Adsorption mechanism modeling using lead (Pb) sorption data on modified rice bran-insoluble fiber as universal approach to assess other metals toxicity

Figures & data

Table 1. Physicochemical properties of RBIF

Samples	Hemicellulose content (%)	Cellulose content (%)	Specific surface area (m^2/g)	CEC (meq/g)
Untreated defatted rice bran	10.652 ± 1.030^a	9.320 ± 0.860^a	0.180^a	0.104^a
RBIF-0.2	22.774 ± 0.201^b	38.450 ± 0.152^b	0.260^b	0.214^b
RBIF-1.25	13.602 ± 0.030^c	53.032 ± 0.080^c	0.450^c	0.159^c
RBIF-2.0	10.723 ± 0.070^a	53.510 ± 0.060^c	0.670^d	0.143^d

Different lowercase letters in the same column represent a significant difference in four samples at p< 0.05; RBIF-0.2,1.25, and 2.0 represent the rice bran modified with boiled 0.2%, 1.25%, and 2.0% H₂SO₄ followed by boiled 1.25% KOH, respectively.

Table 2. In vitro maximum binding capacity (BC_max) of RBIDF for Pb²⁺ at pH 2.0 and 7.0

	BCmax (mg/g) pH = 2.0	pH = 7.0
Untreated defatted rice bran	22.921 ± 3.860^a	97.220 ± 1.051^a
RBIF-0.2	27.120 ± 1.291^ab	157.520 ± 6.143^b
RBIF-1.25	43.362 ± 3.860^c	209.991 ± 3.201^c
RBIF-2.0	33.350 ± 1.582^b	241.073 ± 5.962^d

Different lowercase letters in the same column represent significant difference at p< 0.05; RBIF-0.2, 1.25, and 2.0 represent the rice bran modified with boiled 0.2%, 1.25%, and 2.0% H₂SO₄ followed by boiled 1.25% KOH, respectively.

Figure 1. SEM images of exterior surface of modified rice bran fiber treated with 0.2%, 1.25%, and 2.0% H₂SO₄ combined with 1.25% KOH regimes

Table 3. Effect of Na and Ca on maximum binding capacity (BC_max) for Pb

	BCmax of fiber (mg/g)
	Raw rice bran	RBIF-0.2	RBIF-1.25	RBIF-2.0
Pb^2+	31.512 ± 3.211^a,x	37.122 ± 0.110^b,x	49.240 ± 2.590^c,x	43.800 ± 2.280^bc,x
Ca^2++Pb^2+	21.841 ± 0.510^a,y	30.302 ± 1.860^b,y	42.884 ± 3.130^c,xy	41.173 ± 2.810^c,x
Na^++Pb^2+	22.582 ± 3.930^a,y	29.213 ± 0.040^b,y	39.080 ± 2.020^c,y	41.162 ± 1.750^c,x

Different lowercase letters of a–c in the same line represent significant difference in four samples at p< 0.05; different lowercase letters of w–y in the same column represent significant difference in BC_max for the presence of Ca²⁺ and Na⁺, respectively; RBIF-0.2, 1.25, and 2.0 represent the rice bran modified with boiled 0.2%, 1.25%, and 2.0% H₂SO₄ followed by boiled 1.25% KOH, respectively.

Figure 2. Binding capacities of various RBIFs that produced with 0.2%, 1.25%, and 2.0% H₂SO₄ combined with 1.25% KOH for Pb²⁺ at different time

Table 4. Kinetic parameters for the adsorption of Pb by RBIF

	Pseudo-first-order model (Lagergren model)
	qe,exp (mg/g)	qe,cal (mg/g)	k1 (per min)	R^2
Untreated defatted rice bran	53.731	54.390	0.014	0.967
RBIDF-0.2	63.851	64.788	0.019	0.881
RBIDF-1.25	76.184	76.232	0.014	0.892
RBIDF-2.0	68.015	68.471	0.024	0.907
	Pseudo-second-order model
	qe,exp (mg/g)	qe,cal (mg/g)	K2 (mg/mmol/min)	R^2
Untreated defatted rice bran	53.731	58.823	0.400	0.981
RBIDF-0.2	63.851	65.359	0.400	0.977
RBIDF-1.25	76.184	83.333	0.400	0.901
RBIDF-2.0	68.015	76.336	0.300	0.940
	Intraparticle diffusion model
	qe,exp (mg/g)	I (mg/g)	Ki (mg/g/min^1/2)	R^2
Untreated defatted rice bran	53.731	11.544	2.970	0.992
RBIF-0.2	63.851	4.236	4.607	0.869
RBIF-1.25	76.184	26.603	3.564	0.836
RBIF-2.0	68.015	13.466	3.941	0.928

Figure 3. The plot of intraparticle diffusion modeling of lead ion onto RBIF (C: 10 mmol/L; pH: 6.8)

Table 5. Isotherm constants for Pb removal by RBIDF

		Langmuir isotherm
Fiber samples	Temperature (◦C)	qmax (mg/g)	b (L/mmol)	R^2
Untreated defatted rice bran	25	29.422	2.732	0.999
	31	33.152	2.764	0.999
	37	34.188	3.116	0.999
RBIF-0.2	25	30.666	3.191	0.998
	31	33.774	3.470	0.999
	37	37.503	3.471	0.999
RBIF-1.25	25	33.566	4.504	0.998
	31	35.224	5.760	0.998
	37	38.746	5.881	0.999
RBIF-2.0	25	31.287	3.756	0.999
	31	34.602	3.756	0.999
	37	37.296	3.830	0.999
		Freundlich isotherm
		Kf (mg/g)	1/n	R^2
Untreated defatted rice bran	25	0.088	0.558	0.961
	31	0.108	0.545	0.939
	37	0.103	0.537	0.935
RBIF-0.2	25	0.097	0.551	0.956
	31	0.107	0.533	0.939
	37	0.115	0.523	0.922
RBIF-1.25	25	0.121	0.538	0.961
	31	0.136	0.521	0.956
	37	0.146	0.508	0.936
RBIF-2.0	25	0.103	0.534	0.955
	31	0.113	0.531	0.941
	37	0.121	0.523	0.928
		D–R isotherm
		qmax (mg/g)	E (kJ/mol)	β	R^2
Untreated defatted rice bran	25	25.071	4.132	0.029	0.936
	31	27.350	4.135	0.029	0.956
	37	28.594	4.328	0.027	0.960
RBIF-0.2	25	26.936	4.275	0.027	0.942
	31	29.215	4.327	0.027	0.960
	37	31.287	4.479	0.025	0.969
RBIF-1.25	25	31.494	4.606	0.024	0.941
	31	34.188	4.752	0.022	0.950
	37	36.260	4.936	0.021	0.965
RBIF-2.0	25	28.179	4.433	0.025	0.943
	31	30.251	4.398	0.026	0.960
	37	32.116	4.552	0.024	0.969

Table 6. Calculated r values for Pb²⁺ sorption by RBIFs

	r Values for various initial Pb^2+concentration at 25°C
Samples	5 mmol/L	10 mmol/L	20 mmol/L
Untreated defatted rice bran	0.068	0.035	0.018
RBIF-0.2	0.059	0.030	0.015
RBIF-1.25	0.043	0.022	0.011
RBIF-2.0	0.051	0.026	0.013

Figure 4. Binding capacities of various RBIFs that produced with 0.2%, 1.25%, and 2.0% H₂SO₄ combined with 1.25% KOH for Pb²⁺ at different temperatures

Table 7. Thermodynamic parameters for Pb²⁺ by RBIF

		Thermodynamic parameters
Fiber samples	Temperature (^◦C)	ΔH (kJ/mmol)	ΔG (kJ/mmol)	ΔS (kJ/mol/k)
Untreated defatted rice bran	25		−2.490	0.036
	31	8.375	−2.570	0.036
	37		−2.929	0.036
RBIF-0.2	25		−2.875	0.028
	31	5.404	−3.145	0.028
	37		−3.207	0.028
RBIF-1.25	25		−3.729	0.070
	31	17.161	−4.426	0.071
	37		−4.566	0.070
RBIF-2.0	25		−3.279	0.015
	31	1.233	−3.345	0.015
	37		−3.461	0.015