Fabrication of Soft-Oxometalates {Mo132} Clusters With Novel Azobenzene Surfactants: Size Control by Micelles and Light.

Zhe Wang,Jinfeng Dong,Shengli Chen,Xuefeng Li

doi:10.3389/fchem.2021.625077

Abstract

Soft-oxometalates (SOMs) are colloid suspensions of superstructured assemblies of polyoxometalates (POMs) and are found to be very effective photo-catalysts in a number of chemical reactions. The stabilization of SOMs generally requires legends or stabilizers, e.g., polymers and surfactants. In this paper, a light responsive azobenzene surfactant, C10AZOC2N3, was developed and used to stable {Mo132} SOMs. Various techniques such as Dynamic light scattering, TEM, UV-Vis spectra and cyclic voltammetry were employed to characterize the experimental results. The outstanding structure-directing effect of surfactant self-assembly micelles in solution on inorganic counter-anions was demonstrated. Different amount of cyclohexane was solubilized into C10AZOC2N3 micelles to successfully control the size of {Mo132} SOMs cluster. Furthermore, the clusters exposed to UV light for a certain time can be served as a second trigger to control the size of SOMs due to the trans-cis conformation transition of surfactant molecules. The redox potentials of C10AZOC2N3-{Mo132} SOMs were investigated as the cluster size varied. Interestingly, the redox potential of {Mo132} was not affected by the cluster size, indicating that the presence of surfactant did not change the main function of {Mo132} as an electrochemical catalyst, but merely assisted in the size control of SOM aggregation.

Highlights

Polyoxometalates (POMs) are nano-sized inorganic transition metal-oxide based molecular clusters, attracting wide attention due to their structural, catalytic, electrochemical and biological properties (Miras et al, 2012; Wang and Yang, 2015)
An azobenzene surfactant, C10AZOC2N3 developed in home was used as the template
The hydrodynamic diameter of SOMs were found to increase with increasing the size of micelle templates (Figure 3B), while the size of SOMs prepared with the same micelle size was almost similar, regardless of increase of the concentration ratio of {Mo132} and C10AZOC2N3, {Mo132}/[C10AZOC2N3] (Figure 3C). These results showed that the size of SOMs can be precisely controlled by controlling the size of micelle templates, and the SOM size only depended on the template size and were not affected by the concentration ratio of {Mo132} and surfactant

Summary

INTRODUCTION

Polyoxometalates (POMs) are nano-sized inorganic transition metal-oxide based molecular clusters, attracting wide attention due to their structural, catalytic, electrochemical and biological properties (Miras et al, 2012; Wang and Yang, 2015). A directed effort in catalyst design goes toward controlled design of the catalyst where the catalyst size is engineered These SOMs self-assembled by POMs are often random at most in the range of a few nanometers (Liu, 2010). There are numerous techniques to fabricate ordered supramolecular structure, among them, molecular aggregates constructed by surfactant self-assembly, including spherical micelles, rod-like micelles and vesicles, have been established and understood well (Song et al, 2014). The morphology of these surfactant aggregates can be manipulated by varying various parameters, e.g., concentration, solvent polarity, temperature, pH, electrolyte and additives (Chu et al, 2013; Jiang et al, 2015). All the measurements were performed at room temperature in argon atmosphere. 0.1 mM Na2SO4 was added to the SOM solution to enhance the electrical conductivity

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT