Removal of phenol in aqueous solutions by novel buoyant Composite photocatalysts and the kinetics

Novel buoyant composite photocatalysts were prepared by thermally immobilizing titanium dioxide (TiO2) nanoparticles and powdered activated carbon (PAC) onto polypropylene granules (PPGs). The preparation method was examined and the compositions of the developed composite photocatalysts were quantified. The performance of the various prepared buoyant composite photocatalysts was evaluated for their efficiency in the removal of phenol from aqueous solutions. The experimental results showed that the developed composite photocatalysts were buoyant and can display high adsorption capacity and good photoactivity for the removal of phenol in aqueous solutions. It was found that the adsorption capacity increased generally with the increase of the PAC content and the photocatalytic degradation performance can be satisfactorily described by a first-order rate law. The PAC component in the composite photocatalyst appeared to help concentrating phenol from aqueous solutions to the vicinity of the TiO2 nanoparticles and thus made the photodegradation process of phenol less dependent on the phenol concentration in the solution phase, suggesting that there was a synergistic effect of including PAC with TiO2 in the composite photocatalysts. Different TiO2/PAC mass ratios were found to induce different extents of the synergistic effect, as reflected by the values of the apparent first-order rate constant, and a TiO2/PAC mass ratio of 1:1 appeared to achieve better phenol removal performance than other ratios under the experimental conditions tested. In addition, the presence of PAC in the developed composite photocatalyst was also found to largely shield the inhibition effect of chloride ions in the solutions on phenol removal.