TiO2/Ti Thin Film Electrode Combined External Circuit Photoelectrocatalytic Process for Reducing Silver Ions

• Main Authors: Chao-Lang Kao, 高肇郎
• Other Authors: 謝永旭
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/73503251531787907559

博士 === 國立中興大學 === 環境工程學系所 === 97 === In this study, a nano-class TiO2/Ti thin-film electrode was made using the atmospheric pressure chemical vapor deposition (APCVD). The photoelectrocatalytic reaction system employed the TiO2/Ti thin film as anode and graphite rod as cathode. The electrode was combined with an external circuit and applied potential to study the efficiencies of silver ions reduction and acetic acid decomposition. The effects of pH, concentration of silver ions, concentration of acetic acid, applied potential, TiO2 surface analysis and electrochemical analysis. Results of SEM images and XRD patterns of the TiO2/Ti thin-film electrode surface show that the thin film electrode made using the APCVD method can be as thin as 30 nm with the TiO2 photoelectric catalyst in anatase crystal form. More obvious agglomeration of TiO2 particles was observed by APCVD with 2 hours sprayed times. , Results of the light response study show that the electrode has a rapid response time under UV irradiation, and generation of photocurrent density with 7 μA cm-2. Additionally, results of the photocatalytic studies using the electrode combined with an external circuit in the photoelectrical catalytic studies to reduce silver ions reveal that with a reaction time of 180 min, the photocatalytic process will reduce 70% of silver ions in high-concentrated solution (1000 mg/L as Ag+) and 93% silver ions in low-concentrated solution (108 mg/L as Ag+). When the irradiation time is extended to 240 min, the silver reduction efficiency is as high as 99.8%. The solution pH 7 is favorable to the photoelectrical reduction of silver while the anode bias does not benefit the silver reduction efficiency but favors the decomposition of acetic acid. However, the process decomposes less than 10% of acetic. The external circuit will transmit the photo-generated electrons to the cathode surface thus reducing the combination of electron and electronic holes at the anode surface. As the reduction of precious metals is concerned, the external circuit is capable of avoiding the metal deposition at the catalyst surface to cause catalyst poison or light shielding that are know to reduce the photo utilization efficiency.