Adsorption selectivity of cubic nano-CeO2 and effect of particle size on adsorption thermodynamics

Abstract

Nanoparticles can effectively remove organic dyes from wastewater due to their excellent adsorption performances which are closely related to particle size. Herein, the relations between the thermodynamic properties and the particle size were deduced, and the influence mechanisms were also discussed. Then the adsorptions of four dyes on cubic nano-CeO2 were investigated. We found that cubic nano-CeO2 has strong adsorption selectivity for four dyes and the size dependence of the adsorption thermodynamic properties. This strong selectivity is attributed to electrostatic interaction and hydrogen bonding. Furthermore, with the particle size decreasing, the logarithm of standard adsorption equilibrium constant (lnKo) increase, while the standard molar Gibbs energy change of adsorption (ΔadsGmθ), the standard molar adsorption enthalpy change (ΔadsHmθ) and the standard molar adsorption entropy change (ΔadsSmθ) decrease, and there are good linear relationships between this thermodynamic properties and the reciprocal of the particle size. The essences of effect of particle size on adsorption thermodynamics are that lnKθ and ΔadsGmθ are influenced by both the molar surface area and the difference in surface tensions after adsorption, ΔadsHmθ by the molar surface area, the differences in surface tensions and in temperature coefficients of surface tensions, ΔadsSmθ by the molar surface area and the difference in temperature coefficients of the surface tensions.