Nowadays, the serious resource shortage and environmental polluting issues have attracted tremendous attention worldwide. Renewable energy such as hydroenergy, wind energy and solar energy, has been in high demanded and emerged as promising substitutions of fossil fuel. Among them, solar irradiation is the most valuable energy source in the near future, which is abundant and naturally unlimited. Researchers have devoted to seek methods to efficiently utilize solar energy and practically applied in various areas. Solar evaporation is an attractive strategy to utilize solar energy for distillation without consuming fossil fuels. Recently, different solar absorbers based on diverse materials have been extensively studied to transfer solar energy into heat for vapor generation, such as gold nanoparticles and carbon-based bilayer structures.^{[1], [2]} However, most of the absorbers are fabricated complexly with extra cost, which limits their large-scale application.

In this work, the black polyurethane (PU) sponge with three dimensional porous structures was demonstrated as the solar light absorber for heat localization. The black PU sponge can be recycled from the used packaging materials, which are usually abandoned after utilization and difficult to decompose naturally. Every year, the production of black PU sponge as the packaging materials is numerous. Recycling and reusing the PU sponge contributes to sustainable development. Here, the PU sponge provides porous channels for fluent water supply, low thermal conductivity for heat localization and low intensity to create surface evaporation. A simple hydrophilic treatment of this PU sponge was applied to improve the wettability by being stirred in dopamine solution. An evaporation efficient of 52.2%, which is more than 3 times higher than natural evaporation process, was achieved by this modified sponge in a relatively simple and low cost method. Furthermore, it provides a new idea to reutilize the waste materials for solar energy conversion.

Acknowledgements

This work is financially supported by the Research Grants Council of Hong Kong, China (Project Number: GRF 152109/16E PolyU B-Q52T).

Reference

[1] Neumann, Oara, et al. "Solar vapor generation enabled by nanoparticles." Acs Nano 7.1 (2012): 42-49.

[2] Jiang, Qisheng, et al. "Bilayered Biofoam for Highly Efficient Solar Steam Generation." Advanced Materials 28.42 (2016): 9400-9407.