Influence of atmospheric plasma spraying on the solar photoelectro-catalytic properties of TiO₂ coatings

Titanium dioxide is a widely available material which possesses outstanding properties, chemical stability and low cost. This paper reports the synthesis of nine TiO₂ coating from three commercial TiO₂ rutile and anatase and TiO_2 − x sub-oxide powders onto Inconel alloy substrates by means of atmospheric plasma spray (APS). The influence of this thermally-activating technique on TiO₂ powder feedstocks, the role of its spraying conditions as well as the importance of the final active behavior of the coatings were studied. The performance of the coatings as photoanodes in the solar photoelectrocatalysis (SPEC) treatment of a model azo dye was explored. APS spraying parameters were selected in order to achieve a well-bonded coating, a determined thickness and a specific surface roughness. Moreover, Argon feeding gas of plasma torch played an important role in the quick melting process, particularly related to the heat transferred to the TiO₂ particles and the achievement of non-stoichiometric TiO₂. The prepared coatings were coupled to an air-diffusion cathode inside a photoelectrochemical cell and directly exposed to sunlight irradiation. Through XRD, SEM and surface characterization of the different coatings, the properties of the best TiO₂ material for the dye degradation by SPEC were elucidated.