Binary adsorption studies of Cr(VI) and Cu(II) ions from synthetic wastewater using carbon from Feoniculum vulgare (fennel seeds)

Figures & data

Figure 1. XRD graphs for (a) FS-500, FS-600 & FS-700; (b) KMFS-500, KMFS-600 & KMFS-700.

Figure 2. FTIR spectra for (a) FS-500, FS-600 and fs-700 and (b) KMFS-500, KMFS-600 and KNFS-700.

Figure 3. SEM and EDX results for (a) FS-500, (b) FS-600, (c) FS-700, (d) KMFS-500, (e) KMFS-600 and (f) KMFS-700.

Figure 4. UV-Vis results for (a) FS-500, FS-600 and FS-700; (b) KMFS-500, KMFS-600 and KMFS-700.

Table 1. Point zero charge pH(_PZC) of the adsorbent

Adsorbent	FS-500	FS-600	FS-700	KMFS-500	KMFS-600	KMFS-700
pH(PZC)	11	10.9	11.5	9.4	9.5	10

Figure 5. Effect of concentration for the removal of Cu(II) on (a) FS-500, FS-600 and FS-700; (b) Cr(VI) on FS-500, FS-600; (c) Cu(II) on KMFS-500, KMFS-600 and KMFS-700 and Cr(VI) (d) KMFS-500, KMFS-600 and KMFS-700.[Conditions: pH(5), adsorbent dosage (0.1 g), contact time (2 h), solution volume (20 mL), temperature (298 K) and agitation speed(200 rpm)].

Figure 6. Effect of time for the removal of Cu(II) on (a) FS-500, FS-600 and FS-700; (b) Cr(VI) on FS-500, FS-600; (c) Cu(II) on KMFS-500, KMFS-600 and KMFS-700 and Cr(VI) (d) KMFS-500, KMFS-600 and KMFS-700. [Conditions: pH(5), adsorbent dosage (0.1 g), concentration (100 mg/L, solution volume (20 mL), temperature (298 K) and agitation speed(200 rpm)].

Figure 7. Effect of temperature for the removal of Cu(II) on (a) FS-500, FS-600 and FS-700; (b).

Figure 8. Effect of pH for the removal of Cu(II) on (a) FS-500, FS-600 and FS-700; (b) Cr(VI) on FS-500, FS-600; (c) Cu(II) on KMFS-500, KMFS-600 and KMFS-700 and Cr(VI) (d) KMFS- 500, KMFS-600 and KMFS-700. [Conditions: temperature (298 K), adsorbent dosage (0.1 g), concentration (100 mg/L, solution volume (20 mL), time (2 h) and agitation speed (200 rpm)].

Table 2. Adsorption kinetics studies for carbonized fennel seeds

Model	Parameter	FS-500		FS-600		FS-700
		Cu(II)	Cr(VI)	Cu(II)	Cr(VI)	Cu(II)	Cr(VI)
PFO	Qe (mg/g)	18.341	2.393	15.741	2.460	19.885	8.962
	B	0.404	0.023	0.714	0.089	0.639	0.523
	R^2	0.928	0.991	0.917	0.915	0.999	0.955
PSO	kf	19.186	3.317	15.958	2.774	20.036	9.189
	N	0.046	0.006	0.219	0.045	0.237	0.185
	R^2	0.990	0.987	0.997	0.997	0.985	0.995
IPD	Qe (mg/g)	15.855	1.039	14.999	1.084	19.487	8.257
	ki	0.384	1.063	0.123	0.164	0.052	0.111
	R^2	0.907	0.956	0.953	0.930	0.917	0.949
EPA	%	18.049	52.471	7.602	58.467	2.110	11.888
ESA	%	81.951	47.529	92.298	41.533	97.890	88.112
Experimental	Qe (mg/g)	19.347	2.186	16.233	2.610	19.907	9.371

Table 3. Adsorption kinetics studies for KMnO₄ treated carbonized fennel seeds

Model	Parameter	KMFS-500		KMFS-600		KMFS-700
		Cu(II)	Cr(VI)	Cu(II)	Cr(VI)	Cu(II)	Cr(VI)
PFO	Qe (mg/g)	17.299	4.540	19.844	6.302	19.782	10.039
	B	0.592	0.070	1.019	0.514	0.938	0.563
	R^2	0.951	0.934	0.972	0.958	0.936	0.961
PSO	kf	17.543	5.293	19.882	6.493	19.825	10.249
	N	0.165	0.016	1.160	0.224	0.944	0.203
	R^2	0.989	0.972	0.993	0.996	0.996	0.999
IPD	Qe (mg/g)	16.610	1.471	19.738	5.733	19.658	9.406
	ki	0.102	0.358	0.016	0.090	0.018	0.099
	R^2	0.904	0.954	0.929	0.902	0.949	0.918
EPA	%	5.275	70.785	0.689	12.726	0.882	9.182
ESA	%	94.725	29.215	99.311	87.274	99.118	90.818
Experimental	Qe (mg/g)	17.535	5.035	19.875	6.569	19.833	10.357

Table 4. Adsorption isotherms studies for carbonized fennel seeds

Model	Parameter	FS-500		FS-600		FS-700
		Cu(II)	Cr(VI)	Cu(II)	Cr(VI)	Cu(II)	Cr(VI)
Langmuir	Qe (mg/g)	16.78	1.664	15.02	1.001	19,56	9.882
	B	0.0004	1.845	4.168	4.505	1241	1.324
	R^2	0.989	0.772	0.965	0.961	0.002	0.853
Freundlich	kf	0.175	0.879	0.018	0.002	0.188	0.807
	N	0.997	0.234	0.683	0.710	0.988	0.380
	R^2	0.989	0.984	0.995	0.988	0.999	0.998
Experimental	Qe (mg/g)	16.92	1.722	15.423	1.202	19.892	10.572

Table 5. Adsorption isotherms studies for KMnO₄ treated carbonized fennel seeds

Model	Parameter	KMFS-500		KMFS-600		KMFS-700
		Cu(II)	Cr(VI)	Cu(II)	Cr(VI)	Cu(II)	Cr(VI)
Langmuir	Qe (mg/g)	17.45	3.223	15.68	8.574	19.79	9.674
	b	6.363	0.0004	0.002	5.107	1095	1331
	R^2	0.984	0.922	0.987	0.954	0.002	0.988
Freundlich	kf	0.699	0.059	0.276	0.016	0.181	0.043
	N	0.978	1.161	1.149	0.743	0.980	0.836
	R^2	0.940	0.985	0.988	0.976	0.999	0.997
Experimental	Qe (mg/g)	17.648	3.479	15.735	8.109	19.786	10.572

Table 6. Adsorption thermodynamic studies for carbonized fennel seeds

Model	FS-500		FS-600		FS-700
	Cu(II)	Cr(VI)	Cu(II)	Cr(VI)	Cu(II)	Cr(VI)
ΔH^0 (KJ/mol)	−2.466	−2.099	−0.456	−1.942	−1.912	−0.383
ΔS^0 (KJ/molK)	0.009	0.002	0.001	0.002	0.009	−0.001
ΔG^0 288 K (KJ/mol)	−13.02	−12.28	−0.916	−10.72	−7.564	−4.481
298 K	−2.303	−11.93	−0.874	−10.39	−8.129	−4.569
308 K	−2.884	−11.85	−0.826	−10.29	−9.088	−4.516

Table 7. Comparison with other adsorbents

Adsorbents	Cu(II) Qe(max) (mg/g)	References
Banana biochar	142.86	Amin et al., 2018
Persimmon leaf bio-waste	19.427	Lee & Choi, 2018
Allium cepa seeds	1.62	Sheikh et al., 2021
500 AC-Fennel seeds	16.78	Current study
600 AC-Fennel seeds	15.02	Current study
700 AC-Fennel seeds	19.56	Current study
KMnO4 treated 500 AC-Fennel seeds	17.43	Current study
KMnO4 treated 600 AC-Fennel seeds	15.68	Current study
KMnO4 treated 700 AC-Fennel seeds	19.79	Current study
	Cr(II) Qe(max) (mg/g)
AC-Cocoa shell	94.340	Fotsing et al., 2020
KMno4 treated black cumin seeds	17.5	Thabede et al., 2020
AC-Ziziphus spina-christi leaf	13.81	Abshirini et al., 2019
AC-Leucaena leucocephula seed plot	26.94	Yusuff, 2019
AC-Apple peels	36.01	Enniya et al., 2018
500 AC-Fennel seeds	1.664	Current study
600 AC-Fennel seeds	1.001	Current study
700 AC-Fennel seeds	9.882	Current study
KMnO4 treated 500 AC-Fennel seeds	3.223	Current study
KMnO4 treated 600 AC-Fennel seeds	8.574	Current study
KMnO4 treated 700 AC-Fennel seeds	9.674	Current study

Figure 9. Reusability studies for (a) Cu(II) and (b) Cr(VI) on carbonized fennel seeds and (c) Cu(II) and (d) Cr(VI) on KMnO₄ treated carbonized fennel seeds. Mechanism for Cr(VI) and Cu(II).

Figure 10. Schematic diagram for the adsorption mechanism of Cr(VI) and Cu(II) on the adsorbents surface.

Figure 11. FTIR spectra for Cu(II) and Cr(VI) on FS-600 and KMFS-700 before and after adsorption.

Figure 12. SEM images and EDX results for (a) FS-500, (b) FS-600, (c) FS-700. (d) KMFS-500, (e) KMFS-600 and (f) KMFS-700 after adsorption.

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Data availability statement

The data supporting the findings of the study may be made available from the corresponding authors on request.