Conclusion - Physicochemical Properties and Adsorption Capacity of Biochars Produced from Resid

55 functional groups (i.e., –OH and –COOH) of biochars and N⁺ of MB and SO molecules. This

electrostatic attraction is illustrated in Fig. 4-9.

56 Table. 4- 1 Chemical structure and properties of dyes used in this study

Dyes Chemical structure Classification Mol. wt.

(g/mol)

pKa λmax (nm)

Methylene Blue (MB)

Cationic thiazine dye

319.85 3.8 665 (pH neutral)

Safranin O (SO) Cationic azine

dye

350.84 6.4 530

(pH neutral)

Methyl Orange (MO)

Anionic azo dye 327.3 3.4 465 (pH acid) Bromocresol

Green (BG)

Anionic

sulfonephthaleins dye

698 4.7 443 (pH acid)

Table. 4- 2 Adsorption kinetic models

Kinetic Functional form

Linear form Plot Parameters and Constants Eq.

Pseudo-second order

( )²

2 e t

t k q q

dq = − t

q q k q t

e e t

1 1

2 2

= log t/qt

versus t

qe: Equilibrium adsorption capacity (mg/g);

qt: Time adsorption capacity (mg/g);

t: the contact time (min);

k2: Second-order rate coefficient (g/mg.min)

Elovich equation

) exp( _t

t q

dq = − q_t 1lnt

) 1ln(

 

 ⁺

= qt versus

lnt

qt: Time adsorption capacity (mg/g)

t: the contact time (min);

α: initial adsorption rate (mg/g.min);

β: related to the extended of surface coverage and activation energy for chemisorption (g/mg).

Intraparticle Diffusion

qt = kpt^1/2 + C qt = kpt^1/2 + C

qt versus t^1/2

qt: Time adsorption capacity (mg/g)

kp: the intra-particle diffusion rate constant (mg/g.min^1/2);

t: the contact time (min);

C: the constant related to the thickness of the boundary layer (mg/g).

57 Table. 4- 3 Adsorption isotherm models

Isotherm Functional form

Linear form Plot Parameters and Constants Eq.

Langmuir

e L

e L m

C K

C K q

= + q_e 1

m e m L e e

q C q K q

C = 1 +

e e

C versus Ce

qe: Adsorption capacity (mg/g);

qm: the maximum adsorption capacity (mg/g);

Ce: Equilibrium concentration of the adsorbate (mg/l);

KL: the Langmuir adsorption constant (L/mg).

Freundlich qe = KF Ce1/n log qe = log KF + (1/n) log Ce

log qe versus log Ce

qe: Adsorption capacity (mg/g);

Ce: Equilibrium concentration of the adsorbate (mg/l);

KF: the sorption affinity, (mg/kg)/(mg/L)ⁿ; 1/n: the nonlinearity index (unitless).

Temkin e ^ln(KTCe⁾

q =RT _e _T C_e

b K RT b

q =RTln + ln qe versus lnCe

qe: Adsorption capacity (mg/g);

Ce: Equilibrium concentration of the adsorbate (mg/l);

KT: Equilibrium association constant (l/mg);

b: Variation of the adsorption energy (J/mol)

R: gas constant (8.314 J/mol.K);

T: the absolute temperature in Kelvin (273 + ºC).

58 Table. 4- 4 Error functions used for the analysis of the kinetic and isotherm modelling

Error function Abb. Formula Eq. Parameters

The sum of the squares

of the errors SSE ∑(𝑞𝑒,𝑐𝑎𝑙 − 𝑞𝑒,𝑒𝑥𝑝)²

𝑛

𝑖=1

n: the number of data points;

qe,exp : the experimental adsorption capacity (mg/g);

qe,cal: calculated adsorption capacity (mg/g);

𝑞̅_{𝑒,𝑐𝑎𝑙} : average calculated adsorption capacity (mg/g).

The sum of the absolute

errors SAE ∑|𝑞𝑒,𝑐𝑎𝑙− 𝑞𝑒,𝑒𝑥𝑝|

𝑛

𝑖=1

The mean absolute

deviation MAD ∑ |𝑞_{𝑒,𝑒𝑥𝑝}− 𝑞_{𝑒,𝑐𝑎𝑙}

𝑛 |

𝑛

𝑖=1

The average relative

error ARE ∑ |𝑞_{𝑒,𝑒𝑥𝑝}− 𝑞_{𝑒,𝑐𝑎𝑙}

𝑞𝑒,𝑒𝑥𝑝 |

𝑛𝑖=1

𝑛 × 100 12

The mean square error MSE ∑^𝑛_𝑖=1(𝑞𝑒,𝑒𝑥𝑝− 𝑞𝑒,𝑐𝑎𝑙)²

𝑛 13

Root mean square error RMSE √∑^𝑛_𝑖=1(𝑞_{𝑒,𝑒𝑥𝑝}− 𝑞_{𝑒,𝑐𝑎𝑙})²

𝑛 14

Chi-square χ² ∑(𝑞𝑒,𝑒𝑥𝑝− 𝑞𝑒,𝑐𝑎𝑙)²

𝑞_{𝑒,𝑐𝑎𝑙}

𝑛

𝑖=1

The coefficient of

determination R²

𝑞_{𝑒,𝑒𝑥𝑝}− 𝑞̅_{𝑒,𝑐𝑎𝑙}²

∑^𝑛_𝑖=1(𝑞_{𝑒,𝑒𝑥𝑝}− 𝑞̅_{𝑒,𝑐𝑎𝑙}) ²+ (𝑞_{𝑒,𝑒𝑥𝑝}− 𝑞_{𝑒,𝑐𝑎𝑙})² 16

59 Table. 4- 5 Intra-particle diffusion kinetic parameters for MB, SO, MO and BG adsorption,

calculated by the linearization technique.

Dye Biochar

Intra-particle diffusion (linearized form)

Stage I: t = 1-10 min Stage II: t = 20 -120 min Stage III: t > 120 min

C1 kp1 R² C2 kp2 R² C3 kp3 R²

VRS700 2.04 4.64 0.98 18.82 0.62 0.96 25.34 0.02 0.99 JRS700 0.45 4.07 0.96 17.05 0.66 0.88 23.65 0.05 0.88 VRH700 0.29 3.20 0.96 14.03 0.37 0.95 17.74 0.07 0.86 JRH700 0.64 2.56 0.96 11.83 0.46 0.97 16.71 0.05 0.95

VRS700 1.26 4.65 0.98 19.62 0.39 0.74 23.67 0.06 0.87 JRS700 0.07 4.07 0.97 16.49 0.54 0.79 21.86 0.07 0.85 VRH700 0.49 2.96 0.98 13.60 0.36 0.77 16.69 0.10 0.86 JRH700 0.32 2.53 0.98 11.30 0.47 0.82 15.65 0.08 0.88

VRS700 1.09 4.37 0.98 18.17 0.34 0.80 21.06 0.10 0.97 JRS700 0.56 3.54 0.99 14.00 0.48 0.86 18.94 0.07 0.79 VRH700 0.58 2.52 0.99 7.54 0.51 0.92 12.06 0.12 0.96 JRH700 0.41 2.21 0.98 6.67 0.49 0.94 10.87 0.13 0.98

VRS700 1.15 3.91 0.99 16.54 0.42 0.87 20.60 0.08 0.98 JRS700 0.31 3.30 0.99 13.65 0.35 0.96 16.46 0.14 0.91 VRH700 0.41 2.47 0.97 8.48 0.29 0.81 10.76 0.08 0.91 JRH700 0.41 2.14 0.96 7.12 0.31 0.93 9.91 0.09 0.81

60 Fig. 4- 1 Plot for the pHPZC determination of biochars

Fig. 4- 2 Effect of pH on adsorption capacity of (A) MB, (B) SO, (C) MO and (D) BG (Experimental conditions: T = 25 °C, C0 = 50 mg/L, mbiochar = 2 g/l, t = 240 min, pH = 2 - 10).

Fig. 4- 3 Effect of biochar dosage on percent removal (%) and adsorption capacity (qe, mg/g) of (A) MB, (B) SO, (C) MO and (D) BG (Experimental conditions: T = 25 °C, C0 = 50 mg/L, mbiochar= 1 – 5

g/l, t = 240 min, pH ~ 7 for MB and SO, pH ~ 2 for MO and BG).

Fig. 4- 4 Effect of pyrolysis temperature on the percent removal of MB, SO, MO and BG by Japanese

Koshihikari and Vietnamese IR50404 rice straw and rice husk produced at 300, 500 and 700 °C (Experimental conditions: T = 25 °C, C0 = 50 mg/L, mbiochar = 2 g/l, t = 240 min, pH ~ 7 for MB and SO,

pH ~ 2 for MO and BG).

62 Fig. 4- 5 Effect of contact time and nonlinear fitting of the Pseudo-second-order, Elovich and intra-particle diffusion kinetic models for (A) MB, (B) SO, (C) MO and (D) BG adsorption (Experimental conditions: T = 25 °C, C0 = 50 mg/L, mbiochar = 2 g/l, t = 1 – 720 min, pH ~ 7 for MB and SO, pH ~ 2

for MO and BG).

63 Fig. 4- 6 Intra-particle diffusion plots for (A) MB, (B) SO, (C) MO and (D) BG adsorption (Experimental conditions: T = 25 °C, C0 = 50 mg/L, mbiochar = 2 g/l, t = 1-720 min, pH ~ 7 for MB

and SO, pH ~ 2 for MO and BG).

Fig. 4- 7 Effect of initial dye concentration and nonlinear fitting of Langmuir, Freundlich, and Temkin isotherm models for (a) MB, (b) SO, (c) MO and (d) BG adsorption (Experimental conditions:

T = 25 °C, C0 = 10 - 200 mg/L, mbiochar = 2g/l, t = 240 min, pH ~ 7 for MB and SO, pH ~ 2 for MO and BG).

65 Fig. 4- 8 Possible physical adsorption mechanism of MB, SO, MO and BG onto biochar surface

66 Fig. 4- 9 Possible chemical adsorption mechanism via electrostatic attraction of MB and SO onto biochar surface.

67 4.5 SUPPLEMENTARY MATERIAL

Table. SM4- 1 Basic physical and chemical characteristics of the biochar samples

Feedstock VRS JRS VRH JRH

Pyrolysis Temperature (°C) 300 500 700 300 500 700 300 500 700 300 500 700

Ultimate analysis^a

C (%) 49.68 50.65 46.91 52.30 54.00 51.27 40.61 41.89 43.28 42.92 38.42 37.97

H (%) 1.22 0.65 0.19 1.89 0.99 0.28 1.01 0.78 0.29 1.19 0.56 0.38

N (%) 0.90 0.80 0.48 1.47 0.48 0.31 0.61 0.51 0.48 1.76 0.46 0.34

O^b (%) 13.54 11.54 14.18 9.09 6.97 7.90 15.48 13.80 10.03 11.79 11.67 11.44 H/C atomic ratio 0.29 0.15 0.05 0.43 0.22 0.07 0.30 0.22 0.08 0.33 0.17 0.12 O/C atomic ratio 0.20 0.17 0.23 0.13 0.10 0.12 0.29 0.25 0.17 0.21 0.23 0.23 Proximate analysis^a

Moisture (%) 3.70 2.61 1.95 3.98 3.25 2.12 3.85 2.98 2.08 4.07 3.32 2.12 Volatile (%) 25.38 15.45 8.91 28.79 17.62 9.50 27.46 17.86 10.63 27.54 18.58 10.95 Total ash (%) 30.98 33.76 36.31 31.29 34.32 38.13 38.45 40.05 43.86 38.28 45.58 47.77 Pore characteristics

SBET (m²/g) 51.58 131.37 377.99 23.45 127.78 293.00 25.89 147.13 245.05 19.50 105.28 235.69

Sexternal (m²/g) 6.06 23.42 85.59 6.74 18.10 53.15 5.62 40.13 85.54 0.12 7.83 48.47

Smicropore (m²/g) 45.51 107.95 292.40 16.72 109.69 239.86 20.28 107.00 159.51 19.38 97.45 187.22 Vtotal pore (cm³/g) 0.064 0.111 0.299 0.051 0.171 0.171 0.045 0.107 0.188 0.033 0.070 0.164

Vmicropore (cm³/g) 0.020 0.048 0.129 0.007 0.048 0.106 0.009 0.047 0.070 0.008 0.043 0.082

Vnon-micro (cm³/g) 0.044 0.063 0.170 0.043 0.123 0.065 0.036 0.060 0.118 0.025 0.027 0.082

Average pore size (nm) 4.98 3.38 3.16 8.66 5.37 2.33 6.89 2.92 3.06 6.79 2.74 2.80

Iodine number (mg/g) 186 225 268 168 184 250 179 209 258 128 173 268

a Values are the average of triplicates

b Data are calculated by difference

68 Table. SM4- 2 Pseudo-second-order, Elovich and Intraparticle diffusion kinetic parameters for MB,

SO, MO and BG adsorption by VRS700, JRS700, VRH700 and JRH700, calculated by the nonlinearization optimization technique (Experimental conditions: T = 25 °C, C0 = 50 mg/L, mbiochar =

2 g/l, t = 1 – 720 min, pH ~ 7 for MB and SO, pH ~ 2 for MO and BG).

Dye Biochar

Pseudo-second order Elovich Intra-particle diffusion

qe,exp qe,cal k2 β α C kp

mg/g mg/g g/mg.min g/mg mg/g.min mg/g mg/g.min^1/2

VRS700 24.59 26.19 0.008 0.28 25.64 9.37 0.96 JRS700 23.84 25.39 0.005 0.26 10.04 6.00 1.10 VRH700 22.06 19.40 0.007 0.33 7.94 4.66 0.85 JRH700 20.64 18.37 0.005 0.34 5.08 3.36 0.85

VRS700 22.24 24.37 0.010 0.28 19.86 8.23 0.99 JRS700 19.89 23.16 0.007 0.27 9.30 5.46 1.06 VRH700 17.66 18.48 0.008 0.34 7.43 4.41 0.86 JRH700 16.10 17.14 0.008 0.35 5.33 3.47 0.82

VRS700 21.31 22.58 0.011 0.30 18.72 7.63 0.94 JRS700 19.10 19.78 0.010 0.32 10.49 5.46 0.89 VRH700 11.28 13.16 0.018 0.48 8.49 4.04 0.62

JRH700 9.67 12.24 0.016 0.51 6.33 3.40 0.60

VRS700 19.25 21.62 0.011 0.30 14.23 20.13 0.10 JRS700 18.93 18.45 0.010 0.33 8.10 16.51 0.12 VRH700 10.84 11.77 0.022 0.58 9.96 9.33 0.06

JRH700 9.70 10.85 0.020 0.60 7.01 8.22 0.06

69 Table. SM4- 3 Pseudo-second-order and Elovich kinetic parameters for MB, SO, MO and BG adsorption by VRS700, JRS700, VRH700 and JRH700, calculated by the linearization technique (Experimental conditions: T = 25 °C, C0 = 50 mg/L, mbiochar = 2 g/l, t = 1 – 720 min, pH ~ 7 for MB

and SO, pH ~ 2 for MO and BG).

Dye Biochar Pseudo-second order Elovich

qe,exp qe,cal k2 R² β α R²

mg/g mg/g g/mg.min g/mg mg/g.min MB VRS700 24.59 25.99 0.009 0.99 0.33 75.57 0.87

JRS700 24.62 25.05 0.006 0.99 0.31 26.05 0.88 VRH700 21.16 19.68 0.006 0.99 0.40 20.21 0.89 JRH700 19.65 18.15 0.006 0.99 0.41 14.25 0.90 SO VRS700 22.24 25.36 0.007 0.99 0.34 62.39 0.82 JRS700 19.89 23.90 0.005 0.99 0.32 24.40 0.85 VRH700 17.66 19.50 0.005 0.99 0.40 17.56 0.87 JRH700 16.10 17.85 0.006 0.99 0.41 12.01 0.88 MO VRS700 21.85 23.89 0.005 0.99 0.30 18.72 0.88 JRS700 19.19 20.96 0.006 0.99 0.32 10.49 0.91 VRH700 11.44 15.22 0.005 0.99 0.48 8.49 0.98 JRH700 9.25 14.46 0.004 0.99 0.51 6.33 0.99 BG VRS700 19.25 22.91 0.006 0.97 0.37 39.38 0.90 JRS700 18.93 20.18 0.004 0.96 0.40 19.24 0.93 VRH700 10.84 12.85 0.008 0.95 0.68 25.98 0.92 JRH700 9.70 12.38 0.006 0.92 0.67 13.07 0.96

70 Table. SM4- 4 Non-linear error function analysis of Pseudo-second-order, Elovich and Intraparticle

diffusion kinetic models Dye Kinetic

model

Biochar SSE SAE MAD ARE MSE RMSE χ² R²

Pseudo-second order

VRS700 0.37 1.69 0.17 0.73 0.04 0.19 0.02 0.99 JRS700 2.17 3.62 0.36 1.80 0.22 0.47 0.11 0.98 VRH700 2.24 4.03 0.03 2.52 0.22 0.47 0.15 0.96 JRH700 3.60 3.67 0.37 2.57 0.36 0.60 0.29 0.95 Elovich VRS700 72.34 24.85 2.07 9.73 6.03 2.46 3.26 0.83 JRS700 83.14 25.88 2.16 10.90 6.93 2.63 4.20 0.84 VRH700 44.03 18.20 1.52 10.14 3.67 1.92 3.04 0.85 JRH700 38.46 17.62 1.47 11.35 3.21 1.79 2.90 0.86

Intra-particle diffusion

VRS700 395.41 61.12 8.73 42.05 56.49 7.52 21.73 0.08 JRS700 485.69 65.99 9.43 48.09 69.38 8.33 30.32 0.05 VRH700 271.61 49.15 7.02 46.70 38.80 6.23 22.36 0.09 JRH700 256.37 47.46 6.78 47.73 36.62 6.05 22.92 0.05 SO

Pseudo-second order

VRS700 13.19 9.98 0.83 6.09 1.10 1.05 1.10 0.97 JRS700 9.10 8.41 0.70 6.59 0.76 0.87 0.98 0.98 VRH700 8.54 8.57 0.71 0.97 0.71 0.84 1.19 0.97 JRH700 5.45 6.29 0.52 7.31 0.45 0.67 0.99 0.98 Elovich VRS700 72.68 23.93 1.99 9.79 6.06 2.46 3.55 0.82 JRS700 66.58 22.81 1.90 10.33 5.55 2.36 3.58 0.85 VRH700 38.00 16.65 1.39 9.35 3.17 1.78 2.65 0.87 JRH700 31.62 15.20 1.27 9.33 2.63 1.62 2.37 0.88

Intra-particle diffusion

VRS700 400.78 60.95 8.71 44.15 57.25 7.57 23.85 0.03 JRS700 424.60 61.81 8.83 48.80 60.66 7.79 28.38 0.05 VRH700 252.08 46.77 6.68 46.00 36.01 6.00 20.83 0.14 JRH700 225.83 44.38 6.34 48.05 32.26 5.68 20.26 0.15

Pseudo-second order

VRS700 12.36 9.07 0.76 6.03 1.03 1.01 1.08 0.97 JRS700 9.23 8.99 0.75 6.78 0.77 0.88 0.93 0.97 VRH700 13.32 10.69 0.89 9.25 1.11 1.05 1.28 0.91 JRH700 13.72 10.87 0.91 10.69 1.14 1.07 1.55 0.90 Elovich VRS700 57.06 21.50 1.79 9.60 4.75 2.18 3.04 0.84 JRS700 36.47 16.54 1.38 8.66 3.04 1.74 2.15 0.88

71 VRH700 5.04 5.99 0.50 4.71 0.42 0.65 0.42 0.97 JRH700 2.86 4.40 0.37 4.09 0.24 0.49 0.30 0.98

Intra-particle diffusion

VRS700 332.44 54.36 7.77 42.55 47.49 6.89 20.59 0.06 JRS700 268.92 49.74 7.11 45.99 38.42 6.20 19.64 0.14 VRH700 87.35 28.32 4.05 39.62 12.48 3.53 8.40 0.40 JRH700 71.76 25.09 3.58 37.78 10.25 3.20 7.31 0.49 BG

Pseudo-second order

VRS700 10.15 8.59 0.72 5.75 0.85 0.92 0.85 0.97 JRS700 10.36 9.40 0.78 7.01 0.86 0.93 0.92 0.96 VRH700 4.75 5.62 0.47 6.42 0.40 0.63 0.67 0.95 JRH700 7.45 7.67 0.64 8.79 0.62 0.79 1.04 0.92 Elovich VRS700 48.48 19.05 1.59 8.68 4.04 2.01 2.58 0.91 JRS700 29.23 14.38 1.20 7.97 2.44 1.56 1.97 0.90 VRH700 11.27 9.69 0.81 8.30 0.94 0.97 1.17 0.88 JRH700 5.16 6.25 0.52 6.18 0.43 0.66 0.62 0.95

Intra-particle diffusion

VRS700 398.39 38.72 5.53 69.78 56.91 7.54 19.62 -0.15 JRS700 298.98 35.33 5.05 81.88 42.71 6.54 17.88 -0.05 VRH700 74.96 23.30 3.33 55.97 10.71 3.27 7.79 0.23 JRH700 72.03 23.78 3.40 60.67 10.29 3.21 8.33 0.25

72 Table. SM4- 5Langmuir, Freundlich, and Temkin isotherms parameters for MB, SO, MO and BG

adsorption by VRS700, JRS700, VRH700 and JRH700, calculated by the nonlinearization optimization technique (Experimental conditions: T = 25 °C, C0 = 10 – 200 mg/L, mbiochar = 2 g/l, t =

240 min, pH ~ 7 for MB and SO, pH ~ 2 for MO and BG).

Dye Biochar

Langmuir Freundlich Temkin

qm kL 1/n kF b kT

mg/g L/mg (mg/kg)/(mg/L)ⁿ J/mol l/mg

VRS700 67.69 0.32 0.46 12.21 193.35 4.79

JRS700 56.88 0.23 0.45 9.27 229.24 3.26

VRH700 33.28 0.26 0.36 7.30 402.01 2.84

JRH700 32.81 0.17 0.39 5.94 419.60 2.55

VRS700 60.15 0.11 0.53 6.52 233.16 1.93

JRS700 52.99 0.07 0.55 4.46 247.29 1.13

VRH700 32.36 0.09 0.47 3.86 400.46 1.24

JRH700 30.16 0.08 0.47 3.44 440.36 1.14

VRS700 48.31 0.13 0.46 6.55 276.67 1.88

JRS700 40.44 0.07 0.49 4.20 317.49 0.97

VRH700 18.58 0.06 0.43 2.15 625.29 0.56

JRH700 15.20 0.06 0.41 1.88 770.37 0.55

VRS700 45.47 0.06 0.53 4.19 287.60 1.01

JRS700 37.79 0.07 0.49 4.01 333.22 0.99

VRH700 18.08 0.04 0.52 1.45 640.57 0.45

JRH700 14.78 0.05 0.44 1.63 800.64 0.51

73 Table. SM4- 6 Langmuir, Freundlich, and Temkin isotherms parameters for MB, SO, MO and BG

adsorption by VRS700, JRS700, VRH700 and JRH700, calculated by the linearization technique (Experimental conditions: T = 25 °C, C0 = 10 – 200 mg/L, mbiochar = 2 g/l, t = 240 min, pH ~ 7 for MB

and SO, pH ~ 2 for MO and BG).

Dye Biochar

Langmuir Freundlich Temkin

qm kL R² 1/n kF R² b kT R²

mg/g L/mg (mg/kg)/(mg/L)ⁿ J/mol l/mg

VRS700 66.58 0.37 0.99 0.42 16.28 0.82 219.84 7.05 0.97 JRS700 55.81 0.26 0.99 0.40 12.40 0.82 263.87 5.21 0.97 VRH700 35.56 0.18 0.99 0.35 7.82 0.92 404.96 4.73 0.97 JRH700 34.05 0.14 0.99 0.38 6.50 0.91 427.18 2.79 0.98

VRS700 59.62 0.12 0.99 0.51 7.73 0.89 221.08 1.79 0.99 JRS700 49.36 0.09 0.99 0.52 5.57 0.87 256.20 1.24 0.99 VRH700 32.11 0.09 0.99 0.44 4.39 0.92 414.60 1.34 0.99 JRH700 30.16 0.07 0.99 0.45 3.74 0.94 433.03 1.34 0.99

VRS700 48.82 0.13 0.99 0.45 7.48 0.90 273.32 1.92 0.90 JRS700 39.25 0.08 0.99 0.47 4.70 0.90 319.47 1.01 0.90 VRH700 19.33 0.05 0.99 0.42 2.39 0.89 651.24 0.68 0.89 JRH700 14.85 0.05 0.99 0.40 2.04 0.91 847.02 0.69 0.91

VRS700 46.20 0.07 0.99 0.51 4.72 0.92 277.42 0.93 0.92 JRS700 38.51 0.07 0.99 0.46 4.57 0.91 337.41 1.03 0.91 VRH700 18.78 0.04 0.99 0.48 1.69 0.93 644.67 0.46 0.93 JRH700 14.98 0.05 0.99 0.43 1.73 0.93 822.16 0.57 0.93

74 Table. SM4- 7 Non-linear error function analysis for Langmuir, Freundlich, and Temkin isotherm

models

Dye Isotherm model Biochar SSE SAE MAD ARE MSE RMSE χ² R² MB Langmuir VRS700 61.74 14.89 1.86 11.62 7.72 2.78 5.77 0.98

JRS700 52.83 13.00 1.62 10.69 6.60 2.57 5.62 0.98 VRH700 21.48 9.77 1.22 8.13 2.69 1.64 1.30 0.97 JRH700 3.91 4.61 0.58 3.39 0.49 0.70 0.20 0.99 Freundlich VRS700 1474.97 92.84 11.61 34.87 184.37 13.58 46.12 0.58 JRS700 855.44 72.50 9.06 31.06 106.93 10.34 32.02 0.55 VRH700 167.05 29.72 3.71 15.67 20.88 4.57 6.97 0.80 JRH700 146.75 29.73 3.72 17.33 18.34 4.28 6.64 0.80 Temkin VRS700 151.82 24.29 3.04 9.56 18.98 4.36 4.15 0.96 JRS700 112.22 22.94 2.87 10.61 14.03 3.75 4.48 0.95 VRH700 34.69 15.20 1.90 13.86 4.34 2.08 5.54 0.96 JRH700 12.16 8.85 1.11 4.59 1.52 1.23 0.48 0.98 SO Langmuir VRS700 14.10 7.56 0.95 5.50 1.76 1.33 0.80 0.99 JRS700 26.19 12.59 1.60 8.35 5.63 2.37 1.71 0.98 VRH700 2.89 4.00 1.77 9.87 5.22 2.29 0.13 1.00 JRH700 1.36 2.94 2.12 13.91 9.25 3.04 0.09 1.00 Freundlich VRS700 604.97 56.72 0.95 37.65 98.73 9.94 19.47 0.75 JRS700 465.82 52.82 1.57 20.84 51.26 7.16 17.66 0.71 VRH700 126.72 25.96 0.50 15.04 20.42 4.52 6.06 0.79 JRH700 95.89 22.38 0.37 18.23 16.45 4.06 4.19 0.82 Temkin VRS700 27.55 12.02 7.09 5.50 1.76 4.96 0.87 0.99 JRS700 19.64 9.87 6.60 9.20 3.27 3.75 0.50 0.99 VRH700 5.22 4.59 3.25 2.57 0.36 3.75 0.21 0.99 JRH700 5.51 5.41 2.80 2.66 0.17 4.80 0.34 0.99 MO Langmuir VRS700 3.33 4.44 1.50 24.92 75.62 1.33 0.14 1.00 JRS700 4.53 4.86 1.23 26.58 58.23 1.81 1.00 1.00 VRH700 3.34 4.86 0.57 17.56 15.84 0.60 0.34 0.98 JRH700 1.68 2.42 0.68 15.32 11.99 0.41 0.28 0.98 Freundlich VRS700 369.13 46.45 5.81 5.45 3.44 8.70 13.17 0.71 JRS700 201.34 34.28 4.29 3.85 2.45 7.63 8.41 0.78 VRH700 22.13 11.13 1.39 2.84 0.65 3.98 2.36 0.86 JRH700 12.35 8.04 0.41 4.24 0.69 3.46 1.22 0.83 Temkin VRS700 24.06 11.23 1.40 4.93 3.01 1.86 0.78 0.99 JRS700 14.88 9.17 1.15 4.94 1.86 0.81 0.60 0.98

75 VRH700 2.68 3.56 0.44 4.08 0.34 0.81 0.29 0.98 JRH700 2.34 3.29 0.41 3.81 0.29 0.83 0.18 0.97 BG Langmuir VRS700 19.64 10.69 1.34 6.93 2.46 1.57 1.42 0.98 JRS700 13.67 8.94 1.12 6.16 1.71 1.31 0.93 0.98 VRH700 1.16 2.32 0.29 2.49 0.15 0.38 0.10 0.99 JRH700 1.13 2.20 0.28 2.85 0.14 0.38 0.12 0.99 Freundlich VRS700 198.49 32.81 4.10 18.17 24.81 4.98 7.06 0.84 JRS700 139.08 27.54 3.44 17.32 17.38 4.17 6.44 0.83 VRH700 13.32 7.44 0.93 9.50 1.67 1.29 2.21 0.89 JRH700 12.41 7.87 0.98 10.88 1.55 1.29 1.34 0.87 Temkin VRS700 8.17 6.10 0.76 2.96 1.02 1.01 0.29 0.99 JRS700 2.53 3.67 0.46 1.72 0.32 0.56 0.09 1.00 VRH700 1.36 2.62 0.33 2.98 0.17 0.41 0.13 0.99 JRH700 1.65 2.45 0.31 3.07 0.21 0.45 0.18 0.98

76 Table. SM4- 8 Thermodynamic parameters of MB, SO, MO and BG 50 mg/L sorption process by the biochar samples (Experimental conditions: T = 25 - 45 °C, C0= 10 – 200 mg/L, mbiochar = 2 g/l, t = 240

min, pH ~ 7 for MB and SO, pH ~ 2 for MO and BG).

Dye Biochar T(K) Kc ∆G⁰

(kJ/mol) ∆H⁰

(kJ/mol) ∆S⁰

(kJ/mol*K) R² KL obtained from the Nonlinear method

MB 50 mg/L VRS700 298 308 318

5639862 7373144 7752051

-38.51 -40.49 -41.94

12.62 0.17 0.88

JRS700 298 308 318

4129348 6560279 7509964

-37.74 -40.19 -41.86

23.69 0.21 0.92

VRH700 298 308 318

4560520 4785861 5037611

-37.99 -39.39 -40.80

3.92 0.14 0.99

JRH700 298 308 318

3088406 3236361 4047624

-37.02 -38.38 -40.22

10.58 0.16 0.86

SO 50 mg/L VRS700 298 308 318

2188880 2232187 2333546

-36.17 -37.43 -38.77

2.51 0.13 0.94

JRS700 298 308 318

1412597 1679703 2248295

-35.08 -36.71 -38.67

18.25 0.18 0.97

VRH700 298 308 318

1767232 1679703 2248295

-35.64 -37.01 -38.75

10.67 0.16 0.91

JRH700 298 308 318

1515216 1527692 2037889

-35.26 -36.46 -38.41

11.55 0.16 0.75

MO 50 mg/L VRS700 298 308 318

2325880 2701846 4260403

-36.32 -37.92 -40.36

23.70 0.2 0.91

JRS700 298 308 318

1441685 1530797 2199374

-35.14 -36.47 -38.61

16.50 0.17 0.84

VRH700 298 308 318

1028277 986546 1454887

-34.30 -35.34 -37.52

13.48 0.16 0.64

JRH700 298 308 318

817431 862005 951956

-33.73 -35.00 -36.40

5.98 0.13 0.96

BG 50 mg/L VRS700 298 308 318

2575214 2471391 3389072

-36.27 -37.69 -39.75

15.59 0.17 0.89

JRS700 298 308 318

2558892 2694801 2898502

-36.56 -37.92 -39.34

4.90 0.14 0.99

VRH700 298 308 318

1523709 2220520 2262880

-35.27 -37.42 -38.69

15.73 0.17 0.80

JRH700 298 308 318

1861071 2150269 2219383

-35.77 -37.34 -38.63

6.98 0.14 0.89

77 KL obtained from the Linear method

MB 50 mg/L VRS700 298 308 318

6547289 9173080 10653292

-38.88 -41.05 -4278

19.25 0.20 0.96

JRS700 298 308 318

4662196 6311579 7507093

-38.04 -40.10 -41.86

18.81 0.19 0.98

VRH700 298 308 318

3242001 3772890 4350253

-37.14 -38.78 -40.41

11.58 0.16 0.99

JRH700 298 308 318

2567161 2593592 3780102

-36.56 -37.82 -40.04

15.08 0.17 0.75

SO 50 mg/L VRS700 298 308 318

2343464 2077724 3183109

-36.34 -37.25 -39.59

11.83 0.16 0.47

JRS700 298 308 318

1764211 1935524 2744202

-35.64 -37.07 -39.20

17.29 0.18 0.89

VRH700 298 308 318

1581240 1468567 2351972

-35.36 -36.36 -38.79

15.40 0.17 0.6

JRH700 298 308 318

1252907 1381673 20001152

-34.79 -36.21 -38.36

18.32 0.18 0.89

MO 50 mg/L VRS700 298 308 318

2325880 2701846 4260403

-36.63 -37.92 -40.36

23.70 0.20 0.91

JRS700 298 308 318

1441685 1530797 2199374

-35.14 -36.47 -38.61

16.50 0.17 0.84

VRH700 298 308 318

1028277 986546 1454887

-34.30 -35.34 -37.52

13.48 0.16 0.64

JRH700 298 308 318

817431 862005 951956

-33.73 -35.00 -36.40

5.98 0.13 0.96

BG 50 mg/L VRS700 298 308 318

2554038 2844612 3654679

-36.55 -38.05 -39.95

14.05 0.17 0.94

JRS700 298 308 318

2750850 2814139 3168728

-36.74 -38.03 -39.58

5.53 0.14 0.85

VRH700 298 308 318

1499213 1934337 2182233

-35.23 -37.07 -38.59

14.84 0.17 0.97

JRH700 298 308 318

1777491 1784509 2411296

-35.65 -36.86 -38.85

11.88 0.16 0.74

78 Fig. SM4- 1Plots of nonlinear forms of Langmuir isotherm models for MB adsorption on (a)

VRS700, (b) JRS700, (c) VRH700 and (d) JRH700 at different temperatures (Experimental conditions: T= 25 – 45 °C, C0= 10 – 200 mg/L, mbiochar = 2 g/l, t = 240 min, pH ~ 7).

Fig. SM4- 2Plots of nonlinear forms of Langmuir isotherm models for SO adsorption on (a) VRS700, (b) JRS700, (c) VRH700 and (d) JRH700 at different temperatures (Experimental conditions: T= 25 –

45 °C, C0= 10 – 200 mg/L, mbiochar = 2 g/l, t = 240 min, pH ~ 7).

80 Fig. SM4- 3Plots of nonlinear forms of Langmuir isotherm models for MO adsorption on (a)

VRS700, (b) JRS700, (c) VRH700 and (d) JRH700 at different temperatures (Experimental conditions: T= 25 – 45 °C, C0= 10 – 200 mg/L, mbiochar = 2 g/l, t = 240 min, pH ~ 2).

81 Fig. SM4- 4Plots of nonlinear forms of Langmuir isotherm models for BG adsorption on (A)

VRS700, (B) JRS700, (C) VRH700 and (D) JRH700 at different temperatures (Experimental conditions: T= 25 – 45 °C, C0= 10 – 200 mg/L, mbiochar = 2 g/l, t = 240 min, pH ~ 2).

CHAPTER 5 General Discussion and Conclusions

83 The overarching objectives of this study to evaluate the effect of both rice variety and pyrolysis temperature on the biochar properties and adsorption capacity of model dyes on biochars, were achieved in most cases. The important findings critical to this research work are summarized as follows:

First, pyrolysis temperature and the variety of rice affected the porous characteristics and surface area of the final biochars. In general, the values of surface area increased from 300 to 700 °C then

decreased at 800 °C. The results of the pore size distribution show that the majority of studied biochars were in the range of 1.2- 9.9 nm. Under the same pyrolysis temperature, biochar produced from Vietnamese rice straw (VRS) and rice husk (VRH) showed higher micropores, total pore volume, BET surface area and higher iodine numbers than Japanese rice straw (JRS) and rice husk (JRH), respectively (i.e. VRS>JRS, VRH>JRH). Briefly, Vietnamese rice straw produced at 700 °C (VRS700) and Japanese rice straw produced at 700 °C (JRS700) obtained the highest BET surface area of 378 and 293 m²/g, respectively; followed by Vietnamese rice husk produced at 700 °C

(VRH700) and Japanese rice husk produced at 700 °C (JRH700) with 245 and 236 m²/g, respectively.

Second, biochars produced at high pyrolysis temperatures (> 500 °C) showed higher surface area (approximately 3 times) and higher Si content (by more than 15%), but lower H/C and O/C ratios in comparison with biochars produced at lower temperatures. With regard to rice variety, Japanese Koshihikari biochars had relatively higher volatile matter and ash contents, higher Si content (almost 20%), but lower specific surface area, lower O/C and H/C ratios than Vietnamese IR50404 rice residues biochars.

Lastly, studied biochars effectively removed two cationic dyes, i.e. Methylene Blue (MB) and Safranin O (SO), and two anionic dyes, i.e. Methyl Orange (MO) and Bromocresol Green, from aqueous solution. Vietnamese IR50404 biochars showed higher dye adsorption capacity than Japanese Koshihikari biochars. Cationic dye adsorption on biochars was significantly more effective than anionic dye adsorption. The anionic dye adsorption rate was predictably controlled solely by physisorption through porous diffusion, hydrogen bonding, π-π interaction and π⁺-π interaction. On the other hand, the cationic dye adsorption was simultaneously controlled by physical interaction and by chemical interaction. Chemisorption occurred via electrostatic attraction between the oxygenated surface functional groups (i.e., –OH and –COOH) of biochars and cation N⁺ of MB and SO.

In conclusion, this PhD research successfully investigated the differences in physicochemical

properties of biochars derived from two rice varieties, Japanese Koshihikari and Vietnamese IR50404.

The dissimilarity properties in studied biochars led to the differences in their adsorption capacity for dyes. The findings also demonstrated the potential of using biochars from rice residues as effective adsorbents alternative for the removal of cationic Methylene Blue and Safranin O dyes, and anionic Methyl Orange and Bromocresol Green dyes as model pollutants in wastewater.

84 The dye adsorption capacity of biochar increases with increasing specific surface area in biochar. The large surface area on biochar surface provides many adsorption sites for dye uptake, which directly affect the adsorption results. Therefore, for biochar to be a useful material in sorbent applications, methods used to maximize the surface area of biochar are strongly recommended. Physical or chemical activation methods such as using microwaves, carbon dioxide or superheated steam can improve the surface area of biochar. Also, enhanced aging of biochar using artificial methods, such as steam, air, or chemical oxidation with nitric acid (HNO3) and hydrogen peroxide (H2O2), can increase surface area due to increasing removal volatile organic compounds from biochar.

In addition, the variation of Si element between biochar samples, which affected on their specific surface area, properly due to the differences in the nature of the parent rock, climatic or topographic conditions, and also dissimilarities in Si uptake by the raw rice and by chemicals added to manure rice during rice production in Japan and Vietnam. Further studies for the effects of those factors on the Si content of rice variety feedstocks therefore is expected.

For more adequate explanations and evaluation on the adsorption capacity of biochar to dyes or other pollutants carried different charges, assessment of the surface structure and chemistry of biochar is strongly needed. The measurement of the point of zero net change (using either potentiometric titration or non-specific ion adsorption methods), cation exchange capacity and anion exchange capacity can help to determine the amount of net positive or net negative surface charge on biochar.

Zeta potential and iso-electric point measurement are also necessary for evaluate the surface ion charge of biochar. The Boehm titration method can determine surface acid functional group

distribution on biochar. Therefore, further analysis should be made to fully characterize and compare the properties and adsorption capacities of Japanese Koshihikari and Vietnamese IR50404 biochar.

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ドキュメント内 Physicochemical Properties and Adsorption Capacity of Biochars Produced from Residues of Two Varieties of Rice (Oryza sativa), Japanese Koshihikari and Vietnamese IR50404 (ページ 67-108)