Floating photocatalytic pickering emulsion particles for wastewater treatment
2015-11-18T16:56:24Z (GMT) by
The thesis constitutes an investigation into the production of floating photocatalytic particles (FPP) as a low cost, low carbon footprint and chemical-free wastewater treatment. It is anticipated that this approach would be particularly attractive for developing countries where it could reduce incidences of disease and pollution. The particles were manufactured from cocoa butter (CB), and contained either photocatalytic nanoparticle titanium dioxide TiO2 (P25) or silver-doped TiO2 (0.5% w/w). The photocatalytic activity of the particles was evaluated by means of the decolourisation of the dye indigo carmine (IC). Three arrangements were used; small scale treatment using Petri dishes, an 1800 ml batch-recirculation photoreactor and an 8 litre UV contactor. Membrane emulsification (ME) was the technique used here to generate particles of controlled size. The particles were in effect what are known as Pickering emulsions in which the solid fat core (CB) was stabilised by TiO2 nanoparticles, resulting in composite particles that float easily and can receive incident light to generate highly reactive free radical species. The FPPs were characterised by FEGSEM and EDs mapping analysis, and the images obtained displayed a spherical structure with a rough outer surface, and the EDs showed a good coverage of TiO2 on the surface of at a maximum loading of 10% w/w. Tests were conducted to assess the stability of the particles when used in repeated cycles. Reuse of the particles caused a significant drop of photodegradation activity after four cycles to 42% of that of freshly prepared particles. The correlation of photocatalytic activity with silver dosage was also investigated. The highest photocatalytic activity was achieved at 0.5 wt. % of silver doped TiO2 and was some 10% greater than for un- doped particles. The organic carbon release resulted from TOC analysis for the FPPs that were exposed to UV light for 8.5 hr in water was less than 1 wt. %. First order reaction kinetics were exhibited during decolourisation of IC dye with respect to the initial dye concentration, radiation intensity, percentage coverage of the liquid surface by the FPPs, and the catalytic loading. For a static system (i.e. no forced convection), the most effective surface coverage was identified as being in the range of 60 to 80%. A linear source spherical emission model (LSSE) was adopted to estimate the intensity of the incident radiation on the surface of the FPP layer in the photoreactor and validated. In addition, a preliminary kinetic model to describe of the effect of the photocatalytic active surface concentration of TiO2 as well as the efficient intensity flux in the kinetic model was developed for the FPP layer photoreactor.