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Electrocatalytic oxygen evolution reaction (OER) is a crucial anode reaction where electrocatalysts are the key elements and their dynamic surface chemistry runs throughout the entire process. Herein, we examine the latest advances and challenges in understanding of the dynamic surface chemistry of OER electrocatalysts. There are electrochemical origin and driving force for the dynamic surface nature, where several processes can take place either concurrently or sequentially, including reconstruction (i.e., phase formation/transformation, morphological change, and compositional change), vacancy generation and filling/refilling, and the intermediate adsorption–desorption process on catalytic surface. These dynamic surface processes of OER catalysts are impacted by not only the reaction and service conditions, including the (local) pH and its gradient distribution, applied potential, types and concentration of exotic ions and external fields on top of the nature of catalysts/precatalysts, but also their interactions. Due to the local, time‐dependent and instant nature, there are considerable challenges in tracing, modelling and understanding of the complete dynamic surface chemistry of catalysts in OER, by means of ex situ, in situ and operando experimental investigations. Therefore, computational studies and dynamic simulations help provide key insights in future pursuits, where there is critical need for a multiscale computational modelling approach encompassing all these aspects. Dynamic surface chemistry of catalysts dominates the actual oxygen evolution reaction (OER) process and performance. It involves either the reversible or irreversible dynamics, or both. There are strong effects of electrochemical servicing environments and external fields on OER. Both operando experiments and theoretical insights are particularly important.

Understanding and manipulating gas bubble evolution during electrochemical water splitting is a crucial strategy for optimizing the electrode/electrolyte/gas bubble interface. Here gas bubble dynamics are investigated during the hydrogen evolution reaction on a well-defined platinum microelectrode by varying the electrolyte composition. We find that the microbubble coalescence efficiency follows the Hofmeister series of anions in the electrolyte. This dependency yields very different types of H2 gas bubble evolution in different electrolytes, ranging from periodic detachment of a single H2 gas bubble in sulfuric acid to aperiodic detachment of small H2 gas bubbles in perchloric acid. Our results indicate that the solutal Marangoni convection, induced by the anion concentration gradient developing during the reaction, plays a critical role at practical current density conditions. The resulting Marangoni force on the H2 gas bubble and the bubble departure diameter therefore depend on how surface tension varies with concentration for different electrolytes. This insight provides new avenues for controlling bubble dynamics during electrochemical gas bubble formation.Although gas bubble dynamics during electrochemical processes dramatically affect performance, the fundamental understanding and manipulation of such dynamics have been limited. Now, electrolyte composition is found to be a key factor in inducing a solutal Marangoni instability that impacts both H2 gas detachment and coalescence between H2 microbubbles.

Friction determines whether liquid droplets slide off a solid surface or stick to it. Surface heterogeneity is generally acknowledged as the major cause of increased contact angle hysteresis and contact line friction of droplets. Here we challenge this long-standing premise for chemical heterogeneity at the molecular length scale. By tuning the coverage of self-assembled monolayers (SAMs), water contact angles change gradually from about 10° to 110° yet contact angle hysteresis and contact line friction are low for the low-coverage hydrophilic SAMs as well as high-coverage hydrophobic SAMs. Their slipperiness is not expected based on the substantial chemical heterogeneity of the SAMs featuring uncoated areas of the substrate well beyond the size of a water molecule as probed by metal reactants. According to molecular dynamics simulations, the low friction of both low- and high-coverage SAMs originates from the mobility of interfacial water molecules. These findings reveal a yet unknown and counterintuitive mechanism for slipperiness, opening new avenues for enhancing the mobility of droplets. Surface heterogeneity is generally acknowledged as the major cause of liquid–solid friction, affecting whether droplets slide off the surface or stick to it. Now, a model surface of self-assembled monolayers has been used to investigate how molecular-scale surface heterogeneity affects water contact angle hysteresis and contact line friction. The high-coverage hydrophobic surface is slippery, as—counter-intuitively—is the low-coverage hydrophilic surface.

The controllable packing of functional nanoparticles (NPs) into crystalline lattices is of interest in the development of NP-based materials. Here we demonstrate that the size, morphology and symmetry of such supercrystals can be tailored by adjusting the surface dynamics of their constituent NPs. In the presence of excess tetraethylammonium cations, atomically precise [Au25(SR)18]− NPs (where SR is a thiolate ligand) can be crystallized into micrometre-sized hexagonal rod-like supercrystals, rather than as face-centred-cubic superlattices otherwise. Experimental characterization supported by theoretical modelling shows that the rod-like crystals consist of polymeric chains in which Au25 NPs are held together by a linear SR–[Au(I)–SR]4 interparticle linker. This linker is formed by conjugation of two dynamically detached SR–[Au(I)–SR]2 protecting motifs from adjacent Au25 particles, and is stabilized by a combination of CH⋯π and ion-pairing interactions between tetraethylammonium cations and SR ligands. The symmetry, morphology and size of the resulting supercrystals can be systematically tuned by changing the concentration and type of the tetraalkylammonium cations.Gold nanoparticles typically exhibit hard-sphere-like assembly behaviour, but now the size, morphology and symmetry of crystals of Au25 nanoparticles have been tuned. The presence of excess tetraethylammonium cations has been shown to promote the one-dimensional assembly of the nanoparticles, which in turn form rod-like crystals, by stabilizing dynamically detached ligands from adjacent particles into interparticle linkers through CH⋯π and ion-pairing interactions.

Although the fates of microplastics (0.1–5 mm in size) and nanoplastics (<100 nm) in marine environments are being increasingly well studied1,2, little is known about the behaviour of nanoplastics in terrestrial environments3–6, especially agricultural soils7. Previous studies have evaluated the consequences of nanoplastic accumulation in aquatic plants, but there is no direct evidence for the internalization of nanoplastics in terrestrial plants. Here, we show that both positively and negatively charged nanoplastics can accumulate in Arabidopsis thaliana. The aggregation promoted by the growth medium and root exudates limited the uptake of amino-modified polystyrene nanoplastics with positive surface charges. Thus, positively charged nanoplastics accumulated at relatively low levels in the root tips, but these nanoplastics induced a higher accumulation of reactive oxygen species and inhibited plant growth and seedling development more strongly than negatively charged sulfonic-acid-modified nanoplastics. By contrast, the negatively charged nanoplastics were observed frequently in the apoplast and xylem. Our findings provide direct evidence that nanoplastics can accumulate in plants, depending on their surface charge. Plant accumulation of nanoplastics can have both direct ecological effects and implications for agricultural sustainability and food safety.The accumulation of nanoplastics in terrestrial plants is directly linked to the nanoparticles’ charge and can have ecological effects and implications for agricultural sustainability and food safety.

The solvation of ions changes the physical, chemical and thermodynamic properties of water, and the microscopic origin of this behaviour is believed to be ion-induced perturbation of water’s hydrogen-bonding network. Here we provide microscopic insights into this process by monitoring the dissipation of energy in salt solutions using time-resolved terahertz–Raman spectroscopy. We resonantly drive the low-frequency rotational dynamics of water molecules using intense terahertz pulses and probe the Raman response of their intermolecular translational motions. We find that the intermolecular rotational-to-translational energy transfer is enhanced by highly charged cations and is drastically reduced by highly charged anions, scaling with the ion surface charge density and ion concentration. Our molecular dynamics simulations reveal that the water–water hydrogen-bond strength between the first and second solvation shells of cations increases, while it decreases around anions. The opposite effects of cations and anions on the intermolecular interactions of water resemble the effects of ions on the stabilization and denaturation of proteins. Ions in salt solutions perturb the hydrogen bonding between the surrounding water molecules, altering the properties of water, but how ion polarity affects this is not fully understood. By monitoring the dissipation of terahertz energy in salt solutions, it has now been shown that intermolecular rotational-to-translational energy transfer is enhanced by highly charged cations and reduced by highly charged anions.

Ring-opening polymerization (ROP) is a powerful synthetic methodology for the chemical synthesis of technologically important biodegradable aliphatic polyesters from cyclic esters or lactones. However, the bioderived five-membered γ-butyrolactone (γ-BL) is commonly referred as ‘non-polymerizable’ because of its low strain energy. The chemical synthesis of poly(γ-butyrolactone) (PγBL) through the ROP process has been realized only under ultrahigh pressure (20,000 atm, 160 °C) and only produces oligomers. Here we report that the ROP of γ-BL can, with a suitable catalyst, proceed smoothly to high conversions (90%) under ambient pressure to produce PγBL materials with a number-average molecular weight up to 30 kg mol –1 and with controlled linear and/or cyclic topologies. Remarkably, both linear and cyclic PγBLs can be recycled back into the monomer in quantitative yield by simply heating the bulk materials at 220 °C (linear polymer) or 300 °C (cyclic polymer) for one hour, which thereby demonstrates the complete recyclability of PγBL. Bio-derived γ-butyrolactone (γ-BL) is commonly referred to as ‘non-polymerizable’ due to its low strain energy. Now it has been shown that ring-opening polymerization of γ-BL can in fact proceed to high conversions under ambient pressure with a suitable catalyst, producing high-molecular-weight polymers with controlled topologies and complete recyclability.

Orthopaedic and dental implants have become a staple of the medical industry and with an ageing population and growing culture for active lifestyles, this trend is forecast to continue. In accordance with the increased demand for implants, failure rates, particularly those caused by bacterial infection, need to be reduced. The past two decades have led to developments in antibiotics and antibacterial coatings to reduce revision surgery and death rates caused by infection. The limited effectiveness of these approaches has spurred research into nano-textured surfaces, designed to mimic the bactericidal properties of some animal, plant and insect species, and their topographical features. This review discusses the surface structures of cicada, dragonfly and butterfly wings, shark skin, gecko feet, taro and lotus leaves, emphasising the relationship between nano-structures and high surface contact angles on self-cleaning and bactericidal properties. Comparison of these surfaces shows large variations in structure dimension and configuration, indicating that there is no one particular surface structure that exhibits bactericidal behaviour against all types of microorganisms. Recent bio-mimicking fabrication methods are explored, finding hydrothermal synthesis to be the most commonly used technique, due to its environmentally friendly nature and relative simplicity compared to other methods. In addition, current proposed bactericidal mechanisms between bacteria cells and nano-textured surfaces are presented and discussed. These models could be improved by including additional parameters such as biological cell membrane properties, adhesion forces, bacteria dynamics and nano-structure mechanical properties. This paper lastly reviews the mechanical stability and cytotoxicity of micro and nano-structures and materials. While the future of nano-biomaterials is promising, long-term effects of micro and nano-structures in the body must be established before nano-textures can be used on orthopaedic implant surfaces as way of inhibiting bacterial adhesion.

Replacing synthetic surfactants by natural alternatives when formulating nanoemulsions has gained attention as a sustainable approach. In this context, nanoemulsions based on sweet almond oil and stabilized by saponin from Quillaja bark with glycerol as cosurfactant were prepared by the high-pressure homogenization method. The effects of oil/water (O/W) ratio, total surfactant amount, and saponin/glycerol ratio on their stability were analyzed. The formation and stabilization of the oil-in-water nanoemulsions were analyzed through the evaluation of stability over time, pH, zeta potential, and particle size distribution analysis. Moreover, a design of experiments was performed to assess the most suitable composition based on particle size and stability parameters. The prepared nanoemulsions are, in general, highly stable over time, showing zeta potential values lower than −40 mV, a slight acid behavior due to the character of the components, and particle size (in volume) in the range of 1.1 to 4.3 µm. Response surface methodology revealed that formulations using an O/W ratio of 10/90 and 1.5 wt% surfactant resulted in lower particle sizes and zeta potential, presenting higher stability. The use of glycerol did not positively affect the formulations, which reinforces the suitability of preparing highly stable nanoemulsions based on natural surfactants such as saponins.

Gels formed via metal–ligand coordination typically have very low branch functionality, f , as they consist of ∼2–3 polymer chains linked to single metal ions that serve as junctions. Thus, these materials are very soft and unable to withstand network defects such as dangling ends and loops. We report here a new class of gels assembled from polymeric ligands and metal–organic cages (MOCs) as junctions. The resulting ‘polyMOC’ gels are precisely tunable and may feature increased branch functionality. We show two examples of such polyMOCs: a gel with a low f based on a M 2 L 4 paddlewheel cluster junction and a compositionally isomeric one of higher f based on a M 12 L 24 cage. The latter features large shear moduli, but also a very large number of elastically inactive loop defects that we subsequently exchanged for functional ligands, with no impact on the gel's shear modulus. Such a ligand substitution is not possible in gels of low f , including the M 2 L 4 -based polyMOC. Gels formed by metal–ligand coordination typically consist of single metal ions linked together by polymer chains. Now, metal–organic cages have been used as junctions instead. A gel was prepared that features a large number of polymer chains at each junction, including loops that further serve to functionalize the material.