Study On The Preparation And Properties Of Functional Graphene Oxide Composites

Owing to its superior properties, graphene has drawn tremendous research inter-ests in recent years. Among various graphene derivatives, graphene oxide (GO) shows the greatest potential in the field of composite materials for its abundant oxygen-containing groups, relatively low cost and mass production. The study of GO com-posite materials is still at the stage of fundamental research, where the key issue is how to take full advantage of the characteristics of GO and promote the interaction between GO and polymer matrix for better dispersion.Based on GO and chemically-modified GO, this dissertation successfully devel-oped several novel methods to fabricate functional GO composite materials including smart GO/polymer composites, conductive GO/polymer composites and GO compo-site catalyst. The dissertation is composed of three parts:(1) studying property rein-forcements of GO/polymer composite materials with GO as filler and crosslinker; (2) developing novel methods to prepare conductive and electro-responsive graphene aerogel/polymer composite materials; (3) realizing reversible self-assembly of chemi-cally-modified GO ligands via which GO composites with electrochemical activities were prepared. The detailed results are as follows:1. GO was incorporated into poly(N-isopropylacrylamide) (PNIPAAm) hydrogel via in-situ polymerization. Hydrogen bonds formed between oxygen-containing groups of GO and PNIPAAm leading to uniform dispersion of GO. The composite hydrogels exhibit much higher response rate and better mechanical properties com-pared with PNIPAAm hydrogel. L-ascorbic acid was employed for in-situ chemical reduction of GO within polymer matrix to further improve the mechanical properties of GO/PNIPAAm composite hydrogel.2. GO was employed as macro-crosslinker to prepare thermoset material GO/P(St-co-TMI) by reacting with isocyanate groups in P(St-co-TMI), the copolymer of styrene (St) and 3-isopropenyl-a,a-dimethylbenzyl isocyanate (TMI). GO/P(St-co-TMI) composites exhibit remarkable shape-memory properties with shape fixity ratio above 98% and shape recovery ratio around 99%. The glass transition temperature (Tg) of the polymer was significantly increased upon the incorporation of GO. Tg of 2 wt% GO/P(St-co-TMI) composite is more than 24℃ higher than that of P(St-co-TMI). The strategy of combining the function of reinforcing filler and crosslinker could be employed to simplify the fabrication process of shape-memory composite materials.3. Ultra-lightweight graphene aerogel (RGA) was prepared with large-flake GO and ethylene diamine via reduction, self-assembly, freeze drying and further thermal reduction. RGA was then impregnated with methyl methacrylate (MMA) monomer and RGA/PMMA composite was then prepared via in-situ polymerization. RGA/PMMA exhibited high electrical conductivity (up to 6.27 S/m) at very low filler loading (around 0.3 wt%). Crosslinker was added into the polymerization system to prepare thermoset composite with excellent electro-responsive shape-memory proper-ties. Shape recovery ratio of 91.7% was achieved at a voltage of 8 V and it only took 9.1 s to recover half of the strain. Comonomer ethylacrylate (EA) was employed to tune the T% of the composite. Composites with lower Tg can perform shape-memory behavior at a volatage of 6 V. RGA was further modified with P(St-co-TMI) and ami-no-terminated polyoxypropylene to give low-density composite aerogel with electro-responsive shape-memory properties. Shape recovery ratio of 95.9% was achieved at a voltage of 4 V. The RGA-based strategy to prepare conductive and electro-responsive polymer composites would open a new research field for GO/polymer composites.4. Terpyridine derivative tpy-NH2 was synthesized and covalently grafted onto GO. The resultant tpy-GO ligand can undergo reversible self-assembly via complexa-tion with metal ions. The introduction of N atoms and the 3D structure renders tpy-GO and its complex with Fe2+ (Fe-tpy-GO) superb electrocatalytic activity for oxygen reduction reaction (ORR). The Fe-tpy-GO electrode exhibited comparable diffusion-limited current density and better stability to commercial Pt/C electrode and is free of CO-poisoning and crossover effect. The metal-tpy-GO complexes also show other potential applications in the field of energy storage and conversion such as supercapa-citors and photocurrent generation.