Preparation of Photocatalyst in Iron Oxide-Titania Solid Solution and Silica System through Two-Liquid Phase Separation

本研究在Fe_2O_3-TiO_2-SiO_2体系中，通过熔炼和淬火，制备了由连续氧化铁-二氧化钛固溶体（Fe_<2-x>Ti_xO_3）相组成的复合材料，以制备可见光活性光催化剂。采用固相反应法制备了FeO-Fe_2O_3-TiO_2三元体系的烧结体，并对其晶相、电导率和光电化学性能进行了测试，以寻找氧化铁-二氧化钛固溶体作为光催化剂的最佳组成。随着烧结温度的降低和Ti组分含量的增加，晶相由尖晶石型固溶体转变为α-型，并进一步转变为伪板岩型。同时含有尖晶石型和α相型固溶体的样品具有较高的光电流密度。它们的密度一度随α-相型比例的增加而增加，但在α-相型比例超过60%时，密度急剧下降。试样烧结能力的降低导致了晶界和孔洞的增大。因此，光激发的电子和空穴很容易重新组合。在此基础上，通过对Fe_2O_3-TiO_2-SiO_2三元体系熔体进行淬火，制备了氧化铁-二氧化钛固溶体光催化剂。所制得的玻璃陶瓷具有富SiO_2和富Fe_2O_3-TiO_2相的相分离织构，并考察了所制得的玻璃陶瓷的晶相与电导率的关系。在SiO_2恒定值下，随着Fe组分添加量的增加，晶相由α-相型转变为α-相+伪板岩型，再转变为α-相+尖晶石型固溶体，电导率也依次提高。这些结果与上述FeO-Fe_2O_3-TiO_2三元体系中燃烧体的结果一致。然而，由于所得玻璃陶瓷的成分不均匀，很难控制其晶相，也很难选择性地浸出其中唯一的富SiO_2相。下一步的研究计划是更全面地研究均匀样品中晶相与光电流密度的关系，并通过选择最佳的制备工艺条件来实现可见光活性光催化剂。少

In this study, the composite materials comprising continuous iron oxide-titania solid solution (Fe_<2-x>Ti_xO_3) phase were prepared by melting and quenching of the fired body in Fe_2O_3-TiO_2-SiO_2 system in order to fabricate a visible-light active photocatalyst.The fired bodies in the FeO-Fe_2O_3-TiO_2 ternary system were synthesized by use of the solid reaction process, and their crystalline phases, electric conductivities and photo-electrochemical properties were examined in order to search the optimum composition of iron oxide-titania solid solution as photocatalyst. The crystalline phase changed from spinel-type solid solution to α-phase type, and further to pseudo-brookite type with the decrease of the firing temperature and the increase of the amount of Ti component. The sample which contained both spinel-type and α-phase type solid solution showed high photocurrent density. Their density once increased with the ratio of α-phase type, and steeply decreased over about 60 % of t … More he ratio. The decrement of the sinter ability of the sample caused the increase of the grain boundaries and voids. As a result, the photo-excited electrons and holes easily were apt to recombine.On the base of above results, the preparation of the photocatalyst comprising iron oxide-titania solid solution was tried by quenching the melt in Fe_2O_3-TiO_2-SiO_2 ternary system. The obtained glass ceramics had the phase separation texture comprising SiO_2 rich and Fe_2O_3-TiO_2 rich phases The relation between crystalline phase and electric conductivity of the obtained glass ceramics was examined. The crystalline phase changed from α-phase type to α-phase + pseudo-brookite types, further to α-phase + spinel type solid solution with the increase of the amount of Fe component at the constant value of SiO_2, and the electric conductivity increased in the same order. These results were good agreement with those of the fired body in above FeO-Fe_2O_3-TiO_2 ternary system. However, it was hard to control the crystalline phase in the obtained glass ceramics because of their inhomogeneity of the compositions, and to leach the only SiO_2 rich phase from them, selectively.The next plan of the study is to investigate the relationship between crystalline phase and photo-current density in the homogeneous sample, more fully, and to achieve the visible light active photocatalyst by selecting the optimum conditions of the preparation process. Less