Visible-Light-Driven Co3O4/Nb2O5 Heterojunction Nanocomposites for Efficient Photocatalytic and Antimicrobial Performance in Wastewater Treatment

Abstract

The development of high-performance photocatalysts is vital for combating water pollution and microbial contamination. In this study, visible-light-active Z-scheme heterojunction nanocomposites composed of Co₃O₄ and Nb₂O₅ (CNNC) were synthesized via co-crystallization and subsequent high-pressure annealing to enhance photocatalytic and antimicrobial performance. Structural and optical analyses via XRD, FESEM, TEM, XPS, and PL confirmed the heterojunction formation between porous Co₃O₄ nanoparticles (CONP) and columnar orthorhombic Nb₂O₅ nanoparticles (NONP). The CNNC exhibited significantly improved photocatalytic activity, achieving degradation efficiencies of 95.1% for methylene blue, 72.6% for tetracycline, and 90.0% for Congo red within 150 min. Kinetic studies showed that CNNC's rate constants were 367% and 466% of those of CONP and NONP, respectively. Moreover, CNNC demonstrated a strong antibacterial effect on Staphylococcus aureus and Escherichia coli with ZOI values of 9.3 mm and 6.8 mm, respectively. Mechanistic analysis revealed that the Z-scheme charge-transfer pathway improved charge separation and reduced electron-hole recombination, contributing to the promoted photocatalytic efficiency. The nanocomposite also showed robust stability and recyclability over five times. These results highlight the promise of CNNC as a bifunctional, visible-light-driven photocatalyst for pollutant decomposition and microbial control.

Keywords: Co3O4/Nb2O5 visible-light-driven photocatalyst; antibacterial activities; heterojunction interface; synergistic effect; water pollutants.

Figure 1

FE-SEM images of nanoparticles and nanocomposites: (a) porous CONP, (b) columnar-shaped NONP, (c) CNNC-1 (1:1), (d) CNNC-2 (1:2), and (e) CNNC-3 (2:1).

Figure 2

(a,b) HR-TEM images; (c) lattice fringes of CONP and NONP at the interface; (d) SAED pattern; (e) EDS image; (f–i) EDS elemental mappings; and (j) the EDS spectrum of CNNC-1.

Figure 3

(a) HR-XRD profiles and (b) magnified XRD profiles in the range of 26° to 34° for (a) CONP, (b) NONP, (c) CNNC-1, (d) CNNC-2, and (e) CNNC-3.

Figure 4

(a) XPS survey spectra of nanoparticles and nanocomposites; (b) Co 2p spectrum; (c) Nb 3d spectrum of the CNNC-1 composite; and (d–f) O 1s spectra of CONP, NONP, and CNNC-1.

Figure 5

FT-IR profiles of (a) CONP, (b) NONP, (c) CNNC-1, (d) CNNC-2, and (e) CNNC-3.

Figure 6

Tauc plots of (a) CONP, (b) NONP, (c) CNNC-2, and (d) CNNC-1. The insets show the corresponding UV–Vis absorbance spectra for each sample.

Figure 7

(a) PL spectra (λ_ex = 300 nm) and (b) EIS spectra of synthesized samples.

Figure 8

(a) UV–Vis absorbance spectra of residual MB after treatment with CNNC-1; (b) MB degradation plot; (c) pseudo-first-order kinetic plot; and (d) bar chart of rate constants for MB degradation using different photocatalysts under VL (initial MB concentration: 15 mg/L; catalyst dosage: 500 mg/L).

Figure 9

(a) Digital images of inhibition zones against S aureus for (i) all samples (ii) CONP, NONP, and CNNC-3, and against E. coli for (iii) all samples and (iv) CONP, NONP, and CNNC-3, (b) bar chart representing antibacterial activity, and (c) bacterial colonies visualized via plate count agar tests for Staphylococcus aureus and Escherichia coli under light irradiation. All deviations were taken as statistically significant designated as * p < 0.05 and ** p < 0.01.

Figure 10

A schematic diagram illustrating the mechanism for antibacterial activity.

Figure 11

(a) Recyclability results of CNNC-1 for MB degradation, (b) FT-IR profiles, and (c) XRD spectra of fresh and used CNNC-1.

Figure 12

(a) Determination of pH_PZC for CNNC-1 and (b) influence of pH on the MB decomposition by CNNC-1.

Figure 13

A schematic diagram illustrating the proposed Z-scheme photocatalytic mechanism in CNNC-1.

Scheme 1

Scheme for the synthesis of CNNC nanocomposites via (A) co-crystallization and (B) annealing.