Preparation Of Photoresponsive Azobenzene-surfactant-modified Graphene And Its Composites

Graphene, a two-dimensional sp2-bonded network of carbons, is well-known for its unique physicochemical properties. Its distinctive properties including outstanding thermal conductivity, mechanical strength, charge transport, and flexibility make graphene useful in the application of photoelectric equipment. The main method used to develop graphene’s utility is physicochemical modification, whereby a variety of organic or inorganic compounds are added to graphene’s surface. A substantial research effort is focused on the self-assembly, synergistic effect and interface effect by modifying graphene using this method. Some significant and functional approaches to modifying graphene with Azo have been reported including π-stacking and covalent modification. Because of its unique photoresponse, this materials has extensive application in photoelectric and energy equipment. Although some photoresponsive Azo-graphene hybrids have been reported, it is still a challenge such as steric conformation, microstructure, chemical bonding energy and electronic property by changing dipole moments and tunneling barriers upon light irrad iation. Therefore, future studies focusing on the modification techniques are important and necessary. In this dissertation, a photoresponsive Azo-graphene composite was prepared using an cationic Azo-surfactants to modify the negatively charged surface of GO. Meanwhile, A novel photoresponsive azobenzene-reduced graphene oxide-gold nano particle nanocomposite was prepared using Gemini-type Azo-surfactants as stabilizers. It provides a new modification technique for photoresponsive Azo-graphene composite. The detailed contents are as fellows:(1) Azo-surfactantsThe photoresponsive Azo-surfactants was prepared via organic synthesis and molecular design. The results show that the surfactants containing Azo are easily trans-cis isomerized by UV light(365 nm) and blue(455 nm) light irradiation. Besides, a Gemini Azo-surfactants was prepared and used as stabilizers to fabricate the photoresponsive Graphene-metal nanoparticles nanocomposites.(2) Azo-graphene compositeBased on the charge of the azobenzene surfactants, a photoresponsive Azo-graphene composite was prepared using an cationic Azo-surfactants to modify the negatively charged surface of GO via electrostatic interactions. The introduction of azobenzene surfactant changed the surface potential of graphene, an d the zeta potential rapidly switched from a negative to positive value. The high fluorescence of the Azo-GO indicates that the cationic Azo C7 NO interacts with the negatively charged GO predominantly via electrostatic interactions rather than π-stacking which would lead to quenching of the fluorescence. It provides a theoretical support for the modification of azobenzene surfactant. The results acquired by X-ray diffraction(XRD), Scanning electron microscope(SEM) and Atomic force microscope(AFM) indicated that the Azo-GO has unique self-assembly properties due to the destruction of electrostatic repulsion balance of GO sheets. Besides, The results acquired by Fourier transform infrared spectroscopy(FTIR), X-ray photoelectron spectroscopy(XPS) and Thermal gravity analysis(TGA) indicated that the calculated quantities of grafted Azo on graphene sheets is 1 Azo per 71 carbons of GO.(3) Photoresponsive Azo-graphene compositeBased on the photoresponse of the Azo groups, the photoresponse of Azo-graphene composite was studied. The results acquired by ultraviolet and Visible Spectroscopy(UV-Vis) indicated that the Azo-graphene composite has the photoresponse using the Azo-surfactants to modify the graphene. The results acquired by X-ray diffraction(XRD), Atomic force microscope(AFM) and Raman spectrum indicated that the self-assemble can be reversibly controlled by ultraviolet light(365 nm) and blue light(455 nm) irradiation. Besides, the results acquired by cyclic voltammogrammetry(CV) indicated that the process of self-assemble is driven by the photoinduced polarity change of the cationic azobenzene surfactant and is responsible for the graphene hybrids’ electrochemical performance. In the known Azo-modified graphene hybrids, the photoresponsive propertie s are controlled by the photoisomerization triggered spatial change. Our results show that a polarity change in the azo-surfactants induces the photoresponsive assembly and disassembly of our new Azo-graphene hybrids. Photoresponsive self-assembly phenomenon in graphene is a new phenomenon in graphene dispersion. A sample and theoretical models will be provided for the investigation of self-assembly theory, which will be promoted the development of the self-assembly theory.(4) Photoresponsive Azobenzene-Graphene-Gold NanocompositeFor further development of the application of Azo-surfactant in graphene nanocomposites, a Gemini Azo-surfactants Azo C10N2O22+ was prepared via molecular design. Gemini cationic surfactants Azo C10N2O22+ contain two cationic groups. In this regard, the photoresponsive Azo-RGO-GNP nanocomposite was fabricated using Azo C10N2O22+ as stabilizers through one pot in situ growth and chemical reduction. The results acquired by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Transmission electron microscope(TEM) and Ultraviolet and Visible Spectroscopy(UV-Vis) indicated that a novel Azo-RGO-GNP nanocomposite with a uniform distribution of GNPs was fabricated using Azo C 10N2O22+ as stabilizers, and has photochemical behavior due to the presence of Azo units. This is the first example of a photoresponsive Graphene-Gold nanocomposite using cationic Gemini Azo-surfactants as stabilizers. Besides, the results acquired by cyclic voltammogrammetry(CV) indicated that the photo-response of Azo-RGO-GNP nanocomposite influences the electrochemical performance. We believe that this photoresponsive nanocomposites are useful in photoresponsive sensors and electrochemical industry.