Dextran-graft-poly(hydroxyethyl methacrylate) gels: a new biosorbent for fluoride removal of water

Figures & data

Table 1. Experimental control factors and their levels.

Factors	HEMA concentration (mol/l)	EGDMA concentration (mol/l)	APS concentration (mol/l)
Level 1	0.235	0.030	0.006
Level 2	0.352	0.060	0.012
Level 3	0.470	0.090	0.018

Table 2. Experimental layout of an L₉ standard orthogonal array according to Taguchi design.

Sample code	Factors and their levels
	HEMA concentration (mol/l)	EGDMA concentration (mol/l)	APS concentration (mol/l)
S1	0.235	0.030	0.006
S2	0.235	0.060	0.012
S3	0.235	0.090	0.018
S4	0.352	0.030	0.012
S5	0.352	0.060	0.018
S6	0.352	0.090	0.006
S7	0.470	0.030	0.018
S8	0.470	0.060	0.006
S9	0.470	0.090	0.012

Scheme 1 Outline of the synthesis of dextran-g-poly(HEMA) networks.

Figure 1 FTIR spectra of pure dextran (a), HEMA monomer (b) and sample S3 (c).

Figure 2 TGA (a) and DTG (b) curves of pure dextran and sample S3.

Table 3. Experimental results for water absorption and fluoride adsorption studies.¹

Sample Code	FAC (mg/kg)^3	EWA (g/g)^2
S1	7213 ± 196 ^a	8.10 ± 1.48 ^a,b,c
S2	7812 ± 109 ^b,c,d	9.40 ± 1.26 ^d
S3	8312 ± 104 ^e	11.61 ± 1.11 ^c,d
S4	6037 ± 85 ^c,d	8.29 ± 0.59 ^a,b,c
S5	5539 ± 373 ^d	7.32 ± 0.60 ^a,b
S6	5881 ± 194 ^b	9.66 ± 1.30 ^b,c,d
S7	6143 ± 66 ^b,c,d	5.14 ± 0.42 ^a
S8	5768 ± 137 ^c,d	6.18 ± 0.19 ^a
S9	6361 ± 849 ^b,c	9.57 ± 1.88 ^b,c,d
^1According to analysis of variances (p ⩽ 0.05) the difference between quantities with similar superscripts (a, b, c and d) is not significant for data of each column.^2Equilibrium water absorption at pH = 2 (g absorbed distilled water/g dried gel).^3Fluoride adsorption capacity at pH = 7.4 (mg fluoride/kg dried gel).

Table 4. The results of analysis of variance.

Factor	Degree of freedom	Sum of square	Contribution of factor	Contribution (%)
HEMA concentration	2	3,011,464.7	817.666	55.21
EGDMA concentration	2	209,052.3	178.333	12.03
APS concentration	2	1,253,648.1	485.333	32.76

Table 5. Adsorption capacity and other parameters for the removal of fluoride by different biosorbents.

Number	Absorbent	Adsorption capacity (mg/kg)	Contact time (h)	pH	Temperature (°C)	Reference
1	Magnetic-chitosan particle	18,000	2.5	7.0	25	[28]
2	Lanthanum incorporated chitosan beads	4700	24	5.0	30	[30]
2	Fe(III) loaded carboxylated chitosan beads	4230	1	7.0	25	[26]
3	Protonated chitosan beads	1664	1	7.0	25	[31]
4	dextran-graft-poly(HEMA) gel	8312	24	1.0	25	Present study

Figure 3 SEM image of pure dextran microparticles.

Figure 4 SEM images of sample S3 (a) and sample S3 loaded with silver nanoparticles (b). EDXA spectra of sample S3 (c) and sample S3 loaded with silver nanoparticles (d).