Hydrothermal Synthesis of CeO₂: Structure-AdsorptionPerformance Relationship in Methyl Orange Dye Removal

CeO₂ particles were synthesized via a hydrothermal method to investigate the influenceof precursor molarity and reaction time on their structural, optical, and adsorption characteristics. Ce(NO₃)₃·6H₂O served as the cerium source, while PVP and Triton X-100acted as surfactants to regulate nucleation and particle growth. XRD and Raman analysesconfirmed the formation of single-phase cubic fluorite CeO₂, whereas FTIR spectra verifiedthe presence of Ce-O bonding. SEM observations revealed that a decreasing precursormolarity led to smaller and more uniform particles, while prolonged reaction times enhanced crystallinity. UV-Vis DRS and XPS analyses indicated that both the band gap(3.06-3.12 eV) and the Ce³⁺/Ce⁴⁺ ratio were governed by oxygen vacancies, demonstrating defect-mediated redox behavior. Adsorption studies using methyl orange (MO) dye followed pseudo-second-order kinetics (R² > 0.99), indicating chemisorption as the dominant mechanism. The CP1-8 sample exhibited the highest dye removal efficiency (87%) under acidic conditions (pH < pHPZC). These findings demonstrate that controlled hydrothermal synthesis enables precise tuning of CeO₂ morphology, defect density, and surface chemistry, yielding efficient adsorbent materials for environmental remediation applications.