFs are potential candidates for TES through water adsorption process. The TES can be used as a pivot for heat transformations related to cooling, heat pump, desalination, power generation, water harvesting and dehumidification. The TES performances are mainly determined by water adsorption characteristics such as water uptake/offtake loadings, kinetics and adsorbents-water interaction energy. Therefore, this paper presents a comprehensive analysis on the restructuring of MIL-53 (Al) MOFs for heat transformation applications. In this work, the original MOF is first functionalized with amino or hydroxyl functional groups. Next, the functionalized MOF is protonated with hydrochloric acid. In addition, ligand extension is applied on the original MOF by replacing the original organic linker with the progressively longer linkers. The surface properties of these restructured MOFs are measured by XRD, FTIR, TGA and N2 adsorption analysis. The water uptakes under equilibrium and dynamic conditions are presented in the form of isotherms and kinetic plots. The structural, thermal and cyclic water transfer stabilities of these MOFs are also presented. It is found that the tailored MIL-53 (Al) MOFs modify both the hydrophilicity and hydrophobicity of the original MOFs and improve the water loadings up to 0.9 g/g. The functionalized and protonated MIL-53 (Al) MOFs show higher water transfer with faster kinetics as compared to the parent MIL-53(Al) MOFs. The ligand extended MIL-53 (Al) MOFs provide higher water transfer between humid (relative humidity RH of 80% to 90%) and regenerated (RH of 30%) conditions with promising thermal energy storage density (TESD, up to 1.54 MJ/L).

Water Film-Driven Brucite Nanosheet Growth and Stacking.

Thin water films that form by the adhesion and condensation of air moisture on minerals can initiate phase transformation reactions with broad implications in nature and technology. We here show important effects of water film coverages on reaction rates and products during the transformation of periclase (MgO) nanocubes to brucite [Mg(OH)2] nanosheets. Using vibrational spectroscopy, we found that the first minutes to hours of Mg(OH)2 growth followed first-order kinetics, with rates scaling with water loadings. Growth was tightly linked to periclase surface hydration and to the formation of a brucite precursor solid, akin to poorly stacked/dislocated nanosheets. These nanosheets were the predominant forms of Mg(OH)2 growth in the 2D-like hydration environments of sub-monolayer water films, which formed below ∼50% relative humidity (RH). From molecular simulations, we infer that reactions may have been facilitated near surface defects where sub-monolayer films preferentially accumulated. In contrast, the 3D-like hydration environment of multilayered water films promoted brucite nanoparticle formation by enhancing Mg(OH)2 nanosheet growth and stacking rates and yields. From the structural similarity of periclase and brucite to other metal (hydr)oxide minerals, this concept of contrasting nanosheet growth should even be applicable for explaining water film-driven mineralogical transformations on other related nanominerals.

Three-dimensional study on the interaction between a container ship and freak waves in beam sea

Freak wave occurs unexpectedly in the ocean with an extreme wave crest and focused wave energy, resulting in many marine accidents. The interaction between a container ship and freak waves in beam sea is studied in this paper to better understand the influence of freak waves on ships. A three-dimensional in-house solver is developed and validated for the freak wave generation and the wave-ship interaction. Characteristics of the interaction process, motion responses of the ship and the green water loadings induced by the freak waves are obtained and analyzed. Comparisons are carried out to reveal the influences of the freak wave crest and sequence on the roll, heave and impact pressures. Relations between motion responses of the ship and the green water event are discussed. Influences of ship speeds on the wave-ship interaction are addressed.

Synthesis and performance evaluation of copper and magnesium-based metal organic framework supported ionic liquid membrane for CO2/N2 separation

The CO2 emission is enhancing drastically because of the continuous emission from industries and transport sector. Although the CO2 emission had decreased in the first half of 2020 by 8.8% due to COVID-19 restrictions however, it is again on the rise and it might exceed the estimated level in 2030. The current methods used for CO2 separation have serious operational and environmental constraints. To overcome these problems we have devised a supported ionic liquid membrane (SILM) incorporated with the blend of bimetallic metal-organic framework (MOF) of copper and magnesium ions (CuxMgx) and Trihexyltetradecylphosphonium chloride [P66614] [Cl] ionic liquid (IL). CuxMgx MOF were synthesized and characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and energy dispersive X-ray analysis (EDX). CuxMgx MOF with [P66614] [Cl] IL were immobilized on a flat sheet of polytetrafluoroethylene (PTFE) membrane. Single gas permeation tests of membranes loaded with 0.2/0.8 wt/wt% MOF/IL solution showed the highest CO2 permeability of 2937 Barrer and CO2/N2 selectivity of 33.26. The performance of SILM was also investigated with different water loadings of (30 wt % and 50 wt %) in addition to MOF/IL solution and at different feed pressure varying from 0.5 to 2 bars. Membranes showed enhancement in CO2 permeability to 3738 and 4628 Barrer whereas CO2/N2 selectivity decreased to 23.53 and 21.8 with membranes loaded with 30 and 50 wt % water, respectively, at a feed pressure of 2 bar. The gas permeation results show that the incorporation of CuxMgx MOF with IL in polymeric membrane enhances the CO2/N2 separation under humid conditions but slightly decreases CO2/N2 selectivity with an increase in feed pressure. The SILM synthesized in this research is highly viable for industrial flue gases because of the incorporation of phosphonium-based ILs that have high thermal stability.

Effect of Process Conditions on Catalytic Hydrothermal Oxidation of p-Xylene to Terephthalic Acid

This study investigates the influence of hydrothermal process conditions on the yield of terephthalic acid (TPA). Deionised water was employed as a green reaction medium substitute for acetic acid solvent widely used in the Amoco oxidation process for TPA production. Utilising the unique properties of water at elevated temperature and pressure, TPA was synthesised from p-xylene under subcritical (250 °C, 300 °C and 350 °C) and supercritical (400 °C) water conditions in a 10 mL micro-bomb batch reactor. Process conditions, including hydrogen peroxide (H2O2) oxidant concentrations, manganese bromide (MnBr2) catalyst and water loadings, were varied at a fixed reaction time of 60 minutes. The p-xylene conversion and TPA yield were determined using high-performance liquid chromatography (HPLC). In addition, the presence of chemical functional groups and chemical compositions of the reaction products were examined using Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometer (GC-MS), respectively. It was found that an optimum TPA yield of 94.56% was observed at 350°C with hydrogen peroxide, deionised water and manganese bromide catalyst set at 1.5 mL, 2.5 mL, and 2 mL, respectively. Other major reaction products identified were p-tolualdehyde and 1,4-hydroxymethyl benzaldehyde.

Water Adsorption on Mica Surfaces with Hydrophilicity Tuned by Counterion Types (Na, K, and Cs) and Structural Fluorination.

The stability of adsorbed water films on mineral surfaces has far-reaching implications in the Earth, environmental, and materials sciences. Here, we use the basal plane of phlogopite mica, an atomically smooth surface of a natural mineral, to investigate water film structure and stability as a function of two features that modulate surface hydrophilicity: the type of adsorbed counterions (Na, K, and Cs) and the substitution of structural OH groups by F atoms. We use molecular dynamics simulations combined with in situ high-resolution X-ray reflectivity to examine surface hydration over a range of water loadings, from the adsorption of isolated water molecules to the formation of clusters and films. We identify four regimes characterized by distinct adsorption energetics and different sensitivities to cation type and mineral fluorination: from 0 to 0.5 monolayer film thickness, the hydration of adsorbed ions; from 0.5 to 1 monolayer, the hydration of uncharged regions of the siloxane surface; from 1 to 1.5 monolayer, the attachment of isolated water molecules on the surface of the first monolayer; and for >1.5 monolayer, the formation of an incipient electrical double layer at the mineral-water interface.

Caught while Dissolving: Revealing the Interfacial Solvation of the Mg2+ Ions on the MgO Surface.

Interfaces between water and materials are ubiquitous and are crucial in materials sciences and in biology, where investigating the interaction of water with the surface under ambient conditions is key to shedding light on the main processes occurring at the interface. Magnesium oxide is a popular model system to study the metal oxide–water interface, where, for sufficient water loadings, theoretical models have suggested that reconstructed surfaces involving hydrated Mg2+ metal ions may be energetically favored. In this work, by combining experimental and theoretical surface-selective ambient pressure X-ray absorption spectroscopy with multivariate curve resolution and molecular dynamics, we evidence in real time the occurrence of Mg2+ solvation at the interphase between MgO and solvating media such as water and methanol (MeOH). Further, we show that the Mg2+ surface ions undergo a reversible solvation process, we prove the dissolution/redeposition of the Mg2+ ions belonging to the MgO surface, and we demonstrate the formation of octahedral [Mg(H2O)6]2+ and [Mg(MeOH)6]2+ intermediate solvated species. The unique surface, electronic, and structural sensitivity of the developed technique may be beneficial to access often elusive properties of low-Z metal ion intermediates involved in interfacial processes of chemical and biological interest.

Dynamic Mechanical Behavior of the Frozen Red Sandstone under Coupling of Saturation and Impact Loading

Saturation is one of the critical factors causing frost damage to rock masses in alpine regions, and dynamic stress perturbations further complicate the damage process. Therefore, the effects of water content and loadings should be considered in the construction and maintenance of rock structures during winter in cold regions. In this study, the effects of saturation and impact loading on the dynamic mechanical behavior of frozen red sandstone were investigated using a low-temperature split Hopkinson pressure bar system (LT-SHPB). By combining low-field nuclear magnetic resonance (LF-NMR) and scanning electron microscopy (SEM), the dynamic evolution of the microstructure of the frozen sandstone due to changes in saturation was investigated. The results indicated that the increase of saturation reshapes the pore structure of the frozen sandstone and promotes the expansion of pores of different sizes during freezing, while at complete saturation the frozen samples are mainly developed with meso- and macropores. The dynamic strength, elastic modulus, and brittleness index of the frozen sandstone under impact loading, which are limited by the critical saturation Src, tend to increase and then decrease with saturation. For the four impact loads, the dynamic strength of the samples increased by 21.2%, 27.1%, 32.5%, and 34.3% when the saturation was increased from 0 to 50%, corresponding to 1.38, 1.43, 1.51, and 1.56 times the dynamic strength of the fully saturated samples, respectively. In contrast, the ultimate deformation capacity of the frozen sandstone showed an opposite trend with saturation. As the impact load increases, the dynamic strength, elastic modulus, and peak strain of the frozen sandstone show a significant strengthening effect due to the increase in strain rate, while its brittleness index gradually decreases, dropping by 11.2% at full saturation. In addition, the energy dissipation capacity of the frozen sample first increases and then decreases with increasing saturation, with the enhancement effect of saturation on energy dissipation smaller than the weakening effect.

Mechanical Properties of Soft Rocks Subjected to Water‐Rock Reaction and Cyclic Pressure

Studying the mechanical properties of soft rocks subjected to water and cyclic loading would contribute to a better understanding of the stability analysis of soft rock engineering under the conditions of storm and carrier dynamics. In this paper, two soft rocks from Southwest China (i.e., muddy siltstone and silty mudstone) were selected as test samples. Uniaxial compressive tests were applied to investigate the strength and deformation characteristics under water‐rock reactions. Meanwhile, triaxial tests were carried out to analyse the fatigue damage and failure characteristics by applying cyclic axial loading under different confining pressures. The results indicated a reduction in the uniaxial compressive strength (UCS) under saturated conditions, which is correlated with the disintegration resistance of soft rocks. Moreover, the samples exhibited a softening phenomenon due to water absorption and rock expansion, decreasing the elastic modulus. The triaxial tests demonstrated that axial strain accumulated with the number of loading cycles due to fatigue and even failed when applying increased cyclic loading with certain cycles. The cohesion decreased during cyclic loading, but the friction angle was relatively independent of the number of cycles. In addition, reductions in the dynamic elastic modulus and shear modulus decreased with increasing loading time. This study indicated that water and cyclic loadings could cause significant degradation of the strength and stiffness of soft rocks, which need to be considered carefully during the engineering utilization of such materials.

Shaking Table Experiment on Seismic Performance of a Scaled-Down Arch Dam with Initial Crack

Seismic responses of cracked scaled-down arch dams were investigated by experiment on a shaking table. Two different curvature models (M1 and M2) were cast by using a plan concrete. Dams properties, including materials and dimensions, were carefully simulated. A significant earthquake magnitude with (7.7M) and water pressure were applied on the dam's models. Considering water and seismic loadings, the dynamic reactions of the arch dam's system were investigated. Both models showed crack overstresses or propagation on the dam's model as a result of seismic excitations. The arch dam with a higher degree of curvature was recorded 44 Mpa of stress evaluation which less by 30.7% of the arch dam with the lowest degree of curvature. The results indicated that raising the degree of curvature led to raising the dam's stability, earthquake resistance, less displacement, and less growth of tensile cracks.

Evolution of water structures in metal-organic frameworks for improved atmospheric water harvesting.

Although the positions of water guests in porous crystals can be identified, determination of their filling sequence remains challenging. We deciphered the water-filling mechanism for the state-of-the-art water-harvesting metal-organic framework MOF-303 by performing an extensive series of single-crystal x-ray diffraction measurements and density functional theory calculations. The first water molecules strongly bind to the polar organic linkers; they are followed by additional water molecules forming isolated clusters, then chains of clusters, and finally a water network. This evolution of water structures led us to modify the pores by the multivariate approach, thereby precisely modulating the binding strength of the first water molecules and deliberately shaping the water uptake behavior. This resulted in higher water productivity, as well as tunability of regeneration temperature and enthalpy, without compromising capacity and stability.

Water Bridges Substitute for Defects in Amine-Functionalized UiO-66, Boosting CO2 Adsorption

The binary adsorption of CO2 and water on an amine-functionalized UiO-66 metal-organic framework (MOF) was studied experimentally and computationally. Grand canonical Monte Carlo simulations were used to investigate three additional UiO-66 MOFs with different functionalized linkers. Each MOF was studied in a defect-free form as well as two additional forms with precise linker defects. Binary adsorption isotherms are presented for CO2 at specific water loadings. While water loading in defect-free MOFs reduces the CO2 uptake, the defects slightly boost the CO2 uptake at low water loadings. It was found that water bridges form between the metal oxide cores, replacing the missing linkers. Effectively, this creates smaller pores that are more welcoming of CO2 adsorption. Experimental measurement of the binary isotherms for UiO-66-NH2 shows a behavior that is consistent with this enhancement.

Confinement effects and acid strength in zeolites

Chemical reactivity and sorption in zeolites are coupled to confinement and—to a lesser extent—to the acid strength of Brønsted acid sites (BAS). In presence of water the zeolite Brønsted acid sites eventually convert into hydronium ions. The gradual transition from zeolite Brønsted acid sites to hydronium ions in zeolites of varying pore size is examined by ab initio molecular dynamics combined with enhanced sampling based on Well-Tempered Metadynamics and a recently developed set of collective variables. While at low water content (1–2 water/BAS) the acidic protons prefer to be shared between zeolites and water, higher water contents (n > 2) invariably lead to solvation of the protons within a localized water cluster adjacent to the BAS. At low water loadings the standard free energy of the formed complexes is dominated by enthalpy and is associated with the acid strength of the BAS and the space around the site. Conversely, the entropy increases linearly with the concentration of waters in the pores, favors proton solvation and is independent of the pore size/shape.

In situ aqueous phase hydrodeoxygenation of methyl palmitate to hydrocarbons on Ni catalyst derived from the reduction of LaNiO3 perovskite

A series of Ni–La–O-T catalysts (T-calcination temperature) were prepared via the sol–gel process followed by the calcination. They were tested for in situ aqueous phase hydrodeoxygenation (HDO) of methyl palmitate using methanol as hydrogen donor. In the calcined samples, NiO and La2O2(CO3) formed in Ni–La–O-550 and Ni–La–O-650. Apart from NiO and La2O2(CO3), there was LaNiO3 perovskite in Ni–La–O-750. Only LaNiO3 perovskite existed in Ni–La–O-800. After the reduction at 650 °C, metallic Ni and La2O3 appeared in all the catalysts. During in situ HDO, decarbonylation/decarboxylation was dominating, accompanying with the C–C bond hydrogenolysis and aqueous phase reforming of alkanes. H2 was generated from not only the aqueous phase reforming of methanol but also that of alkanes. Liquid C6–C16 alkanes were produced and C15 alkane was main product. Among the catalysts, Ni–La–O-750 afforded the highest activity for deoxygenation, C–C bond hydrogenolysis and aqueous phase reforming. The reaction temperature, reaction time, water and methanol loadings remarkably affected the products distribution. At a suitable condition, the yield of C6–C16 alkanes reached 71.1% on Ni–La–O-750. Additionally, Ni–La–O-750 was also very active for in situ HDO of methyl palmitate without methanol, however, the C–C bond hydrogenolysis was more serious.

Nanoscale Hydration in Layered Manganese Oxides.

Birnessite is a layered MnO2 mineral capable of intercalating nanometric water films in its bulk. With its variable distributions of Mn oxidation states (MnIV, MnIII, and MnII), cationic vacancies, and interlayer cationic populations, birnessite plays key roles in catalysis, energy storage solutions, and environmental (geo)chemistry. We here report the molecular controls driving the nanoscale intercalation of water in potassium-exchanged birnessite nanoparticles. From microgravimetry, vibrational spectroscopy, and X-ray diffraction, we find that birnessite intercalates no more than one monolayer of water per interlayer when exposed to water vapor at 25 °C, even near the dew point. Molecular dynamics showed that a single monolayer is an energetically favorable hydration state that consists of 1.33 water molecules per unit cell. This monolayer is stabilized by concerted potassium–water and direct water–birnessite interactions, and involves negligible water–water interactions. Using our composite adsorption–condensation–intercalation model, we predicted humidity-dependent water loadings in terms of water intercalated in the internal and adsorbed at external basal faces, the proportions of which vary with particle size. The model also accounts for additional populations condensed on and between particles. By describing the nanoscale hydration of birnessite, our work secures a path for understanding the water-driven catalytic chemistry that this important layered manganese oxide mineral can host in natural and technological settings.

Transition between Different Diffusion Regimes and Its Relationship with Structural Properties in Nafion by High Field Diffusion NMR in Combination with Small-Angle X-ray and Neutron Scattering.

Pulsed field gradient (PFG) NMR at high field was utilized to directly observe a transition between two different diffusion regimes in a Nafion 117 membrane loaded with water and acetone. Although water self-diffusivity at small water loadings was observed to be diffusion time-independent in the limit of small and large diffusion times, it showed a significant decrease with increasing diffusion time at intermediate times corresponding to root mean square displacements on the order of several microns. Under our experimental conditions, no self-diffusivity dependence on diffusion time was found for water at large water loadings and for acetone at all studied acetone loadings. The diffusion time-dependent self-diffusivity at small water concentration is explained by the existence of finite domains of interconnected water channels with sizes in the range of several microns that form in Nafion in the presence of acetone. The domain sizes and permeance of transport barriers separating adjacent domains are estimated based on the measured PFG NMR data. At large water concentrations, the water channels form a fully interconnected network, resulting in time-independent self-diffusivity. The absence of such a percolation-like transition with increasing molecular concentration for acetone is attributed to a difference in the regions available for water and acetone diffusion in Nafion. The diffusion data are correlated with and supported by structural data obtained using small-angle X-ray and neutron scattering techniques. These techniques reveal distinct water channels with radial dimensions in the nanometer range increasing upon water addition, while acetone appears to be in an interfacial perfluoroether region, reducing the size of the radial channel dimension.

Analytical Computational Models for Relationship between Ultimate Bending Moment of Concrete Segments and Axial Force

Concrete segments are widely used to support soil and water loadings in shield-excavated tunnels. Concrete segments burden simultaneously to the loadings of bending moments and axial forces. Based on plane deformation assumption of material mechanics, in which plane section before bending remains plane after bending, ultimate bending moment model is proposed to compute ultimate bearing capacity of concrete segments. Ultimate bending moments of concrete segments computed by analytical models agree well with numerical simulation results by FEM. The accuracy of proposed analytical computational model for ultimate bending moment of concrete segments is numerically verified. The analytical computational model and numerical simulation for a practical engineering case indicate that the ultimate bending moment of concrete segments increases with increase of axial force on concrete segment in the case of large eccentricity compressive state.