Preparation Of Graphene-based Composites And Their Photocatalytic Performances

Carbonaceous materials (such as fullerenes, carbon nanotubes, activated carbon, etc.) have received significant attention owing to their unique structure and excellent properties. As a new member of carbonaceous materials, graphene and its derivatives have attracted more and more attentions due to their unique properties and potential applications in such fields. Due to their special two-dimensional nanostructure, graphene-based sheets possess huge specific surface area, which can be utilized as supports to disperse semiconductor particles, reduce aggregation between these particles, improve the surface area of the as-prepared catalyst, which results in the improvement of their photocatalytic activity. In addition, due to their special electronic transmission ability, graphene sheets can reduce the recombination of photoinduced carrier and improve their life time, thus the photocatalysis ability can be enhanced. In this dissertation, we will use the aforementioned characteristics of graphene to improve the activity of photocatalysts. The content including two main parts:(1) We used graphene oxide as support to disperse Ag@AgCl catalyst, and evaluated their photocatalysis performances of methyl orange degradation under visible light irradiation; (2) Graphene sheets were utilized to modify TiO2, in order to improve the separation efficiency of electron-hole derived from TiO2, boosting their activity of photocatalytic reduction of nitro compounds. Furthermore, we also used dye to sensitize the TiO2-graphene composites in order to broaden their response of visible light. The dissertation is mainly focused on:(1) Graphene oxide-supported uniform Ag@AgCl core-shell nanoparticles composites have been successfully prepared by a facile two-step synthetic process. First, graphene oxide sheets were used as carriers to anchor and disperse Ag nanoparticles on their surface. Then these fixed Ag nanoparticles on carbon sheets are utilized as precursors, around which AgCl nanocrystal form in situ using FeCl3 as oxidant, forming graphene oxide-supported Ag@AgCl core-shell nanoparticles composites. The composition of these attached Ag@AgCl core-shell nanoparticles can be easily controlled by adjusting the usage of FeCl3, resulting in the formation of controllable core-shell nanostructures. Furthermore, these as-prepared graphene oxide-Ag@AgCl nanoparticles composites display effective photodegradation of methylene orange dye under visible light irradiation, which indicates their potential applications in environmental areas.(2) Graphene sheets have been considered as acceptors and transporters of photoinduced electrons generated from illuminated photocatalysts. Herein, we utilize these electrons with the help of grapheme sheets in photocatalytic selective reduction. First, graphene-modified TiO2 hybrids are prepared by electrostatic assembly and in situ photocatalytic reduction processes using P25 and graphene oxide as precursors and then the photocatalytic reduction of nitro-aromatics to the corresponding amino-aromatics with these hybrids is examined under UV light irradiation. Results indicate that the addition of graphene sheets can effectively minimize the recombination of photogenerated charge carriers derived from the irradiated TiO2 and better encourage these separated electrons to participate in the reactions, which effectively improves the reduction ability of these TiO2-graphene hybrids in the presence of oxalic acid as hole scavengers. Besides the enhanced conversion rate, higher yields of amino-aromatics are achieved when using the graphene-modified TiO2 as a photocatalyst compared with those for pure TiO2.(3) Dye sensitization is an efficient way to make broadband gap semiconductor sensitive to visible light. Herein, we hope that TiO2-graphene will show a high activity for photocatalytic selective reduction of nitro-aromatics under visible light after sensitized by dye. We use Eosin Y to modify TiO2-graphene catalysts and then evaluate their photocatalytic reduction of nitro-aromatics to the corresponding amino-aromatics under visible light irradiation. The preliminary experimental results show that Eosin Y-sensitized TiO2-graphene catalysts can reduce nitro-aromatics to amino-aromatics under visible light irradiation.