Hydrothermal Synthesis of CeO2: Structure–Adsorption Performance 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.