Adsorption isotherm studies of Cu (II) and Co (II) in high concentration aqueous solutions on photocatalytically modified diatomaceous ceramic adsorbents

Photocatalytically modified ceramic adsorbents were synthesized for the removal of high concentration Cu (II) and Co (II) ions from their aqueous solutions. The raw material, diatomaceous aluminosilicate mineral was modified using silver and anatase titanium oxide nanoparticles. Batch adsorption experiment was carried out on the targeted metal ions and the results were analyzed by the Langmuir and Freundlich equation at different concentrations (100–1000 mg/l) and the characteristic parameters for each adsorption isotherm were determined. As-received raw materials do not exhibit any sorption capacity for high concentration Cu2+ and Co2+ adsorbates. However, the adsorption isotherms for modified diatomaceous ceramic adsorbents could be fitted well by the Langmuir model for both Cu2+ and Co2+ with correlation coefficient (R) of up to 0.99953. The highest and lowest monolayer coverage (qmax) were 121.803 and 31.289 mg/g for Cu2+ and Co2+, respectively. The separation factor (RL) in the experiment was less than one (<1), indicating that the adsorption of metal ions on the Ag–TiO2-modified ceramic adsorbent is favorable. The highest adsorption capacity (Kf) and intensity (n) constants obtained from Freundlich model are 38.832 (Cu2+ on ZEO-T) and 5.801 (Co2+ on STOX-Z).