Impact of preparative pH conditions on the structure and morphology of Graphene oxide-CoFe2O4 composite: Exploration of adsorption isotherm models and photocatalysis

GO-CoFe2O4 composite was prepared by hydrothermal method at three different pH conditions (pH 3, 7 and 11) to study the surface chemistry of the samples. The study of the interface involving a solid and liquid is quite complex and is characteristic of the preparation condition. The extent of adsorption depends on the surface nature of the catalyst which can vary considerably with the preparation conditions. An attempt is made to study the applications of various adsorption isotherms like Langmuir, Freundlich, Temkin and Flory-Huggins models. The best fit for all the three composite catalysts were found by taking the value of regression coefficient (R-2). Influence of pH on the structure, particle size, surface morphology and adsorption characteristics was studied in detail. Variation of particle size was studied by using Field Emission Scanning Electron Microscopic technique (FESEM). Photoluminescence spectroscopic technique and electrochemical techniques like cyclic voltammetry and electrical impedance measurement studies give an insight into the charge transfer reactions at the interface. Photocatalytic activity of the prepared samples was tested for the degradation of 4-nitrophenol (4-NP). Based on the obtained experimental results suitable model for the adsorption characteristics is proposed for each catalyst. The higher activity of the GO-CoFe2O4 sample prepared at neutral pH conditions is accounted for its excellent adsorption characteristics, continuous framework of GO, smaller crystallite size, lower resistance and higher interfacial charge transfer process. Influence of adsorption isotherms on the kinetics of heterogeneous catalysis is studied.