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Supporting Information

Novel Onion-Like Graphene Aerogel Beads for Efficient Solar Vapor Generation

under Non-concentrated Illumination

Xiaming Fenga, Jinliang Zhaoa, Dawei Suna,b, Logesh Shanmugama, Jang-Kyo Kima,

Jinglei Yanga,*

aDepartment of Mechanical and Aerospace Engineering, The Hong Kong University of

Science and Technology, Clear Water Bay, Kowloon, Hong Kong

bCollege of Materials Science and Engineering, Beijing University of Technology,

Beijing 100124, P.R. China

*Corresponding author.

Email address: maeyang@ust.hk; Fax: +852-2358 1543; Tel: +852-3469 2298

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A.This journal is © The Royal Society of Chemistry 2019

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Experimental

1. Materials

GO slurry (2.0 wt%, 0.2~10 μm) was purchased from Shanghai Ashine Technology

Development Co., Ltd., China. MoS2 (99.5%, <2μm) was provided by Shanghai

Aladdin Bio-Chem Technology Co., Ltd. Sodium hydroxide (≥98%), L-Ascorbic acid,

NaOH and polyethylenimine (branched, average Mw ~800) were bought from Sigma-

Aldrich. The real seawater was taken from the South China Sea near to HKUST.

2. Preparation of graphene aerogel beads

The preparation of graphene aerogel beads in this work is based on our previous

reports[1, 2]. In order to achieve the complete movement and rearrangement of GO

sheets in one droplet, thus forming the onion-like structure. we tried to reduce the

concentration of GO solution and make the extruding speed low enough (3mL/min) in

this work. Furthermore, in consideration of water treatment application of GO beads in

this work, the 1 wt% PEI solution was chosen as the coagulating bath, because which

can not introduce the foreign ions to GO beads compared to the CaCl2 and CTAB

solution. The detail preparation process is as following procedure. 0.2g MoS2

microflakes were firstly dispersed in 120 mL DI water to form a uniform dispersion

through simultaneously stirring and sonicating. After that, 80g GO slurry (1.0 wt%)

was mixed with MoS2 dispersion by mechanical stirring to form a hybrid solution. After

degasification, the GO/MoS2 hybrid solution was extruded into a polyethylenimine

coagulation bath (1.0 wt%) by a syringe (die diameter is about 2 mm) with the

assistance of a stepper motor (3.0 mL/min). The formed wet GO/MoS2 hybrid beads

were coagulated for one day and then washed by DI water no less than five times. After

that, the GO/MoS2 hybrid beads were reduced in 200 mL of sodium ascorbate solution

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(0.04 mol/L) at 90 oC for 24h. Finally, the RGO/MoS2 hybrid aerogel beads were

obtained after washing and drying. The drying process can be freeze drying, or directly

drying in the air after ethanol-water replacement. In parallel, the RGO aerogel beads

were prepared by the same procedure (0.5 wt% GO solution) without the addition of

MoS2 microflakes.

3. Characterization

Morphologies of aerogel beads were exmined by SEM (JSM-6390, JEOL). Raman

spectroscopy was performed on a Micro-Raman spectroscopy (InVia, Renishaw) with

excitation provided in back-scattering geometry by a 514.5 nm argon laser line.

Transmission electron microscopy (TEM) (JEM 100CXII, JEOL) was used to study the

micromorphology of GO. Thermographic images were taken by a Fluke Ti25 Thermal

Imager. Contact angle test was conducted on a contact angle meter (Attension Theta

Lite, Biolin Scientific). Mechanical performances of graphene aerogel beads were

characterized by a micro-compression device developed by Sottos et al38. Solar

intensity was tested by a solar power meter (ISM 410, ISO-TECH). The absorbance

spectra of samples were monitored through a UV-Vis-NIR spectrophotometer

(3700DUV, Shimadzu). The concentrations of the ions were tested by using Inductively

Coupled Plasma-Optical Emission Spectrometer (ICP-OES) (725-ES, Varian,

Australia).

4. Solar steam generation experiments

The seawater was held in a glass vessel, and the aerogel beads were self-floated on

the top of the water in different kinds and amount. The surface temperature was

monitored by a Fluke Ti25 Thermal Imager. The weight change of seawater was

recorded per unit time by an electronic mass balance (0.1 mg in accuracy). The

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illumination system was performed with a light source (MHAB-150W). The outdoor

experiment was carried out using a large-scale homemade device (0.05 m2 in active

area) with MoS2/RGO hybrid beads under natural sunlight for 10 hours (08:00−18:00,

20 March 2018, HKUST). The solar intensity was tested by a solar power meter (ISM

410, ISO-TECH).

5. Water collection efficiency

The collection efficiency was calculated according to the following equation.

𝜂𝑐𝑜𝑙𝑙𝑒𝑐𝑡𝑖𝑜𝑛 =𝑚𝑐𝑜𝑛𝑑ℎ𝐿𝑉

𝐴𝑒𝑣𝑎𝑝∫𝑞𝑠𝑜𝑙𝑎𝑟(𝑡)𝑑𝑡'

where ηcollection is the water collection efficiency, Aevap is the mass of condensate

collected daily, qsolar(t) is the time-dependent solar intensity, and the denominator is the

total daily solar energy.

Fig. S1. SEM image of MoS2 micro-flakes.

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Fig. S2. Digital photo of 1.0 wt% GO slurry (left) and TEM image of GO sheets

(right).

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Concentration of GO SEM image

1.5 wt%

1.0 wt%

0.5 wt%

X 25

X 35

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Lower concentration/higher nozzle-bath distance

Fig. S3. Effect of concentration of GO solution on the morphology of obtained GO

aerogel beads.

Fig. S4. SEM images of bottom view (left) and cross section (right) of graphene

aerogel beads.

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Fig. S5. SEM images of external surface of (a, b) RGO beads and (c, d) RGO/MoS2

hybrid beads taken at different magnifications.

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Fig. S6a. SEM image and the corresponding EDX elemental maps of external surface

of RGO/MoS2 hybrid bead.

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Fig. S6b. SEM image and the corresponding EDX elemental maps of inner surface of

RGO/MoS2 hybrid bead.

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Fig. S7. Raman spectra of MoS2, RGO beads and RGO/MoS2 hybrid beads.

Fig. S8. SEM images of inner structure (left) and external surface (right) of

RGO/MoS2 hybrid beads after steam generation experiments.

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Fig. S9. SEM image of inner structure of RGO/MoS2 hybrid beads after steam

generation experiment with washing in seawater.

Fig. S10. SEM image of inner structure of RGO/MoS2 hybrid beads after steam

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generation experiment without any washing process.

Fig. S11. Solar intensity (upper panel) and outdoor temperature curves (lower panel).

Fig. S12. Facile characterization of water purity by monitoring the electrical

resistance using a multimeter.

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References

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[2] Zhang, S., Zhao, K., Zhao, J., Liu, H., Chen, X., Yang, J., & Bao, C. (2018). Large-

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