The Study of Microwave-Induced Degradation of Chlorobenzene Agueous Soulution

[[abstract]]介質在微波（MW）照射，微波能量輻射將選擇與介電常數較高之物質偶合，極性分子將產生激烈轉動及移動，而摩擦生熱致使溶液溫度快速增加，此時的極性分子激烈運動致使分子處於較高激態，增加反應體間碰撞數目，降低活化能加速污染物質的分解速率。本研究以奈米零價鐵、堇青石塗覆零價鐵、TiO2、堇青石塗覆TiO2、新鉑/鈀/銠觸媒觸媒、廢棄鉑/鈀/銠觸媒、鉑/鈀/銠觸媒塗覆TiO2及廢棄鉑/鈀/銠觸媒塗覆TiO2等為微波介質。探討於氯苯水溶液中添加這些類型介質經由微波照射與未經微波照射條件下對降解速率之影響，以及比較這些類型介質在微波照射下對降解速率之差異。結果顯示，於相同微波輻射條件下(MW 250 W，總輻射時間300秒)，濃度100 mg/L氯苯（CB）溶液中添加1.0 g 零價鐵（Feo）去除率較沒有加入零價鐵（Feo）可提高2.8倍(82.6% vs 28.6%)，活化能降低5.7 kJ/mole。另一方面，比較堇青石、Fe0/堇青石及Fe0對氯苯（CB）降解率之影響(反應溫度為25 oC，時間240分鐘)，結果顯示，奈米零價鐵，顆粒容易懸浮溶液中，有較多數量零價鐵（Feo）可與氯苯（CB）接觸因而提高去除率，而Fe0/堇青石其塗覆量僅為0.1克，且形狀為圓柱型固體於氯苯溶液中能與氯苯（CB）接觸零價鐵（Feo）數量有限，因此零價鐵（Feo）去除率為26.2%優於Fe0/堇青石12.9%。 TiO2受到微波幅射激發，產生之電子-電洞除了會和表面吸附分子進行氧化還原外，抑制電子-電洞的再結合(electron and hole recombination)作用發生，延長光催化的時間，提升TiO2光降解效果。此外TiO2 Anatase晶相型態之價電帶與導電帶間的能隙較大，電子傳輸速率較快，電子-電洞之間壽命較長再結合率較低。相同微波輻射條件(微波輸出能量30W，總微波輻射時間300秒)，比較P-25 TiO2、製備TiO2、TiO2/堇青石及堇青石對CB降解速率。CB去除率排序分為P-25 TiO2 (70.1 %)>製備TiO2 (55.6%)> TiO2/堇青石 (49.1%)>堇青石 (14.8%)。由於P-25 TiO2無論在Anatase及Rutile其晶相含量皆高，混合在以Anatase為主體晶相結構中的Rutile，可視為Anatase晶相的表面缺陷，產生的電子可溢流至Anatase晶相，形成電子-電洞分離，延緩電子-電洞再結合的速率，提升光觸媒的活性。 當微波照射穿透溶液中到達TiO2表面，TiO2吸收微波具高能量有益促進於在催化劑表面形成更多缺陷活性位置，抑制半導體表面電子-電洞再結合，且吸收微波能量轉變成熱能於整個溶液中較均勻，還可提供更多與污染物接觸面積，加速降解反應進行，因而提高氯苯去除效率。於相同微波輻射條件(30W，總微波時間300秒)，新三元觸媒較廢棄三元觸媒有較好的氯苯去除率(64.4% vs. 58%)，而新三元塗覆TiO2觸媒也較廢棄三元塗覆TiO2觸媒具有較佳的去除效率(73.3% vs. 70.3%)。 藉由吸收微波介質觸媒結合低能階微波技術，適合做為處理含鹵素有機染物高效益處理技術，此外廢觸媒循環使用除可降低微波處理之成本，也是一種創新技術嘗試，增加廢棄物再利用之附加價值。[[abstract]]Abstract When media of various dielectric constants are placed in a microwave field, the microwave radiation will preferentially couple with the media that have higher dielectric constants. Additionally, under microwave irradiation, polar molecules in a solution will be transformed and shifted vigorously to generate frictional heat that causes the solution temperature to increase rapidly. The microwave irradiation also causes higher activated status for the molecules, and promotes collision among the pollutant molecules to reduce their activation energy so that they are decomposed at higher rates. In this research, 7 different dielectric media, i.e. nano-scale zero-valent iron particles (Feo), cordierite covered with zero-valent iron (cordierite/Feo), TiO2, cordierite covered with TiO2 (cordierite/TiO2), fresh platinum/palladium/rhodium (fresh Pt-Pd-Rh) catalyst, recovered Pt-Pd-Rh catalyst (recovered Pt-Pd-Rh), fresh Pt-Pd-Rh catalyst covered with TiO2 (TiO2/Pt-Pd-Rh), and recovered Pt-Pd-Rh catalyst covered with TiO2 (TiO2/Pt-Pd-Rh), were tested as microwave absorbing media for decomposing chlorobenzene (CB) in solution. Laboratory results show that under similar irradiation conditions (250 W microwave energy applied for 300 sec.), nano-scale zero-valent iron particles reduce the CB solution activation energy by 5.7 kJ/mole, and remove 2.8 (82.6% vs 28.6%) times more CB from 100 mg/L CB solution than without application of zero-valent iron particles. On the other hand, when the solution temperature is maintained at 25 oC for 240 minutes with microwave irradiation, nano-scale zero-valent iron particles have the highest CB removal efficiency. When suspended in solution, the extremely small particles have larger contact surface with the soluble pollutants in the solution to raise the CB removal efficiency. In contrast, the cordierite particles covered with 0.1 g of zero-valent iron have cylindrical shape with limited contact surface, their CB removal efficiency is 26.2%, which is superior to the 12.9% for the zero-valent iron particles covered with cordierite. When exited by microwave radiation, TiO2 will produce electron-electron hole pair, which will assist in oxidizing/reducing the molecules adsorbed, suppress electron and hole recombination, and prolong the time of photo-catalysis to raise the TiO2 photo-decomposition efficiency. In addition, the Anatase crystal structure has relatively large gap between the valence band and the conductivity band so that electrons have higher transmission rate to lower the electron-electron hole recombination rate, and prolong the life of electron-electron hole pair. Under similar experimental conditions (30 w microwave irradiation for 300 sec.), the CB removal efficiencies are 70.1% for P-25 TiO2, 55.6% for prepared TiO2, 49.1% for TiO2/cordierite, and 14.8% for cordierite. P-25 TiO2 particles have high strength in Anatase and Rutile crystal phases, the Rutile mixed in the Anatase structure can be considered as the surface defect of Anatase crystal structure. The electrons produced can overflow to the Anatase crystal to separate electrons from electron holes thus prolonging the recombination rate of electron-electron hole pairs that raises activities of the photo-catalyst. When the microwave radiation penetrates the solution to reach the surface of TiO2 particles, the microwave energy absorbed by the TiO2 enhances the formation of more defective sites on the catalyst surface. Hence, the recombination of electron-electron hole pairs on the semi-conductor surface is inhibited. The absorbed microwave energy is converted into heat energy that is evenly distributed in the whole solution in addition to providing more contact between the pollutant and the solution so that the CB decomposition and removal efficiencies are enhanced. Under similar experimental conditions (30W microwave irradiation applied for 300 sec.), fresh Pt-Pd-Rh catalyst has better CB removal efficiency than the recovered Pt-Pd-Rh catalyst (64.4% vs. 58%). Further, fresh Pt-Pd-Rh particles covered with TiO2 also show better CB removal efficiency than the Pt-Pd-Rh particles covered with TiO2 (73.3% vs. 70.3%). In this experiment, the efficiency of microwave-enhanced technology for removing halogen-containing organic matter is further improved by using the various combinations of various dielectric media. Additionally, using the recovered catalyst in the combined dielectric media as experimented in this study is a new approach to reducing the treatment cost of microwave-enhanced technology in addition to increasing the add-on value of catalyst-containing wastes