Laminated chitosan/graphene nanoplatelets aerogel for 3D interfacial solar desalination with harnessing wind energy

Abstract

Interfacial solar steam generation (ISSG) is a novel approach to freshwater generation. In practical utilization of new ISSG technology, achieving high evaporation rate is a crucial step. A three-dimensional (3D) solar absorber can increase the exposed surface area and enhance the escape of water molecules to the surrounding environment. However, vigorous evaporation induces to dry out the evaporator quickly, leading to damage its structure or decreased efficiency. In this context, a transversely laminated aerogel-based 3D evaporator is proposed. For this, chitosan/graphene nanoplatelets (CG) are incorporated to create laminated CG (LCG) aerogels having two different densities in a single structure. The results demonstrate that LCG aerogels exhibit rapid water-rise ability and excellent solar absorption characteristics. The laminated structure enhances mechanical strength and maintains balanced water and ion gradients sustainably, inducing a wettable and evaporation-enhanced condition. With these advantages, the evaporation rate of LCG aerogels with aspect ratio (AR) of 7 achieves 2.17 kg m−2h−1. In addition, evaporation experiments were conducted by applying precisely-controlled wind in a wind tunnel to the 3D evaporator. At a wind speed of 6 m s−1, the proposed evaporator achieves a maximum evaporation rate of 5.98 kg m−2h−1. Aerogel with a single density is better suited for situations where only solar radiation is present, while the LCG aerogel, which can utilize the features of two densities at the same time, is more effective in windy conditions. The evaporation efficiency is over 73 % for seawater and 20 wt% high-concentration NaCl solution, showing excellent durability with salt-resistance. The proposed aerogel-based evaporators would be utilized as a sustainable seawater desalination technology for environmentally friendly freshwater production.