S1

Supporting Information

Flexible Salt-Rejecting Photothermal Paper Based on Reduced Graphene Oxide and

Hydroxyapatite Nanowires for High-Efficiency Solar Energy-Driven Vapor Generation

and Stable Desalination

Zhi-Chao Xiong,†,‡ Ying-Jie Zhu,*,†,‡ Dong-Dong Qin,†,‡ and Ri-Long Yang†,‡

† State Key Laboratory of High Performance Ceramics and Superfine Microstructure,

Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, P. R. China

‡ Center of Materials Science and Optoelectronics Engineering, University of Chinese

Academy of Sciences, Beijing 100049, P. R. China

*Corresponding author (Ying-Jie Zhu).

E-mail: y.j.zhu@mail.sic.ac.cn. Tel: 0086-21-52412616. Fax: 0086-21-52413122.

S2

Figure S1. Digital images of the testing device for solar energy-driven vapor generation.

S3

Figure S2. Digital images of aqueous suspensions. (a) Ultralong hydroxyapatite nanowires

(HNs); (b) graphene oxide (GO); (c) GO/HN nanocomposite.

S4

Figure S3. (a–d) Digital images of the fabrication process of the GO/HN paper with a

diameter of 20 cm using a commercial paper sheet former by the vacuum-assisted filtration

method, and a free-standing GO/HN paper is obtained after drying at 95 oC for 10 min.

S5

Figure S4. Digital images and SEM images of the GO and rGO membranes. (a) A the

vacuum-assisted filter for preparing the GO membrane; (b) the as-prepared GO membrane on

a filter paper; (c, d) the surface and cross-section SEM micrographs of the GO membrane; (e,

f) the surface and cross-section SEM micrographs of the rGO membrane.

S6

Figure S5. (a, b) TEM micrographs of the as-prepared HNs; (c, d) the surface and cross-

section SEM micrographs of the HN paper containing 20 wt.% glass fibers.

S7

Figure S6. XRD patterns of HNs, GO/HN, and hydroxyapatite (JCPDS No. 09–0432).

S8

Figure S7. SEM micrographs: (a, b) glass fibers; (c, d) the surface SEM images of the

GO/HN paper containing 18 wt.% glass fibers.

S9

Figure S8. TEM micrograph of GO nanosheets.

S10

Figure S9. Mechanical properties of the HN paper, GO/HN paper, rGO/HN-I photothermal

paper, and rGO/HN-II photothermal paper. (a) Stress-strain curves; (b) ultimate tensile

strength; (c) strain at failure.

S11

Figure S10. FTIR spectra of ultralong hydroxyapatite nanowires (black curve) and GO/HN

paper (red curve).

S12

Figure S11. XPS patterns of the GO/HN paper (black curve), rGO/HN-I paper (red curve),

and rGO/HN-II paper (blue curve).

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Figure S12. FTIR spectra of GO (black curve), rGO obtained after thermal treatment of GO

at 150 oC for 2 h (rGO-I, red curve), and rGO obtained after thermal treatment of GO at 150

oC for 6 h (rGO-II, blue curve).

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Figure S13. Surface and cross-section SEM images of the rGO/HN photothermal paper. (a–c)

The rGO/HN-I photothermal paper; (d–f) the rGO/HN-II photothermal paper.

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Figure S14. (a–d) Digital images of the wetting process of the rGO/HN-I photothermal paper

in contact with a wet air-laid paper for different times, the top surface of the rGO/HN-I paper

can be wetted rapidly by water. (e–g) Digital images of the rGO/HN-II photothermal paper in

contact with a wet air-laid paper for different times, the top surface of the rGO/HN-II paper

cannot be wetted by water. (h) Digital image of the bottom surface of the rGO/HN-II paper

after being in contact with a wet air-laid paper for 5 min, water drops can adhere to the bottom

surface of the rGO/HN-II paper.

S16

Figure S15. Atomic force microscopy (AFM) images. (a) The GO/HN paper; (b) the

rGO/HN-I photothermal paper; (c) the rGO/HN-II photothermal paper. The corresponding

surface roughness value is measured to be 57.3, 52.0, and 58.5 nm, respectively.

S17

Figure S16. IR thermal images of paper samples over time under one sun illumination in air

for 600 s. (a) The HN paper; (b) the GO/HN paper; (c) the rGO/HN-I photothermal paper; (d)

the rGO/HN-II photothermal paper.

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Figure S17. IR thermal images of paper samples over time during the water evaporation

process under one sun illumination. (a) The HN paper; (b) the GO/HN paper; and (c) the

rGO/HN-II photothermal paper.

S19

Figure S18. Cumulative mass change of water in the presence of the rGO/HN-I photothermal

paper sheets with different rGO contents versus solar light irradiation time under one sun

illumination.

S20

Figure S19. (a–c) UV-vis absorption spectra and (d) corresponding digital images of aqueous

solution of congo red, rose bengale, and brilliant green, and the collected water after solar

energy-driven water purification.

S21

Figure S20. (a) Concentrations, (b) rejection percentages and (c) corresponding digital

images of aqueous solution containing Fe3+, Cu2+, and Ni2+ ions, and the collected water after

solar energy-driven water purification.

S22

Figure S21. Digital images and SEM micrographs of the rGO/HN-II photothermal paper

before (a) and after (b) continuous solar energy-driven desalination of the actual seawater

sample for 20 days (8 h light irradiation each day) under one sun illumination.

S23

Table S1. Calculation results of energy conversion efficiency under one sun illumination

[R1] Dortmund Data Bank Software & Separation Technology, DDBST GmbH, Oldenburg

2016.

Materials m (kg m-2 h-1) hLV (kJ kg-1) [R1] η (%)

HN paper 0.36 2340 15.6

GO/HN paper 1.29 2352 76.5

rGO/HN-I paper 1.48 2361 89.2

rGO/HN-II paper 1.25 2358 74.1

S24

Table S2. Comparison of solar vapor generation performance of some previously reported

photothermal materials and the rGO/HN photothermal paper under one sun illumination

Materials Evaporation rate

(kg m-2 h-1)

Energy

efficiency (%)

Reference Year

Graphene oxide membrane 1.45 80 S1 2016

Reduced graphene oxide-sodium alginate-

carbon nanotube aerogel

1.622 83 S2 2017

Carbonized mushrooms 1.475 78 S3 2017

Plasmonic Wood 1.1 67 S4 2017

3D printed porous carbon black/graphene oxide

composite

1.27 87.5 S5 2017

Graphene oxide/SBA-15 1.31 83 S6 2017

Three-dimensional gold nanoflower gel 1.356 85.6 S7 2018

Graphite-coated wood 1.15 80 S8 2018

Carbon black/ polymethylmethacrylate/

polyacrylonitrile membrane

1.3 72 S9 2018

3D graphene foam 1.3 87 S10 2018

Geopolymer-biomass mesoporous carbon

composite

1.58 84.95 S11 2018

Reduced graphene oxide-wrapped plant fiber

sponges

1.375 88.8 S12 2018

Carbonized moldy bread 0.96 71.4 S13 2018

Reduced graphene oxide-multi-walled carbon

nanotubes composite membrane

1.22 80.4 S14 2018

Hollow carbon nanotubes aerogel 1.44 86.8 S15 2019

Three dimensional MXene architecture 1.41 88.7 S16 2019

Nitrogen-doped hydrophilic graphene

nanopetals with hydrophobic graphene foam

1.27 88.6 S17 2019

Biomimetic MXene textures 1.37 90.1 S18 2019

Wood-polypyrrole composite 1.27 88.6 S19 2019

Vertically aligned Janus MXene aerogel 1.46 87 S20 2019

Reduced graphene oxide/hydroxyapatite

nanowires photothermal paper 1.48 89.2 This work

S25

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