Composite powder in sub-micrometer size was prepared using a primary nano-TiO 2 powder and polyethylene glycol (PEG). The nano-TiO 2 coating was deposited through vacuum cold spray using both the composite powder and primary nano- TiO 2 powder. The influence of annealing treatment on coating adhesion and photocatalytic activity was investigated. The coating adhesion was estimated through erosion test by water jet. The photocatalytic performance of the TiO 2 coatings was evaluated through photodegradation of phenol in water. The results showed that annealing of the coating at a temperature from 450 to 500 °C yielded both higher activity and better adhesion. The adhesion of the coating deposited using the composite powder was better than that using primary nano- TiO 2 powder. It was found that TiO 2 coating resulting from the composite powder presented much higher activity than that deposited with primary nano-particles. The better activity is attributed to the existence of large pores resulting from the stacking of composite powder, which benefits the reactants transportation through the porous coating.

Deposition of nanocrystalline TiO 2 coatings at low temperatures is becoming more attractive due to the possibility for continuous roll production of coatings for assembly lines of dye-sensitized solar cell at a low cost. In this study, porous nano-TiO 2 coatings were deposited by vacuum cold spraying at room temperature on a conducting glass substrate using commercial P25 nanocrystalline TiO 2 powder. The microstructure of TiO 2 coatings was characterized by field emission scanning electron microscopy and N 2 adsorption test. A commercial dye (N719) was adsorbed on the surface of TiO 2 particles within the coating to assemble a dye-sensitized solar cell. The cell performance was evaluated employing simulated solar light at an intensity of 100 mW/cm 2 . The results showed that TiO 2 coatings were deposited by the agglomerates of nano-TiO 2 powders. The BET test of the as-sprayed TiO 2 coatings yielded a porosity of 49% and an average pore size of 17 nm. The assembled solar cell yielded a short-circuit current density of 7.3 mA/cm 2 and an energy conversion efficiency of 2.4%. The test result indicates that vacuum cold spraying was a promising method to deposit nanocrystalline TiO 2 coating at low temperature applied to the dye-sensitized solar cell.

The control of microstructure of TiO 2 coating through preparation methods influences significantly the performance of the coating. In this study, vacuum cold spray process as a new coating technology is employed to deposit nanocrystalline TiO 2 coatings on glass and stainless steel substrates. TiO 2 deposits were formed using two types of nanocrystalline TiO 2 powders having mean particle diameters of 200 nm and 25 nm. The microstructure of the coating was characterized by scanning electron microscopy, x-ray diffraction analysis. The results demonstrate that a thick nanocrystalline TiO 2 coating can be deposited by vacuum cold spray process. The coating was stacked of particles in agglomerate of several hundred nanometers. The coating presents a mesoporous microstructure which would be effective for applications in photocatalytic degradation, dye-sensitized solar cell and so on.