Multifunctional NaNbO3: Photocatalytic Degradation of Methylene Blue and Intrinsic Antimicrobial Activity against Enterococcus faecalis and Candida albicans

In this paper, sodium niobate (NaNbO3) was synthesized by the microwave-assisted hydrothermal method at 150 °C for 70 min, followed by calcination at 550 °C for 2 h. X-ray diffraction revealed the coexistence of orthorhombic P21ma and Pbma phases, while scanning electron microscopy showed a one-dimensional rod-like morphology with an average diameter of about 200 nm. The material exhibited a specific surface area of 5.45 m2/g, a pore volume of 0.0269 cm3/g, and an average pore diameter of 20.52 nm. X-ray photoelectron spectroscopy indicated the presence of defect-related species, while photoluminescence emissions in the blue and green regions provided complementary evidence for defect-related electronic states. The optical band gap, estimated by diffuse reflectance spectroscopy, was approximately 3.56 eV. Mott–Schottky analysis indicated n-type semiconductor behavior and flat-band potential of −0.76 V vs Ag/AgCl. Electrochemical impedance spectroscopy showed improved interfacial charge-transfer behavior under light irradiation. The material exhibited efficient photocatalytic activity, achieving complete degradation of methylene blue (MB) under UV irradiation, with good stability after five successive reuse cycles. Radical scavenger experiments revealed that h+, ·OH, and ·O2– species are active in the photocatalytic mechanism. The synthesized NaNbO3 demonstrated effective antimicrobial activity against Enterococcus faecalis and Candida albicans, completely inhibiting microbial growth at concentrations ≥1.25 mg/mL. To the best of our knowledge, this is the first evidence of antimicrobial activity against these microorganisms using NaNbO3, highlighting its potential for environmental and biomedical applications.