Supporting information

Wood-polypyrrole composite as photothermal conversion device for solar

evaporation enhancement

Zhe Wang,1 Yutao Yan,1 Xiaoping Shen,1 Chunde Jin,1 Qingfeng Sun,*,1 and Huiqiao

Li*,2,3

1. School of Engineering, Zhejiang A & F University, Hangzhou, 311300, P. R. China

2. State Key Laboratory of Material Processing and Die & Mould Technology, School

of Materials Science and Engineering, Huazhong University of Science and

Technology (HUST), Wuhan, 430074, P. R. China

3. Shenzhen Research Institute of Huazhong University of Science and Technology,

Shenzhen, 518000, P. R. China

*Corresponding author E-mail: qfsun@zafu.edu.cn (Qingfeng Sun); hqli@hust.edu.cn

(Huiqiao Li)

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

Figure S1. Morphology and microstructure of raw wood. (a) Photo image of raw wood. (b-d) Cross section SEM images under different amplification.

Figure S2. TEM images of PPy under different amplification.

Figure S3. Water contact angles of wood transection and wood transection decorated with PPy coating.

Figure S4. The wetting process images of wood substrate.

Figure S5. Light energy absorption of the natural wood and PPy coated wood.

Figure S6. Thermal conductivities of the natural wood and PPy coated wood.

Figure S7. Evaporation rate and efficiency of the PPy coated wood after different cycles of usage (a) and long-term storage (b).

Figure S8. Photos of the homemade solar steam collection system.

Figure S9. The weights of sample without the collected water via solar steam collection system (a) and with the collected water via solar steam collection system under 1 sun for 3 h.

Table S1. Assignment of the main absorption peaks of wood.

Absorption peak (cm-1) Assignment

3424 O–H stretching

2924 C–H stretching

1735 C=O stretching

1637 C=O stretching

1506 Aromatic skeletal vibration

1371 O–H bending

1240 CO–OR stretching

1160 C–O anti-symmetric stretching

1032 C–O stretching

Table S2. Solar steam generation performance of PPy-wood compared with other materials.

SamplePower density

(kW m-2)

Efficiency

(%)Ref

Functionalized graphene 1 48 1

CuFeSe2 decorated wood 1 67.7 2

Carbonized poplar wood 10 <70 3

Graphene aerogel 1 53.6±2.5 4

rGO/PEI/mixed cellulose esters 1 60 5

Exfoliated graphite coated carbon

foam1 64 6

CNT decorated flexible wood 1 65 7

Bilayer wood with carbonized surface 1 57.3 8

PPy coated stainless steel mesh 1 ≈58 9

Carbon black/PMMA/PAN 1 51 10

Plasmonic wood 1 ≈67 11

Au/NPT 1 ≈64 12

rGO/PU nanocomposite foam 1 65 13

Dopamine covered PU sponges 1 52.2 14

PPy-wood 1 72.5 This work

Table S3. The main cationic concentrations (mg L-1) of the seawater and desalted water.Ions Na+ Mg2+ K+ Ca2+

Seawater 10545.92 1028.55 480.26 411.50Desalted water 1.09 0.43 1.65 0.83

Section 1. Bulk densities and porosities

The bulk densities and porosities measurements have been carried out on raw wood and

PPy-wood. The bulk densities of raw wood and PPy-wood were calculated using the

following formula15,16:

（1）𝜌 =

𝑚𝑉

where m and V are the weight and volume of the raw wood and PPy-wood, respectively.

The bulk densities of the raw wood and PPy-wood were 0.077g cm-3 and 0.085 g cm-3

according to the above formula.

The porosity was calculated using the following equation:

（2）𝑝𝑜𝑟𝑜𝑠𝑖𝑡𝑦 (%) = (1 ‒

𝜌𝜌𝑠

) × 100

where ρ and ρs are the volumetric mass densities of the wood (or PPy-wood) and

corresponding solid scaffold (wood cell wall and PPy treated wood cell wall) ,

respectively.

Considering that the PPy treated material can be regarded as a composite of wood and

PPy, its density was calculated according to the following equation:

（3）

𝜌𝑠 = 1

𝜔𝑤𝑜𝑜𝑑

𝜌𝑤𝑜𝑜𝑑+

𝜔𝑃𝑃𝑦

𝜌𝑃𝑃𝑦

= 1

1 ‒ 𝜔𝑃𝑃𝑦

𝜌𝑤𝑜𝑜𝑑+

𝜔𝑃𝑃𝑦

𝜌𝑃𝑃𝑦

where ωwood is the weight fraction of wood in the PPy-wood and ωPPy is the weight

fraction of PPy. ρwood was fixed at 1.5 g cm-3 based on literature data15,16 and ρPPy at 1.2

g cm-3 according to the data measured in this study. ωPPy was estimated as follows:

（4）𝜔𝑃𝑃𝑦 =

𝑚𝑃𝑃𝑦 ‒ 𝑤𝑜𝑜𝑑 ‒ 𝑚𝑤𝑜𝑜𝑑

𝑚𝑃𝑃𝑦 ‒ 𝑤𝑜𝑜𝑑 × 100

where mPPy-wood and mwood are the dry weights of the PPy-wood and raw wood,

respectively.

According to formula (2) and (3), the raw wood porosity was calculated: (1-

0.077/1.5)×100, the obtained result was 94.87%.According to formula (2), (3) and (4), the PPy-wood porosity was calculated: (1-0.085/1.45)×100, the obtained result was 94.14%.

Section 2. Steady-state energy balance analysisThe energy loss of the evaporation system has been calculated. The energy loss of the

evaporation system mainly involves radiation loss, convection loss and conduction

loss.7,17

The energy loss of the solar evaporation system under illumination is composed of 1)

radiation loss Prad, 2) convection loss Pconv and 3) conduction loss Pcond, detailed energy

loss analysis was performed as following calculations.

Radiation:

The radiation flux Prad can be calculated by Stefan-Boltzmann law.Prad=εAσ(T1

4-T24) (5)

Where Prad denotes radiation heat flux, ε is the emissive rate (It is assumed that the

absorber has a maximum emissivity of 1.00), A is the surface area, σ is the Stefan-

Boltzmann constant (assumed to be 5.67 × 10−8 W m-2 K-4), T1 is the average

temperature of the absorber(~41°C), and T2 is the ambient temperature (~35°C). As a

result, the radiation heat flux is estimated to be 41 W/m2, and the radiation loss rate is

about 4.1%.

Convection:

The convection loss Pconv can be calculated by Newton's law of cooling.Pconv=h(T1-T2) (6)where Pconv denotes convection heat flux, h is the convection heat transfer coefficient

(assumed to be 10 W m-2 K−1). Here, the convection heat is estimated as ≈ 60 W/m2,

and the convection loss rate is about 6%.

Conduction:

Conduction loss Pcond is based on Fourier's law.Pcond=Cm△T (7)Where C is the specific heat capacity of water (4.2 J °C-1 g-1), m denotes the weight of bulk water and ΔT represents the increased temperature of the bulk water after stable steam generation. In this work, m = 35 g, ΔT = 2.5 °C. Thus, the conductive loss is about 145 W m-2 and the conductive heat loss rate is about 14.5 %.

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