Contaminant Removal from Nature's Self-Cleaning Surfaces

Waterborne Recoatable Transparent Superhydrophobic Coatings with Excellent Self-Cleaning and Anti-Dust Performance

Superhydrophobic surfaces have attracted tremendous attention due to their intriguing lotus-leaf-like water-repelling phenomenon and wide applications, however, most superhydrophobic coatings are prepared with environmentally unfriendly organic solvents and suffer from poor mechanical strength. To solve these issues, waterborne recoatable superhydrophobic (WRSH) coatings are developed based on a novel self-synthesized water-soluble fluorinated acrylic polymer and hydrophobic modified silica nanoparticles. The trade-off between waterborne and superhydrophobicity is well mediated by protonation and deprotonation of the fluorinated acrylic polymer. When the coating is damaged, it can be easily repaired and recoated using WRSH coatings without the need to remove the damaged superhydrophobic layer, providing a sustainable and environmentally friendly solution for maintaining a superhydrophobic surface. The coating exhibits good mechanical properties with the WRSH coating maintaining mechanical stability even after abrasion with 2000 mesh sandpaper for 20 m or impact from 100 g of sand. Additionally, the visible light transmittance of WRSH coating glass reaches as high as ≈94.0%, which is superior to the bare glass of ≈91.7%. Moreover, the WRSH coatings exhibit excellent self-cleaning performance and anti-dust performance when applied on solar panels.

Wood Surface-Embedding of Functional Monodisperse SiO2 Microspheres for Achieving Robust, Durable, Nature-Inspired, Programmable Superrepellent Interfaces

Nature-inspired, robust, durable, liquid-repellent interfaces have attracted considerable interest in the field of wood biomimetic intelligence science and technology application. However, realizing green environmental protection and low maintenance and replacement cost wood surfaces constructed with micro/nanoarchitectures is not an easy task. Aiming at the problem of poor waterproof performance of wood, a silicon dioxide/polydimethylsiloxane (SiO2/PDMS) self-cleaning programmable superhydrophobic coating was biomimetically constructed on the wood substrate by surface-embedded dual-dipping design based on the "substrates + nanoparticles" hybrid principle of the lotus leaf effect. This robust, durable, nature-inspired, self-cleaning, programmable superhydrophobic coating was found to have no observable impact on the original color and texture of the natural wood. The SiO2/PDMS/wood prepared exhibited exceptional liquid repellency and a high static water contact angle (WCA) of 158.5° and a low slide angle (SA) of 10°, including everyday general-purpose droplets, indicating that the introduction of the monodisperse SiO2 microspheres can effectively enhance the superhydrophobic properties of the hydrophilic wood. We applied this strategy to a variety of substrates, including wood-cellulose aerogel and wood-cellulose paper, and demonstrated that the liquid-repellent nature of the self-cleaning superhydrophobic coating remained unchanged. Moreover, the superhydrophobic surface of SiO2/PDMS/wood was preserved even after harsh abrasion conditions, including mechanical damage (sandpaper, sharp steel blade, and tapes), thermal damage (UV irradiation and low/high-temperature exposure such as steaming and freezing), chemical damage, and solvent corrosion (immersion in acid, alkali), demonstrating robust stability of the superhydrophobic coating. Furthermore, the SiO2/PDMS programmable superhydrophobic coating exhibits exceptional exciting self-cleaning and stain-resistant properties, making it offer greater possibilities in terms of scientific challenges and real-world problem-solving at biomimetic smart superhydrophobic interfaces in wood.

Coalescence Mechanism Induced by Different Wetting States of Ti and Al Droplets on Rough Surfaces

There is currently increasing interest in droplet transportation and coalescence on rough surfaces. However, the relationship among wettability, coalescence mode, and substrate characteristics (roughness and nanopillar height) remains unclear. In this work, two coalescence modes, climbing coalescence and contacting coalescence, are first observed in the dynamic behaviors of Ti and Al droplets on rough substrates. Due to the nonsynchronized wetting state transition of the droplets, the coalescence mode with increasing substrate characteristics differs, transitioning from contacting coalescence to climbing coalescence and then returning to the contacting mode. In general, the mode of coalescence correlates closely with the respective wetting states. Typically, Ti and Al droplets coalesce in the contacting mode when they have the same wetting state, but if they have different wetting states, they coalesce in the climbing mode. Our results emphasize the complicated relationship between the surface structure and the wettability of droplets, which could provide insights into self-assembly, three-dimensional printing, and microfluidic devices.

Bioinspired Hierarchical T Structures for Tunable Wettability and Droplet Manipulation by Facile and Scalable Nanoimprinting

Developing surfaces that effectively repel low-surface-tension liquids with tunable adhesive properties remains a pivotal challenge. Micronano hierarchical re-entrant structures emerge as a promising solution, offering a robust structural defense against liquid penetration, minimizing area fraction, and creating narrow gaps that generate substantial upward Laplace pressure. However, the absence of an efficient, scalable, and tunable construction method has impeded their widespread applications. Here, drawing inspiration from springtail epidermal structures, octopus suckers, and rose petals, we present a scalable manufacturing strategy for artificial micronano hierarchical T-shaped structures. This strategy employs double-transfer UV-curing nanoimprint lithography to form nanostructures on microstructured surfaces, offering high structural tunability. This approach enables precise control over topography, feature size, and arrangement of nano- and microscale sections, resulting in superamphiphobic surfaces that exhibit high contact angles (>150°) and tunable adhesive forces for low-surface-energy liquids. These surfaces can be applied to droplet-based microreactors, programmable droplet-transfer systems, and self-cleaning surfaces suitable for various liquids, particularly those with low surface tension. Remarkably, we have also succeeded in fabricating the hierarchical structures on flexible and transparent substrates. We demonstrate the advantages of this strategy in the fabrication of hierarchical micronanostructures, opening up a wide range of potential applications.

Bioinspired Slippery Surfaces for Liquid Manipulation from Tiny Droplet to Bulk Fluid

Slippery surfaces, which originate in nature with special wettability, have attracted considerable attention in both fundamental research and practical applications in a variety of fields due to their unique characteristics of superlow liquid friction and adhesion. Although research on bioinspired slippery surfaces is still in its infancy, it is a rapidly growing and enormously promising field. Herein, a systematic review of recent progress in bioinspired slippery surfaces, beginning with a brief introduction of several typical creatures with slippery property in nature, is presented. Subsequently,this review gives a detailed discussion on the basic concepts of the wetting, friction, and drag from micro- and macro-aspects and focuses on the underlying slippery mechanism. Next, the state-of-the-art developments in three categories of slippery surfaces of air-trapped, liquid-infused, and liquid-like slippery surfaces, including materials, design principles, and preparation methods, are summarized and the emerging applications are highlighted. Finally, the current challenges and future prospects of various slippery surfaces are addressed.

Self-assembled B-doped flower-like graphitic carbon nitride with high specific surface area for enhanced photocatalytic performance

Graphitic carbon nitride (g-C3N4) is a promising nonmetallic photocatalyst. In this manuscript, B-doped 3D flower-like g-C3N4 mesoporous nanospheres (BMNS) were successfully prepared by self-assembly method. The doping of B element promotes the internal growth of hollow flower-like g-C3N4 without changing the surface roughness structure, resulting in a porous floc structure, which enhances the light absorption and light reflection ability, thereby improving the light utilization rate. In addition, B element provides lower band gap, which stimulates the carrier movement and increases the activity of photogenerated carriers. The photocatalytic mechanism and process of BMNS were investigated in depth by structural characterization and performance testing. BMNS-10 % shows good degradation for four different pollutants, among which the degradation effect on Rhodamine B (RhB) reaches 97 % in 30 min. The apparent rate constant of RhB degradation by BMNS-10 % is 0.125 min-1, which is 46 times faster compared to bulk g-C3N4 (BCN). And the photocatalyst also exhibits excellent H2O2 production rate under visible light. Under λ > 420 nm, the H2O2 yield of BMNS-10 % (779.9 μM) in 1 h is 15.9 times higher than that of BCN (48.98 μM). Finally, the photocatalytic mechanism is proposed from the results of free radical trapping experiments.

Exploring the Heat of Water Intrusion into a Metal-Organic Framework by Experiment and Simulation

Wetting of a solid by a liquid is relevant for a broad range of natural and technological processes. This process is complex and involves the generation of heat, which is still poorly understood especially in nanoconfined systems. In this article, scanning transitiometry was used to measure and evaluate the pressure-driven heat of intrusion of water into solid ZIF-8 powder within the temperature range of 278.15-343.15 K. The conditions examined included the presence and absence of atmospheric gases, basic pH conditions, solid sample origins, and temperature. Simultaneously with these experiments, molecular dynamics simulations were conducted to elucidate the changing behavior of water as it enters into ZIF-8. The results are rationalized within a temperature-dependent thermodynamic cycle. This cycle describes the temperature-dependent process of ZIF-8 filling, heating, emptying, and cooling with respect to the change of internal energy of the cycle from the calculated change in the specific heat capacity of the system. At 298 K the experimental heat of intrusion per gram of ZIF-8 was found to be -10.8 ± 0.8 J·g-1. It increased by 19.2 J·g-1 with rising temperature to 343 K which is in a reasonable match with molecular dynamic simulations that predicted 16.1 J·g-1 rise. From these combined experiments, the role of confined water in heat of intrusion of ZIF-8 is further clarified.