Biomass hydrogels combined with carbon nanotubes for water purification via efficient and continuous solar-driven steam generation

Solar vapor generation is a promising, environmentally friendly solution for water purification. The development and design of new materials and supporting devices for efficient energy conversion and clean water production are essential for the practical application of solar-driven desalination and water purification. In this study, an environmentally friendly and economical biomass hydrogel-based solar evaporator with a controllable shape was developed in a simple method by integrating carbon nanotubes (CNTs) into a sodium alginate (SA) hydrogel network. The evaporator had a high solar absorption rate (94.3%) and satisfactory hydrophilicity and could effectively avoid salt crystallization during the desalination process. This study took advantage of the aforementioned merits, and a high evaporation rate of 1.699 kg m-2 h-1 and a conversion efficiency of 86% were achieved under 1.0 sun irradiation. The evaporator could efficiently remove Na+, K+, Ca2+, and Mg2+ from seawater with a removal rate of up to 99.3% and a good decolorization effect on methylene blue (MB) and methyl orange (MO) dye wastewater, whose colour could be completely removed. This study provides a simple, practical, and economical method to prepare hydrogel-based evaporators that utilize abundant solar energy for large-scale desalination and wastewater treatment.