Zinc oxide pieces obtained by pressing and slip casting: physical, structural and photocatalytic properties

Photocatalysis is a promising alternative for the decontamination of effluents. In this paper, immobilized ZnO-based photocatalysts were obtained by pressing and by slip casting. The cylindrical pieces were heat-treated at 800°C. The samples were characterized by the method based on the principle of Archimedes, XRD, FTIR, Raman, diffuse reflectance and SEM. The samples obtained by slip casting presented lower apparent density (3.12 ± 0.04 g/cm³), higher apparent porosity (44.87 ± 0.47%) and smaller grain size (0.48 ± 0.05 µm) when compared to the pressed samples, with mean apparent density of 5.37 ± 0.08 g/cm³, apparent porosity of 1.56 ± 0.10% and grain size of 0.64 ± 0.02 µm. The performances of the samples were attested by the photocatalytic degradation of Rhodamine B (RhB) under UV-C irradiation (maximum intensity at 254 nm). The samples obtained by slip casting showed photocatalytic degradation between 80% and 90%, while the pressed samples showed degradation between 40% and 60%. The reuse of the photocatalysts was evaluated over five cycles of photocatalytic degradation, in which there was no loss of performance of the samples obtained by slip casting; however, the pressed samples showed a loss of photocatalytic efficiency starting from the third-cycle. Photocatalytic assays were carried out with different dye concentrations, in which the slip casting samples showed better photocatalytic efficiency (degradation of 80% for a RhB concentration of 10 mg/L) due to higher porosity and surface area compared to pressed samples, and there was a loss of performance in higher concentrations.