Fabrication of 3D Gelatin Hydrogel Nanocomposite Impregnated Co-Doped SnO2 Nanomaterial for the Catalytic Reduction of Environmental Pollutants

Abstract

In the catalytic reduction of various environment pollutants, cobalt-doped tin oxide, i.e., Co-SnO₂ intercalated gelatin (GL) hydrogel nanocomposite was prepared via direct mixing of Co-SnO₂ doped with GL. Then, it was crosslinked internally using formaldehyde within a viscous solution of gelatin polymer, which led to the formation of GL/Co-SnO₂ hydrogel nanocomposite. GL/Co-SnO₂ hydrogel nanocomposite was fully characterized by using field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (XRD), and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). The FESEM images indicate that the Co-SnO₂ composite has a spherical structure on the GL matrix while EDX elucidates the elemental composition of each atom in the crosslinked GL/Co-SnO₂ hydrogel nanocomposite. The GL/Co-SnO₂ nanocomposite was checked for the reduction of various pollutants, including 2-nitro-phenol (2-NP), 2,6-dinitro-phenol (2,6-DNP), 4-nitro-phenol (4-NP), Congo red (CR), and methyl orange (MO) dyes with a strong sodium borohydride (NaBH₄) reducing agent. The GL/Co-SnO₂ nanocomposite synergistically reduced the MO in the presence of the reducing agent with greater reduction rate of 1.036 min^-1 compared to other dyes. The reduction condition was optimized by changing various parameters, such as the catalyst amount, dye concentration, and the NaBH₄ amount. Moreover, the GL/Co-SnO₂ nanocomposite catalyst can be easily recovered, is recyclable, and revealed minimal loss of nanomaterials.

Keywords: Co-SnO2 nanomaterial; catalytic reduction; environmental remediation; gelatin hydrogel; recyclability.

Figure 1

FESEM images of pure Co-SnO₂ nanomaterial (a) and GL/Co-SnO₂ nanocomposite material (b) of low and high magnification images (a’,b’), respectively.

Figure 2

EDX spectra of Co-SnO₂ nanomaterial (a) and GL/Co-SnO₂ hydrogel nanocomposite material (b).

Figure 3

XRD patterns of Co-SnO₂ nanomaterial (dark line) and GL/Co-SnO₂ hydrogel nanocomposite material (red line).

Figure 4

FTIR spectra of Co-SnO₂ nanomaterial (a) and GL/Co-SnO₂ hydrogel nanocomposite (b).

Figure 5

Typical UV-visible absorbance spectra of 2-NP (a), 2,6-DNP (b), and 4-NP (c) and their ln(A_t/A₀) vs. time plot for the reduction reactions where the amount of the GL/Co-SnO₂ catalyst used was 0.2 gm (d).

Figure 6

Typical UV-visible absorbance spectra of CR (a), MO (b), and their and ln(A_t/A₀) vs. time plot for the reduction reactions (c,d), where 0.2 gm of the amount of the GL/Co-SnO₂ catalyst was used respectively.

Figure 7

UV-visible spectra of MO reduction (a) and the plot of ln(C_t/C₀) versus time for CR by changing the amount of GL/Co-SnO₂ catalyst, (b) changing the amount of NaBH₄, (c) and different concentrations of dye (d).

Figure 8

Recyclability of the GL/Co-SnO₂ nanocomposite catalyst.

Figure 9

Catalytic reduction of MO in the presence of NaBH₄ onto the GL/Co-SnO₂ nanocomposite catalyst.

Figure 10

Preparation of GL/Co-SnO₂ hydrogel nanocomposite materials.