Interfacial Hydrogen Bonds Research Articles

Mechanochemical Synthesis of Type III Porous Liquids from Solid Precursors for the Removal and Conversion of Waste CO2 from CH4.

Porous liquids (PLs) have emerged as a promising class of flow porous materials, offering distinctive benefits for sustainable separation processes coupled with catalytic transformations in the chemical industry. Despite their potential, challenges remain in the realms of synthesis complexity, stability, and the strategic engineering of separation and catalytic sites. In this study, a scalable mechanochemical synthetic approach is reported to fabricate Type III PLs from solid precursors with high stability. In these Type III PLs, ZIF-8 nanocrystals are dispersed in the deep eutectic solvents formed by solid hydrogen-bond donors and acceptors. Owing to the presence of multiple interfacial hydrogen and coordination bonds, these PLs not only maintain porosity and fluidity with high stability, enabling efficient CH4 purification by CO2 removal and sequestration, but also facilitate the catalytic conversion of stored CO2 into valuable products under ambient conditions. This strategy advances the green production of stable and well-dispersed PLs, showing the potential of PLs in the sustainable separation and catalysis coupling system in the chemical industry.

Extreme Environment-Adaptable and Ultralong-Life Energy Storage Enabled by Synergistic Manipulation of Interfacial Environment and Hydrogen Bonding

The broad applications of energy storage systems have brought improving demands for stable electrodes with robust tolerance to extreme environmental challenges. MXenes show promising pseudocapacitive behaviors, however, the poor thermodynamical and mechanical stability makes them unfavorable for applications under complex and harsh environments. Herein, we break these limitations by aramid nanofibers (ANF)-driven interfacial nanofilling and hydrogen-bonds effects in MXenes. Theoretical and experimental results unveil that ANF with unique polarity preferentially interacts with H2O molecules and forms hydrogen bonding networks to restrain oxidative and mechanical attack toward MXene, at the same time, the nanofilling enables interfacial mass transport intensification for increment in redox dynamics. As such, the synergistically coupled ANF-MXene microstructure (AM) unlocks superior mechanical properties for facing hash forces, i.e., tensile strength of 115.2 MPa and toughness of 1.8 MJ m-3, and an ultra-long cycling life with a capacitance retention of 90.7% after 40,000 cycles. Besides, the effective IR thermal camouflage performance (IR-emissivity: 20.9%) further renders the power supply working invisibly after fast charge/discharge-driven heat generation. Moreover, the performances can be well maintained when subjected to strong acid/alkali, high-temperature (200°C), and cryogenic (-196°C) treatments. These results highlight the key role of interfacial species synergy in accelerating versatile and robust energy applications.

Regulating Interfacial Hydrogen-Bonding Networks by Implanting Cu Sites with Perfluorooctane to Accelerate CO2 Electroreduction to Ethanol.

Efficient CO2 electroreduction (CO2RR) to ethanol holds promise to generate value-added chemicals and harness renewable energy simultaneously. Yet, it remains an ongoing challenge due to the competition with thermodynamically more preferred ethylene production. Herein, we presented a CO2 reduction predilection switch from ethylene to ethanol (ethanol-to-ethylene ratio of ~5.4) by inherently implanting Cu sites with perfluorooctane to create interfacial noncovalent interactions. The 1.83 %F-Cu2O organic-inorganic hybrids (OIHs) exhibited an extraordinary ethanol faradaic efficiency (FEethanol) of ∼55.2 %, with an impressive ethanol partial current density of 166 mA cm-2 and excellent robustness over 60 hours of continuous operation. This exceptional performance ranks our 1.83 %F-Cu2O OIHs among the best-performing ethanol-oriented CO2RR electrocatalysts. Our findings identified that C8F18 could strengthen the interfacial hydrogen bonding connectivity, which consequently promotes the generation of active hydrogen species and preferentially favors the hydrogenation of *CHCOH to *CHCHOH, thus switching the reaction from ethylene-preferred to ethanol-oriented. The presented investigations highlight opportunities for using noncovalent interactions to tune the selectivity of CO2 electroreduction to ethanol, bringing it closer to practical implementation requirements.

Coordination and Hydrogen Bond Chemistry in Tungsten Oxide@Polyaniline Composite toward High-Capacity Aqueous Ammonium Storage.

Aqueous ammonium ion batteries (AAIBs) have garnered significant attention due to their unique energy storage mechanism. However, their progress is hindered by the relatively low capacities of NH4 + host materials. Herein, the study proposes an electrodeposited tungsten oxide@polyaniline (WOx@PANI) composite electrode as a NH4 + host, which achieves an ultrahigh capacity of 280.3 mAh g-1 at 1 A g-1, surpassing the vast majority of previously reported NH4 + host materials. The synergistic interaction of coordination chemistry and hydrogen bond chemistry between the WOx and PANI enhances the charge storage capacity. Experimental results indicate that the strong interfacial coordination bonding (N: →W6+) effectively modulates the chemical environment of W atoms, enhances the protonation level of PANI, and thus consequently the conductivity and stability of the composites. Spectroscopy analysis further reveals a unique NH4 +/H+ co-insertion mechanism, in which the interfacial hydrogen bond network (N-H···O) accelerates proton involvement in the energy storage process and activates the Grotthuss hopping conduction of H+ between the hydrated tungsten oxide layers. This work opens a new avenue to achieving high-capacity NH4 + storage through interfacial chemistry interactions, overcoming the capacity limitations of NH4 + host materials for aqueous energy storage.

Tuning Hydrogen Evolution and Oxidation Electrocatalysis through Interfacial Hydrogen Bonds

Designing electrochemical water splitting and its reverse process is crucial for fuel cells to achieve high efficiency. Conventional design of catalysts has focused on tuning the surface electronic structures and binding strength of intermediates, while recent studies show that changing electrolyte compositions, such as cations and pH, can also significantly alter catalytic activity, highlighting new opportunities in tuning noncovalent interactions in the electrolytes to control activities. Yet, the mechanistic role of electrolytes and their structures at the electrochemical double-layer remain poorly understood. Challenges arise in characterizing the interface and understanding the reaction mechanisms under operando processes.In this talk, we tailor non-covalent hydrogen bonding interactions at the electrified interface to control electrochemical proton-coupled electron transfer reactions, and uncover the interfacial molecular mechanisms. We investigate hydrogen evolution and oxidation reactions (HER/HOR) by systematically confining water in organic matrixes. Tuning the hydrogen-bonding networks by changing the water concentration and altering the donor number of organic solvents shifted the onset potentials. High donor number solvents, such as DMSO, suppress HER more significantly due to its stabilization effect of isolated water, while the enhancement effect of HER with low donor number solvents, such as acetonitrile, is due to the promotion of interfacial hydrogen-bonded water. In situ surface-enhanced infrared absorption spectroscopy (SEIRAS) measurements and molecular dynamics simulations provide further support to the changes in interfacial hydrogen bonding during the reactions. These findings provide design principles for electrolytes and open up immense opportunities for using non-covalent hydrogen bonding interactions at the electrified interface to control the kinetics. The understanding would also be impactful across other reactions involving proton-coupled electron transfer that are crucial for energy storage, such as CO2 reduction and aqueous batteries.

(Invited) Influence of Hydrogen Bond Networks on Hydrogen Evolution Reaction in Aqueous Systems

Hydrogen evolution reaction (HER) is one of the key issues to achieve “carbon neutrality”. Driving the electrocatalytic HER in aqueous solutions with solar-energy cells is considered as a green and sustainable way to produce hydrogen molecules (H2). To achieve effective H2 production, it is required to reduce HER overpotential using appropriate heterogeneous electrocatalysts such as Pt. The HER activities of catalytic metals have a strong correlation with the hydrogen adsorption free energies on their surfaces, which is known as a so-called volcano-like relation. Because the optimum adsorption energy and hence maximum HER activity are found at the top of the volcano, most of the studies to develop electrocatalysts focus on tuning of the adsorption energy. However, the hydrogen adsorption step, i.e., discharge reaction of proton, at the surface is strongly influenced by hydrogen bonding with the bulk phase of liquid water. Recently, we have developed a surface-selective THz-vibrational spectroscopy based on surface-enhanced Raman scattering, which can obtain dynamical and structural information on hydrogen bond networks of water at interfaces with the frequency range of 10 - 100 cm-1 (0.3 – 3 THz) [1-6]. Using this technique, we have examined the potential-induced behavior of interfacial hydrogen bonds under the HER process on various metal surfaces with different HER activities and found that there is a correlation between the HER activities and hydrogen bond structures at interface. The details will be discussed in the presentation. We will also present a new strategy to produce hydrogen gas more efficiently using a non-traditional electrochemical cell structure.[1] M. Inagaki, K. Motobayashi, K. Ikeda, J. Phys. Chem. Lett., 8, 4236-4240 (2017).[2] M. Inagaki, T. Isogai, K. Motobayashi, K. -Q. Lin, B. Ren, K. Ikeda, Chem. Sci., 11, 9807-9717 (2020).[3] M. Inagaki, K. Motobayashi, K. Ikeda, Nanoscale, 12, 22988-22994 (2020).[4] R. Kamimura, T. Kondo, K. Motobayashi, K. Ikeda, Phys. Status Solidi B, 259, 2100589 (2022).[5] T. Kondo, M. Inagaki, K. Motobayashi, K. Ikeda, Catal. Sci. Technol., 12, 2670-2676 (2022).[6] T. Isogai, M. Inagaki, M. Uranagase, K. Motobayashi, S. Ogata, K. Ikeda, Chem. Sci. 14, 6531-6537 (2023).

Friction mechanisms of WS2 in humid environments: Investigating H2O adsorption via DFT computations and sliding friction experiments

Tungsten disulfide is increasingly used for space and nuclear applications owing to its low friction in vacuum, but the friction increases drastically in humid environments. The increased friction has been conventionally attributed to the oxidation of WS2. This study investigated the frictional behaviour of WS2 in humid atmospheres through sliding friction experiments combined with density functional theory computations. The results showed that the increased friction can be attributed to the formation of O-H···S type interfacial hydrogen bonds between WS2 layers by adsorbed H2O, without significant oxidation. This interaction led to enhanced interlayer bonding and adhesion, consequently elevating friction. This study provides atomistic insights into the friction mechanism of WS2 and design guidelines for thin films operatable in humid environments.

Interfacial Hydrogen-Bond Interactions Driven Assembly toward Polychromatic Copper Nanoclusters.

Constructing versatile metal nanoclusters (NCs) assemblies through noncovalent weak interactions between inter-ligands is a long-standing challenge in interfacial chemistry, while compelling interfacial hydrogen-bond-driven metal NCs assemblies remain unexplored so far. Here, the study reports an amination-ligand o-phenylenediamine-coordinated copper NCs (CuNCs), demonstrating the impact of interfacial hydrogen-bonds (IHBs) motifs on the luminescent behaviors of metal NCs as the alteration of protic solvent. Experimental results supported by theoretical calculation unveil that the flexibility of interfacial ligand and the distance of cuprophilic CuI···CuI interaction between intra-/inter-NCs can be tailored by manipulating the cooperation between the diverse IHBs motifs reconstruction, therewith the IHBs-modulated fundamental structure-property relationships are established. Importantly, by utilizing the IHBs-mediated optical polychromatism of aminated CuNCs, portable visualization of humidity sensing test-strips with fast response is successfully manufactured. This work not only provides further insights into exploring the interfacial chemistry of NCs based on inter-ligands hydrogen-bond interactions, but also offers a new opportunity to expand the practical application for optical sensing of metal NCs.

Rapid Assembly of Ultrafine Palladium Nanoparticle-Decorated HOF-101 Triggered by Guest Enzyme Encapsulation.

Rapid enzyme immobilization is essential for enzyme catalysis and sensing applications, yet constructing effective immobilization systems is challenging due to the need to balance enzyme activity with the properties of the surrounding framework. Herein, taking glucose oxidase (GOx) as a model, a rapid and straightforward approach was presented for synthesizing palladium nanoparticles (PdNPs)-decorated GOx encapsulated in HOF-101 nanocomposite materials (designated as PdNPs/GOx@HOF-101) through an in situ photoreduction and enzyme-triggering HOF-101 encapsulation. The enzyme's surface residues trigger the nucleation of HOF-101 around it through the hydrogen-bonded bio interface, completing the self-assembly of HOF-101 in 0.5 h. Furthermore, the biocomposites loaded with ultrafine PdNPs show satisfactory photoelectrochemical (PEC) properties. As a proof-of-concept, a PEC biosensor was constructed by utilizing PdNPs/GOx@HOF-101 as a photoactive probe, which can quickly and sensitively detect glucose and simultaneously remain stable within the circumstance of 30-60 °C and pH 4-8. These attributes pave the way for diverse applications, including improved enzyme immobilization techniques, advanced biosensors, and more efficient biocatalytic processes.

Probing atomic-scale processes at the ferrihydrite-water interface with reactive molecular dynamics

Interfacial processes involving metal (oxyhydr)oxide phases are important for the mobility and bioavailability of nutrients and contaminants in soils, sediments, and water. Consequently, these processes influence ecosystem health and functioning, and have shaped the biological and environmental co-evolution of Earth over geologic time. Here we employ reactive molecular dynamics simulations, supported by synchrotron X-ray spectroscopy to study the molecular-scale interfacial processes that influence surface complexation in ferrihydrite-water systems containing aqueous MoO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext {MoO}_4}^{2-}$$\\end{document}. We validate the utility of this approach by calculating surface complexation models directly from simulations. The reactive force-field captures the realistic dynamics of surface restructuring, surface charge equilibration, and the evolution of the interfacial water hydrogen bond network in response to adsorption and proton transfer. We find that upon hydration and adsorption, ferrihydrite restructures into a more disordered phase through surface charge equilibration, as revealed by simulations and high-resolution X-ray diffraction. We observed how this restructuring leads to a different interfacial hydrogen bond network compared to bulk water by monitoring water dynamics. Using umbrella sampling, we constructed the free energy landscape of aqueous MoO42-\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\ ext {MoO}_4}^{2-}$$\\end{document} adsorption at various concentrations and the deprotonation of the ferrihydrite surface. The results demonstrate excellent agreement with the values reported by experimental surface complexation models. These findings are important as reactive molecular dynamics opens new avenues to study mineral-water interfaces, enriching and refining surface complexation models beyond their foundational assumptions.Graphic

Polyelectrolyte Additive-Modulated Interfacial Microenvironment Boosting CO2 Electrolysis in Acid.

Acidic CO2 electrolysis offers a promising strategy to achieve high carbon utilization and high energy efficiency. However, challenges still remain in suppressing the competitive hydrogen evolution reaction (HER) and improving product selectivity. Although high concentrations of potassium ions (K+) can suppress HER and accelerate CO2 reduction, they still inevitably suffer from salt precipitation problems. In this study, we demonstrate that the sulfonate-based polyelectrolyte, polystyrene sulfonate (PSS), enables to reconstruct the electrode-electrolyte interface to significantly enhance the acidic CO2 electrolysis. Mechanistic studies reveal that PSS induces high local K+ concentrations through the electrostatic interaction between PSS anions and K+. In situ spectroscopy reveals that PSS reshapes the interfacial hydrogen-bond (H-bond) network, which is attributed to the H-bonds between PSS anions and hydrated proton, as well as the steric hindrance of the additive molecules. This greatly weakens proton transfer kinetics and leads to the suppression of undesirable HER. As a result, a Faradaic efficiency of 93.9 % for CO can be achieved at 250 mA cm-2, simultaneous with a high single-pass carbon efficiency of 72.2 % on commercial Ag catalysts in acid. This study highlights the important role of the electrode-electrolyte interface induced by polyelectrolyte additives in promoting electrocatalytic reactions.

Thermochromic behavior of pigment red 254 in nylon 6 polymer for high-chromaticity engineering plastics

Advancement in Color-Material-Finishing (CMF) plays a crucial role in enhancing the visual appeal of plastic products, particularly for the high-chroma nylon plastics that are currently in vogue. However, it is inevitable to encounter pigment-dyeing issues in polar engineering plastics during the high-temperature extrusion process, which can lead to intense fluorescence and color fading. This phenomenon, characterized by the dissolution of pigments in a polar environment, can adversely affect the color saturation and weatherability of the pigment, which ultimately cause sharp reduction of aesthetic quality and durability of the plastic. Herein, we develop a modified strategy combined with thermal annealing to realize rapid color recovery in nylon 6, and further reveal the fluorescence and discoloration mechanism of pigment red 254 in nylon 6. Through improving the mobility of nylon chain segments, the rigid heterogeneous nucleation regions centered on the interfacial hydrogen bond between nylon 6 and the pigment molecules loosens with the help of heat treatment, and then the dissolved pigment molecules reaggregate to induce fluorescence quenching. Importantly, as a consequence of the increased lubricity segments, the required thermal annealing temperature and time for color recovery and fluorescence quenching could be significantly shortened from 180 °C for 5 h to 100 °C for 0.5 h. This work provides a feasible approach for the industrial production of high-chroma polar engineering plastics.

Hydrogen bonding network in the electrical double layer mediates fast proton skipping to Get Rid of Fenton reaction pH dependence enables highly efficient alkaline water purification

A fundamental scientific quandary in environmental has always been the pH dependence in Fenton reaction, that is, the reaction kinetics decreases by approximately 1–3 orders of magnitude upon transitioning from an acidic to an alkaline state. Here, we discovered that protons significantly contribute to the Fenton reaction through an examination of the reaction's interfacial behavior characteristics. Proton transfer mediated by hydrogen bond network connectivity in the electric double layer is responsible for the pH dependence of Fenton reaction kinetics. On this basis, the surface potential of Fenton reaction catalyst was modified to optimize the distribution of H2O in the electrical double layer, enhancing the connectivity of the interfacial hydrogen bond network and providing a fast channel for rapid proton transfer. The consecutive hydrogen bond network mediates rapid proton hopping, increasing the proton concentration in the Helmholtz layer, and consequently promoting the proton conductivity from 5.38×10−7 S·cm−2 to 4.35×10−6 S·cm−2 in alkaline conditions for Fenton reaction. Meanwhile, the kinetics reaction rate was improved 20 times, and the pH dependence was reduced from 70.9 % to 12.6 %. This discovery clarifies the key role of the interfacial hydrogen bond network and proton transfer in Fenton reaction kinetics pH dependence. It provides new theories and methods for achieving alkaline high Fenton reaction kinetics.

Dual functional bio-inspired additives reconstruct metal-organic interface stability for wearable energy storage system

Aqueous zinc-ion batteries (AZIBs) hold significant promise across wearable energy storage devices due to their superior safety and cost-effectiveness. However, the instability of the electrode/electrolyte interface leads to severe hydrogen evolution reaction (HER) and dendritic growth. Herein, a bio-inspired additive, keratin (Ker), is introduced to construct a robust interfacial layer. The hydrogen bonding donors homogenize the distribution of interfacial hydrogen bond networks and increases the electron density in Zn2+-OH interaction, stabilizing bound H2O molecules and effectively inhibiting HER. Additionally, electron transfer from the highly reactive thiol (-SH) motivates the formation of Zn-S chemical linkage, enhancing interface stability. These features endow Zn||Zn symmetric cells with an impressive cycle life, reaching up to 3364 h at 1 mA cm−2/1 mAh cm−2. The Zn||α-MnO2 and Zn||VO2 full cells also exhibit a substantial capacity retention after 1000 cycles. Incorporating multi-step laser cutting technology enables the fabrication of flexible, large-area micro-batteries with prolonged cycle life. This study presents an advanced methodology for heralding a promising pathway to improve the reversibility of aqueous energy storage systems.

The Loss of Interfacial Water-Adsorbate Hydrogen Bond Connectivity Position Surface-Active Hydrogen as a Crucial Intermediate to Enhance Nitrate Reduction Reaction.

The electrochemical nitrate reduction reaction (NO3RR) offers a promising solution for remediating nitrate-polluted wastewater while enabling the sustainable production of ammonia. The control strategy of surface-active hydrogen (*H) is extensively employed to enhance the kinetics of the NO3RR, but atomic understanding lags far behind the experimental observations. Here, we decipher the cation-water-adsorbate interactions in regulating the NO3RR kinetics at the Cu (111) electrode/electrolyte interface using AIMD simulations with a slow-growth approach. We demonstrate that the key oxygen-containing intermediates of the NO3RR (e.g., *NO, *NO2, and *NO3) will stably coordinate with the cations, impeding their integration with the hydrogen bond network and further their hydrogenation by interfacial water molecules due to steric hindrance. The *H can migrate across the interface with a low energy barrier, and its hydrogenation barrier with oxygen-containing species remains unaffected by cations, offering a potent supplement to the hydrogenation process, playing the predominant factor by which the *H facilitates NO3RR reaction kinetic. This study provides valuable insights for understanding the reaction mechanism of NO3RR by fully considering the cation-water-adsorbate interactions, which can aid in the further development of the electrolyte and electrocatalysts for efficient NO3RR.

Molecular dynamics simulation of nanocellulose and cement matrix composites

The interfacial properties of nanocellulose and cement matrix are the key factors affecting the mechanical properties of composite materials. However, it is challenging to study the interface combination through conventional experiments and microscopic characterization techniques. Molecular dynamics simulation (MD), as a nanoscale analytical method, can be used to calculate and analyze the strength, deformation, destruction and interfacial interaction of materials on the atomic scale. Since the existing methods of C-S-H modeling and fiber pull-out from the matrix in molecular dynamics simulations were not suitable for cellulose/C-S-H composite models. In this paper, a molecular dynamics simulation method for nanocellulose cement matrix composites was proposed. Based on the embedded composite model, the tensile stress-strain, interfacial interaction energy, hydrogen bond, and interface failure mode were studied when cellulose was pulled out of the matrix. The results showed that adding cellulose could improve the local ductility and tensile strength of cement matrix materials. The interfacial interaction energy between cellulose and C-S-H was approximately −1.09 J/m2, which was much higher than that between carbon nanotubes and C-S-H. Cellulose would adsorb hydrogen and oxygen atoms on H2O, OH− and silica tetrahedron in C-S-H. In the pull-out simulation of cellulose in C-S-H, C-S-H on the surface of cellulose would be destroyed and attached to the cellulose surface and moved along with it, indicating that cellulose could play a good bridging role in the matrix. The simulation results revealed the action mechanism of cellulose in cement matrix materials.

Polyelectrolyte Additive‐Modulated Interfacial Microenvironment Boosting CO2 Electrolysis in Acid

Acidic CO2 electrolysis offers a promising strategy to achieve high carbon utilization and high energy efficiency. However, challenges remain in suppressing the competitive hydrogen evolution reaction (HER) and improving product selectivity. High concentrations of potassium ions (K+) can suppress HER and accelerate CO2 reduction, but they still inevitably suffer from salt precipitation problems. In this study, we demonstrate that the sulfonate‐based polyelectrolyte, polystyrene sulfonate (PSS), enables to reconstruct the electrode‐electrolyte interface to significantly enhance the acidic CO2 electrolysis. Mechanistic studies reveal that PSS induces high local K+ concentrations through electrostatic interaction between PSS anions and K+. In situ spectroscopy reveals that PSS reshapes the interfacial hydrogen–bond (H–bond) network, which is attributed to the H–bonds between PSS anions and hydrated proton as well as the steric hindrance of the additive molecules. This greatly weakens proton transfer kinetics and leads to the suppression of undesirable HER. As a result, a Faradaic efficiency of 93.9% for CO can be achieved at 250 mA cm–2, simultaneous with a high single‐pass carbon efficiency of 72.2% on commercial Ag catalysts in acid. This study highlights the important role of the electrode‐electrolyte interface induced by polyelectrolyte additives in promoting electrocatalytic reactions.

Topological properties of interfacial hydrogen bond networks

Topological properties of interfacial hydrogen bond networks

Positive and Negative Impacts of Interfacial Hydrogen Bonds on Photocatalytic Hydrogen Evolution.

Understanding the behavior of water molecules at solid-liquid interfaces is crucial for various applications such as photocatalytic water splitting, a key technology for sustainable fuel production and chemical transformations. Despite extensive studies conducted in the past, the impact of the microscopic structure of interfacial water molecules on photocatalytic reactivity has not been directly examined. In this study, using real-time mass spectrometry and Fourier-transform infrared spectroscopy, we demonstrated the crucial role of hydrogen bond (H-bond) networks on the photocatalytic hydrogen evolution in thickness-controlled water adsorption layers on various TiO2 photocatalysts. Under controlled water vapor environments with relative humidity (RH) below 70%, we observed a monotonic increase in the H2 formation rate with increasing RH, indicating that reactive water molecules were present not only in the first adsorbed layer but also in several overlying layers. In contrast, at RH > 70%, when more than three water layers covered the catalyst surface, the H2 formation rate turned to decrease dramatically because of the structural rearrangement and hardening of the interfacial H-bond network induced during further water adsorption. This unique many-body effect of interfacial water was consistently observed for various TiO2 particles with different crystalline structures, including brookite, anatase, and a mixture of anatase and rutile. Our results demonstrated that depositing several water layers in a water vapor environment with RH ∼ 70% is optimal for photocatalytic hydrogen evolution rather than liquid-phase reaction conditions in aqueous solutions. This study provides molecular-level insights into designing interfacial water conditions to enhance photocatalytic performance.

Study of Interfacial Properties of Anionic–Nonionic Surfactants Based on Succinic Acid Derivatives via Molecular Dynamics Simulations and the IGMH Method

Surfactants are widely used in fields such as oil recovery and flotation. The properties and mechanisms of surfactants can be effectively studied using molecular dynamics (MD) simulations. Herein, the aggregation behavior of surfactants was studied at the oil–water interface by MD simulation, and the micro-morphology of surfactants was analyzed under a low concentration and saturated state at the oil–water interface, respectively. The visualization results of the MD simulation showed that DTOA was saturated at the oil–water interface at 120 surfactant molecules, whereas 160 surfactant molecules were required for BEMA. In addition, the effect of surfactant concentration on the interfacial thickness and hydrogen bond distribution was studied, with the inflection point of hydrogen bond distribution identified as a characteristic parameter for surfactant saturation at the oil–water interface. The aggregation behavior of their hydrophobic and hydrophilic chains at the oil–water interface was qualitatively assessed using order parameters. Finally, the aggregation state of surfactants in salt-containing systems was studied, and it was found that the surfactants could effectively adsorb magnesium ions and calcium ions at the oil–water interface. However, the curve of the number of hydrogen bonds varies greatly, with a possible reason being that BEMA has a different coordination manner with diverse metal ions. This study provides some original insights into both the theoretical study and practical application of anionic and nonionic surfactants.