Self-floating maize straw/graphene aerogel synthesis based on microbubble and ice crystal templates for efficient solar-driven interfacial water evaporation

Abstract

Water purification via the solar-driven evaporation of water is a promising solution to alleviate water crises. Herein, a novel three-dimensional interconnected porous structure and ultra-light maize straw/graphene aerogel is facilely synthesized through a low-temperature hydrothermal reduction process and atmospheric drying using microbubbles and ice crystals as templates. The capillary action of the natural pore structure of biomass maize straw accelerated the transportation of water to the heating interface, and the aerogel is also advantageous to use because of the excellent light absorption capacity of graphene. During the synthesis process, the degree of self-assembly, and the density and wettability of the aerogel were controlled via tuning the maize straw/graphene ratio. An optimal sample of maize straw/graphene aerogel displayed a three-dimensional interconnected porous network structure, low density (9.67 mg cm⁻³), excellent mechanical properties (compression strength of up to 11.4 kPa at 70% strain), and high evaporation rate (2.71 kg m⁻² h⁻¹) under 1 solar radiation. More significantly, maize straw/graphene aerogels were nitrogen-doped through the addition of urea, and these outperformed state-of-the-art graphene-based photothermal materials in solar-driven water evaporation, with rates of up to 3.22 kg m⁻² h⁻¹, which was attributed to the formation of a super-hydrophilic, porous, and ultra-light aerogel that further accelerated water transport and the diffusion of water molecules. The nitrogen doping also improved the mechanical properties (compression strength of up to 16.7 kPa at 70% strain), and the aerogel exhibited excellent stability and salt resistance, and accomplished high levels of desalination. The aerogel exhibited excellent mechanical properties and resilience, excellent thermal insulation properties, a wide sunlight absorption spectrum, fast water transmission, and a large pore structure that is conducive to vapor diffusion and high desalination, and, thus, there is great potential for this aerogel to be used for practical applications.