Cu(ii) immobilized on Fe3O4@HNTs-tetrazole (CFHT) nanocomposite: synthesis, characterization, investigation of its catalytic role for the 1,3 dipolar cycloaddition reaction, and antibacterial activity

Abstract

In the present study, Cu(ii) immobilized on an Fe₃O₄@HNTs-tetrazole (CFHT) nanocomposite was designed and prepared. For this, halloysite nanotubes (HNTs) as natural mesoporous substances were modified during several chemical reactions. The synthesis of the CFHT nanocomposite was investigated step by step with the required physicochemical techniques such as FT-IR, EDX, SEM, TEM, XRD, VSM, TGA and CHNS analyses. After ensuring that the nanocomposite was successfully prepared, its catalytic application in the synthesis of the 5-substituted 1H-tetrazole derivatives via multicomponent reactions (MCRs) between aromatic aldehydes, malononitrile, and sodium azide was assessed. According to the experimental results, the prepared nanocomposite exhibited excellent capability for conducting this MCR reaction. All desired products were obtained in a short reaction time (30-40 min) with high productivity (90-97%) and without a complicated workup procedure. Furthermore, the magnetic property of the synthesized heterogeneous nanocomposite empowers it to be recovered and reused in five times successive reactions without any significant reduction in reaction efficiency. Moreover, the remarkable antibacterial activity of the nanocomposite against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was evaluated by agar diffusion and plate-count methods. The zones of inhibition were around 16 and 20 mm for E. coli and S. aureus bacteria, respectively. Also, colony analysis confirms the killing of bacteria by using the CFHT nanocomposite.

Fig. 1. The preparation pathway of the CFHT nanocomposite and production of 5-substituted 1H-tetrazoles derivatives.

Fig. 2. The FT-IR spectra of the Fe₃O₄@HNTs (a), Fe₃O₄@HNTs–CPTS (b) and CFHT nanocomposite (c).

Fig. 3. EDX analysis of the Fe₃O₄@HNTs–CPTS (a), the CFHT nanocomposite (b) and mapping images of the CFHT nanocomposite (c).

Fig. 4. SEM images of the CFHT nanocomposite.

Fig. 5. TEM images of the CFHT nanocomposite.

Fig. 6. VSM analysis of Fe₃O₄@HNTs (a) and the CFHT nanocomposite (b).

Fig. 7. TGA analysis of the Fe₃O₄@HNTs–CPTS (a), the Fe₃O₄@HNTs–tetrazole (b) and the CFHT nanocomposite (c).

Fig. 8. XRD analysis of the CFHT nanocomposite (a), the Fe₃O₄, HNTs and Cu patterns (b).

Fig. 9. Recycling diagram of the CFHT nanocatalyst in the synthesis of 4a.

Fig. 10. Suggested mechanism for the synthesis of 5-substituted 1H-tetrazoles derivatives (4a–h) in the presence of the CFHT nanocatalyst.

Fig. 11. Inhibition zones of (1) Cu(ii), (2) 1H-tetrazoles, (3) Fe₃O₄@HNTs–CPTS, (4) Fe₃O₄@HNTs–tetrazole and (5) CFHT nanocomposite against (a) S. aureus and (b) E. coli bacteria for 24 h.

Fig. 12. Colony counter images of S. aureus (a) and E. coli (b) after 24 h of incubation, (1) before treatment (control plate), after treatment with (2) Fe₃O₄@HNTs–CPTS, (3) Fe₃O₄@HNTs–tetrazole, and (4) synthesized CFHT nanocomposite.