Table 6 Isotherm constants of methylene blue and congo red adsorption by activated carbons.

From: Twigs-derived activated carbons via H3PO4/ZnCl2 composite activation for methylene blue and congo red dyes removal

Activated carbon

TAC1

TAC2

TAC3

TAC4

TAC5

TAC6

Methylene blue

Qe,exp (mg/g)

16.9

401

413

130

264

221

Qe,exp (mmol/g)

0.053

1.25

1.29

0.406

0.825

0.692

Langmuir model

Qm (mg/g)

15.7

425

438

137

249

217

Qm (mmol/g)

0.049

1.33

1.37

0.429

0.779

0.678

b (L/mg)

0.521

0.053

0.052

0.016

0.152

0.079

SSE

16.5

2,162

2,265

1,790

888

282

R2

0.9031

0.9937

0.9937

0.9616

0.9929

0.9978

Freundlich model

Kf ((mg/g)(L/mg)1/n)

7.70

77.6

81.5

21.5

58.1

48.7

n

8.44

3.62

3.63

3.63

4.25

4.23

SSE

15.35

28,557

32,063

606

7,044

4,789

R2

0.9087

0.9210

0.9152

0.9777

0.9450

0.9476

Redlich–Peterson model

K

15.5

22.7

22.9

66.1

54.3

19.5

a

1.47

0.053

0.052

2.44

0.331

0.11

g

0.932

1.00

1.00

0.761

0.932

0.969

SSE

2.59

2,162

2,265

463

146

214

R2

0.9845

0.9937

0.9937

0.9825

0.9988

0.9982

Congo red

Qe,exp (mg/g)

90.3

161

176

119

214

190

Qe,exp (mmol/g)

0.13

0.231

0.253

0.171

0.307

0.273

Langmuir model

Qm (mg/g)

92.4

165

180

123

217

194

Qm (mmol/g)

0.133

0.236

0.258

0.176

0.312

0.278

b (L/mg)

0.025

0.037

0.036

0.051

0.035

0.038

SSE

19.9

30.1

38.0

99.0

371

97.5

R2

0.9984

0.9994

0.9996

0.9960

0.9972

0.9991

Freundlich model

Kf ((mg/g)(L/mg)1/n)

13.1

26.6

28.7

24.6

34.2

31.4

N

3.41

3.58

3.53

4.04

3.49

3.56

SSE

931

2,958

3,087

2,662

2,731

3,151

R2

0.9313

0.9387

0.9474

0.8967

0.9694

0.9547

Redlich–Peterson model

K

2.31

6.02

6.94

6.27

11.0

8.72

A

0.025

0.037

0.043

0.051

0.089

0.06

G

1.00

1.00

0.98

1.00

0.91

0.95

SSE

19.9

30.1

30.5

99.0

143

39.4

R2

0.9984

0.9994

0.9996

0.9960

0.9987

0.9996