Tailoring Urchin-Like Nb2O5 Nanostructures with Molybdenum Doping to Enhance Adsorption Efficiency and Selectivity toward Cationic Dyes in Wastewater Treatment

Abstract

Effective wastewater treatment is essential for mitigating organic pollutants, such as dyes and antibiotics. In this study, the enhancement of niobium pentoxide (Nb₂O₅) nanostructures via molybdenum (Mo) doping to improve adsorption efficiency, selectivity, and reusability is investigated. Mo doping, successfully confirmed by X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, demonstrates effective integration into the Nb₂O₅ lattice, inducing lattice expansion and modifying its structural and surface properties. Mo-doped Nb₂O₅ exhibits increased adsorption capacities for methylene blue (MB) and crystal violet (CV), improving from 26.9 and 17.0 (undoped) to 35.4 and 44.8 mg g⁻¹, respectively. In contrast, the capacities for Congo red and tetracycline decrease from 31.6 and 36.8 to 16.7 and 32.0 mg g⁻¹, respectively. Isotherm modeling shows Langmuir-type adsorption with maximum capacities of 48.6 mg g⁻¹ for MB and 52.4 mg g⁻¹ for CV. Point of zero charge analysis indicates improved cationic dye selectivity, while recyclability tests demonstrate that Mo-doped Nb₂O₅ can retain over 96% of its capacity after five cycles. In thermodynamic studies, an exothermic and spontaneous process is revealed, with pseudo-second-order kinetics confirming chemisorption as the dominant mechanism. In these findings, Mo-doped Nb₂O₅ is established as a highly effective material for treatment applications.