Improving the Adsorption Properties of Keratin-Based Goat Hair Toward Reactive Dyes in Dyeing Wastewater by Steam Explosion

Figures & data

Figure 1. Preparation schematics of the three bio-adsorbents CGH, FDGH and EGHP.

Figure 2. Effect of the adsorption bath pH on adsorption quantity of RB 19 onto EGHP (Conditions of steam explosion: 1.2 MPa, 120 s; Adsorption conditions: initial dye concentration 3000 mg/L, pH 2.0–9.5, amount of EGHP 10 g/L.).

Figure 3. Adsorption mechanisms of RB 19 on at pH value lower than its isoelectric point of around pH 4.1.

Figure 4. (a) Adsorption kinetic curves and fitted adsorption kinetic curves of RB 19 onto CGH, FDGH and EGHP with (b) pseudo-first-order and (c) pseudo-second-order model (Conditions of steam explosion: 1.3 MPa, 150 s; Adsorption conditions: pH 2.0, initial dye concentration for CGH 300 mg/L, for FDGH 1400 mg/L and for EGHP 3000 mg/L, amount of CGH, FDGH and EGHP 10 g/L.).

Table 1. Adsorption kinetic parameters of RB19 onto CGH, FDGH and EGHP.

Samples	qe,exp (mg/g)	Pseudo-first-order			Pseudo-second-order
		qe,cal (mg/g)	k1 (h^−1)	R^2	qe,cal (mg/g)	k2 (g/mg.h)	R^2
CGH	25.2	20.95	0.14	0.96	24.0	0.0218	0.980
FDGH	116.6	85.29	0.47	0.97	126.0	0.0103	0.999
EGHP	286.3	243.47	0.88	0.93	296.5	0.0087	0.998

q_e,exp and q_e,cal are the experimental and calculated amounts of RB 19 dye adsorbed onto goat hair at equilibrium, respectively.

Figure 5. Removal efficiency and adsorption at equilibrium of (a) CGH, (b) FDGH and (c) EGHP toward RB19 under the different initial dye concentration; Langmuir and Freundlich adsorption isotherm curves of (d) CGH, (e) FDGH and (f) EGHP toward RB19.(Adsorption conditions for CGH: initial dye concentration 50–1100 mg/L, pH 2.0, amount of CGH 10 g/L, adsorption time 28 h; Adsorption conditions for FDGH: initial dye concentration 400–3000 mg/L, pH 2.0, amount of FDGH 10 g/L, adsorption time 8 h; Conditions of steam explosion: 1.3 MPa,150 s; Adsorption conditions for EGHP: initial dye concentration 2400–5000 mg/L, pH 2.0, amount of EGHP 10 g/L, adsorption time 8 h.).

Table 2. Adsorption isotherm parameters and correlation coefficient R² of fitting the adsorption of RB19 on goat hair with Langmuir and Freundlich isotherm models.

Goat hair	Langmuir			Freundlich
	b (L/mg)	qmax (mg/g)	R^2	KF ((mg·g^−1)(L·mg^−1)^1/n)	1/n	R^2
CGH	0.019	55.24	0.99	15.6	0.3029	0.93
FDGH	0.997	124.75	0.99	25.21	0.4029	0.82
EGHP	4.570	286.30	0.99	26.51	0.3593	0.90

Figure 6. Effects of (a) steam pressure and (b) steam treatment time on adsorption capacity of EGHP toward RB19(Adsorption conditions: initial dye concentration 3500 mg/L, pH 2.0, amount of EGHP 10 g/L, adsorption time 8 h.).

Figure 7. SEM images (х800) of goat hair (a) before and (b) ~ (h) after being steam exploded under different conditions.

Figure 8. (a) Electric photo of CGH and SEM images of (b) FDGH and (c) EGHP.

Figure 9. XRD spectra of CGH and EGHP after the different steam explosion conditions (a) Different steam pressure for the steam treatment time of 150 s; (b) the steam pressure of 1.5 MPa for different time of 30–240 s.

Table 3. Effect of steam pressure and steam treatment time on the crystal index (CI) of EGHP.

Conditions of steam explosion		$\mathit{I}9°$	$\mathit{I}14°$	CI (%)
Original goat hair (CGH)		3342	2337	30.1
Different steam pressure	1.3 MPa,150s	2189	2012	8.1
	1.5 MPa,150s	2062	1951	5.4
	1.8 MPa, 150s	2011	1959	2.6
Different steam treatment time	1.5 MPa, 30s	2138	1977	8
	1.5 MPa, 90s	2063	1935	6.2
	1.5 MPa, 150s	2062	1951	5.4
	1.5 MPa, 240s	2067	1959	5.2

Figure 10. Nitrogen adsorption-desorption isotherm curves for different goat hair (Lower curve: adsorption curve; Upper curve: desorption curve). (a) CGH, (b) FDGH, (c) EGHP-1.3mpa, (d)eghp-1.5mpa and (e)eghp-1.8mpa.

Table 4. BET surface area and pore size of CGH, FDGH and EGHP.

Goat hair	BET specific surface area/(m^2/g)	BJH adsorption cumulative surface area of pores /(m^2/g)	BJH adsorption cumulative volume of pores/(mm^3/g)	BJH adsorption average pore width (4V/A) /Å
CGH	0.678	0.269	0.170	25.332
FDGH	1.054	0.310	0.175	22.601
EGHP(1.3MPa, 150s)	3.052	2.187	2.091	38.244
EGHP(1.5MPa,150s)	4.410	3.189	3.405	42.720
EGHP(1.8MPa,150s)	8.583	5.539	5.419	39.134

BJH adsorption cumulative surface area and volume of pores between 17 Å and 3000 Å width.

Table 5. Concentration of free NH₂ groups for CGH, FDGH and EGHP.

Bioadsorbents	Concentration of free NH2 /(mmol/g)
CGH	0.176
FDGH	0.228
EGHP(1.8MPa,150s)	0.458

Figure 11. The adsorption capacity of EGHP after different adsorption-desorption cycles toward RB 19 (Conditions of steaming explosion: 1.3 MPa, 150 s; Adsorption conditions: initial dye concentration 3500 mg/L, pH 2.0, amount of EGHP 10 g/L).

Table 6. Comparison of adsorption capacities of other recently reported adsorbents for the anionic dyes.

Adsorbents	Anionic dyes	Adsorption capacity qe (mg/g)	pH	References
Cationic metal-organic framework	Anionic methyl orange	310	3	Liu et al. (2022)
Nanoporous silica hydyogel	Rhodamine B	163.54	7	Lahiri et al. (2022)
TiO(OH)2 microstructures	Methylene blue	257	7	Xing et al. (2022)
Modified resin DK 110	Acidic orange/reactive red	109.45/111.94	2-10	Ma et al. (2022)
EGHP (1.8MPa, 150s)	RB 19	427	2.0	This work

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