Abstract

In this study, aggregation of TiO2 (rutile and anatase) submicron particles in deionized (DI) water under ultra-violet (UV) light irradiation was investigated. While no aggregation was observed in the dark, rutile and anatase submicron particles started aggregating upon application of UV light and ceased aggregation in about 2 and 8.4 h, respectively. It has been demonstrated that UV light directly mitigated the particle mobility of TiO2, resulting in a neutralization effect of the Zeta potential. It was also observed that rutile particles aggregated much faster than anatase particles under UV radiation, indicating that the Zeta potential of as-prepared rutile is less than that of anatase in deionized (DI) water. In addition, the interaction energy of rutile and anatase particles was simulated using the Derjaguin–Landau–Verwey–Overbeek (DLVO) model. The results showed a significant reduction of barrier energy from 118.2 kBT to 33.6 kBT for rutile and from 333.5 kBT to 46.1 kBT for anatase, respectively, which further validated the remarkable influence of UV irradiation on the aggregation kinetics of rutile and anatase submicron particles. This work presents a further understanding of the aggregation mechanism of light-controlled submicron particles and has a promising potential application in environmental remediation.

Highlights

  • Aqueous micromotors driven by external energy from either a chemical reaction with an electrolyte or an environmental stimulus such as light, magnetic fields, temperature gradients, concentration gradients, etc., have drawn a lot of research interest [1,2,3,4]

  • UV light–controlled aggregation of TiO2 submicron particles in aqueous suspensions was investigated and it was shown that aggregation of both rutile and anatase particles can be facilitated by UV irradiation

  • The reduction of the Zeta potential enhanced the attraction among TiO2 particles, and facilitated aggregation

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Summary

Introduction

Aqueous micromotors driven by external energy from either a chemical reaction with an electrolyte or an environmental stimulus such as light, magnetic fields, temperature gradients, concentration gradients, etc., have drawn a lot of research interest [1,2,3,4]. It was concluded that the decrease of the repulsive force between nanoparticles facilitated TiO2 aggregation In addition to those investigations on pure TiO2 particles, TiO2-graphene (TiO2: 70–80 nm) composite nanoparticles were reported to aggregate after 20 h of UV irradiation due to a decrease in hydrophilicity [14,15]. Those aforementioned studies mainly focused on the behaviors of TiO2 particles induced by light at a nano-scale. Theoretical models were implemented to correlate and explain the experimental results

Aggregation Experiments
Particle Mobility Measurement
Particle Mobility and Zeta Potential
DLVO Model
Results and Discussion
Particle Mobility
Conclusions

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