Reduction of 4-nitrophenol and 2-nitroaniline using immobilized CoMn2O4 NPs on lignin supported on FPS

Abstract

In the present work, fibrous phosphosilicate (FPS) was functionalized by using octakis[3-(3-aminopropyltriethoxysilane)propyl]octasilsesquioxane (APTPOSS) groups that act as strong performers. In this regard, the nanoparticles of CoMn₂O₄ were dispersed, properly, on FPS microsphere (CoMn₂O₄/APTPOSS@FPS) fibers. Agricultural and industrial waste waters contain nitrophenols. They are amongst the most common organic pollutants. In water, low concentrations are harmful to human health and aquatic life owing to the potential mutagenic and carcinogenic influences of nitrophenols. 4-Nitrophenol (4-NP), as well as 2-nitroaniline (2-NA), are known hazardous toxic waste contaminants and are included in the United States Environmental Protection Agency (USEPA) list. Thus, to eliminate them, novel methods are necessary. In addition, o-phenylenediamine (o-PDA) and 4-aminophenol (4-AP) are considered as significant intermediates for the synthesis of dyes and drugs, which are synthesized from 2-NA and 4-NP. Nanoparticles of CoMn₂O₄/APTPOSS@FPS utilized for the reduction of 2-NA and 4-NP, increase the efficiency of the reaction with considerable chemoselectivity. The results showed that the P and O atoms of lignin-FPS gold nanoparticles (NPs) were stable and the morphology and structure of FPS increased the catalytic activity.

Scheme 1. Reduction of 4-NP and 2-NA from alkylphenols in the presence of the CoMn₂O₄/APTPOSS@FPS NPs.

Scheme 2. Schematic illustration of the synthesis of CoMn₂O₄/APTPOSS@FPS.

Fig. 1. FESEM images of the FPS NPs (a) and CoMn₂O₄/APTPOSS@FPS NPs (b); and TEM images of the FPS NPs (c) and CoMn₂O₄/APTPOSS@FPS NPs (d).

Fig. 2. XRD analysis of (a) the FPS NPs, and (b) the CoMn₂O₄/APTPOSS@FPS NPs.

Fig. 3. EDX spectrum of CoMn₂O₄/APTPOSS@FPS.

Fig. 4. Three-dimensional AFM images of the CoMn₂O₄/APTPOSS@FPS NPs.

Fig. 5. TGA diagram of (a) FPS, and (b) the CoMn₂O₄/APTPOSS@FPS NPs.

Fig. 6. Fourier transform infrared spectroscopy (FTIR) spectra of (a) FPS NPs, and (b) CoMn₂O₄/APTPOSS@FPS NPs.

Fig. 7. UV-vis spectra of (a) 4-NP before and after adding the solution of NaBH₄; (b) the consecutive reduction of 4-NP to 4-AP; as well as (c) 2-NA to o-PDA on the CoMn₂O₄/APTPOSS@FPS NPs catalyst.

Fig. 8. Plots of C_t/C₀ (a) and ln(C_t/C₀) (b) versus reaction time for the reduction of 4-NP over the CoMn₂O₄/APTPOSS@FPS NPs.

Scheme 3. A plausible mechanism for the reduction of p-nitrophenol catalyzed by the CoMn₂O₄/APTPOSS@FPS NPs catalyst in the presence of NaBH₄.

Fig. 9. The reusability of catalysts for the reduction of 4-NP and 2-NA with NaBH₄.

Fig. 10. Kinetic data for the catalyst followed by four recycling runs.

Fig. 11. Recyclability of the catalyst for the reduction of p-nitrophenol.

Fig. 12. Reaction kinetics, Hg(0) poisoning, and hot filtration studies for the reduction of p-nitrophenol.

Fig. 13. (a) EDX, (b) XRD, (c) TEM, and (d) FESEM images of the recovered CoMn₂O₄/APTPOSS@FPS NPs after the tenth run for the reduction of p-nitrophenol.