Performance and Mechanism of As(III/V) Removal from Aqueous Solution by Fe3O4-Sunflower Straw Biochar

Abstract

Humans and ecosystems are severely damaged by the existence of As(III/V) in the aquatic environment. Herein, an advanced Fe₃O₄@SFBC (Fe₃O₄-sunflower straw biochar) adsorbent was fabricated by co-precipitation method with sunflower straw biochar (SFBC) prepared at different calcination temperatures and different SFBC/Fe mass ratios as templates. The optimal pH for As(III/V) removal was investigated, and Fe₃O₄@SFBC shows removal efficiency of 86.43% and 95.94% for As(III) and As(V), respectively, at pH 6 and 4. The adsorption effect of calcining and casting the biochar-bound Fe₃O₄ obtained at different temperatures and different SFBC/Fe mass ratios were analyzed by batch experiments. The results show that when the SFBC biochar is calcined at 450 °C with an SFBC/Fe mass ratio of 1:5, the adsorption of As(III) and As(V) reaches the maximum, which are 121.347 and 188.753 mg/g, respectively. Fe₃O₄@SFBC morphology, structure, surface functional groups, magnetic moment, and internal morphology were observed by XRD, FTIR, SEM, TEM, and VSM under optimal working conditions. The material shows a small particle size in the range of 12-14 nm with better magnetic properties (54.52 emu/g), which is suitable for arsenic removal. The adsorption mechanism of As(III/V) by Fe₃O₄@SFBC indicates the presence of chemisorption, electrostatic, and complexation. Finally, the material was used for five consecutive cycles of adsorption-desorption experiments, and no significant decrease in removal efficiency was observed. Therefore, the new adsorbent Fe₃O₄@SFBC can be efficiently used for arsenic removal in the aqueous system.

Keywords: As(III/V); Fe3O4; adsorption; magnetic composite; sunflower straw biochar.

Figure 1

XRD spectra of Fe₃O₄ nanomaterials prepared by biochar at different calcination temperatures (a) and XRD spectra of Fe₃O₄ nanomaterials prepared by different SFBC/Fe mass ratios (b).

Figure 2

FTIR spectra of Fe₃O₄ nanomaterials prepared using biochar at different calcination temperatures (a) and FTIR spectra of Fe₃O₄ nanomaterials prepared by different SFBC/Fe mass ratios (b).

Figure 3

Effect of pH on the removal of As(III/V) (experimental conditions: pH = 3–11, dose = 1 g/L, initial concentration = 5 mg/L, T = 25 °C), Y error bars indicate the standard deviation of each data point (n = 3).

Figure 4

Adsorption kinetics of As(III) (a) and As (V) (b) on Fe₃O₄@SFBC (prepared from biochar at different calcination temperatures) (experimental conditions: pH = 6 and 4, dose = 1 g/L, initial concentration = 5 mg/L, T = 25 °C).

Figure 5

Adsorption kinetics of As(III) (a) and As(V) (b) on Fe₃O₄@SFBC (different SFBC/Fe mass ratios) (experimental conditions: pH = 6 and 4, dosage = 1 g/L, initial concentration = 5 mg/L, T = 25 °C).

Figure 6

Adsorption isotherms of Langmuir (a) and Freundlich (b) on As(III) by Fe₃O₄@SFBC (prepared from biochar at different calcination temperatures) (experimental conditions: pH = 6, dose = 1 g/L, initial concentration = 0.1–10 mg/L, T = 25 °C).

Figure 7

Adsorption isotherms of Langmuir (a) and Freundlich (b) on As(V) by Fe₃O₄@SFBC (prepared from biochar at different calcination temperatures) (experimental conditions: pH = 4, dose = 1 g/L, initial concentration = 0.1–10 mg/L, T = 25 °C).

Figure 8

Adsorption isotherms of Langmuir (a) and Freundlich (b) on As(III) by Fe₃O₄@SFBC (different SFBC/Fe mass ratios) (experimental conditions: pH = 6, dose = 1 g/L, initial concentration = 0.1–10 mg/L, T = 25 °C).

Figure 9

Adsorption isotherms of Langmuir (a) and Freundlich (b) on As(V) by Fe₃O₄@SFBC (different SFBC/Fe mass ratios) (experimental conditions: pH = 4, dose = 1 g/L, initial concentration = 0.1–10 mg/L, T = 25 °C).

Figure 10

SEM images of SFBC (a) and Fe₃O₄@SFBC (b). TEM particle size distribution (c) and TEM lattice stripe (d) patterns of Fe₃O₄@SFBC.

Figure 11

Magnetic hysteresis loop of Fe₃O₄ and Fe₃O₄@SFBC nanoparticles.

Figure 12

XPS spectra of Fe₃O₄@SFBC before and after arsenic adsorption: O 1s (a), Fe 2p (b), As 3d (c), C 1s (d).

Figure 13

FTIR spectra of Fe₃O₄@SFBC before and after the adsorption of As(III/V).

Figure 14

Recycling performance of different Fe₃O₄@SFBC materials (pH = 6 and 4, dose = 1 g/L, initial concentration = 5 mg/L, T = 25°C).