pH-Controlled Synthesis of Nb2O5 Nanoparticles with Enhanced Performance for Photodegradation of Organic Pollutants and H2 Production.

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.