Titania surface cleaning

Lam, S.W., Soetanto, A. and Amal, R. (2009) Self-cleaning performance of polycarbonate surfaces coated with titania nanoparticles. Journal of Nanoparticle Research, 11, 1971-1979. 

Given their modest acidity and low temperature, LPD methods are ideally suited to polymer substrates. We applied Method 1 (pH =3.8 room temperature) to unactivated PMR-15. RBS analysis showed that the deposited titania was 90 nm thick after 24 h and a 450 nm film was deposited in 48 h. Variability in the onset time for film formation may account for the seemingly slower initial growth. Method 1 titania growth on clean silicon wafers for these same time intervals gave 250 and 450 nm respectively. All samples were amorphous, as had been reported for this method on variously treated silicon wafers.12 An adherent, amorphous, titania film (420 nm thick in 48 h) also formed on a PMR-15 surface that had been sulfonated by exposure to SO3 gas. 

LPD films of Ti02 on BMI and on Kapton were stable to sonication in water and could not be removed by a standard tape test. Figure 2 shows cross-sectional SEM of samples of BMI and Kapton with surface oxide films ranging in thicknesses from 200-700 nm. The thickness of the titania layer is independent of the activation of the surface or the kind of polymer. The thicker films (Figure 2b and 2d) are comparable ( 20%) to those reported on sulfonate-monolayers (400 nm).12 Thinner films (Figure 2a and 2c) were somewhat thicker than those reported on a clean silicon wafer (200-300 nm vs. 80 nm), likely due to variability in the time needed for the onset of film deposition. 

The Pt NMR of small platinum particles on classic oxide supports show s that the clean-surface LDOS is largely independent of the support (sihca, alumina, and titania) and of the method of preparation (impregnation, ion exchange, and deposition of colloids). At a given resonance position, one always finds the same relaxation rate, independent of particle size or support. The shape of the spectrum is related to the sample dispersion. The same is true lor particles protected in fihiis of PVP. [However, samples prepared under conditions giving strong SMSIs behave differently 171)]... 

Compact, continuous, and uniform anatase nanotubules with diameters in the range 50-70 nm were produced inside PAO nano-templates by pressure impregnating the PAO pores with titanium isopropoxide and then oxidatively decomposing the reagent at 500 °C [230], Cleaning the surface of the template and repeating the process several times produced titania nanotubules with a wall thickness of 3 nm per impregnation. The tube exteriors appeared to be faithful replicas of the pores in which they were formed. 

For high coverages of titania and large exposures of H at 300 K, the total coverage of hydrogen, including the activated state, is within 20% of the coverage on the clean Ni surface. 

Figure 9. Comparison of the turnover frequency (TOF) for methane synthesis over a clean Ni and a titania-containing Ni surface based on model calculations at a total pressure of 120 Torr and an H /CO ratio of 4.

Figure 10. Surface coverages for clean Ni and titania-containing Ni as a function of temperature corresponding to the curves of Figure 9.

Methanation rates for Pt with 400 Torr H2 and 100 Torr CO are shown in Figure 1. The rates for the niobia and titania-covered surfaces were measured with an oxide coverage which completely suppressed H2 and CO adsorption. As discussed earlier, our experimental apparatus allowed us to examine the surface by AES both before and after reaction. On the clean surface, we found that no impurities, including carbon, were present following reaction. Also, below 750K, the titania and niobia layers were unaffected by reaction conditions. 

Temperature resistant oxide supports for catalytic active phases are necessary for the catalytic combustion of hydrocarbon pollutants in the field of environment as well for energy production through hydrocarbon clean combustion. Four commonly used pure support oxides in catalysis silica, alumina, titania, and zirconia were synthesised by the sol-gel and aerogel methods and, in parallel, the same oxides were doped with yttria. Pure yttria aerogel was also made and characterised. Heat treatments were performed from ambient up to 1200°C and BET surface areas and XRD patterns were recorded after heat treatments at 300, 600, 900 and 1200 °C for pure and doped oxides, respectively. 

Titania also exhibited some of the characteristics that distinguished alumina from silica. Two distinct isolated hydroxyl groups were observed and a possible third type was suggested by the spectra of deuterated samples. The spectra were not as clean-cut as the other two and large differences appeared between the rutile and anatase forms. The relative ease of reduction of titania compared to alumina and silica may contribute to this. Yates (33) suggested that the different OH peaks may be associated with hydroxyls on the surface of different crystal faces. Since these studies have raised more questions than they have answered, much work remains to be done. 

The cements containing active photocatalytic titania nanoparticles have widespread applications to create environmentally clean surfaces. These applications include self-cleaning surfaces, anti-soiling, depollution of VOCs and NOx contaminants and antifungal/microbial activities [521-528]. The relevant photocatalytic processes may occur both at the air-solid interface and at the liquid-solid interface. 

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