Photocatalytic and bactericidal properties and molecular docking analysis of TiO2 nanoparticles conjugated with Zr for environmental remediation

Abstract

Despite implementing several methodologies including a combination of physical, chemical and biological techniques, aquatic and microbial pollution remains a challenge to this day. Recently, nanomaterials have attracted considerable attention due to their extraordinary prospective for utilization toward environmental remediation. Among several probable candidates, TiO₂ stands out due to its potential for use in multifaceted applications. One way to improve the catalytic and antimicrobial potential of TiO₂ is to dope it with certain elements. In this study, Zr-doped TiO₂ was synthesized through a sol-gel chemical method using various dopant concentrations (2, 4, 6, and 8 wt%). Surface morphological, microstructural and elemental analysis was carried out using FESEM and HR-TEM along with EDS to confirm the formation of Zr-TiO₂. XRD spectra showed a linear shift of the (101) anatase peak to lower diffraction angles (from 25.4° to 25.08°) with increasing Zr⁴⁺ concentration. Functional groups were examined via FTIR, an ample absorption band appearing between 400 and 700 cm^-1 in the acquired spectrum was attributed to the vibration modes of the Ti-O-Ti linkage present within TiO₂ nanoparticles, which denotes the formation of TiO₂. Experimental results indicated that with increasing dopant concentrations, photocatalytic potential was enhanced significantly. In this respect, TiO₂ doped with 8 wt% Zr (sample 0.08 : 1) exhibited outstanding performance by realizing 98% elimination of synthetic MB in 100 minutes. This is thought to be due to a decreased rate of electron-hole pair recombination that transpires upon doping. Therefore, it is proposed that Zr-doped TiO₂ can be used as an effective photocatalyst material for various environmental and wastewater treatment applications. The good docking scores and binding confirmation of Zr-doped TiO₂ suggested doped nanoparticles as a potential inhibitor against selected targets of both E. coli and S. aureus. Hence, enzyme inhibition studies of Zr-doped TiO₂ NPs are suggested for further confirmation of these in silico predictions.

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

Fig. 2. Photocatalytic mechanism of dye degradation in the presence of Zr–TiO₂ photocatalyst.

Fig. 3. 3D-structure of target proteins of E. coli, (a) dihydrofolate reductase (PDB: 2ANQ), (b) dihydropteroate synthase (PDB: 5U0V), (c) DNA gyrase (PDB: 6KZX) and for S. aureus (d) dihydrofolate reductase (PDB: 3FY8), (e) dihydropteroate synthase (PDB: 4HB7), (f) DNA gyrase (PDB: 5CTU).

Fig. 4. Structure of Zr-doped TiO₂ nanoparticles.

Fig. 5. (a) XRD pattern (a′) zoomed area of (101) plane (b–e) SAED profiles of as-prepared and Zr-doped TiO₂, respectively (f) FTIR spectra.

Fig. 6. (a) Absorbance spectra obtained from pure and Zr-doped TiO₂ nanoparticles (b) band gap determination (c) PL spectra of prepared samples.

Fig. 7. (a–e) FESEM images of 0 : 1, 0.02 : 1, 0.04 : 1, 0.06 : 1, and 0.08 : 1 samples, respectively (a′–e′) corresponding HR-TEM micrographs of TiO₂ and 0 : 02 : 1, 0.04 : 1, 0.06 : 1, and 0.08 : 1 samples, respectively.

Fig. 8. HR-TEM images up to 10 nm resolution used for measuring interlayer spacing of samples for (a) pure TiO₂ (b) 0.02 : 1 (c) 0.04 : 1 (d) 0.06 : 1.

Fig. 9. (a–d) EDS profiles of prepared samples (a) 0 : 1 (b) 0.02 : 1 (c) 0.04 : 1 (d) 0.08 : 1.

Fig. 10. (a and b) XPS spectra of Zr : TiO₂ (0.08 : 1) (a) O 1s (b) Ti 2p.

Fig. 11. (a) Plot of concentration ratio (C_t/C₀) versus time (b) Plot of −ln(C_t/C_o) versus time spectra for dye reduction.

Fig. 12. (a and b) Plots of C_t/C_ovs. time for reusability of 0.06 : 1, and 0.08 : 1, samples respectively (c) stability of Zr-doped samples (0.06 : 1, and 0.08 : 1).

Fig. 13. (a) In vitro antimicrobial efficacy of TiO₂ (control), (b) 2% Zr-doped (c) 4%-doped, (d) 6%-doped, (e) 8%-doped against E. coli (f) graphical presentation.

Fig. 14. (a) In vitro antimicrobial efficacy of TiO₂ (control), (b) Zr-doped TiO₂ (2%), (c) (4%), (d) (6%), (e) (8%) against S. aureus (f) graphical presentation.

Fig. 15. Binding interaction pattern of Zr-doped TiO₂ nanoparticles with active site residues of (a) dihydrofolate reductase, (b) dihydropteroate synthase, and (c) DNA gyrase from E. coli.

Fig. 16. Binding interaction pattern of Zr-doped TiO₂ nanoparticles with active site residues of (a) dihydrofolate reductase, (b) dihydropteroate synthase, (c) DNA gyrase from S. aureus.