Oriented TiO₂ Nanostructured Pillar Arrays: Synthesis and Characterization

Abstract

TiO 2 with tailored porosity, particle size, and shape in the nanometer range is attracting a lot of attention because of its potential use in photocatalysis and energy conversion. As far as photocatalysis applications are concerned, the use of high surface area TiO 2 as a photocatalyst for pollutant degradation and for water splitting is of particular interest. [1][2][3][4][5][6][7] The presence of bulk defects and grain boundary barriers-associated with the small dimensions of the particles, recombination of electrons, and holes generated by band-gap excitation-is limiting the photoconversion efficiency. [8][9][10] To improve charge separation and the associated catalytic efficiency, researchers have essentially followed two strategies. The first centers on tailoring of the size, shape, and threedimensional organization of TiO 2 particles [1,2,11,12] or of Ti-O-Ti wires with semiconductor character. [5,[13][14][15][16] The second strategy focuses on improving the photocatalytic properties: i) by incorporating metal cations and anions (mainly nitrogen, sulphur, iodine, and other elements) into the bulk; [6,14,[17][18][19][20][21][22][23] ii) by supporting metal particles (mainly Au, Ag, Pt, Ni). [1,3,[24][25][26][27][28][29][30][31] Interesting results are obtained when the two abovementioned research directions are combined to benefit from the sum of their advantages. [32] Several strategies have been adopted for the development of energy conversion applications in solar cells. [1,3,[33][34][35][36] Among them, the use of dye-sensitized TiO 2 nanostructures has an outstanding reputation and both experimental and theoretical evaluations of the efficiency-limiting factors have been identified. [33,37,38] Recently, it has been shown that the use of ordered arrays of TiO 2 nanostructures (either pure, such as nanotubes, nanowires, and nanorods [39][40][41] or TiO 2 -based architectures, [15,42,43] which replace the traditional nanoparticle film) can improve the efficiency. [9,34,40,[43][44][45][46][47][48][49] Moreover, it is evident from recent literature data [1,3,9,44,50] that the innovative synthesis of TiO 2 particle arrays, either pure or anchored to conducting substrates, plays a leading role in both photocatalysis and energy conversion applications.In this paper, we describe a new method for the synthesis of parallelly aligned TiO 2 micropillars, either pure or fixed to a rigid carbon support. Accurate characterization shows that, depending upon the synthesis conditions, the micropillars constitute of partially cemented pure anatase or a mixture of coexisting anatase and rutile particles with a diameter in the 10-20 nm range. The obtained materials combine high surface areas ($60 m 2

Radially organized pillars in TiO2 and in TiO2/C microspheres: Synthesis, characterization and photocatalytic tests

“…Several approaches to control the size, shape and agglomeration state of TiO 2 nanoparticles have been attempted [4]. Nanotubes [30], nanorods [31,32], monolithic porous structures [15,33,34], inverse opals [35] and microspheres [19,[36][37][38][39][40][41] have been studied.…”

Nanocrystalline TiO2 micropillar arrays grafted on conductive glass supports: microscopic and spectroscopic studies

“…The deposition area has been estimated to be larger than FTO-coated supports. The TIP and FA quantities were selected on the basis of a previous work, in which high-surface-area TiO 2 micropillars were obtained as a bulk material [35]. The polymerization, which is highly exothermic, was controlled by keeping the temperature of the materials at 373 K for 180 min and then by rising up to 473 K (heating rate 2 K/min), as obtained by preliminary differential scanning calorimetry (DSC) analysis (Data not shown for the sake of brevity).…”

“…In the past, the method has been effectively used, to obtain highsurface-area mesoporous carbons [39], as well as nanostructured oxides (SnO 2 [33], TiO 2 [35] and ZnO [40]) by starting from an oxide precursor acting as a Lewis acid catalyst to promote the polymerization of furfuryl alcohol. In Fig.…”

Zinc Oxide Nanostructures: From Chestnut Husk-Like Structures to Hollow Nanocages, Synthesis and Structure

“…The common synthetic to be quite different when compared to the one of ZnO, coming from the combustion of metal Zn. This means that only the Zn-O couples that are present on extended and prismatic and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) faces are able to dissociate hydrogen, where a cooperative mechanism between surface zinc and oxygen species could be hypothesized to cause the hydrogen molecule polarization and then its consequent breaking. It must be underlined that the ability of prismatic faces to become covered by reversibly adsorbed H 2 at room temperature, makes ZnO unique among the oxidic systems, (like MgO, Al 2 O 3 , SiO 2 , etc.)…”