Immobilizing photocatalysts on microscale supports can be applied in industrial photocatalytic reactors and in microbial deactivation applications requiring slow release. Glass microspheres (GMs) as photocatalyst support have minimal opacity, are cheap, easily separated from the aqueous phase, and are reusable. In this study, Titania nanotubes (TNTs) were synthesized and immobilized on 710 and 106 µm diameter GMs using polyethylene glycol in isopropanol as excipients. Commercial P25 was also immobilized for comparison. The tubular and spherical morphology of TNTs and P25 respectively was confirmed by scanning electron microscopy. Successful immobilization on the GMs was confirmed by optical microscopy. The final products contained 4-10 wt% TiO2 with the immobilization efficiency following the trend: 106 µm > 710 µm (GMs diameters) and P25 > TNT. Calcination led to crystallinity and phase changes in TiO2 as observed by XRD and Raman spectroscopy. The measured bandgap energy of TNT and P25 was 3.4 eV and 3.2 eV respectively, and these reduced by 0.4 eV after immobilization due to the combined effect of calcination and excipients. Aqueous phase elutriation revealed 1% of the photocatalyst was leached after 6 h (for all cases) buttressing the efficacy of the technique. Changes in aqueous phase electrical conductivity (in µS/cm) and total dissolved solids (in mg/L) were observed during elutriation. The photocatalytic activity of freshly immobilized GMs with 3-day leached versions was compared using methylene blue degradation at 365 nm. For P25 on 106 µm GMs, the degradation reduced from 67% to 40%. For TNT on 106 µm GMs, it reduced from 23% to 16%. The freshly immobilized TNTs had 65% degradation under the same conditions with the loss in performance due to immobilization. This study has successfully demonstrated that minimal elutriation can be achieved when TiO2 is immobilized on GMs and their activity can be retained for various applications.
