Supporting Information

Water Desalination under One Sun Using Graphene-based Material

Modified PTFE Membrane

Lu Huang, Junxian Pei, Haifeng Jiang*, and Xuejiao Hu*

Key Laboratory of Hydraulic Machinery Transients (Wuhan University), Ministry of

Education, School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei

430072, China

*Corresponding authors. E-mail addresses: hfjiang@whu.edu.cn (H. Jiang),

xjhu@whu.edu.cn (X. Hu).

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Table of contents

SI-1 Mechanical performance of the composite films……..………………………….3

SI-2 Evaporation efficiency calculation and analysis of Heat Loss…….……..………3

SI-3 Comparison of the evaporation performance between pDA-rGO membrane and

several reported photothermal membrane for solar desalination…………….………..5

SI-4 The specifications of all used chemicals…………………………………………6

SI-Video 1…………………………………………………………………………..…6

References………………………………………………………….………………….7

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SI-1 Mechanical performance of the composite films

To evaluate the mechanical features of our composite membranes, the rGO/PTFE film

is continuously folded over 30 times. As shown in Fig. S1, the film can retain the

excellent mechanical integrity without causing notable damages.

SI-2 Evaporation efficiency calculation and analysis of Heat Loss

The solar energy conversion efficiency was calculated by the following equation:

ηeva=m hLV

I (S1)

Where ηeva is the evaporation efficiency, ṁ represents the stable evaporation rates

under one-sun irradiation (kg m-2 h-1), hLV is the total enthalpy of sensible heat and the

liquid-vapor phase change (kJ kg-1). I represents the power density of solar irradiation

(kW m-2). In our work, I is 1 kW m-2.

Based on the Eq. S1, the corresponding conversion efficiencies of the pure water,

GO, rGO and pDA-rGO are 27.3%, 35.1%, 44.9 %and 49.0%, respectively.

Analysis of Heat Loss

The energy consumption of the absorber mainly originates from: (1) reflection and

absorption energy loss from pDA-rGO membrane, PMMA, and water, (2) conduction

heat loss from the pDA-rGO membrane to water, (3) radiation and (4) convection heat

loss from the pDA-rGO membrane to air environment.

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Fig. S1. (a) The optical image of a folded rGO/PTFE film. (b) The optical image of an unfolded rGO/PTFE film after folding over 30 times.

(b)(a)

(1) Reflection and absorption energy loss

The measured average reflection rate of the pDA-rGO membrane over the whole solar

spectrum (300-2500 nm) is 15.1%. The average reflection and absorption rate of

water and PMMA on top of the absorber is about 10%.

(2) Conduction heat loss

The conduction heat energy loss Qcond can be calculated by the following equation:

Qcond=Cm∆T (S2)

Where C is the specific heat capacity of water (4.2 kJ kg‒1 oC‒1), m is the weight of

water (4 g) in the test system, and ΔT (~12 oC under 1 kW m–2 solar irradiation)

represents the temperature variation of water before and after stable solar steam

generation after one hour. Based on Eq. S2, we can calculate that the conduction heat

loss of the system accounts for ∼5% of the input energy.

(3) Radiation heat loss

The radiation flux Φrad follows the Stefan-Boltzmann law:

Φrad=εAσ(Tfilm4 – Tenv

4) (S3)

Where ε and σ are the emissivity and Stefan-Boltzmann constant, A is the film surface

area (12.56 cm2). It is assumed that the emissivity of the absorber surface is 1. Tfilm and

Tenv represent the stabilized surface temperature of membrane under solar irradiation

and ambient temperature (29 oC). Under 1 kW m–2 solar irradiation, the Tfilm is

measured to be 42 oC. Based on Eq. S3, we can calculate that the radiation heat loss of

the system accounts for ∼8.6% of the input energy.

(4) Convection heat loss

The convection heat loss Qconv is caused by the air flowing and it follows the Newton’s

law of cooling:

Qconv = hA∆T (S4)

Where h is convection heat transfer coefficient [5 W m-2 K-1], A is the membrane

surface area (12.56 cm2), and ΔT is the difference between the absorber and ambient

temperature (~13 oC under 1 kW m–2 solar irradiation). Based on Eq. S4, we can

calculate that the convection heat loss of the syetem accounts for ∼6.5% of the input

energy.

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Therefore, in addition to the solar energy used for evaporation (ηeva=49%),

reflection and absorption loss (25.1%), the main heat losses including conduction,

radiation and convection are calculated to be ~20.1%. Apart from the above

mentioned energy loss, a small amount of water evaporation and condensation also

exists inside the evaporating chamber wall, which account for ~6% energy

consumption.

SI-3 Comparison of the evaporation performance between pDA-rGO membrane

and several reported photothermal membrane for solar desalination.

Table S1 Comparison of photothermal layers from different studies.

Photothermal Materials

Power density

（kW m-2）Absorption

(%)

Evaporation

Efficiency (%)Ref.

Exfoliated graphite

and Carbon foam1 ＞99 53 S1

Black gold film

and micropore tape20 91 57 S2

Wood-Graphene

Oxide Composite12 － 83 S3

Carbon black NPs

and polyvinyl

alcohol fiber coating

0.7 － 53.8 S4

Carbon black NPs

on a hydrophobic

PVDF membrane

1.3 － 40-74.6 S5

Porous polymer

skeleton embedded

graphite flakes and

carbon fibers

1 >97 62.7 S6

Black TiOx and SS 1 91.3 50.3 S7

5

mesh

PDA-rGO modified

hydrophobic PTFE

membrane

1 84.9 49This

work

Notes: References S4 and S5 were similar to our photothermal membrane distillation

study.

SI-4 The specifications of all used chemicals

Table S2 The specifications of all used chemicals in our paper

Chemical name Chemical formula specification

Sodium nitrate NaNO3 ≥99% AR

Sodium chloride NaCl ≥99.5%AR

Concentrated sulfuric H2SO4 ≥98% AR

Potassium permanganate KMnO4 AR

Hydrogen peroxide H2O2 AR

Cyclohexanone C6H10O ≥99.5％ AR

Dopamine hydrochloride C8H11NO2.HCl ≥98% AR

Tris(hydroxymethyl)

aminomethaneNH2C(CH2OH)3 ≥99.5% AR

Hydriodic acid HI 55-58%

Notes: the all used chemicals are from Sinopharm Chemical Reagent Co., Ltd.

SI-Video 1 A short video of condensed water collection in a typical experiment.

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