Preparation of Cotton Linters' Aerogel-Based C/NiFe2O4 Photocatalyst for Efficient Degradation of Methylene Blue

Abstract

At present, the research focus has been aimed at the pursuit of the design and synthesis of catalysts for effective photocatalytic degradation of organic pollutants in wastewater, and further exploration of novel materials of the photodegradation catalyst. In this paper, the Sol-gel route after thermal treatment was used to produce NiFe₂O₄ carbon aerogel (NiFe₂O₄-CA) nanocomposites with cotton linter cellulose as the precursor of aerogel, by co-precipitating iron and nickel salts onto its substrate. The structure and composition of these materials were characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), Raman spectra, high-resolution scanning electron microscopy (HR-SEM), high-resolution scanning electron microscope mapping (SEM-mapping), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET)'s surface area. The magnetic properties of the material were analyzed by a vibrating-sample magnetometer (VSM). Moreover, diffuse reflectance spectra (DRS), electrochemical impedance spectroscopy (EIS) and photo-luminescence spectroscopy (PL) characterized the photoelectric properties of this cellulose-aerogels-based NiFe₂O₄-CA. Methylene blue (MB) acted as the simulated pollutant, and the photocatalytic activity of NiFe₂O₄-CA nanocomposites under visible light was evaluated by adjusting H₂O₂ content and the pH value. The results showed that the optical absorption range of nickel ferrite was broadened by doping cellulose-aerogels-based carbon, which exerted more positive effects on photocatalytic reactions. This is because the doping of this aerogel carbon promoted a more uniform distribution of NiFe₂O₄ particles. Given the Methylene blue (MB) degradation reaction conformed to the first-order kinetic equation, the NiFe₂O₄-CA nanocomposites conducted excellent catalytic activity by maintaining almost 99% of the removal of MB (60 mg/L) within 180 min and upheld excellent stability over four consecutive cycles. This study indicated that NiFe₂O₄-CA nanocomposites reserved the potential as a future effective treatment of dye wastewater.

Keywords: NiFe2O4; carbon aerogel; cellulose; magnetism; photo-Fenton.

Scheme 1

Instructions on the formation route of NiFe₂O₄-CA.

Figure 1

(a) XRD of different calcinated temperatures of cotton linters’ cellulose/NiFe₂O₄-CA-600 °C; (b) EDS of cellulose/NiFe₂O₄-CA-600 °C; (c) Raman spectrum of cellulose/NiFe₂O₄-CA-600 °C and cellulose carbon aerogels; (d–h) XPS spectra of cotton linters’ cellulose/50%NiFe₂O₄-CA-600 °C.

Figure 2

HR-SEM of (a) cellulose aerogels; (b) cellulose carbon aerogels; (c) NiFe₂O₄ nanoparticles; (d–f) cellulose/50%NiFe₂O₄-CA-600 °C; (g) EDS-mapping image of cotton linter cellulose/NiFe2O4-CA-600 °C.

Figure 3

(a) Hysteresis loops of NiFe₂O₄, cellulose/50%NiFe₂O₄-CA-600 °C, cellulose/50%NiFe₂O₄ hybrid aerogels; N₂ isothermal adsorption/desorption and pore diameter distribution curves of (b) NiFe₂O₄, (c) cellulose/50%NiFe₂O₄-CA-600 °C, (d) cellulose/50%NiFe₂O₄ hybrid aerogels.

Figure 4

(a) Electrochemical impedance spectroscopy; (b) FLS of NiFe₂O₄ and cellulose/50%NiFe₂O₄-CA-600 °C (λ_ex = 325 nm); (c) DRS and (d) Tauc plots of NiFe₂O₄, cellulose/50%NiFe₂O₄-CA-600 °C, cellulose/50%NiFe₂O₄.

Figure 5

(a) Adsorption equilibrium curves under different loads. (b) Photodegradation curves under different loads (C₀ = 20 mg/L, m(cellulose/50%NiFe₂O₄-CA-600 °C) = 50 mg). (c) Effects of different calcination temperatures on photodegradation. (d) Effects of different dosages of H₂O₂ on photodegradation., (e) Kinetic curves of different H₂O₂ dosages. (f) UV-visible absorption spectrum (n(H₂O₂) = 20 mmol). (C₀(MB) = 20 mg/L).

Figure 6

(a) Effects of different pH values. (b) Photodegradation kinetics curves with different pH values (C₀(MB) = 20 mg/L, n(H₂O₂) = 20 mmol, m(cellulose/50%NiFe₂O₄-CA-600 °C) = 50 mg). (c) Photodegradation effects under different conditions.

Figure 7

(a) Degradation effects and kinetic curves at different MB concentrations (n(H₂O₂) = 20 mmol, m(cellulose/50%NiFe₂O₄-CA-600 °C) = 50 mg, pH = 11). (b) Degradation effects and kinetic curves at different catalyst concentrations (n(H₂O₂) = 20 mmol, C₀(MB) = 40 mg/L, pH = 11). (c) Time change diagram of cyclic experiments. (d) Bar chart of run efficiency (m(cellulose/50%NiFe₂O₄-CA-600 °C) = 20 mg, C_(MB) = 20 mg/L, n(H₂O₂) = 20 mmol, pH = 11).