Recyclable nanoscale zero-valent iron-based magnetic polydopamine coated nanomaterials for the adsorption and removal of phenanthrene and anthracene

Figures & data

Table 1. Selected properties of phenanthrene and anthracene.

Compound	Abbreviation	Structure	MW* (g/mol)	π electron	log Kow*	Cs*(mg/g)	References
Phenanthrene	PHE		178.2	14	4.57	1.29	[7, 13, 35, 36]
Anthracene	ANT		178.2	14	4.54	0.073	[37]

* MW: molecular weight; K_ow: octanol–water partition coefficient; C_s: water solubility.

Figure 1. Schematic illustration of the synthesis of Fe@SiO₂@PDA nanocomposites.

Figure 2. TEM images of (a) Fe@SiO₂, (b) Fe@SiO₂@PDA; size distribution histograms of (c) Fe@SiO₂ and (d) Fe@SiO₂@PDA; and corresponding EDS spectra of (e) Fe@SiO₂ and (f) Fe@SiO₂@PDA.

Figure 3. XRD pattern of Fe@SiO₂ (a); overview (b) and high-resolution XPS spectra for Fe (c) and C (d). FTIR (e) and VSM hysteresis curves (f) of Fe@SiO₂ and Fe@SiO₂@PDA nanocomposites.

Table 2. Comparison of several iron-based nanoparticles.

Material	Diameter (nm)	Ms (emu g^−1)	Reference
Fe^0@γ-Fe2O3- FeOOH@G	1–5	19	[54]
Fe3O4@SiO2	80–100	11.8	[55]
Fe3O4@SiO2@SiO2-C18	200	7.35	[55]
Fe3O4-SH	—	5.35–11.11	[56]
Fe@SiO2	50	12	[57]
Fe@SiO2	<10	51.98	Present work

G: graphene.

Figure 4. Influence of pH (a), ionic strength (b), HA concentration (c) and initial concentration (d) on the removal of PHE and ANT by the as-prepared Fe@SiO₂@PDA.

Figure 5. Kinetics of PHE and ANT removal by Fe@SiO₂@PDA nanocomposites (a) and the fitted curves of pseudo-first-order model (b), pseudo-second-order model (c) and intraparticle diffusion model (d).

Table 3. Adsorption rate constants for kinetic models at 298 K pH 7.0.

Kinetic models	PHE			ANT
	k	qe (cal)	R^2	k	qe (cal)	R^2
Pseudo-first-order	0.003 (min^−1)	0.089(mg g^−1)	0.795	0.003(min^−1)	0.035(mg g^−1)	0.772
Pseudo-second-order	0.15 (g mg^−1 min^−1)	0.194(mg g^−1)	0.998	2.22(g mg^−1 min^−1)	0.367(mg g^−1)	0.999
Intraparticle diffusion	0.003(mg g^−1 min^0.5)	–	0.767	3 × 10^−5(mg g^−1 min^0.5)	–	0.740

Figure 6. Adsorption isotherms of PHE (a), ANT (b) at 298, 303 and 308 K.

Table 4. Regression parameters of isotherm models.

Isotherm	Analytes	Temperature (K)	Parameters
Langmuir			KL (l mg^−1)	qm (mg g^−1)	R^2
	PHE	298	4.87	0.484	0.855
		303	2.80	0.572	0.868
		308	2.73	0.512	0.820
	ANT (low*/high*)	298	260/–14.7	0.094/–0.184	0.993/0.977
		303	216/–10.8	0.094/–0.259	0.972/0.817
		308	148/–4.71	0.101/–0.663	0.979/0.829
Freundlich			KF (l g^−1)	n	R^2
	PHE	298	0.662	1.50	0.992
		303	0.729	1.25	0.975
		308	0.614	1.28	0.965
	ANT (low*/high*)	298	0.297/118	2.99/0.528	0.996/0.978
		303	0.293/34.9	2.92/0.626	0.986/0.949
		308	0.399/7.93	2.38/0.824	0.999/0.985
Temkin			A (L g^−1)	b (kJ mol^−1)	R^2
	PHE	298	120	34.9	0.847
		303	66.5	31.1	0.914
		308	61.5	33.3	0.908
	ANT (low*/high*)	298	3143/58.9	130.4/7.79	0.988/0.862
		303	2683/56.6	132.6/9.09	0.955/0.846
		308	1552/58.7	111.3/12.3	0.984/0.909
D–R			qm′ (mol kg^−1)	EDR (kJ mol^−1)	R^2
	PHE	298	0.292	5	0.932
		303	0.339	4.08	0.985
		308	0.306	4.08	0.976
	ANT (low*/high*)	298	0.132/4.88	10/3.54	0.996/0.967
		303	0.128/2.54	9.13/3.54	0.974/0.929
		308	0.153/1.24	8.45/4.08	0.994/0.970

^* Low: C₀ (initial concentration) < 0.1 mg l^–1; high: C₀ (initial concentration) ≥ 0.1 mg l^–1.

Figure 7. Adsorption isotherms of ANT fitting by two stages at 298 K, (a) Langmuir, (b) Freundlich, (c) Temkin, (d) D–R model.

Table 5. Thermodynamic parameters of PHE and ANT.

Thermodynamic parameters	PHE		ANT
		Whole	Low*	High*
ΔG^0 (kJ mol^−1)
298 K	−2.40	−5.15	−11.4	−2.91
303 K	−1.55	−4.94	−10.1	−2.88
308 K	−0.735	−4.74	−8.96	−2.86
ΔH^0 (kJ mol^−1)	−51.2	−17.1	−81.5	−4.22
ΔS^0 (kJ mol^−1 K^−1)	−0.164	−0.04	−0.235	−0.004

^* Low: C₀ (initial concentration) < 0.1 mg l^–1; high: C₀ (initial concentration) ≥ 0.1 mg l^–1.

Figure 8. Recyclable adsorption of ANT by Fe@SiO₂@PDA.

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