Novel kinetic modeling of thiabendazole removal by adsorption and photocatalysis on porous organic polymers: Effect of pH and visible light intensity

Abstract

Visible light mediated heterogeneous photocatalysis of the fungicide thiabendazole (TBZ; initial concentration of 50 μmol/L) has been investigated using amorphous porous organic polymers (POPs). Reversible adsorption in the dark and photocatalytic degradation under light irradiation are experimentally monitored. Then, both TBZ concentrations in liquid phase and on the catalyst surface are for the first time kinetically quantified via coupled continuity equations during a sequence of dark/light periods. The final model takes into account the effect of light intensity (28–120 W/m2) and pH (3–9) on the adsorption and photocatalytic degradation processes. It is found that light intensity maintains a linear relation with both the degradation rate in the solution and on the catalyst surface, while it does not significantly affect the adsorption/desorption rates. The effect of pH was investigated in relation to the speciation of TBZ and its impact on adsorption/desorption and degradation coefficients. Accordingly, the different TBZ species have distinct adsorption and desorption coefficients with their charge conditions. Furthermore, changes in pH can exert a significant effect on the overall removal by either adsorption (highest at pH 6.8) or actual degradation (highest at pH 4.4). The proposed model was satisfactory to describe the experimental data with a root-mean-square deviation (RMSD) of 1.88 μmol/L (i.e., deviations below 4%). In addition, photocatalytic experiments under natural sunlight with a variable visible light intensity of 10 to 125 W/m2 were successfully accounted for with the aid of the proposed model. Furthermore, the reusability of the photocatalysts was validated along with superior performance in terms of calculated quantum yield (2.8 × 10–6 molecules/photon) and the space time yield (1.5 × 10–6 molecules/(photon mgcat)), which is an order of magnitude higher than earlier reported values.