Solar evaporation is considered a promising technology to address the issue of fresh water scarcity. Although many efforts have been directed towards increasing the solar-thermal conversion efficiency, there remain challenges to develop efficient and cost-effective solar-thermal materials from readily available raw materials. Furthermore, further structural modification of the original biomass structure, particularly at multiple length scales, are seldom reported, which may further improve the solar-thermal performance of these material systems. Herein, a novel low-cost system is developed based on a common bio-waste, pomelo peels (PPs), through a bioinspired fractal structural design strategy, fractal carbonized pomelo peels (FCPP). This FCPP system shows an extremely high solar spectrum absorption of ≈98%, and marvelous evaporation rate of 1.95 kg m −2 h −1 with a solar-thermal efficiency of 92.4%. In addition, the mechanisms of the evaporation enhancement by fractal structural design are identified by numerical and experimental methods. Moreover, using FCPP in solar desalination shows great superiority in terms of cost and its potential in sewage treatment is also studied. The present work is an insightful attempt on providing a novel proposal to develop bio-waste-derived solar-thermal materials and construct biomimetic structures for efficient solar evaporation and applications.

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Solar-driven interfacial evaporation system is attracting intensive attention for harvesting clean water in the utilization of solar energy. To improve solar-driven interfacial evaporation performance for better application, structuring a solar absorber with high solar–thermal conversion efficiency is critical. Semiconductor materials with stable and economic properties are good candidates as solar absorbers. Semiconductors with a narrow band gap have been proved to offer a broad solar absorption spectrum in the applications of photoelectricity and photocatalysis. However, the correlation between band gap and solar-driven interfacial evaporation performance has not been systematically studied. Herein, TiO2 is selected as a semiconductive absorber and a reproducible process is developed to fabricate band gap engineered TiO2 to understand the relationship between the “electronic structure” and the “performance” in the field of solar-driven interfacial evaporation. After the band gap engineering from 3.2 to 2.23 eV, correlative tests of solar-driven interfacial evaporation performance as well as first-principles calculations are employed to study the correlation mentioned above. As a result, we find that a narrower band gap contributes to improved solar–thermal conversion efficiency and the Ti3+-doped TiO2 (Ti3+-TiO2) with the narrowest band gap of 2.23 eV outperforms other samples, achieving the highest evaporation rate of 1.20 kg m–2 h–1 (solar–thermal conversion efficiency of 77.1%). Besides, the Ti3+-TiO2 also shows the good ability of photocatalytic degradation. This work may provide a way for semiconductor materials to be designed as solar absorbers with higher solar–thermal conversion efficiency and better solar-driven interfacial evaporation performance for applications in clean water harvesting.

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