Chitosan microspheres as a template for TiO2 and ZnO microparticles: studies on mechanism, functionalization and applications in photocatalysis and H2S removal

Abstract

In the past few decades, several studies have used nanoparticles for photocatalytic reactions. For practical applications, the use of nanomaterials may not be advantageous due to the difficulties in removing them from processed liquids, and they also pose possible health risks. We have developed a procedure that uses chitosan to convert nanosized photocatalysts into micron sized materials without losing their efficiency or surface area. Additionally, the synthetic method offers the possibility of adding functionality like macroporosity and doping carbon or gold nanoparticles. The synthesis involves ultrasonic emulsification of tetradecane in an aqueous chitosan solution containing photocatalytic nanoparticles. Tetradecane-core chitosan/photocatalyst composite-shelled microspheres were produced during the ultrasonic emulsification process. Calcination of these microspheres resulted in the formation of carbon doped micron-sized photocatalytic particles with macroporous structure. Detailed characterisations were carried out using dynamic light scattering, zeta potential, SEM, TEM, BET, XRD and XPS measurements. A possible mechanism for the formation of micron-sized photocatalytic particles is proposed. The photocatalytic efficiencies of synthesised microparticles and their reusability through filtration were evaluated and compared with that of starting nanomaterials using two organic dyes as model pollutants. One of the catalysts (gold doped photocatalyst) was also tested for H₂S gas removal by adsorption. The regeneration of the adsorbent was also achieved after room temperature photocatalysis. The results indicate that the synthetic procedure can be used to produce macroscale photocatalysts with a size range of 10–20 μm as efficient as the starting nanopowders (size range of 20–50 nm).