The newly engineered HPNCs have shown the ability to kill bacteria in biofluids under visible light, overcoming the rapid degradation typically seen in such materials when exposed to light and moisture. These findings were recently published in Nano Letters.
HPNCs are known for their exceptional optical and electrical properties, making them valuable for applications like solar energy, bioimaging, and photocatalysis. When exposed to light, these materials can generate reactive oxygen species capable of neutralizing biological contaminants in fluids. However, their tendency to break down in water has limited their use in biomedical and environmental contexts.
"The drawback with these materials has been stability. They're cheap and easy to make but prone to degradation," explained Jun Lou, a professor and associate chair of materials science and nanoengineering at Rice University.
The new dual-layer silicon dioxide coating resolves this issue. Initial attempts using a single layer failed to maintain HPNC efficacy, with antimicrobial properties decreasing by 63% within a day. The thicker coating compromised the mechanism of energy transfer needed for reactive oxygen species production.
"Transfer of energy from perovskites can produce reactive oxygen species," noted Zhu, a postdoctoral researcher in Lou's lab. "The challenge is to get the right thickness to protect the perovskite while still allowing energy transfer."
By refining their approach, Zhu and his team developed a two-layer coating method that achieves an optimal balance. Tests demonstrated that the double-layer coating protected the HPNCs from degradation while preserving their antimicrobial functionality. When exposed to visible light, lead-based and bismuth-based HPNCs destroyed over 90% of E. coli bacteria in solutions within six hours and showed minimal degradation over four days.
The researchers highlighted another advantage of the coating: reduced leaching of lead into the surrounding environment. Even after prolonged exposure to water, the lead levels remained well below World Health Organization limits.
"The leaching amount of lead was well below (World Health Organization) limits," Zhu said.
While lead-based HPNCs exhibited the best antimicrobial performance, bismuth-based variants also performed well and offer an advantage in avoiding the use of lead, particularly for potential biomedical applications. "The benefit of bismuth is avoiding the use of lead, which is always a concern if put into the body," Lou commented.
The study underscores the potential of double-layer silicon dioxide-coated HPNCs as photocatalytic antimicrobial agents. This innovation opens avenues for water treatment applications and potentially therapeutic uses, although further testing under real-world conditions is necessary.
"After many years of investment in research into these materials, they are approaching reality," Lou added.
Research Report:Double Layer SiO2-Coated Water-Stable Halide Perovskite as a Promising Antimicrobial Photocatalyst under Visible Light
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