High-temperature annealing of ZnO nanoparticles increases the dissolution magnitude and rate in water by altering O vacancy distribution

Hongping He,Jianglin Cao,Xunchang Fei,Ning Duan

doi:10.1016/j.envint.2019.104930

Abstract

The effects and mechanism of high-temperature annealing, a frequently-used strategy to modulate the properties of nanoparticles (NPs), on the dissolution of zinc oxide (ZnO) NPs are investigated in this study. The results show that annealing increases the ZnO NPs dissolution magnitude via increasing O vacancy abundance on the surface and in the bulk crystal. The face-dependent distribution of O vacancy is revealed by characterizing ZnO single crystal, and the (000-1) face has a higher abundance than the (10-10) face. Particularly, O vacancy abundance in the bulk (000-1) is about 3 times higher than in the bulk (10-10). Annealing further strengthens the face-dependence of O vacancy distribution, therefore both raw and annealed (000-1) faces contribute dominantly to the dissolution of ZnO NPs. Typical topographies of the surface defect sites on the (000-1) face and their evolutions during dissolution are collected. Annealing promotes the formation of larger and deeper etching pits. Elevated solution temperature and annealing synergize to further accelerate ZnO dissolution. The dissolution behaviors of ZnO NPs with different annealing statuses, surface properties, and solution temperatures investigated in this study have potential implications to the evaluations of environmental fate and risk of metal oxide NPs.

Highlights

Metal oxide nanoparticles (NPs), e.g., zinc oxide (ZnO) NPs, have been witnessed increasingly more applications in the recent decades due to their unique optical, electronic, and structural properties (Lee et al, 2015; Zhu and Zeng, 2017; G.R. Li et al, 2008; Q.L. Li et al, 2008)
Our results suggest that dissolution of metal oxide NPs might accelerate unexpectedly if solution temperature is raised to enhance the reaction mediated by NPs, which deserves an additional attention
This study shows that annealing increases the magnitude of ZnO NPs dissolution via increasing O vacancy abundance on the surface and in the bulk crystal

Summary

Introduction

Metal oxide nanoparticles (NPs), e.g., zinc oxide (ZnO) NPs, have been witnessed increasingly more applications in the recent decades due to their unique optical, electronic, and structural properties (Lee et al, 2015; Zhu and Zeng, 2017; G.R. Li et al, 2008; Q.L. Li et al, 2008). Particle size is frequently studied which critically influences the surface Gibbs free energy (Batley et al, 2013; Misra et al, 2012). The contribution of surface Gibbs free energy to overall Gibbs free energy relates inversely to the particle sizes of NPs (Rao et al, 2002; Zhang et al, 2010). The effects of various environmental factors on the dissolution of metal oxide NPs have been frequently explored (Misra et al, 2012; Li et al, 2011), but the effect of solution temperature on metal oxide NPs with different defect abundances is not fully understood

Methods

Results

Conclusion