Scalable, eco-friendly and ultrafast solar steam generators based on one-step melamine-derived carbon sponges toward water purification

Solar steam generation can be a practical and sustainable technology for wastewater purification and seawater desalination. However, both the inefficient utilization of solar energy and high complicity/cost of current solar steam generators hinder the scalable application of this technique. Herein, we demonstrate a facile, scalable and low-cost approach to produce highly-efficient solar steam generator via a one-step calcination of commercial melamine sponges (MS) in air. The in-air calcinated MS (AMS) with thermal insulator achieves an ultrafast solar evaporation rate (1.98 kg m−2 h−1) and a high photothermal efficiency (~92%) under one sun illumination (1 kW m−2), superior to most reported values. This high solar evaporation rate is attributed to the effective heat localization and adequate water supply in AMS, caused by the low bulk thermal conductivity, high porosity and hydrophilicity of AMS, as well as the set-up of a thermal insulator. The AMS is found to be highly efficient and stable, and it can be used to purify various types of waste water, including river water, seawater, and strong acid/alkaline water. Performance analysis of a large-scale prototype device based on the AMS design for field tests promises significant opportunities for highly-efficient, reusable, portable and low-cost water purification systems.