Nanostructuring Titania: Control over Nanocrystal Structure, Size, Shape, and Organization

Abstract

Control over crystal structure, size, shape, and organization of TiO2 nanocrystals has been achieved by means of wet chemistry. Hydrolysis and polycondensation of titanium alkoxide [Ti(OR)4] has been performed in the presence of tetramethylammonium hydroxide (Me4NOH). This base both catalyzes the reaction and provides an organic cation that stabilizes the anatase polyanionic cores formed in this medium. These anatase clusters are organized so as to favour self‐assembly into intermediate nanocrystals, which, in turn, self‐assemble into superlattices. This self‐assembling process has been exploited for the processing of highly structured titania films. Furthermore, larger anatase TiO2 nanocrystals of different sizes and shapes have been obtained by adjusting the relative concentrations of titanium alkoxide and Me4NOH, the reaction temperature, and the pressure. HRTEM, XRD, and EXAFS have been used to characterize the various samples and to elucidate the growth of titania anatase. Our observations are in accordance with theoretically predicted condensation and growth pathways. The formation of mesoscopic structures through a self‐assembling process of the multiply charged polytitanate anions in the presence of Me4N+ is also discussed.

Titanium oxide nanoribbons

“…Some Ti-O-Ti bonds linking between TiO 6 octahedra are broken and the basic building units (octahedra) re-assemble to link together by sharing edges, so as to form dimers [13]. These dimers condense with a zig-zag structure by an oxolation pathway, according to the partial charge model [13], leading to a favored linear growth in the [0 0 1] direction of the anatase phase. Another growth direction is [1 0 1] with dense stacking through the oxolation process, resulting in the width of the nanoribbons.…”

“…The fringes parallel to the ribbon axis (or [0 0 1] plane) correspond to a interplannar distance of about 0.75 nm. This set of fringes can correspond to the structural features of cis-skewed chains and are characteristic of the anatase crystal phase in the [0 0 1] direction [13]. This fringe spacing is also comparable to the shell spacing of titania nanotubes [5] 1 0 1] fringes, the bending angle could be evaluated to be about 15°C.…”

“…4a), which is characteristic of a stepped [1 0 1] surface. A similar case of corrugated sides has been reported in the titania nanocrystals obtained by hydrolysis and polycondensation of titanium alkoxide in the presence of tetramethylammonium hydroxide [13], which was believed to be a consequence of cluster-cluster growth and condensation of skewed octahedra. Other HRTEM images also displayed that some of the titania nanoribbons consist of two side layers of amorphous phases, especially at the end zones of the ribbons.…”

Synthesis of Silver Nanodisks Using Polystyrene Mesospheres as Templates

“…2 Although the synthesis of spherical nanocrystals is well developed for many materials, systematic manipulation of the shapes of nanocrystals is a significant challenge. Recent work devoted to making nonspherical nanocrystals via anisotropic inorganic nanocrystal growth in liquid media (including electrochemical growth) has yielded Au rods, 5 BaCrO 4 rods, 6 TiO 2 rods, 7 Ag rods, 8 Pt cubes and pyramids, 9 and rod-, arrow-, teardrop-, and tetrapod-shaped CdSe nanocrystals. 10,11 Fabrication of these materials is useful not only for understanding fundamental phenomena such as quantum confinement but also for obtaining "building blocks" featuring optical and electronic properties that are desirable for advanced applications in photovoltaic solar cells, light-emitting diodes, and biological diagnostics.…”

Nanoplasmonics and its Applied Devices

“…Scientist gained significant control both the over size [7] and surfaces [8][9][10][11][12] for nanoparticles. They have demonstrated that anisotropy in nanostructure like triangular prisms [13][14][15][16][17][18], nanoscale rods [19][20][21][22][23][24][25][26], nanoshells [27][28][29][30][31], multipods [32][33][34], disks [35][36][37][38][39] and cubes [40][41][42] shows better performance over solid spheres. …”