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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: [email protected] (H. Jiang),
[email protected] (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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