Water at hydrophobic surfaces: weak hydrogen bonding and strong orientation effects

Segregation of Chemical Groups at PMMA/H2O Interface Leads to Different Local Hydrophobicity

The local hydrophilicity of polymer surfaces is essential for many applications, such as coatings and biocompatibility, but revealing its structural origin is challenging. Here, we used poly(methyl methacrylate) (PMMA) film as a model and excavated several SFG spectral features, generated by femtosecond sum-frequency generation vibrational spectroscopy (SFG-VS), to elucidate the nature of microscopic hydrophilicity of a polymer/H2O interface. For the first time, we successfully probed the SFG spectra of the bend-libration combination band of interfacial water, which exhibits high sensitivity to solvent-water interactions. Two local hydrophilic domains are observed at the PMMA/H2O interface. The segregation of -OCH3 and -CH3 groups to the PMMA/H2O interface results in the formation of a local hydrophobic domain, where weak solvent-water interactions, slow vibrational dynamics of OH stretching, and no ice-like interfacial water are detected. In contrast, when both C═O and -OCH3 groups segregate to the PMMA/water interface, a local hydrophilic domain is formed, leading to strong solvent-water interactions, fast vibrational dynamics of OH stretching, and the presence of ice-like interfacial water. The water molecules around the hydrophobic domains of the PMMA surface are mainly liquid-like water rather than ice-like water. This work contributes to a molecular-level understanding of the local hydrophilicity of polymer surfaces.

Computational Insights into Reorientation-Mediated Water Diffusion on Pt(111): Comparison to H2O/Pd(111)

Understanding water diffusion on metal surfaces is essential for catalysis, corrosion, and scientifically significant electrochemical processes. Using density functional theory (DFT) calculations, we found that water reorientation on metal surfaces plays a critical role in modulating orbital competition modes, coherent HOMO couplings, electron transfer, and vibronic couplings. However, Pd(111) and Pt(111) show significantly different abilities to modulate the reorientational water diffusion. Water diffusion on Pt(111) obviously breaks the orientation-dependent orbital competition discovered on Pd(111) and shows unbalanced orbital competition controlling both H-down and H-up water diffusion except for HVP, where balanced orbital competition takes place. Furthermore, the electronic rule of orientation-dependent coherent HOMO coupling modes identified on Pd(111) shows a breakdown for the Pt(111)-supported HDW mechanism, which, on the contrary, exhibits reduced amplitudes of coherent HOMO couplings. Likewise, the orientational dependence of net electron transfer obtained on Pd(111) also shows a breakdown for the Pt(111)-supported HUF mechanism, which instead shows increased oscillation amplitudes of the net electron transfer pattern. Moreover, the coupled vibronic couplings between the water bending mode and HOMO couplings observed in the H2O/Pd(111) system are unexpectedly absent in H2O/Pt(111), where only the decoupled vibronic couplings between symmetric HOH stretching (phonons) and coherent HOMO couplings are observed in its HVP mechanism. Our investigations have revealed the bonding nature of water-metal interactions during transient surface diffusion, which can be valuable for understanding electronic catalytic mechanisms involving water on metal surfaces.

The Correlated States Theory of the Hydrophobic Effect

Starting from Frank and Evans' "iceberg" model of hydrophobic hydration of small molecules (the "microscopic" hydrophobic effect, HE) published in 1945, much has been done with respect to understanding the nature of HE and elaborating a quantitative theory able to describe the thermodynamic profile (the "signature" of HE) for the large volume of experimental data accumulated to date. Generally, three sets of approaches addressing this issue were suggested, ranging from the approval of the central role of the water shell to the complete denial of its role, with the focus placed on the solute and its interactions with surrounding water. For this reason, some controversy is still present in understanding the fundamental nature of HE, even at the "microscopic" scale. Nevertheless, the general tendency of the past decade seems to have shifted toward a greater role of the water environment in determining the thermodynamic profile of HE, with a designated place for solute-water interactions as a fine-tuning of thermodynamic observables. In the present work, we developed a novel view on HE at the microscopic scale, appearing as a consequence of solute-water correlated translational and orientational vibration motion, emerging as a new property of hydrophobic hydration/solvation (the Correlated States Theory of HE). We built a fully analytical description of this process, which has enabled us to quantify the "signature" of HE for extended thermodynamic data sets without employing molecular simulations or any numerical functions in the core of the theory. As a consequence, our approach provides a self-consistent view on the known major experimental manifestations of HE across an extended temperature range, addresses some controversial issues existing to date, and creates a new augmentation to current knowledge. Most importantly, the suggested approach offers a paradigm shift from the currently dominating views on HE as a consequence of water-water interactions and the "excluded volume effect" toward the central role of solute-water interactions, and provides the first nonempirical proof of the validity of SASA-based computational models of hydrophobic hydration/solvation, which have been utilized on an empirical basis for more than 40 years.

Hydrophilic Single-Atom Interface Empowered Pure Formic Acid Fuel Cells

Single-atom catalysts (SACs), offering high mass activity and enhanced resistance to poisoning, are regarded as superior alternatives to traditional Pt/Pd nanocatalysts for direct formic acid fuel cells (DFAFCs). However, failure toward operation in concentrated formic acid (FA), which is critical for portable electronics, challenges their antipoisoning advantage and highlights a missing part in the understanding of the reaction. We herein demonstrate that the interfacial hydrophilicity of SACs is pivotal for high-performance DFAFCs, enabling, for the first time, stable operation with pure FA (>99%). By incorporating transition metal single atoms (Co, Fe, Ni, Ru) into Ir/NC catalysts, we engineered highly hydrophilic interfaces, as validated by molecular dynamics simulations and experimental studies. The optimized IrCo/NC anode exhibited a mass activity 342 times higher than that of nanoparticle-based catalysts and represented as the first SAC to achieve a higher peak power density (107.7 mW cm-2). A new reaction mechanism is revealed, where CO acts as a reactive intermediate rather than a poison. Further, in situ spectroscopy and isotope kinetic analyses identified water intermediate involvement in the rate-determining step, underscoring the critical role of hydrophilic interface engineering in DFAFC.

Self-Assembled Monolayer Interface with Reconstructed Hydrogen-Bond Network for Enhanced CO2 Electroreduction

CO2 electrolysis is a promising approach to reduce CO2 emissions while achieving high-value multi-carbon (C2+) products. Except for the key role of electrocatalyst for electrochemical CO2 reduction reaction (CO2RR), Reaction microenvironment is another critical factor influencing catalytic performance for these catalysts. Herein, a self-assembled monolayer (SAM) is proposed with reconstructed hydrogen-bond network to form an efficient three-phase interface that admins mass transport and ion-electron transfer. This approach is realized by co-assembly of the fluorinated SAM (F-SAM) and siloxane on commercial Cu catalyst (Cu@F-Si composite catalyst). Molecular dynamics simulations (MDS) and interfacial species analysis show that the F-SAM effectively facilitates CO2 mass transport, while the siloxane hydrogen bond network maintains an ideal H+/e- transfer pathway. Combined with density functional theory (DFT) calculations, this strategy reveals the mechanism by which optimizing *H/*CO coverage enhances C2+ product selectivity. Ultimately, the Cu@F-Si catalyst maintains a high current density of 502.5 mA cm-2 with over 85% C2+ Faradaic efficiency (FE) and operates stably for more than 100 h at ≈300 mA cm-2. This interface engineering strategy offers a promising solution for improving the efficiency of CO2RR, with broader applications in multiphase catalytic systems.

Hydrogel-based nonwoven with persistent porosity for whole-stage hypertonic wound healing by regulating of water vaporization enthalpy

Moisture induced by wound exudate is crucial throughout the wound repair process. The dressing directly affects the absorption, permeation, and evaporation of the wound exudate. However, most dressings in clinical often result in excessive dryness or moisture of wound due to their monotonous structure and function, leading to ineffective thermodynamic control of evaporation enthalpy. Herein, a hydrogel-based nonwoven dressing (Gel-Fabric) with asymmetric amphiphilic surface and persistent microscopic porous structure is constructed by integrating intrinsic hydrophilic absorbent hydrogel fibers and hydrophobic ultrafine PET fibers. The novel Gel-Fabric facilitates rapid vertical drainage of wound exudate through the capillary effect and Laplace pressure synergy. Additionally, dynamic stepwise moisture management is also achieved by regulating the vaporization enthalpy of exudate. In vivo experiments confirm that Gel-Fabric significantly promotes wound healing, vascularization, and endothelialization, achieving a higher healing rate than ordinary dressings. Furthermore, compared to the clinical dressings, Gel-Fabric significantly reduces the frequency of dressing changes, offering improved outcomes for patients and more efficient wound management for healthcare providers.

Plasmon-activated water innovatively applicable for improving the performance of surface-enhanced Raman scattering

The effect of surface-enhanced Raman scattering is responsible for its sensibility, and the reproducibility of its corresponding surface-enhanced Raman spectroscopy (SERS) is evaluated using the relative standard deviation (RSD); these are two important performances in sensing. Interestingly, innovative plasmon-activated water (PAW) is a kind of pure water, which features an electron-doping structure with reduced-affinity hydrogen bonds (HBs). This review describes the innovative green applications of PAW to improve SERS performances with higher sensitivity and lower RSDs in sensing model probe molecules of rhodamine 6G (R6G) and pesticides. First, we report a facile one-step fabrication method of SERS-active Au and Ag substrates with improved SERS activity and excellent signal reproducibility using simple oxidation-reduction cycles (ORCs) performed in PAW solutions, compared to deionized water (DIW) solutions. Then, based on the designed in situ PAW, SERS enhancement of two-fold higher intensity of R6G and a corresponding low RSD of 5 %, which was comparable to and even better than those based on complicated processes shown in the literature, are encouraging. Furthermore, for SERS-active substrates with gold/silver (Au/Ag) nanocomposites prepared using galvanic replacement reactions (GRRs) based on the PAW system, the intensity and corresponding RSDs of the SERS signal of R6G were higher and lower, respectively, compared to the DIW system. Moreover, using PAW to dissolve analytes, including pesticides, was effective in improving SERS performances. Finally, environmentally friendly etchants of vapor from in situ PAW to improve SERS sensing of pesticides are discussed.

Insights into Dendrite Regulation by Polymer Hydrogels for Aqueous Batteries

Aqueous batteries, renowned for their high capacity, safety, and low cost, have emerged as promising candidates for next-generation, sustainable energy storage. However, their large-scale application is hindered by challenges, such as dendrite formation and side reactions at the anode. Hydrogel electrolytes, which integrate the advantages of liquid and solid phases, exhibit superior ionic conductivity and interfacial compatibility, giving them potential to suppress dendrite evolution. This Perspective first briefly introduces the fundamentals underlying dendrite formation and the unique features of hydrogels. It then identifies the key role of water and polymer networks in inhibiting dendrite formation, highlighting their regulation of water activity, ion transport, and electrode kinetics. By elucidating the principles of hydrogels in dendrite suppression, this work aims to provide valuable insights to advance the implementation of aqueous batteries incorporating polymer hydrogels.

Unraveling Oxyanion Effects on Oxygen Evolution Electrocatalysis of Nickel Hydr(oxy)oxides: The Critical Role of Fe Impurities

Electrolyte modulation can enhance the performance of electrocatalysts for the oxygen evolution reaction (OER) by tailoring the electrocatalyst-electrolyte interface, but the role of anion additives remains controversial. Herein, we report our findings on unraveling the effects of oxyanions (NO3-, SO42-, and PO43-) and identifying Fe impurities as the key factor driving OER activity enhancement in Ni hydr(oxy)oxide model catalysts. Fe impurities, introduced via oxyanion salts, significantly enhance OER activity, while oxyanions themselves have minimal direct impact when Fe ions are removed. Our results, including operando Raman spectroscopy, reveal that Fe enhances Ni reducibility/redox reversibility. X-ray absorption spectroscopy and density functional theory calculations indicate that Fe preferentially adsorbs on Ni surface sites with higher deprotonation energy. These findings reveal the critical role of surface-adsorbed Fe in modulating Ni hydr(oxy)oxide activity and highlight overlooked impurity effects in electrocatalysis when studying additive effects in electrolyte modulation.

Coordination of Mg2+ with Chitosan for Enhanced Triboelectric Performance

In this work, Mg2+ modified chitosan (Mg2+/CS) is proposed and successfully designed. By investigating the effects of the Mg2+ and CS interaction on hydrogen bonding, dipoles, charge density, surface potential, and roughness, the coordination between Mg2+ and CS is verified and the mechanism of coordination improving tribological properties is elucidated. The Mg2+/CS coordination structure enhances intermolecular interactions, promoting the formation of new hydrogen bonds and increasing the dipoles. Compared to CS, the relative dielectric constant of Mg2+/CS increased by 76%, the surface potential increased by 70 mV, and the root mean square roughness increased by 39.4 nm. The open-circuit voltage, short-circuit current, and charge density of the triboelectric nanogenerator (TENG) fabricated from Mg2+/CS were increased by 100%, 94%, and 75%, respectively, compared to the CS-TENG fabricated from pure CS. The coordination of Mg2+ increased the charge density of the Mg2+/CS-TENG, significantly enhancing its charge transfer capability. The Mg2+/CS-TENG successfully provided power for photodetectors and LEDs. Mg2+/CS exhibited excellent flexibility and skin adhesion, and the Mg2+/CS-TENG successfully converted the mechanical energy generated by human joint motion into electrical signals. The coordination structure of Mg2+ with CS enhances the triboelectric performance of Mg2+/CS-TENG, providing new light for the research of chitosan-based TENGs.

Li+(ionophore) nanoclusters engineered aqueous/non-aqueous biphasic electrolyte solutions for high-potential lithium-based batteries

The use of aqueous/non-aqueous biphasic electrolyte solutions in Li-based battery systems circumvents the limitations of poor reductive stability of aqueous electrolyte solutions, broadening their electrochemical stability window. However, aqueous/non-aqueous electrolytes suffer from biphasic mixing and high impedance when Li ions cross the biphasic interface. Here we propose the use of 12-crown-4 (12C4) and tetraglyme (G4) as lithium ionophores to form Li+(ionophore) nanoclusters in both non-aqueous and aqueous phases to overcome the interface challenges in biphasic electrolytes. The Li+(ionophore) nanoclusters have the H2O-excluding inner Li+ solvation structure in non-polar 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), allowing fast charge transport across the biphasic interface without solvent mixing or water shuttling. A tailored electrolyte formulation comprising the lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, 12C4, TTE and H2O solvents (labelled LiTFSI-12C4@TTE/H2O) demonstrates low impedance (2.7 Ω cm-2) at the TTE/H2O interface and enabling 2,000 cycles of prelithiated graphite||LiFePO4 coin cells at 850 mA g-1 with an average Coulombic efficiency of 99.8%. Single-layer 22.5 mAh Li||LiMn2O4 pouch cells using LiTFSI-12C4@TTE/H2O electrolyte with G4 delivered a stable discharge capacity of about 1.3 mAh cm-2 for 80 cycles at 0.5 mA cm-2.

Water structure and electric fields at the interface of oil droplets

Interfacial water exhibits rich and complex behaviour1, playing an important part in chemistry, biology, geology and engineering. However, there is still much debate on the fundamental properties of water at hydrophobic interfaces, such as orientational ordering, the concentration of hydronium and hydroxide, improper hydrogen bonds and the presence of large electric fields2-5. This controversy arises from the challenges in measuring interfacial systems, even with the most advanced experimental techniques and theoretical approaches available. Here we report on an in-solution, interface-selective Raman spectroscopy method using multivariate curve resolution6,7 to probe hexadecane-in-water emulsions, aided by a monomer-field theoretical model for Raman spectroscopy8. Our results indicate that oil-water emulsion interfaces can exhibit reduced tetrahedral order and weaker hydrogen bonding, along with a substantial population of free hydroxyl groups that experience about 95 cm-1 redshift in their stretching mode compared with planar oil-water interfaces. Given the known electrostatic zeta potential characteristic of oil droplets9, we propose the existence of a strong electric field (about 50-90 MV cm-1) emanating from the oil phase. This field is inferred indirectly but supported by control experiments and theoretical estimates. These observations are either absent or opposite in the molecular hydrophobic interface formed by small solutes or at planar oil-water interfaces. Instead, water structural disorder and enhanced electric fields emerge as unique features of the mesoscale interface in oil-water emulsions, potentially contributing to the accelerated chemical reactivity observed at hydrophobic-water interfaces10-13.

Simultaneous High Current Density and Selective Electrocatalytic CO2-to-CH4 through Intermediate Balancing

The electrochemical reduction of CO2 to CH4 is promising for carbon neutrality and renewable energy storage but confronts low CH4 selectivity, especially at high current densities. The key challenge lies in promoting *CO intermediate and *H coupling while minimizing side reactions including C-C coupling and H-H coupling, which is particularly difficult at high current density due to abundant intermediates. Here we report a cooperative strategy to address this challenge using Cu-based catalysts comprising Cu-N coordination polymer and CuO component that can simultaneously manage the key intermediates *CO and *H. A fast CO2-to-CH4 conversion rate of 3.14 mmol cm-2 h-1 is achieved at 1,300 mA cm-2 with a Faradaic efficiency of 51.7 %. In situ spectroscopy and theoretical calculations show that the increased Cu-Cu distance in the Cu-N coordination polymer component favors multistep *CO hydrogenation over the dimerization, and the CuO component ensures an adequate supply of *H, together contributing to the selective CO2-to-CH4 conversion at high current densities. This work develops a cooperative strategy for the electrosynthesis of CH4 with simultaneous high current density and high selectivity by rational catalyst design, paving the way for its applications.

Boosting Electrocatalytic Nitrate Reduction through Enhanced Mass Transfer in Cu-Bipyridine 2D Covalent Organic Framework Films

Electrocatalytic nitrate reduction (NO3RR) is a promising method for pollutant removal and ammonia synthesis and involves the transfer of eight electrons and nine protons. As such, the rational design of catalytic interfaces with enhanced mass transfer is crucial for achieving high ammonia yield rates and Faradaic efficiency (FE). In this work, we incorporated a Cu-bipyridine catalytic interface and fabricated crystalline 2D covalent organic framework films with significantly exposed catalytic sites, leading to improved FE and ammonia yield (FE=92.7 %, NH3 yield rate=14.9 mg ⋅ h-1cm-2 in 0.5 M nitrate) compared to bulk catalysts and outperforming most reported NO3RR electrocatalysts. The film-like morphology enhances mass transfer across the Cu-bipyridine interface, resulting in superior catalytic performance. We confirmed the reaction pathway and mechanism through in situ characterizations and theoretical calculations. The Cu sites act as primary centers for adsorption and activation, while the bipyridine sites facilitate water adsorption and dissociation, supplying sufficient H* and accelerating proton-coupled electron transfer kinetics. This study provides a viable strategy to enhance mass transfer at the catalytic interface through rational morphology control, boosting the intrinsic activity of catalysts in the NO3RR process.

New evidence for the photocatalytic efficiency of natural raw vermiculites to produce hydrogen from aqueous methanol solution

The potential of vermiculites as environmentally friendly photocatalysts for hydrogen production and pollutant degradation was demonstrated by a photocatalytic test in an aqueous 50 % methanol solution (MeOH50). After 4 h of irradiation with the commercial TiO2 Evonik P25 catalyst, the H2 yield was of 656.9 ± 4.2 μmol/gcat. For vermiculites Vm1, Vm3, and Vm4, hydrogen yields were comparable (H₂ = 420.6 ± 5.8 μmol/gcat; H₂ = 414.2 ± 1.8 μmol/gcat, and 449.3 ± 1.8 μmol/gcat, respectively) but were lower in the presence of vermiculite-chlorite intermediate Vm2 (H₂ = 385.1 ± 6.6 μmol/gcat). After the extended 24-h irradiation, hydrogen yield was promoted by the negative tetrahedral charge, while the positive octahedral charge inhibited the photocatalytic decomposition of the MeOH50 into hydrogen in favor of the formation of CO and CH4 byproducts. The decrease in methanol yield in the MeOH50 was effectively assessed by the red shift of the C-O and C-H bands in the Raman spectrum, corresponding to the photocatalytic production of H2.

Recombination of Autodissociated Water Ions in a Nanoscale Pure Water Droplet

The recombination of water ions has diverse scientific and practical implications, ranging from acid-base chemistry and biological systems to planetary environments and applications in fuel cell and carbon conversion technologies. While spatial confinement affects the physicochemical properties of water dynamics, its impact on the recombination process has rarely been studied. In this work, we investigate the dynamics of water, the water ion distribution, and the ion recombination process in water droplets as a function of droplet size through molecular dynamics simulations and adaptive quantum mechanical/molecular mechanical calculations. We compare the dynamics of recombination in water droplet sizes ranging from 100 to 18 000 waters, both in their interiors and on their surfaces. We found that the self-diffusion of water dramatically decreases in droplets with a diameter below 2.2 nm. Using a classical RexPoN force-field, we found that the ions in 1000 H2O's spend almost 50% of the time on the surface and 0.5 nm beneath it with a slight preference for OH- ion to reside longer on the surface. We estimate that, on average, recombination in these drops occurs at 400 ps in 1000 H2O's and 1 ns in 3000 H2O's. We also found that recombination is not limited by the local structure of the surface or the size of the droplet but can be influenced by the geometry of the water wire connecting the ions as they approach each other, which can often prevent recombination. Our results provide insights to the reaction microenvironments presented by nanoscopic water droplets.

In Situ Probing the Anion-Widened Anodic Electric Double Layer for Enhanced Faradaic Efficiency of Chlorine-Involved Reactions

The electric double layer (EDL), which is directly related to ions, influences the electrocatalytic performance. However, the effects of anions on the anodic EDL and reaction kinetics are unclear, especially in water-mediated electrosynthesis. Here, ClO4- anions are discovered to widen the anodic EDL to inhibit the competitive oxygen evolution reaction (OER) for the gram-scale electrosynthesis of 2-chlorocyclohexanol with a 90% Faradaic efficiency (FE) at 100 mA cm-2. The combined results of molecular dynamics simulations and in situ spectroscopies provide solid evidence for the widened EDL that originates from the repulsion of water molecules from the interface by ClO4-. The addition of ClO4- has a negligible effect on chlorination kinetics because of the electrostatic interaction between the anode and Cl- but obviously suppresses the interaction between water and the anode, leading to high FEs of anodic electrosynthesis by increasing the energy barrier of the undesirable OER. In addition, this method is suitable for other chlorination reactions with enhanced FEs at 100 mA cm-2.

The Role of Interfaces and Charge for Chemical Reactivity in Microdroplets

A wide variety of reactions are reported to be dramatically accelerated in aqueous microdroplets, making them a promising platform for environmentally clean chemical synthesis. However, to fully utilize the microdroplets for accelerating chemical reactions requires a fundamental understanding of how microdroplet chemistry differs from that of a homogeneous phase. Here we provide our perspective on recent progress to this end, both experimentally and theoretically. We begin by reviewing the many ways in which microdroplets can be prepared, creating water/hydrophobic interfaces that have been frequently implicated in microdroplet reactivity due to preferential surface adsorption of solutes, persistent electric fields, and their acidity or basicity. These features of the interface interplay with specific mechanisms proposed for microdroplet reactivity, including partial solvation, possible gas phase channels, and the presence of highly reactive intermediates. We especially highlight the role of droplet charge and associated electric fields, which appears to be key to understanding how certain reactions, like the formation of hydrogen peroxide and reduced transition metal complexes, are thermodynamically possible in microdroplets. Lastly, we emphasize opportunities for theoretical advances and suggest experiments that would greatly enhance our understanding of this fascinating subject.

Colored Cellulose Nanoparticles with High Stability and Easily Modified Surface for Accurate and Sensitive Multiplex Lateral Flow Assay

Decentralized testing using multiplex lateral flow assays (mLFAs) to simultaneously detect multiple analytes can significantly enhance detection efficiency, reduce cost and time, and improve analytic accuracy. However, the challenges, including the monochromatic color of probe particles, interference between different test lines, and reduced specificity and sensitivity, severely hinder mLFAs from wide use. In this study, we prepared polydopamine (PDA)-coated dyed cellulose nanoparticles (dCNPs@P) with tunable colors as the probe for mLFAs. Cellulose nanoparticles (CNPs) were synthesized with uniform spheric shapes and tunable sizes. Dye molecules were loaded on CNPs via a mature industrial dyeing method. The PDA shell provided a reactive surface for facile receptor conjugation and protected the dye from leaking. dCNPs@P displayed a higher signal intensity than gold nanoparticles. They also had higher stability to tolerate salt and varied pH. The dCNP@P-based mLFAs were successfully applied to detect multiple mycotoxins in cereals and determine the levels of inflammatory biomarkers to differentiate between viral and bacterial infections. The tests represented high specificity and accuracy and were more sensitive than the tests using gold nanoparticles. The quantified detection was accessible by measuring the intensities of the colorimetric or photothermal signals. Overall, this study provides a practical system solution for mLFAs based on colored dCNPs@P.

Toward Long-Life High-Voltage Aqueous Li-Ion Batteries: from Solvation Chemistry to Solid-Electrolyte-Interphase Layer Optimization Against Electron Tunneling Effect

Water is pursued as an electrolyte solvent for its non-flammable nature compared to traditional organic solvents, yet its narrow electrochemical stability window (ESW) limits its performance. Solvation chemistry design is widely adopted as the key to suppress the reactivity of water, thereby expanding the ESW. In this study, an acetamide-based ternary eutectic electrolyte achieved an ESW ranging from 1.4 to 5.1 V. The electrolyte confines water molecules within the primary solvation sheath of Li-ions, reducing the free water and breaking the hydrogen bond network. Despite this, initial capacity retention is suboptimal due to inadequate formation of solid-electrolyte-interphase (SEI) layers. To address this, additional hydrogen evolution reaction is induced by widening the operation voltage range, thereby optimizing the SEI layer to mitigate the electron tunneling effect. This approach resulted in a denser LiF-rich SEI layer, effectively preventing water decomposition and improving long-term cycle stability. The optimized SEI layer reduced the electron tunneling barrier, achieving a discharge capacity of 152 mAh g-1 at 1 C and maintaining 76% of its capacity (116 mAh g-1) after 1000 cycles. This study highlights the critical role of both solvation structure and SEI layer optimization in enhancing the performance of high-voltage aqueous Li-ion batteries.

Gold nanocomposites in colorectal cancer therapy: characterization, selective cytotoxicity, and migration inhibition

The third most prevalent type of cancer in the world, colorectal cancer, poses a significant treatment challenge due to the nonspecific distribution, low efficacy, and high systemic toxicity associated with chemotherapy. To overcome these limitations, a targeted drug delivery system with a high cytotoxicity against cancer cells while maintaining a minimal systemic side effects represents a promising therapeutic approach. Therefore, the aim of this study was to develop an efficient gold nanocarrier for the targeted delivery of the anticancer agent everolimus to Caco-2 cells. A novel gold nanocomposite (EV-β-CD-HA-Chi-AuNCs) functionalized with a targeting ligand (hyaluronic acid), a permeation enhancement excipient (chitosan), and an anticancer inclusive compound consisting of beta-cyclodextrin and everolimus was proposed and prepared via Turkevich method. Characterization was performed with a UV spectrometer, FTIR, Zetasizer, and HRTEM. Its drug release profile was also evaluated in media with three different pH values. Cytotoxicity and biocompatibility studies were performed on a colorectal cancer cell line (Caco-2) and a normal fibroblast line (MRC-5), respectively, via xCELLigence real-time cellular analysis (RTCA) technology. The inhibitory effect on migration was also further tested via the xCELLigence RTCA technique and a scratch assay. Characterization studies revealed the successful formation of EV-β-CD-HA-Chi-AuNCs with a size and charge which are suitable for the use as targeted drug delivery carrier. In the cytotoxic study, the EV-β-CD-HA-Chi-AuNCs showed a lower IC50 (16 ± 1 µg/ml) than the pure drug (25 ± 3 µg/ml) toward a colorectal cell line (Caco-2). In the biocompatibility study, the EV-β-CD-HA-Chi-AuNCs have minimal toxicity, while the pure drug has severe toxicity toward healthy fibroblasts (MRC-5) despite its low concentration. In the cell migration study, the EV-β-CD-HA-Chi-AuNCs also showed a greater inhibitory effect than the pure drug. Compared with the pure drug, the EV-β-CD-HA-Chi-AuNCs exhibit an excellent selective cytotoxicity between cancerous colorectal Caco-2 cells and healthy MRC-5 cells, making it a potential carrier to carry the drug to the cancerous site while maintaining its low toxicity to the surrounding environment. In addition, an increase in the cytotoxic activity of the EV-β-CD-HA-Chi-AuNCs toward cancerous colorectal Caco-2 cells was also observed, which can potentially improve the treatment of colorectal cancer.

Wetting Transition from Wenzel to Cassie States: Thermodynamic Analysis

Superhydrophobicity is closely linked to the chemical composition and geometric characteristics of surface roughness. Building on our structural studies on water and air-water interfaces, this work aims to elucidate the mechanism underlying the wetting transition from the Wenzel to the Cassie state on a hydrophobic surface. In the Wenzel state, the grooves are filled with water, meaning that the surface roughness becomes embedded in the liquid. To evaluate the effects of surface roughness on water structure, a wetting parameter (WRoughness) is proposed, which is closely related to the geometric characteristics of roughness, such as pillar size, width, and height. During the wetting transition from Wenzel to Cassie states, the critical wetting parameter (WRoughness,c) may be expected, which corresponds to the critical pillar size (ac), width (wc), and height (hc). The Cassie state is expected when the WRoughness is less than WRoughness,c (ac), decreasing width (hc). Additionally, molecular dynamic (MD) simulations are conducted to demonstrate the effects of surface roughness on superhydrophobicity.

Using the pH sensitivity of switchable surfactants to understand the role of the alkyl tail conformation and hydrogen bonding at a molecular level in elucidating emulsion stability

HYPOTHESIS

The monoalkyl diamine surfactant, N-dodecylpropane-1,3-diamine (DPDA), is expected to exhibit a pH-dependent charge switchability. In response to pH changes, the interfacial self-assembly of DPDA becomes an intermediary constituent that can potentially modify the interfacial interactions and structural assembly of both the oil and water phases. Hence, we hypothesize that as we change the pH, DPDA will respond to it by changing its charge and alkyl tail conformation as well as the conformation of adjacent phases at the molecular level, consequently affecting emulsion formation and stability. A neutral pH, resulting in a mono-cationic dialkyl amine, affects the conformation, driving an ordered self-assembly and stable emulsion.

EXPERIMENTS

The pH-sensitivity and interfacial activity of DPDA were evaluated through pH titration and interfacial tension measurements. Subsequently, a molecular-level study of DPDA, as a pH-sensitive switchable surfactant, was performed at the dodecane-water interface using SFG spectroscopy. The interpretation of the vibrational spectra was further reinforced by determining the gauche defects in the interfacial alkyl chain organization and the extent of hydrogen (H) bonding between the interfacial water molecules.

FINDINGS

By adjusting the pH of water, the charge of the adsorbed DPDA molecules, their self-assembly, the organization of interfacial molecules, and ultimately the stability of the emulsion were tuned. At pH 7.0, the SFG spectra of DPDA showed that the interfacial alkyl chains were relatively well-ordered, while water molecules also had stronger H-bonding interactions. As a result, the oil-water emulsion showed improved stability. When water was at a high pH, the water molecules had fewer H-bonding interactions and relatively disordered alkyl chains at the interface, providing desirable conditions for demulsification. These observations were compatible with the observation in bulk emulsion preparation, confirming that alkyl chain packing and water H-bonding interactions at the interface contribute to overall emulsion stability.

Preparation of a CNF porous membrane and in situ synthesis of silver nanoparticles (AgNPs)

We prepared a cellulose nanofiber (CNF)-based porous membrane with three dimensional cellular structures. CNF was concentrated via a surfactant-induced assembly by mixing CNF with a cationic surfactant, domiphen bromide (DB). Furthermore, they were accumulated by centrifugation to obtain a CNF-DB sol. Next, when the CNF-DB sol was naturally dried, a membrane composed of densely packed CNF was obtained. On the other hand, when the CNF-DB sol was freeze-dried, a porous membrane with the anisotropic cellular structure could be obtained. The interspace between layered CNF sheets was tunable by the DB concentration in the assembly process and the centrifugal force in the accumulation process. FT-IR analysis of the porous membrane showed the formation of hydrogen bonds between the CNF, resulting in facilitation of crosslinking of the CNF and formation of the cellular structures. The obtained CNF-DB membrane exhibited high water resistance. They showed a high ability to absorb hydrophobic dyes such as Nile red and rhodamine B (RhB) due to the presence of the hydrophobic core of DB micelles. Then, the release of RhB could be controlled by the ionic strength in the medium. In addition, they possessed a high ability to adsorb cationic metals such as Ag ions due to the presence of carboxyl moieties of CNF. Next, in situ synthesis of silver nanoparticles (AgNPs) was carried out by employing the CNF-DB membrane as a template for Ag ion adsorption and reduction. Deposition of AgNPs could be observed on the CNF-DB membrane, which suppressed aggregation of AgNPs. Almost all AgNPs were arrayed apart from each other to generate the hotspots, which could enhance surface-enhanced Raman scattering (SERS) of AgNPs. Such an AgNPs-CNF composite membrane could be applied for a label-free analysis of adsorbed RhB.

Unveiling Ionized Interfacial Water-Induced Localized H* Enrichment for Electrocatalytic Nitrate Reduction

Electrocatalytic nitrate reduction reaction (NO3RR) is a process that requires the participation of eight electrons and nine protons. The regulation of active hydrogen (H*) supply and a deep understanding of related processes are necessary for improving the ammonia yield rate and Faradaic efficiency (FE). Herein, we synthesized a series of atomically precise copper-halide clusters Cu2X2(BINAP)2 (X=Cl, Br, I), among which the Cu2Cl2(BINAP)2 cluster shows the optimal ammonia FE of 94.0 % and an ammonia yield rate of 373 μmol h-1 cm-2. In situ experiments and theoretical calculations reveal that halogen atoms, especially Cl in Cu2Cl2(BIANP)2, can significantly affect the distance of alkali metal-ionized water on the catalyst surface, which can promote the water dissociation to enhance the localized H* enrichment for the continues hydrogenation of nitrate to ammonia. This work explains the role of H* in the hydrogenation process of NO3RR and the importance of localized H* enrichment strategy for improving the FEs.

Compressible, anti-fatigue, extreme environment adaptable, and biocompatible supramolecular organohydrogel enabled by lignosulfonate triggered noncovalent network

Achieving a synergy of biocompatibility and extreme environmental adaptability with excellent mechanical property remains challenging in the development of synthetic materials. Herein, a "bottom-up" solution-interface-induced self-assembly strategy is adopted to develop a compressible, anti-fatigue, extreme environment adaptable, biocompatible, and recyclable organohydrogel composed of chitosan-lignosulfonate-gelatin by constructing noncovalent bonded conjoined network. The ethylene glycol/water solvent induced lignosulfonate nanoparticles function as bridge in chitosan/gelation network, forming multiple interfacial interactions that can effectively dissipate energy. The organohydrogel exhibits high compressive strength (54 MPa) and toughness (3.54 MJ/m3), 100 and 70 times higher than those of pure chitosan/gelatin hydrogel, meanwhile, excellent self-recovery and fatigue resistance properties. Even when subjected to severe compression up to a strain of 0.5 for 500,000 cycles, the organohydrogel still remains intact. This organohydrogel also demonstrates notable biocompatibility both in vivo and vitro, environment adaptability at low temperature, as well as recyclability. Such all natural organohydrogel provides a promising route towards the development of high-performance load-bearing materials.

Boosting Alkaline Hydrogen Oxidation Kinetics through Interfacial Environments Induced Surface Migration of Adsorbed Hydroxyl

Constructing bifunctional sites through heterojunction engineering to accelerate water formation has become a pivotal strategy to improve the alkaline hydrogen oxidation reaction (HOR) kinetics, which is mainly focused on the synergistic effect of neighboring sites and the energetics of the surface reaction steps. However, the roles of the surface migration of key intermediates that go beyond the bifunctional mechanism limited to neighboring atoms have usually been ignored. Using the heterostructured Ni3C-Ni catalyst as a model, we found that the rapid surface migration of OHad species from the positively charged Ni3C to the negatively charged Ni component played a decisive role in facilitating water formation. Such unprecedented surface migration of OHad is induced by the large discrepancy between the local surface charge densities and interfacial environments of the Ni3C and Ni components under operating conditions. Benefiting from this, the resultant Ni3C-Ni exhibited outstanding mass activity for the alkaline HOR, which was approximately 19-fold and 21-fold higher than those of Ni and Ni3C, respectively. These findings not only provide novel insights into the alkaline HOR mechanism of heterostructured catalysts but also open new avenues for developing advanced electrocatalysts for alkaline fuel cells.

Mimicking on-water surface synthesis through micellar interfaces

The chemistry of the on-water surface, characterized by enhanced reactivity, distinct selectivity, and confined reaction geometry, offers significant potential for chemical and materials syntheses. However, the utilization of on-water surface synthesis is currently limited by the requirement for a stable air-water interface, which restricts its broader synthetic applications. In this work, we present a approach that mimics on-water surface chemistry using micelles. This method involves the self-assembly of charged surfactant molecules beyond their critical micelle concentration (CMC), forming micellar structures that simulate the air-water interface. This creates an environment conducive to chemical reactions, featuring a hydrophobic core and surrounding water layer. Utilizing such mimicking on-water surface with the assembly of porphyrin-based monomers featuring distinct confined geometry and preferential orientations, we achieve reactivity and selectivity (≥99%) in fourteen different reversible and irreversible chemical reactions. Extending the versatility of this approach, we further demonstrate its applicability to two-dimensional (2D) polymerization on micellar interfaces, successfully achieving the aqueous synthesis of crystalline 2D polymer thin layers. This strategy significantly broadens the accessibility of on-water surface chemistry for a wide range of chemical syntheses.

Independent Control Over the H/OH Adsorption: Breaking the Trade-Off Between H/OH-Adsorption and H2O-Dissociation of Platinum-Group Metal Electrocatalyst for Hydrogen Evolution Reaction

Platinum-group metals catalysts (such as Rh, Pd, Ir, Pt) have been the most efficient hydrogen evolution reaction (HER) electrocatalysts due to their moderate H adsorption strength, while the high H2O-dissociation barrier in alkaline media restrains the catalytic performance of PGM catalysts. However, the optimization of the H2O-dissociation barrier and *H/*OH binding energy toward their individual optima is limited due to the constraints of their scaling relationship on a single active site. Here, a coordinatively unsaturated "M─Ox─W" (M = Rh, Pd, Ir, Pt) active area is constructed, where H and OH species are anchored on Pt-group metal sites and inactive W sites for individual regulation. By combining experiments and density functional theory calculations, the introduction of extra OH-adsorption sites (coordinatively unsaturated WO3-x) avoids the competitive adsorption of H and OH on the single site, while the enhanced OH-adsorption capacity on the coordinatively unsaturated WO3-x effectively facilitates the adsorption/dissociation of interfacial H2O. As a result, the representative Rh-WO3-x catalyst exhibits outstanding catalytic activity and durability for HER. The findings of this work not only provide valuable insights for the design of efficient PGM catalysts for HER but also shed light on the development of electrocatalysts for other catalytic reactions.

Regulation of Molecular Microheterogeneity in Electrolytes Enables Ampere-Hour-Level Aqueous LiMn2O4||Li4Ti5O12 Pouch Cells

Aqueous batteries are attractive due to their high safety and fast reaction kinetics, but the narrow electrochemical stability window of H2O limits their applications. It is a big challenge to broaden the electrochemical operation window of aqueous electrolytes while retaining fast reaction kinetics. Here, a new organic aqueous mixture electrolyte of manipulatable (3D) molecular microheterogeneity with H2O-rich and H2O-poor domains is demonstrated. H2O-poor domains molecularly surround the reformed microclusters of H2O molecules through interfacial H-bonds, which thus not only inhibit the long-range transfer of H2O but also allow fast and consecutive Li+ transport. This new design enables low-voltage anodes reversibly cycling with aqueous-based electrolytes and high ionic conductivity of 4.5 mS cm-1. LiMn2O4||Li4Ti5O12 full cells demonstrate excellent cycling stability over 1000 cycles under various C rates and a low temperature of -20 °C. 1 Ah pouch cell delivers a high energy density of 79.3 Wh kg-1 and high Coulombic efficiency of 99.4% at 1 C over 200 cycles. This work provides new insights into the design of electrolytes based on the molecular microheterogeneity for rechargeable batteries.

High-Performance Nanofiltration Membrane with Dual Resistance to Gypsum Scaling and Biofouling for Enhanced Water Purification

Nanofiltration (NF) technology is pivotal for ensuring a sustainable and reliable supply of clean water. To address the critical need for advanced thin-film composite (TFC) polyamide (PA) membranes with exceptional permselectivity and fouling resistance for emerging contaminant purification, we introduce a novel high-performance NF membrane. This membrane features a selective polypiperazine (PIP) layer functionalized with amino-containing quaternary ammonium compounds (QACs) through an in situ interfacial polycondensation reaction. Our investigation demonstrated that precise QAC functionalization enabled the construction of the selective PA layer with increased surface area, enhanced microporosity, stronger electronegativity, and reduced thickness compared to the control PIP membrane. As a result, the QAC NF membrane exhibited an approximately 51% increase in water permeance compared to the control PIP membrane, while achieving superior retention capabilities for divalent salts (>99%) and emerging organic contaminants (>90%). Furthermore, the incorporation of QACs into the PIP selective layer was proved to be effective in mitigating mineral scaling by allowing selective passage of scale-forming cations, while simultaneously exhibiting strong antimicrobial properties to combat biofouling. The in situ QAC incorporation strategy presented in this study provides valuable guidelines for the fit-for-purpose design of the selective PA layer, which is crucial for the development of high-performance NF membranes for efficient water purification.

Panthenol Additives with Multiple Coordination Sites Induce Uniform Zinc Deposition and Inhibited Side Reactions for High Performance Aqueous Zinc Metal Battery

Application of aqueous zinc metal batteries (AZMBs) in large-scale new energy systems (NESs) is challenging owing to the growth of dendrites and frequent side reactions. Here, this study proposes the use of Panthenol (PB) as an electrolyte additive in AZMBs to achieve highly reversible zinc plating/stripping processes and suppressed side reactions. The PB structure is rich in polar groups, which led to the formation of a strong hydrogen bonding network of PB-H2O, while the PB molecule also builds a multi-coordination solvated structure, which inhibits water activity and reduces side reactions. Simultaneously, PB and OTF- decomposition, in situ formation of SEI layer with stable organic-inorganic hybrid ZnF2-ZnS interphase on Zn anode electrode, can inhibit water penetration into Zn and homogenize the Zn2+ plating. The effect of the thickness of the SEI layer on the deposition of Zn ions in the battery is also investigated. Hence, this comprehensive regulation strategy contributes to a long cycle life of 2300 h for Zn//Zn cells assembled with electrolytes containing PB additives. And the assembled Zn//NH4V4O10 pouch cells with homemade modules exhibit stable cycling performance and high capacity retention. Therefore, the proposed electrolyte modification strategy provides new ideas for AZMBs and other metal batteries.

A Stable High-Performance Zn-Ion Batteries Enabled by Highly Compatible Polar Co-Solvent

Uncontrollable growth of Zn dendrites, irreversible dissolution of cathode material and solidification of aqueous electrolyte at low temperatures severely restrict the development of aqueous Zn-ion batteries. In this work, 2,2,2-trifluoroethanol (TFEA) with a volume fraction of 50% as a highly compatible polar-solvent is introduced to 1.3 M Zn(CF3SO3)2 aqueous electrolyte, achieving stable high-performance Zn-ion batteries. Massive theoretical calculations and characterization analysis demonstrate that TFEA weakens the tip effect of Zn anode and restrains the growth of Zn dendrites due to electrostatic adsorption and coordinate with H2O to disrupt the hydrogen bonding network in water. Furthermore, TFEA increases the wettability of the cathode and alleviates the dissolution of V2O5, thus improving the capacity of the full battery. Based on those positive effects of TFEA on Zn anode, V2O5 cathode, and aqueous electrolyte, the Zn//Zn symmetric cell delivers a long cycle-life of 782 h at 5 mA cm-2 and 2 mA h cm-2. The full battery still declares an initial capacity of 116.78 mA h g-1, and persists 87.73% capacity in 2000 cycles at -25 °C. This work presents an effective strategy for fully compatible co-solvent to promote the stability of Zn anode, V2O5 cathode and aqueous electrolyte for high-performance Zn-ion batteries.

Research on the Thermal Aging Mechanism of Polyvinyl Alcohol Hydrogel

Polyvinyl alcohol (PVA) hydrogels find applications in various fields, including machinery and tissue engineering, owing to their exceptional mechanical properties. However, the mechanical properties of PVA hydrogels are subject to alteration due to environmental factors such as temperature, affecting their prolonged utilization. To enhance their lifespan, it is crucial to investigate their aging mechanisms. Using physically cross-linked PVA hydrogels, this study involved high-temperature accelerated aging tests at 60 °C for 80 d and their performance was analyzed through macroscopic mechanics, microscopic morphology, and microanalysis tests. The findings revealed three aging stages, namely, a reduction in free water, a reduction in bound water, and the depletion of bound water, corresponding to volume shrinkage, decreased elongation, and a "tough-brittle" transition. The microscopic aging mechanism was influenced by intermolecular chain spacing, intermolecular hydrogen bonds, and the plasticizing effect of water. In particular, the loss of bound water predominantly affected the lifespan of PVA hydrogel structural components. These findings provide a reference for assessing and improving the lifespan of PVA hydrogels.

Selective CO2 Electroreduction to Multi-Carbon Products on Organic-Functionalized CuO Nanoparticles by Local Micro-Environment Modulation

Surface functionalization of Cu-based catalysts has demonstrated promising potential for enhancing the electrochemical CO2 reduction reaction (CO2RR) toward multi-carbon (C2+) products, primarily by suppressing the parasitic hydrogen evolution reaction and facilitating a localized CO2/CO concentration at the electrode. Building upon this approach, we developed surface-functionalized catalysts with exceptional activity and selectivity for electrocatalytic CO2RR to C2+ in a neutral electrolyte. Employing CuO nanoparticles coated with hexaethynylbenzene organic molecules (HEB-CuO NPs), a remarkable C2+ Faradaic efficiency of nearly 90% was achieved at an unprecedented current density of 300 mA cm-2, and a high FE (> 80%) was maintained at a wide range of current densities (100-600 mA cm-2) in neutral environments using a flow cell. Furthermore, in a membrane electrode assembly (MEA) electrolyzer, 86.14% FEC2+ was achieved at a partial current density of 387.6 mA cm-2 while maintaining continuous operation for over 50 h at a current density of 200 mA cm-2. In-situ spectroscopy studies and molecular dynamics simulations reveal that reducing the coverage of coordinated K⋅H2O water increased the probability of intermediate reactants (CO) interacting with the surface, thereby promoting efficient C-C coupling and enhancing the yield of C2+ products. This advancement offers significant potential for optimizing local micro-environments for sustainable and highly efficient C2+ production.

Stable Zinc Anode Facilitated by Regenerated Silk Fibroin-modified Hydrogel Protective Layer

Inherent dendrite growth and side reactions of zinc anode caused by its unstable interface in aqueous electrolytes severely limit the practical applications of zinc-ion batteries (ZIBs). To overcome these challenges, a protective layer for Zn anode inspired by cytomembrane structure is developed with PVA as framework and silk fibroin gel suspension (SFs) as modifier. This PVA/SFs gel-like layer exerts similar to the solid electrolyte interphase, optimizing the anode-electrolyte interface and Zn2+ solvation structure. Through interface improvement, controlled Zn2+ migration/diffusion, and desolvation, this buffer layer effectively inhibits dendrite growth and side reactions. The additional SFs provide functional improvement and better interaction with PVA by abundant functional groups, achieving a robust and durable Zn anode with high reversibility. Thus, the PVA/SFs@Zn symmetric cell exhibits an ultra-long lifespan of 3150 h compared to bare Zn (182 h) at 1.0 mAh cm-2-1.0 mAh cm-2, and excellent reversibility with an average Coulombic efficiency of 99.04% under a large plating capacity for 800 cycles. Moreover, the PVA/SFs@Zn||PANI/CC full cells maintain over 20 000 cycles with over 80% capacity retention under harsh conditions at 5 and 10 A g-1. This SF-modified protective layer for Zn anode suggests a promising strategy for reliable and high-performance ZIBs.

Fast fabrication of "all-in-one" injectable hydrogels as antibiotic alternatives for enhanced bacterial inhibition and accelerating wound healing

Skin wound infection has become a notable medical threat. Herein, the polysaccharide-based injectable hydrogels with multifunctionality were developed by a simple and fast gelation process not only to inactivate bacteria but also to accelerate bacteria-infected wound healing. Sodium nitroprusside (SNP) loaded PCN-224 nanoparticles were introduced into the polymer matrix formed by the dynamic and reversible coordinate bonds between Ag+ with carboxyl and amino or hydroxyl groups on carboxymethyl chitosan (CMCS), hydrogen bonds and electrostatic interactions in the polymer to fabricate SNP@PCN@Gel hydrogels. SNP@PCN@Gel displayed interconnected porous structure, excellent self-healing capacity, low cytotoxicity, good blood compatibility, and robust antibacterial activity. SNP@PCN@Gel could produce reactive oxygen species (ROS) and NO along with Fe2+, and showed long-term sustained release of Ag+, thereby effectively killing bacteria by synergistic photothermal (hyperthermia), photodynamic (ROS), chemodynamic (Fenton reaction), gas (NO) and ion (Ag+ and -NH3+ in CMCS) therapy. Remarkably, the hydrogels significantly promoted granulation tissue formation, reepithelization, collagen deposition and angiogenesis as well as wound contraction in bacteria-infected wound healing. Taken together, the strategy represented a general method to engineer the unprecedented photoactivatable "all-in-one" hydrogels with enhanced antibacterial activity and paved a new way for development of antibiotic alternatives and wound dressing.

Catalyst-free selective oxidation of C(sp3)-H bonds in toluene on water

The anisotropic water interfaces provide an environment to drive various chemical reactions not seen in bulk solutions. However, catalytic reactions by the aqueous interfaces are still in their infancy, with the emphasis being on the reaction rate acceleration on water. Here, we report that the oil-water interface activates and oxidizes C(sp3)-H bonds in toluene, yielding benzaldehyde with high selectivity (>99%) and conversion (>99%) under mild, catalyst-free conditions. Collision at the interface between oil-dissolved toluene and hydroxyl radicals spontaneously generated near the water-side interfaces is responsible for the unexpectedly high selectivity. Protrusion of free OH groups from interfacial water destabilizes the transition state of the OH-addition by forming π-hydrogen bonds with toluene, while the H-abstraction remains unchanged to effectively activate C(sp3)-H bonds. Moreover, the exposed free OH groups form hydrogen bonds with the produced benzaldehyde, suppressing it from being overoxidized. Our investigation shows that the oil-water interface has considerable promise for chemoselective redox reactions on water without any catalysts.

Interfacial Water Is Separated from a Hydrophobic Silica Surface by a Gap of 1.2 nm

The interaction of liquid water with hydrophobic surfaces is ubiquitous in life and technology. Yet, the molecular structure of interfacial liquid water on these surfaces is not known. By using a 3D atomic force microscope, we characterize with angstrom resolution the structure of interfacial liquid water on hydrophobic and hydrophilic silica surfaces. The combination of 3D AFM images and molecular dynamics simulations reveals that next to a hydrophobic silica surface, there is a 1.2 nm region characterized by a very low density of water. In contrast, the 3D AFM images obtained of a hydrophilic silica surface reveal the presence of hydration layers next to the surface. The gap observed on hydrophobic silica surfaces is filled with two-to-three layers of straight-chain alkanes. We developed a 2D Ising model that explains the formation of a continuous hydrocarbon layer on hydrophobic silica surfaces.

Modeling Vibrational Sum Frequency Generation Spectra of Interfacial Water on a Gold Surface: The Role of the Fermi Resonance

Studying the hydrogen bonding structure of H2O at the metal-water interface is a highly complex yet fascinating endeavor. The intricate interactions and diverse orientations of water molecules on metal surfaces with varying potentials pose a significant challenge in elucidating the coupling between O-H stretching and H-O-H bending modes. In this study, we employed DFT-MD simulation to explore how the orientation of interfacial water molecules changes with the applied potential on the Au(111) surface. Based on the surface-specific velocity-velocity correlation function (ssVVCF) formula, we calculated vibrational sum frequency generation (VSFG) spectra for the O-H stretches. We found that three assigned peaks (∼3300, ∼3450, and 3650 cm-1) shifted toward lower frequencies as the potential moved toward more negative values. Our results align remarkably well with experimental Raman spectroscopy data. Notably, our VSFG analysis revealed a significant change in the VSFG spectra of the hydrogen-bonded O-H groups (∼3300 cm-1), switching from a negative to a positive sign with decreasing potential. This alteration suggests a substantial change in the orientation of these low-frequency O-H groups owing to their increased interactions with the Au surface. In contrast, the orientations of both the high-frequency O-H groups (∼3450 cm-1) and the dangling O-H groups (∼3650 cm-1) remained unaffected by the applied potentials. Furthermore, our analysis of the decomposed vibrational density of states (VDOS) for the H-O-H bending mode uncovered the coupling between the H-O-H bending and O-H stretching vibrations, known as the Fermi resonance. Our work suggests that the H-O-H bending vibration becomes restricted when water molecules transition from the ″one-H-down″ to the ″two-H-down″ conformation, leading to a redshift in the O-H stretching vibration through the Fermi resonance. By constructing the VSFG and decomposed VDOS spectra, we gained valuable insights into the structural changes that Raman spectra alone cannot fully interpret. Specifically, our analysis revealed the critical role of the Fermi resonance effect in shaping the spectroscopic signature of interfacial water molecules on the Au(111) surface.

Unlocking Dynamic Solvation Chemistry and Hydrogen Evolution Mechanism in Aqueous Zinc Batteries

Understanding the interfacial hydrogen evolution reaction (HER) is crucial to regulate the electrochemical behavior in aqueous zinc batteries. However, the mechanism of HER related to solvation chemistry remains elusive, especially the time-dependent dynamic evolution of the hydrogen bond (H-bond) under an electric field. Herein, we combine in situ spectroscopy with molecular dynamics simulation to unravel the dynamic evolution of the interfacial solvation structure. We find two critical change processes involving Zn-electroplating/stripping, including the initial electric double layer establishment to form an H2O-rich interface (abrupt change) and the subsequent dynamic evolution of an H-bond (gradual change). Moreover, the number of H-bonds increases, and their strength weakens in comparison with the bulk electrolyte under bias potential during Zn2+ desolvation, forming a diluted interface, resulting in massive hydrogen production. On the contrary, a concentrated interface (H-bond number decreases and strength enhances) is formed and produces a small amount of hydrogen during Zn2+ solvation. The insights on the above results contribute to deciphering the H-bond evolution with competition/corrosion HER during Zn-electroplating/stripping and clarifying the essence of electrochemical window widened and HER suppression by high concentration. This work presents a new strategy for aqueous electrolyte regulation by benchmarking the abrupt change of the interfacial state under an electric field as a zinc performance-enhancement criterion.

Probing the structure of water in individual living cells

Water regulates or even governs a wide range of biological processes. Despite its fundamental importance, surprisingly little is known about the structure of intracellular water. Herein we employ a Raman micro-spectroscopy technique to uncover the composition, abundance and vibrational spectra of intracellular water in individual living cells. In three different cell types, we show a small but consistent population (~3%) of non-bulk-like water. It exhibits a weakened hydrogen-bonded network and a more disordered tetrahedral structure. We attribute this population to biointerfacial water located in the vicinity of biomolecules. Moreover, our whole-cell modeling suggests that all soluble (globular) proteins inside cells are surrounded by, on average, one full molecular layer (about 2.6 Angstrom) of biointerfacial water. Furthermore, relative invariance of biointerfacial water is observed among different single cells. Overall, our study not only opens up experimental possibilities of interrogating water structure in vivo but also provides insights into water in life.

Effect of counterions on the structure and dynamics of water near a negatively charged surfactant: a theoretical vibrational sum frequency generation study

Charged aqueous interfaces are of paramount importance in electrochemical, biological and environmental sciences. The properties of aqueous interfaces with ionic surfactants can be influenced by the presence of counterions. Earlier experiments involving vibrational sum frequency generation (VSFG) spectroscopy of aqueous interfaces with negatively charged sodium dodecyl sulfate (Na+DS- or SDS) surfactants revealed that the hydrogen bonding strength of the interfacial water molecules follows a certain order when salts of monovalent and divalent cations are added. It is known that cations do not directly participate in hydrogen bonding with water molecules, rather they only influence the hydrogen bonded network through their electrostatic fields. In the current work, we have simulated the aqueous interfacial systems of sodium dodecyl sulfate in the presence of chloride salts of mono and divalent countercations. The electronic polarization effects on the ions are considered at a mean-field level within the electronic continuum correction model. Our calculations of the VSFG spectra show a blue shift in the presence of added countercations whose origin is traced to different relative contributions of water molecules from the solvation shells of the surfactant headgroups and the remaining water molecules in the presence of countercations. Furthermore, the cations shield the electric fields of the surfactant headgroups, which in turn influences the contributions of water molecules to the total VSFG spectrum. This shielding effect becomes more significant when divalent countercations are present. The dynamics of water molecules is found to be slower at the interface in comparison to the bulk. The interfacial depth dependence of various dynamical quantities shows that the interface is structurally and dynamically more heterogeneous at the microscopic level.

Optical Actuation of Nanoparticle-Loaded Liquid-Liquid Interfaces for Active Photonics

Liquid-liquid interfaces hold the potential to serve as versatile platforms for dynamic processes, due to their inherent fluidity and capacity to accommodate surface-active materials. This study explores laser-driven actuation of liquid-liquid interfaces with and without loading of gold nanoparticles and further exploits the laser-actuated interfaces with nanoparticles for tunable photonics. Upon laser exposure, gold nanoparticles were rearranged along the interface, enabling the reconfigurable, small-aperture modulation of light transmission and the tunable lensing effect. Adapting the principles of optical and optothermal tweezers, we interpreted the underlying mechanisms of actuation and modulation as a synergy of optomechanical and optothermal effects. Our findings provide an analytical framework for understanding microscopic interfacial behaviors, contributing to potential applications in tunable photonics and interfacial material engineering.

Nuclear quantum effects on the vibrational dynamics of the water-air interface

We have applied path-integral molecular dynamics simulations to investigate the impact of nuclear quantum effects on the vibrational dynamics of water molecules at the water-air interface. The instantaneous fluctuations in the frequencies of the O-H stretch modes are calculated using the wavelet method of time series analysis, while the time scales of vibrational spectral diffusion are determined from frequency-time correlation functions and joint probability distributions. We find that the inclusion of nuclear quantum effects leads not only to a redshift in the vibrational frequency distribution by about 120 cm-1 for both the bulk and interfacial water molecules but also to an acceleration of the vibrational dynamics at the water-air interface by as much as 35%. In addition, a blueshift of about 45 cm-1 is seen in the vibrational frequency distribution of interfacial water molecules compared to that of the bulk. Furthermore, the dynamics of water molecules beyond the topmost molecular layer was found to be rather similar to that of bulk water.

The Surface of Colloidal Metal-Organic Framework Nanoparticles Revealed by Vibrational Sum Frequency Scattering Spectroscopy

Solvation shells strongly influence the interfacial chemistry of colloidal systems, from the activity of proteins to the colloidal stability and catalysis of nanoparticles. Despite their fundamental and practical importance, solvation shells have remained largely undetected by spectroscopy. Furthermore, their ability to assemble at complex but realistic interfaces with heterogeneous and rough surfaces remains an open question. Here, we apply vibrational sum frequency scattering spectroscopy (VSFSS), an interface-specific technique, to colloidal nanocrystals with porous metal-organic frameworks (MOFs) as a case study. Due to the porous nature of the solvent-particle boundary, MOF particles challenge conventional models of colloidal and interfacial chemistry. Their multiweek colloidal stability in the absence of conventional surface ligands suggests that stability may arise in part from solvation forces. Spectra of colloidally stable Zn(2-methylimidazolate)2 (ZIF-8) in polar solvents indicate the presence of ordered solvation shells, solvent-metal binding, and spontaneous ordering of organic bridging linkers within the MOF. These findings help explain the unexpected colloidal stability of MOF colloids, while providing a roadmap for applying VSFSS to wide-ranging colloidal nanocrystals in general.

Evaporation-driven interfacial restructuring induces highly efficient methanogenesis of waste biomass

Methanogenesis of waste biomass (WB) is a promising method for global sustainable development, reduction of pollution and carbon emission levels, and recovering bioenergy. Unlike in the methanogenesis of organic wastewater, in which microbial cells come into direct contact with the dissolved substrate, the 'solid-liquid-solid' modes in WB and between WB and microbial cells, which involve numerous solid-liquid interfaces, greatly hinder the methanogenesis efficiency of WB. Amongst all WB, waste activated sludge is the most complex, poorly biodegradable and representative. Herein, we highlight the role of water evaporation-driven solid-liquid interfacial restructuring of sludge in determining its methanogenesis efficiency. Non-free water evaporation increased surface roughness and adhesion, and compressed pore structure with numerous capillaries in sludge, resulting in a new solid-liquid interface of sludge with great capillary force and highly ordered interfacial water molecules, which provides an extremely favourable condition for high mass transfer and proton-coupled electron transfer (PCET) in sludge. This restructuring was confirmed to induce the enhancement of solid-liquid interfacial noncovalent interactions and electron transfer efficiency in the subsequent methanogenesis process (P < 0.05), promoting the effective contact between the sludge substrate and microbial cells, thereby enriching the methanogenic consortia (i.e., Clostridia and Methanosarcina were increased by 290.0 % and 239.7 %, respectively) and improving the activities of key enzymes. Stable isotope tracing and metagenomic analysis further reveal that this restructuring promoted the participation of water molecules in the methane formation by PCET-driven release of protons from water, and enhanced main methanogenesis metabolic pathways, especially the metabolic pathway of CO2-reduction methanogenesis (+65.2 %), thereby resulting in a great advance in methane generation (+147 %, P < 0.001). The findings can provide a reference for regulating directional anaerobic biotransformation of water-rich multiphase complex substrates by interfacial restructuring inducement.

Water-enabling strategies for asymmetric catalysis

Water possesses unique advantages, including abundance, environmental friendliness and mild effects. Undoubtedly, it is an ideal solvent or reagent in chemical syntheses. Water also shows unique abilities in catalytic asymmetric synthesis. It can accelerate reaction rates, improve diastereo- or enantioselectivities, initiate reactions, diversify chemo, diastereo- or enantioselectivities through various effects (hydrophobic, hydrogen bonding, protonation). Several reviews have demonstrated the positive effects of water in asymmetric synthesis. In this review, we summarize water-enabling strategies in the last decade, and focus on advances which reveal how water affects a reaction.

Mechanistic Insights into Surfactant-Modulated Electrode-Electrolyte Interface for Steering H2O2 Electrosynthesis

Electrocatalytic reactions taking place at the electrified electrode-electrolyte interface involve processes of proton-coupled electron transfer. Interfacial protons are delivered to the electrode surface via a H2O-dominated hydrogen-bond network. Less efforts are made to regulate the interfacial proton transfer from the perspective of interfacial hydrogen-bond network. Here, we present quaternary ammonium salt cationic surfactants as electrolyte additives for enhancing the H2O2 selectivity of the oxygen reduction reaction (ORR). Through in situ vibrational spectroscopy and molecular dynamics calculation, it is revealed that the surfactants are irreversibly adsorbed on the electrode surface in response to a given bias potential range, leading to the weakening of the interfacial hydrogen-bond network. This decreases interfacial proton transfer kinetics, particularly at high bias potentials, thus suppressing the 4-electron ORR pathway and achieving a highly selective 2-electron pathway toward H2O2. These results highlight the opportunity for steering H2O-involved electrochemical reactions via modulating the interfacial hydrogen-bond network.

Ag supraparticles with 3D hot spots to actively capture molecules for sensitive detection by surface enhanced Raman spectroscopy

To achieve highly sensitive detection using surface-enhanced Raman spectroscopy (SERS), it is imperative to fabricate a substrate with a high density of hot spots and facilitate the entry of target molecules into these hot spot regions. However, steric hindrance arising from the presence of surfactants and ligands on the SERS substrate may impede the access of target molecules to the hot spots. Here, we fabricate non-close-packed three-dimensional (3D) supraparticles with high-density hot spots to actively capture molecules. The formation of 3D supraparticles is attributed to the minimization of free energy during the gradual contraction of the droplet. The numerous capillaries present in non-close-packed supraparticles induce the movement of target molecules into the hot spot region through capillary force along with the solution. The results demonstrate that the SERS enhancement effect of 3D supraparticles is at least one order of magnitude higher than that of multi-layered nanoparticle structures formed under natural drying conditions. In addition, the SERS performance of 3D supraparticles is evaluated with diverse target molecules, including antimicrobial agents and drugs. Hence, this work provides a new idea for the preparation of non-close-packed substrates for SERS sensitive detection.