2016 年 37 巻 2 号 p. 87-92
The titania that was prepared as a packing material in our laboratory, which changed its color on heating, microwave irradiation, and heating under vacuum during nitrogen adsorption. We assumed that the compound adsorbed on titania was oxidized or oxidatively polymerized on heating, leading to the color change. The color faded on heating the sample at 270°C. The catalytic ability of titania is assumed to accelerate its coloration and decoloration. We demonstrated the catalytic ability of titania using glycerol as an adsorbate; silica gel was used as an adsorbent for comparison with titania. Titania accelerated the oxidation or oxidative polymerization of the adsorbate and the decomposition of the oxidized or polymeric compound obtained. Furthermore, the catalysis of titania led to the modification of its surface by adsorbate oxidation or oxidative polymerization; also, surface modification was demonstrated by using glycerol as the adsorbate. Two different modified titania were prepared as packing material by heating the mixture of titania and glycerol at 120°C and 200°C for up to 2 h after coloration. The retention behavior of purine, allopurinol, hypoxanthine, and oxypurinol on these two modified titania and non-modified one was investigated. Oxypurinol eluted faster than hypoxanthine on titania modified at 120°C although it was more strongly retained on non-modified titania than hypoxanthine. Thus, the retention site of oxypurinol is similar to that of glycerol on non-modified titania, that is, the surface modification by glycerol oxidation or oxidative polymerization blocked the site and accelerated its elution. The results could be used for explaining not only the modification of the surface but also the retention mechanism on titania.
