4.6 Summary and Outlook
In this chapter, the synthesis of TiO 2–x photocatalysts was carefully discussed and
scientifically classified into two main categories, where the reactions take place
under reducing or oxidizing atmosphere. These methods include reducing gas heat
treatment, in situ reduction, metal reduction, vacuum activation treatment, hydrogen
plasma reduction, electrochemical reduction, UV light irradiation treatment, and
oxidation methods starting from Ti, Ti(II), or Ti(III) precursors. The obtained
TiO 2–x photocatalysts, resulting from hydrogen incorporation or oxygen removal,
are proved to achieve efficient photocatalytic performance such as photodegradation
of organic compound, hydrogen generation from water splitting, photocatalytic CO 2
reduction, dye-sensitized solar cells, lithium-ion batteries, etc. The development of
TiO 2–x materials has provided a promising way to solve the increasing environment
and energy problems in the twenty-first century. In order to further improve the
activities of TiO 2–x and better prepare this catalyst in industrial applications, some
approaches are introduced for the modification of TiO 2–x materials, such as doping
with nonmetal elements (N, S, I, B, and F), grafting with metals (Pt, Au, Pd, Ag, and
Cu), compositing with other materials (graphene, CNTs, g-C 3 N 4 , and MoS 2 ),
designing of ordered morphology (hollow porous, mesoporous, core shell, yolk
shell, nanocage, and inverse opal structures), and special facet exposure ({101},
{001}, and {110} facets).
However, there are still new challenges we are facing on the investigation of
TiO 2–x material and its industrial applications. Although we have already studied the
incorporation of hydrogen or the removal of oxygen at atomic levels with the help of
highly advanced instruments, the process of the reaction is now still difficult to
record and visualize. The low solar utilization and the high cost of solar energy
systems also greatly limit the applications of this material. Cleaner, higher efficient,
and more affordable systems are still greatly required in the future.
References
1. Fujishima A, Honda K (1972) Electrochemical photolysis of water at a semiconductor
electrode. Nature 238(5358):37–38
2. Komaguchi K, Nakano H, Araki A, Harima Y (2006) Photoinduced electron transfer from
anatase to rutile in partially reduced TiO 2 (P-25) nanoparticles: an ESR study. Chem Phys Lett
428(4–6):338–342
3. Diebold U, Anderson JF, Ng KO, Vanderbilt D (1996) Evidence for the tunneling site on
transition-metal oxides: TiO 2 (110). Phys Rev Lett 77(7):1322–1325
4. Cronemeyer DC (1959) Infrared absorption of reduced rutile TiO 2 single crystals. Phys Rev
113(5):1222–1226
5. Epling WS, Peden CHF, Henderson MA, Diebold U (1998) Evidence for oxygen adatoms on
TiO 2 (110) resulting from O 2 dissociation at vacancy sites. Surf Sci 412-413(0):333–343
6. Di Valentin C, Pacchioni G, Selloni A (2009) Reduced and n-type doped TiO 2 : nature of Ti
3+
species. J Phys Chem C 113(48):20543–20552
96
4 Preparation of Reduced TiO 2–x for Photocatalysis
In this chapter, the synthesis of TiO 2–x photocatalysts was carefully discussed and
scientifically classified into two main categories, where the reactions take place
under reducing or oxidizing atmosphere. These methods include reducing gas heat
treatment, in situ reduction, metal reduction, vacuum activation treatment, hydrogen
plasma reduction, electrochemical reduction, UV light irradiation treatment, and
oxidation methods starting from Ti, Ti(II), or Ti(III) precursors. The obtained
TiO 2–x photocatalysts, resulting from hydrogen incorporation or oxygen removal,
are proved to achieve efficient photocatalytic performance such as photodegradation
of organic compound, hydrogen generation from water splitting, photocatalytic CO 2
reduction, dye-sensitized solar cells, lithium-ion batteries, etc. The development of
TiO 2–x materials has provided a promising way to solve the increasing environment
and energy problems in the twenty-first century. In order to further improve the
activities of TiO 2–x and better prepare this catalyst in industrial applications, some
approaches are introduced for the modification of TiO 2–x materials, such as doping
with nonmetal elements (N, S, I, B, and F), grafting with metals (Pt, Au, Pd, Ag, and
Cu), compositing with other materials (graphene, CNTs, g-C 3 N 4 , and MoS 2 ),
designing of ordered morphology (hollow porous, mesoporous, core shell, yolk
shell, nanocage, and inverse opal structures), and special facet exposure ({101},
{001}, and {110} facets).
However, there are still new challenges we are facing on the investigation of
TiO 2–x material and its industrial applications. Although we have already studied the
incorporation of hydrogen or the removal of oxygen at atomic levels with the help of
highly advanced instruments, the process of the reaction is now still difficult to
record and visualize. The low solar utilization and the high cost of solar energy
systems also greatly limit the applications of this material. Cleaner, higher efficient,
and more affordable systems are still greatly required in the future.
References
1. Fujishima A, Honda K (1972) Electrochemical photolysis of water at a semiconductor
electrode. Nature 238(5358):37–38
2. Komaguchi K, Nakano H, Araki A, Harima Y (2006) Photoinduced electron transfer from
anatase to rutile in partially reduced TiO 2 (P-25) nanoparticles: an ESR study. Chem Phys Lett
428(4–6):338–342
3. Diebold U, Anderson JF, Ng KO, Vanderbilt D (1996) Evidence for the tunneling site on
transition-metal oxides: TiO 2 (110). Phys Rev Lett 77(7):1322–1325
4. Cronemeyer DC (1959) Infrared absorption of reduced rutile TiO 2 single crystals. Phys Rev
113(5):1222–1226
5. Epling WS, Peden CHF, Henderson MA, Diebold U (1998) Evidence for oxygen adatoms on
TiO 2 (110) resulting from O 2 dissociation at vacancy sites. Surf Sci 412-413(0):333–343
6. Di Valentin C, Pacchioni G, Selloni A (2009) Reduced and n-type doped TiO 2 : nature of Ti
3+
species. J Phys Chem C 113(48):20543–20552
96
4 Preparation of Reduced TiO 2–x for Photocatalysis