Tailored Graphene Oxide Aerogels for Solar-Driven Evaporation

Interfacial solar evaporation is a promising technology for clean water production, requiring advanced materials with efficient water transport and photothermal conversion. This work focuses on the development and optimization of graphene oxide (GO) aerogels via directional freeze-casting to achieve a hierarchical structure for enhanced capillary action.

GO was synthesized via a modified Hummers-Offeman method. Aerogels were fabricated through unidirectional freezing followed by lyophilization. The effects of key synthesis parameters were systematically studied: freezing temperature (-196 °C vs. -17 °C), lateral flake size (adjusted by sonication), and chemical modification with lignin (GOL). The materials were characterized using SEM, FT-IR, UV-Vis, and water contact angle measurements, while water transport was evaluated through wetting time and droplet absorption rate. 

Results demonstrate that slower freezing (-17 °C) promotes the formation of aligned, lamellar pores with larger diameters (284 µm²) compared to the disordered, smaller pores (114 µm²) obtained with liquid nitrogen. Flake size reduction via sonication produced aerogels with smaller pores but significantly faster water transport. Chemical modification with lignin (GO:lignin 1:10) notably increased surface hydrophilicity, decreasing the contact angle from 67° to 52°. The combination of lignin modification and isopropanol (IPOL) as a co-solvent (20% v/v) produced the most promising material (AGOL1:10-IPOL20%), exhibiting highly aligned pores and rapid water absorption (3-4 seconds).

In conclusion, we demonstrate that the microstructure and hydrophilicity of graphene oxide aerogels can be precisely tuned by controlling freezing parameters, flake size, and chemical functionalization. The optimized material, AGOL1:10-IPOL20%, exhibits excellent water transport properties, making it a strong candidate for efficient interfacial solar evaporators.