Controllable and Continuous Hollow Fiber Swimmers Based on the Marangoni Effect

Programmable assemblies of photothermal anisotropic micromotors for multimodal motion

Light-driven micromotors with multiple motion modes offer significantly greater application potential than single-mode micromotors. However, achieving such versatility often requires complex structural designs and precise light focusing on specific micromotor regions, presenting challenges for dynamic operations and microscale precisions. This study introduces programmable assemblies of anisotropic micromotors driven by the photothermal Marangoni effect, produced in bulk via microfluidic technology. Under full-area near-infrared (NIR) irradiation, the micromotor exhibits multiple motion modes, including translation and revolution, while micromotor assemblies display additional rotational motion. Self-assembly of these micromotors is highly controllable and programmable, enabling easy customization of assembled structures to achieve desired motion modes. These features are expected to advance the development of various intelligent self-propelling systems, using multimodal individual micromotors as foundational building blocks.

High-Performance MXene Hydrogel for Self-Propelled Marangoni Swimmers and Water-Enabled Electricity Generator

Developing multifunctional materials that integrate self-propulsion and self-power generation is a significant challenge. This study introduces a high-performance MXene-chitosan composite hydrogel (CM) that successfully combines these functionalities. Utilizing Schiff base bond and hydrogen bond interactions, the CM hydrogel, composed of chitosan, vanillin, and MXene, achieves exceptional self-propulsion on water driven by Marangoni forces. The hydrogel demonstrates rapid movement, extended operation, and controllable trajectories. Notably, the CM hydrogel also exhibits superior degradability, recyclability, and repeatability. Furthermore, the nano-confined channels within the hydrogel play a crucial role in enhancing its water-enabled electricity generation (WEG) performance. By efficiently adsorbing water molecules and selectively transporting cations through these channels, the hydrogel can generate electricity from water molecules and cations more efficiently. As a result, the CM-WEG achieves a stable open-circuit voltage of up to 0.83 V and a short-circuit current of 0.107 mA on seawater, with further improvements in K2CO3-containing water, reaching 1.26 V and 0.922 mA. Leveraging its unique combination of self-propulsion and WEG functionalities, the CM hydrogel is successfully used for cargo delivery while simultaneously powering electronic devices. This research represents a significant step toward the development of self-powered, autonomous soft robotics, opening new research directions in the field.

Electrospun Nanofiber Materials for Photothermal Interfacial Evaporation

Photothermal interfacial evaporation with low cost and environmental friendliness has attracted much attention. However, there are still many problems with this technology, such as heat loss and salt accumulation. Due to their different structures and adjustable chemical composition, electrospun nanofiber materials generally exhibit some unique properties that provide new approaches to address the aforementioned issues. In this review, the rational design principles for improving the total efficiency of solar evaporation are described for thermal/water management systems and salt-resistance strategies. And we review the state-of-the-art advancements in photothermal evaporation based on nanofiber materials and discuss their derivative applications in desalination, water purification, and power generation. Finally, we highlight key challenges and opportunities in both fundamental research and practical applications to inform further developments in the field of interfacial evaporation.

A Multi-engine Marangoni Rotor with Controlled Motion for Mini-Generator Application

Marangoni rotors are smart devices that are capable of self-propulsive motions based on the Marangoni effect, namely interfacial flows caused by a gradient of surface tension. Owing to the features of untethered motions and coupled complexity with fluid, these Marangoni devices are attractive for both theoretical study and applications in biomimicking, cargo delivery, energy conversion, etc. However, the controllability of Marangoni motions dependent on concentration gradients remains to be improved, including the motion lifetime, direction, and trajectories. The challenge lies in the flexible loading and adjustments of surfactant fuels. Herein, we design a multi-engine device in a six-arm shape with multiple fuel positions allowing for motion control and propose a strategy of diluting the surfactant fuel to prolong the motion lifetime. The resulting motion lifetime has been extended from 140 to 360 s by 143% compared with conventional surfactant fuels. The motion trajectories could be facilely adjusted by changing both the fuel number and positions, leading to diverse rotation patterns. By integrating with a coil and a magnet, we obtained a system of mini-generators based on the Marangoni rotor. Compared with the single-engine case, the output of the multi-engine rotor was increased by 2 magnitudes owing to increased kinetic energy. The design of the above Marangoni rotor has addressed the problems of concentration-gradient-driven Marangoni devices and enriched their applications in harvesting energy from the environment.

Continuous g-C3N4 layer-coated porous TiO2 fibers with enhanced photocatalytic activity toward H2 evolution and dye degradation

TiO₂/g-C₃N₄ composite photocatalysts with various merits, including low-cost, non-toxic, and environment friendliness, have potential application for producing clean energy and removing organic pollutants to deal with the global energy shortage and environmental contamination. Coating a continuous g-C₃N₄ layer on TiO₂ fibers to form a core/shell structure that could improve the separation and transit efficiency of photo-induced carriers in photocatalytic reactions is still a challenge. In this work, porous TiO₂ (P-TiO₂)@g-C₃N₄ fibers were prepared by a hard template-assisted electrospinning method together with the g-C₃N₄ precursor in an immersing and calcination process. The continuous g-C₃N₄ layer was fully packed around the P-TiO₂ fibers tightly to form a TiO₂@g-C₃N₄ core/shell composite with a strong TiO₂/g-C₃N₄ heterojunction, which greatly enhanced the separation efficiency of photo-induced electrons and holes. Moreover, the great length–diameter ratio configuration of the fiber catalyst was favorable for the recycling of the catalyst. The P-TiO₂@g-C₃N₄ core/shell composite exhibited a significantly enhanced photocatalytic performance both in H₂ generation and dye degradation reactions under visible light irradiation, owing to the specific P-TiO₂@g-C₃N₄ core/shell structure and the high-quality TiO₂/g-C₃N₄ heterojunction in the photocatalyst. This work offers a promising strategy to produce photocatalysts with high efficiency in visible light through a rational structure design.

TiO₂@g-C₃N₄ core/shell fibers with a continuous g-C₃N₄ layer packing around exhibit high photocatalytic efficiency toward H₂ production and RhB degradation due to the intimate core/shell structure with a high-quality TiO₂/g-C₃N₄ heterojunction.

CoS2-TiO2@C Core-Shell fibers as cathode host material for High-Performance Lithium-Sulfur batteries

Owing to the low cost, high energy density, and high theoretical specific capacity, lithium-sulfur batteries have been deemed as a potential choice for future energy storage devices. However, they also have suffered from several scientific and technical issues including low conductivity, polysulfides migration, and volume changes. In this study, CoS₂-TiO₂@carbon core-shell fibers were fabricated through combination of coaxial electrospinning and selective vulcanization method. The core-shell fibers are able to efficiently host sulfur, confine polysulfides, and accelerate intermediates conversion. This electrode delivers an initial specific capacity of 1181.1 mAh g^-1 and a high capacity of 736.5 mAh g^-1 after 300 cycles with high coulombic efficiency over 99.5% (capacity decay of 0.06% per cycle). This strategy of isolating interactant and selective vulcanization provides new ideas for effectively constructing heterostructure materials for lithium-sulfur batteries.

Hollow fibers: from fabrication to applications

Hollow fibers have attracted more and more attention due to their broad range of applications in numerous fields. We review the latest advance and summarize the fabrication methods, types and applications of hollow fibers. We mainly introduce the fabrication methods of hollow fibers, including co-extrusion/co-axial spinning methods, template methods, 3D printing methods, electrospinning methods, self-crimping methods and gas foaming process. Meanwhile, we summarize four types of hollow fibers: one-layered hollow fibers, multi-layered hollow fibers, multi-hollow fibers and branched hollow fibers. Next, we focus on the main applications of hollow fibers, such as gas separation, cell culture, microfluidic channels, artificial tubular tissues, etc. Finally, we present the prospects of the future trend of development. The review would promote the further development of hollow fibers and benefit their advance in sensing, bioreactors, electrochemical catalysis, energy conversion, microfluidics, gas separation, air purification, drug delivery, functional materials, cell culture and tissue engineering. This review has great significance for the design of new functional materials and development of devices and systems in the related fields.