Supporting Information for

An all-in-one strategy for the adsorption of heavy metal ions and

photodegradation of organic pollutants using steel slag-derived

calcium silicate hydrate

Ningning Shao a, Shun Li a, Feng Yan a, Yiping Su a, Fei Liu a, Zuotai Zhang *a ,b

a. Guangdong Provincial Key Laboratory of Soil and Groundwater Pollution

Control, School of Environmental Science and Engineering, Southern University

of Science and Technology, Shenzhen 518055, P.R. China

b. Key Laboratory of Municipal Solid Waste Recycling Technology and

Management of Shenzhen City, Shenzhen 518055, P.R. China

*Corresponding author:

Email: zhangzt@sustc.edu.cn; Tel: 86-0755-88018019

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1.1 Reactive species trapping test

The reactive species generated during the photocatalytic reaction were detected

through a trapping test by EDTA-2Na, IPA, and BQ, which were introduced as

scavengers to detect holes (h+), hydroxyl radicals (·OH), and superoxide radicals

(·O2-), respectively. The trapping tests were conducted under the same conditions as

the photocatalytic degradation of MB, and 1 mM of all these scavengers was added to

the photocatalytic systems.

1.2 Estimation for the operational cost

To estimate the total operational cost of the purification of effluent with the

integrated technique in this study, we made the following calculations:

1) Given conditions for the estimation

As actual conditions are quite different from that in lab and the price level is also

different in different nations and areas. So, we should give special conditions for the

estimation of the operation cost, which are as follows:

a) On the basis of the price level of China (details are shown in Table 1);

b) On the basis of a medium-sized sewage treatment plant with the sewage

treatment ability of 50,000 cubic meters of wastewater [1];

c) The target effluent contains common Cu2+ and methylene blue (MB) in general

concentrations (10 mg/L Cu2+ + 10 mg/L MB) [2];

d) According to our market survey on the operational situation of sewages

treatment plants (STP) in China, the total number of the employees in a STP with

sewage treatment ability of 50,000 m3/day is about 50, and the average wages for a

worker is about 25 US $ / day. So, we estimated the manpower cost to be: (50×25) /

50,000 = 0.025 $ / m3 effluent.

2) Calculation formula

The operational cost was estimated with the follow calculation formula:

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CT = (Cm + Ctf + Ce + Cmp)

Where CT refers to the total operational cost, and Cm, Ctf, Ce, Cmp refer to the cost

of CSH manufacturing, transport, electric charge, and manpower cost, respectively.

3) Detailed calculation tables

Table 1 The price level of energy and resources in China

Item steel slag sodium silicate NaOH electric transportprice/ US $ 0/t 131-175/t 436-727/t 0.145/kW·h 14.5/(t/100 Km)

Notes: a) Steel slag is one of the high-volume solid wastes in China, the price is

almost 0. In some areas, factories can even receive some subsidy from the

government for the disposal of steel slag; b) For commercial manufacturing, the price

of the raw materials comes from materials of industrial level, for instance, the price of

sodium silicate is that of industrial sodium water glass.

Table 2 Manufacturing cost for the synthesis of CSH

Item steel slag sodium silicate NaOHprice / US $ 0 / t 131-175 / t 436-727 / tdosage / g 5 10 6.8cost / $ 0 0.00131-0.00175 0.0029-0.0049CSH output / g 6-7 g (based on our experiment)CSH manufacturing cost / $/g 0.0006-0.0011

Table 3 Details for the estimation of the total operational cost

Item Cm Ctf Ce Cmp

Price / $0.0006-0.0011/ g

14.5 / t /100Km

0.2-0.3 kW·h / m3

sewage25 US $ /

person, dayCost / m3

sewage0.018-0.033 0.00044 0.029-0.0435 0.025

Total cost (CT)/ $ / m3 sewage

0.08-0.10

Notes: a) For the estimation of Cm, we took advantage of our study in lab, in which

the CSH dosage is 20 mg for 40 ml of wastewater (10-30 mg/L heavy metal ions + 20

mg/L MB). Thus, in this estimation, the CSH dosage is estimated to be 300g / m3

sewage (10 mg/L Cu2+ + 10 mg/L MB). b) Cm is estimated on the basis that CSH-M

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could be reused for 10 times; c) Ct contains the cost for the transport of steel slag and

CSH, and the total distance was valued to be 100 km.

Therefore, after the above analysis, the total cost for the purification of target

effluent (10 mg/L Cu2+ + 10 mg/L MB) is calculated to be only 0.0797-0.102 $ / m3

effluent.

1.3 Quality assurance and quality control of experiments

For the heavy metals adsorption experiment, ICP-MS was employed to measure

the concentration of residual heavy metal ions in solutions after CSH adsorption. The

detection limit of ICP-MS was 0.1 ppb (g/L). The quality assurance and control

procedures were implemented by the analysis of blank control (BC) and standard

reference control (SRC, from Agilent Tech.). BC was employed for the analysis of the

sample contamination during the whole experiment, and SRC with different

concentrations (20, 50, 200, 500, 1000 g/L) were used for the estimation of the

accuracy of the method. Treatment for BC and SRC were same with real samples.

Before the ICP-MS test, standard heavy metal solutions (from Agilent Tech.) in 6

different concentration gradients (0, 20, 50, 200, 500, 1000 g/L) were used to

establish the linear relationship between heavy metal concentration and ICP intensity.

The linear correlation coefficients for Cu2+, Zn2+, Ni2+, Cr3+ and Pb2+ were 0.997,

0.999, 0.999, 0.996 and 0.997, respectively. Each batches of sample were detected for

3 times. The heavy metals concentration for BC were all lower than detection limit.

The average recovery rates of SRC for Cu2+, Zn2+, Ni2+, Cr3+ and Pb2+ were 94.2, 97.3,

96.8, 91.5 and 93.3 %, respectively.

For the measurement of the photodegradation of organic pollutants by CSH-M, a

special multichannel photocatalytic reactor, in which the light sources could rotate to

ensure each sample receive same light irradiation, was used for the parallel isothermal

photodegradation experiment. For each batch of photocatalytic experiment, 3 parallel

experiments were conducted simultaneously to reduce the data error. In addition, to

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ensure the accuracy of the experiment, all the samples were weighed within the

difference values of 0.1 mg (<0.5 % for 20 mg catalyst). MB was used to estimate the

accuracy of UV-vis spectrophotometer. The detected concentration of BC were all

lower than the detection limit of the method (~0.002 mg/L). The recovery rate for

standard MB solutions control was 89.1 %.

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Fig. S1 SEM, TEM, and HAADF-STEM mapping images of CSH-Cu (a-c), CSH-Zn

(d-f), CSH-Ni (g-i), CSH-Cr (j-l), and CSH-Pb (m-o), respectively.

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Fig. S2 BET adsorption-desorption isotherms of different heavy metals loaded CSH.

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Fig. S3 SAED pattern and HR-TEM image of CSH-Ni sample.

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Fig. S4 Adsorption kinetics and isotherm results of CSH towards five different heavy

metal ions. (a) Removal efficiency versus contact time (b) Pseudo-second-order

kinetic fitting plots. (c) Adsorption isotherms at pH 5.0 and temperature 303 K. (d)

Langmuir isotherm fitting plots.

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Fig. S5 Photocatalytic degradation kinetic curves towards MB of (a) blank control

(without CSH and in different concentrations of Cu2+ solutions); (b-f) batches of CSH

in different concentrations of heavy metal solutions (b-f refers to the single heavy

metal solutions of Cu(II), Zn(II), Ni(II), Cr(III), and Pb(II), respectively).

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Fig. S6 (a) Residual concentrations of different heavy metals in

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Fig. S7 (a) XRD pattern of TiO2 (inset: TEM images of TiO2); (b) DRS spectra of

TiO2.

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Fig. S8 DRS spectra of (a) CSH and CSH loaded with different heavy metals; (b) the

samples of CSH-Cu that coated with different content of Cu.

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References:

[1] Jin, L., Zhang, G. and Tian, H. (2014) Current state of sewage treatment in China.

Water Research 66, 85-98.

[2] Meena, R.A.A., Sathishkumar, P., Ameen, F., Yusoff, A.R.M. and Gu, F.L. (2018)

Heavy metal pollution in immobile and mobile components of lentic ecosystems—a

review. Environmental Science and Pollution Research 25(5), 4134-4148.

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