Green synthesis of single phase of ZrO₂ nanoparticles via Sonchus asper aqueous extract: antibacterial, antioxidant, cytotoxic, and photocatalytic applications

Producing metal nanoparticles (NPs) using plant extracts has recently become an interesting topic in nanoscience and nanobiotechnology because of its many benefits over traditional physicochemical methods. This study innovatively and successfully prepared nanocrystalline zirconium oxide powder (ZrO₂-NPs) by low-cost and nontoxic production via a green method using Sonchus asper leaf extract (SALE) as a reducing and chelating agent. An XRD study revealed the ZrO₂'s crystalline structure and showed that the crystalline form was cubic with an average crystalline size of 11.94 nm. Additionally, SEM confirmed the cubic presence of ZrO₂. The elemental analysis data from EDX showed that zirconium and oxygen made up 61.8% and 38.2%, respectively. Crystal lattice NPs with well-aligned orders were observed in HRTEM and SAED images. The zeta potential (15.7 mV) indicated the ZrO₂-NPs stability. The bandgap energy was 4.15 eV, which is unique to ZrO₂, and UV–visible spectroscopy revealed a distinctive peak at 350 nm. ZrO₂-NPs demonstrated significant antioxidant capacity by scavenging 1, 1-diphenyl-2-picrylhydrazyl (DPPH) free radicals. The NPs had excellent bactericidal activity against Escherichia coli, Pseudomonas aeruginosa (G^−ve), Staphylococcus aureus, and Streptococcus mutans (G^+ve). Moreover, ZrO₂-NPs have cytotoxic effects against the non-cancerous HGF and Cal 27 cell lines. The photodegradation of the target pollutant (methylene blue (MB) dye) is evaluated to determine the photocatalytic efficacy of ZrO₂-NPs when exposed to UV light irradiation. The ZrO₂ catalyst has photodegraded MB by up to 93% within 180 min. The findings indicate that ZrO₂-NPs mediated by SALE have great potential for antibacterial, antioxidant, cytotoxic, and photocatalytic applications.