Hydrogen-bonded Water Research Articles

Heterodyne‐Detektierte Summenfrequenzerzeugungs‐Vibrationsspektroskopie Enthüllt die Molekulare Struktur des Wassers an der Suspendierten Graphen/Wasser‐Grenzfläche

AbstractGraphen, ein transparentes, zweidimensionales, leitfähiges Material, hat verschiedenen wässrigen technologischen Systemen, wie Entsalzungsmembranen, chemischen Sensoren, Energiespeichern und Energieumwandlungsgeräten, neue Perspektiven eröffnet. Informationen auf molekularer Ebene von Graphen im Kontakt mit wässrigen Elektrolyten, wie z. B. Wasserorientierung und die Struktur von Wasserstoffbrückenbindungen, sind jedoch nach wie vor schwer fassbar oder umstritten. Hier setzen wir oberflächenspezifische heterodyne detektierte Summenfrequenzspektroskopie (HD‐SFG) ein, um die molekulare Wasserstruktur an einer frei schwebenden Graphen/Wasser‐Grenzfläche zu untersuchen.Wir vergleichen die Antwort des Luft/Graphen/Wasser Systems mit der der Luft/Wasser‐Grenzfläche. Unsere Ergebnisse deuten darauf hin, dass das ‐Spektrum, des Luft/Graphen/Wasser‐Systems von den obersten 1–2 Wasserschichten in Kontakt mit Graphen herrührt, wobei das Graphen selbst keine signifikantes SFG‐Signal erzeugt. Im Vergleich zum Signal an der Luft/Wassergrenzfläche beeinflusst das Vorhandensein von Monolagen‐Graphen Wasser an der Grenzfläche nur schwach. Graphen wirkt sich schwach auf die hängende O−H‐Gruppe aus, indem es ihre Frequenz durch die Wechselwirkung mit der Graphenschicht senkt, und hat eine geringe Wirkung auf die Wasserstoffbrücken‐gebundene O−H‐Gruppe. Molekulardynamiksimulationen bestätigen unsere experimentellen Beobachtungen. Unsere Arbeit bietet einen molekularen Einblick in die Grenzflächenstruktur an einer suspendierten Graphen/Wasser‐Grenzfläche, die für verschiedene technologische Anwendungen von Graphen relevant ist.

Heterodyne-Detected Sum-Frequency Generation Vibrational Spectroscopy Reveals Aqueous Molecular Structure at the Suspended Graphene/Water Interface.

Graphene, a transparent two-dimensional conductive material, has brought extensive new perspectives and prospects to various aqueous technological systems, such as desalination membranes, chemical sensors, energy storage, and energy conversion devices. Yet, the molecular-level details of graphene in contact with aqueous electrolytes, such as water orientation and hydrogen bond structure, remain elusive or controversial. Here, we employ surface-specific heterodyne-detected sum-frequency generation (HD-SFG) vibrational spectroscopy to re-examine the water molecular structure at a freely suspended graphene/water interface. We compare the response from the air/graphene/water system to that from the air/water interface. Our results indicate that the spectrum recorded from the air/graphene/water system arises from the topmost 1-2 water layers in contact with the graphene, with the graphene itself not generating a significant SFG response. Compared to the air/water interface response, the presence of monolayer graphene weakly affects the interfacial water. Graphene weakly affects the dangling O-H group, lowering its frequency through its interaction with the graphene sheet, and has a very small effect on the hydrogen-bonded O-H group. Molecular dynamics simulations confirm our experimental observation. Our work provides molecular insight into the interfacial structure at a suspended graphene/water interface, relevant to various technological applications of graphene.

The NaClO4-water eutectic electrolyte for environmentally friendly electrical double-layer capacitors operating at low temperature

Herein, owing to its remarkable ionic conductivity, the 8.84 mol kg−1 NaClO4 water-in-salt (WIS) eutectic electrolyte is suggested for the low temperature operation of electrical double-layer capacitors down to -35 °C. Molecular dynamic simulations reveal that the local structure of the solution remains relatively stable from RT to -35 °C, with distinct channel-like domains formed by hydrogen-bonded water molecules, which facilitate the ionic diffusion within the bulk of the electrolyte. Interestingly, on activated carbon (AC) electrodes, the electrolyte demonstrates an electrochemical stability window (ESW) increasing from 1.8 V to 2.1 V as temperature decreases from 25 °C to -35 °C. The high ESW of this electrolyte is due to i) pH close to neutrality enabling high overpotential of water reduction on porous AC electrodes; ii) WIS characteristics with a reduced amount of free water in the Stern layer under positive polarization of AC; iii) higher oxidation potential at low temperature ascribed to the enhanced immobilization of the ClO4− anions in the Stern layer as well as reduced diffusion of water molecules in the AC electrode porosity. The electrochemical investigations on laminate AC//AC cells in the NaClO4-water electrolyte demonstrate low values of their resistive components down to -30 °C, while the devices can operate with rated voltage of 2.0 V and 1.7 V at -30 °C and RT, respectively. At -30 °C and under discharge power as high as 10 kW kg−1, the AC//AC capacitor in the NaClO4-water electrolyte outperforms the specific output energy of a traditional AC//AC cell in the 1 M TEABF4/ACN electrolyte. Hence, for sub-ambient temperatures, the presented environmentally friendly EDLC holds promise to compete with traditional devices implementing an organic electrolyte.

Ni(II) triggered sensing and reversible uptake of ammonia by tetrazole based Ni(II) metallogel: A one-pot mechanistic approach

The release of ammonia gas and its removal through traditional approaches is a critical challenge inhibiting the sustainability of chemical industries. The quest to improve sustainability has triggered interest to develop chemoprobe and reusable adsorbent for toxic gases such as ammonia. The present study offers the first example of a novel one-pot synthesis of a stable Ni(II)metallogel (Ni(II)MG) from 1, 4 adiponitrile and sodium azide. The Ni(II)MG is composed of Ni(II) coordinated with four in-situ formed CN-Tz (5-(1H-tetrazol-5-yl)pentanenitrile) ligands and two water molecules forming predominant octahedral geometry. The Ni(II)MG has good strength, and viscoelastic, thixotropic, and self-healing properties. The Ni(II)MG and its xerogel (Ni(II)XG) have been thoroughly characterized and utilized for ammonia sensing and reversible adsorption at ambient condition. The mesoporous nature and presence of hydrogen-bonded water molecules in the pores make this material effective for reversible adsorption of ammonia. The lewis acidic Ni(II) increases the cloud network of hydrogen-bonded water molecules and triggers the coordinated water molecules to activate hydrogen-bonded water molecules for binding the ammonia molecules. The Ni(II) triggered extended hydrogen bonding through coordinated water molecule is also supported by DFT studies. The Ni(II)XG shows good ammonia adsorption capacity (8 mmol/gm) which is confirmed by TPD studies. The properties of Ni(II)XG are found to be intact after ammonia adsorption even after 20 cycles. Hence, it could be a promising low cost, sustainable and reusable material as a chemoprobe for removal of ammonia.

Low-salt organohydrogel electrolytes for wide-potential-window flexible all-solid-state supercapacitors

Flexible supercapacitors have received increasing attention due to their high power density, long cycle life and excellent safety, however, their limited energy density restrains their practical applications. Here, a designed organohydrogel electrolyte strategy boosted the electrochemical potential window (ESW) for flexible all-solid supercapacitor was demonstrated, by which a record-high ESW of 5 V is achieved, accompanied by improved cyclic stability and wider temperature adaptability. Hydrogen-bond of water to DMSO was found to be competitive with cationic hydration, and a wide ESW was achieved at lower salt and DMSO concentrations. DMSO-H2O/alginate/PAAm hydrogel electrolytes were prepared by simple solvent exchange, and it was found that the synergistic interactions between DMSO, water and hydrogel significantly reduced water activity in the hydrogel and realized the high ESW. Moreover, Dimethyl sulfoxide forms abundant hydrogen bonds with water and the hydrogel skeleton, which significantly improves the mechanical properties, freezing resistance, and temperature adaptability of the hydrogel electrolyte. The flexible all-solid-state supercapacitor assembled based on DMSO-H2O/alginate/PAAm hydrogel electrolyte and interdigital electrodes exhibits 2.4 V ESW, stability under different folding angles, adaptability to different temperatures ranging from −20 to 70 °C, and integration performance. The device demonstrates excellent cycling stability and retains 98.66% of capacitance after 10,000 cycles, suggesting that it has the potential to meet the requirements of flexible electronics.

Effects of multi-walled carbon nanotubes on microstructure transformation of water before carbon dioxide hydrate formation

There is no consensus on the micro mechanism of gas hydrate formation. The essence of water conversion into hydrates is the transformation of disorderly arranged water into the water with specific structure under a certain condition. This study used different multi-walled carbon nanotubes (MWCNTs) as solid promoters for gas hydrate formation. By comparing the effects of nanotubes modified with hydroxyl, carboxyl and amidogen on the microstructure transformation of water before CO2 hydrate formation, the micro mechanism and influence rules of gas hydrate formation were systematically study. The results indicated that the conversion of water to hydrates mainly manifested as the mutual conversion of strong/weak hydrogen bonding water. Due to the Brownian motion and dispersion of MWCNTs, the hydrogen bonds of the weak hydrogen-bonded water weakened (the corresponding peak blue shifts), and the distance between water molecules (dO−O) expanded, forming relatively loose hydrate, which was conducive to gas diffusion in the solid hydrate phase and increased the final gas consumption. Meanwhile, the strengthening of strong hydrogen bonded water increased the rate of hydrate formation.

Experiment-based new insights into hydrogen bonds between alcohol and water through reduced-hydrogen-bonded plasmon-activated water

The molecular structure of water and alcohol connected by hydrogen bonds (HBs) remains unclear. In this study, innovative plasmon-activated water (PAW) with fewer HBs was produced from bulk deionized water (DIW). The HBs between pure ethanol and water were stronger than those of pure DIW, which was confirmed by analyses of measured densities and the spectra of nuclear magnetic resonance (NMR) T1 and Raman OH-stretching of PAW with fewer HBs for the first time. Moreover, the intrinsic HBs between hydrophilic alcohol molecules were destroyed by hot electron transfer, reducing the original HBs, such as in PAW. For extremely polar DIW, the degree of non–hydrogen-bonded water (DNHBW) was approximately 0.21. For alcohols, the non–hydrogen-bonded alcohol (DNHBA) was also first similarly defined. The calculated values of DNHBA are 0.48, 0.68, and 0.87 for methanol, ethanol, and propanol, respectively. These values were consistent with their corresponding solvent polarities and HB strength. Moreover, the relative intensity of weak HBs (RIWHBs) is first defined utilizing the Raman spectra of water and alcohol/water mixtures. The calculated values of RIWHBs were consistent with our recognized strength of HBs of alcohol/water mixtures, as illustrated by PAW with intrinsically reduced HBs.

Hydrogen-bond transformations of confined water and abnormal mechanical responses of hydrated AlPO4-11 framework under in situ high pressure

The behaviors of water under non-ambient conditions, especially in confinement environment, have long been of special interest due to the important roles in biological and geological processes. Here, we have performed an infrared spectroscopic investigation on the pressure-induced hydrogen-bond transformation of water in one-dimensional, elliptical channels of AlPO4-11. Upon compression, the hydrogen-bonds of confined water strengthen and water molecules transform from tetrahedral coordination configuration to low and intermediate configurations, which may be a high-density disordered state. This transformation is distinct from the commonly accepted liquid–solid and solid–solid phase transition in bulk water. Stronger hydrogen-bonds are formed and a further transformation of hydrogen-bonded water takes place in the hydrostatic environment of Ar than the case without pressure transmitting medium (PTM). In addition, the mechanical compressible behaviors and framework deformation of the host matrix are also discussed. X-ray diffraction study shows that the hydrated AlPO4-11 exhibits an unexpected high compressibility in Ar. Its bulk modulus before framework collapse is 14.1 GPa, 4 ∼ 5 times smaller than that in silicone. The anisotropic axial compressibilities of AlPO4-11 demonstrate that the ellipticity of the channel cross-section increases in silicone oil while it decreases in Ar because the relatively contractive behavior along minor axis direction is slowed down. Such pressure-induced responses are ascribed to the complex Ar-H2O-framework interaction after Ar penetration. This study offers us a new knowledge of crystal-fluid interaction in determining the mechanical behaviors of open-framework materials under high pressure and provides implications for the water evolution and circulation in water-carrying natural zeolites under extreme geological conditions in nature.

The Advantages of Flexibility: The Role of Entropy in Crystal Structures Containing C-H···F Interactions.

Molecular crystal structures are often interpreted in terms of strong, structure directing, intermolecular interactions, especially those with distinct geometric signatures such as H-bonds or π-stacking interactions. Other interactions can be overlooked, perhaps because they are weak or lack a characteristic geometry. We show that although the cumulative effect of weak interactions is significant, their deformability also leads to occupation of low energy vibrational energy levels, which provides an additional stabilizing entropic contribution. The entropies of five fluorobenzene derivatives have been calculated by periodic DFT calculations to assess the entropic influence of C-H···F interactions in stabilizing their crystal structures. Calculations reproduce inelastic neutron scattering data and experimental entropies from heat capacity measurements. C-H···F contacts are shown to have force constants which are around half of those of more familiar interactions such as hydrogen bonds, halogen bonds, and C-H···π interactions. This feature, in combination with the relatively high mass of F, means that the lowest energy vibrations in crystalline fluorobenzenes are dominated by C-H···F contributions. C-H···F contacts occur much more frequently than would be expected from their enthalpic contributions alone, but at 150 K, the stabilizing contribution of entropy provides, at -10 to -15 kJ mol-1, a similar level of stabilization to the N-H···N hydrogen bond in ammonia and O-H···O hydrogen bond in water.

Facet-dependent dispersion and aggregation of aqueous hematite nanoparticles.

Nanoparticle aggregates in solution controls surface reactivity and function. Complete dispersion often requires additive sorbents to impart a net repulsive interaction between particles. Facet engineering of nanocrystals offers an alternative approach to produce monodisperse suspensions simply based on facet-specific interaction with solvent molecules. Here, we measure the dispersion/aggregation of three morphologies of hematite (α-Fe2O3) nanoparticles in varied aqueous solutions using ex situ electron microscopy and in situ small-angle x-ray scattering. We demonstrate a unique tendency of (104) hematite nanoparticles to maintain a monodisperse state across a wide range of solution conditions not observed with (001)- and (116)-dominated particles. Density functional theory calculations reveal an inert, densely hydrogen-bonded first water layer on the (104) facet that favors interparticle dispersion. Results validate the notion that nanoparticle dispersions can be controlled through morphology for specific solvents, which may help in the development of various nanoparticle applications that rely on their interfacial area to be highly accessible in stable suspensions.

Investigation of encapsulated water wire within self-assembled hydrophilic nanochannels, in a modified γ4-amino acid crystals: Tracking thermally induced changes of intermolecular interactions within a crystalline hydrate

Nanostructures formed by the self-assembly of modified/unmodified amino acids have the potential to be useful in several biological/nonbiological applications. In that regard, the greater conformational space provided by γ-amino acids, owing to their additional backbone torsional degrees of freedom and enhanced proteolytic stability, compared to their α-counterparts, should be explored. Though, modified single amino acid-based nanomaterials such as nanobelts or hydrogels are developed by utilizing the monosubstituted γ-amino acids derived from the backbone homologation of phenylalanine (Phe). Examples of a single γ-amino acid-based porous nanostructure capable of accommodating solvent molecules are not really known. The crystal structures of a modified γ4(R)Phe residue, Boc-γ4(R)Phe-OH, at different temperatures, showed that hydrogen-bonded water molecules are forming a wire inside hydrophilic nanochannels. The dynamics of intermolecular interactions between the water wire and the inner wall of the channel with relation to the temperature change was investigated by analyzing the natural bonding orbital (NBO) calculation results performed with the single crystal structures obtained at different temperature points. The NBO results showed that from 325 K onward, the strength of water–water interactions in the water wire are getting weaker, whereas, for the water–inner wall interactions, it getting stronger, suggesting a favorable change in the orientation of water molecules with temperatures, for the latter.

Tip-like Fe-N4 Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction.

Single atom catalysts with defined local structures and favorable surface microenvironments are significant for overcoming slow kinetics and accelerating O2 electroreduction. Here, enriched tip-like FeN4 sites (T-Fe SAC) on spherical carbon surfaces were developed to investigate the change in surface microenvironments and catalysis behavior. Finite element method (FEM) simulations, together with experiments, indicate the strong local electric field of the tip-like FeN4 and the more denser interfacial water layer, thereby enhancing the kinetics of the proton-coupled electron transfer process. In situ spectroelectrochemical studies and the density functional theory (DFT) calculation results indicate the pathway transition on the tip-like FeN4 sites, promoting the dissociation of O-O bond via side-on adsorption model. The adsorbed OH* can be facilely released on the curved surface and accelerate the oxygen reduction reaction (ORR) kinetics. The obtained T-Fe SAC nanoreactor exhibits excellent ORR activities (E1/2 =0.91 V vs. RHE) and remarkable stability, exceeding those of flat FeN4 and Pt/C. This work clarified the in-depth insights into the origin of catalytic activity of tip-like FeN4 sites and held great promise in industrial catalysis, electrochemical energy storage, and many other fields.

Tip‐like Fe−N4 Sites Induced Surface Microenvironments Regulation Boosts the Oxygen Reduction Reaction

AbstractSingle atom catalysts with defined local structures and favorable surface microenvironments are significant for overcoming slow kinetics and accelerating O2 electroreduction. Here, enriched tip‐like FeN4 sites (T−Fe SAC) on spherical carbon surfaces were developed to investigate the change in surface microenvironments and catalysis behavior. Finite element method (FEM) simulations, together with experiments, indicate the strong local electric field of the tip‐like FeN4 and the more denser interfacial water layer, thereby enhancing the kinetics of the proton‐coupled electron transfer process. In situ spectroelectrochemical studies and the density functional theory (DFT) calculation results indicate the pathway transition on the tip‐like FeN4 sites, promoting the dissociation of O−O bond via side‐on adsorption model. The adsorbed OH* can be facilely released on the curved surface and accelerate the oxygen reduction reaction (ORR) kinetics. The obtained T−Fe SAC nanoreactor exhibits excellent ORR activities (E1/2=0.91 V vs. RHE) and remarkable stability, exceeding those of flat FeN4 and Pt/C. This work clarified the in‐depth insights into the origin of catalytic activity of tip‐like FeN4 sites and held great promise in industrial catalysis, electrochemical energy storage, and many other fields.

Competitive Coordination Structure Regulation in Deep Eutectic Electrolyte for Stable Zinc Batteries.

Rechargeable zinc-based batteries are finding their niche in energy storage applications where cost, safety, scalability matter, yet they are plagued by rapid performance degradation due to the lack of suitable electrolytes to stabilize Zn anode. Herein, we report a competitive coordination structure to form unique quaternary hydrated eutectic electrolyte with ligand-cation-anion cluster. Unraveled by experiment and calculation results, the competing component can enter initial primary coordination shell of Zn2+ ion, partially substituting Lewis basic eutectic ligands and reinforcing cation-anion interaction. The hydration-deficient complexes induced between competing eutectic as hydrogen bond donor-accepter and water also broaden the electrochemical window and confine free water activity. The altered coordination further leads to robust hybrid organic-inorganic enriched solid electrolyte interphase, enabling passivated surface and suppressed dendrite growth. Noticeably, stable Zn plating/stripping for 8000 cycles with high Coulombic efficiencies of 99.6 % and long cycling life of 10000 cycles for Zn-organic batteries are obtained. Even under harsh conditions (small N/P ratio, low temperature), the profits brought by the competitive eutectic electrolyte are still very prominent. This design principle leveraged by eutectic electrolytes with competitive coordination offers a new approach to improve battery performance.

Investigating the properties of the water−vapor and water−graphite interfaces by PC-SAFT based density functional theory: A comparative study of different association functionals and PC-SAFT water parameter sets

In this work, we apply the perturbed-chain statistical associating fluid theory (PC-SAFT) based classical density functional theory to investigate the thermodynamics and structures of the water−vapor and water−graphite interfaces. For the water−vapor interface, we examine the surface tension as well as structural characteristics such as density profiles and hydrogen bonding distributions along the interface. For the water−graphite interface, we investigate these same structural features at a contact angle of 90° at 300 K. Specifically, we focus on comparing the results obtained from the three association functionals and six PC-SAFT water parameter sets from literature with experimental data and molecular simulation results. We find that the three association functionals exhibit qualitatively similar behavior in the calculation of surface tension, and it is more influenced by the parameter set rather than the association functional. The optimal functional or parameter set for the calculation of density profile of the vapor − liquid interface remains inconclusive, whereas preferable parameter sets and functionals have been identified for the water−graphite interface. Furthermore, the three functionals demonstrate a remarkably similar and qualitatively accurate depiction of the hydrogen bonding structures at both interfaces when compared with molecular simulation results. The level of quantitative accuracy, however, relies on whether the parameter set accurately reproduces the average number of hydrogen bonds of bulk water as observed in this particular set of molecular simulation results. The results of the present work offer valuable guidance for further investigation into the adsorption and wetting behavior of water on graphite-like surface, as well as the properties of water confined at the nanoscale.

Polarity of Aqueous Solutions

This short review describes the expansion of the solvatochromic approach utilizing water-soluble solvatochromic dyes to the analysis of solvent features of aqueous media in solutions of various compounds. These solvent features (polarity/dipolarity, hydrogen bond donor ability (HBD acidity), and hydrogen bond acceptor ability (HBA basicity)) vary depending on the nature and concentration of a solute. Furthermore, the solvent features of water (the solvent dipolarity/polarizability and hydrogen bond donor ability) in solutions of various compounds describe multiple physicochemical properties of these solutions (such as the solubility of various compounds in aqueous solutions, salting-out and salting-in constants for polar organic compounds in the presence of different inorganic salts, as well as water activity, osmotic coefficients, surface tension, viscosity, and the relative permittivity of aqueous solutions of different individual compounds) and are likely related to changes in the arrangement of hydrogen bonds of water in these solutions.

Exploiting Deep Eutectic Solvent-like Mixtures for Fractionation Biomass, and the Mechanism Removal of Lignin: A Review

Green solvents, which include deep eutectic solvent-like mixtures (DES-like mixtures), are categorized as ecological and economical solvents for the pretreatment and fractionation of different types of biomasses. DES-like mixtures represent a group of the most promising green solvents for lignocellulosic pretreatment and are currently used effectively in the biomass pretreatment process. The present work describes the latest applications of DES-like mixtures in biomass delignification processes and, at the same time, summarizes the mechanism of action and influence of DES-like mixture systems on the removal of lignin from different types of biomasses. The results of this review indicate that the physicochemical properties (acidity, hydrogen bond capacity, polarity, viscosity, and water content) of DES-like mixtures have a significant effect on the biomass fractionation process. In addition to the nature of components forming DES-like mixtures, the reaction conditions (temperature, time) influence the efficiency of delignification. Active protons obtained from the hydrogen bond donor facilitate proton-catalyzed bond cleavage during fractionation, where the most significant step is the destruction of the ether and ester bonds between polysaccharides and lignin. DES-like mixtures can depolymerize lignin with subsequent breakdown of the β−O−4 bonds.

Atomic-resolution structure analysis inside an adaptable porous framework

We introduce a versatile metal-organic framework (MOF) for encapsulation and immobilization of various guests using highly ordered internal water network. The unique water-mediated entrapment mechanism is applied for structural elucidation of 14 bioactive compounds, including 3 natural product intermediates whose 3D structures are clarified. The single-crystal X-ray diffraction analysis reveals that incorporated guests are surrounded by hydrogen-bonded water networks inside the pores, which uniquely adapt to each molecule, providing clearly defined crystallographic sites. The calculations of host-solvent-guest structures show that the guests are primarily interacting with the MOF through weak dispersion forces. In contrast, the coordination and hydrogen bonds contribute less to the total stabilization energy, however, they provide highly directional point interactions, which help align the guests inside the pore.

Controlled Degradation and Erosion of Polyrotaxane Solids via the Formation of Multivalent Hydrogen Bonding in Water

Controlled Degradation and Erosion of Polyrotaxane Solids via the Formation of Multivalent Hydrogen Bonding in Water

Breaking hydrogen-bonds in aqueous electrolytes towards highly reversible zinc-ion batteries

An electrolyte additive with uniquely symmetric structure breaks water's hydrogen bonds and modifies the primary solvation structure of Zn2+ in aqueous zinc batteries, enhancing battery performance and stability.