Construction Of Three - Dimensional Graphene And Its Photocatalytic Application

Graphene is a two-dimensional crystal structure of the single atomic layer, which is formed by six carbon atoms via sp2 hybridization into the hexagonal honeycomb structure. The raw materials of graphene are abundant, inexpensive, non-toxic, as well as the preparation technology of graphene is relatively simple, mature, easy to industrialization. The two-dimensional nanostructure is very easily combined with semiconductor photocatalyst to generate heterostructure, and demonstrates the unique photoelectric properties. Because the long range order of π electron structure of graphene shows the unique chemical, optical, electrical, thermal and strength properties. Graphene has a unique application prospect in hydrogen production material, solar photovoltaic cells, lithium batteries, super capacitors, photoelectric detector, photocatalyst, and other fields. Especially, due to the graphene-based macrostructure containing both fundamental attributes of two-dimensional graphene and three-dimensional porous morphology, many fields in the optical and electrical physical properties, adsorbing catalytic degradation, biological compatibility and so on, showed lots of features, such as three-dimensional structure with high adsorption performance, strong mechanical performance, high conductivity, low body resistance, fast electron transport properties, large specific surface area and plasticity, etc. We focused on how to construct 3D graphene-based structure with semiconductor photocatalyst (such as titanium dioxide). At the same time, the properties of the heterostructure in adsorption, photocatalysis, photon-generated carrier dynamics were further researched, the details are as follows:1. Flaky graphite was oxidized to prepare graphene oxide by controlling the ratio of oxidants, and graphene oxide was reduced into single or less layers of graphene via the high temperature hydrothermal reaction. To analyze the structure and morphology of graphene and graphene oxide, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM) were used respectively. Infrared spectroscopy (FT-IR) and Raman spectroscopy (Raman) were applied for confirming element composition of graphene and graphene oxide, as well as the reduction degree of graphene. Finally, UV-Vis absorption spectroscopy (UV-Vis) and fluorescence spectroscopy (PL) were adopted to study their optical properties, in order to further explore the 3D graphene-based composites with photocatalyst.2. Reduced graphene oxide (RGO) nanosheets (NSs) decorated with TiO2 nanoparticles (NPs) were bound to activated carbon fibers (ACF) forming three-dimensional (3D) macroscopic composites with nanoscale building blocks by a one-pot hydrothermal self-assembly method. The integration of adsorption capacity enhanced by RGO NSs and photocatalytic activity introduced by TiO2 NPs in the resultant ACF-RGO-TiO2 composite was demonstrated via the proof-of-concept application of disposing organic dyes, i.e. Rhodamine B (RhB). Moreover, the photocatalytic degradation of laden RhB dye can effectively make ACF-RGO-TiO2 composites regenerate the adsorption capacity, promoting two practical values:(1) eliminating rather than removing dye pollutants and (2) recycling rather than consuming adsorbents. The synergistic functionalization highlights the potential of 3D ACF-RGO-TiO2 composite as a promising massive adsorbent with photocatalytic activities for environment purifications.3. The construction of photonic nanosystems with highly accessible photon harvesting and charge collection attracts intense interest in the fields of photovoltaic and photoelectrochemical (PEC) cells. It is desirable to build three-dimensional (3D) porous photoelectrodes that ensure high active surface area and promote light-trapping, charge separation and transport. Herein, we execute the hierarchical assembly of reduced graphene oxide (RGO) and scattered TiO2 nanoparticles (NPs) to fabricate a heterogenous 3D porous photoanode, which yields a high photocurrent density of 2.59 mA cm-2 at a low bias of 0.6 V (vs. Ag/AgCl) with an impressive solar-to-hydrogen conversion efficiency of 0.5% for water splitting without the need of any sacrificial reagents. The significantly increased PEC activity in RGO-TiO2 composite photoanode relative to TiO2 NPs-based analogues is demonstrated to be benefit from the positive roles of 3D RGO framework in confining the incident light, promoting electron transport, activating thermal effect, improving catalyst loading and electrolyte penetration.