Defect-Tailored Ag₂SeO₃: Morphology and Function Tuned by pH-Driven Sonochemical Synthesis

Ag₂SeO₃ particles were synthesized via a pH-driven sonochemical route (pH = 2, 5, and 12) to elucidate how defect chemistry and morphology govern photocatalytic and antimicrobial performance. X-ray diffraction and Raman spectroscopy confirmed the formation of monoclinic Ag₂SeO₃, while increasing synthesis pH progressively destabilized the lattice, inducing preferred orientation, short-range disorder, and partial segregation of metallic Ag under alkaline conditions. XPS revealed a gradual shift in silver speciation from Ag⁺-dominated lattices toward mixed Ag⁺/Ag⁰ states and reduced lattice oxygen at high pH, consistent with enhanced defect density. Morphological evolution from microrods (pH 2) to shortened rods (pH 5) and sheet-like particles (pH 12) was observed, driven by pH-dependent nucleation and growth kinetics. Optical analyses showed comparable band gaps (∼3.5-3.7 eV), while photoluminescence deconvolution evidenced defect-mediated suppression of charge recombination, particularly for alkaline-synthesized Ag₂SeO₃. Consequently, the pH 12 sample exhibited superior photocatalytic activity toward ciprofloxacin degradation (∼98% under UV irradiation), governed predominantly by ^•O₂H and ¹O₂ species, as demonstrated by scavenger and probing experiments. Toxicity assays confirmed that photocatalytic residues were nontoxic toward Staphylococcus aureus and Lactuca sativa, despite limited mineralization. Antibacterial tests revealed tunable, pH-dependent selectivity: acidic samples favored Gram-positive inhibition, while alkaline samples enhanced Gram-negative activity via synergistic ROS generation and Ag⁺ release. Cytotoxicity and intracellular redox analyses demonstrated concentration-dependent oxidative stress, underscoring the importance of post-treatment separation. Overall, this study establishes pH modulation during sonochemical synthesis as an effective strategy to engineer defect landscapes and multifunctionality in Ag₂SeO₃ for environmental remediation and antimicrobial applications.