以常壓電漿輔助程序製造氮摻雜二氧化鈦可見光觸媒奈米微粒之研究

Abstract

本研究目的為利用常壓電漿輔助奈米微粒製造程序（Atmospheric Pressure Plasma Enhanced Nanoparticle Synthesis；APPENS）製造均勻粒徑之N摻雜TiO2奈米微粒，其可為能源材料或光觸媒使用，此外亦可應用作為均勻氣膠產生器(monodisperse aerosol generator)，提供對奈米顆粒健康效應等研究者一個簡易的奈米微粒即時產生源。 本研究利用自行開發之APPENS系統，在常溫常壓下，藉由各種不同製程條件之電漿反應器系統產生奈米微粒，再將所得之微粒利用SEM、TEM、XPS、XRD等儀器分析微粒之物理化學特性。研究結果顯示，本程序所合成之光觸媒微粒粒徑分佈約為20nm~40nm。經過XRD及XPS分析後確認為含氮摻雜之anatase TiO2。將製造所得之光觸媒以甲苯及異丙醇為揮發性有機物指標物種進行紫外光及可見光光催化批次反應，結果顯示本研究之觸媒在以可見光光源照射40分鐘，對甲苯及異丙醇分別有40%及100%去除效率，而在紫外光下對甲苯效率則提升為60%，對異丙醇則在30分鐘內達到100%。利用連續式光催化反應來比較本研究製造得之光觸媒與商用光觸媒(P-25、ST01)之活性，結果顯示在可見光照下確實有較優於商用觸媒之去除效率。本研究亦探討在不同製程條件下製造各種不同氮摻雜光觸媒之表面鍵結特性，研究顯示可見光觸媒表面鍵結型態為影響光催化活性之關鍵，OX-Ti-NY 型態摻雜（doping）對可見光的催化效果較Ti-(NO)為佳，而無論是Ti-N、Ti-N及OX-Ti-NY 型態的氮摻雜 都有可見光的催化效果， Ti-(NO2) 型態的氮摻雜則可能會對可見光的催化效果有負影響。 研究中並針對合成程序條件對生成微粒之影響，發現在無電漿環境下形成的可見光觸媒微粒會成雙峰分佈，其平均粒徑為100 nm及400 nm; 而在電場強度9.6 kV/cm之電漿環境下形成之微粒則成單峰分佈，粒徑大小依不同前驅物濃度而改變，範圍約在30-60 nm左右，此外改變不同電場強度及頻率亦會改變粒徑的分佈。本研究結果顯示本系統不僅能製造出高均勻度之奈米微粒，且該電漿系統具有參數調整容易之優點，可迅速的產生所需粒徑之奈米微粒，且在可見光觸媒製造上可獲致品質佳且較其他製程應用性更廣之成品。

An Atmospheric Pressure Plasma Enhanced Nanoparticle Synthesis (APPENS) process was proposed to produce nitrogen doped (N-doped) titanium dioxide (TiO2) visible light photocatalyst. The effect of N-doping statuses on the photocatalytic activity of N-doped TiO2 photocatalysts was investigated. The potential application of APPENS reactor as an aerosol generator was studied. The results showed that photocatalytic activity of the N-doped TiO2 photocatalyst is higher than the commercial ST01 and P25 photocatalysts in terms of toluene removals in a continuous flow reactor. The light absorption in the visible light range for N-doped TiO2 was also confirmed by a clear red shift of the UV-visible spectra. The N-doped TiO2 particles with OX-Ti-NY and -(NO) dopants are produced via N2 plasma gas followed by air or N2 annealing gases. They have better visible and UV photocatalytic activities as compared to the pure TiO2 photocatalysts prepared under O2/Ar plasma and annealing gases. The results reveal that the OX-Ti-NY and -(NO) dopants may have positive effects on the visible light photocatalytic activity while the -(NO2) dopant tends to have a negative effect on the visible light photocatalytic activity. For the aerosol generator employs the APPENS process of alternative current (AC), the influences of applied voltage, frequency and molar ratios of precursor on the generated particles were characterized by the SEM, XRD and SMPS analyses. Results showed that TiO2 nanoparticles appear to be in a broad size range of bi-modal distribution when no voltage is applied. After applying the AC plasma, uni-modal distribution with average sizes range of 30-60 nm was observed. The applied electric frequency can be adjusted to either generate nanoparticles after the plasma reactor or develop a thin film in the reactor. An increase in the precursor molar ratio leads to larger particles with a broader size distribution.