A controlled solvethermal approach to synthesize nanocrystalline iron oxide for congo red adsorptive removal from aqueous solutions

Nanocrystalline Fe3O4 xerogel with tunable sizes and alpha-Fe2O3 nanoplates have been successfully synthesized through a facile sol-gel method combined solvothermal process under alcohol solvents or water medium without any surfactants. The influence of organic solvent type on the structural properties of Fe3O4 xerogel is discussed. The hydroxyl groups and polarity of alcohols make a crucial role in tuning the size of the Fe3O4 xerogels. Herein, larger specific surface area was obtained in Fe3O4 xerogel (93.6 m(2) g(-1)) and alpha-Fe2O3 nanoplates (26.9 m(2) g(-1)) compared with common iron oxides. The adsorption performances of Fe3O4 xerogel and alpha-Fe2O3 nanoplates are examined as adsorbents in congo red (CR) removal and the adsorption experiments were performed based on various parameters, such as initial CR concentrations, solution pH, and contact time. The Langmuir, Freundlich isotherm models were employed to discuss the adsorption behavior. The results indicated that the equilibrium data were perfectly represented by the Langmuir isotherm. The maximum adsorption capacity reached 244.50 and 251.89 mg g(-1). Pseudo-first-order and pseudo-second-order models were employed to analyze the kinetics data and the adsorption behavior can be better described by pseudo-second-order model. Furthermore, adsorbents of Fe3O4 xerogel possess excellent recycle ability which can be effectively and rapidly extracted from water through its magnetic property. These Fe3O4 xerogel and alpha-Fe2O3 nanocrystals have the potential to be promising low-cost and efficient candidates for future water treatment.