Development of Mesoporous Silica Nanocatalyst for Dental Bleaching Application

接合鐵離子的中孔洞二氧化矽奈米分子篩已被證實是一種有效且不需光照催化的牙齒漂白催化劑，但其理想的反應作用環境與催化劑的穩定性目前仍是不甚清楚。因此本研究的目的是以Fe3+-histidine@Al-MSN做為牙齒漂白催化劑，利用試管及牙齒染色模型為測試模型，評估起始反應pH值與過氧化氫濃度對其漂白化學反應的催化影響效應以及穩定性，進而找出最適合的反應條件，以做為設計診間強力牙齒美白藥劑的參考。試管模型以0.15mM Orange II當作染色劑，在不同的起始反應pH值（pH 3、5、7、9、11）及過氧化氫濃度（0、1、2、4、6、8、10%）的反應條件下，於設定時間點測量溶液pH值與Orange II殘留量，以評估Fe3+-histidine@Al-MSN催化劑的催化效力。同時利用重複使用的方式，將使用過的催化劑回收與新的Orange II與過氧化氫作用，以測試催化劑的穩定性。牙齒染色模型使用0.15mM Orange II染色72小時，再以Fe3+-histidine@Al-MSN催化劑與4%或10%過氧化氫於起始反應pH 7的環境下進行漂白，利用影像分析技術藉由CIE色彩系統進行色彩分析。結果顯示在試管模型中，除了起始反應pH 3組別的pH值維持穩定外，起始反應pH 5、7、9組別在反應進行的前15分鐘內都有pH值下降，且之後穩定的現象。起始反應pH 3、5、7、9組別其最終穩定pH值皆在3~3.5之間，其Fe3+-histidine@Al-MSN催化劑的催化效力明顯優於起始反應pH 11組別；起始反應pH 11組別的pH值只有下降到pH 7左右，不利於類費頓反應進行，因此催化效果較差。當過氧化氫濃度由0%上升到4%，可觀察到催化劑的催化效力隨過氧化氫濃度增加而提升，顯示提升過氧化氫濃度有助於提升催化劑的催化效力；但大於4%過氧化氫組別則會因為高濃度過氧化氫的自由基消除反應，使得催化效力不會隨著過氧化氫濃度增加而提升。在催化劑重複使用後，隨著使用次數增加，催化劑的催化效力有逐漸下降的趨勢，而與4%過氧化氫反應的催化劑其效力下降較少，維持最好的效果。在SEM的觀察下，可發現反應過後的催化劑有分子互相凝結的現象；同時由ICP-MS的研究結果也證實鐵離子及鋁離子有滲漏的現象，這些可能是造成催化劑催化效力下降的原因。在牙齒模型中，Fe3+-histidine@Al-MSN催化劑與4%過氧化氫在起始反應pH 7的環境下進行漂白反應，有與10%過氧化氫組別沒有顯著差異的漂白效果。經由以上實驗，總結Fe3+-histidine@Al-MSN催化劑與4%過氧化氫於起始反應pH 7的條件下進行漂白反應，可做為製作診間強力牙齒美白藥劑的參考。Several mesoporous silica nanoparticles (MSN) with immobilized ferric or ferrous ions via histidine have been reported as efficient catalysts for light-free tooth bleaching. However, the optimal working environment and the catalyst stability are still unclear. The purpose of this study was to investigate the effects of initial environmental pH, concentration of H2O2, and the stability of catalysts on the tooth bleaching reaction using Fe3+-histidine@Al-MSN as the catalyst, and furthermore to find out the best reacting condition for in-office power bleaching. Orange II (0.15mM) was selected as the dye used to evaluate the bleaching activity of H2O2 in test tubes and stained tooth models. The efficacy of the catalyst, Fe3+-histidine@Al-MSN, on the bleaching reaction of H2O2 with different concentrations (0, 1, 2, 4, 6, 8 and 10%) at different initial pH environments (3, 5, 7, 9 and 11) was evaluated by measuring the final pH value of environment and residual Orange II concentration after reaction. Furthermore, the used catalyst was collected and then reacted with fresh Orange II and H2O2 to investigate the stability of the catalyst. In stained tooth model, the teeth were stained with Orange II (0.15mM) solution for 72 hours, and bleached with 4% or 10% H2O2, which were catalyzed by Fe3+-histidine@Al-MSN at initial pH 7. Image analysis technique with CIE color code analysis was used to analyze the color change of bleached teeth. In test tube model, there was no obvious change of environmental pH during the reaction in the group with initial pH 3. However, the other groups with higher initial pH demonstrated a significant dropdown of environmental pH within 15 minutes after reaction and became plateau latter. The groups reacted at initial pH 3, 5, 7 and 9, in which the final pH values were between 3 and 3.5 after reaction, exhibited more Orange II degradation than the group reacted at initial pH 11, in which the final pH value was 7 and unfavorable for Fenton-like reaction. The efficacy of Fe3+-histidine@Al-MSN catalyst on bleaching reaction increased when the concentration of H2O2 increased from 0% to 4%, but presented similar when the concentration of H2O2 was over 4%. These results indicate that raising H2O2 concentration, up to 4%, may enhance the catalytic effect of Fe3+-histidine@Al-MSN , but no benefit when the concentration of H2O2 was over than 4%, because of the scavenge effect. In addition, when the reused-cycle increased, the efficiency of used catalysts declined gradually, and 4% H2O2 had most benefit for the catalyst with less decline of its catalytic effect. Consistently, with ICP-MS analysis and SEM observes, we found Fe and Al leaching out from the catalyst and aggregation of the used catalyst, which would cause the decline of the efficiency. In stained tooth model, H2O2 solution with Fe3+-histidine@Al-MSN as a catalyst showed noticeable bleaching effect. The group reacted with 4% H2O2 had similar efficiency with 10% H2O2 at initial pH 7. Due to these results, it was concluded that Fe3+-histidine@Al-MSN reacted with 4% H2O2 at initial pH 7 is the best reacting condition for developing in-office power bleaching agent