Novel onion-like graphene aerogel beads for efficient solar vapor generation under non-concentrated illumination†
Graphene aerogel has attracted great attention due to its unique properties in solar vapor generation for water purification and desalination. However, many challenges remain in promoting their development and practical application, such as scalable fabrication and facile use in a large area of water. Herein, we report a simple self-assembly approach to prepare onion-like graphene aerogel beads on a millimeter scale. The floatable, low-density graphene aerogel beads are used to promote water evaporation under non-concentrated illumination for the first time. MoS2 microflakes with a strong light absorption capability in the visible and near-infrared regions are incorporated to form hybrid beads with a much enhanced water evaporation performance. A record steam generation efficiency of 74% is obtained under illumination of only 0.5 kW m−2 with a single layer of hybrid beads, corresponding to a remarkable evaporation rate of 0.54 kg m−2 h−1. When scaled up to a 0.05 m2 active area in a home-made solar water still for use in an outdoor environment, the hybrid beads are easily dispersed on the water surface by self-spreading action. Their freshwater generation rate is about 2.0 L m−2 day−1 on a typical spring day in Hong Kong, which is sufficient to satisfy the daily drinking needs of a person. By simultaneously addressing both the requirements of high-efficiency operation and facile fabrication, the graphene aerogel beads developed in this study may offer a viable solution for drinking water problems in water-stressed regions.