Chemical activation of hickory and peanut hull hydrochars for removal of lead and methylene blue from aqueous solutions

Figures & data

Table 1. Bulk properties of activated hickory and peanut hull hydrochars.

Feedstock	Activating chemical	Wt. after activation (g)	Wt. after washing (g)	Final yield (%)	BET-SA (m^2 g^−1)	BJH-PV (mL g^−1)	C (wt. %)	H (wt. %)	N (wt. %)
Hickory	Nonactivated	–	–	–	8	0.121	68.7	5.31	0.2
	H3PO4	5.8	2	40	1436	0.028	66.5	2.34	0.3
	KOH	7.9	2.7	54	222	0.050	71.6	2.08	0.2
Peanut hull	Nonactivated	–	–	–	7	0.010	70.6	6.04	1.9
	H3PO4	6.5	2.6	52	1091	0.079	75.2	1.74	1.8
	KOH	7.8	2.7	54	571	0.075	70.5	1.66	1.6

Note: SA = specific surface area and PV = pore volume.

Figure 1. Comparison of chemically AHC with physically AHC and raw HC for the sorption of contaminants. (A) methylene blue and (B) lead.

Figure 2. Methylene blue adsorption kinetics: (A) H₃PO₄ hickory, (B) KOH hickory, (C) H₃PO₄ peanut, and (D) KOH peanut.

Figure 3. Lead adsorption kinetics: (A) H₃PO₄ hickory, (B) KOH hickory, (C) H₃PO₄ peanut, and (D) KOH peanut.

Table 2. Best-fit model parameters of lead sorption on AHCs.

		Parameter 1	Parameter 2	R^2
Hickory H3PO4	First-order	k1 = 4.178	qe = 109.8	0.574
	Second-order	k2 = 0.151	qe = 111.0	0.480
	Elovich	α = 2.7 × 10^16	β = 0.610	0.146
	Langmuir	K = 0.074	Smax = 92.1	0.927
	Freundlich	Kf = 11.697	n = 0.346	0.840
Hickory KOH	First-order	k1 = 0.921	qe = 157.2	0.939
	Second-order	k2 = 0.008	qe = 169.1	0.993
	Elovich	α = 1408	β = 0.042	0.933
	Langmuir	K = 0.022	Smax = 135.7	0.997
	Freundlich	Kf = 7.560	n = 0.494	0.981
Peanut H3PO4	First-order	k1 = 2.325	qe = 90.5	0.833
	Second-order	k2 = 0.049	qe = 94.0	0.901
	Elovich	α = 4.9 × 10^5	β = 0.148	0.996
	Langmuir	K = 0.032	Smax = 162.1	0.996
	Freundlich	Kf = 12.34	n = 0.473	0.947
Peanut KOH	First-order	k1 = 1.459	qe = 122.5	0.676
	Second-order	k2 = 0.016	qe = 131.2	0.737
	Elovich	α = 3916	β = 0.063	0.696
	Langmuir	K = 0.026	Smax = 158	0.957
	Freundlich	Kf = 11.810	n = 0.458	0.863

Table 3. Best-fit model parameters of methylene blue sorption on AHCs.

		Parameter 1	Parameter 2	R^2
Hickory H3PO4	First-order	k1 = 0.677	qe = 195.8	0.888
	Second-order	k2 = 0.004	qe = 214.6	0.962
	Elovich	α = 660.553	β = 0.028	0.956
	Langmuir	K = 70.343	Smax = 187.3	0.822
	Freundlich	Kf = 134.004	n = 0.132	0.578
Hickory KOH	First-order	k1 = 1.014	qe = 51.9	0.721
	Second-order	k2 = 0.023	qe = 56.7	0.799
	Elovich	α = 325.760	β = 0.115	0.838
	Langmuir	K = 2.350	Smax = 49.8	0.870
	Freundlich	Kf = 23.798	n = 0.244	0.958
Peanut H3PO4	First-order	k1 = 0.451	qe = 142.5	0.936
	Second-order	k2 = 0.003	qe = 161.1	0.979
	Elovich	α = 196.470	β = 0.032	0.983
	Langmuir	K = 51.852	Smax = 135.5	0.920
	Freundlich	Kf = 93.080	n = 0.206	0.888
Peanut KOH	First-order	k1 = 0.603	qe = 48.8	0.683
	Second-order	k2 = 0.013	qe = 55.2	0.823
	Elovich	α = 97.433	β = 0.097	0.922
	Langmuir	K = 1.808	Smax = 49.9	0.869
	Freundlich	Kf = 23.290	n = 0.247	0.955

Figure 4. Methylene blue adsorption isotherms: (A) H₃PO₄ hickory, (B) KOH hickory, (C) H₃PO₄ peanut, and (D) KOH peanut.

Figure 5. Lead adsorption isotherms: (A) H3PO4 hickory, (B) KOH hickory, (C) H3PO4 peanut, and (D) KOH peanut.

Figure 6. Relationship between surface area and amount of contaminant sorbed by raw HC and AHCs. (A) methylene blue and (B) lead.