Acid blue 40 dye decolorization using magnetite nanoparticles with reduced graphene oxide and mesoporous silica as Fenton catalysts

Abstract

Synthetic dyes are predominantly emitted into the eco-environment resulting, in harmful effects on the environment and human. This study presents a new perspective on the mesoporous silica (SBA-16) and reduced graphene oxide (rGO) obtained from rice husk ash as substrates for Fe₃O₄ nanoparticles (NPs) to investigate their morphological and Fenton catalytic characteristics towards degradation of synthetic acid blue 40 dye (AB40). The adsorption and Fenton catalytic properties of AB40 dye by the prepared Fe₃O₄, Fe₃O₄/SBA-16 and Fe₃O₄/rGO catalysts were examined. The successful synthesis of such catalysts was affirmed by the results obtained from FE-SEM, EDX, TEM, FTIR, XRD and nitrogen adsorption measurements. The adsorption of AB40 dye followed the Langmuir model, with maximum adsorption capacities of 169.2, 21.1 and 16.6 mg/g for Fe₃O₄, for Fe₃O₄/SBA-16 and Fe₃O₄/rGO, respectively. This result was explained based on their specific surface areas. The decolorization efficiency was estimated through several factors, including initial dye concentration, pH and H₂O₂ concentration. The results disclosed that a catalyst dose = 1 g/L, initial dye concentration = 50 mg/L, pH = 3 and [H₂O₂] = 15 mmol/L are the optimum conditions for full decolorization of AB40 within 60 min at 35 °C. The prepared Fe₃O₄ NPs exhibited a superior Fenton activity at 25 °C and pH 3. However, both composites increased Fenton performance above 25 °C, indicating that SBA-16 and rGO substrates can enhance the stability of Fe²⁺ to generate a higher amount of hydroxyl radicals. Regeneration results disclosed that the obtained Fenton-like catalysts revealed notably high catalytic efficiency (> 95%) and stability, with minimal decrease in activity observed after running four cycles of AB40 dye degradation at pH 3 and 35 °C. Thus, this study demonstrated that both SBA-16 and rGO substrates obtained from rice husk ash improved the reusability and stability of Fe₃O₄ catalysts in wastewater treatment using heterogeneous Fenton reactions.

Keywords: Fe3O4; Fenton-like heterogeneous catalysis; Reduced graphene oxide; Rice husk ash; SBA-16.

Fig. 1

Molecular structure of acid blue 40 dye.

Fig. 2

FE-SEM images of (a) Fe₃O₄ NPs, (b) rGO, (c) Fe₃O₄/rGO, (d) SBA-16 and (e) Fe₃O₄/SBA-16.

Fig. 3

EDX spectra of the as-prepared samples.

Fig. 4

TEM images of (a) Fe₃O₄, (b) Fe₃O₄/SBA-16, and (c) Fe₃O₄/rGO at 100 nm and 200 nm scales, respectively (yellow circles indicate Fe₃O₄ distribution).

Fig. 5

FTIR spectra of prepared samples (a) before and (b) after Fenton reaction.

Fig. 6

XRD patterns of the prepared samples.

Fig. 7

NLDFT pore size distribution analysis of prepared based samples.

Fig. 8

N₂ adsorption–desorption measurements of prepared samples.

Fig. 9

Adsorption isotherm plateau of samples toward AB40 dye (pH = 3, Time = 24 h and T = 25 °C).

Fig. 10

Removal efficiency at different AB40 dye concentrations (Time = 24 h and T = 25 °C).

Fig. 11

Linear Plot of Langmuir isotherm model for prepared samples.

Fig. 12

Linear Plot of Freundlich isotherm model for prepared samples.

Fig. 13

Effect of pH on decolorization (%) of AB40 dye (catalyst dose = 1 g/L, C_o = 50 mg/L, time = 60 min, T = 25 °C, and [H₂O₂] = 15 mmol/L).

Fig. 14

Effect of temperature on decolorization (%) of AB40 dye (catalyst dose = 1 g/L, C_o = 50 mg/L, time = 60 min, pH = 3 and [H₂O₂] = 15 mmol/L).

Fig. 15

Effect of [H₂O₂] on decolorization (%) of AB40 dye (catalyst dose = 1 g/L, C_o = 50 mg/L, T = 35 °C, time = 60 min and pH = 3).

Fig. 16

Effect of AB40 concentration on its decolorization (%) (catalyst dose = 1 g/L, [H₂O₂] = 45 mmol, pH = 3, time = 60 min and T = 35 °C).

Fig. 17

Plot of first-order kinetic model for AB40 dye degradation.

Fig. 18

Plot of second-order kinetic model for AB40 dye degradation.

Fig. 19

Reusability of samples for degradation of AB40 dye (catalyst dose = 1 g/L, C_o = 100 mg/L, pH = 3, T = 35 °C, time = 60 min and [H₂O₂] = 45 mmol/L).