Catalytic degradation of azo dyes by bimetallic nanoparticles loaded in smart polymer microgels

Abstract

The contamination of water by azo dyes is increasing rapidly due to their waste use in textile industries. These dyes are very toxic for living things. Therefore, it is very important to remove these dyes from water. Various materials are reported for this purpose. Here, the most effective system of bimetallic nanoparticles in smart polymer microgels was prepared. The microgel system of N-isopropylmethacrylamide (NMA) (monomer) and methacrylic acid (MAa) (comonomer) was synthesized by a free radical precipitation polymerization method and then bimetallic (Ag/Ni) nanoparticles were encapsulated into the P(NMA-MAa) microgels by in situ reduction of both silver and nickel salts by NaBH₄ (reductant) after insertion of both (Ag⁺/Ni²⁺) ions. The P(NMA-MAa) microgels and Ag/Ni-P(NMA-MAa) hybrid microgels were characterized with FTIR, UV-vis, TGA, XRD, DLS, EDX, and STEM. The pH and temperature responsive behavior of Ag/Ni-P(NMA-MAa) was also evaluated. The catalytic efficiency of Ag/Ni-P(NMA-MAa) was assessed for degradation of methyl orange (MOr), congo red (CRe), eriochrome black T (EBlT) and methyl red (MRe) dyes under various conditions in aqueous medium. The apparent rate constant (k ₀) value for MOr, CRe, EBlT and MRe was found to be 0.925 min^-1, 0.486 min^-1, 0.540 min^-1 and 0.525 min^-1 respectively. The Ag/Ni-P(NMA-MAa) was found to be an excellent recyclable catalyst.

Fig. 1. Pictorial diagram of synthesis of P(NMA-MAa) and Ag/Ni-P(NMA-MAa).

Fig. 2. FTIR spectra of synthesized P(NMA-MAa) and Ag/Ni-P(NMA-MAa).

Fig. 3. EDX results of (A) P(NMA-MAa) and (B) Ag/Ni-P(NMA-MAa).

Fig. 4. UV-visible spectra of P(NMA-MAa) and Ag/Ni nanoparticles loaded in P(NMA-MAa) at 26 °C and pH = 5.5.

Fig. 5. (A) TGA spectra of P(NMA-MAa) and Ag/Ni nanoparticles loaded in P(NMA-MAa) and (B) DLS results at 26 °C and pH = 5.5.

Fig. 6. UV-visible spectra of Ag/Ni nanoparticles loaded P(NMA-MAa) microgels at room temperature (26 °C) and pH = 6.5.

Fig. 7. UV-visible spectra of Ag/Ni-P(NMA-MAa) at (A) various pH (1–11) and (B) various temperature (20–80 °C).

Fig. 8. Controlled experiment of catalytic degradation of MOr at (A) NaBH₄, MOr, and Ag/Ni-P(NMA-MAa) [conditions: [MOr] = 0.080 mM, [NaBH₄] = 9.65 mM, Ag/Ni-P(NMA-MAa) = 85.71 μg mL⁻¹], (B) MOr, NaBH₄ and P(NMA-MAa) [conditions: [MOr] = 0.080 mM, P(NMA-MAa) = 9.65 μg mL⁻¹, [NaBH₄] = 9.65 mM] (C) MOr and NaBH₄ [conditions: [MOr] = 0.080 mM, [NaBH₄] = 9.65 mM, without addition of P(NMA-MAa) and Ag/Ni-P(NMA-MAa)], (D) MOr and Ag/Ni-P(NM) [conditions: [MOr] = 0.080 mM, Ag/Ni-P(NMA-MAa) = 85.71 μg mL⁻¹, in the absence of NaBH₄].

Fig. 9. Degradation of MOr dye (A) time vs. ln(A_t/A₀) plot under various concentrations of Ag/Ni-P(NMA-MAa) [conditions: NaBH₄ = 9.65 mM, pH = 5.56, concentration of MeOr = 0.080 mM, Ag/Ni-P(NMA-MAa) = (54.74–118.22) μg mL⁻¹] and (B) catalytic dose vs. k₀ at 26 °C.

Fig. 10. Kinetics of catalytic degradation of MOr at 26 °C (A) ln(A_t/A₀) vs. T function for degradation of MOr (0.070–0.100 mM) in the presence of NaBH₄ (9.65 mM) and Ag/Ni-P(NMA-MAa) (85.71 μg mL⁻¹), (B) the k₀vs. MOr concentration dependent graph.

Fig. 11. Effect of concentration of NaBH₄ on catalytic degradation of MOr at 26 °C (A) ln(A_t/A₀) vs. T function for degradation of MOr (0.080 mM) in the presence of NaBH₄ (7.52–12.98 mM) and Ag/Ni-P(NMA-MAa) (85.71 μg mL⁻¹), (B) the k₀vs. NaBH₄ concentration dependent graph.

Fig. 12. Proposed mechanism of catalytic degradation reaction of MOr in the presence of Ag/Ni-P(NMA-MAa) and NaBH₄.

Fig. 13. The catalytic activity percentage of Ag/Ni-P(NMA-MAa) system used for catalytic degradation of MOr [conditions: Ag/Ni-P(NMA-MAa) = 85.71 μg mL⁻¹, concentration of MOr = 0.080 mM, NaBH₄ = 9.65 mM].