EXPERIMENTAL PART
Pretreatment of the substrate
The pretreatment of the substrate (Ti) is one of the most important factors to control the quality of the coating of SnO2. However, there are a
variety of methods of pretreatment, and significant differences are observed in their results. We chose to use the procedure reported by Lipp and
Pletcher [4], who had electrodes with good reproducibility. Thus, the working electrodes (strips of titanium - 0.25 mm x 1 cm x 4 cm - from Aldrich
®, 99.7% purity) were subjected to the following pre-treatment:
a) Blasting the surface of Ti using glass microspheres with grain size from 60 to 70 micrometres followed by ultrasonic cleaning bath for 20 min,
immersed in 2-propanol;
b) Before preparation of the oxide film, etching of Ti in boiling concentrated HCl for 1 min, followed by profuse rinsing with water and air drying.
In some cases, the substrate so pretreated was platinized through a galvanostatic electrodeposition (250 mA cm -2), using a solution of H2PtCl6 (20 g
L -1) + HCl (300 g L -1) at 65 ° C for 10 min; a cylindrical platinum net was used as counter electrode.
Preparation of SnO2 films
After all the pre-treatment steps have been completed, the oxide films were prepared as follows:
a) Application, with a soft brush, a thin layer of an alcoholic (2-propanol) solution of SnCl2*2H2O 13% w/v 3 + SbCl3 0.2% w/v or SnSO4 12.3% w/v +
Sb2(SO4)3 0.15%, evaporating the excess alcohol in air oven at 90°C for 10 min;
b) After two applications, formation of oxide layer thermally in an oven at 500°C for 20 min with a slow, continuous flow of oxygen;
c) Repetition of steps a) and b) by 10 times;
d) Annealing the film in the oven at 500°C for 60 min with a slow, continuous flow of oxygen.
The thickness of obtained films was estimated from their mass, taking into account the density of the oxide and its coverage area (see below).
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