# Hydrothermal Synthesis of CeO2: Structure–Adsorption Performance Relationship in Methyl Orange Dye Removal

## TL;DR

This study explores how to synthesize CeO2 particles to efficiently remove methyl orange dye from water.

## Contribution

The study introduces a hydrothermal method to control CeO2 structure and adsorption performance for dye removal.

## Key findings

- Lower precursor molarity produces smaller and more uniform CeO2 particles.
- Adsorption of methyl orange follows pseudo-second-order kinetics, indicating chemisorption.
- The CP1-8 sample achieved 87% dye removal efficiency under acidic conditions.

## Abstract

CeO2 particles were synthesized via a hydrothermal method to investigate the influence of 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-100 acted as surfactants to regulate nucleation and particle growth. XRD and Raman analyses confirmed the formation of single-phase cubic fluorite CeO2, whereas FTIR spectra verified the presence of Ce–O bonding. SEM observations revealed that a decreasing precursor molarity 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.