| dc.description.abstract | Metal oxide (TiO2 and WO3) heterojunction material was developed in order to harvest light, store solar energy, and apply them to water treatment. Two TiO2 structures were applied, i.e., TiO2 nanoparticles (TiNP) and TiO2 nanotube (TiNT); and were hybridized with WO3 using different weight ratios of TiO2 to WO3 (e.g., 25:75, 50:50, 75:25). To investigate the ability of the TiO2-WO3 composite to utilize the captured electrons, hexavalent chromium (Cr(VI)) was used as model target compound. Three different treatment systems were investigated: a) batch photocatalytic system using dispersed particles, b) photoelectrochemical (PEC) system, and c) composites-laden membrane filtration system. The batch system showed that using TiNP resulted in complete Cr(VI) reduction at acidic and neutral pH, whereas TiNT were less effective even at low pH. The surface properties of TiNP and TiNT were characterized to investigate the effect of TiO2 morphology on their photocatalytic activities. TiNP was found to have a greater photocatalytic activity than TiNT because it is more crystalline, has less structural oxygen defects, has slower recombination of the photogenerated electrons, and has more oxygen vacancies closer to the conduction band (CB). These results were the basis for designing the composites of TiNP- WO3 and TiNT-WO3 and characterizing their performances.
In the PEC system where different combinations and weight ratios of TiNP or TiNT to WO3 were evaluated, TW25 showed the best performance among all combinations. It was able to completely reduce Cr(VI) to Cr(III) in 4 hours of reaction time under light irradiation as well as in the dark. However, only 70 % of initial Cr(VI) concentration was reduced in 4 hours of reaction time with TNW 25 under the same experimental conditions. The surface properties of the TW and TNW electrodes were characterized using SEM/EDS, elemental mapping, and UV-Vis spectra in order to investigate surface morphology, elemental composition, and flat-band position of the composites.
The composites-laden membrane filtration system using charged TiO2-WO3 composite materials showed the feasibility of reducing Cr(VI) to Cr(III) at natural pH. Cr(VI) reduction was more substantial in the system using TW 50 than in the system where material TNW 50 was utilized. | en |
