Polydopamine-Coated Natural Rubber Sponge for Highly Efficient Vapor Generation

The global water crisis is becoming more and more serious, and solar steam generation has recently been investigated for clean water production and wastewater treatment. However, the efficiency of solar vapor transfer is still low. It is a great challenge to find photothermal materials which simultaneously have high energy transfer efficiency, facile production, and are low cost. To address this, we propose a method which is simple, low cost and suitable for large-scale preparation to fabricate the photothermal materials based on using recycled natural rubber sponge (NRS) coated with polydopamine (PDA). X-ray photoelectron spectroscopy analysis confirmed that when the PDA coated the surface of the NRS, the hydrophilicity of the sponge was significantly improved. Scanning electron microscopy characterization showed that the PDA-coated natural rubber sponge (PNRS) maintained the porous 3D skeleton of the pristine sponge. As a result, PNRS exhibits excellent photothermal properties, a very high evaporation rate of 1.35 kg m^-2 h^-1, and an energy transfer efficiency of 84.6% can be achieved under a light intensity of 1 sun (1 kW m^-2). It is worth noting that the vapor generation of PNRS is still at a high level with 1.06 and 1.09 kg m^-2 h^-1 in the corrosive liquids of 1 M H₂SO₄ and 0.5 M NaOH, respectively. The photothermal materials based on using recycled NRS have good application prospects in seawater desalination and the purification of wastewater, which also provides a new method for the recycling of waste NRS.