以改質光觸媒結合電透析程序併同處理六價鉻與奈磺酸鹽之研究

Removal of chromium(VI) and naphthalenesulfonate by nitrogen-doped TiO2 nano-powder with visible light photocatalysis and membrane electrolysis

陳玉珊(Yu-Shan Chen)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境工程與管理研究所/碩士(2010年)

摘要

本研究以高溫煅燒法備製出含氮二氧化鈦N-TiO2光觸媒，應用於連續式可見光光催化系統，經由可見光激發反應生成電子-電洞對，產生e-與h+同步進行氧化與還原作用，再以創新概念結合離子交換膜透析程序，併同處理極度氧化態的六價鉻Cr(VI)與極度還原態的奈磺酸鹽NS，以更進一步對於含氮二氧化鈦N-TiO2光觸媒之使用壽命、結合離子交換膜透析程序之差異性，及目標污染物之實驗影響因子之反應機制進行探討。
在連續式可見光光催化系統結合離子交換膜透析程序中，固定無機污染物Cr(VI)濃度50 mg/L、水力停留時間60 min、電流密度4.0 mA/cm2，以及燈源λmax = 419 nm，在含氮二氧化鈦N-TiO2光觸媒之使用壽命部分，N-TiO2光觸媒併同處理目標污染物之去除效率於62小時之前，可達95%以上，相較於未改質光觸媒併同處理目標污染物之去除效率僅在48小時之前，主因是表面將會被目標污染物佔據，而產生光觸媒毒化現象，直接影響觸媒的使用性。然於是否結合離子交換膜透析程序之差異性方面，結合離子交換膜透析程序，相較於無結合離子交換膜透析程序，亦能增加15%左右之去除效率，且電流密度4.0 mA/cm2亦不影響本研究併同處理目標污染物之同步氧化還原反應，也不造成薄膜嚴重阻塞。而於不同pH值3.0 ~ 10.0、不同光觸媒劑量0.5 ~ 2.0 g/L及不同電洞捕捉劑濃度0 ~ 400 mg/L條件下，探討併同處理目標污染物與影響因子之反應機制，本實驗結果顯示，經反應10小時後，隨著pH值由3.0 ~ 10.0，併同處理之去除效果增加，於pH值為3.0時，併同處理目標污染物之去除效果達95%以上，然在本研究添加光觸媒劑量於0.5 ~ 1.0 g/L範圍內，隨著光觸媒劑量增加併同處理之反應效果亦增加，於光觸媒添加量為1.0 g/L時，併同處理目標污染物之去除效果達95%以上，而本研究添加電洞捕捉劑濃度部分，則是在50 mg/L時，併同處理目標污染物之去除效果達95%以上為最佳。
有機污染物NS經由連續式可見光光催化系統結合離子交換膜透析程序與無機污染物Cr(VI)併同處理後，會生成SO42-，經由計算將有機污染物NS與SO42-換算成S，是將近1：1的轉換率，故有機污染物NS as S與SO42- as S呈現質量平衡之狀態。根據實驗結果亦可顯示，併同處理反應10小時後，有32%左右的總有機碳TOC損失，以無機碳CO2型態方式逸散至空氣中，但其仍有68%以上的有機物仍以未知的型態存在於水體中，因此利用氣相層析質譜儀(GC/MS)進行分析，所生成之副產物包含了二氧化碳、SO42-，以及低分子量之有機酸-甲酸。而反應速率常數之評估，本研究為假一階反應，反應速率常數會隨著pH值、光觸媒劑量及電洞捕捉劑濃度不同，而有一定之趨勢關係，pH值為3.0時，反應速率常數kobs值分別為k Cr(VI) 0.2027 hr-1及kNS 0.1712 hr-1，光觸媒劑量為1.0 g/L時，反應速率常數kobs值分別為k Cr(VI) 0.2227 hr-1及kNS 0.2150 hr-1，至於當電洞捕捉劑濃度50 mg/L，反應速率常數kobs值，分別為k Cr(VI) 0.1326 hr-1及kNS 0.1448 hr-1。

關鍵字

可見光光催化 ； 含氮二氧化碳N-TiO2 ； 併同處理 ； 氧化還原 ； 六價鉻Cr(VI) ； 奈磺酸鹽NS ； 電透析程序

並列摘要

This study was proposed for simultaneous oxidization of naphthalenesulfonate(NS) /reduction of chromium(VI) by electron- hole pair (e－-h+) using a novel technology of N-doped TiO2 with visible light photocatalysis. To extend the absorption range of TiO2 into the visible-light region, the simple procedure for preparing nitrogen doped titanium dioxide nanocrystal (TiOxNy) by calcinating the mixture of Degussa P-25 (DP-25) TiO2 and NH4Cl at temperatures of 400 °C under airtight condition. The highest nitrogen content in TiOxNy is 19.22 at. %, occurred in the sample of TiOxNy with TiO2: NH4Cl weight ratio 1:6. Furthermore, the application of cation-exchange membrane (CEM) combining electrolysis was used to enhance the efficiency for prevention of the recombination of the electrons with the electron-hole. Therefore, the objectives of this study were to investigate: (1) the effects of N-doped TiO2 dosage, pH, and NS initial concentration; (2) the photocatalytic kinetics and mechanism of the N-doped TiO2/ Cr(VI)/ NS reaction. There were three different parameters: N-doped TiO2 dosages (0.5 - 2.0 g/L), pH (3 - 10) and NS initial concentrations (0 - 400 mg/L).
In the continuous photocatalytic system combining membrane electrolysis, the Cr(VI) removal efficiency increased with decreasing system pH from 20% on average for pH 10 system to about 99% for pH 3 system with N-doped TiO2 dosage of 1.0 g/L after 10 hours. Therefore, N-TiO2 photocatalysis successfully reduced Cr(VI) to Cr(III) from synthetic textile wastewaters at pH 3 under visible-light illumination. The degradation efficiency of Cr(VI) and NS increased with increasing the amounts up to 1.0 g/L, and the efficiency decreased slightly for dosage higher than 1.0 g/L. Addition of NS concentration facilitated Cr(VI) reduction in comparison with the same system. The Cr(VI) removal rates increased as NS concentration increased because the electron/hole recombination might be reduced by electrons transfer from carboxyl group to positive holes of the valence band of the N-TiO2. This synergy effect helped the reaction by hindering the electron-shuttle mechanism that occurred in NS and Cr(VI). The decomposition of NS accompanies with the diminish of TOCs and generation of sulfate. As the pH decreased, the NS removal efficiency increased. When the pH was controlled at 3 with N-doped TiO2 dosage of 1.0 g/L for 10 hours, about 95.3 % of NS removal was achieved. The yield of sulfate was formed from the degradation of NS of nearly 100%. Meanwhile, the yield of sulfate as S increased with increased in degradation of NS as S with concentration of NS from 0 to 400 mg/L.
When N-doped TiO2 dosage was 1.0 g/L, both higher KCr and KNS were obtained in continuous photocatalysis combining cationic exchange membrane electrolysis. Moreover, the degradation efficiency of Cr(VI) and NS increased with increasing the amounts up to 1.0 g/L, and the efficiency decreased slightly for dosage higher than 1.0g/L. The mineralization reaction of NS can be stoichiometrically calculated. Meanwhile, the yield of sulfate as S is consistent with the increase of degradation of NS as S for the cases examined.

並列關鍵字

Continuous photocatalytic system ； N-dope TiO2 ； Simultaneous treatment ； Chromium(VI)；Naphthalenesulfonate (NS)；Membrane electrolysis

參考文獻

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