Bioinspired asymmetric amphiphilic surface for triboelectric enhanced efficient water harvesting

Water-Triboelectrification-Complemented Moisture Electric Generator

Energy harvesting from ubiquitous natural water vapor based on moisture electric generator (MEG) technology holds great potential to power portable electronics, the Internet of Things, and wireless transmission. However, most devices still encounter challenges of low output, and a single MEG complemented with another form of energy harvesting for achieving high power has seldom been demonstrated. Herein, we report a flexible and efficient hybrid generator capable of harvesting moisture and tribo energies simultaneously, both from the source of water droplets. The moisture electric and triboelectric layers are based on a water-absorbent citric acid (CA)-mediated polyglutamic acid (PGA) hydrogel and porous electret expanded polytetrafluoroethylene (E-PTFE), respectively. Such a waterproof E-PTFE film not only enables efficient triboelectrification with water droplets' contact but also facilitates water vapor to be transferred into the hydrogel layer for moisture electricity generation. A single hybrid generator under water droplets' impact delivers a DC voltage of 0.55 V and a peak current density of 120 μA cm-2 from the MEG, together with a simultaneous AC output voltage of 300 V and a current of 400 μA from the complementary water-based triboelectric generator (TEG) side. Such a hybrid generator can work even under harsh wild environments with 5 °C cold and saltwater impacts. Significantly, an optical alarm and wireless communication system for wild, complex, and emergency scenarios is demonstrated with power from the hybrid generators. This work expands the applications of water-based electricity generation technologies and provides insight into harvesting multiple potential energies in the natural environment with high output.

Exploring Wettability: A Key to Optimizing Liquid-Solid Triboelectric Nanogenerators

Nowadays, the liquid-solid triboelectric nanogenerator (L-S TENG) has gained much attention among researchers because of its ability to be a part of self-powering technology by harvesting ultra-low-frequency vibration in the environment. The L-S TENG works with the principle of contact electrification (CE) and electrostatic induction, in which CE takes place between the solid and liquid. The exact mechanism behind the CE at the L-S interface is still a debatable topic because many physical parameters of both solid and liquid triboelectric layers contribute to this process. In the L-S TENG device, water or solvents are commonly used as liquid triboelectric layers, for which their wettability over the solid triboelectric layer plays a significant role. Hence, this review is extensively focused on the influence of the wettability of solid surfaces on the CE and the corresponding impact on the output performance of L-S TENGs. The present review starts with introducing the L-S TENG, a mechanism that contributes to CE at the L-S interface, the significance of hydrophobic materials/surfaces in TENG devices, and their fabrication methods. Further, the impact of the contact angle over the electron/ion transfer over various surfaces has been extensively analyzed. Finally, the challenges and future prospects of the fabrication and utilization of superhydrophobic surfaces in the context of L-S TENGs have been included. This review serves as a foundation for future research aimed at optimizing the L-S TENG performance and inspiring new approaches in material design and multifunctional energy-harvesting systems.

Electrically switched asymmetric interfaces for liquid manipulation

External field driven fluid manipulation, in particular electric field, offers the advantages of real-time control and exceptional flexibility, rendering it highly promising for applications in microfluidic devices, liquid separation and energy catalysis. However, it is still challenging for controlled liquid transport and fine control of droplet splitting. Herein, we demonstrate a strategy to achieve direction-controlled liquid transport and fine droplet splitting on an anisotropic groove-microstructured electrode surface via an electrically switched asymmetric interface. The balance of asymmetric capillary force generated by microstructures and electro-capillary force is critical in determining directional liquid transport and fine droplet splitting. Asymmetric bubbles generated by liquid electrolysis form an asymmetric liquid-gas-solid interface and result in gradient liquid wetting behavior on the two neighboring electrode surfaces. The electric field further enhances the asymmetric wetting of a liquid droplet on the electrode surface, exhibiting electric field direction-dependent motion. Moreover, the groove-microstructured electrode surface can strengthen the liquid droplet anisotropic wetting and correspondingly refine the volume range of the splitting sub-droplet. Even unidirectional/bidirectional liquid droplet transport can be controlled in collaboration with the asymmetric groove-microstructure and electric field. Thus, this work provides a new route for liquid transport and droplet splitting, showing great potential in controllable separation, microreaction and microfluidic devices.

Sustainable Water Management with Photocatalytic Janus Mesh: Efficient Fog Harvesting, Water Purification, and Microbial Disinfection

Water scarcity is a critical global challenge, especially in arid and semiarid regions. Fog harvesting has emerged as a promising solution; however, concerns about air pollution and bacterial growth in humid environments have raised doubts about the safety and sustainability of such systems. This study introduces a Janus mesh with asymmetric wettability on its two faces, fabricated through a simple and scalable method. The unique design of the Janus mesh enables the transport of water droplets from the superhydrophobic side to the hydrophilic side in a unidirectional manner, enhancing its fog harvesting efficiency. The mesh's photocatalytic properties not only elevate the fog harvesting rate to 4.7 kg·m-2h-1 but also effectively purify the harvested water by removing organic contaminants (94%) and microbial impurities (99.98%). Additionally, its inherent bactericidal activity prevents biofouling, ensuring sustained efficiency in water collection. The mesh's self-cleaning abilities through photocatalysis maintain its surface integrity, promising long-term stability for fog harvesting applications. This technological advancement in fog harvesting offers a sustainable and economical solution to water scarcity concerns, addressing safety and sustainability issues associated with existing systems. By potentially transforming the livelihoods of communities struggling with water scarcity, this innovation paves the way for a more sustainable future.

Multi-Bioinspired Fog Harvesting Structure with Asymmetric Surface for Hydrogen Revolution

The urgent need for sustainable energy storage drives the fast development of diverse hydrogen production based on clean water resources. Herein, a unique type of multi-bioinspired functional device (MFD) is reported with asymmetric wettability that combines the curvature gradient of cactus spines, the wetting gradient of lotus, and the slippery surface of Nepenthes alata for efficient fog harvesting. The precisely printed MFDs with microscale features, spanning dimensions, and a thin wall are endowed with asymmetric wettability to enable the Janus effects on their surfaces. Fog condenses on the superhydrophobic surface of the MFDs in the form of microdroplets and unidirectionally penetrates its interior due to the Janus effects, and drops onto the designated area with a better fog harvesting rate of 10.64 g cm-2 h-1. Most significantly, the collected clean water can be used for hydrogen production with excellent stability and durability. The findings demonstrate that safe, large-scale, high-performance water splitting and gas separation and collection with fog collection based on MFDs are possible.

Universal droplet propulsion by dynamic surface-charge wetting

Controllable droplet propulsion on solid surfaces plays a crucial role in various technologies. Many actuating methods have been developed; however, there are still some limitations in terms of the introduction of additives, the versatilities of solid surfaces, and the speed of transportation. Herein, we have demonstrated a universal droplet propulsion method based on dynamic surface-charge wetting by depositing oscillating and opposite surface charges on dielectric films with unmodified surfaces. Dynamic surface-charge wetting propels droplets by continuously inducing smaller front contact angles than rear contact angles. This innovative imbalance is built by alternately storing and spreading opposite charges on dielectric films, which results in remarkable electrostatic forces under large gradients and electric fields. The method exhibits excellent droplet manipulation performance characteristics, including high speed (~130 mm/s), high adaptability of droplet volume (1 μL-1 mL), strong handling ability on non-slippery surfaces with large contact angle hysteresis (CAH) (maximum angle of 35°), significant programmability and reconfigurability, and low mass loss. The great application potential of this method has been effectively demonstrated in programmable microreactions, defogging without gravity assistance, and surface cleaning of photovoltaic panels using condensed droplets.

Porous Spindle-Knot Fiber by Fiber-Microfluidic Phase Separation for Water Collection and Nanopatterning

Porous spindle-knot structures have been found in many creatures, such as spider silk and the root of the soybean plant, which show interesting functions such as droplet collection or biotransformation. However, continuous fabrication of precisely controlled porous spindle-knots presents a big challenge, particularly in striking a balance among good structural controllability, low-cost, and functions. Here, we propose a concept of a fiber-microfluidics phase separation (FMF-PS) strategy to address the above challenge. This FMF-PS combines the advantages of a microchannel regulated Rayleigh instability of polymer solution coated onto a fiber with the nonsolvent-induced phase separation of the polymer solution, which enables continuous and cost-effective production of porous spindle-knot fiber (PSKF) with well-controlled size and porous structures. The critical factors controlling the geometry and the porous structures of the spindle-knot by FMF-PS have been systematically investigated. For applications, the PSKF exhibited faster water droplet nucleation, growth, and maximum water collection capability, compared to the control samples, as revealed by in situ water collection growth curves. Furthermore, high-level fabrics of the PSKFs, including a two-dimensional network and three-dimensional architecture, have been demonstrated for both large-scale water collection and art performance. Finally, the PSKF is demonstrated as a programmable building block for surface nanopatterning.

Deriving Superhydrophobicity Directly and Solely from Molecules: A Facile and Emerging Approach

Nature-inspired superhydrophobic surfaces have gained significant attention due to their various potential applications. Artificial superhydrophobic surfaces were fabricated through co-optimization of topography and low-surface-energy chemistry. In the conventional approach, artificial superhydrophobic surfaces are developed through associating mostly polymer, metal, alloys, nanoparticles, microparticles, etc. and commonly encounter several challenges related to scalability, durability, and complex fabrication processes. In response to these challenges, molecule-based approaches have emerged as a promising alternative, providing several advantages such as prolonged shelf life of depositing solution, higher solvent compatibility, and a simple fabrication process. In this Perspective, we have provided a concise overview of traditional and molecule-based approaches to fabricating superhydrophobic surfaces, highlighting recent advancements and challenges. We have discussed various molecule-based strategies for tailoring water wettability, customizing mechanical properties, developing substrate-independent coatings, prolonging the shelf life of deposition solutions, and so on. Here, we have illustrated the potential of molecule-based approaches in overcoming existing limitations and its importance to diverse and prospective practical applications.

Triboelectrically Empowered Biomimetic Heterogeneous Wettability Surface for Efficient Fog Collection

Biomimetic engineering surfaces featuring heterogeneous wettability are vital for atmospheric water harvesting applications. Existing research predominantly focuses on the coordinated regulation of surface wettability through structural and chemical modifications, often overlooking the prevalent triboelectric charge effect at the liquid-solid interface. In this work, we designed a heterogeneous wettability surface by strategic masking and activated its latent triboelectric charge using triboelectric brushes, thereby enhancing the removal and renewal of surface droplets. By examining the dynamic evolution of droplets, the mechanism of triboelectric enhancement in the water collection efficiency is elucidated. Leveraging this inherent triboelectric charge interaction, fog collection capacity can be augmented by 29% by activating the system for 5 s every 60 s. Consequently, the advancement of triboelectric charge-enhanced fog collection technology holds both theoretical and practical significance for overcoming the limitations of traditional surface wettability regulation.

Synchronous Switching Strategy to Enhance the Real-Time Powering and Charging Performance of Triboelectric Nanogenerator

Triboelectric nanogenerators (TENGs) are of great significance as sustainable power sources that harvest energy from the human body and environment. Nevertheless, due to TENG's impedance-dependent output voltage characteristics, in traditional strategy (TS), real-timely powering a sensor with TENG has a poor sensing on/off ratio (or response), and directly charging a capacitor with TENG shows a low charging efficiency. This degraded real-time powering and charging performance of TENG compared to a commercial constant voltage source is a huge challenge of the TENG field for a long time. This work proposes a synchronous switching strategy (SSS) for TENG to real-timely power sensors or charge capacitors without degrading its performance. Compared with TS, this new strategy enables sensors to have 5-7 times sensing on/off ratio enhancement when using TENG as a power source, reaching the powering ability of a commercial constant voltage source, it makes the powering performance of TENG stable under different driving frequency, improving the powering robustness of TENG. In addition, compared with TS, SSS can also enhance the charging efficiency of TENG in every charging cycle by up to 2.4 times when charging capacitors. This work contributes to real-timely powering or charging the distributed, mobile and wireless electronics using TENG.

Multibioinspired Hybrid Superwetting Surface for Efficient Fog Collection and Power Generation

Obtaining water and renewable energy from the atmosphere provides a potential solution to the growing energy shortage. Leveraging the synergistic inspiration from desert beetles, cactus spines, and rice leaves, here, a multibioinspired hybrid wetting rod (HWR) is prepared through simple solution immersion and laser etching, which endows an efficient water collection from the atmosphere. Importantly, benefiting from the bionic asymmetric pattern design and the three-dimensional structure, the HWR possesses an omnidirectional fog collection with a rate of up to 23 g cm-2 h-1. We further show that the HWR could be combined with a droplet-based electricity generator to convert kinetic energy from falling droplets into electrical energy with a maximum output voltage of 200 V and a current of 2.47 μA to light up 28 LEDs. Collectively, this research provides a strategy for synchronous fog collection and power generation, which is promising for environmentally friendly energy production.

Charge Transfer Mechanisms of Adaptive Multicomponent Solutions at Solid-Liquid Interfaces for Real-Time Coolant State Monitoring

Charge-transfer mechanisms in adaptive multicomponent solutions at liquid-solid interfaces with triboelectric probes are crucial for understanding chemistry dynamics. However, liquid-solid charge transfer becomes unpredictable, due to the components or interactions in solutions, restricting its potential application for precise monitoring of liquid environments. This study utilizes triboelectric probes to investigate the charge transfer of chemicals, applying this approach to real-time coolant state monitoring. Analysis of electrical signal dynamics induced by ethylene glycol and its oxidation byproduct, oxalic acid, in ethylene glycol solutions reveals that hydrogen bond and ion adsorption diminishes the efficiency of electron transfer at the liquid-solid interface. These findings promote the engineering of the triboelectric probe that enhances coolant quality with remarkable sensitivity (detection limit: 0.0001%) and a broad freezing point operational range (0 to -49 °C). This work advances the precise control of the charge dynamics and demonstrates the potential of triboelectric probes for interdisciplinary applications.

High-Entropy Ceramics Enhanced Droplet Electricity Generator for Energy Harvesting and Bacterial Detection

The droplet electricity generator (DEG) is a solid-liquid triboelectric nanogenerator with transistor-inspired bulk effect, which is regarded as an effective strategy for raindrop energy harvesting. However, further enhancement of DEG output voltage is necessary to enable its widespread applications. Here, high-entropy ceramics are integrated into the design of DEG intermediate layer for the first time, achieving a high output voltage of 525 V. High-entropy ceramics have colossal dielectric constant, which can help to reduce the triboelectric charge decay for DEG. Furthermore, the effect of factors on DEG output performance when employing high-entropy ceramics as the intermediate layer is extensively analyzed, and the underlying mechanisms and mathematical models are explored. Finally, the enhanced output voltage of DEG not only facilitates faster energy harvesting but also develops a novel method for rapid bacterial detection. This work successfully integrates high-entropy ceramics into DEG design, significantly enhances the output voltage, and offers a novel direction for DEG development.

Smart Lanceolate Surface with Fast Fog-Digesting Performance for Triboelectric Energy Harvesting

Utilizing the ubiquitous fog in nature to create decentralized energy-harvesting devices, free from geographical and hydrological constraints, presents an opportunity to foster sustainable power generation. Extracting electrical energy from fog relies heavily on fog-digesting performance. Improving the efficiency of fogwater utilization remains a formidable challenge for existing fogwater energy-harvesting technologies. Inspired by the water-harvesting behavior of Tillandsia leaves, a smart lanceolate surface is developed to harvest triboelectric energy by rapidly digesting fog. Such a surface exhibits capabilities in fog management, encompassing precise fog capture, transportation, and critical droplet separation. Specifically, fog droplets condense at hydrophilic sites of acylated cellulose ester, subsequently migrating toward the rear under Laplace pressure, thereby producing energy as they traverse through the tail end. Such architecture yields a brief voltage restoration period (with an average of 9.36 s), can rush the capacitor to 11.59 V within 20 s, and achieves a water-digestion rate of up to 71.05 kg/m2 h. This biomimetic approach enhances the water-digestion efficacy of the atmospheric water energy apparatus and offers perspectives on mitigating deficiencies in power resources.

Symbiotic defect-reinforced bimetallic MOF-derived fiber components for solar-assisted atmospheric water collection

Conversion of atmospheric water to sustainable and clean freshwater resources through MOF-based adsorbent has great potential for the renewable environmental industry. However, its daily water production is hampered by susceptibility to agglomeration, slow water evaporation efficiency, and limited water-harvesting capacity. Herein, a solar-assisted bimetallic MOF (BMOF)-derived fiber component that surmounts these limitations and exhibits both optimized water-collect capacity and short adsorption-desorption period is proposed. The proposed strategy involves utilizing bottom-up interface-induced assembly between carboxylated multi-walled carbon nanotube and hygroscopic BMOF on a multi-ply glass fiber support. The designed BMOF (MIL-100(Fe,Al)-3) skeleton constructed using bimetallic-node defect engineering exhibits a high specific surface area (1,535.28 m2/g) and pore volume (0.76 cm3/g), thereby surpassing the parent MOFs and other reported MOFs in capturing moisture. Benefiting from the hierarchical structure of fiber rods and the solar-driven self-heating interface of photothermal layer, the customized BMOF crystals realize efficient loading and optimized water adsorption-desorption kinetics. As a result, the resultant fiber components achieve six adsorption-desorption cycles per day and an impressive water collection of 1.45 g/g/day under medium-high humidity outdoor conditions. Therefore, this work will provide new ideas for optimizing the daily yield of atmospheric water harvesting techniques.

'Rewritable' and 'liquid-specific' recognizable wettability pattern

Bio-inspired surfaces with wettability patterns display a unique ability for liquid manipulations. Sacrificing anti-wetting property for confining liquids irrespective of their surface tension (γLV), remains a widely accepted basis for developing wettability patterns. In contrast, we introduce a 'liquid-specific' wettability pattern through selectively sacrificing the slippery property against only low γLV (<30 mN m-1) liquids. This design includes a chemically reactive crystalline network of phase-transitioning polymer, which displays an effortless sliding of both low and high γLV liquids. Upon its strategic chemical modification, droplets of low γLV liquids fail to slide, rather spill arbitrarily on the tilted interface. In contrast, droplets of high γLV liquids continue to slide on the same modified interface. Interestingly, the phase-transition driven rearrangement of crystalline network allows to revert the slippery property against low γLV liquids. Here, we report a 'rewritable' and 'liquid-specific' wettability pattern for high throughput screening, separating, and remoulding non-aqueous liquids.

Directional Moisture-Wicking Triboelectric Materials Enabled by Laplace Pressure Differences

Wearable sensors are experiencing vibrant growth in the fields of health monitoring systems and human motion detection, with comfort becoming a significant research direction for wearable sensing devices. However, the weak moisture-wicking capability of sensor materials leads to liquid retention, severely restricting the comfort of the wearable sensors. This study employs a pattern-guided alignment strategy to construct microhill arrays, endowing triboelectric materials with directional moisture-wicking capability. Within 2.25 s, triboelectric materials can quickly and directionally remove the droplets, driven by the Laplace pressure differences and the wettability gradient. The directional moisture-wicking triboelectric materials exhibit excellent pressure sensing performance, enabling rapid response/recovery (29.1/37.0 ms), thereby achieving real-time online monitoring of human respiration and movement states. This work addresses the long-standing challenge of insufficient moisture-wicking driving force in flexible electronic sensing materials, holding significant implications for enhancing the comfort and application potential of electronic skin and wearable electronic devices.

An Amphiphilic Surface with Improved Thermal Radiation for Water Harvesting

Water scarcity poses a significant challenge for people living in arid areas. Despite the effectiveness of many bioinspired surfaces in promoting vapor condensation, their water-harvesting efficiency is insufficient. This is often exacerbated by overheating, which decreases the performance in terms of the micro-droplet concentration and movement on surfaces. In this study, we used a spotted amphiphilic surface to enhance the surfaces' water-harvesting efficiency while maintaining their heat emissivity. Through hydrophilic particle screening and hydrophobic groove modifying, the coalescence and sliding characteristics of droplets on the amphiphilic surfaces were improved. The incorporation of boron nitride (BN) nanoparticles further enhanced the surfaces' ability to harvest energy from condensation. To evaluate the water-harvesting performance of these amphiphilic surfaces, we utilized a real-time recording water-harvesting platform to identify microscopic weight changes on the surfaces. Our findings indicated that the inclusion of glass particles in hydrophobic grooves, combined with 1.0 wt.% BN nanoparticles, enhanced the water-harvesting efficiency of the amphiphilic surfaces by more than 20%.

Orbital Electrowetting-on-Dielectric for Droplet Manipulation on Superhydrophobic Surfaces

Electrowetting-on-dielectric (EWOD), recognized as the most successful electrical droplet actuation method, is essential in diverse applications, ranging from thermal management to microfluidics and water harvesting. Despite significant advances, it remains challenging to achieve repeatability, high speed, and simple circuitry in EWOD-based droplet manipulation on superhydrophobic surfaces. Moreover, its efficient operation typically requires electrode arrays and sophisticated circuit control. Here, a newly observed droplet manipulation phenomenon on superhydrophobic surfaces with orbital EWOD (OEW) is reported. Due to the asymmetric electrowetting force generated on the orbit, flexible and versatile droplet manipulation is facilitated with OEW. It is demonstrated that OEW droplet manipulation on superhydrophobic surfaces exhibits higher speed (up to 5 times faster), enhanced functionality (antigravity), and manipulation of diverse liquids (acid, base, salt, organic, e.g., methyl blue, artificial blood) without contamination, and good durability after 1000 tests. It is envisioned that this robust droplet manipulation strategy using OEW will provide a valuable platform for various processes involving droplets, spanning from microfluidic devices to controllable chemical reactions. The previously unreported droplet manipulation phenomenon and control strategy shown here can potentially upgrade EWOD-based microfluidics, antifogging, anti-icing, dust removal, and beyond.

Hydrostability, mechanical resilience, and biodegradability of paper straws fabricated through lignin-based polyurethane and chitosan binary emulsion bonding

This study focuses on enhancing the strength and water stability of paper straws through a novel approach involving a binary emulsion of lignin-based polyurethane and chitosan. Kraft lignin serves as the raw material for synthesizing a blocked waterborne polyurethane, subsequently combined with carboxylated chitosan to form a stable binary emulsion. The resulting emulsion, exhibiting remarkable stability over at least 6 months, is applied to the base paper. Following emulsion application, the paper undergoes torrefaction at 155 °C. This process deblocks isocyanate groups, enabling their reaction with hydroxyl groups on chitosan and fibers, ultimately forming ester bonds. This reaction significantly improves the mechanical strength and hydrophobicity of paper straws. The composite paper straws demonstrate exceptional mechanical properties, including a tensile strength of 47.21 MPa, Young's modulus of 4.33 GPa, and flexural strength of 32.38 MPa. Notably, its water stability is greatly enhanced, with a wet tensile strength of 40.66 MPa, surpassing commercial paper straws by 8 folds. Furthermore, the composite straw achieves complete biodegradability within 120 days, outperforming conventional paper straws in terms of environmental impact. This innovative solution presents a promising and sustainable alternative to plastic straws, addressing the urgent need for eco-friendly products.

Droplet Energy Harvesting System Based on Total-Current Nanogenerator

The droplet-based nanogenerator (DNG) is a highly promising technology for harvesting high-entropy water energy in the era of the Internet of Things. Yet, despite the exciting progress made in recent years, challenges have emerged unexpectedly for the AC-type DNG-based energy system as it transitions from laboratory demonstrations to real-world applications. In this work, we propose a high-performance DNG system based on the total-current nanogenerator concept to address these challenges. This system utilizes the water-charge-shuttle architecture for easy scale-up, employs the field effect to boost charge density of the triboelectric layer, adopts an on-solar-panel design to improve compatibility with solar energy, and is equipped with a novel DC-DC buck converter as power management circuit. These features allow the proposed system to overcome the existing bottlenecks of DNG and empower the system with superior performances compared with previous ones. Notably, with the core architecture measuring only 15 cm × 12.5 cm × 0.3 cm in physical dimensions, this system reaches a record-high open-circuit voltage of 4200 V, capable of illuminating 1440 LEDs, and can charge a 4.7 mF capacitor to 4.5 V in less than 24 min. In addition, the practical potential of the proposed DNG system is further demonstrated through a self-powered, smart greenhouse application scenario. These demonstrations include the continuous operation of a thermohygrometer, the operation of a Bluetooth plant monitor, and the all-weather energy harvesting capability. This work will provide valuable inspiration and guidance for the systematic design of next-generation DNG to unlock the sustainable potential of distributed water energy for real-world applications.

Improved Fog Collection on a Hybrid Surface with Acylated Cellulose Coating

Fog collection serves as an efficient method to alleviate water scarcity in foggy, water-stressed regions. Recent research has focused on constructing a hybrid surface to enhance fog collection efficiency, with one approach being the prevention of liquid film formation at hydrophilic sites. Inspired by the desert beetle, a coating (10-MCC) made by partially acylating microcrystalline cellulose (MCC) exhibits hydrophilic sites alongside a hydrophobic skeleton enabling rapid droplet capture despite its overall hydrophobicity. The captured droplets quickly coalesce into a large droplet driven by the wetting gradient created by the hydrophobic backbone and hydrophilic sites. To achieve greater fog collection efficiency, a hydrophobic-superhydrophobic hybrid surface is formed by combining a coating of 10-MCC with a superhydrophobic surface. The construction of superhydrophobic surfaces typically involves creating a rough surface with a distinctive structure produced by the anodization technique and modifying it with stearic acid. The superhydrophobic surface exhibits excellent corrosion resistance and mechanical stability. Moreover, the hybrid surface shows high efficiency in fog collection, with a tested maximum efficiency of approximately 1.5092 g/cm2/h, 1.77 times that of the original Al sheets. The results demonstrate a remarkable enhancement in fog collection capacity. Furthermore, this work serves as an inspiration for the low-cost and innovative design of engineered surfaces for efficient fog collection.

Enhanced and controlled droplet ejection on magnetic responsive polydimethylsiloxane microarrays

Efficient removal of droplets from solid surfaces is significant in various fields, including fog collection and condensation heat transfer. However, droplets removal on common surfaces with static structures often occurs passively, which limits the possibility of increasing removal efficiency and lacks intelligent controllability. In this paper, an active strategy based on extrusion ejection is proposed and demonstrated on the magnetic responsive polydimethylsiloxane (PDMS) superhydrophobic microplates (MPSM). The MPSM can reversibly transit between the upright and tilted state as the external magnetic field is alternately applied and removed. Under the magnetic field, the direction and trajectories of droplets departure can be intelligently controlled, demonstrating excellent controllability. More importantly, compared with the static structure where the droplet must reach a certain size before departure, droplets can be ejected at smaller sizes as the MPSM is tilted. These advantages are of great significance in many fields, such as a highly efficient fog harvesting system. This strategy of extrusion ejection based on dynamic surface structure control reported in this work may provide fresh ideas for efficient droplet manipulation.

Recent advances in solid-liquid triboelectric nanogenerator technologies, affecting factors, and applications

Converting dispersed mechanical energy into electrical energy can effectively improve the global energy shortage problem. The dispersed mechanical energy generated by liquid flow has a good application prospect as one of the most widely used renewable energy sources. Solid-liquid triboelectric nanogenerator (S-L TENG) is an inspiring device that can convert dispersed mechanical energy of liquids into electrical energy. In order to promote the design and applications of S-L TENG, it is of vital importance to understand the underlying mechanisms of energy conversion and electrical energy output affecters. The current research mainly focuses on the selection of materials, structural characteristics, the liquid droplet type, and the working environment parameters, so as to obtain different power output and meet the power supply needs of diversified scenarios. There are also studies to construct a theoretical model of S-L TENG potential distribution mechanism through COMSOL software, as well as to obtain the adsorption status of different kinds of ions with functional groups on the surface of friction power generation layer through molecular dynamics simulation. In this review, we summarize the main factors affecting the power output from four perspectives: working environment, friction power generation layer, conductive part, and substrate shape. Also summarized are the latest applications of S-L TENG in energy capture, wearable devices, and medical applications. Ultimately, this review suggests the research directions that S-L TENG should focus on in the future to enhance electrical energy output, as well as to expand the diversity of application scenarios.

Gradient-Janus Wires for Simultaneous Fogwater Harvesting and Electricity Generation

A Gradient-Janus wire (GJW) with a diameter of 0.3 mm has been fabricated on a large scale through liquid confined modification, enabling the opposite conical wetting phenomenon along the same orientation of the GJW, characterized by an increasing superhydrophilic region and a decreasing hydrophobic region. This property allows the GJW to exhibit controllable water hovering, transport, and pinning during fog harvesting, i.e., at a large tilting angle α of 60° (mass increased with decreased α), the GJW can hover 0.6 mg of harvested fogwater in 30 s, can transport 3 mg of fogwater along the gradient in 30 s at α = 4° (with maximal mass reaching up to 4.3 mg at α = -10°), and finally, pin the water droplet at the end of the GJW. Such ability generates an effective torque that serves as the driving force for rotation. We designed a GJWs-wheel by radially arranging 60 GJWs together, resulting in an extremely lightweight structure weighing only 1.9 g. The cumulative torque generated during fog harvesting activates the rotation of the GJWs-wheel. When loaded with a coil within a magnetic field, electricity is generated as output power peaks at around 0.25 μW while maintaining a high water harvesting efficiency averaging approximately 38 ± 2.12 mg/min. This finding is significant as it provides valuable insights into designing materials capable of efficiently harnessing both energy and water resources.

Dynamic Thermostable Cellulosic Triboelectric Materials from Multilevel-Non-Covalent Interactions

Triboelectric materials present great potential for harvesting huge amounts of dispersed energy, and converting them directly into useful electricity, a process that generates power more sustainably. Triboelectric nanogenerators (TENGs) have emerged as a technology to power electronics and sensors, and it is expected to solve the problem of energy harvesting and self-powered sensing from extreme environments. In this paper, a high-temperature-resistant triboelectric material is designed based on multilevel non-covalent bonding interactions, which achieves an ultra-high surface charge density of 192 µC m-2 at high temperatures. TENGs based on the triboelectric material exhibit more than an order of magnitude higher power output (2750 mW m-2 at 200 °C) than the existing devices at high temperatures. These remarkable properties are achieved based on enthalpy-driven molecular assembly in highly unbonded states. Thus, the material maintains bond strength and ultra-high surface charge density in entropy-dominated high-temperature environments. This molecular design concept points out a promising direction for the preparation of polymers with excellent triboelectric properties.

High Strength and Toughness Polymeric Triboelectric Materials Enabled by Dense Crystal-Domain Cross-Linking

Lightweight, easily processed, and durable polymeric materials play a crucial role in wearable sensor devices. However, achieving simultaneously high strength and toughness remains a challenge. This study addresses this by utilizing an ion-specific effect to control crystalline domains, enabling the fabrication of a polymeric triboelectric material with tunable mechanical properties. The dense crystal-domain cross-linking enhances energy dissipation, resulting in a material boasting both high tensile strength (58.0 MPa) and toughness (198.8 MJ m-3), alongside a remarkable 416.7% fracture elongation and 545.0 MPa modulus. Leveraging these properties, the material is successfully integrated into wearable self-powered devices, enabling real-time feedback on human joint movement. This work presents a valuable strategy for overcoming the strength-toughness trade-off in polymeric materials, paving the way for their enhanced applicability and broader use in diverse sensing applications.

Underwater Bubble Manipulation on Surfaces with Patterned Regions with Infused Lubricants

The flexible manipulation of underwater gas bubbles on solid substrates has attracted considerable research interest from scientists in the fields of water electrolysis, bubble microreactions, drug delivery, and heat transfer. Inspired by the oxygen-binding mechanisms of aquatic organisms, scientists have designed a series of interfacial materials for use in collecting gases, detecting and grading bubbles, and conducting microbubble reactions. Aerophilic surfaces are commonly used in underwater bubble manipulation platforms due to their excellent gas-trapping properties. However, during bubble transport, some of the bubbles are retained in the rough structure of the aerophilic surface and cause gas loss, which in the long run reduces the gas transport function. In addition, the aerophilic surface is prone to failure in high-humidity and high-pressure underwater environments. The lubricant-infused surface features an oil layer that remains stable on a rough substrate and is immiscible with water. Additionally, the bubbles are transported over the oil layer without causing losses other than those dissolved in water. These attributes make it more favorable than the aerophilic surface. Inspired by the unique properties of Nepenthes and cactus spines, we developed a patterned slippery surface [patterned lubricant-infused surface (PLIS)] through laser etching and ammonia etching that facilitates the coexistence of superaerophobic and aerophilic surfaces. The PLIS executes bubble capture utilizing a difference in wettability measuring 78°, transports bubbles through Laplace force and buoyancy, and regulates bubble release by restricting the contact area on the PLIS. The PLIS can be prepared rapidly and affordably in just about an hour, and its potential for large-scale production is high. Following tests for shear, acid and alkali resistance, and corrosion resistance, the PLIS exhibited impressive weathering resistance and appears to have potential for application in some extreme environments.

Insight into the Feasibility of Fatty Acyl Chlorides with 10-18 Carbons for the Ball-Milling Synthesis of Thermoplastic Cellulose Esters

Fatty acid cellulose esters (FACE) are common cellulose-based thermoplastics, and their thermoplasticity is determined by both the contents and the lengths of the side chains. Herein, various FACE were synthesized by the ball-milling esterification of cellulose and fatty acyl chlorides containing 10-18 carbons, and their structures and thermoplasticity were thoroughly studied. The results showed that FACE with high degrees of substitution (DS) and low melting flow temperatures (Tf) were achieved as the chain lengths of the fatty acyl chlorides were reduced. In particular, a cellulose decanoate with a DS of 1.85 and a Tf of 186 °C was achieved by feeding 3 mol of decanoyl chloride per mole anhydroglucose units of cellulose. However, cellulose stearate (DS = 1.53) synthesized by the same protocols cannot melt even at 250 °C. More interestingly, the fatty acyl chlorides with 10 and 12 carbons resulted in FACE with superior toughness (elongation at break up to 94.4%). In contrast, due to their potential crystallization of the fatty acyl groups with 14-18 carbons, the corresponding FACE showed higher tensile strength and Young's modulus than the others. This study provides some theoretical basis for the mechanochemical synthesis of thermoplastic FACE with designated properties.

Micro "Hyper-Channels" on Laser-Refined Cellulose Structures

Controlled liquid transportation is widely applied in both academia and industry. However, liquid transport applications are limited by parameters such as driving forces, precision, and velocity. Herein, a simple laser-refining technology is presented to produce micro "hyper-channels". A cellulose substrate is rendered hydrophobic through silanization and refined with a laser to produce both hierarchical nanostructures and a wettability contrast simultaneously. Such a method enables faster ("hyper"-channel) aqueous liquid transportation (≈25X, 50 mm s-1 ) compared to conventional methods. Complex patterns can be readily produced at different scales with spatial resolution as low as 50 µm. This technique also controls the refining depth on the thin paper substrate. Shallow channels can be fabricated on thin paper substrates that enable fluidic channel-crossover without liquid mixing. With certain parameters, the technique creates "portals" through the substrate, allowing trans-dimensional liquid transportation between two layers of a single sheet of substrate. The fluid throughput can be increased, while also permitting fluidic channel crossover without liquid mixing. By introducing multiple portals, the controlled fluid can transfer trans-dimensionally several times, enabling further fluidic complexity. The real-life utility of the method is demonstrated by creating a trans-dimensional microfluidic device for colorimetric detection.

Carboxymethyl cellulose-based hydrogel with high-density crack microstructures inspired from the multi-tentacles of octopus for ultrasensitive flexible sensing microsystem

Constructing high-density contact-separation sites on conductive materials highly determines the sensitivity of flexible resistance-type sensors relying on the crack microstructures. Herein, inspired from the multiple-tentacle structures on octopus, we demonstrated a sort of novel carbonized ZIF-8@loofah (CZL) as conductive material to develop ultrasensitivity flexible sensor, in which the carbonized ZIF-8 nanoparticles (~100 nm) served as tentacles. Originating from the formation of high-density contact-separation sites, the fabricated CZL-based strain sensor delivered ultrahigh sensitivity of GFmax = 15,901, short response time of 22 ms and excellent durability over 10,000 cycles. These features enable the sensor with efficient monitoring capacity for complex human activities, such as pulse rate and phonation. Moreover, when CZL was assembled into triboelectric nanogenerator (TENG), CZL-based TENG can effectively convert the irregular biomechanical energy into electric energy, providing sustainable power supply for the continuous operation of the sensing micro-system. Our findings established a novel platform to develop high-performance self-powered sensing systems of physiological parameter of human inspired from the nature.

Phospholipid Bilayer Inspired Sandwich Structural Nanofibrous Membrane for Atmospheric Water Harvesting and Selective Release

Atmospheric water harvesting (AWH) has been broadly exploited to meet the challenge of water shortage. Despite the significant achievements of AWH, the leakage of hydroscopic salt during the AWH process hinders its practical applications. Herein, inspired by the unique selective permeability of the phospholipid bilayer, a sandwich structural (hydrophobic-hydrophilic-hydrophobic) polyacrylonitrile nanofibrous membrane (San-PAN) was fabricated for AWH. The hydrophilic inner layer loaded with LiCl could capture water from the air. The hydrophobic microchannels in the outer layer could selectively allow the free transmission of gaseous water molecules but confine the hydroscopic salt solution in the hydrophilic layer, achieving continuous and recyclable water sorption/desorption. As demonstrated, the as-prepared AWH devices presented high-efficient adsorption kinetics from 1.66 to 4.08 g g-1 at 30% to 90% relative humidity. Thus, this work strengthens the understanding of the water transmission process along microchannels and provides insight into the practical applications of AWH.

Advanced Fog Harvesting Method by Coupling Plasma and Micro/Nano Materials

Harvesting fog is a potential and effective way to alleviate the crisis of water resource shortage. A highly efficient and economical fog harvesting method has always been a global and common goal. Here, a promising fog harvesting method by coupling plasma and micro/nano materials is proposed, which can achieve 93% fog collection efficiency with consuming power of only 0.76 W/0.04 m2. The basic method is to utilize nanoparticles to decorate both the discharge electrode and the collecting electrode of the micro/nano electrostatic fog collector. For the discharge electrode, the nanoparticles can achieve an order of magnitude higher electric field strength and a 28.6% decrease in the operating voltage (14 kV decreases to 10 kV). For the collecting electrode, a novel composite structure of hydrophobic/hydrophilic (HB/HL) is proposed. The core advantage is the directional droplet transport at the junction of HB and HL caused by surface tension can adjust the accumulated droplets on the two sides, which avoids the droplet residue and mesh blockage in the general structure. This technology provides an innovative approach for the collection of microdroplets and a new design idea for the fog collector to deal with the water crisis.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

Durable Janus membrane with on-demand mode switching fabricated by femtosecond laser

Despite their notable unidirectional water transport capabilities, Janus membranes are commonly challenged by the fragility of their chemical coatings and the clogging of open microchannels. Here, an on-demand mode-switching strategy is presented to consider the Janus functionality and mechanical durability separately and implement them by simply stretching and releasing the membrane. The stretching Janus mode facilitates unidirectional liquid flow through the hydrophilic micropores-microgrooves channels (PG channels) fabricated by femtosecond laser. The releasing protection mode is designed for the in-situ closure of the PG channels upon encountering external abrasion and impact. The protection mode imparts the Janus membrane robustness to reserve water unidirectional penetration under harsh conditions, such as 2000  cycles mechanical abrasion, 10 days exposure in air and other rigorous tests (sandpaper abrasion, finger rubbing, sand impact and tape peeling). The underlying mechanism of gridded grooves in protecting and enhancing water flow is unveiled. The Janus membrane serves as a fog collector to demonstrate its unwavering mechanical durability in harsh real-world conditions. The presented design strategy could open up new possibilities of Janus membrane in a multitude of applications ranging from multiphase separation devices to fog harvesting and wearable health-monitoring patches.

Charge Dispersion Strategy for High-Performance and Rain-Proof Triboelectric Nanogenerator

Triboelectric nanogenerator (TENG) is becoming a sustainable and renewable way of energy harvesting and self-powered sensing because of low cost, simple structure, and high efficiency. However, the output current of existing TENGs is still low. It is proposed that the output current of TENGs can be dramatically improved if the triboelectric charges can distribute inside the triboelectric layers. Herein, a novel single-electrode conductive network-based TENG (CN-TENG) is developed by introducing a conductive network of multiwalled carbon nanotubes in dielectric triboelectric layer of thermoplastic polyurethane (TPU). In this CN-TENG, the contact electrification-induced charges distribute on both the surface and interior of the dielectric TPU layer. Thus, the short-circuit current of CN-TENG improves for 100-fold, compared with that of traditional dielectric TENG. In addition, this CN-TENG, even without packing, can work stably in high-humidity environments and even in the rain, which is another main challenge for conventional TENGs due to charge leakage. Further, this CN-TENG is applied for the first time, to successfully distinguish conductive and dielectric materials. This work provides a new and effective strategy to fabricate TENGs with high output current and humidity-resistivity, greatly expanding their practical applications in energy harvesting, movement sensing, human-machine interaction, and so on.

High Toughness, Multi-dynamic Self-Healing Polyurethane for Outstanding Energy Harvesting and Sensing

Triboelectric nanogenerators (TENGs) are an emerging class of energy harvesting devices with considerable potential across diverse applications, including wearable electronic devices and self-powered sensors. However, sustained contact, friction, and incidental scratches during operation can lead to a deterioration in the electrical output performance of the TENG, thereby reducing its overall service life. To address this issue, we developed a self-healing elastomer by incorporating disulfide bonds and metal coordination bonds into the polyurethane (PU) chain. The resulting elastomer demonstrated exceptional toughness, with a high value of 85 kJ m-3 and an impressive self-healing efficiency of 85.5%. Specifically, the TENG based on that self-healing PU elastomer generated a short circuit current of 12 μA, an open circuit voltage of 120 V, and a transfer charge of 38.5 nC within a 2 cm × 2 cm area, operating in contact-separation mode. With an external resistance of 20 MΩ, the TENG achieved a power density of 2.1 W m-2. Notably, even after self-healing, the electrical output performance of the TENG was maintained at 95% of the undamaged device. Finally, the self-healing TENG was employed to construct a self-powered noncontact sensing system that can be applied to monitor human motion accurately. This research may expand the application prospects of PU materials in future human-computer interaction and self-powered sensing fields.

Biodegradable Dual-Network Cellulosic Composite Bioplastic Metafilm for Plastic Substitute

With the escalating environmental and health concerns over petroleum-based plastics, sustainable and biodegradable cellulosic materials are a promising alternative to plastics, yet remain unsatisfied properties such as fragility, inflammability and water sensitivity for practical usage. Herein, we present a novel dual-network design strategy to address these limitations and fabricate a high-performance cellulosic composite bioplastic metafilm with the exceptional mechanical toughness (23.5 MJ m-3 ), flame retardance, and solvent resistance by in situ growth of cyclotriphosphazene-bridged organosilica network within bacterial cellulose matrix. The phosphorus, nitrogen-containing organosilica network, verified by the experimental and theoretical results, plays a triple action on significantly enhancing tensile strength, toughness, flame retardance and water resistance of composite bioplastic metafilm. Furthermore, cellulosic bioplastic composite metafilm demonstrates a higher maximum usage temperature (245 °C), lower thermal expansion coefficient (15.19 ppm °C-1 ), and better solvent resistance than traditional plastics, good biocompatibility and natural biodegradation. Moreover, the composite bioplastic metafilm have a good transparency of average 74 % and a high haze over 80 %, which can serve as an outstanding substrate substitute for commercial polyethylene terephthalate film to address the demand of flexible ITO films. This work paves a creative way to design and manufacture the competitive bioplastic composite to replace daily-used plastics.

Selective separation of hemicellulose from poplar by hydrothermal pretreatment with ferric chloride and pH buffer

As an environmentally friendly lignocellulosic biomass separation technology, hydrothermal pretreatment (HP) has a strong application prospect. However, the low separation efficiency is a main factor limiting its application. In this study, the poplar components were separated using HP with ferric chloride and pH buffer (HFB). The optimal conditions were ferric chloride concentration of 0.10 M, reaction temperature of 150 °C, reaction time of 15 min and pH 1.9. The separation of hemicellulose was increased 34.03 % to 77.02 %. The pH buffering resulted in the highest cellulose and lignin retention yields compared to ferric chloride pretreatment (FC). The high efficiency separation of hemicellulose via HFB pretreatment inhibited the degradation of xylose. The hydrolysate was effectively reused for five times. The fiber crystallinity index reached 60.05 %, and the highest C/O ratio was obtained. The results provide theoretical support for improving the efficiency of HP and promoting its application.

Study of a bioinspired rigid-flexible coupling structure based on dragonfly wing by optical/electron microscopy and finite element analysis

In this work, mechanical properties of veins and membrane of dragonfly wing were studied by means of optical/electron microscopy, tensile test and nano-indentation. It indicates that veins exhibit significantly higher strength and elastic modulus, as compared with membrane. Furthermore, finite element analysis (FEA) demonstrates that the fluctuation of Von Mises stress and displacement between varying models is undermined, due to presence of the membrane, indicating higher stability. Consequently, according to FEA of varying models involving presence of membrane, the membrane in dragonfly wing not only provides the capability to fly, but also improves obviously the strength and stability of wing structure, despite of its significantly low strength and elastic modulus. It is found that based on proper biomimetic design, bioinspired rigid-flexible coupling structure exhibits superior strength and stability, as compared with conventional rigid structure, which will provide great potential to make novel, smart, and functional structures.

Overview of the design of bionic fine hierarchical structures for fog collection

Nature always uses its special wisdom to construct elegant and suitable schemes. Consequently, organisms in the flora and fauna are endowed with fine hierarchical structures (HS) to adapt to the harsh environment due to many years of evolution. Water is one of the most important resources; however, easy access to it is one the biggest challenges faced by human beings. In this case, fog collection (FC) is considered an efficient method to collect water, where bionic HS can be the bridge to efficiently facilitate the process of the FC. In this review, firstly, we discuss the basic principles of FC. Secondly, the role of HS in FC is analyzed in terms of the microstructure of typical examples of plants and animals. Simultaneously, the water-harvesting function of HS in a relatively new organism, fungal filament, is also presented. Thirdly, the HS design in each representative work is analyzed from a biomimetic perspective (single to multiple biomimetic approaches). The role of HS in FC, and then the FC performance of each work are analyzed in order of spatial dimension from a bionic perspective. Finally, the challenges at this stage and the outlook for the future are presented.

Recent Advances in Functional Fiber-Based Wearable Triboelectric Nanogenerators

The quality of human life has improved thanks to the rapid development of wearable electronics. Previously, bulk structures were usually selected for the fabrication of high performance electronics, but these are not suitable for wearable electronics due to mobility limitations and comfortability. Fibrous material-based triboelectric nanogenerators (TENGs) can provide power to wearable electronics due to their advantages such as light weight, flexibility, stretchability, wearability, etc. In this work, various fiber materials, multiple fabrication methods, and fundamentals of TENGs are described. Moreover, recent advances in functional fiber-based wearable TENGs are introduced. Furthermore, the challenges to functional fiber-based TENGs are discussed, and possible solutions are suggested. Finally, the use of TENGs in hybrid devices is introduced for a broader introduction of fiber-based energy harvesting technologies.

A UV-Resistant Heterogeneous Wettability-Patterned Surface

Preparing UV-resistant heterogeneous wettability patterns is critical for the practical application of surfaces with heterogeneous wettability. However, combining UV-resistant superhydrophobic and superhydrophilic materials on heterogeneous surfaces is challenging. Inspired by the structure of cell membranes, a UV-resistant heterogeneous wettability-patterned surface (UPS) is designed via laser ablation of the coating of multilayer structures. UV-resistant superhydrophobic silica patterns can be created in situ on surfaces covered with superhydrophilic TiO2 nanoparticles. The UV resistance time of the UPS with a TiO2 -based surface is more than two orders of magnitude higher than that obtained with other surface molecular modification methods that require a mask. The cell-membrane-like structure of the UPS regulates the migration of internal siloxane chain segments in the hydrophilic and hydrophobic regions of the surface. The UPS enables efficient patterning of functional materials under UV irradiation, controlling the wetting behavior of liquids in open-air systems. Furthermore, its heterogeneous wettability remains stable even after 50 h of intense UV irradiation (365 nm, 500 mW cm-2 ). These UV-resistant heterogeneous wettability patterned surfaces will likely be applied in microfluidics, cell culture, energy conversion, and water collection in the future.

Recent Progress of Advanced Materials for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) have received intense attention due to their broad application prospects in the new era of internet of things (IoTs) as distributed power sources and self-powered sensors. Advanced materials are vital components for TENGs, which decide their comprehensive performance and application scenarios, opening up the opportunity to develop efficient TENGs and expand their potential applications. In this review, a systematic and comprehensive overview of the advanced materials for TENGs is presented, including materials classifications, fabrication methods, and the properties required for applications. In particular, the triboelectric, friction, and dielectric performance of advanced materials is focused upon and their roles in designing the TENGs are analyzed. The recent progress of advanced materials used in TENGs for mechanical energy harvesting and self-powered sensors is also summarized. Finally, an overview of the emerging challenges, strategies, and opportunities for research and development of advanced materials for TENGs is provided.

Ca-MOF-Derived Porous Sorbents for High-Yield Solar-Driven Atmosphere Water Harvesting

The development of high-yield, metal-organic framework (MOF)-based water harvesters in arid areas remains challenging due to the absence of effective strategies for enhancing water sorption capacity and kinetics. Herein, we presented a novel strategy for in situ fabrication of calcium chloride (CaCl2) decorated MOF-derived porous sorbents (PCC-42) through pyrolysis Ca-MOF and subsequently hydrochloric acid (HCl) vapor treatment process. The resulting PCC-42 sorbents exhibited a high water adsorption capacity of 3.04 g g-1 at 100% relative humidity (RH), outstanding photothermal performance, and rapid water uptake-release kinetics, surpassing most reported MOFs adsorbents. At 20, 30, 40, and 50% RH, PCC-42 demonstrated water uptake capacity of 0.45, 0.59, 0.76, and 0.9 g g-1, which represented an increase of 421 and 940% (at 20% RH) and 333 and 351% (at 30% RH) compared to Ca-MOF and CaCl2·2H2O, respectively. Approximately 80% of the adsorbed water in PCC-42 could be released under one sun within 50 min. Indoor water harvesting experiments demonstrated that PCC-42 is a promising adsorbent for various humidity environments. Additionally, outdoor solar-driven atmospheric water harvesting (AWH) tests revealed a high daily water production of 1.13 L/kgadsorbent under typical arid conditions (30-60% RH). The proposed strategy helps the design of high-performance adsorbents for solar-driven AWH in arid environments.

Unveiling the Interactions between Water Molecule Clusters and Conical Structures via Molecular Dynamics Simulations

Water scarcity presents a pressing global challenge, necessitating innovative solutions, such as the collection of water from the air using conical structures. However, current research primarily focuses on mist collection rather than on nanoscale clusters of water molecules. Under standard atmospheric conditions, water vapor predominantly exists as imperceptible clusters. Therefore, it is crucial to investigate the interactions between these water molecule clusters and conical structures, particularly regarding whether the conical shape induces Laplace pressure difference on the adhering cluster formations. To gain deeper insights and determine optimal droplet collection structures, we conducted molecular dynamics simulations to investigate interactions between water molecule clusters and conical structures. Our investigations focused on studying the interactions between conical structures and water molecule clusters with varying densities, as well as the impact of surface energies on the collection of water by these conical structures. Notably, our simulations unveiled the significant roles played by van der Waals forces and Laplace pressure in the process of collecting water molecule clusters. Furthermore, our simulations revealed that Janus conical structures, featuring two distinct surface energy regions, played a crucial role in promoting the aggregation of water molecules, resulting in the formation of larger droplets. This aggregation was driven by surface tension gradients, which arise from the contrasting wetting properties in different regions of the Janus structure. As a consequence, under the influence of gravitational forces, these larger droplets could eventually detach from the structure. Through the combined effects of surface tension gradients and gravitational forces, Janus conical structures offer a promising avenue for enhancing the collection efficiency of water from the air. Our research sheds light on the fundamental mechanisms governing water molecule cluster-based water collection and provides valuable insights for the design of more efficient and effective water collection systems.

Intestinal Villi-Inspired Mathematically Base-Layer Engineered Microneedles (IMBEMs) for Effective Molecular Exchange during Biomarker Enrichment and Drug Deposition in Diversified Mucosa

The mucosa-interfacing systems based on bioinspired engineering design for sampling/drug delivery have manifested crucial potential for the monitoring of infectious diseases and the treatment of mucosa-related diseases. However, their efficiency and validity are severely restricted by limited contact area for molecular transfer and dissatisfactory capture/detachment capability. Herein, inspired by the multilayer villus structure of the small intestine that enables high nutrient absorption, a trigonometric function-based periodic pattern was fabricated and integrated on the base layer of the microneedle patch, exhibiting a desirable synergistic effect with needle tips for deep sample enrichment and promising molecular transfer, significantly improving the device-mucosa bidirectional interaction. Moreover, mathematical modeling and finite element analysis were adopted to visualize and quantify the microcosmic molecular transmission process, guiding parameter optimization in actual situation. Encouragingly, these intestinal villi-inspired mathematically base-layer engineered microneedles (IMBEMs) have demonstrated distinguished applicability among mucosa tissue with varying surface curvatures, tissue toughness, and local environments, and simultaneously, have gained favorable support from healthy volunteers receiving preliminary test of IMBEMs patches. Overall, validated by numerous in vitro and in vivo tests, the IMBEMs were confirmed to act as a promising candidate to facilitate mucosa-based sampling and topical drug delivery, indicating highly clinical translation potential.

Diameter-Optimum Spreading for the Impinging of Water Nanodroplets on Solid Surfaces

The impinging of water nanodroplets on solid surfaces is crucial to many nanotechnologies. Through large-scale molecular dynamics simulations, the size effect on the spreading of water nanodroplets after impinging on hydrophilic, graphite, and hydrophobic surfaces under low impinging velocities has been systematically studied. The spreading rates of nanodroplets first increase and then decrease and gradually become constant with the increase of nanodroplet diameter. The nanodroplets with the diameters of 17-19 nm possess the highest spreading rates because of the combined effect of the strongest interfacial interaction and the strongest surface interaction within water molecules. The highest water molecule densities, hydrogen bond numbers, and dielectric constants of interface and surface layers mainly contribute to the lowest interface work of adhesion and surface tension values at optimal diameters. These results unveil the nonmonotonic characteristics of spreading velocity, interface work of adhesion and surface tension with nanodroplet diameter for nanodroplets on solid surfaces.

Gradience Free Nanoinsertion of Fe3O4 into Wood for Enhanced Hydrovoltaic Energy Harvesting

Hydrovoltaic energy harvesting offers the potential to utilize enormous water energy for sustainable energy systems. Here, we report the utilization and tailoring of an intrinsic anisotropic 3D continuous microchannel structure from native wood for efficient hydrovoltaic energy harvesting by Fe3O4 nanoparticle insertion. Acetone-assisted precursor infiltration ensures the homogenous distribution of Fe ions for gradience-free Fe3O4 nanoparticle formation in wood. The Fe3O4/wood nanocomposites result in an open-circuit voltage of 63 mV and a power density of ∼52 μW/m2 (∼165 times higher than the original wood) under ambient conditions. The output voltage and power density are further increased to 1 V and ∼743 μW/m2 under 3 suns solar irradiation. The enhancement could be attributed to the increase of surface charge, nanoporosity, and photothermal effect from Fe3O4. The device exhibits a stable voltage of ∼1 V for 30 h (3 cycles of 10 h) showing good long-term stability. The methodology offers the potential for hierarchical organic-inorganic nanocomposite design for scalable and efficient ambient energy harvesting.

3D-printing-assisted fabrication of hierarchically structured biomimetic surfaces with dual-wettability for water harvesting

Freshwater acquisition methods under various environments are required because water scarcity has intensified worldwide. Furthermore, as water is an essential resource for humans, a freshwater acquisition method that can be utilized even under harsh conditions, such as waterless and polluted water environments, is highly required. In this study, a three-dimensional (3D) printing-assisted hierarchically structured surface with dual-wettability (i.e., surface with both hydrophobic and hydrophilic region) for fog harvesting was developed by mimicking the biological features (i.e., cactus spines and elytra of Namib Desert beetles) that have effective characteristics for fog harvesting. The cactus-shaped surface exhibited self-transportation ability of water droplet, derived from the Laplace pressure gradient. Additionally, microgrooved patterns of the cactus spines were implemented using the staircase effect of 3D printing. Moreover, a partial metal deposition method using wax-based masking was introduced to realize the dual wettability of the elytra of the Namib Desert beetle. Consequently, the proposed surface exhibited the best performance (average weight of 7.85 g for 10 min) for fog harvesting, which was enhanced by the synergetic effect between the Laplace pressure gradient and surface energy gradient. These results support a novel freshwater production system that can be utilized even in harsh conditions, such as waterless and polluted water environments.