Nanoparticles of anatase

Ionic liquids have been used to prepare piu-e anatase by mixing [BMIM] [PF5] and tetra-M-butyl titanate [47] addition of water and stirring at 80 °C produced nanoparticles of anatase with a size close to 5 run. 

Figure C2.17.8. Powder x-ray diffraction (PXRD) from amoriDhous and nanocry stalline Ti02 nanocrystals. Powder x-ray diffraction is an important test for nanocrystal quality. In the top panel, nanoparticles of titania provide no crystalline reflections. These samples, while showing some evidence of crystallinity in TEM, have a major amoriDhous component. A similar reaction, perfonned with a crystallizing agent at high temperature, provides well defined reflections which allow the anatase phase to be clearly identified.

In this study, nanoparticles of titanium dioxide (TiCh) have been successfully synthesized by. reduction method. These nanoparticles were characterized by using X-ray diffraction (XRD) and TEM (transmission electron microscopy). XRD revealed the presence of pure TiCL NPs. XRD studies suggested that the titanium dioxide, TiCL exists in anatase form. The nanostructured character of the produced titania powders was characterised by Scherer method and TEM examinations. The TEM images indicate that the crystalline size of titanium dioxide precipitates varies from 1.81 nm to 13.15 nm This shows that nanoparticles obtained from reduction method are in more nanorange as compared to those obtained for precipitation method. 

Abstract A colloidal solution of titanium dioxide (TiO ) nanoparticles was prepared by the solvothermal method and dip-coated onto a polypropylene fabric with TMOS binder. The prepared TiO particles, colloidal solution and the coated fabrics were characterized by X-ray diffraction, SEM and TEM. The results showed that the TiO particles prepared by the solvothermal method were composed of anatase which uniformly coated the snbstrate. Photocatalysis induced bactericidal properties of coated fabrics were tested by measuring the viability of Escherichia coli. It was fonnd that solvothermally prepared TiO coatings have the ability to kill E. coli. This nniqne property of TiO makes it an ideal candidate in producing self-sterilizing protective masks and in providing bactericidal and self-cleaning properties to a variety of snrfaces. 

Fig. 5. a SEM image of hollow Ti02 spheres, b TEM image of hollow Ti02 spheres. The spheres were produced after calcining 640 nm diameter PS spheres coated with four layers of Ti02 nanoparticles (5 nm diameter). Each nanoparticle layer was separated by three polyelectrolyte layers. The hollow spheres are composed of anatase crystals. (Adapted from [41] by permission of the American Chemical Society)... 

Fig. 16.7 HRTEM micrographs and reconstructed shapes of anatase Ti02 nanoparticles (a, b) truncated cube (c, d) prism [Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission from Feldhoff et al, (2007)]...

Incorporation of titanium oxide species within the framework of mesoporous silicas has been shown to produce highly efficient photocatalytic materials. Extremely careful preparation conditions [84] leads to highly structured materials comprising anatase nanoparticles of dimension between 5 and 10 run. The channeled structure, together with the hydrophobic/hydrophilic character, are also key features controUing their enhanced photoreactivity. The photocatalytic activity of such mesoporous catalysts has been studied for the degradation of phenol in aqueous solutions [85]. It was observed that for structured mesoporous materials with low Ti content, the turnover frequency was four times greater than that for standard P25. 

Chemical vapor condensation (CVC) was applied by Lee for the production of Ti02 nanoparticles by decomposition of Ti(0)(acac)2. In the temperature range of 800-1000 °C hollow-shell nanoparticles (10-40 nm diameter, 4-5 nm thick) of anatase-rutile mixed phases were obtained. The formation of the hollow structure is a result of the competition... 

FIGURE 19. SEM image of anatase nanoparticles derived from Xi(acac)2(OPr-i)2 in CCb/EtOH at 150 kXorr and 250 Reproduced from Reference 292 by permission of Elsevier... 

First we consider the transformation mechanism of anatase to rutile in order to determine the reason for the dependence of the transformation rate on particle size. Penn and Banfield (1998 1999) showed that the oriented assembly of nanoparticles to form larger crystals (see below for details) is accompanied by formation of twins that introduce new atomic arrangements at particle-particle interfaces. In the case of anatase, a 112 twin represents a slab of brookite and thus, a structural state intermediate between anatase and rutile. Penn and Banfield (1999) proposed that the activation barrier for rutile nucleation is lowered by the presence of these twins. Simultaneously, it was noted that the transformation of anatase to rutile in air (Gribb and Banfield 1997) and under hydrothermal conditions (Penn and Banfield 1999) rarely generates partially reacted crystals, suggesting a high activation barrier for rutile nucleation but rapid rutile growth. 

New kinetic models were developed to incorporate interface nucleation (Zhang and Banfield 1999) and surface nucleation (Zhang and Banfield 2000), thus to quantitatively interpret the kinetic behavior in the nanocrystalline anatase-rutile system. Surface nucleation and bulk nucleation come into play as temperature increases (Zhang and Banfield 2000). Particle size has been explicitly incorporated into the kinetic equations. The transformation rate scales with the square of the number of anatase nanoparticles in the case of interface nucleation (Zhang and Banfield 1999), or with the number of anatase nanoparticles in the case of surface nucleation (Zhang and Banfield 2000). If the transformation is governed only by interface nucleation, the kinetic equation is ... 

Fig. 5.4. Transmission electron micrographs of anatase Ti02 nanoparticles prepared by solvothermal treatment of Ti(OR)4 after hydrolysis with tetramethylammonium hydroxide. The inset in the upper micrograph displays a Fourier transform with discrete...

The photoactivities of ultrafme Ti02 nanoparticles in anatase, rutile, or mixed phases were tested in the photocatalytic degradation of phenol [322]. For Ti02 nanoparticles, mainly in the anatase phase and mixed-phases, the photocatalytic activities increased significantly with the content of the amorphous part decreasing. The completely crystallized rutile nanoparticles exhibited size effects in this photocatalytic reaction and the photocatalytic activity of rutile-type Ti02 nanoparticles with a size of 7.2 nm was much higher than that with 18.5 nm or 40.8 nm and was comparable to that of anatase nanoparticles. 

Wu et al. [59] have used a combined procedure of microemulsion-mediated hydrothermal method (MMH) to prepare uniform-sized nanoparticles of Ti02 (both rutile and anatase). Tetrabutyl titanate was dissolved in HC1 or HNO3, and the solution was then allowed to disperse in an organic phase to prepare the microemulsion. The aqueous core of the system, water/cyclohexane/Triton XIOO/hexanol was used as the microreactor for the controlled growth of Ti02 particles under hydrothermal conditions. The influences... 

It is elaborated, that the generation of titanium oxide species of tailored and uniform size into Si-MCM-41 as host material does not only depend on the amount of titanium compounds added in one step, but also on the repeated addition and hydrolysis of the titanium compound in consecutive steps. Anatase nanoparticles of a well-defined size of up to 3 nm, Ti(IV) oxide oligomers and mononuclear Ti(IV) oxide species, respectively, were generated without a substantial etmichment of titanium oxide particles on the external surface of the Si-MCM-41 host. Depending on the size and content of the Ti(lV) oxide species, the fluorescence of co-impregnated dye molecules was statically quenched to varying extent. 

Phenol is one of the toxic materials in municipal and wastewater. Titanium dioxide nanoparticles of both anatase and rutile forms were synthesized by hydrothermal treatment of microemulsions and used in the wet oxidation of phenol [363]. The advantage of this method of preparation is that the size of particles can be affected by the ratio of surfactant to water. Size of water droplets in the reverse microemulsions is approximately the same as that of formed particles. The main reactions in phenol degradation are [363] ... 

---