Defect Design, Chemical Synthesis and Associated Properties of Multifunctional TiO2-Based Nanocrystals
Date
2017
Authors
Sun, Qingbo
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Canberra, ACT : The Australian National University
Abstract
Local defect structures are significant to determine material
properties since defects introduced into host materials would
affect the local/average crystal environments and thus lead to a
change of macroscopic physicochemical performances. The
intentional design of specific local defects not only depends on
the selected synthesis method and preparation process but also
relies on the selected dopant or co-dopant ions. A deep
understanding of the intrinsic relationships between local defect
structures, chemical synthesis and associated properties is
thought as one major framework of material genome plan. It also
pushes the design, development and application of novel
multifunctional materials.
Based on local defect structural design coupled with new
synthesis strategies, indium and niobium co-doped anatase
titanium oxide nanocrystals are synthesized. It is experimentally
demonstrated that the dual mechanisms of nucleation and diffusion
doping are responsible for the synergistic incorporation of
indium difficult-dopants and niobium easy-dopants, and
theoretically evidenced that the local defect structures created
by indium, niobium co-dopants, reduced titanium and oxygen
vacancies are composed of defect clusters and defect pairs. These
introduced local defect structures act as nucleation centres of
baddeleyite- and lead oxide-like metastable polymorphic phases
and induce an abnormal trans-regime structural transition of
co-doped anatase titanium oxide nanocrystals under high pressure.
Furthermore, these small co-doped nanocrystals can be used as raw
materials to manufacture titania-based ceramic capacitors
designed in terms of electron-pinned defect dipole mechanism. The
sintering temperature is thus lowered to 1200 °C, which conquers
the technological bottleneck using this material.
To develop the third generation of high-efficient visible light
catalysts, nitrogen and niobium co-doped anatase titania
nanocrystals are synthesized. Experimental and theoretical
investigations demonstrate that the formation of highly
concentrated defect-pairs is key to significantly enhance visible
light catalytic efficiency. In further combination of local
defect structural design and the exploration of new synthesis
strategies, anatase nanocrystals containing nitrogen and reduced
titanium ions are synthesized. The formation of local defect
clusters is demonstrated to play an important role on the obvious
enhancement of Rhodamine B degradation efficiency under only
visible light illumination. It is thus unveiled that a
fundamental understanding of the functions of local defect
structures and a well-controlled synthetic strategy are critical
to develop highly efficient visible light catalysts with
unprecedented photocatalytic performances.
Through these systematic investigations, it is concluded that
local defect structures generated by introduced co-dopants are
complicated in strong-correlated titania systems and differ from
case to case. A major difficulty to efficiently introduce
difficult-dopant ions such as nitrogen and indium at high
concentrations is solved. Two high-efficient visible light
catalysts are achieved for environmental remediation by using the
clean and renewable solar energy; and one raw material for
manufacturing new ceramic capacitors and new metastable
polymorphic phases is provided. The discussion on the doping
mechanisms, the defect formation and their associated impacts on
material performances will not only benefit the future
development of physical chemistry, material science and defect
chemistry, but also opens a new route to design novel
multifunctional materials based on local defect structure
design.
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Keywords
solvothermal, titanium dioxide, co-doping, photocatalysts, colossal permittivity materials
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