利用二氧化錳改質之氮摻雜還原氧化石墨烯增強電容去離子處理效率研究

Abstract

電容去離子是利用雙電層原理(electrical double-layer)的電化學水處理方法，去離子的效率主要取決於電極材料，因此，電極材料若具有高比表面積、高電化學效應，則可以有效提升去離子的能力。 本研究利用微波法氮摻雜還原氧化石墨烯，二氧化錳氮摻雜還原氧化石墨烯作為電容去離子的電極材料。運用氮摻雜去改善零能隙的石墨烯高漏電流問題與增加導電度電，提升電容去離子的吸附(electrosorption)效能。並探討材料之合成條件最佳化及材料電化學測試，並探討二氧化錳氮摻雜還原氧化石墨烯複合材料之電離子去離子效益。 本研究結果顯示，還原氧化石墨烯在合成條件以170 °C且反應時間為30分鐘條件下，其比表面積可達404.4 m2/g且電容值達98.8 F/g，並合成氮摻雜還原氧化石墨烯，其氮摻雜含量為6.5 %，其比電容值可提升至159.3 F/g，而二氧化錳之複合材比電容值為213.4 F/g。最後利用二氧化錳氮摻雜還原氧化石墨烯做電吸附之測試；當欲處理之水樣為200 mL且濃度為50 mg/L時，在不同電壓下，其鈉離子及銅離子分別在1.6 V及1.4 V下會得到高效率之累積去除率(98.9 %及99.0 %)，及比較在不同鈉離子及銅離子之濃度(100 mg/L、500 mg/L、1000 mg/L)下，其累積去除率會隨著溶液濃度上升而降低；最後利用在不同濃度之NaCl溶液下，進行去除銅離子之電吸附效率之比較，其濃度為100 mg/L下，其銅離子去除率為99.7 %。 這些結果表明，利用urea合成氮摻雜還原氧化石墨烯和二氧化錳氮摻還原氧化石墨稀複合材，可有效提升電化學效應及比電容值，進而提升電吸附之效率。

Capacitive deionization (CDI) is a water desalination technique offering an appro-priate route to purify water. CDI is based on the high-surface-area electrodes, when electrically charged, can adsorb ionic components from water, thereby resulting in de-salination. In this study, a capacitive deionization electrode material was fabricated by using nitrogen-doped reduced graphene oxide (N-rGO) and manganese oxide (MnO2) via microwave synthesis method. To increase the conductivity of the materials, the elec-trosorption theory was used in this study. As-synthesized rGO at 170 °C for 30 min offered the surface area of 404.4 m2/g with the capacitance value of 98.8 F/g. After the used mixture of urea as a nitrogen doping agent, the electrical capacitance value increased to 159.3 F/g. In addition with MnO2 during the nanocomposites preparation, the electrical capacitance value signifcantly increased to 213.4 F/g. Under the deionization condition of 50 mg/L of dilute NaCl and CuSO4 solution at 1.4 V and 1.6V respectively, and the efficiency of the de-ionization behaviors are 98.9 % and 99.0 % respectively. In comparison with different sodium ion and copper ion concentration (100, 500, and 1000 mg/L), the removal effiency will decrease as the concentration of ion increase. In the mixture of 100 mg/L NaCl solution and 500 mg/L of copper ion, the efficiency of deionization can be up to 99.7 %.