Pd-TiO₂and Graphene-based Nanocomposite Thin Film And Its Photo-electrochemical Catalysis Performance

Developing garment industries will result in consumption of dye in textile industries, from which the ecosystems have been seriously affected by colored wastewater day by day. Many methods have been studied in industrial wastewater treatment including electrochemical, photochemical, absorption and some mixed techniques. Among them, electrochemical technology has received much attention due to its high removal efficiency, low-cost by using only electrons as reagents. However, significant issue is the parasitic reactions usually compete with the electrolysis of contaminants that reduce the removal efficiency. Moreover, in large-scale techniques, energy saving has became more important. Meanwhile, the photoreduction using natural available energy resources from sun light is considered as green technique. Therefore, the main idea of this study is the implementation of electrochemical and photochemical in combined photo-electrochemical technique which could become a good solution to increase the efficiency, minimize energy usage and further fabricate a "green" technique for wastewater treatment.In the first chapter, literature review about using titanium dioxide and its potential applications in catalysis for environmental treatments. In addition, graphene was also mentioned as an attractive selection in the fabrication of photo and electrocatalysts to apply on laboratory and industry scale.In the second chapter, the experimental methods and procedures which were used in whole of the study is described including the experimental drugs, material fabrication methods, experimental designs and analytical instruments.In the third chapter, Pd-TiO2wrapped by reduced Graphene Oxide (r-GO@Pd-TiO2) which exhibited high photocatalytic activity under visible light was synthesized from commercial chemicals. The classic sol-gel method and the Ar gas bubbling composition were used in the fabrication of catalyst. Furthermore, the best Pd-doping concentration in crystals, the wrapping concentration of r-GO over nanoparticles, and the optimal calcination temperature were also investigated to enhance the photocatalytic activity of the hybrid catalyst. The experimental results showed that the catalysis of r-GO@Pd-TiO2reached maximum efficiency at the optimum synthesis conditions:0.7wt%Pd- doped TiO2by sol-gel process, calcination temperature of550℃, wrapping of1mg GO for100gram wrapped Pd-TiO2.X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) techniques were conducted to determine nanostructure of catalysts. The average crystallite size of nanoparticles was14nm with the perfect dispersion of Pd dots and wrapping of r-GO membrane. Methyl Blue was applied as a model of organic dye to test the ability in wastewater treatment of catalysts. Besides, a comparison between different catalysts’ characteristics was studied in these experiments. The r-GO@Pd-TiO2showed the higher photocatalytic activity compared to Pd-TiO2and commercial P25. Additionally, the complete dye reduction under excitation visible light indicated that wrapping of r-GO on Pd-TiO2improve the photocatalytic activity of catalysts. The stability of r-GO@Pd-TiO2was determined which showed that its photocatalysis remains persistent over several times of recycling examination. Therefore, r-GO@Pd-TiO2was highly appreciated in wastewater treatment.The catalysts which are studied in powdered form face with the difficulty in its recollection for recycling. In the fourth chapter, r-GO/Pd-TiO2/r-GO thin film was also fabricated in the form of moon pie on silica glass slices by low-cost sol-gel facile coating method and studied its photocatalytic activity in degradation of Methylene Blue dye. The thin film was characterized by various techniques which revealed that the average crystallite size of15nm and the film thickness is170nm of Pd-TiO2wrapped by r-GO layers. The stability and strength of the thin film was increased with graphene by preventing breakage of Pd-TiO2thin film during calcination and also the oxidation during chemical reaction. The reduced graphene oxide sandwiched Pd-TiO2thin film showed excellent activity in photochemical degradation of Methylene Blue dye, and retained its activity and stability for10times of recycling. The removal rate on r-GO/Pd-TiO2/r-GO was greater than1.4×10-5g (minxm2)-1in all experiments compared to bare Pd-TiO2which dropped markedly to less than0.60x10’5g (minxm2)-1after second run. This study can be considered as simple, environment friendly, cost effective for treatment of wastewater.The fifth chapter focus on the combination of Pd-TiO2composite and r-GO in fabrication of the electrodes. The r-GO/Pd-TiO2/r-GO/CP and r-GO/Pd-TiO2/r-GO/ITO electrodes were fabricated and considered to exhibit the good removal efficiency in electrochemical and photo-electrochemical reduction of MB. The decolorization of MB is considered due to the reduction of MB to LCM by receiving electrons from electrode and the oxidization by generated·OH free radical. Temperature of electrolyte at30℃, applied bias potential of-0.8V to-1.0V are the best conditions for electrochemical reduction of MB. The efficiency of MB reduction on electrode was enhanced with the aid of light energy, thus photo-electrochemical method could be good selection for environmental treatment.