Photoelectrocatalytic degradation of polar pesticides by Pt loaded nanotubes structure of TiO2 photoanodes

In this thesis nanotube structured TiO2's on Ti surface were prepared in hydrogen fluoride (Ti/TiO2NTHF) and ethylene glycol (Ti/TiO2NTEG) medium by different anodic oxidation times and calcination temperatures. Additionally, Pt loaded Ti/TiO2NTEG photoanodes were also prepared by cyclic voltammetry method for different cycles and the optimum loaded Pt amount was determined for the most active Ti/TiO2NTEG photoanode. These photoanodes were characterized by using XRD, SEM-EDX, and photocurrent methods. XRD studies showed that almost all TiO2's are in anatase phase. SEM analyses show that nanotubes and Pt nanoparticles on nanotube surface dispersed almost homogeneously. The longest nanotubes were obtained in the ethylene glycol medium and the nanotube length increased by increasing applied anodic oxidation time. In addition, it was found a linear correlation between nanotube length and XRD peak intensity. Moreover SEM-EDX and XRD analyses evidence that Pt nanoparticles on nanotube surface are in cubic structure. Additionally, photocurrent values of Ti/TiO2NTEG photoanode are higher than that of Ti/TiO2NTHF. By increasing loaded Pt amount on Ti/TiO2NTEG photoanode, photocurrent values decreases linearly. The first photoelectrocatalytic degradation of paraquat and diquat, most commonly used polar pesticides, were performed by the prepared photoanodes. The pesticides were completely degraded (100% conversion) for 3h reaction time. Moreover electrocatalytic and photocatalytic degradation of the pesticides were also investigated for comparison, however lower activities were observed. Especially almost no activity (1% conversion) was obtained for electrocatalytic degradation of pesticides. These results are evidence that the photoanodes show a synergy for PEC activity. In addition activity results show that photoelectrocatalytic and photocatalytic degradation of diquat is faster than that of paraquat. The highest photoelectrocatalytic degradation activity was obtained by using nanotube structured TiO2, prepared in ethylene glycol medium by anodic oxidation for 3 hours and calcinated at 500 oC and then Pt loaded with 4 cycles (Ti/TiO2NTEG-3h-500-Pt-4d).