Kinetics, mechanism, isotherm and thermodynamic studies of liquid phase adsorption of Pb²⁺ onto wood activated carbon supported zerovalent iron (WAC-ZVI) nanocomposite

Figures & data

Table 1. Physicochemical properties of WAC-nZVI nanocomposites

Physicochemical properties	WAC-nZVI
pH	7.53
PZC	5.60
BET surface area	101.5033 m²/g
t-Plot micropore area	78.6414 m²/g
t-Plot external surface area	22.8619 m²/g
BJH adsorption cumulative surface area of pores between 17.000 and 3,000.000 Å diameter	8.389 m²/g
Pore volume
Single-point adsorption total pore volume of pores less than 1,094.743 Å diameter at P/Po = 0.981990668	0.056673 cm³/g
t-Plot micropore volume	0.036247 cm³/g
BJH Adsorption cumulative volume of pores between 17.000 and 3,000.000 Å diameter	0.024482 cm³/g
Pore size
Adsorption average pore width (4 V/A by BET)	22.3334 Å
BJH Adsorption average pore diameter (4 V/A)	116.727 Å

Figure 1. FTIR spectra for (a) WAC-nZVI before adsorption and (b) Pb–WAC-nZVI after adsorption.

Table 2. Important FTIR bands of WAC-nZVI with their possible functional groups before and after Pb²⁺ adsorption

Functional group(s)/peaks		Intensities
Functional group(s)	Vibration bands/peaks (cm^−1)	WAC-nZVI before adsorption	Pb(II)-loaded WAC-nZVI after adsorption
O–H stretching	3,417.98	42.474	3
H–O–H bending	1,637.62	84.066	2.5
C=C	1,340.57–1,309.71	53.881	0
Si–O-Al	966.37	61.453	1.5
C–O	860.28	67.45	1
Fe^0	688.61	68.624	1.02
	574.81	56.232	0.5
	414.71	82.49	1.5

Figure 2. SEM images of (a) WAC-nZVI before adsorption and (b) Pb–WAC-nZVI after adsorption.

Figure 3. EDX analysis of (a) WAC-nZVI before adsorption and (b) Pb–WAC-nZVI after adsorption.

Figure 4. The effect of pH on Pb²⁺ adsorbed onto WAC-nZVI.

Notes: Experimental conditions: Pb2+ Concentration= 200 mg/L; WAC-nZVI dose = 100 mg ; Volume of Pb2+ solution = 50 mL; Stirring speed = 200 rpm; Contact time = 30 min, and Temperature = 25± 2°C.

Figure 5. Effect of WAC-nZVI dose on Pb²⁺ adsorbed.

Notes: Experimental conditions: Pb2+ Concentration = 200 mg/L; Volume of Pb2+ solution = 50 mL; pH = 6, Stirring speed = 200 rpm; Contact time = 30 min, and Temperature = 25± 2°C.

Figure 6. Effect of contact time on Pb²⁺ adsorbed onto WAC-nZVI .

Notes: Experimental conditions: Pb2+ Concentration= 200 mg/L; WAC-nZVI dose = 100 mg ; Volume of Pb2+ solution = 50 mL; Stirring speed = 200 rpm; Temperature = 25± 2°C.

Figure 7. (a–d): Linear plots of (a) Pseudo-first-order, (b) Pseudo-second-order, (c) Elovich, (d) Fractional power.

Table 3. Adsorption kinetic models’ parameters for the sorption of Pb²⁺ onto WAC-nZVI

Pseudo-first-order	WAC-nZVI	Pseudo-second-order		Elovich		Fractional power
k1 (min^−1)	0.035	k2 (g/mg/min)	0.020	α (g.min^2/mg)	1.60 × 10^+34	v (min^−1)	0.012
h1 (mg/g/min)	0.193	h2 (mg/g/min)	166.667	β (g.min/mg)	0.933	k3 (mg/g)	83.946
R^2	0.932	R^2	1.000	R^2	0.953	R^2	0.954
SSE	6993.642	SSE	2.921	SSE	0.026	SSE	0.0842
χ^2	1255.140	χ^2	0.032	χ^2	3 × 10^−4	χ^2	0.001
Δq	23.438	Δq	0.479	Δq	0.0448	Δq	0.081
qe,exp (mg/g)	89.200	qe,exp (mg/g)	89.200	qe,exp (mg/g)	89.200	qe,exp (mg/g)	89.200
qe,cal (mg/g)	5.572	qe,cal (mg/g)	90.909	qe,cal (mg/g)	89.040	qe,cal (mg/g)	88.909

Figure 8. (a–d) Linear plots of (a) Intraparticle Diffusion, (b) External Diffusion, (c) Bangham, and (d) Boyd mechanism models for adsorption of Pb²⁺ onto WAC-nZVI.

Table 4. Adsorption mechanism models for immobilization of Pb²⁺ onto WAC-nZVI

Intraparticle diffusion	WAC-nZVI	External diffusion		Bangham		Boyd
kip (mg/g/min ^0.5)	0.348	kfd	0.002	Ko	0.022	R^2	0.933
C	85.440			Α	0.012
R^2	0.987	R^2	0.967	R^2	0.954

Figure 9. Percentage and quantity of Pb²⁺ adsorbed onto WAC-nZVI at various initial Pb²⁺concentrations.

Table 5. Different adsorption isotherm models (15, 21, 44–46)

S/N	Isotherms	Nonlinear form	Linear form	Equations	Plots
1	Freundlich	$q{}_e=K{}_{f}C{}_e^{1/n_f}$	$logq{}_e=log{K}_f+1/n_{f}logC{}_e$	(21)	log qe vs. log Ce
2	Langmuir	$q{}_e=q_{\text{max}}\frac{K{}_{L}C{}_e}{1+K{}_{L}C{}_e}$	$\frac{C_e}{q_e}=\frac{1}{K_L{q}_{\text{max}}}+\frac{C{}_e}{q{}_{\text{max}}}$ $R_L=\frac{1}{1+K_L{C}_o}$	(22) and (23)	$\frac{C_e}{q_e}$ vs. Ce
3	Temkin	$q{}_e=\frac{RT}{b_T}ln\left(A_{T}C{}_e\right)$	$q{}_e=\frac{RT}{b_T}ln{A}_T+\left(\frac{RT}{b_T}\right)ln{C}_e$	(24)	qe vs. ln Ce
4	Dubinin–Radushkevich (D–R)	qe = qd exp ( - ADKRɛ^2)	ln qe = ln qd − ADKRɛ^2 $E=-\left[\frac{1}{\sqrt{2A{}_{D-R}}}\right]$	(25)	ln qe vs. ɛ^2
5	Halsey	$q_e=Exp\left(\frac{ln{k}_H-lnCe}{n_H}\right)$	$\ell n{q}_e=\left[\left(\frac{1}{n_H}\right)\ell nK\right]-\left(\frac{1}{n_H}\right)\ell n{C}_e$	(26)	ln qe vs. ln Ce
6	Harkin–Jura	$q_e={\left(\frac{A}{B_2-log{C}_e}\right)}^{1/2}$	$\frac{1}{q_e^2}=\left[\frac{B}{A}\right]-\left[\frac{1}{A}\right]log{C}_e$	(27)	$\frac{1}{q_e^2}$ vs. log Ce
7	Jovanovic	$q_e=q_{\text{max}}\left(1-{exp}^{\left(K_j{C}_e\right)}\right)$	ln qe = ln qmax − kjCe	(28)	ln qe vs. Ce

Figure 10. (a–e): Linear plots of (a) Freundlich, (b) Langmuir, (c) Temkin, (d) D-R, (e) Halsey (f) Harkin–Jura, (g) Jovanovic isotherm models for sorption of Pb²⁺ onto WAC-nZVI, and (h) Plot of Langmuir dimensionless separation factor for adsorption of Pb²⁺ onto WAC-nZVI.

Table 6. Isotherm models’ parameters and evaluated values for adsorption of Pb²⁺ onto WAC-nZVI

Langmuir	Values	Freundlich	Values	Temkin	Values	D-R	Values
qmax (mgg^−1)	77.519	kf	32.885	bT (J mol ^−1)	277.892	qd	82.163
KL (Lmg^−1)	1.344	1/nf	0.283	β (Lg^−1)	8.916	ADKR	4 × 10^−8
RL	7.44 × 10^−2–3.77 × 10^−3	nf	3.53	AT (Lg^−1)	180.925	E (J/mol)	3,535.5
R^2	0.972	R^2	0.64	R^2	0.842	R^2	0.969
SSE	131.231	SSE	259.091	SSE	112.375	SSE	342.532
χ^2	1.748	χ^2	3.251	χ^2	1.514	χ^2	4.204
Δq	4.502	Δq	6.326	Δq	4.166	Δq	7.306
Halsey	Values	Harkin–Jura	values	Jovanovic	values
1/nH	−0.283	A	133.33	qmax	18.5061
nH	−3.53	B	1.0933	Kj	−0.0482
KH	4.42 × 10^−6	1/A	0.0075
R^2	0.6402	R^2	0.3417	R^2	0.45
SSE	259.693	SSE	nd	SSE	78.7266
χ^2	3.257	χ^2	nd	χ^2	0.8537
Δq	6.333	Δq	nd	Δq	2.6616

Note: nd = non-determinate.

Table 7. Comparison of the previously reported adsorbents used in Pb²⁺ uptake with the present ones under investigation

S/N	Adsorbents	Adsorption capacity (mg/g)	Ref
1	Amino-functionalized Fe3O4-SiO2 magnetic nanomaterial	76.6	(48)
2	Copolymer 2-hydroxyethyl methacrylate with monomer methyl methacrylate	31.5	(49)
3	Silica-supported dithiocarbamate	70.4	(50)
4	Nanometer TiO2	22.5	(51)
5	Exfoliated Graphene Nanosheets	35.5	(52)
6	Modified nanometer SiO2	6	(53)
7	Amino-functionalized mesoporous	57.74	(54)
Nanomesoporous silica
8	Magnetic Chitosan/GO	76.94	(55)
9	WAC-nZVI	77.5194	Present study

Figure 11. Effect of temperature on Pb²⁺ adsorbed onto WAC-nZVI.

Figure 12. Van’t Hoff plot for the adsorption of Pb²⁺ onto WAC-nZVI.

Table 8. Thermodynamic parameters for adsorption of Pb²⁺ onto WAC-nZVI

T (^oC)	T (K)	ΔG (kJ mol^−1)	ΔH (kJ mol^−1)	ΔS (J mol^−1 K^−1)	Kc
25	298	−6592	4.761	38.169	14.297
35	308	−7009			15.434
45	318	−7397			16.401
55	328	−7769			17.262
65	338	−8115			17.943

Figure 13. Ionic strength on Pb²⁺ adsorbed onto WAC-nZVI.

Notes: Experimental conditions: Pb2+ Concentration= 200 mg/L; Volume of Pb2+ Solution = 50 mL; WAC-nZVI dose = 100 mg; pH =6, contact time = 30 min, Stirring speed = 200 rpm and temperature = 25± 2°C.

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