Construction Of Graphene-based Photocatalysts For Pollutant Removal From Water: Properties And Mechanisms

Graphene is layered two-dimensional nanomaterial,which is made up of sp² hybridization of carbon atoms.Graphene has been verified as a promising material because of its unique and excellent properties in terms of electronic and adsorption.These potential attributes have often been applied in different applications,such as electronics,energy and environmental pollution control.Graphene based metal/metal oxide composite as photocatalytic material can speed up the separation of electronic and hole,which can improve the catalytic activity of photocatalyst.In addition,the layered structure of graphene has large specific surface area,which is beneficial to the adsorption of pollutants.Therefore,the construction of highly active graphene based photocatalytic materials have become one of hot topic in academic research in recent years.This thesis here introduces the structure and properties of graphene and graphene oxide along with role of oxygen-containing functional groups on graphene oxide during the photocatalytic reaction.GO nanosheets were mixed with Fe³⁺ ions to form the GO-Fe???complex which was characterized by SEM,TEM,STEM,AFM,FTIR,and XPS.Subsequently,the GO-Fe???complex was introduced to an aqueous environment with Cr???under visible light irradiation.The photoreduction of Cr???to Cr???by GO-Fe???was investigated under different experimental conditions.The different characteristic of the GO-Fe???complex before and after the photoreduction were also studied.In addition,through the control of graphene morphology and the size of nanometer catalyst construct a stable and highly active graphene based 3D aerogel and thin film photocatalytic materials.The study focused on the catalytic degradation of organic pollutants and structure-properties relationship on the graphene-based photocatalytic materials.We employed a facile synthetic method for FeO?OH?-doped graphene aerogels as an effective and original photo-Fenton catalyst.The aerogel structure not only has developed the internal pore network,but solved the aggregation of two-dimensional graphene layers and fully exposed the active sites promoting the migration of the electrons in the reaction process.The nano-FeO?OH?uniformly dispersed in the graphene aerogel with a particle size of?3 nm.The FeO?OH?/rGA induced photo-Fenton degradation of 4-chlorophenol.Moreover,the ferric ions turn into nanometer FeO?OH?that is firmly fixed in rGA via strong ?-? interaction between the rGO layers,preventing iron leaching.In order to improve the light transmission of graphene composite,self-assembly construction of TiO₂?B?-graphene membrane.The composite membrane material has mechanical flexibility,hydrophilicity,and effective degradation of dye solution.Nano-TiO₂?B?has thickness of?3 nm.Through two-dimensional TiO₂?B?and 2D graphene self-assembly built into the composite membrane material with large interface contact area,rapid migration of the electrons and effective adsorption/degradation of pollutants.This study provides a theoretical basis for the construction of graphene-based photocatalytic materials and catalytic transformation of pollutants.The main innovative conclusions of this thesis are as follows:?1?The structure,catalytic performance and influencing factors of the GO-Fe???complex catalyst were investigated.The role and structural characteristics of GO in the reaction process were revealed.This work suggests that GO will form photoactive complex with Fe???in the aqueous environment.The GO-Fe???complex may effectively reduce Cr???to Cr???under visible light irradiation because of the decarboxylation on GO.The losing of carboxyl groups on GO generates rGO which is also able to adsorb Cr???but easier to aggregate and precipitate.The transformation of GO with the help of iron ions under visible light indicated a promising route to convert and remove the highly toxic Cr???pollutant from the aqueous environment.?2?A novel nano FeO?OH?-graphene aerogels as Fenton-like catalysts were synthesized.This study employed a facile synthetic method for iron-doped-rGO aerogels as an effective and original photo-Fenton catalyst.The obtained aerogel not only had a stable macrostructure and lighter density but also a prominent catalytic activity for phenolic organic degradation at near neutral pH values with less iron leaching after 10 cycles of consecutive uses.The minimal iron leaching was mainly attributed to smaller FeO?OH?crystals?average size?3 nm?,which were immobilized and dispersed on the rGO layers,and these iron crystals possess a higher catalytic activity than pure iron oxides.The sp² regions of rGO were recovered by sodium ascorbate reduction to ensure fewer defects after iron doping.Consequently,this FeO?OH?-rGA aerogel is an ideal photo-Fenton catalyst that overcomes the disadvantages of conventional Fenton reactions and can be applied to practical applications for effective removal of organic pollutants.?3?The composite membrane materials based on 2D TiO₂?B?and 2D graphene nanometer layer were prepared to reveal the synergistic mechanism between membrane separation,enrichment and photocatalytic degradation.Using a UV light self-assembly preparation two-dimensional TiO₂?B?-graphene membrane?MrGO-TiO₂?B??loading on the nylon base membrane.MrGO-TiO₂?B?has soft,flexible,stability and good light transmission.The MrGO-TiO₂?B?was also super-hydrophilic,which was beneficial for water molecules to penetrate the membrane and achieve separation from pollutants.Moreover,the water flux of MrGO-TiO₂?B?will increase with the increase of the addition of nano-TiO₂?B?.Under the condition of simulated sunlight/visible light irradiation,nano-TiO₂?B?in MrGO-TiO₂?B?will produce photoelectron and holes.The electron was transferred to rGO and captured by the adsorption of H₂O₂ producing · OH,which can oxidize and degrade dye molecule.