Microfluidic-Enabled Elastic Photothermal Helical Gel Microfibers for High-Efficiency Solar Evaporation With Spatially Regulated Light-Thermal-Water Management.

Abstract

Fibrous films and fabrics have been extensively employed for solar photothermal interfacial evaporation due to their high specific surface area, flexibility and scalability. However, the inherent planar geometry of fibrous films/fabrics restricts the evaporation area, and vapor/mass diffusion, limiting the evaporation efficiency and inducing salt accumulation. Herein, we propose a strategy of shifting the planar fabrics to photothermal helical microfiber evaporators via microfluidic technology, featuring intrinsic three-dimensional structure, prominent elasticity and flexibility. The distinctive central cavity in helical gel microfibers enables spatial regulation of light, thermal and water transport, not only expanding evaporation area but also efficiently localizing thermal energy and capturing additional energy. By tuning the helical pitch, the water transport, vapor diffusion and light capture capabilities are synergistically optimized, achieving an evaporation rate of 3.65 kg m^- ² h^- ¹ under 1 sun irradiation with superior salt resistance. Moreover, the excellent flexibility of the helical microfiber fabric imparts exceptional structural adjustability, allowing to perform solar-tracking evaporation. Outdoor tests using such solar-tracking system with enlarged evaporation area deliver a stable evaporation rate of 8.57 kg m^- ² h^- ¹ under solar intensity of ∼950 W m^- ², which demonstrates a viable design concept for high-performance fabric-based evaporators in sustainable solar interfacial evaporation.