A High Energy Density Azobenzene/Graphene Oxide Hybrid with Weak Nonbonding Interactions for Solar Thermal Storage

Wenhui Pang,Hua Pang,Jijun Xue

doi:10.1038/s41598-019-41563-w

Abstract

Incorporating photochromic chromophores into polymer composites provides the possibility of a reversible photoswitch of the intrinsic properties of these materials. In this paper we report a route to attach azobenzene (AZO) moiety covalently to graphene oxide (GO) to create chromophore/graphene oxide (AZO-GO) hybrid, in which GO is both part of the chromophore and the template. Due to the high grafting density of AZO moiety and the low mass of the novel structure, the hybrid is a potential solar thermal storage material with high energy density of about 240 Wh·kg−1. It is found that C-H···π interaction between the cis-AZO chromophores and the aromatic rings of the substrate induces collective electronic modifications of GO at critical percentage of cis-isomers and reduce the thermal barrier of π-π* transition of the chromophores directly, which results in two sections of first-order reactions during the photoisomerization of trans- to cis-hybrid and also thermally stabilizes the cis-hybrid. Our findings demonstrate that high-performance AZO–GO hybrid can be manipulated by optimizing intermolecular nonbonding interactions.

Highlights

Can be formed by a coupling reaction between a diazonium salt and a coupling agent
The interlayer effect and the crystallization of pristine graphene oxide (GO) and RGO were analyzed by X-ray diffraction (XRD) spectra (Fig. S1(a)) which showed that GO and RGO were well dispersed before functionalization with AZO19
According to the Fourier transform infrared spectroscopy (FT-IR) spectra (Fig. S1(b)), the oxygen functional groups attached to the GO and RGO surfaces mainly composed of hydroxyl (-OH), epoxy and alkoxy (C-O-C), and carboxylic (-COOH) groups

Summary

Introduction

The benzene diazonium salt behaves as a weak electrophile and attacks carbon atoms with high electron cloud density in phenol ring, such as hydroxyl (-OH) para- or ortho-carbon sites. Considering that the edges and surfaces of GO are coated with -OH groups, it is reasonable to adopt GO as a coupling agent to yield AZO-GO hybrid containing a nitrogen atom in the diazo salt covalently bonded to a carbon atom in the aromatic ring of GO (Fig. 1). The mechanism of the kinetics during the trans-to-cis isomerization of the hybrid has been attributed to the effect of C-H···π interactions between cis-AZO chromophores and the aromatic rings of the substrate, which leads to impressive thermal stability of the cis-hybrid

Methods

Results

Discussion

Conclusion