Ag ₃PO ₄ decorated black urchin-like defective TiO ₂ for rapid and long-term bacteria-killing under visible light

Abstract

Both phototherapy via photocatalysts and physical puncture by artificial nanostructures are promising substitutes for antibiotics when treating drug-resistant bacterial infectious diseases. However, the photodynamic therapeutic efficacy of photocatalysts is seriously restricted by the rapid recombination of photogenerated electron–hole pairs. Meanwhile, the nanostructures of physical puncture are limited to two-dimensional (2D) platforms, and they cannot be fully used yet. Thus, this research developed a synergistic system of Ag ₃PO ₄ nanoparticles (NPs), decorated with black urchin-like defective TiO ₂ (BU–TiO _2-X/Ag ₃PO ₄). These NPs had a decreased bandgap compared to BU-TiO _2-X, and BU-TiO _2-X/Ag ₃PO ₄ (3:1) exhibited the lowest bandgap and the highest separation efficiency for photogenerated electron–hole pairs. After combination with BU-TiO _2-X, the photostability of Ag ₃PO ₄ improved because the oxygen vacancy of BU-TiO _2-X retards the reduction of Ag ⁺ in Ag ₃PO ₄ into Ag ⁰, thus reducing its toxicity. In addition, the nanospikes on the surface of BU-TiO _2-X can, from all directions, physically puncture bacterial cells, thus assisting the hybrid's photodynamic therapeutic effects, alongside the small amount of Ag ⁺ released from Ag ₃PO ₄. This achieves synergy, endowing the hybrid with high antibacterial efficacy of 99.76 ± 0.15% and 99.85 ± 0.09% against Escherichia coli and Staphylococcus aureus, respectively, after light irradiation for 20 min followed by darkness for 12 h. It is anticipated that these findings may bring new insight for developing synergistic treatment strategies against bacterial infectious diseases or pathogenic bacterial polluted environments.

Graphical abstract

Highlights

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  BU-TiO _2-X/Ag ₃PO ₄ (3:1) hybrid improved the photostability of Ag ₃PO ₄.

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  BU-TiO _2-X/Ag ₃PO ₄ (3:1) hybrid exhibited outstanding photodynamic therapeutic effects.

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  The nanospikes from all directions on the BU-TiO _2-X physically punctured bacterial cells.

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  The physical puncture combined with the Ag ⁺ released by Ag ₃PO ₄ had long-term bacteriostatic efficacy.