Titanium-Defected Undoped Anatase TiO_2 with p-Type Conductivity, Room-Temperature Ferromagnetism, and Remarkable Photocatalytic Performance

摘要

Defects are critically important for metal oxides in chemical and physical applications. Compared with the often studied oxygen vacancies, engineering metal vacancies in n-type undoped metal oxides is still a great challenge, and the effect of metal vacancies on the physiochemical properties is seldom reported. Here, using anatase TiO_2, the most important and widely studied semiconductor, we demonstrate that metal vacancies (V_(Ti)) can be introduced in undoped oxides easily, and the presence of V_(Ti) results in many novel physiochemical properties. Anatase Ti_(0.905)O_2 was synthesized using solvothermal treatment of tetrabutyl titanate in an ethanol-glycerol mixture and then thermal calcination. Experimental measurements and DFT calculations on cell lattice parameters show the unstoichiometry is caused by the presence of V_(Ti) rather than oxygen interstitials. The presence of V_(Ti) changes the charge density and valence band edge of TiO_2, and an unreported strong EPR signal at g = 1.998 presents under room temperature. Contrary to normal n-type and nonferromagnetic TiO_2, Ti-defected TiO_2 shows inherent p-type conductivity with high charge mobility, and room-temperature ferromagnetism stronger than Co-doped TiO_2 nanocrystalline. Moreover, Ti-defected TiO_2 shows much better photocatalytic performance than normal TiO_2 in H_2 generation (4.4-fold) and organics degradation (7.0-fold for phenol), owing to the more efficient charge separation and transfer in bulk and at semiconductor/electrolyte interface. Metal-defected undoped oxides represent a unique material; this work demonstrates the possibility to fabricate such material in easy and reliable way and thus provides new opportunities for multifunctional materials in chemical and physical devices.