Preparation Of TiO₂-graphene-based Composites And Their Applications In Dye Wastewater Purification

Titanium dioxide?TiO₂?has become one of the most attractive photocatalysts due to that it is stable,abundant,economical,and environmentally friendly.However,the photo-generated electron-hole pairs of TiO₂ have a wide energy band?about 3.2 e V?and the recombination is rapid,which result in a low visible light utilization efficiency.Studies have shown that the composites consisting of TiO₂ and the suitable dopants?such as some metal elements and their compounds,nitrogen,sulfur and other non-metallic elements?can inhibit the combination of photo-generated electron-hole and increase the absorption of visible light.As one fascinating carbon-based material,graphene has a two-dimensional honeycomb-like network composed of a single layer of sp2 hybrid carbon atoms.The reduced graphene oxide?r GO?and the three-dimensional graphene aerogel?GA?possess large surface area,abundant pore structure,excellent charge mobility and electrical conductivity.Therefore,both of them have aroused the interest of many researchers since they have been found.Pure r GO,GA and their corresponding composites show excellent photoelectric conversion and photocatalytic performance.In this thesis,a series of TiO₂-GA,g-C₃N₄-TiO₂-GA,Fe2O3-TiO₂-GA,TiO₂-r GO,and Ag-TiO₂-r GO composites were sucessfully prepared.The materials were characterizatized by various techniques such as XRD,FT-IR,DR UV-Vis,Raman,SEM,TEM,XPS,N2 adsorption-desorption,and TG.Meanwhile,the adsorptivity and visible light-driven photocatalytic activity for the degradation of rhodamine B?Rh B?of the resulting materials were investigated in details.Furthermore,the possible mechanism for photo-degradation of Rh B over the composites under visible light irradiation was also explored.The main work is as follows:?1?A series of TiO₂-GA composites were prepared from butyl titanate and graphene oxide?GO?by using a one-pot hydrothermal process combined with freeze-drying.The results showed that the TiO₂-GA composites maintained the macroscopic columnar three-dimensional structure of GA.The anatase phase TiO₂ nanoparticles were uniformly dispersed into GA.Moreover,these composites possessed high specific surface area and abundant pores.Among them,TiO₂-GA?5?displayed the highest surface area?SBET = 409.0 m2 g-1?and the largest pore volume?Vp = 0.512 cm3 g-1?.TiO₂-GA?5?also showed the best removal performance: The total removal rate of Rh B was as high as 98.7% under the experimental conditions?room temperature,5 mg of the composites,25 m L of 20 mg L-1 Rh B?during 180 min.In addition,the resulting composites also displayed excellent cyclic stability.The removal rate of Rh B was still kept at about 72.0% after four cycles over TiO₂-GA?5?.?2?Graphitic carbon nitride?g-C₃N₄?was prepared by thermal decomposition of tripolycyanamide.Then it was dispersed into the precursor solution of TiO₂-GA?5?to synthesize a series of g-C₃N₄-TiO₂-GA ternary heterojunction composites with the similar method to that of the aforementioned TiO₂-GA.It was found that the composites kept the macroscopic columnar 3D structure of GA,and the anatase phase TiO₂ and g-C₃N₄ were uniformly dispersed into GA.Meanwhile,the incoporation of g-C₃N₄ enhanced the purification performance of TiO₂-GA and g-C₃N₄-TiO₂-GA?5%?exhibited the best removal performance: The total removal rate of Rh B was as high as 98.4% under the experimental conditions?room temperature,5 mg of the composites,25 m L of 20 mg L-1 Rh B?during 60 min.In addition,the resulting composites also displayed excellent cyclic stability.The removal rate of Rh B was still kept at about 75.6% after four cycles over g-C₃N₄-TiO₂-GA?5%?.?3?Ferric nitrate was disolved in the precursor solution of TiO₂-GA?5?to prepare a series of Fe2O3-TiO₂-GA heterojunction composites with the similar method to that of the aforementioned TiO₂-GA.The results showed that these composites kept the macroscopic columnar 3D structure of GA and both the anatase phase TiO₂ and Fe2O3 were uniformly dispersed.Comparing with other composites in this thesis,the Fe2O3-TiO₂-GA composites showed more excellent adsorptivity under the same conditions.The adsorption rate of Rh B was as high as 95.0% during 60 min over Fe2O3-TiO₂-GA?30%?.Furthermore,Fe2O3-TiO₂-GA?25%?exhibited the best removal ability under visible light irradiation.The total removal rate of Rh B was as high as 97.7% during 60 min.In addition,the resulting composites also displayed excellent cyclic stability.The removal rate of Rh B was still kept at about 81.8% after four cycles over Fe2O3-TiO₂-GA?25%?.?4?Spherical TiO₂ nanocrystallines with anatase phase were hydrothermally prepared from butyl titanate using P123 as the structure-directing agent.Then,the resulting TiO₂ with the predesigned amount was ultrasonicated into GO to synthesize a series of TiO₂-r GO composites by an ice-crystal template method and combined with calcination.The results showed that the mesoporous TiO₂ nanoparticles were well dispersed onto r GO.The resulintg TiO₂-r GO composites exhibited much better adsorptive and photocatalytic activity than the pure TiO₂ and TiO₂-r GO?20?was the best one.The adsorption rate of Rh B was 66.7% during 180 min and the total removal rate of Rh B was as high as 81.0% under visible light irradiation during 320 min over TiO₂-r GO?20?.In addition,the resulting composites also displayed excellent cyclic stability.The removal rate of Rh B remained 91.8% of the initial value after four cycles over TiO₂-r GO?20?.?5?Silver nitrate was disolved into the precursor solution of TiO₂-r GO?20?to prepare a series of Ag-TiO₂-GA heterojunction composites by using the UV-light reduction method combined with the aforementioned ice-crystal template method and calcination.It was found that the the adsorptivity of the Ag-TiO₂-r GO composites were not as good as that of TiO₂-r GO.Even so,the incorporation of Ag enhanced the photo-degradation activity of TiO₂-r GO to some extent.Among them,Ag-TiO₂-r GO?0.1?exhibited the best performance under the present conditions.The absorption rate of Rh B was 52.3% and the total removal rate was 67.0% under 180 min over Ag-TiO₂-r GO?0.1?.In addition,the Rh B removal rate remained 79.5% of the initial value after four cycles over Ag-TiO₂-r GO?0.1?.