| Abstract: | 本研究以電化學陽極氧化法來製作由二氧化鈦奈米管所組成之孔層膜試片。在含1.0 M硫酸之0.2 M氟化鈉溶液中，調整pH 在2~6之間，控制兩極電位在5~20 V，可以製作出由不同管徑二氧化鈦奈米管組成之多孔膜。經場發射掃描式電子顯微鏡觀察，顯示多孔膜中奈米管之直徑隨兩極電位之增高(由5至20 V)而增加(由20增加至100 nm)，同時有顏色之變化。低掠角X-光繞射分析(GAXRD)結果顯示:電化學陽極氧化法製作之多孔膜屬於非晶質結構，此膜經450℃加熱1小時後，由非晶態轉變成銳鈦礦結構。退火後之多孔膜分別進泡於銀、銅、鐵之0.5M 硝酸鹽溶液中30分鐘，以紫外光(256nm波長)照射60分鐘後，即在0.5M碳酸氫鈉水溶液及紫外光照射下進行下列各種測試。包括開路電位、循環伏安、定電位還原及氣體層析(gas chromatography, GC)分析來研究其光觸媒特性。 開路電位量測得知多孔膜經450℃熱處理後，其開路電位由0.5V降至0.0 V，摻雜銀、銅、鐵之試片，其開路電位亦有降低。 循環伏安(cyclic voltammetry, CV)之結果得知:不同多孔膜試片，經450℃退火後，置於0.5M NaHCO3水溶液中，經紫外光照射，顯示出下列還原峰，分別為純TiO2(-0.228V, -0.057mA)、Ag-doped TiO2(-0.090V, -0.078mA) 、Cu-doped TiO2(-0.209V,-0.102mA)、 Fe-doped TiO2(-0.272V,-0.120mA)。所得還原峰之電位，推定為CO32- 之特性還原電位。 選定由CV所得之特性還原電位，進行定電位還原反應一小時，監測其對應之電流，獲得電流之大小，依序為 Fe-doped TiO2(-90mA) > Cu-doped TiO2(-30mA) > Ag-doped TiO2(-20mA) > pure TiO2(-15mA)。GC分析，以甲醇產生率計算，結果顯示:摻雜試片之催化活性，以Fe-doped TiO2(1.85ppm)試片最高，Ag-doped TiO2(0.80ppm)試片居次，Cu-doped TiO2(0.55ppm)試片第三，Pure TiO2(0.40ppm)試片最低。掺雜金屬之二氧化鈦奈米管之光觸媒還原活性優於單純之二氧化鈦奈米管多孔試片。 Porous films constructed by TiO2 nano tubes were prepared by electrochemical anodizing on the titanium substrate. The diameter of the nano tubes in the film was determined by the electrical voltage applied between the electrodes and the pH (in the range from 2 to 6) of the electrolyte containing 1.0 M sulfuric acid and 0.2 M sodium fluoride. f Ti metal. Examining through field emission scanning electron microscope (FESEM), we found that the diameter of the nano-tubes in the films increases with increasing the electrical voltage. The pore size influences the color of the film under illumination. Grazing Incident x-ray diffractometer analysis depicted that the as-deposited anodizing film belongs to amorphous, and it turns to anatase crystals characterized by (101) and (211) planes after annealing at 450℃ for 1 h. The annealed film was immersed in 0.5 M silver (I), copper (II) and iron (III) nitrate solution, respectively, for 30 min. and removed to be illuminated by ultraviolet (UV) light (wavelength at 256 nm) for 60 min and prepare for photo-catalytic tests including measurement of open circuit potential (OCP), cyclic voltammtery, potentiostatic reduction and gas chromatography. The OCP for the as-deposited film was at 0.50 V and it shifted to 0.0 V post 450℃-annealing. This shift implied the enhancement of photo-catalytic activity by annealing. The dope of Ag, Cu, Fe on the porous film shift the OCP to the active end to different extent. This reflects that the catalytic activity of the films varies with different impurity doped. Cyclic Voltammetry (CV) of the annealed films in 0.5 sodium bicarbonate solution illuminated by ultraviolet light (UV) was useful to find the characteristic reduction peak of the carbonate ions. The characteristic potential and current estimated from CV are listed in the following: pure TiO2 (-0.228V, -0.057mA),Ag-doped TiO2 (-0.09V,-0.078mA), Cu-doped TiO2 (-0.209V,-0.102mA) and Fe-doped TiO2 (-0.272V,-0.120mA). The reduction on Ag-doped film takes place at higher potential but the reduction current is the highest on the Fe-doped film. Potentiostatic reduction was carried out at the characteristic potential for different film for 1 h and the reduction current was monitored. The reduction current measured decreases in the order: Fe-doped TiO2(90mA) > Cu-doped TiO2(30mA) > Ag-doped TiO2(20mA) > pure TiO2(15mA). This order is parallel to the catalytic activity of the film. Gas chromatography(GC) analysis provided another estimation of catalytic activity by determination the formation of methanol reduced from carbonate. The quantity of methanol was in the order Fe-doped TiO2(1.85ppm) > Ag-doped TiO2(0.80ppm) > Cu-doped TiO2(0.55ppm) > Pure TiO2(0.40ppm). The catalytic activity of Ag, Cu, and Fe-doped films are superior to the pure TiO2 films on carbonate reduction. |
