Negative Surface Energies of Nickel Ferrite Nanoparticles under Hydrothermal Conditions

Zs Rák,D W Brenner

doi:10.1155/2019/5268415

Abstract

The formation of nickel ferrite (NiFe2O4) nanoparticles under hydrothermal conditions has been modeled using a method that combines results of first-principle calculations, elements of aqueous thermochemistry, and experimental free energies of formation. The calculations predict negative formation energies for the (111) surfaces and positive free energies for the formation of bulk nickel ferrite. Based on classical nucleation theory, the combination of the negative surface and positive bulk energies yields thermodynamically stable nickel ferrite nanoparticles with sizes between 30 and 150 nm in the temperature range of 300 to 400 K under alkaline conditions. The surface and bulk energetics as well as the stability of the nickel ferrite nanoparticle as a function of temperature and pH are discussed.

Highlights

Nanostructured materials can display physical properties that are very different from what they exhibit on the macroscale
Nickel ferrite nanoparticles have been synthesized through conventional techniques including solid-state reaction, sol-gel combustion, coprecipitation, and hydrothermal methods [9,10,11,12,13,14,15,16,17]
Hydrothermal synthesis appears to be a promising technique to produce highly crystallized, weekly agglomerated powder, where particle size, morphology, and other characteristics can be controlled by adjustment of temperature, time, and pH value [18, 19]

Summary

Introduction

Nanostructured materials can display physical properties that are very different from what they exhibit on the macroscale. The reduction in particle size leads to a larger relative surface area, and this can alter the chemical reactivity and strength of the material These characteristics make nanostructured materials to be of great scientific and technological interests [1,2,3]. Nickel ferrite nanoparticles have been synthesized through conventional techniques including solid-state reaction, sol-gel combustion, coprecipitation, and hydrothermal methods [9,10,11,12,13,14,15,16,17] Among these methods, hydrothermal synthesis appears to be a promising technique to produce highly crystallized, weekly agglomerated powder, where particle size, morphology, and other characteristics can be controlled by adjustment of temperature, time, and pH value [18, 19]. We use the first-principle informed thermodynamics method developed earlier [20, 21], to model the nucleation and formation of nickel ferrite nanoparticles from solvated ionic species under hydrothermal conditions

Theoretical Method

Nucleation

Results and Discussions

Conclusion