鉑金改質二氧化鈦之光觸媒降解室內甲醛之研究

Control of Formaldehyde in Indoor Environment by Pt-loaded TiO2 Photocatalyst

楊詠勝(Yong-Sheng Yang)

指導教授 ： 李慧梅

國立臺灣大學/工學院/環境工程學研究所/碩士(2014年)

https://doi.org/10.6342/NTU.2014.01163

摘要

環保署在2012年開始施行室內空氣品質管理法，室內環境之空氣品質與民眾息息相關。甲醛為規範之室內空氣污染物之一，目前國內對甲醛濃度規範值為0.08ppm，室內甲醛來源包含室外來源以及室內來源，其中室外來源主要有發電廠、焚化爐、煉油廠、工廠廢氣和交通工具廢氣排放等；室內來源主要由家具建材、木製消費性產品、裝潢塗料與室內烹調燃燒等，其對人體健康危害如眼、鼻與黏膜組織刺激，易引起呼吸道病變及鼻咽腫瘤，國際癌症研究署(International Agency for Research on Cancer, IARC)將甲醛列為第一類致癌物質。
本實驗使用光沉積法製備Pt/TiO2光觸媒，將觸媒披覆於蜂巢狀陶瓷載體，置於不鏽鋼反應器內進行降解甲醛反應，測試第一階段未開光由觸媒直接降解甲醛以及第二階段開啟紫外光激發Pt/TiO2降解甲醛之轉化率。利用蜂巢狀陶瓷載體置入光纖，其孔洞可增加反應表面積及觸媒可披覆面積，提供254nm紫外光深入照射。Pt/TiO2光觸媒製備使用氯鉑酸(H2PtCl6)披覆，利用光沉積法將鉑金還原至Degussa P25 TiO2表面上，並使用X光粉末廣角繞射儀(X-Ray Powder Diffractometer)、場發射電子顯微鏡(Field Emission Gun Scanning Electron Microscopy)、比表面積分析儀(Specific Surface Area)及感應耦合電漿質譜分析儀(ICP-MS)儀器鑑定材料特性。實驗利用注射針筒驅動法配置甲醛氣體，以1400ml/min之氣體流率在不同相對溼度(30%、50%、70%)及接近室內環境甲醛之濃度(0.6ppm、0.8ppm、1.0ppm、1.2ppm、1.4ppm)進行實驗，以瞭解Pt/TiO2在不同相對濕度和進流濃度之甲醛轉化率。
本研究改質之Pt/TiO2比表面積為51.2992±0.3640m2/g，觸媒表面金屬含量為4018μg/g。於各條件實驗結果顯示，在此濃度與濕度範圍內進行實驗，在各條件下之甲醛轉化率未有顯著差異，第一階段未開光降解甲醛效率為51.87%±2.96%，第二階段開光降解甲醛效率為94.29%±1.02%，總降解效率為97.27%±0.43%。而濃度由0.6ppm增至1.4ppm，未開啟紫外光階段之反應速率由0.46±0.01×10-3μ-mol/m2-s增至1.01±0.02×10-3μ-mol/m2-s，而開啟紫外光階段之反應速率由0.40±0.01×10-3μ-mol/m2-s增至0.99±0.02×10-3μ-mol/m2-s，反應速率皆隨著濃度提高而上升。與林(2013)之研究比較，使用光沉積法置備鉑金改質二氧化鈦(Pt/TiO2)，披覆於載體之觸媒量使用0.45±0.02g，僅林(2013)未改質光觸媒(TiO2)的七分之一，本實驗以Pt/TiO2處理甲醛之轉化率約97.27%±0.43%，較林(2013)未改質之降解效率(90%至95%)為佳，並於未開光階段即有約52%的降解效率。

關鍵字

甲醛 ； 鉑 ； 二氧化鈦 ； 光觸媒 ； 蜂巢狀陶瓷載體 ； VOCs

並列摘要

Environmental Protection Agency began to implement the Indoor Air Quality Management Act in 2012. Formaldehyde (HCHO) is one of the indoor air pollutants, and standard value of formaldehyde concentration is 0.08ppm in Taiwan. Sources of interior formaldehyde include outdoor source and indoor source. Outdoor source include power plant, incinerator, petroleum refinery, factory waste gas and vehicle exhaust emissions. Indoor source include wooden furniture, consumer products, paint and cooking. Formaldehyde is harmful to human health, such as eyes, nose and mucosal tissues irritation, and IARC (International Agency for Research on Cancer) classified it as carcinogenic to humans.
The P25 TiO2 supported Pt catalysts were using chloroplatinic acid (H2PtCl6) as the Pt precursor compound, and prepared by photo-deposition method in this study. The catalysts would coat on honeycomb monolith which supply more reaction area. Through optical fibers, the UV lamp could irradiate into honeycomb monolith to excite catalysts, and estimate the first stage (unirradiated) and the second stage (irradiated with UV254nm) formaldehyde conversion. Formaldehyde was degraded by photocatalytic reactor, the reactor include Pt/TiO2 supported honeycomb monolith. Pt/TiO2 catalysts were characterized by using XRD, SEM-EDX, BET and ICP-MS. The gas flow rate was controlled at 1.4 LPM with formaldehyde inlet concentration ranged from 0.6ppm to 1.4ppm under RH 30%, 50% and 70%.
The BET surface area of Pt/TiO2 catalysts were increased to 51.2992±0.3640m2/g, and catalysts surface Pt loading were 4018μg/g. The first stage formaldehyde conversion is 51.87%±2.96%, second stage formaldehyde conversion is 94.29%±1.02% and total conversion is 97.27%±0.43%. These results demonstrated that various humidity and inlet concentration were not affect the activity of the catalysts. The oxidation rate constants of formaldehyde with inlet concentration ranged from 0.6ppm to 1.4ppm are increase from 0.46±0.01×10-3μ-mol/m2-s to 1.01±0.02×10-3μ-mol/m2-s at the first stage, and increase from 0.40±0.01×10-3μ-mol/m2-s to 0.99±0.02×10-3μ-mol/m2-s at the second stage. Formaldehyde conversion reaches 97.27%±0.43% when the weight of Pt/TiO2 catalysts coated on honeycomb monolith is 0.45±0.02g. Lin(2013) had used 3.27±0.05g P25 TiO2 to degrade low concentration formaldehyde, and HCHO conversion varied between 90% to 95%. Obviously, the Pt supported P25 TiO2 could reach higher formaldehyde conversion.

並列關鍵字

formaldehyde ； Pt ； TiO2 ； photocatalyst ； honeycomb monolith ； volatile organic compounds

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