Synthesis And Optical/Electrical Properties Of Graphene Oxide Based Composites

Huge amounts of pollutants generated from pharmaceutical,textile dyes and industrial processes have been discharged into wastewater,rivers and oceans,including some harmful substances that cannot be naturally degraded,such as,dyes,phenols,heavy metals etc.Some of them accumulated in animals and plants,infiltrated into the human body through the food chain,eventually may cause human poisoning,nervous disorders and dermatitis.Therefore,constructing a low-cost,fast and effective method for the removal of organic dyes in wastewater and the trace detection of phenolic substances is of great practical significance.Graphene oxide,a two-dimensional layered structure,has high surface area,good thermal conductivity and mechanical properties.Over past decade,graphene-based nanocomposite materials had a remarkable increase on the study of the degradation of pollutants,and water splitting as well as artificial photosynthesis.In this thesis,IL-GO and rGO-Au-TiO₂ composites based on ultrasonic exfoliated graphene oxide were synthesized.The photocatalytic performance of ionic liquid diethylamine formate?DEAF,IL?and IL-GO for MB dye degradation using visible light were studied.Meanwhile,a novel electrochemical sensor based on IL-GO modified glass carbon was developed for p-chlorophenol?4-CP? and p-nitrophenol?4-NP?simultaneousdetermination.Inaddition,thepropertiesfor photoelectrochemical catalytic water splitting to oxygen evolution and Rhodamine B degradation under visible light of rGO-Au-TiO₂ were investigated,respectively.The main research contents are as follows:1.Synthesis and photodegradation properties of DEAF and IL-GO?1?In this study,ionic liquid diethylamine formate?DEAF? was synthesized,the photocatalytic performance of DEAF was evaluated by the degradation of different concentrations of MB aqueous solution under ultraviolet light,visible light and solar light irradition,respectively.DEAF shows good photodegradation efficiency under visible light irradiation.When the concentration of MB aqueous solution is 10 mg/L,the MB degradation rate was up to 97% just in 10 min.In the presence of 25 vol% DEAF and MB almost completely degraded in 5 minutes with 75 vol% DEAF.?2?IL?DEAF?was covalently modified to the surface of graphene oxide,and the SEM,TEM,UV,XRD,XPS and other characterization methods indicated the successful synthesis of IL-GO composites.The photocatalytic degradation of 50 mg/L MB was studied with GO and IL-GO under visible light irradiations.After stirring in dark for 30 min and visible light irradiation for 120 min,the removal rates of 75% IL-GO,20%IL-GO and GO for MB were 92.3%,95.2% and 85.7%,respectively.The degradation of MB by GO and IL-GO accorded with the first-order kinetic equation.And the rate constants of 75% IL-GO,20%IL-GO and GO were 0.02052,0.01779 and0.0094 min^-1,respectively.The modification of ionic liquid DEAF to GO flakes has significant photodegradation effect on MB and has potential applications in dye wastewater treatment.2.Simultaneous determination of p-chlorophenol and p-nitrophenol by IL-GO modified glassy carbon electrodeIonic liquid functionalized graphene oxide modified glassy carbon electrode acted as the working electrode to detect 4-CP and 4-NP.The results of electrochemical characterization and electrochemical behavior showed that IL-GO can be used as an electrode modifier to detect 4-CP and 4-NP simultaneously.4-CP and 4-NP undergo an irreversible oxidation reaction on the electrode and are adsorption-controlled process.Under the optimized conditions,the quantitative analysis of 4-CP and 4-NP were investigated by DPV.When detected separately,4-CP?0.05¹00?M?and 4-NP?0.5¹00?M?displayed a good linear relationship,and detection limits were 33.33 nM and 0.167?M,respectively.For the mixture solution of 4-CP and 4-NP?constant concentration of 40?M 4-CP and 50?M 4-NP?,the oxidation peak currents displayed a good linear relationship to concentration in the ranges from 0.1 to 100?M for 4-CP and 0.5 to 100?M for 4-NP,with detection limits of 0.13?M and 0.39?M for individual 4-CP and 4-NP,respectively.In addition,the sensor exhibits good sensitivity,reproducibility,stability and strong anti-interference ability.3.Synthesis and properties of rGO-Au-TiO₂rGO-Au-TiO₂ doped with GO and AuNPs were prepared via solvothermal method using titanium sulfate.The crystal structures and morphologies of the obtained samples were characterized using XRD and TEM,respectively.The photoelectrochemical decomposition of oxygen under visible light shows that the photocurrent density of rGO-Au-TiO₂ is twice that of rGO-TiO₂,and the maximum photocurrent was 0.791?A/cm².The LSV showed that the external bias had little effect on the oxygen production performance of the electrolyzed water,while the current changes were caused by the photoexcited electrons.Rhodamine B was used as a target degradation product to explore its degradation activity under visible light irradition.After 120 min irradiation,the degradation rates of rGO-Au-TiO₂,rGO-TiO₂ and TiO₂ were 90.24%,68.9% and 27.72%,respectively.The degradation of Rhodamine B by TiO₂,rGO-TiO₂ and rGO-Au-TiO₂ accorded with the first-order kinetic equation,and the rGO-Au-TiO₂ had the highest rate constant of0.01642 min^-1,which possess the best photocatalytic performance.Results showed that doping GO and AuNPs into TiO₂ broadened the visible light response of TiO₂,and then improved the photocatalytic efficiency.