pH-Controlled Synthesis of Nb₂O₅ Nanoparticles with Enhanced Performance for Photodegradation of Organic Pollutants...

Niobium pentoxide (Nb₂O₅) is a promising photocatalyst for environmental remediation and solar hydrogen production; however, the role of synthesis parameters in governing its phase composition and charge-carrier dynamics remains insufficiently understood. Herein, we systematically investigate the effect of synthesis pH (2, 4, and 6) on the structural, morphological, electronic, and photocatalytic properties of Nb₂O₅ nanoparticles prepared via two hydrothermal routes. pH variation in Route 1 promotes a phase transition from pseudohexagonal TT-Nb₂O₅ (pH 2) to hydrated Nb₂O₅ nH₂O (pH 4-6), accompanied by pronounced morphological evolution from nanoneedles to lamellar structures. In contrast, Route 2 preserves the TT-Nb₂O₅ phase regardless of post-treatment pH, highlighting its structural stability. In organic pollutant degradation, all samples were active toward Rhodamine B and amiloride, where mechanistic studies revealed a hole-dominated oxidation pathway with secondary involvement of superoxide radicals. Hydrated Nb₂O₅·nH₂O phases exhibited strong adsorption capacity, whereas TT-Nb₂O₅ showed higher intrinsic photocatalytic efficiency. Stability tests confirmed sustained activity over four cycles. TT-Nb₂O₅ materials also exhibited superior charge-transfer properties and were active in H₂ evolution, achieving up to 4104.5 μmol g^-1 after 8 h (Nb₂O₅-AP2). Optimization of Pt loading revealed an optimal cocatalyst content of 0.5 wt %, while long-term assays confirmed stable H₂ production over 24 h of operation. Photoluminescence results indicated that recombination suppression contributes to performance enhancement but does not solely govern activity. These findings demonstrate that synthesis pH governs phase formation, surface chemistry, and charge-carrier dynamics in Nb₂O₅, providing fundamental insights into the rational design of niobium-based photocatalysts tailored for integrated environmental and energy applications.