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Flatband λ-Ti3O5 towards extraordinary solar steam generation

Nature volume 622, pages 499–506 (2023)Cite this article

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Abstract

Solar steam interfacial evaporation represents a promising strategy for seawater desalination and wastewater purification owing to its environmentally friendly character1,2,3. To improve the solar-to-steam generation, most previous efforts have focused on effectively harvesting solar energy over the full solar spectrum4,5,6,7. However, the importance of tuning joint densities of states in enhancing solar absorption of photothermal materials is less emphasized. Here we propose a route to greatly elevate joint densities of states by introducing a flat-band electronic structure. Our study reveals that metallic λ-Ti3O5 powders show a high solar absorptivity of 96.4% due to Ti–Ti dimer-induced flat bands around the Fermi level. By incorporating them into three-dimensional porous hydrogel-based evaporators with a conical cavity, an unprecedentedly high evaporation rate of roughly 6.09 kilograms per square metre per hour is achieved for 3.5 weight percent saline water under 1 sun of irradiation without salt precipitation. Fundamentally, the Ti–Ti dimers and U-shaped groove structure exposed on the λ-Ti3O5 surface facilitate the dissociation of adsorbed water molecules and benefit the interfacial water evaporation in the form of small clusters. The present work highlights the crucial roles of Ti–Ti dimer-induced flat bands in enchaining solar absorption and peculiar U-shaped grooves in promoting water dissociation, offering insights into access to cost-effective solar-to-steam generation.

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Fig. 1: Reflectivity spectra and electronic structures.
Fig. 2: 2D-SSE system and experimental results.
Fig. 3: Water adsorption and dissociation assisted by the λ-Ti3O5 \({\boldsymbol{(}}{\bf{1}}\bar{{\bf{1}}}{\bf{0}}{\boldsymbol{)}}\) surface.
Fig. 4: 3D solar steam evaporation system and experimental results.
Fig. 5: Water evaporation rate versus solar-to-steam efficiency for known 2D- and 3D-SSEs under 1 sun of irradiation.

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Data availability

Raw data that support the plots in this paper and other findings in the paper and the Supplementary Information are available from the corresponding author on request. Source data are provided with this paper.

Code availability

VASP is a source suite of computational tools available at www.vasp.at. The other codes written for use in this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We are grateful to N. Wang and H. L. Qu at Analytical and Testing Center, Northeastern University, for the photoluminescence measurements and to Y. N. Jiang at Analytical and Testing Center, Institute of Metal Research, Chinese Academy of Sciences for the thermal conductivity measurements. This work was supported by the Program of Introducing Talents of Discipline Innovation to Universities 2.0 (grant no. BP0719037), China.

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Authors and Affiliations

  1. Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang, China

    Bo Yang, Zhiming Zhang, Xiankai Fu, Ruolan Tang, Xiran Du, Wanqi Chen, Song Li, Haile Yan, Zongbin Li, Xiang Zhao, Gaowu Qin & Liang Zuo

  2. Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China

    Peitao Liu, Jiantao Wang, Yu Cao & Xing-Qiu Chen

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Contributions

B.Y., S.L., X.-Q.C., G.Q. and L.Z. conceived the idea and designed the experiments. Z.Z., R.T. and W.C. performed most of the experiments. P.L., J.W., Y.C., X.F. and H.Y. performed the first-principles calculations. Z.L., X.Z. and X.D. provided some help with the data analysis. B.Y., X.-Q.C., P.L. and L.Z. co-wrote the paper. All authors discussed the results, revised and approved the paper.

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Correspondence to Liang Zuo.

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Extended data figures and tables

Extended Data Fig. 1 Structural and morphological characterization, and hydrophilicity test of λ-Ti3O5.

a, Rietveld refinement of the experimental XRD pattern. b, Raman spectrum. c, SEM image. d, TEM bright-field image. e, High-resolution TEM image (Inset: the Fast-Fourier transformation of the dotted blue area). f, Contact angle test. More details are given in Supplementary Information 1.1 and 1.2.

Extended Data Fig. 2 Surface temperatures and heat capacities of TSOs.

a, Surface temperature variations of TSO pills (~2 mm in thickness) and blank PE foam (18 mm in thickness) under one sun irradiation (left panel) and infrared photographs taken at the irradiation time of 900 s (right panel). b, Specific heat capacities of TSOs at different temperatures. More details are given in Supplementary Information 2.3.

Extended Data Fig. 3 Experimental photoluminescence (PL) spectra of λ-Ti3O5 and rutile-TiO2 at room temperature (excitation light: 344 nm, emission lights: 360–2250 nm).

a, 360–800 nm. b, 800–1600 nm. c, 1200–2250 nm. More details are given in Supplementary Information 2.4.

Extended Data Fig. 4 Schematic of the solar-to-heat conversion in λ-Ti3O5.

a, Intraband optical transition and electron/hole-phonon (e-ph/h-ph) interactions in the NIR region. b, Interband optical transition, electron-electron (e-e) scattering and e-ph/h-ph interactions in the UV-Vis region. Note that the e-e scattering and e-ph interactions in b may exchange during the relaxation of excited hot electrons, as indicated by dotted line with double arrows. More details are given in Supplementary Information 2.5.

Extended Data Fig. 5 Raman spectra of bulk water and interfacial water on 2D λ-Ti3O5 evaporator in the energy range of O-H stretching modes.

a, Bulk water. b, interfacial water on 2D λ-Ti3O5 evaporator. More details are given in Supplementary Information 4.7.

Extended Data Fig. 6 Water mass changes (left column) and mean measured water evaporation rates (right column) of PVA hydrogel-based 3D-SSEs (15 mm in diameter).

a-b, 3D-SSEs (7 mm in effective height) with or without an addition of 6 wt% TSO powders. c-d, 3D-SSEs (6 wt% λ-Ti3O5 powders) with different effective height. e-f, 3D-SSEs (20 mm in effective height) with a conical cavity (14 mm in diameter and 6 mm in depth) and different weight percentage of λ-Ti3O5 powders. More details are given in Supplementary Information 5.2. The error bars in b, d, f are the standard deviations of the mean (n = 3, n is the number of evaporation rates for each sample used to derive statistics).

Extended Data Fig. 7 Outdoor desalination performance of cylindrical 3D-SSEs with a conical cavity under natural sunlight irradiation.

a, Conceptual design and photographs of the solar water desalination system for salty water purification. b, Variations of the solar flux, water collection rate and yield of purified water with day time. c, Variations of the temperature and humidity (inside and outside the solar water desalination system) with day time. d, Average daily solar fluxes and water collection rates for a duration of 10 h on three cloudy days and four sunny days. More details are given in Supplementary Information 5.5.

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Yang, B., Zhang, Z., Liu, P. et al. Flatband λ-Ti3O5 towards extraordinary solar steam generation. Nature 622, 499–506 (2023). https://doi.org/10.1038/s41586-023-06509-3

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