Dye degradation performance, bactericidal behavior and molecular docking analysis of Cu-doped TiO2 nanoparticles

Abstract

Copper-doped TiO₂ was prepared with a sol-gel chemical method. Various concentrations (3, 6, and 9 wt%) of Cu dopant were employed. Several techniques were implemented to assess the structural, optical, morphological and chemical properties of the synthesized samples. Evaluation of elemental composition using SEM-EDS and XRF techniques showed the presence of dopant element in the prepared samples. XRD analysis confirmed the presence of anatase (TiO₂) phase with interstitial doping. Incorporation of dopant was observed to enhance the crystallinity and increase the crystallite size of the synthesized products. SAED profiles revealed a high degree of crystallinity in the prepared specimens, which was also evident in the XRD spectra. Optical properties studied using UV-vis spectroscopy depicted a shift of the maximum absorption to the visible region (redshift) that signified a reduction in the band gap energy of Cu-doped TiO₂ samples. Examination of morphological features with scanning and high-resolution transmission electron microscopes revealed the formation of spherical nanoparticles with a tendency to agglomerate with increasing dopant concentration. Molecular vibrations and the formation of Ti-O-Ti bonds were revealed through FTIR spectra. PL spectroscopy recorded the trapping efficiency and migration of charge carriers, which exhibited electron-hole recombination behavior. Doped nanostructures showed enhanced bactericidal performance and synergism against S. aureus and E. coli. In summary, Cu-doped TiO₂ nanostructures were observed to impede bacteria effectively, which is deemed beneficial in overcoming ailments caused by pathogens such as microbial etiologies. Furthermore, molecular docking analysis was conducted to study the interaction of Cu-doped TiO₂ nanoparticles with multiple proteins namely β-lactamase (binding score: -4.91 kcal mol^-1), ddlB (binding score: -5.67 kcal mol^-1) and FabI (binding score: -6.13 kcal mol^-1) as possible targets with active site residues. Dye degradation/reduction of control and Cu-doped samples were studied through absorption spectroscopy. The obtained outcomes of the performed experiment indicated that the photocatalytic activity of Cu-TiO₂ enhanced with increasing dopant concentration, which is thought to be due to a decreased rate of electron-hole pair recombination. Consequently, it is suggested that Cu-TiO₂ can be exploited as an effective candidate for antibacterial and dye degradation applications.

Fig. 1. Synthesis process for TiO₂ and Cu-doped TiO₂ nanoparticles.

Fig. 2. Photocatalytic mechanism of dye degradation in the presence of Cu-TiO₂ photocatalyst.

Fig. 3. 3D-Structure of target proteins of S. aureus, (a) beta lactamase (PDB 1MWU), (b) ddlB (PDB 2I80), (c) FabI (PDB 4Z8D).

Fig. 4. Structure of Cu-doped TiO₂ nanoparticles in (a) 2D and (b) 3D view.

Fig. 5. (a) XRD pattern (a′) zoomed area of (101) plane (b–e) SAED profiles of as-prepared and Cu-doped TiO₂ (b) 0 : 1 (c) 0.03 : 1 (d) 0.06 : 1 (e) 0.09 : 1 (f) FTIR spectra.

Fig. 6. (a) Optical absorbance spectra (b–e) band gap determination.

Fig. 7. Schematic representation of band gap energy reduction.

Fig. 8. (a–d) SEM images of 0 : 1, 0.03 : 1, 0.06 : 1, and 0.09 : 1 samples, respectively (a′–d′) HR-TEM micrographs of TiO₂ and 0 : 03 : 1, 0.06 : 1, and 0.09 : 1 samples, respectively.

Fig. 9. (a–d) d-Spacings calculated from HR-TEM images obtained from Cu-TiO₂ (a) 0 : 1 (b) 0.03 : 1 (c) 0.06 : 1 (d) 0.09 : 1 samples.

Fig. 10. (a) PL spectra (b–d) EDS profiles of prepared samples (b) 0.03 : 1 (c) 0.06 : 1 (d) 0.09 : 1.

Fig. 11. (a–d): XRF data of Cu-doped TiO₂ (a) 0 : 1 (b) 0.03 : 1 (c) 0.06 : 1 (d) 0.09 : 1 samples.

Fig. 12. (a) Plot of concentration ratio (C_t/C_o) versus time (b) plot of −ln(C_t/C_o) versus time spectra for dye reduction (c) rate constants of all samples (d) degradation (%) comparison of all samples.

Fig. 13. (a and b) Plots of C_t/C_ovs. time for reusability of 0.06 : 1, and 0.09 : 1, respectively (c) stability of Cu-doped samples.

Fig. 14. (a–d) for S. aureus of all samples, name as mentioned in figure, respectively (e) graphical demonstration.

Fig. 15. (a) In vitro antimicrobial efficacy of TiO₂ (control), (b) 3% Cu-doped TiO₂ (c) 6% Cu-doped TiO₂, (d) 9% Cu-doped TiO₂ for E. coli (e) graphical presentation.

Fig. 16. (a and b) Binding interaction pattern of Cu-doped TiO₂ nanoparticle with active site residues of d-alanine-d-alanine ligase (ddlB), (c and d) β-lactamase from S. aureus.

Fig. 17. Binding interaction pattern of Cu-doped TiO₂ nanoparticles with active site residues of enoyl-[acyl-carrier-protein] reductase (FabI) from S. aureus.