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). For the first time, both reversible adsorption in the dark and photocatalytic degradation under light irradiation are simultaneously monitored and kinetically modeled via coupled continuity equations for TBZ in both liquid phase and on the catalyst surface 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. It is shown that the different TBZ species have distinct adsorption and desorption coefficients with their charge conditions. Furthermore, changes in pH have a significant effect on the overall removal by 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, corresponding to deviations below 4%. In addition, photocatalytic experiments under natural sunlight with a variable visible light intensity of 10 to 125 W/m2 and reusability of the photocatalyst was successfully validated by the proposed model. Furthermore, the calculated quantum yield for the used POP mounts up to 2.8×10-6 molecules/photon with the space time yield reaches 1.5×10-6 molecules/(photon mgcat), which is an order of magnitude higher than earlier reported values.