Defect-Tailored Ag ₂ SeO ₃ : 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.