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the oxygen mono-coordinated titanium, pK1 for >Ti-OH2+ ¡ú >Ti-OH + H+ is 2.60, pK2 for >Ti-OH ¡ú > Ti-O- + H+ is 9.00 while for oxygen di-coordinated titanium, the pK2 value for. >Ti2=OH¡ú >Ti2=O- + H+ is 5.50. It can be seen when the acidity of the medium is less than pH 4, the bridging group >Ti2OH was fully in the molecular form. The surface charge of the column mainly stemmed from the species of >TiOH2+. In this case, an EOF might be reversal. At pH over the range from 4 to 7, the terminal group on the coated material is >TiOH. The surface charge might originate from the dissociation of the bridging group >Ti2OH but at pH 4¨C5.5, only a little current was found. Much less surface charge is probably the reason, since its pK value is 5.50. At pH above 6, anodic EOF was switched into cathodic EOF due to the presence of highly dissociated >Ti2OH. A buffer region was observed at pH around 9. This corresponds to the pK2 value of the terminal >TiOH group. Ï£Íû¸÷λ³æÓѰïÎÒ¿´¿´£¬°Ñ´óÖµÄÒâ˼дÏÂÀ´¾Í¿ÉÒÔÁË£¬²»Ê¤¸Ð¼¤£¡ |
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ÊÔ×Å··£º Ñõµ¥ÅäλµÄîÑ£¬ >Ti-OH2+ ¡ú >Ti-OH + H+ pK1 Ϊ2.60, >Ti-OH ¡ú > Ti-O- + H+ pK2 Ϊ9.00 ¶øÑõË«ÅäλµÄîÑ£¬ >Ti2=OH¡ú >Ti2=O- + H+ pK2 Ϊ5.50. ¿É¼û£¬µ±½éÖʵÄËáÖµpHСÓÚ4ʱ£¬ÇÅ»ù>Ti2OH ÍêȫΪ·Ö×ÓÐÎʽ£¨¼´²»»á½âÀë²úÉúÀë×Ó£©¡£Öù±íÃæµÄµçºÉÖ÷ÒªÀ´×ÔÓÚ>TiOH2+¡£ÔÚÕâÖÖÇé¿öÏ£¬EOF(µçÉøÁ÷£¿)¿ÉÄÜÏà·´¡£ÔÚpHΪ4¡«7Ö®¼äʱ£¬²ÄÁϱíÃæÍ¿²ãµÄÄ©¶Ë»ùÍÅΪ>TiOH£¬±íÃæµçºÉ¿ÉÄÜÔ´ÓÚ >Ti2OH ÕâÖÖÇÅ»ùµÄ½âÀ룻¶øµ±pHÔÚ4-5.5ʱ£¬Ö»·¢ÏÖÓÐÉÙÁ¿µÄµçÁ÷£¬ÆäÔÒò¿ÉÄÜÔÚÓÚ±íÃæµçºÉºÜÉÙ£¬ÒòΪpKΪ5.50¡£µ±pH>6ʱ£¬Ñô¼«EOF×ªÒÆÖÁÒõ¼«EOF£¬ÒòΪ>Ti2OH·¢Éú¸ß¶È½âÀë¡£ÔÚpH=9¸½½üΪһ¸ö»º³åÇøÓò£¬ÕâÓë¶Ë»ù>TiOH µÄpK2ÖµÏàÒ»Ö¡£ |

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It can be seen when the acidity of the medium is less than pH 4, the bridging group >Ti2OH was fully in the molecular form. ¿ÉÒÔ¿´³ö£¬µ±ÌåϵµÄËá¶ÈÖµµÍÓÚPH=4£¬ÄÇôÇÅÁ¬»ùÍÅ¡·Ti2OHÖ÷ÒªÊÇÒÔ·Ö×ÓµÄÐÎʽ´æÔÚ¡£ ºÃÄÑ Ã»ÓÐÉÏÏÂÎÄ ²»ºÃ·Òë |

2Â¥2007-10-12 18:00:26
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