碳作為全球暖化和氣候變遷及生地化循環中的重要元素，在地球上的生物圈、岩石圈、土壤圈、水圈及大氣中進行交換，而黑炭則在過往研究中被認為是碳循環中扮演穩定碳庫的重要角色。黑炭是生物通過光合作用吸收二氧化碳形成生物質，經燃燒熱解產生未完全燃燒的有機碳殘留物，因黑炭結構中富含多環芳香烴使整體性質較為穩定不易降解，一旦生成便會長時間留存在地層中，然而地層中黑炭含量在現實累積數據和估算數據存在巨大差異，意味著黑炭在環境中降解可能被嚴重低估。
過去我們在天然土壤樣品中發現含有奈米礦物(二氧化鈦、鈦鐵礦、赤鐵礦等)，這些奈米礦物具有作為光觸媒的潛力，同時過往光催化反應主要應用在有機廢水處理或者塗料上，對於其在天然環境中所扮演的角色探討很少，因此本研究假設天然奈米礦物在光催化作用下可以對環境中穩定的有機碳降解。根據過去對於二氧化鈦光觸媒的研究，發現二氧化鈦複合物與氫化後產生的無序化的二氧化鈦在光催化的表現上比未經處理的二氧化鈦優異，而複合物或者較無序化的二氧化鈦與自然環境中的物質狀態較為貼近。首先環境中的二氧化鈦不容易是純相的，與複合物概念相近但只是簡單混合而並非採用合成構建，其產物光催化效果需進行驗證，因而本研究採取兩種礦物粉末按不同比例直接混合的方式觀察並比較光催化效率。另外環境中風化、淋洗、氧化還原的波動等相互影響的因素導致礦物在自然環境中要產生完好的晶型並不容易，因此本研究中也設計了由單寧酸這種自然環境中常見的有機質與二氧化鈦熱水合反應後對其光催化效率的影響。並利用甲基藍的染劑模型進行篩選後，採用優化比例的混合相奈米礦物進行光催化實驗降解黑炭，並檢測降解效果和降解產物。
本實驗結果顯示二氧化鈦混入少量（比例<10%）α相三氧化二鐵、四氧化三鐵等能隙較低但是電動填充速率較高的奈米礦物可顯著提升光催化效率，在甲基藍染劑模型試驗，產生類似複合物增強的光催化效果。因此推斷自然環境中存在的此類含鐵奈米礦物雖因為電動填充速率太快以致幾乎無光催化能力，但其少量的存在並混合二氧化鈦可產生不可忽略的光催化降解的能力，因其普遍存在，對於對有機碳、黑炭的降解可能是被嚴重低估的。利用單寧酸在熱水合反應對二氧化鈦的改質，改質後的二氧化鈦沒有在甲基藍染劑模型試驗直接提高光催化效率，但在高濃度單寧酸處理顯示出強大的吸附能力。在低濃度的處理中，一定程度地促進光催化降解，推測丹寧酸熱反應後少量吸附在改質的二氧化鈦表面，縮短光觸媒與待降解物質間距離並促進了光催化的進行。推測在環境中對有機碳光催化降解可能會有所類似的影響。利用混合相奈米礦物及改質二氧化鈦的黑炭降解實驗驗證光催化反應確實能夠降解黑炭，但依目前質譜數據資料還無法解出黑炭在降解過程中產生的中間產物確切是什麼，這部分問題有待在未來研究持續努力解決。綜合我們的實驗結果，結論是環境中的混合相含鐵含鈦奈米礦物的光催化反應能降解有機碳，特別是過去被認為極為穩定、循環週期長的黑炭，且各種因素的加和效應導致光催化的效率可能比以往認知更高。本研究為黑炭在環境的宿命更準確的評估開展一個嶄新的視角，自然環境天然奈米混合相礦物對黑炭降解和循環的定量亟需許多深入的探討。

Black carbon (BC) originates from incomplete combustion of biomass and fossil fuels, and is rich in polycyclic aromatic hydrocarbons. Overall, BC is relatively stable and not easy to degrade and may stay in natural environments for a long time. However, the big gap between the buried BC and estimation of total BC formed by burning and natural fires raises questions about a vast underestimation of BC degradation. The nanominerals in soil that can act as photocatalysts may play an underestimated role in BC degradation, which warrants further research. We propose that iron-containing oxides in low abundance in nature may boost the photocatalytic capacity of natural titanium oxides and their mixing phases may carry great potential for organic carbon degradation. We also aim to test the photocatalytic degradation of BC using mixed phases of iron and titanium-containing oxides. Our study results verified that the mixed-nanominerals with TiO2 as the dominant component could improve photocatalytic efficiency when compared to pure TiO2 nanomineral. Modified TiO2 exhibited improved photocatalytic degradation of methylene blue (MB) due to additional absorption. Photocatalysis could effectively degrade BC to some extent though the specific compounds were not identified. This study provides a new perspective for photocatalytic degradation of organic carbon in natural environment with a low dose of iron-containing oxides, indicating a more accurate estimation of the fate of BC is needed. More study is needed for the degradation of BC by mixed nanominerals in natural environments.

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